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  • 1.
    Berglund, Martin
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Microsystems Technology.
    Gruden, Mathias
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Electronics.
    Thornell, Greger
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Microsystems Technology.
    Persson, Anders
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Applied Nuclear Physics. Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Microsystems Technology.
    Evaluation of a microplasma source based on a stripline split-ring resonator2013In: Plasma sources science & technology (Print), ISSN 0963-0252, E-ISSN 1361-6595, Vol. 22, no 5, p. 055017-Article in journal (Refereed)
    Abstract [en]

    In this paper, a stripline split-ring resonator microwave-induced plasma source, aimed for integration in complex systems, is presented and compared with a traditional microstrip design. Devices based on the two designs are evaluated using a plasma breakdown test setup for measuring the power required to ignite plasmas at different pressures. Moreover, the radiation efficiency of the devices is investigated with a Wheeler cap, and their electromagnetic compatibility is investigated in a variable electrical environment emulating an application. Finally, the basic properties of the plasma in the two designs are investigated in terms of electron temperature, plasma potential and ion density. The study shows that, with a minor increase in plasma ignition power, the stripline design provides a more isolated and easy-to-integrate alternative to the conventional microstrip design. Moreover, the stripline devices showed a decreased antenna efficiency as compared with their microstrip counterparts, which is beneficial for plasma sources. Furthermore, the investigated stripline devices exhibited virtually no frequency shift in a varying electromagnetic environment, whereas the resonance frequency of their microstrip counterparts shifted up to 17.5%. With regard to the plasma parameters, the different designs showed only minor differences in electron temperature, whereas the ion density was higher with the stripline design.

  • 2.
    Berglund, Martin
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Microsystems Technology.
    Persson, Anders
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy.
    Kratz, Henrik
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Microsystems Technology.
    Thornell, Greger
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Microsystems Technology.
    Microfluidics integrable plasma source powered by a silicon through-substrate split-ring resonator2013In: Solid-State Sensors, Actuators and Microsystems (TRANSDUCERS EUROSENSORS XXVII), 2013, p. 2608-2611Conference paper (Other academic)
    Abstract [en]

    A novel microplasma source, based on a microstrip split-ring resonator design with electrodes integrated in its silicon substrate, was designed, manufactured and evaluated. This device should offer straightforward integration with other MEMS components, and has a plasma discharge gap with a controlled volume and geometry, with potential for microfluidics. Two realized devices were resonant at around 2.9 GHz with quality factors of 26.6 and 18.7. Two different plasma ignition modes were observed, where the plasma at low pressures was not confined to the gap but rather appeared between the ends of the electrodes on the backside.

  • 3.
    Berglund, Martin
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Microsystems Technology.
    Persson, Anders
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Microsystems Technology.
    Thornell, Greger
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Microsystems Technology.
    A High-Performance Microplasma Source for Highly Sensitive and Robust Gas Analysis2014In: Proc. of Micronano System Workshop 2014, Uppsala, Sweden, May 15-16, 2014, 2014Conference paper (Other academic)
  • 4.
    Berglund, Martin
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Microsystems Technology.
    Persson, Anders
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Microsystems Technology.
    Thornell, Greger
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Microsystems Technology.
    Evaluation of dielectric properties of HTCC alumina for realization of plasma sources2015In: Journal of Electronic Materials, ISSN 0361-5235, E-ISSN 1543-186X, Vol. 44, no 10, p. 3654-3660Article in journal (Refereed)
    Abstract [en]

    As the sensitivity of optogalvanic spectroscopy based on prototype microplasma sources increases, contamination from composite materials in the printed circuit board used starts to become a concern. In this paper, a transfer to high-temperature cofired alumina and platinum is made and evaluated. The high-purity alumina provides an inert plasma environment, and allows for temperatures above 1000A degrees C, which is beneficial for future integration of a combustor. To facilitate the design of high-end plasma sources, characterization of the radio frequency (RF) parameters of the materials around 2.6 GHz is carried out. A RF resonator structure was fabricated in both microstrip and stripline configurations. These resonators were geometrically and electrically characterized, and epsilon (r) and tan were calculated using the RF waveguide design tool Wcalc. The resulting epsilon (r) for the microstrip and stripline was found to be 10.68 (+/- 0.12) and 9.65 (+/- 0.14), respectively. The average tan of all devices was found to be 0.0011 (+/- 0.0007). With these parameters, a series of proof-of-concept plasma sources were fabricated and evaluated. Some problems in the fabrication stemmed from the lamination and difficulties with the screen-printing, but a functioning plasma source was demonstrated.

  • 5.
    Berglund, Martin
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Applied Materials Sciences.
    Persson, Anders
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Applied Nuclear Physics.
    Thornell, Greger
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Applied Materials Sciences.
    Operation characteristics and optical emission distribution of a miniaturized silicon through-substrate split-ring resonator microplasma source2014In: Journal of microelectromechanical systems, ISSN 1057-7157, E-ISSN 1941-0158, Vol. 23, no 6, p. 1340-1345Article in journal (Refereed)
    Abstract [en]

    There are many new microplasma sources being developed for a wide variety of applications, each with different properties tailored to its specific use. Microplasma sources enable portable instruments for, e.g., chemical analysis, sterilization, or activation of substances. A novel microplasma source, based on a microstrip split-ring resonator design with electrodes integrated in its silicon substrate, was designed, manufactured, and evaluated. This device has a plasma discharge gap with a controlled volume and geometry, and offers straightforward integration with other microelectromechancial systems (MEMS) components, e.g., microfluidics. The realized device was resonant at around 2.9 GHz with a quality factor of 18.7. Two different operational modes were observed with the plasma at high pressure being confined in the gap between the electrodes, whereas the plasma at low pressures appeared between the ends of the electrodes on the backside. Measurement of the angular distribution of light emitted from the device with through-substrate electrodes showed narrow emission lobes compared with a reference plasma source with on-substrate electrodes.

  • 6.
    Berglund, Martin
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Microsystems Technology.
    Sturesson, Peter
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Microsystems Technology. Swedish Defence University.
    Thornell, Greger
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Microsystems Technology.
    Persson, Anders
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Microsystems Technology.
    Manufacturing Miniature Langmuir probes by Fusing Platinum Bond Wires2015In: Journal of Micromechanics and Microengineering, ISSN 0960-1317, E-ISSN 1361-6439, Vol. 25, no 10, article id 105012Article in journal (Refereed)
    Abstract [en]

    This paper reports on a novel method for manufacturing microscopic Langmuir probes with spherical tips from platinum bond wires for plasma characterization in microplasma sources by fusing. Here, the resulting endpoints, formed by droplets of a fused wire, are intended to act as a spherical Langmuir probe. For studying the fusing behavior, bond wires were wedge-bonded over a 2 mm wide slit, to emulate the final application, and fused at different currents and voltages. For electrical isolation, a set of wires were coated with a 4 µm thick layer of Parylene before they were fused. After fusing, the gap size, as well as the shape and area of the ends of the remaining stubs were measured. The yield of the process was also investigated, and the fusing event was studied using a high-speed camera for analyzing the dynamics of fusing. Four characteristic tip shapes were observed: spherical, semi-spherical, serpentine shaped and folded. The stub length leveled out at ~420µm. The fusing of the coated wires required a higher power for attaining a spherical shape. Finally, a Parylene coated bond wire was integrated into a stripline split-ring resonator (SSRR) microplasma source, and fused to form two Langmuir probes with spherical endpoints. These probes were used for measuring the I-V characteristics of a plasma generated by the SSRR. In a voltage range between -60 V and 60 V, the fused stubs exhibited the expected behavior of spherical Langmuir probes and will be considered for future integration.

  • 7.
    Berglund, Martin
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Microsystems Technology.
    Thornell, Greger
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Microsystems Technology.
    Persson, Anders
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy. Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Microsystems Technology.
    Microplasma source for optogalvanic spectroscopy of nanogram samples2013In: Journal of Applied Physics, ISSN 0021-8979, E-ISSN 1089-7550, Vol. 114, no 3, p. 033302-Article in journal (Refereed)
    Abstract [en]

    The demand for analysis of smaller samples in isotopic ratio measurements of rare isotopes is continuously rising with the development of new applications, particularly in biomedicine. Interesting in this aspect are methods based on optogalvanic spectroscopy, which have been reported to facilitate both 13C-to-12C and 14C-to-12C ratio measurements with high sensitivity. These methods also facilitate analysis of very small samples, down to the microgram range, which makes them very competitive to other technologies, e.g., accelerator mass spectroscopy. However, there exists a demand for moving beyond the microgram range, especially from regenerative medicine, where samples consist of, e.g., DNA, and, hence, the total sample amount is extremely small. Making optogalvanic spectroscopy of carbon isotopes applicable to such small samples, requires miniaturization of the key component of the system, namely the plasma source, in which the sample is ionized before analysis. In this paper, a novel design of such a microplasma source based on a stripline split-ring resonator is presented and evaluated in a basic optogalvanic spectrometer. The investigations focus on the capability of the plasma source to measure the optogalvanic signal in general, and the effect of different system and device specific parameters on the amplitude and stability of the optogalvanic signal in particular. Different sources of noise and instabilities are identified, and methods of mitigating these issues are discussed. Finally, the ability of the cell to handle analysis of samples down to the nanogram range is investigated, pinpointing the great prospects of stripline split-ring resonators in optogalvanic spectroscopy.

  • 8.
    Eilers, Gerriet
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Applied Nuclear Physics.
    Persson, Anders
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Applied Nuclear Physics.
    Gustavsson, Cecilia
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Applied Nuclear Physics.
    Ryderfors, Linus
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Applied Nuclear Physics.
    Mukhtar, Emad
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry - Ångström, Physical Chemistry.
    Possnert, Göran
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Applied Nuclear Physics.
    Salehpour, Mehran
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Applied Nuclear Physics.
    The Radiocarbon Intracavity Optogalvanic Spectroscopy Setup at Uppsala2013In: Radiocarbon, ISSN 0033-8222, E-ISSN 1945-5755, Vol. 55, no 3-4, p. 237-250Article in journal (Refereed)
    Abstract [en]

    Accelerator mass spectrometry (AMS) is by far the predominant technology deployed for radiocarbon tracer studies. Applications are widespread from archaeology to biological, environmental, and pharmaceutical sciences. In spite of its excellent performance, AMS is expensive and complicated to operate. Consequently, alternative detection techniques for 14C are of great interest, with the vision of a compact, user-friendly, and inexpensive analytical method. Here, we report on the use of intracavity optogalvanic spectroscopy (ICOGS) for measurements of the 14C/12C ratio. This new detection technique was developed by Murnick et al. (2008). In the infrared (IR) region, CO2 molecules have strong absorption coefficients. The IR-absorption lines are narrow in line width and shifted for different carbon isotopes. These properties can potentially be exploited to detect 14CO2, 13CO2, or 12CO2 molecules unambiguously. In ICOGS, the sample is in the form of CO2 gas, eliminating the graphitization step that h is required in most AMS labs. The status of the ICOGS setup in Uppsala is presented. The system is operational but not yet fully developed. Data are presented for initial results that illustrate the dependence of the optogalvanic signal on various parameters, such as background and plasma-induced changes in the sample gas composition.

