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Thin Film Electroacoustic Devices for Biosensor Applications
Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Electronics. (Fasta tillståndets elektronik, Solid State Electronics)
2009 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Biosensors are today important devices within various application areas.

In this thesis a new type of label-free biosensor device is studied, which is fabricated using the same processes used for the fabrication of integrated circuits. This enables tighter integration and further sensors/biosensor miniaturization. The device is a so-called Thin Film Bulk Acoustic Resonator (FBAR). Within this thesis a low temperature reactive sputtering process for growing AlN thin films with a c-axis inclination of 20-30o has been developed. This enables shear mode FBAR fabrication suitable for in-liquid operation, essential for biosensor applications. Shear mode FBARs were fabricated operating at frequencies above 1GHz exhibiting Q values of 100-200 in water and electromechanical coupling factors kt2 of about 1.8%. This made it possible to move the thickness excited shear mode sensing of biological layers into a new sensing regime using substantially higher operation frequencies than the conventionally used quartz crystal microbalance (QCM) operating at 5-20MHz. Measured noise levels of shear mode FBARs in contact with water showed the resolution to be in the range 0.3ng/cm2 to 7.5ng/cm2. This demonstrated the FBAR resolution without any averaging or additional stabilization measures already to be in the same range as the conventional QCM (5ng/cm2), suggesting that FBARs may be a competitive and low cost alternative to QCM. The linear thickness limit for sensing of biomolecular layers was concluded to be larger than the thickness of the majority of the molecular systems envisaged for FBAR biosensor applications. A temperature compensated shear mode FBAR composite structure was demonstrated with retained coupling factor and Q-value by utilizing the second mode of operation. Understanding has been gained on the sensor operation as well as on how the design parameters influence its performance. Specifically, sensitivity amplification utilizing low acoustic impedance layers in the FBAR structure has been demonstrated and explained. Further, temperature compensated Lamb mode (FPAR) devices were also studied and demonstrated with optimized electromechanical couplings.

Place, publisher, year, edition, pages
Uppsala: Acta Universitatis Upsaliensis , 2009. , p. 96
Series
Digital Comprehensive Summaries of Uppsala Dissertations from the Faculty of Science and Technology, ISSN 1651-6214 ; 609
National Category
Other Electrical Engineering, Electronic Engineering, Information Engineering
Research subject
Electronics
Identifiers
URN: urn:nbn:se:uu:diva-89424ISBN: 978-91-554-7432-4 (print)OAI: oai:DiVA.org:uu-89424DiVA, id: diva2:173426
Public defence
2009-03-27, Å2005, Ångströmlaboratoriet, Lägerhyddsvägen 1, Uppsala, 10:15 (English)
Opponent
Supervisors
Projects
wisenetAvailable from: 2009-03-06 Created: 2009-02-13 Last updated: 2011-01-17Bibliographically approved
List of papers
1. Synthesis of textured thin piezoelectric AlN films with a nonzero C-axis mean tilt for the fabrication of shear mode resonators
Open this publication in new window or tab >>Synthesis of textured thin piezoelectric AlN films with a nonzero C-axis mean tilt for the fabrication of shear mode resonators
2006 (English)In: IEEE Transactions on Ultrasonics, Ferroelectrics and Frequency Control, ISSN 0885-3010, E-ISSN 1525-8955, Vol. 53, no 11, p. 2095-2100Article in journal (Refereed) Published
Abstract [en]

A method for the deposition of thin piezoelectric aluminum nitride (AlN) films with a nonzero c-axis mean tilt has been developed. The deposition is done in a standard reactive magnetron sputter deposition system without any hardware modifications. In essence, the method consists of a two-stage deposition process. The resulting film has a distinct tilted texture with the mean tilt of the c-axis varying roughly in the interval 28 to 32 degrees over the radius of the wafer excluding a small exclusion zone at the center of the latter. The mean tilt angle distribution over the wafer has a circular symmetry. A membrane-type shear mode thickness-excited thin film bulk acoustic resonator together with a micro-fluidic transport system has been subsequently fabricated using the two stage AIN deposition as well as standard bulk micro machining of Si. The resonator consisted of a 2-mu m-thick AlN film with 200-nm-thick A1 top and bottom electrodes. The resonator was characterized with a network analyzer when operating in both air and water. The shear mode resonance frequency was about 1.6 GHz, the extracted device Q around 350, and the electromechanical coupling k(t)(2) 2% when the resonator was operated in air, whereas the latter two dropped down to 150 and 1.8%, respectively, when the resonator was operated in pure water.

