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Synthesis of textured thin piezoelectric AlN films with a nonzero C-axis mean tilt for the fabrication of shear mode resonators
Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Electronics.
Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Electronics.
Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Electronics.
2006 (English)In: IEEE Transactions on Ultrasonics, Ferroelectrics and Frequency Control, ISSN 0885-3010, E-ISSN 1525-8955, Vol. 53, no 11, 2095-2100 p.Article 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.

Place, publisher, year, edition, pages
2006. Vol. 53, no 11, 2095-2100 p.
National Category
Engineering and Technology
Identifiers
URN: urn:nbn:se:uu:diva-23532DOI: 10.1109/TUFFC.2006.149ISI: 000241566400014OAI: oai:DiVA.org:uu-23532DiVA: diva2:51306
Available from: 2007-01-30 Created: 2007-01-30 Last updated: 2017-12-07Bibliographically approved
In thesis
1. Thin Film Electroacoustic Devices for Biosensor Applications
Open this publication in new window or tab >>Thin Film Electroacoustic Devices for Biosensor Applications
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. 96 p.
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:nbn:se:uu:diva-89424 (URN)978-91-554-7432-4 (ISBN)
Public defence
2009-03-27, Å2005, Ångströmlaboratoriet, Lägerhyddsvägen 1, Uppsala, 10:15 (English)
Opponent
Supervisors
Projects
wisenet
Available from: 2009-03-06 Created: 2009-02-13 Last updated: 2011-01-17Bibliographically approved
2. Advanced Thin Film Electroacoustic Devices
Open this publication in new window or tab >>Advanced Thin Film Electroacoustic Devices
2007 (English)Doctoral thesis, comprehensive summary (Other academic)
Alternative title[sv]
Avancerade Elektroakustiska Tunnfilmskomponenter
Abstract [en]

The explosive development of the telecom industry and in particular wireless and mobile communications in recent years has lead to a rapid development of new component and fabrication technologies to continually satisfy the mutually exclusive requirements for better performance and miniaturization on the one hand and low cost on the other. A fundamental element in radio communications is time and frequency control, which in turn is achieved by high performance electro-acoustic components made on piezoelectric single crystalline substrates. The latter, however, reach their practical limits in terms of performance and cost as the frequency of operation reaches the microwave range. Thus, the thin film electro-acoustic technology, which uses thin piezoelectric films instead, has been recently developed to alleviate these deficiencies.

This thesis explores and addresses a number of issues related to thin film synthesis on the one hand as well as component design and fabrication on other. Specifically, the growth of highly c-axis textured AlN thin films has been studied and optimized for achieving high device performance. Perhaps, one of the biggest achievements of the work is the development of a unique process for the deposition of AlN films with a mean c-axis tilt, which is of vital importance for the fabrication of resonators operating in contact with liquids, i.e. biochemical sensors. This opens the way for the development of a whole range of sensors and bio-analytical tools. Further, high frequency Lamb wave resonators have been designed, fabricated and evaluated. Performance enhancement of FBAR devices is also addressed, e.g. spurious mode suppression, temperature compensation, etc. It has been demonstrated, that even without temperature compensation, shear mode resonators operating in a liquid still exhibit an excellent performance in terms of Q (200) and coupling (~1.8%) at 1.2 GHz, resulting in a mass resolution better than 2 ng cm-2 in water, which excels that of today’s quartz sensors.

Place, publisher, year, edition, pages
Uppsala: Acta Universitatis Upsaliensis, 2007. 84 p.
Series
Digital Comprehensive Summaries of Uppsala Dissertations from the Faculty of Science and Technology, ISSN 1651-6214 ; 280
Keyword
Technology, aluminum nitride, FBAR, shear mode resonator, lamb wave devices, liquid sensor, biosensor, temperature compensation, reactive sputtering, TEKNIKVETENSKAP
National Category
Engineering and Technology
Identifiers
urn:nbn:se:uu:diva-7672 (URN)978-91-554-6819-4 (ISBN)
Public defence
2007-03-30, Polhemssalen, Ångströmlaboratoriet, Lägerhyddsvägen 1, Uppsala, 09:30 (English)
Opponent
Supervisors
Available from: 2007-03-08 Created: 2007-03-08 Last updated: 2010-02-18Bibliographically approved

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