  • 9.
    Eilers, Gerriet
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Applied Nuclear Physics.
    Persson, Anders
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Applied Nuclear Physics.
    Gustavsson, Cecilia
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Applied Nuclear Physics.
    Ryderfors, Linus
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Applied Nuclear Physics.
    Mukhtar, Emad
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry - Ångström, Physical Chemistry.
    Possnert, Göran
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Applied Nuclear Physics.
    Salehpour, Mehran
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Applied Nuclear Physics.
    The Radiocarbon Intracavity Optogalvanic Spectroscopy Setup at Uppsala2013In: Radiocarbon, ISSN 0033-8222, E-ISSN 1945-5755, Vol. 55, no 3-4, p. 237-250Article in journal (Refereed)
    Abstract [en]

    Accelerator mass spectrometry (AMS) is by far the predominant technology deployed for radiocarbon tracer studies. Applications are widespread from archaeology to biological, environmental, and pharmaceutical sciences. In spite of its excellent performance, AMS is expensive and complicated to operate. Consequently, alternative detection techniques for 14C are of great interest, with the vision of a compact, user-friendly, and inexpensive analytical method. Here, we report on the use of intracavity optogalvanic spectroscopy (ICOGS) for measurements of the 14C/12C ratio. This new detection technique was developed by Murnick et al. (2008). In the infrared (IR) region, CO2 molecules have strong absorption coefficients. The IR-absorption lines are narrow in line width and shifted for different carbon isotopes. These properties can potentially be exploited to detect 14CO2, 13CO2, or 12CO2 molecules unambiguously. In ICOGS, the sample is in the form of CO2 gas, eliminating the graphitization step that h is required in most AMS labs. The status of the ICOGS setup in Uppsala is presented. The system is operational but not yet fully developed. Data are presented for initial results that illustrate the dependence of the optogalvanic signal on various parameters, such as background and plasma-induced changes in the sample gas composition.

  • 10. Gavagnin, Marco
    et al.
    Wanzenboeck, Heinz D
    Belic, Domagoj
    Shawrav, Mostafa M
    Persson, Anders
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Applied Nuclear Physics.
    Gunnarsson, Klas
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Physics.
    Svedlindh, Peter
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Physics.
    Bertagnolli, Emmerich
    Magnetic force microscopy study of shape engineered FEBID iron nanostructures2014In: Physica Status Solidi (a) applications and materials science, ISSN 1862-6300, E-ISSN 1862-6319, Vol. 211, no 2, p. 368-374Article in journal (Refereed)
    Abstract [en]

    The capability to control matter down to the nanoscale level in combination with the novel magnetic properties of nanomaterials have attracted increasing attention in the last few decades due to their applications in magnetic sensing, hard disc data storage and logic devices. Therefore, many efforts have been devoted to the implementation of both nanofabrication methods as well as characterization of magnetic nanoelements. In this study, Fe-based nanostructures have been synthesized on Si(100) by focused electron beam induced deposition (FEBID) utilizing iron pentacarbonyl as precursor. The so obtained nanostructures exhibit a remarkably high iron content (Fe>80at.%), expected to give rise to a ferromagnetic behaviour. For that reason, magnetic force microscopy (MFM) analyses were performed on the obtained FEBID Fe nanostructures. Moreover, object oriented micromagnetic framework (OOMMF) magnetic simulations have been executed to study the influence of the geometry on the magnetic properties of iron single-domain nanowires. FEBID is a mask-less nanofabrication method based on the injection of precursor gas molecules in proximity of the deposition area where their decomposition is locally induced by a focused electron beam.

  • 11. Gavagnin, Marco
    et al.
    Wanzenboeck, Heinz D.
    Wachter, Stefan
    Shawrav, Mostafa M.
    Persson, Anders
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Applied Nuclear Physics.
    Gunnarsson, Klas
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Physics.
    Svedlindh, Peter
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Physics.
    Stoeger-Pollach, Michael
    Bertagnolli, Emmerich
    Free-Standing Magnetic Nanopillars for 3D Nanomagnet Logic2014In: ACS Applied Materials and Interfaces, ISSN 1944-8244, E-ISSN 1944-8252, Vol. 6, no 22, p. 20254-20260Article in journal (Refereed)
    Abstract [en]

    Nanomagnet logic (NML) is a relatively new computation technology that uses arrays of shape-controlled nanomagnets to enable digital processing. Currently, conventional resist-based lithographic processes limit the design of NML circuitry to planar nanostructures with homogeneous thicknesses. Here, we demonstrate the focused electron beam induced deposition of Fe-based nanomaterial for magnetic in-plane nanowires and out-of-plane nanopillars. Three-dimensional (3D) NML was achieved based on the magnetic coupling between nanowires and nanopillars in a 3D array. Additionally, the same Fe-based nanomaterial was used to produce tilt-corrected high-aspect-ratio probes for the accurate magnetic force microscopy (MFM) analysis of the fabricated 3D NML gate arrays. The interpretation of the MFM measurements was supported by magnetic simulations using the Object Oriented MicroMagnetic Framework. Introducing vertical out-of-plane nanopillars not only increases the packing density of 3D NML but also introduces an extra magnetic degree of freedom, offering a new approach to input/output and processing functionalities in nanomagnetic computing.

  • 12. Gurgurewicz, Joanna
    et al.
    Mège, Daniel
    Grygorczuk, Jerzy
    Wiśniewski, Łukasz
    Berglund, Martin
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Microsystems Technology.
    Carrère, Véronique
    Gritsevich, Maria
    Kalarus, Maciej
    Peltoniemi, Jouni
    Persson, Anders
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Microsystems Technology.
    Rataj, Mirosław
    Thornell, Greger
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Microsystems Technology.
    Wawer, Piotr
    Zubko, Nataliya
    Studying the composition of Phobos' surface using HOPTER (Highland Terrain Hopper)2016Conference paper (Refereed)
  • 13.
    Lekholm, Ville
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Microsystems Technology.
    Persson, Anders
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Microsystems Technology.
    Klintberg, Lena
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Microsystems Technology.
    Thornell, Greger
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Microsystems Technology.
    Investigation of a zirconia co-fired ceramic calorimetric microsensor for high-temperature flow measurements2015In: Journal of Micromechanics and Microengineering, ISSN 0960-1317, E-ISSN 1361-6439, Vol. 25, no 6, article id 065014Article in journal (Refereed)
    Abstract [en]

    This paper describes the design, fabrication and characterization of a flow sensor for high-temperature, or otherwise aggressive, environments, like, e.g. the propulsion system of a small spacecraft. The sensor was fabricated using 8 mol% yttria stabilized zirconia (YSZ8) high-temperature co-fired ceramic (HTCC) tape and screen printed platinum paste. A calorimetric flow sensor design was used, with five 80 mu m wide conductors, separated by 160 mu m, in a 0.4 mm wide, 0.1 mm deep and 12.5 mm long flow channel. The central conductor was used as a heater for the sensor, and the two adjacent conductors were used to resistively measure the heat transferred from the heater by forced convection. The two outermost conductors were used to study the influence of an auxiliary heat source on the sensor. The resistances of the sensor conductors were measured using four-point connections, as the gas flow rate was slowly increased from 0 to 40 sccm, with different power supplied through the central heater, as well as with an upstream or downstream heater powered. In this study, the thermal and electrical integrability of microcomponents on the YSZ8 substrate was of particular interest and, hence, the influence of thermal and ionic conduction in the substrate was studied in detail. The effect of the ion conductivity of YSZ8 was studied by measuring the resistance of a platinum conductor and the resistance between two adjacent conductors on YSZ8, in a furnace at temperatures from 20 to 930 degrees C and by measuring the resistance with increasing current through a conductor. With this design, the influence of ion conductivity through the substrate became apparent above 700 degrees C. The sensitivity of the sensor was up to 1 m Omega sccm(-1) in a range of 0-10 sccm. The results show that the signal from the sensor is influenced by the integrated auxiliary heating conductors and that these auxiliary heaters provide a way to balance disturbing heat sources, e.g. thrusters or other electronics, in conjunction with the flow sensor.

  • 14.
    Lekholm, Ville
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Microsystems Technology.
    Persson, Anders
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy.
    Palmer, Kristoffer
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Microsystems Technology.
    Ericson, Fredric
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Microsystems Technology.
    Thornell, Greger
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Microsystems Technology.
    High-temperature zirconia microthruster with integrated flow sensor2013In: Journal of Micromechanics and Microengineering, ISSN 0960-1317, E-ISSN 1361-6439, Vol. 23, no 5, p. 055004-Article in journal (Refereed)
    Abstract [en]

    This paper describes the design, fabrication and characterization of a ceramic, heated cold-gas microthruster device made with silicon tools and high temperature co-fired ceramic processing. The device contains two opposing thrusters, each with an integrated calorimetric propellant flow sensor and a heater in the stagnation chamber of the nozzle. The exhaust from a thruster was photographed using schlieren imaging to study its behavior and search for leaks. The heater elements were tested under a cyclic thermal load and to the maximum power before failure. The nozzle heater was shown to improve the efficiency of the thruster by 6.9%, from a specific impulse of 66 to 71 s, as calculated from a decrease of the flow rate through the nozzle of 13%, from 44.9 to 39.2 sccm. The sensitivity of the integrated flow sensor was measured to 0.15 m Omega sccm(-1) in the region of 0-15 sccm and to 0.04 m Omega sccm(-1) above 20 sccm, with a zero-flow sensitivity of 0.27 m Omega sccm(-1). The choice of yttria-stabilized zirconia as a material for the devices makes them robust and capable of surviving temperatures locally exceeding 1000 degrees C.

  • 15.
    Nguyen, Hugo
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Microsystems Technology.
    Persson, Anders
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Microsystems Technology.
    Tailoring the properties of a magnetic tunnel junction to be used as a magnetic field sensor2011In: Conf. on solid state physics and materials VII (SPMS 2011), Ho Chi Minh, 7-9 November 2011, 2011Conference paper (Refereed)
    Abstract [en]

    A magnetic tunnel junction (MTJ) can be used as an effective magnetic field sensor thank to its high magnetoresistance ratio. To be used as a magnetic field sensor in different applications, the possibility of tuning the performance of the MTJ is important. Different means of tuning, such as voltage and magnetic field biasing, can be used. In this work, an external magnetic field from a permanent magnet was used to bias the sensing layer of a MTJ along its hard axis, and the effect of the biasing on the sensitivity, detection limit, and hysteresis of the MTJ was investigated. The experiments showed that the hysteresis of the MTJ languished away at a certain applied magnetic field. Moreover, the sensitivity and noise level decreased, whereas the detection limit increased with increasing bias field strength. The motivation of this experiment is not only to find a power- and cost-effective method of tuning the MTJ, but also to study what happens with the sensing layer, and with electron transport within the MTJ when an external magnetic field is applied.