National Category
Engineering and Technology
Identifiers
urn:nbn:se:uu:diva-23532 (URN)10.1109/TUFFC.2006.149 (DOI)000241566400014 ()
Available from: 2007-01-30 Created: 2007-01-30 Last updated: 2017-12-07Bibliographically approved
2. Temperature compensation of liquid FBAR sensors
Open this publication in new window or tab >>Temperature compensation of liquid FBAR sensors
2007 (English)In: Journal of Micromechanics and Microengineering, ISSN 0960-1317, E-ISSN 1361-6439, Vol. 17, no 3, p. 651-658Article in journal (Refereed) Published
Abstract [en]

In this work we demonstrate a practically complete temperature compensation of the second harmonic shear mode in a composite Al/AlN/Al/SiO2 thin film bulk acoustic resonator (FBAR) in the temperature range 25 °C–95 °C. The main advantages of this mode are its higher Q value in liquids as well as its higher frequency and hence higher resolution for sensor applications. For comparative reasons the non-compensated fundamental shear mode is also included in these studies. Both modes have been characterized when operated both in air and in pure water. Properties such as Q value, electromechanical coupling, dissipation and sensitivity are studied. An almost complete temperature compensation of the second harmonic shear mode was observed for an oxide thickness of 1.22 µm for an FBAR consisting of 2 µm thick AlN and 200 nm thick Al electrodes. Thus, the measured temperature coefficient of frequency (TCF) in air for the non-compensated fundamental shear mode (1.25 GHz) varied between −31 and −36 ppm °C−1 over the above temperature range while that of the compensated second harmonic shear mode (1.32 GHz) varied between +2 ppm °C−1 and −2 ppm °C−1 over the same temperature interval. When operated in pure water the former type shows a Q value and coupling coefficient, k2t, around 180 and 2%, respectively, whereas for the second harmonic these are 230 and 1.4%, respectively.

National Category
Engineering and Technology
Identifiers
urn:nbn:se:uu:diva-10269 (URN)10.1088/0960-1317/17/3/030 (DOI)000245433800030 ()
Projects
WISENET
Available from: 2007-03-09 Created: 2007-03-09 Last updated: 2017-12-11Bibliographically approved
3. Shear mode AlN thin film electro-acoustic resonant sensor operation in viscous media
Open this publication in new window or tab >>Shear mode AlN thin film electro-acoustic resonant sensor operation in viscous media
Show others...
2007 (English)In: Sensors and actuators. B, Chemical, ISSN 0925-4005, E-ISSN 1873-3077, Vol. 123, no 1, p. 466-473Article in journal (Refereed) Published
Abstract [en]

A shear mode thin film bulk acoustic resonator (FBAR) operating in liquid media together with a microfluidic transport system is presented. The resonator has been fabricated utilizing a recently developed reactive sputter-deposition process for AlN thin films with inclined c-axis relative to the surface normal with a mean tilt of around 30°. The resonator has a resonance frequency of around 1.2 GHz and a Q value in water of around 150. Sensor operation in water and glycerol solutions is characterized. Theoretical analysis of the sensor operation under viscous load as well as of the sensitivity and stability in general is presented. The theoretical predictions are compared with experimental measurements. The results demonstrate clearly the potential of FBAR biosensors for the fabrication of highly sensitive low cost biosensors, bioanalytical tools as well as for liquid sensing in general.

Keywords
AlN, Biosensor, FBAR, Quasi-shear polarized acoustic wave, Thickness mode resonator, Tilted films
National Category
Engineering and Technology
Identifiers
urn:nbn:se:uu:diva-10554 (URN)10.1016/j.snb.2006.09.028 (DOI)000246171200068 ()
Projects
WISENET
Available from: 2007-04-04 Created: 2007-04-04 Last updated: 2017-12-11Bibliographically approved
4. Immunosensor utilizing a shear mode thin film bulk acoustic sensor
Open this publication in new window or tab >>Immunosensor utilizing a shear mode thin film bulk acoustic sensor
2007 (English)In: Sensors and actuators. B, Chemical, ISSN 0925-4005, E-ISSN 1873-3077, Vol. 127, no 1, p. 248-252Article in journal (Refereed) Published
Abstract [en]

An AlN thin film electro-acoustic resonator has been fabricated employing a reactive sputtering process for the deposition of an AlN thin film with inclined c-axis for excitation of the shear mode for operation in liquid media. The main objective is to investigate the efficiency of the micro-fluidic channel system integrated in the silicon wafer underneath the AlN resonator. A comparative study between the shear mode thin film bulk acoustic resonator (FBAR) and a quartz crystal microbalance (QCM) using a competitive antibody–antigen association process for detection of drug molecules is presented.

Keywords
Competitive immunosensor, Shear mode FBAR, Drug detection
National Category
Engineering and Technology
Identifiers
urn:nbn:se:uu:diva-11757 (URN)10.1016/j.snb.2007.07.051 (DOI)000250691100039 ()
Available from: 2007-10-16 Created: 2007-10-16 Last updated: 2017-12-11Bibliographically approved
5. Mass sensitivity of multilayer thin film resonant BAW sensors
Open this publication in new window or tab >>Mass sensitivity of multilayer thin film resonant BAW sensors
2008 (English)In: Sensors and Actuators A-Physical, ISSN 0924-4247, E-ISSN 1873-3069, Vol. 148, no 1, p. 88-95Article in journal (Refereed) Published
Abstract [en]