  • 16.
    Nguyen, Hugo
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Microsystems Technology.
    Persson, Anders
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Microsystems Technology.
    Thornell, Greger
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Microsystems Technology.
    Material- and fabrication-governed performance of a tunnelling magnetometer2010Conference paper (Refereed)
  • 17.
    Nguyen, Hugo
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Microsystems Technology.
    Persson, Anders
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Microsystems Technology.
    Thornell, Greger
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Microsystems Technology.
    Material- and fabrication-governed performance of a tunnelling magnetometer2010In: Advances in Natural Sciences: Nanoscience and Nanotechnology, ISSN 2043-6254, E-ISSN 2043-6262, Vol. 1, no 4, p. 045006-Article in journal (Refereed)
    Abstract [en]

    Miniaturization of sensitive magnetic sensors for nano- and picosatellites has come to the point where the traditional sensors with magnetic coils soon can be replaced. Thin film technology offers the possibility of making extremely small magnetic field sensors that employ the effect of anisotropic, giant and tunneling magnetoresistance (AMR, GMR and TMR). In this paper, the development status of sensors based on microelectromechanical systems technology (MEMS), starting from a TMR layer structure is presented. The sensors have been successfully fabricated and integrated onto an electronic circuit designed for space application. The system as a whole, and the sensors in particular, have not only been characterized with respect to sensitivity, resolution, and noise level, but also to launch vibration and space radiation. The sensor performance and limitations are strongly dependent on the deposited materials, sensor design, and fabrication process. Since the sensor elements are small and sensitive (with lateral dimensions of some tens of micrometres, and resolution of 100 pT at frequencies of MHz), they are also promising for other MEMS applications.

  • 18.
    Nguyen, Hugo
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Microsystems Technology.
    Persson, Anders
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Microsystems Technology.
    Thornell, Greger
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Microsystems Technology.
    Material- and fabrication-governedperformance of a tunnellingmagnetometer2010In: Material- and fabrication-governedperformance of a tunnellingmagnetometer, 2010Conference paper (Refereed)
    Abstract [en]

    Miniaturization of sensitive magnetic sensors for nano- and picosatellites has come to the point where the traditional sensors with magnetic coils soon can be replaced. Thin film technology offers the possibility of making extremely small magnetic field sensors that employ the effect of anisotropic, giant and tunneling magnetoresistance (AMR, GMR and TMR). In this paper, the development status of sensors based on microelectromechanical systems technology (MEMS), starting from a TMR layer structure is presented. The sensors have been successfully fabricated and integrated onto an electronic circuit designed for space application. The system as a whole, and the sensors in particular, have not only been haracterized with respect to sensitivity, resolution, and noise level, but also to launch vibration and space radiation. The sensor performance and limitations are strongly dependent on the deposited materials, sensor design, and fabrication process. Since the sensor elements are small and sensitive (with lateral dimensions of some tens of micrometres, and resolution of 100 pT at frequencies of MHz), they are also promising for other MEMS applications

  • 19.
    Nguyen, Hugo
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Microsystems Technology.
    Thornell, Greger
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Microsystems Technology.
    Persson, Anders
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Microsystems Technology.
    Material considerations and fabrication methods for rapid prototyping of MTJs2009In: Konf. on solid state physics and materials VI, I-007, 2009, 2009, p. 9-Conference paper (Other academic)
  • 20.
    Persson, Anders
    Uppsala University, Disciplinary Domain of Science and Technology, Mathematics and Computer Science, Department of Information Technology, Division of Visual Information and Interaction. Uppsala University, Disciplinary Domain of Science and Technology, Mathematics and Computer Science, Department of Information Technology, Computerized Image Analysis and Human-Computer Interaction.
    Implicit bias in predictive data profiling within recruitments2016In: Privacy and Identity Management: Facing up to Next Steps, Springer, 2016, p. 212-230Chapter in book (Refereed)
  • 21.
    Persson, Anders
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Microsystems Technology, Ångström Space Technology Centre (ÅSTC).
    Magnetoresistance and Space: Micro- and Nanofeature Sensors Designed, Manufactured and Evaluated for Space Magnetic Field Investigations 2011Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    In recent years, the interest for miniaturization of spaceborne instruments and subsystems has increased steadily, as this enables development of small and lightweight satellite classes as well as more versatile payloads on traditional spacecraft.

    In essence, this thesis work is an investigation of the applicability of magnetoresistive technology to a magnetometer intended for space. Two types of magnetoresistive sensors, promising with respect to performance competiveness also after considerable miniaturization, were developed and evaluated, namely magnetic tunnel junctions and planar Hall effect bridge sensors.

    In the case of the magnetic tunnel junctions, much effort was put on the micromanufacturing process. Two schemes were developed and evaluated for sensor contouring: one employing focused ion beam processes for rapid prototyping, and the other combining sputtering and x-ray photoelectron spectroscopy for precise etch depth monitoring during ion etching. For the former, the resulting implantation damages were investigated with chemical analysis and correlated to the sensor properties. In the latter, the depth of the etching was monitored live with a resolution sufficient to stop the etching in the 1 nm thick tunneling barrier. The effect and extent of redeposition were investigated by transmission electron microscopy and micromagnetic analysis. With the knowledge so gained, the tunneling magnetoresistance of the manufactured junctions could be improved significantly and their inherent noise could be reduced. As a step in space flight qualification, the magnetic tunnel junctions were subjected to both g and particle radiation, leaving them unaffected by the first, but rendering them a reduced tunneling magnetoresistance ratio and an increased coercivity by the latter.

    In the case of the planar Hall effect bridge sensors, their inherent noise was thoroughly investigated, revealing both electric and magnetic 1/f noise at low frequencies along with thermal noise at higher frequencies. In addition, an analytical model of the magnetic properties of the planar Hall effect bridges was developed, and a design process, based on the model, was established to optimize the bridges for a particular application.

    In conclusion, both types of sensors show great promises for use in space. Of the two, the planar Hall effect bridge sensors had a better detection limit at low frequencies, whereas the magnetic tunnel junctions were more precise at higher frequencies. However, both sensors had a bandwidth greatly exceeding that of traditional spaceborne magnetometers. A magnetometer employing the magnetic tunnel junctions from this work is currently included as payload onboard the Vietnamese satellite F-1 scheduled for launch this year. A magnetometer using magnetoresistive sensors – planar Hall effect sensors, magnetic tunnel junctions, or both – enables a mass reduction of more than two orders of magnitudes compared with traditional systems.

    List of papers
    1. Low-frequency noise in planar Hall effect bridge sensors
    Open this publication in new window or tab >>Low-frequency noise in planar Hall effect bridge sensors
    Show others...
    (English)Manuscript (preprint) (Other academic)
    Abstract [en]

    The low-frequency characteristics of planar Hall effect bridge sensors are investigated as function of the sensor bias current and the applied magnetic field. The noise spectra reveal a Johnson-like spectrum at high frequencies, and a 1/f-like excess noise spectrum at lower frequencies, with a knee frequency of around 400 Hz. The 1/f-like excess noise can be described by the phenomenological Hooge equation with a Hooge parameter of gH=0.016. The detectivity is shown to depend on the total length, width and thickness of the bridge branches. Increasing the total length by a factor of 10 improves the detectivity by a factor of 101/2. Moreover, the detectivity is shown to depend on the amplitude of the applied magnetic field, revealing a magnetic origin to part of the 1/f noise.

    Keywords
    Magnetoresistance, Planar Hall effect, Low-frequency noise, Detectivity
    National Category
    Materials Engineering
    Research subject
    Engineering Science with specialization in Solid State Physics; Engineering Science with specialization in Microsystems Technology
    Identifiers
    urn:nbn:se:uu:diva-153314 (URN)
    Funder
    Knut and Alice Wallenberg FoundationSwedish Research Council
    Available from: 2011-05-10 Created: 2011-05-10 Last updated: 2011-07-01Bibliographically approved
    2. Low-frequency picotesla field detection with planar Hall effect bridge sensors
    Open this publication in new window or tab >>Low-frequency picotesla field detection with planar Hall effect bridge sensors
    Show others...
    (English)Manuscript (preprint) (Other academic)
    Abstract [en]

    The applicability of miniaturized magnetic field sensors are being explored in several fields of magnetic field detection, due to their integratability, low mass, and potentially low cost. In this respect, different thin-film technologies, especially those employing magnetoresistance, show great potential, being compatible with micro- and nanotechnology batch processing. For low-frequency magnetic field detection, sensors based on the planar Hall effect, especially planar Hall effect bridge (PHEB) sensors, show promising performance given their inherent low-field linearity, limited hysteresis and moderate noise figure. In this work, the applicability of such PHEB sensors to different areas is investigated. An analytical model was constructed, to estimate the performance of an arbitrary PHEB in terms of e.g. sensitivity and detectivity. The model incorporates a number of approximations and, to validate the results, modelled data is compared to measurements on actual PHEBs. It is concluded that the model slightly underestimated the detectivity, especially at low frequencies and when demagnetizing effects becomes apparent. The model is also sensitive to fabrication process induced variations of the material parameters of the sensors. Nevertheless, accounting for these discrepancies, the modelled data is typically within 10% from the experimental data and the model can be used to estimate the performance of a particular PHEB design. The model is also used to establish a design process for optimizing a PHEB to a particular set of requirements on the bandwidth, detectivity, compliance voltage and amplified signal-to-noise ratio. By applying this design process, the size, sensitivity, resistance, bias current and power consumption of the PHEB can be calculated. The model shows that PHEBs are applicable to several different science areas including archaeological surveying, satellite attitude determination, scientific space missions, and magnetic bead detection in lab-on-a-chip applications.

    National Category
    Materials Engineering
    Research subject
    Engineering Science with specialization in Solid State Physics; Engineering Science with specialization in Microsystems Technology
    Identifiers
    urn:nbn:se:uu:diva-153315 (URN)
    Funder
    Knut and Alice Wallenberg FoundationSwedish Research Council
    Available from: 2011-05-10 Created: 2011-05-10 Last updated: 2011-07-01Bibliographically approved
    3. Rapid prototyping of magnetic tunnel junctions with focused ion beam processes
    Open this publication in new window or tab >>Rapid prototyping of magnetic tunnel junctions with focused ion beam processes
    2010 (English)In: Journal of Micromechanics and Microengineering, ISSN 0960-1317, E-ISSN 1361-6439, Vol. 20, no 5, p. 055039-Article in journal (Refereed) Published
    Abstract [en]

    Submicron sized Magnetic tunnel junctions (MTJs) are most often fabricated by time-consuming and expensive e-beam lithography. From a research and development perspective, a short lead time is one of the major concerns. Here, a rapid process scheme for fabrication of micrometer size MTJs with focused ion beam processes is presented. The magnetic properties of the fabricated junctions is investigated in terms of magnetic domain structure, tunnelling magnetoresistance (TMR) and coercivity, with extra attention to the effect of Ga implantation from the ion beam. In particular, the effect of the implantation on the minimum junction size and the magnetization of the sensing layer are studied. In the latter case, magnetic force microscopy and micromagnetic simulations, with the Object Oriented Micromagnetic Framework (OOMMF), are used to study the magnetization reversal. The fabricated junctions show considerable coercivity both along their hard and easy axes. Interestingly, the sensing layer exhibit two remanent states: one with a single and one with a double domain. The hard axis TMR loop has kinks at about ±20 mT which is attributed to a non-uniform lateral coercivity, where the rim of the junctions, which is subjected to Ga implantation from the flank of the ion beam, is more coercive than the unirradiated centre. The width of the coercive rim is estimated to 160 nm from the hard axis TMR loop. The easy axis TMR loop shows more coercivity than an unirradiated junction and, this too, is found to stem from the coercive rim, as seen from the simulations. It is concluded that the process scheme has three major advantages. Firstly, it has a high lateral and depth resolution – the depth resolution is enhanced by end point detection – and is capable of making junctions of sizes down towards the limit set by the width of the irradiated rim. Secondly, the most delicate process steps are preformed in unbroken vacuum enabling the use of materials prone to forming oxides in the MTJ film stack. Thirdly, the scheme is both uncomplicated and quick and makes it possible to go from design to characterization in the order of hours.

    Place, publisher, year, edition, pages
    IOP, 2010
    National Category
    Materials Engineering
    Research subject
    Materials Science
    Identifiers
    urn:nbn:se:uu:diva-134753 (URN)10.1088/0960-1317/20/5/055039 (DOI)000277305000039 ()
    Available from: 2010-12-01 Created: 2010-11-30 Last updated: 2017-12-12Bibliographically approved
    4. Ga Implantation in a MgO-based Magnetic Tunnel Junction With Co60Fe20B20 Layers
    Open this publication in new window or tab >>Ga Implantation in a MgO-based Magnetic Tunnel Junction With Co60Fe20B20 Layers
    Show others...
    2011 (English)In: IEEE transactions on magnetics, ISSN 0018-9464, E-ISSN 1941-0069, Vol. 47, no 1, p. 151-155Article in journal (Refereed) Published
    Abstract [en]

    A Co60Fe20B20-based tunneling magnetoresistance multilayer stack with an MgO barrier has been exposed to 30 keV Ga ions at doses corresponding to ion etching and metal deposition in a focused ion beam (FIB) instrument, to study the applicability of these processes to magnetic tunnel junction (MTJ) fabrication. MTJs were fabricated and irradiated to investigate how the exposures affected their coercivity and magnetoresistance. Elemental depth profiles, acquired using electron spectroscopy for chemical analysis, showed that Ga gathered in and around the two Co60Fe20B20 layers. Correlated with the results of the magnetic measurements, this Ga presence was found to cause a reduction of magnetoresistance and an increase in coercivity. Quantitatively, a dose of 1014 Ga+cm-2 reduced the magnetoresistance by 60%, whereas a dose of 1015 Ga+cm-2 reduced the magnetoresistance by 67% and also increased the coercivity by 2 mT and changed the dipole coupling between the sensing and the pinning layers by 1.6 mT. The latter was attributed to an imbalance in the synthetic antiferromagnetic structure, where the stack's Ru spacer served as an implantation barrier. The magnetoresistance was lost at a dose of 1016 Ga+cm-2. Annealing reduced the content of Ga around the magnetic layers but also caused diffusion of Cu from one of the layers in the stack. Apart from the observation and explanation of implantation damages in the multilayer, this work concludes on the applicability of FIB processes for prototyping of MTJs.

    Keywords
    Focused ion beam, gallium implantation, magnetic tunnel junction, tunneling magnetoresistance
    National Category
    Materials Engineering
    Research subject
    Engineering Science with specialization in Microsystems Technology
    Identifiers
    urn:nbn:se:uu:diva-142866 (URN)10.1109/TMAG.2010.2089634 (DOI)000285843800001 ()
    Available from: 2011-01-18 Created: 2011-01-17 Last updated: 2017-12-11Bibliographically approved
    5. Material- and fabrication-governed performance of a tunnelling magnetometer
    Open this publication in new window or tab >>Material- and fabrication-governed performance of a tunnelling magnetometer
    2010 (English)Conference paper, Published paper (Refereed)
    National Category
    Engineering and Technology
    Identifiers
    urn:nbn:se:uu:diva-140889 (URN)
    Conference
    The 5th International Workshop on Advanced Materials Science and Nanotechnology, IWAMSN2010, Hanoi, Vietnam, 2010
    Available from: 2011-01-10 Created: 2011-01-10 Last updated: 2015-01-07
    6. Etch-stop technique for patterning of tunnel junctions for a magnetic field sensor
    Open this publication in new window or tab >>Etch-stop technique for patterning of tunnel junctions for a magnetic field sensor
    2011 (English)In: Journal of Micromechanics and Microengineering, ISSN 0960-1317, E-ISSN 1361-6439, Vol. 21, no 4, p. 045014-045022Article in journal (Refereed) Published
    Abstract [en]

    Spin-dependent tunnelling devices, e. g. magnetic random access memories and highly sensitive tunnelling magnetoresistance (TMR) sensors, often consist of a large number of magnetic tunnel junctions (MTJs) of uniform quality over the whole device. The uniformity and yield of the fabrication of such a device are therefore very important. A major source of yield loss is the short-circuiting of junctions by redeposition of etch residues. This can be prevented by terminating of the etch in the typically 1 nm thick tunnelling barrier. Here, electron spectroscopy for chemical analysis for monitoring the etching semi-continuously is proposed. The fabrication scheme employs Ar ion milling for etching the MTJs, and photoelectron spectroscopy for analysing the composition of the etched surface in situ. Junctions etched either to or through the barrier were used for this. The quality of the etch stop was investigated using transmission electron microscopy (TEM), and it was confirmed that the etch could be stopped in the MgO barrier. The TEM imaging also showed clear signs of redeposition. Such redeposition was attributed to being partly caused by the reduction of the TMR ratio of the junctions etched through the barrier, which was only 15% as compared with 150% for junctions etched to the barrier. Also, the latter junctions exhibited 2.7 times less noise in the low-frequency regime, resulting in a 27 times improvement of the signal-to-noise ratio with the etch stop. The barrier also proved effective in protecting the bottom contact from oxidation during the capping and contacting of the junctions.

    National Category
    Engineering and Technology
    Research subject
    Engineering Science with specialization in Microsystems Technology
    Identifiers
    urn:nbn:se:uu:diva-151972 (URN)10.1088/0960-1317/21/4/045014 (DOI)000288751400016 ()
    Available from: 2011-04-26 Created: 2011-04-20 Last updated: 2017-12-11Bibliographically approved
    7. Radiation tolerance of a spin-dependent tunnelling magnetometer for space applications
    Open this publication in new window or tab >>Radiation tolerance of a spin-dependent tunnelling magnetometer for space applications
    2011 (English)In: Measurement science and technology, ISSN 0957-0233, E-ISSN 1361-6501, Vol. 22, no 4, p. 045204-Article in journal (Refereed) Published
    Abstract [en]

    To meet the increasing demand for miniaturized space instruments, efforts have been made to miniaturize traditional magnetometers, e. g. fluxgate and spin-exchange relaxation-free magnetometers. These have, for different reasons, turned out to be difficult. New technologies are needed, and promising in this respect are tunnelling magnetoresistive (TMR) magnetometers, which are based on thin film technology. However, all new space devices first have to be qualified, particularly in terms of radiation resistance. A study on TMR magnetometers' vulnerability to radiation is crucial, considering the fact that they employ a dielectric barrier, which can be susceptible to charge trapping from ionizing radiation. Here, a TMR-based magnetometer, called the spin-dependent tunnelling magnetometer (SDTM), is presented. A magnetometer chip consisting of three Wheatstone bridges, with an angular pitch of 120 degrees, was fabricated using microstructure technology. Each branch of the Wheatstone bridges consists of eight pairs of magnetic tunnel junctions (MTJs) connected in series. Two such chips are used to measure the three-dimensional magnetic field vector. To investigate the SDTM's resistance to radiation, one branch of a Wheatstone bridge was irradiated with gamma rays from a Co-60 source with a dose rate of 10.9 rad min(-1) to a total dose of 100 krad. The TMR of the branch was monitored in situ, and the easy axis TMR loop and low-frequency noise characteristics of a single MTJ were acquired before and after irradiation with the total dose. It was concluded that radiation did not influence the MTJs in any noticeable way in terms of the TMR ratio, coercivity, magnetostatic coupling or low-frequency noise.

    Keywords
    radiation tolerant, magnetic tunnel junction, tunnelling magnetoresistance, magnetometer
    National Category
    Engineering and Technology
    Identifiers
    urn:nbn:se:uu:diva-150729 (URN)10.1088/0957-0233/22/4/045204 (DOI)000288454500010 ()
    Available from: 2011-04-05 Created: 2011-04-05 Last updated: 2017-12-11Bibliographically approved
  • 22.
    Persson, Anders
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Microsystems Technology, Ångström Space Technology Centre (ÅSTC).
    Bejhed, Rebecca
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Physics.
    Gunnarsson, Klas
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Physics.
    Nguyen, Hugo
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Microsystems Technology, Ångström Space Technology Centre (ÅSTC).
    Dalslet, Bjarke T.
    Dept. of Micro- and Nanotechnology, Technical University of Denmark.
    Oesterberg, Frederik W.
    Dept. of Micro- and Nanotechnology, Technical University of Denmark.
    Hansen, Mikkel F.
    Svedlindh, Peter
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Physics.
    Low-frequency picotesla field detection with planar Hall effect bridge sensorsManuscript (preprint) (Other academic)
    Abstract [en]

    The applicability of miniaturized magnetic field sensors are being explored in several fields of magnetic field detection, due to their integratability, low mass, and potentially low cost. In this respect, different thin-film technologies, especially those employing magnetoresistance, show great potential, being compatible with micro- and nanotechnology batch processing. For low-frequency magnetic field detection, sensors based on the planar Hall effect, especially planar Hall effect bridge (PHEB) sensors, show promising performance given their inherent low-field linearity, limited hysteresis and moderate noise figure. In this work, the applicability of such PHEB sensors to different areas is investigated. An analytical model was constructed, to estimate the performance of an arbitrary PHEB in terms of e.g. sensitivity and detectivity. The model incorporates a number of approximations and, to validate the results, modelled data is compared to measurements on actual PHEBs. It is concluded that the model slightly underestimated the detectivity, especially at low frequencies and when demagnetizing effects becomes apparent. The model is also sensitive to fabrication process induced variations of the material parameters of the sensors. Nevertheless, accounting for these discrepancies, the modelled data is typically within 10% from the experimental data and the model can be used to estimate the performance of a particular PHEB design. The model is also used to establish a design process for optimizing a PHEB to a particular set of requirements on the bandwidth, detectivity, compliance voltage and amplified signal-to-noise ratio. By applying this design process, the size, sensitivity, resistance, bias current and power consumption of the PHEB can be calculated. The model shows that PHEBs are applicable to several different science areas including archaeological surveying, satellite attitude determination, scientific space missions, and magnetic bead detection in lab-on-a-chip applications.

  • 23.
    Persson, Anders
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Microsystems Technology, Ångström Space Technology Centre (ÅSTC).
    Bejhed, Rebecca
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Physics.
    Nguyen, Hugo
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Microsystems Technology, Ångström Space Technology Centre (ÅSTC).
    Gunnarsson, Klas
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Physics.
    Dalslet, Bjarke T.
    Dept. of Micro- and Nanotechnology, Technical University of Denmark.
    Oesterberg, Frederik W.
    Dept. of Micro- and Nanotechnology, Technical University of Denmark.
    Hansen, Mikkel F.
    Svedlindh, Peter
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Physics.
    Low-frequency noise in planar Hall effect bridge sensorsManuscript (preprint) (Other academic)
    Abstract [en]

    The low-frequency characteristics of planar Hall effect bridge sensors are investigated as function of the sensor bias current and the applied magnetic field. The noise spectra reveal a Johnson-like spectrum at high frequencies, and a 1/f-like excess noise spectrum at lower frequencies, with a knee frequency of around 400 Hz. The 1/f-like excess noise can be described by the phenomenological Hooge equation with a Hooge parameter of gH=0.016. The detectivity is shown to depend on the total length, width and thickness of the bridge branches. Increasing the total length by a factor of 10 improves the detectivity by a factor of 101/2. Moreover, the detectivity is shown to depend on the amplitude of the applied magnetic field, revealing a magnetic origin to part of the 1/f noise.