Abstract: A systematic study of the mass sensitivity and its dependence on the material's properties and thicknesses in composite multilayer Thin Film Bulk Acoustic Resonators (FBAR) is presented. The Mason transmission line model has been employed in combination with the acoustic energy balance principle for the determination of the FBAR mass sensitivity. The results have been experimentally verified. Further, the mass sensitivity dependence on various parameters has been studied and correlated with wave reflection and interference within the composite structure in addition to the well-known dependence on resonator acoustic impedance and operation frequency. The mass sensitivity for both the fundamental and the second harmonic mode of operation has been studied in view of their practical relevance. In particular, sensitivity amplification induced by the presence of an on-top deposited low acoustic impedance layer has been identified for the first harmonic and its potential applicability discussed in terms of gas and in-liquid sensing. Optimized structures for both sensing applications are suggested by considering the overall sensor resolution defined by both the mass sensitivity and the FBAR performance.

Keywords
Mass sensitivity, Bulk acoustic resonator, FBAR, Sensitivity amplification
National Category
Other Electrical Engineering, Electronic Engineering, Information Engineering
Research subject
Electronics
Identifiers
urn:nbn:se:uu:diva-86872 (URN)10.1016/j.sna.2008.07.023 (DOI)000260804500015 ()
Projects
WISENET
Available from: 2008-12-09 Created: 2008-12-08 Last updated: 2018-06-26Bibliographically approved
6. On the applicability of high frequency acoustic shear mode biosensing in view of thickness limitations set by the film resonance
Open this publication in new window or tab >>On the applicability of high frequency acoustic shear mode biosensing in view of thickness limitations set by the film resonance
Show others...
2009 (English)In: Biosensors & bioelectronics, ISSN 0956-5663, E-ISSN 1873-4235, Vol. 24, no 11, p. 3387-3390Article in journal (Refereed) Published
Abstract [en]

The IC-compatible thin film bulk acoustic resonator (FBAR) technology has made it possible to move the thickness excited shear mode sensing of biological layers into a new sensing regime using substantially higher operation frequencies than the conventionally used Quartz Crystal Microbalance (QCM). The limitations of the linear range set by the film resonance using viscoelastic protein films are here for the first time addressed specifically for FBARs operating at 700MHz up to 1.5GHz. Two types of protein multilayer sensing were employed; one utilizing alternating layers of Streptavidin and Biotinated BSA and the other using stepwise cross-linking of fibrinogen with EDC/NHS activation of its carboxyl groups. In both cases the number of protein layers within the linear regime is well above the number of protein layers usually used in biosensor applications, further verifying the applicability of the FBAR as a biosensor. Theoretical calculations are also presented using well established physical models to illustrate the expected behavior of the FBAR sensor, in view of both the frequency and the dissipation shifts.

Keywords
Shear mode electroacoustic sensing, Streptavidin–biotinated BSA, Fibrinogen, High frequency, Thin film bulk acoustic resonator (FBAR)
National Category
Engineering and Technology
Research subject
Electronics
Identifiers
urn:nbn:se:uu:diva-89406 (URN)10.1016/j.bios.2009.04.021 (DOI)000267577900035 ()
Available from: 2009-02-12 Created: 2009-02-12 Last updated: 2018-06-26Bibliographically approved
7. Micromachined thermally compensated thin film Lamb wave resonator for frequency control and sensing applications
Open this publication in new window or tab >>Micromachined thermally compensated thin film Lamb wave resonator for frequency control and sensing applications
2009 (English)In: Journal of Micromechanics and Microengineering, ISSN 0960-1317, E-ISSN 1361-6439, Vol. 19, no 3, p. 035018-Article in journal (Refereed) Published
Abstract [en]

Micromachined thin film plate acoustic wave resonators (FPAR) utilizing the lowest order symmetric Lamb wave (S0) propagating in highly textured 2μm thick Aluminum Nitride (AlN) membranes have been successfully demonstrated [1]. The proposed devices have a SAW-based design and exhibit Q factors of up to 3000 at a frequency around 900MHz as well as design flexibility with respect to the required motional resistance. However, a notable drawback of the proposed devices is non-zero temperature coefficient of frequency (TCF) which lies in the range -20 ppm/K to –25 ppm/K. Thus, despite the promising features demonstrated, further device optimization is required. In this work temperature compensation of thin AlN film Lamb wave resonators is studied and experimentally demonstrated. Temperature compensation while retaining at the same time the device electromechanical coupling is experimentally demonstrated. The zero TCF Lamb wave resonators are fabricated onto composite AlN/SiO2 membranes. Q factors of around 1400 have been measured at a frequency of around 755 MHz. Finally, the impact of technological issues on the device performance is discussed in view of improving the device performance.

National Category
Other Electrical Engineering, Electronic Engineering, Information Engineering
Research subject
Electronics
Identifiers
urn:nbn:se:uu:diva-89404 (URN)10.1088/0960-1317/19/3/035018 (DOI)000263678200019 ()
Projects
WISENET
Funder
Swedish Research Council, 2009-5056
Available from: 2009-02-12 Created: 2009-02-12 Last updated: 2018-06-26Bibliographically approved

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