  • 24.
    Persson, Anders
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Microsystems Technology.
    Bejhed, Rebecca S
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Physics.
    Nguyen, Hugo
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Microsystems Technology.
    Gunnarsson, Klas
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Physics.
    Dalslet, Bjarke T
    Dept of Micro- and Nanotechnology, Technical University of Denmark, DTU Nanotech, Kongens Lyngby, Danmark.
    Oesterberg, Frederik W
    Dept of Micro- and Nanotechnology, Technical University of Denmark, DTU Nanotech, Kongens Lyngby, Danmark.
    Hansen, Mikkel F
    Svedlindh, Peter
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Physics.
    Low-frequency noise in planar Hall effect bridge sensors2011In: Sensors and Actuators A-Physical, ISSN 0924-4247, E-ISSN 1873-3069, Vol. 171, no 2, p. 212-218Article in journal (Refereed)
    Abstract [en]

    The low-frequency characteristics of planar Hall effect bridge sensors are investigated as function of the sensor bias current and the applied magnetic field. The noise spectra reveal a Johnson-like spectrum at high frequencies, and a 1/f-like excess noise spectrum at lower frequencies, with a knee frequency of around 400 Hz. The 1/f-like excess noise can be described by the phenomenological Hooge equation with a Hooge parameter of γH = 0.016. The detectivity is shown to depend on the total length, width and thickness of the bridge branches. The detectivity is improved by the square root of the length increase. Moreover, the detectivity is shown to depend on the amplitude of the applied magnetic field, revealing a magnetic origin to part of the 1/f noise.

  • 25.
    Persson, Anders
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Microsystems Technology.
    Bejhed, Rebecca Stjernberg
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Physics.
    Oesterberg, Frederik W.
    Dept. of Micro- and Nanotechnology, Technical University of Denmark.
    Gunnarsson, Klas
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Physics.
    Nguyen, Hugo
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Microsystems Technology.
    Rizzi, Giovanni
    Hansen, Mikkel F.
    Svedlindh, Peter
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Physics.
    Modelling and design of planar Hall effect bridge sensors for low-frequency applications2013In: Sensors and Actuators A-Physical, ISSN 0924-4247, E-ISSN 1873-3069, Vol. 189, p. 459-465Article in journal (Refereed)
    Abstract [en]

    The applicability of miniaturized magnetic field sensors is being explored in several areas of magneticfield detection due to their integratability, low mass, and potentially low cost. In this respect, differentthin-film technologies, especially those employing magnetoresistance, show great potential, being compatible with batch micro- and nanofabrication techniques. For low-frequency magnetic field detection,sensors based on the planar Hall effect, especially planar Hall effect bridge (PHEB) sensors, show promising performance given their inherent low-field linearity, limited hysteresis and moderate noise figure. Inthis work, the applicability of such PHEB sensors to different areas is investigated. An analytical modelis constructed to estimate the performance of an arbitrary PHEB sensor geometry in terms of, e.g., sensitivity and detectivity. The model is valid for an ideal case, e.g., disregarding shape anisotropy effects, andalso incorporates some approximations. To validate the results, modelled data was compared to measurements on actual PHEBs and was found to predict the measured values within 13% for the investigatedgeometries. Subsequently, the model was used to establish a design process for optimizing a PHEB to aparticular set of requirements on the bandwidth, detectivity, compliance voltage and amplified signalto-noise ratio. By applying this design process, the size, sensitivity, resistance, bias current and powerconsumption of the PHEB can be estimated. The model indicates that PHEBs can be applicable to severaldifferent areas within science including satellite attitude determination and magnetic bead detection inlab-on-a-chip applications, where detectivities down towards 1 nT Hz−0.5at 1 Hz are required, andmaybeeven magnetic field measurements in scientific space missions and archaeological surveying, where thedetectivity has to be less than 100 pT Hz−0.5at 1 Hz.

  • 26.
    Persson, Anders
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Applied Nuclear Physics.
    Berglund, M.
    Salehpour, Mehran
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Applied Nuclear Physics.
    Improved optogalvanic detection with voltage biased Langmuir probes2014In: Journal of Applied Physics, ISSN 0021-8979, E-ISSN 1089-7550, Vol. 116, no 24, p. 243301-Article in journal (Refereed)
    Abstract [en]

    Optogalvanic detectors show great potential for infrared spectroscopy, especially in cavity enhanced techniques where they, in contrast to ordinary absorption detectors, can perform intracavity measurements. This enables them to utilize the signal-to-noise ratio improvement gained from the extended effective path length inside an optical cavity, without losing signal strength due to the limited amount of light exiting through the rear mirror. However, if optogalvanic detectors are to become truly competitive, their intrinsic sensitivity and stability has to be improved. This, in turn, requires a better understanding of the mechanisms behind the generation of the optogalvanic signal. The study presented here focuses on an optogalvanic detector based on a miniaturized stripline split-ring resonator plasma source equipped with Langmuir probes for detecting the optogalvanic signal. In particular, the effect of applying a constant bias voltage to one of the probes is investigated, both with respect to the sensitivity and stability, and to the mechanism behind the generation of the signal. Experiments with different bias voltages at different pressures and gas composition have been conducted. In particular, two different gas compositions (pure CO2 and 0.25% CO2 in 99.75% N-2) at six different pressures (100 Pa to 600 Pa) have been studied. It has been shown that probe biasing effectively improves the performance of the detector, by increasing the amplitude of the signal linearly over one order of magnitude, and the stability by about 40% compared with previous studies. Furthermore, it has been shown that relatively straightforward plasma theory can be applied to interpret the mechanism behind the generation of the signal, although additional mechanisms, such as rovibrational excitation from electron-molecule collisions, become apparent in CO2 plasmas with electron energies in the 1-6 eV range. With the achieved performance improvement and the more solid theoretical framework presented here, stripline split-ring resonator optogalvanic detectors can evolve into a compact, inexpensive, and easy-to-operate alternative for future infrared spectrometers. (C) 2014 AIP Publishing LLC.

  • 27.
    Persson, Anders
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Microsystems Technology.
    Berglund, Martin
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Microsystems Technology.
    Spatial distribution of the optogalvanic signal in a microplasma detector for lab-on-a-chip gas analysis2016In: Laser Physics Letters, ISSN 1612-2011, E-ISSN 1612-202X, Vol. 13, no 7, article id 075703Article in journal (Refereed)
    Abstract [en]

    Gas sensors are characterized by their sensitivity and selectivity. This is preferably combined with versatility, where the selectivity can be altered, without complex modifications and whiteout losing sensitivity. If aimed at lab-on-a-chip applications, the sensor also must be able to analyze small samples. Today, sensors combining selectivity and versatility for chip-level gas analysis are scarce; however, this paper investigates how miniaturized optogalvanic spectroscopy can fill this gap. By studying the spatial distribution of the optogalvanic signal inside a microplasma, it is shown that the signal is generated in the minuscule gas volume of the sheath surrounding the plasma probe that collects it. Nevertheless, a strong and stable spectroscopic signal can be extracted from the sheath, and the sample concentrations can be calculated using straightforward plasma theory. The minimum detectable absorption and the noise equivalent absorption sensitivity of the system are estimated to be less than 1.4  ×  10−9 Hz−0.5 and 2.8  ×  10−9 cm−1 Hz−0.5, respectively, without cavity enhancement. Combined with inherited versatility from absorption spectroscopy and the capability of handling sub-nanogram samples, this makes optogalvanic spectrometry an excellent candidate for future lab-on-a-chip gas analyzers.

  • 28.
    Persson, Anders
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Microsystems Technology, Ångström Space Technology Centre (ÅSTC).
    Berglund, Martin
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Microsystems Technology, Ångström Space Technology Centre (ÅSTC).
    Khaji, Zahra
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Microsystems Technology.
    Sturesson, Peter
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Microsystems Technology, Ångström Space Technology Centre (ÅSTC). Swedish Def Univ, Div Mil Technol, Dept Mil Sci, Stockholm, Sweden.
    Söderberg, Johan
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Microsystems Technology, Ångström Space Technology Centre (ÅSTC).
    Thornell, Greger
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Microsystems Technology, Ångström Space Technology Centre (ÅSTC).
    Optogalvanic spectroscopy with microplasma sources – Current status and development towards lab on a chip2016In: Journal of Micromechanics and Microengineering, ISSN 0960-1317, E-ISSN 1361-6439, Vol. 26, no 10, article id 104003Article in journal (Refereed)
    Abstract [en]

    Miniaturized optogalvanic spectroscopy (OGS) shows excellent prospects of becoming ahighly sensitive method for gas analysis in micro total analysis systems. Here, a status reporton the current development of microwave induced microplasma sources for OGS is presented,together with the first comparison of the sensitivity of the method to conventional single-passabsorption spectroscopy. The studied microplasma sources are stripline split-ring resonators(SSRRs), with typical ring radii between 3.5 and 6 mm and operation frequencies around2.6 GHz. A linear response (R2 = 0.9999), and a stability of more than 100 s are demonstratedwhen using the microplasma source as an optogalvanic detector. Additionally, saturationeffects at laser powers higher than 100 mW are observed, and the temporal response of theplasma to periodic laser perturbation with repletion rates between 20 Hz and 200 Hz arestudied. Finally, the potential of integrating additional functionality with the detector isdiscussed, with the particular focus on a pressure sensor and a miniaturized combustor toallow for studies of solid samples.

  • 29.
    Persson, Anders
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Microsystems Technology.
    Berglund, Martin
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Microsystems Technology.
    Khaji, Zahra
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Microsystems Technology.
    Sturesson, Peter
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Microsystems Technology.
    Söderberg, Johan
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Microsystems Technology.
    Thornell, Greger
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Microsystems Technology.
    Optogalvanic spectroscopy with microplasma sources – Current status and development towards Lab-On-A-Chip2015Conference paper (Refereed)
    Abstract [en]

    Miniaturized optogalvanic spectros-copy shows excellent prospects of becoming a highly sensitive method for gas analysis in micro total analysis systems. Here, a status report on the current development of microplasma sources for optogalvan-ic spectroscopy is presented, together with the first comparison of the sensitivity of the method to con-ventional single-pass absorption spectroscopy. The stability and reproducibility of the microplasma source when used as a detector for optogalvanic spectroscopy is also investigated, and a roadmap of future developments is presented, with the particular focus of integrating sensors for measuring the pres-sure, temperature and flow of the sample gas through the detector, and combining the detector with a miniaturized combustor to allow for studies of solid samples.

  • 30.
    Persson, Anders
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Applied Nuclear Physics.
    Berglund, Martin
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Microsystems Technology.
    Thornell, Greger
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Microsystems Technology.
    Possnert, Göran
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Applied Nuclear Physics.
    Salehpour, Mehran
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Applied Nuclear Physics.
    State of the art Intracavity Optogalvanic Spectroscopy at Uppsala University2013Conference paper (Refereed)
    Abstract [en]

    About five years ago, the first reports of a novel and ultrasensitive method for ro-vibrational spectroscopy of isotope ratios were published [1-3]. The method was called intracavity optogalvanic spectroscopy (ICOGS), and claimed a sensitivity and limit-of-detection (LOD) for detection of radiocarbon in the 10-15range. Applied to measuring the isotopic composition of carbon samples, ICOGS utilizes the narrow linewidth ro-vibrational absorption lines of CO2 in the long-wavelength IR spectrum, typically between 10 - 13 µm [4]. These absorption lines are strongly dependent on the isotopic composition of the CO2 molecule, where a 14CO2 line typically is separated by several hundred linewidths form the nearest 12CO2 and 13CO2 lines. In order to facilitate unambiguous detection of radiocarbon, which is typically 1010-1012 times less abundant than the isotopes 12C and 13C, the sample is moved inside the laser cavity of a 14CO2 laser. This intracavity approach has been claimed to increase the sensitivity of the detection by almost seven orders of magnitude as compared to traditional ‘extracavity’ optogalvanic spectroscopy [3]. However, despite the methodical and thorough efforts of at least five research groups worldwide, the exceptional claims regarding the sensitivity and LOD of ICOGS have not been possible to confirm.

          As the first research group to properly repeat the original experiments, we recently reported [5] serious deficiencies in the reproducibility of the original results [1-3]. We found that ICOGS in its original embodiment suffers from considerable problems with the stability and reproducibility of the optogalvanic signal, and that these uncertainties, together with mix-ups and mistakes, likely are the explanation for the extraordinary sensitivity in the original reports. An example of the irreproducibility of the original results can be seen in Fig. 1 (a) where the shape of the P20 line of 14C16O2 with different 14C concentrations is shown. As can be seen, the previously reported Voight profile-like line shape, indicating resonant absorption [3], was not found for 14C concentrations in the 10-13 ‒10-11 range, but only for samples with much higher 14C concentration. The problems with stability and reproducibility can be traced back to instabilities in the plasma source, in which the sample is partially ionized in order to extract the optogalvanic signal. The plasma sources currently used in ICOGS are based on 30 years old technology and suffer from problems with both electromagnetic interference and reproducibility in terms of the discharge conditions (pressure, temperature, etc.).

          In order to overcome these problems, we aim to deploy a completely novel kind of plasma source, based on a stripline split-ring resonator (SSRR), for ICOGS, Fig. 1 (b). We have recently published a report on the applicability of such a plasma source for ordinary optogalvanic spectroscopy [6], and now intend to optimize it for ICOGS. Based on its intrinsic properties, an SSRR could not only improve the stability of the signal, but also reduce the non-resonant background in the spectrum, and facilitate analysis of smaller samples. The latter is due to its extremely small size, with an analyzed volume in the order of 10 µl, Fig. 1 (c). In this report, we summarize our criticism towards the original publications on ICOGS, and report on the latest development regarding our efforts in the deployment of the SSRR plasma source.

  • 31.
    Persson, Anders
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Applied Nuclear Physics.
    Berglund, Martin
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Microsystems Technology.
    Thornell, Greger
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Microsystems Technology.
    Possnert, Göran
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Applied Nuclear Physics.
    Salehpour, Mehran
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Applied Nuclear Physics.
    Stripline split-ring resonator with integrated optogalvanic sample cell2014In: Laser Physics Letters, ISSN 1612-2011, Vol. 11, no 4, p. 045701-Article in journal (Refereed)
    Abstract [en]

    Intracavity optogalvanic spectroscopy (ICOGS) has been proposed as a method for unambiguous detection of rare isotopes. Of particular interest is 14C, where detection of extremely low concentrations in the 1:1015 range (14C:12C), is of interest in, e.g., radiocarbon dating and pharmaceutical sciences. However, recent reports show that ICOGS suffers from substantial problems with reproducibility. To qualify ICOGS as an analytical method, more stable and reliable plasma generation and signal detection are needed. In our proposed setup, critical parameters have been improved. We have utilized a stripline split-ring resonator microwave-induced microplasma source to excite and sustain the plasma. Such a microplasma source offers several advantages over conventional ICOGS plasma sources. For example, the stripline split-ring resonator concept employs separated plasma generation and signal detection, which enables sensitive detection at stable plasma conditions. The concept also permits in situ observation of the discharge conditions, which was found to improve reproducibility. Unique to the stripline split-ring resonator microplasma source of in this study, is that the optogalvanic sample cell has been embedded in the device itself. This integration enabled improved temperature control and more stable and accurate signal detection. Significant improvements are demonstrated, including reproducibility, signal-to-noise ratio and precision.

  • 32.
    Persson, Anders
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Applied Nuclear Physics.
    Eilers, Gerriet
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Applied Nuclear Physics.
    Ryderfors, Linus
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Applied Nuclear Physics.
    Mukhtar, Emad
    Uppsala University, Disciplinary Domain of Science and Technology, Chemistry, Department of Chemistry - Ångström, Physical Chemistry.
    Possnert, Göran
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Applied Nuclear Physics.
    Salehpour, Mehran
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Applied Nuclear Physics.
    Evaluation of Intracavity Optogalvanic Spectroscopy for Radiocarbon Measurements2013In: Analytical Chemistry, ISSN 0003-2700, E-ISSN 1520-6882, Vol. 85ASAP, no 14, p. 6790-6798Article in journal (Refereed)
    Abstract [en]

    Ever since the first publication of intracavity optogalvanic spectroscopy (ICOGS) in 2008, this novel technique for measuring the 14C/12C ratio in carbon dioxide has rendered considerable attention. As a result, there are currently at least five different research groups pursuing research on ICOGS. With a claimed limit of detection of 10–15 (14C/12C), i.e., in the same order as accelerator mass spectroscopy, achieved with a relatively inexpensive and uncomplicated table-top system, ICOGS has major scientific and commercial implications. However, during the past 5 years, no research group has been able to reproduce these results or present additional proof for ICOGS’s capability of unambiguous 14C detection, including the authors of the original publication. Starting in 2010, our group has set up a state-of-the-art ICOGS laboratory and has investigated the basic methodology of ICOGS in general and tried to reproduce the reported experiments in particular. We have not been able to reproduce the reported results concerning the optogalvanic signals dependence on14C concentration and wavelength and, ultimately, not seen any evidence of the capability of ICOGS to unambiguously detect 14C at all. Instead, we have found indications that the reported results can be products of measurement uncertainties and mistakes. Furthermore, our results strongly indicate that the reported limit of detection is likely to be overestimated by at least 2 orders of magnitude, based on the results presented in the original publication. Hence, we conclude that the original reports on ICOGS cannot be confirmed and therefore must be in error.

  • 33.
    Persson, Anders
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Microsystems Technology.
    Ericson, Fredric
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Microsystems Technology.
    Thornell, Greger
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Microsystems Technology.
    Nguyen, Hugo
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Microsystems Technology.
    Etch-stop technique for patterning of tunnel junctions for a magnetic field sensor2011In: Journal of Micromechanics and Microengineering, ISSN 0960-1317, E-ISSN 1361-6439, Vol. 21, no 4, p. 045014-045022Article in journal (Refereed)
    Abstract [en]

    Spin-dependent tunnelling devices, e. g. magnetic random access memories and highly sensitive tunnelling magnetoresistance (TMR) sensors, often consist of a large number of magnetic tunnel junctions (MTJs) of uniform quality over the whole device. The uniformity and yield of the fabrication of such a device are therefore very important. A major source of yield loss is the short-circuiting of junctions by redeposition of etch residues. This can be prevented by terminating of the etch in the typically 1 nm thick tunnelling barrier. Here, electron spectroscopy for chemical analysis for monitoring the etching semi-continuously is proposed. The fabrication scheme employs Ar ion milling for etching the MTJs, and photoelectron spectroscopy for analysing the composition of the etched surface in situ. Junctions etched either to or through the barrier were used for this. The quality of the etch stop was investigated using transmission electron microscopy (TEM), and it was confirmed that the etch could be stopped in the MgO barrier. The TEM imaging also showed clear signs of redeposition. Such redeposition was attributed to being partly caused by the reduction of the TMR ratio of the junctions etched through the barrier, which was only 15% as compared with 150% for junctions etched to the barrier. Also, the latter junctions exhibited 2.7 times less noise in the low-frequency regime, resulting in a 27 times improvement of the signal-to-noise ratio with the etch stop. The barrier also proved effective in protecting the bottom contact from oxidation during the capping and contacting of the junctions.

  • 34.
    Persson, Anders
    et al.
    University of California.
    Kavathatzopoulos, Iordanis
    Uppsala University, Disciplinary Domain of Science and Technology, Mathematics and Computer Science, Department of Information Technology, Division of Visual Information and Interaction. Uppsala University, Disciplinary Domain of Science and Technology, Mathematics and Computer Science, Department of Information Technology, Computerized Image Analysis and Human-Computer Interaction.
    How to Make Decisions with Algorithms: Ethical Decision-Making Using Algorithms within Predictive Analytics2017In: CEPE/Ethicomp 2017: ElectronicCollection / [ed] Richard Volkman, Torino: Università degli Studi di Torino , 2017, p. 1-13Conference paper (Refereed)
    Abstract [en]

    The use of automated decision-making support, such as algorithms within predictive analytics,will inevitably be more and more relevant and will be affecting society. Sometimes it is good,and sometimes there seems to be negative effect, such as with discrimination. The solutionfocused on in this paper is how humans and algorithms, or ICT, could interact within ethicaldecision-making. What predictive analytics can produce is, arguably, mostly implicit knowledge,so what a human decision-maker could, possibly, help with is the explicit thought processes.This could be one way to conceptualize an interactive effect between humans and algorithms thatcould be fruitful. Presently there does not seem to be very much research regarding predictiveanalytics and ethical decisions, concerning this human-algorithm interaction. Rather it is often afocus on pure technological solutions, or with laws and regulation.

  • 35.
    Persson, Anders
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Microsystems Technology.
    Khaji, Zahra
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Microsystems Technology.
    Klintberg, Lena
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Microsystems Technology.
    Dynamic Behaviour and Conditioning Time of a Zirconia Flow Sensor for High-Temperature Applications2016In: Sensors and Actuators A-Physical, ISSN 0924-4247, E-ISSN 1873-3069, Vol. 251, p. 59-65Article in journal (Refereed)
    Abstract [en]

    The temperature dependent ion conductivity of yttria stabilized zirconia (YSZ) can be used to create a miniaturized flow sensor using a calorimetric measurement scheme. Such a sensor is compatible with harsh environments, and can sustain temperatures of up to 1000 degrees C, although thermal crosstalk will limit its performance as the temperature rises. This paper investigates if the integration of thermal isolation in the form of sealed cavities can mitigate the detrimental effect of the thermal crosstalk, particularly by studying the conditioning time of the sensor to temperature changes. To this end, high temperature co-fired ceramic (HTCC) sensors were fabricated from tapes of 8 mol-% YSZ that were screen printed with platinum paste. Definition of channels and structures were made by milling the green tapes, and sacrificial inserts were placed in all cavities to give mechanical support during lamination and sintering. Cavities with widths of 240 mu m, 400 mu m and 560 mu m were investigated, and sensors without cavities were also made to serve as references. Additionally, two different positions of the sensor element with respect to the edge of the cavity (560 or 800 mu m) were investigated. The results showed that it was possible to improve the conditioning time of the sensor by up to five times by the use of isolating cavities, and that this improvement is translated into a reduction in rate-dependent hysteresis for measurements with long elapse times. The latter effect is most pronounced for the sensors with the largest cavities.

  • 36.
    Persson, Anders
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Microsystems Technology.
    Lekholm, Ville
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Microsystems Technology.
    Thornell, Greger
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Microsystems Technology.
    Klintberg, Lena
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Microsystems Technology.
    A high-temperature calorimetric flow sensor employing ion conduction in zirconia2015In: Applied Physics Letters, ISSN 0003-6951, E-ISSN 1077-3118, Vol. 106, no 19, article id 194103Article in journal (Refereed)
  • 37.
    Persson, Anders
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Microsystems Technology.
    Nguyen, Hugo
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Microsystems Technology.
    Riddar, Frida
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Applied Materials Sciences.
    Thornell, Greger
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Microsystems Technology.
    Micro- and nanostructured magnetic field sensor for space applications2009In: 15th International Conference on Solid-State SensorsTransducers 2009: Actuators and Microsystems, 2009, p. 1190-1193Conference paper (Refereed)
    Abstract [en]

    Magnetometers are popular payloads on scientific space missions. Here, the design and fabrication process of a miniaturized magnetometer based on tunneling magnetoresistance is presented. The process is capable of making magnetic tunnel junctions in a wide size range, by employing both UV lithography and focused ion beam milling and deposition. Ga implantation in the ferromagnetic electrodes of the junction is studied in more detail. It was shown that Ga implantation may harm the magnetometer if the irradiation dose exceeds 1014 Ga+ cm-2.

  • 38.
    Persson, Anders
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Microsystems Technology.
    Riddar, Frida
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Microsystems Technology.
    Nguyen, Hugo
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Microsystems Technology.
    Ericson, Fredric
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Microsystems Technology.
    Thornell, Greger
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Microsystems Technology.
    Ga Implantation in a MgO-based Magnetic Tunnel Junction With Co60Fe20B20 Layers2011In: IEEE transactions on magnetics, ISSN 0018-9464, E-ISSN 1941-0069, Vol. 47, no 1, p. 151-155Article in journal (Refereed)
    Abstract [en]

    A Co60Fe20B20-based tunneling magnetoresistance multilayer stack with an MgO barrier has been exposed to 30 keV Ga ions at doses corresponding to ion etching and metal deposition in a focused ion beam (FIB) instrument, to study the applicability of these processes to magnetic tunnel junction (MTJ) fabrication. MTJs were fabricated and irradiated to investigate how the exposures affected their coercivity and magnetoresistance. Elemental depth profiles, acquired using electron spectroscopy for chemical analysis, showed that Ga gathered in and around the two Co60Fe20B20 layers. Correlated with the results of the magnetic measurements, this Ga presence was found to cause a reduction of magnetoresistance and an increase in coercivity. Quantitatively, a dose of 1014 Ga+cm-2 reduced the magnetoresistance by 60%, whereas a dose of 1015 Ga+cm-2 reduced the magnetoresistance by 67% and also increased the coercivity by 2 mT and changed the dipole coupling between the sensing and the pinning layers by 1.6 mT. The latter was attributed to an imbalance in the synthetic antiferromagnetic structure, where the stack's Ru spacer served as an implantation barrier. The magnetoresistance was lost at a dose of 1016 Ga+cm-2. Annealing reduced the content of Ga around the magnetic layers but also caused diffusion of Cu from one of the layers in the stack. Apart from the observation and explanation of implantation damages in the multilayer, this work concludes on the applicability of FIB processes for prototyping of MTJs.

  • 39.
    Persson, Anders
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Microsystems Technology.
    Salehpour, Mehran
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Applied Nuclear Physics.
    Comment on “Intracavity OptoGalvanic Spectroscopy Not Suitable for Ambient Level Radiocarbon Detection"2016In: Analytical Chemistry, ISSN 0003-2700, E-ISSN 1520-6882, Vol. 88, no 8, p. 4578-4579Article in journal (Refereed)
    Abstract [en]

    Every new discovery must undergo thorough scientific scrutiny before being recognized. One important step in the process is confirmation by independent experiments. The case at hand is intracavity optogalvanic spectroscopy (ICOGS), which was first published by Murnick et al. in 2008, and claimed to have the potential to revolutionize rare-isotope measurements in general and those of radiocarbon in particular. Since then, no data has been reported in any shape or form to support it. On the contrary, in spite of extensive efforts at five different sites around the world – apart from Murnick’s group at Rutgers University, Professor Meijer’s group at the Energy and Sustainability Research Institute Groningen at University of Groningen, Professor Lackner’s group at the Department of Earth and Environmental Engineering at Columbia University, our group at the Department of Physics and Astronomy at Uppsala University, and the company Planetary Emission Management Inc. – the original data still remains unconfirmed, and a number of publications have seriously questioned the scientific validity of the original report.

  • 40.
    Persson, Anders
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Applied Nuclear Physics. Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Microsystems Technology.
    Salehpour, Mehran
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Applied Nuclear Physics.
    Intracavity optogalvanic spectroscopy: Is there any evidence of a radiocarbon signal?2015In: Nuclear Instruments and Methods in Physics Research Section B: Beam Interactions with Materials and Atoms, ISSN 0168-583X, E-ISSN 1872-9584, Vol. 361, p. 8-12Article in journal (Refereed)
    Abstract [en]

    In 2008, the first report of an ultrasensitive method for ro-vibrational spectrometry of radiocarbon dioxide was published. The method, called intracavity optogalvanic spectroscopy (ICOGS), claimed a sensitivity and limit-of-detection comparable to accelerator mass spectroscopy. ICOGS was claimed to utilize the isotope-dependent ro-vibrational absorption lines of carbon dioxide in the infrared spectrum. In order to facilitate unambiguous detection of radiocarbon, the sample was placed inside the cavity of a radiocarbon dioxide laser. This intracavity approach was claimed to increase the sensitivity by seven orders of magnitude compared with traditional optogalvanic methods. However, despite the methodical and thorough efforts of several research groups worldwide, these claims have not been possible to reproduce. Instead, we have previously reported serious deviations from the original results, where we found that ICOGS suffers from considerable problems with the stability and reproducibility of the optogalvanic signal, and that misinterpretations of these uncertainties likely are the explanation for the claimed sensitivity in the first reports. Having identified the stability and reproducibility of the detection as major concerns, we decided to improve the setup by with state-of-the-art plasma source technology. Deploying a custom-made stripline split-ring resonator optogalvanic detector, we have now investigated the applicability of ICOGS to radiocarbon detection even further. Measurements have been made with a wide range of parameters including different gas mixtures at various pressures and wavelengths. We have also conducted measurements with gas flowing through the sample cell to investigate the effect of plasma induced decomposition of the sample. Still, we have seen no indications of a significant radiocarbon signal in a concentration range between 0.29 Modern and 9.7 Modern, i.e., the range of interest to the radiocarbon community. Hence, our conclusions after four years of working in this field, is that ICOGS is not a viable method for radiocarbon detection. 

  • 41.
    Persson, Anders
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Microsystems Technology.
    Thornell, Greger
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Microsystems Technology.
    Bejhed, Rebecca
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Physics.
    Gunnarsson, Klas
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Physics.
    Nguyen, Hugo
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Microsystems Technology.
    Changing the attitude towards magnetoresistance2011In: Changing the attitude towards magnetoresistance, 2011Conference paper (Refereed)
    Abstract [en]

    Magnetometers are one of the most common instruments on spacecrafts. They are used for both satellite attitude determination and for scientific purposes, such as mapping of Earth’s magnetic field. The most common magnetometer for low-frequency applications is the fluxgate. High-end fluxgates are generally quite bulky, with a mass of around 1 kg, but there exist miniature version, weighing only around 100 g, but with worse noise figure. Interest in such miniature models has increased with the adaption of the Faster-Better-Cheaper philosophy, and the introduction of small satellite classes. However, downscaling of fluxgates beyond the present 100 g has proven difficult, wherefore other technologies have earned more and more interest, especially those employing different kinds of magnetoresistance.

    Here, a review of different magnetoresistive techniques, and their past, present and potential use in space is presented. Magnetoresistive sensors based on anisotropic, giant, and tunneling magnetoresistance is covered, and extra attention is directed towards sensors based on the planar Hall effect. The latter have the potential of overcoming some of the major disadvantages of other magnetoresistive sensors, such as poor detectivity at low frequencies, and the need for external biasing coils to improve linearity and reduce hysteresis by, e.g., set-reset protocols and magnetic feedback.

    Moreover, the design of two such planar Hall effect sensors is tailored to meet the requirements set on a magnetometer aimed for, firstly, attitude determination and, secondly, mapping of Earth’s magnetic field. It is concluded that planar Hall effect sensors is one of the prime candidates for the next generation of miniaturized low-frequency space magnetometers.

  • 42.
    Persson, Anders
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Microsystems Technology.
    Thornell, Greger
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Microsystems Technology.
    Nguyen, Hugo
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Microsystems Technology.
    A microstructured magnetoresistive magnetometer for space applications2010In: Proceedings of Micronano System Workshop 2010, Stockholm, Sweden, May 4-5, 2010, 2010Conference paper (Refereed)
  • 43.
    Persson, Anders
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Microsystems Technology.
    Thornell, Greger
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Microsystems Technology.
    Nguyen, Hugo
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Microsystems Technology.
    Radiation tolerance of a spin-dependent tunnelling magnetometer for space applications2011In: Measurement science and technology, ISSN 0957-0233, E-ISSN 1361-6501, Vol. 22, no 4, p. 045204-Article in journal (Refereed)
    Abstract [en]

    To meet the increasing demand for miniaturized space instruments, efforts have been made to miniaturize traditional magnetometers, e. g. fluxgate and spin-exchange relaxation-free magnetometers. These have, for different reasons, turned out to be difficult. New technologies are needed, and promising in this respect are tunnelling magnetoresistive (TMR) magnetometers, which are based on thin film technology. However, all new space devices first have to be qualified, particularly in terms of radiation resistance. A study on TMR magnetometers' vulnerability to radiation is crucial, considering the fact that they employ a dielectric barrier, which can be susceptible to charge trapping from ionizing radiation. Here, a TMR-based magnetometer, called the spin-dependent tunnelling magnetometer (SDTM), is presented. A magnetometer chip consisting of three Wheatstone bridges, with an angular pitch of 120 degrees, was fabricated using microstructure technology. Each branch of the Wheatstone bridges consists of eight pairs of magnetic tunnel junctions (MTJs) connected in series. Two such chips are used to measure the three-dimensional magnetic field vector. To investigate the SDTM's resistance to radiation, one branch of a Wheatstone bridge was irradiated with gamma rays from a Co-60 source with a dose rate of 10.9 rad min(-1) to a total dose of 100 krad. The TMR of the branch was monitored in situ, and the easy axis TMR loop and low-frequency noise characteristics of a single MTJ were acquired before and after irradiation with the total dose. It was concluded that radiation did not influence the MTJs in any noticeable way in terms of the TMR ratio, coercivity, magnetostatic coupling or low-frequency noise.

  • 44.
    Persson, Anders
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Microsystems Technology.
    Thornell, Greger
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Microsystems Technology.
    Nguyen, Hugo
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Microsystems Technology.
    Rapid prototyping of magnetic tunnel junctions with focused ion beam processes2010In: Journal of Micromechanics and Microengineering, ISSN 0960-1317, E-ISSN 1361-6439, Vol. 20, no 5, p. 055039-Article in journal (Refereed)
    Abstract [en]

    Submicron sized Magnetic tunnel junctions (MTJs) are most often fabricated by time-consuming and expensive e-beam lithography. From a research and development perspective, a short lead time is one of the major concerns. Here, a rapid process scheme for fabrication of micrometer size MTJs with focused ion beam processes is presented. The magnetic properties of the fabricated junctions is investigated in terms of magnetic domain structure, tunnelling magnetoresistance (TMR) and coercivity, with extra attention to the effect of Ga implantation from the ion beam. In particular, the effect of the implantation on the minimum junction size and the magnetization of the sensing layer are studied. In the latter case, magnetic force microscopy and micromagnetic simulations, with the Object Oriented Micromagnetic Framework (OOMMF), are used to study the magnetization reversal. The fabricated junctions show considerable coercivity both along their hard and easy axes. Interestingly, the sensing layer exhibit two remanent states: one with a single and one with a double domain. The hard axis TMR loop has kinks at about ±20 mT which is attributed to a non-uniform lateral coercivity, where the rim of the junctions, which is subjected to Ga implantation from the flank of the ion beam, is more coercive than the unirradiated centre. The width of the coercive rim is estimated to 160 nm from the hard axis TMR loop. The easy axis TMR loop shows more coercivity than an unirradiated junction and, this too, is found to stem from the coercive rim, as seen from the simulations. It is concluded that the process scheme has three major advantages. Firstly, it has a high lateral and depth resolution – the depth resolution is enhanced by end point detection – and is capable of making junctions of sizes down towards the limit set by the width of the irradiated rim. Secondly, the most delicate process steps are preformed in unbroken vacuum enabling the use of materials prone to forming oxides in the MTJ film stack. Thirdly, the scheme is both uncomplicated and quick and makes it possible to go from design to characterization in the order of hours.

  • 45.
    Qejvanaj, F.
    et al.
    NanOsc AB, S-16440 Kista, Sweden.;KTH Royal Inst Technol, Sch Informat & Commun Technol, Dept Mat & Nano Phys, S-16440 Kista, Sweden..
    Mazraati, H.
    NanOsc AB, S-16440 Kista, Sweden.;KTH Royal Inst Technol, Sch Informat & Commun Technol, Dept Mat & Nano Phys, S-16440 Kista, Sweden..
    Jiang, S.
    KTH Royal Inst Technol, Sch Informat & Commun Technol, Dept Mat & Nano Phys, S-16440 Kista, Sweden..
    Persson, Anders
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Applied Nuclear Physics.
    Sani, S. R.
    KTH Royal Inst Technol, Sch Informat & Commun Technol, Dept Mat & Nano Phys, S-16440 Kista, Sweden..
    Chung, S.
    KTH Royal Inst Technol, Sch Informat & Commun Technol, Dept Mat & Nano Phys, S-16440 Kista, Sweden.;Univ Gothenburg, Dept Phys, S-41296 Gothenburg, Sweden..
    Magnusson, F.
    NanOsc AB, S-16440 Kista, Sweden..
    Åkerman, J.
    NanOsc AB, S-16440 Kista, Sweden.;KTH Royal Inst Technol, Sch Informat & Commun Technol, Dept Mat & Nano Phys, S-16440 Kista, Sweden.;Univ Gothenburg, Dept Phys, S-41296 Gothenburg, Sweden..
    Planar Hall-Effect Bridge Sensor With NiFeX (X = Cu, Ag, and Au) Sensing Layer2015In: IEEE transactions on magnetics, ISSN 0018-9464, E-ISSN 1941-0069, Vol. 51, no 11, article id 4005404Article in journal (Refereed)
    Abstract [en]

    This paper presents a new material alloy for planar Hall-effect bridge (PHEB) sensors and the accurate analysis of the resistance and sensitivity of these materials. The sensing layer is based on NiFeX (X = Cu, Ag, and Au). These alloys have a lower resistance without a significant loss of sensitivity. The presented PHEB sensors with NiFeX sensing layer show a coercivity of 1.7 Oe, lower than that of PHEB sensors with NiFe sensing layers, which have coercivities of 2.2 Oe.

  • 46. Qejvanaj, Fatjon
    et al.
    Zubair, M.
    Persson, Anders
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Applied Nuclear Physics.
    Mohseni, S. M.
    Fallahi, V.
    Sani, S. R.
    Chung, S.
    Le, Tuan
    Magnusson, F.
    Akerman, J.
    Thick Double-Biased IrMn/NiFe/IrMn Planar Hall Effect Bridge Sensors2014In: IEEE transactions on magnetics, ISSN 0018-9464, E-ISSN 1941-0069, Vol. 50, no 11, article id 4006104Article in journal (Refereed)
    Abstract [en]

    In this paper, we present a new material stack for planar Hall effect bridge (PHEB) sensors and a detailed investigation of the sensitivity and noise properties of PHEB sensors made from these. The sputter deposited material stack was based on a ferromagnetic (FM) NiFe sensing layer surrounded by two layers of anti-FM IrMn. This material stack enables implementation of a thick NiFe layer without loss of sensitivity. We present an improvement in detectivity in the PHEB by changing the shape and the materials of the corners between the sensors in a meander shape. A significant reduction of noise also comes from the thick NiFe layer, due to the reduced resistance of the sensor.

  • 47.
    Seton, Ragnar
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Microsystems Technology.
    Sturesson, Peter
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Microsystems Technology. Dept. of Military Sciences, Swedish Defence University, Stockholm, Sweden.
    Persson, Anders
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Microsystems Technology.
    Investigating the plasma properties of a Xe-microplasma thruster2018In: 29th Micromechanics and Microsystems Europe workshop, Bratislava, Slovakia, August 26-29, 2018, Bratislava, Slovenia, 2018Conference paper (Other academic)
    Abstract [en]

    By combining optical emission spectroscopy (OES) and Langumuir probes, the plasma properties of a Xenon-microplasma thruster have been investigated. Using IV-curve analysis the properties of the plasma have been determined and correlated to the power fed into it. Satisfactory agreement has been obtained with the results of OES measurements (line-ratio technique) and shock-cell distance calculations. While the fuel consumption of the thruster decreased very linearly with the power fed to the plasma, the plasma properties was found to have behave in a more complex way. In the studied power range, the density ratio between at least two ions, with upper configurations 5p5(2P◦3/2)7p and 5p5(2P◦3/2)6p, strongly indicated that the ionization processes of the former was favorable in terms of thrust for the geometry of the nozzle. This was supported electron temperature measurements from IV-curves. 

  • 48.
    Snögren, Pär
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Microsystems Technology, Ångström Space Technology Centre (ÅSTC).
    Berglund, Martin
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Microsystems Technology, Ångström Space Technology Centre (ÅSTC).
    Persson, Anders
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Microsystems Technology, Ångström Space Technology Centre (ÅSTC).
    Combined pressure and flow sensor integrated in a split-ring resonator microplasma source2016In: Applied Physics Letters, ISSN 0003-6951, E-ISSN 1077-3118, Vol. 109, no 17, article id 173508Article in journal (Refereed)
    Abstract [en]

    Monitoring and control of the principal properties of a discharge or plasma is vital in many applications, and sensors for measuring them must be integrated close to the plasma source in order to deliver reliable results. This is particularly important, and challenging, in miniaturized systems, where different compatibility issues sets the closest level of integration. In this paper, a sensor for simultaneous measurement of the pressure and flow through a stripline split-ring resonator microplasma source is presented. The sensor utilize fully integrated electrodes positioned upstream and downstream of the microplasma source to study these parameters, and was found to deliver uniform and unambiguous results in a pressure and flow range of 1-6 Torr and 1-15 sccm, respectively. Furthermore, hysteresis and drift in the measurements was found to be mitigated by introducing a resistor in parallel with the plasma, in order to facilitate discharging of the electrodes. Combined, the results show that the sensor is fully compatible with miniaturized microfluidic systems in general, and a system for optogalvanic spectroscopy in particular.

  • 49.
    Sturesson, Peter
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Microsystems Technology, Ångström Space Technology Centre (ÅSTC). Försvarshögskolan/Swedish National Defence College.
    Berglund, Martin
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Microsystems Technology, Ångström Space Technology Centre (ÅSTC).
    Söderberg, Johan
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Microsystems Technology, Ångström Space Technology Centre (ÅSTC).
    Klintberg, Lena
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Microsystems Technology, Ångström Space Technology Centre (ÅSTC).
    Persson, Anders
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Microsystems Technology, Ångström Space Technology Centre (ÅSTC).
    Thornell, Greger
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Microsystems Technology, Ångström Space Technology Centre (ÅSTC).
    Fabrication of Suspended All-Metal Sensor Elements in Ceramic Laminates2016In: Proc. of Micronano System Workshop 2016, Lund, Sweden, May 17-18, 2016, 2016Conference paper (Other academic)
    Abstract [en]

    To target a wide range of high-temperature applications [1-4], the Ångström Space Technology Centre has added High-Temperature Co-fired Ceramics, HTTC, technology to its repertoire. Usually, this technology follows a processing scheme where thin sheets of green-body ceramics are metallized through screen printing and structured by embossing, punching or milling, before they are laminated and sintered to form components. A limitation with this, is the difficulty of realizing freely suspended metal structures, which is a disadvantage in, e.g., the fabrication of calorimetric sensors or electric field probes. In this work, the embedding of platinum wires in HTCC is explored experimentally, and demonstrated for use in pressure and plasma I-V sensing.

  • 50.
    Sturesson, Peter
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Microsystems Technology, Ångström Space Technology Centre (ÅSTC). Försvarshögskolan/Swedish National Defence College.
    Seton, Ragnar
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Microsystems Technology, Ångström Space Technology Centre (ÅSTC).
    Klintberg, Lena
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Microsystems Technology.
    Thornell, Greger
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Microsystems Technology, Ångström Space Technology Centre (ÅSTC).
    Persson, Anders
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Microsystems Technology, Ångström Space Technology Centre (ÅSTC). Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Applied Nuclear Physics.
    Effect of Resistive and Plasma Heating on the Specific Impulse of a Ceramic Cold Gas ThrusterIn: Journal of microelectromechanical systems, ISSN 1057-7157, E-ISSN 1941-0158Article in journal (Refereed)
    Abstract [en]

    Research and development of small satellites has continued to expand over the last decades. However, propulsion systems with adequate performance have persisted to be a great challenge. In this paper, the effects of three different heaters on the specific impulse and overall thrust efficiency of a cold gas microthruster are presented. They consisted of a conventional, printed resistive thick-film element, a freely suspended wire, and a stripline split-ring resonator microplasma source and were integrated in a single device made from high-temperature co-fired ceramics (HTCC). The devices were evaluated in two setups, where the first measured thrust and the other shock cell geometry. In addition, the resistive elements were evaluated as gas temperature sensors. The microplasma source was found to provide the greatest improvement in both specific impulse and thrust efficiency, increasing the former from an un-heated level of 44 s to 55 s when heating with a power of 1.1 W. This corresponded to a thrust efficiency of 53 %. This could be compared to the results from the wire and printed heaters which were 50 s and 18 %, and 45 s and 14 %, respectively. The combined results also showed that imaging the shock cells of a plasma heated thruster was a simple and effective way to determine its performance compared to the traditional thrust balance method.

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