Dual-mode thin film bulk acoustic resonator (TFBAR) devices are fabricated with c-axis tilted AlN films. To fabricate dual-mode TFBAR devices, the off-axis RF magnetron sputtering method for the growth of tilted piezoelectric AlN thin films is adopted. In this report, the AlN thin films are deposited with tilting angles of 15° and 23°. The frequency response of the TFBAR device with 23° tilted AlN thin film is measured to reveal its ability to provide dual-mode resonance. The sensitivities of the longitudinal and shear modes to mass loading are calculated to be 2295？Hz？cm2/ng and 1363？Hz？cm2/ng with the mechanical quality factors of 480 and 287, respectively. The sensitivities of the longitudinal and shear modes are calculated to be 0 and 15？Hz？cm2/μg for liquid loading. 1. Introduction Surface and bulk acoustic resonator devices are attracting increasing attention owning to their use in various novel sensors, including UV sensors, mass sensors, biosensors, and others [1–3]. Surface acoustic resonators have been developed and examined for potential sensor applications because they are cheap and small. However, surface acoustic resonators suffer from high insertion loss and poor power handling. Therefore, thin film bulk acoustic resonator (TFBAR) devices have been studied globally; they have a low insertion loss, a high power handling capability, small size, and high sensitivity [4–6]. Lakin classified FBAR devices into three types, which were via-isolated resonators, air gap-isolated resonators, and solidly mounted resonators [7]. The general purpose of these structures is to form a free or clamped interface beneath the resonance zone. This work develops a dual-mode TFBAR device based on an adapted via-isolated resonator with piezoelectric thin film whose c-axis is tilted. The back-etched cavity is used as the sensing area. Despite the use of various piezoelectric films in TFBAR devices, including PZT, ZnO, and AlN thin films [8–12], most of the many studies of piezoelectric thin films have focused on PZT piezoelectric materials. However, the use of PZT is limited for environmental reasons [13, 14]. Hence, ZnO and AlN thin films have become the most promising materials for piezoelectric applications. This study concerns piezoelectric thin films of AlN, whose high quality factor makes them useful for elucidating the sensing properties of TFBAR for liquids. TFBAR has two major resonance modes longitudinal and shear. The longitudinal mode is typically used when TFBAR is utilized as a communication device at high operating frequencies. For biosensor
References
[1]
C.-L. Wei, Y.-C. Chen, J.-L. Fu, K.-S. Kao, D.-L. Cheng, and C.-C. Cheng, “UV detection based on a ZnO/LiNbO3 layered surface acoustic wave oscillator circuit,” Journal of Vacuum Science and Technology A, vol. 27, no. 6, pp. 1343–1346, 2009.
[2]
R.-C. Lin, Y.-C. Chen, W.-T. Chang, C.-C. Cheng, and K.-S. Kao, “Highly sensitive mass sensor using film bulk acoustic resonator,” Sensors and Actuators A, vol. 147, no. 2, pp. 425–429, 2008.
[3]
I.-Y. Huang and M.-C. Lee, “Development of a FPW allergy biosensor for human IgE detection by MEMS and cystamine-based SAM technologies,” Sensors and Actuators B, vol. 132, no. 1, pp. 340–348, 2008.
[4]
R. C. Ruby, P. Bradley, Y. Oshmyansky, and A. Chien, “Thin film bulk wave acoustic resonators (FBAR) for wireless applications,” in Proceedings of the IEEE Ultasonics Symposium, pp. 813–821, October 2001.
[5]
J. D. Larson, R. C. Ruby, P. D. Bradley, J. Wen, S.-L. Kok, and A. Chien, “Power handling and temperature coefficient studies in FBAR duplexers for the 1900？MHz PCS band,” in Proceedings of the IEEE Ultasonics Symposium, pp. 869–874, October 2000.
[6]
K. M. Lakin, K. T. McCarron, J. Belsick, and R. Rose, “Filter banks implemented with integrated thin film resonators,” in Proceedings of the IEEE Ultasonics Symposium, pp. 851–854, October 2000.
[7]
K. M. Lakin, “Thin film resonator technology,” IEEE Transactions on Ultrasonics, Ferroelectrics, and Frequency Control, vol. 52, no. 5, pp. 707–716, 2005.
[8]
Q.-X. Su, P. Kirby, E. Komuro, M. Imura, Q. Zhang, and R. Whatmore, “Thin-film bulk acoustic resonators and filters using ZnO and lead-zirconium-titanate thin films,” IEEE Transactions on Microwave Theory and Techniques, vol. 49, no. 4, pp. 769–778, 2001.
[9]
R.-C. Lin, K.-S. Kao, C.-C. Cheng, and Y.-C. Chen, “Deposition and structural properties of RF magnetron-sputtered ZnO thin films on Pt/Ti/SiNx/Si substrate for FBAR device,” Thin Solid Films, vol. 516, no. 16, pp. 5262–5265, 2008.
[10]
R.-C. Lin, Y.-C. Chen, and K.-S. Kao, “Two-step sputtered ZnO piezoelectric films for film bulk acoustic resonators,” Applied Physics A, vol. 89, no. 2, pp. 475–479, 2007.
[11]
C.-J. Chung, Y.-C. Chen, C.-C. Cheng, and K.-S. Kao, “An improvement of tilted AlN for shear and longitudinal acoustic wave,” Applied Physics A, vol. 94, no. 2, pp. 307–313, 2009.
[12]
C.-L. Wei, Y.-C. Chen, S.-R. Li, C.-C. Cheng, K.-S. Kao, and C.-J. Chung, “Effects of reflecting layers on resonance characteristics of a solidly mounted resonator with (1/4)λ mode configuration,” Applied Physics A, vol. 99, no. 1, pp. 271–278, 2010.
[13]
European Union, Waste Electrical and Electronic Equipment [WEEE] Regulations, EU-Directive 96/EC, 2002.
[14]
European Union, Restriction of the Use of Certain Hazardous Substances in Electrical and Electronic Equipment [ROHS] Regulations, EU-Directive 95/EC, 2002.
[15]
H. Zhang and E. S. Kim, “Micromachined acoustic resonant mass sensor,” Journal of Microelectromechanical Systems, vol. 14, no. 4, pp. 699–706, 2005.
[16]
M. Minakata, N. Chubachi, and Y. Kikuchi, “Variation of c-axis orientation of ZnO thin films deposited by DC diode sputtering,” Japanese Journal of Applied Physics, vol. 12, no. 3, pp. 474–475, 1973.
[17]
F. Martin, M.-E. Jan, S. Rey-Mermet et al., “Shear mode coupling and tilted grain growth of AlN thin films in BAW resonators,” IEEE Transactions on Ultrasonics, Ferroelectrics, and Frequency Control, vol. 53, no. 7, pp. 1339–1343, 2006.
[18]
M. Link, M. Schreiter, J. Weber et al., “C-axis inclined ZnO films deposited by reactive sputtering using an additional blind for shear BAW devices,” in Proceedings of the IEEE Ultrasonics Symposium, vol. 1, pp. 202–205, September 2005.
[19]
J. S. Wang, K. M. Lakin, and A. R. Landin, “Sputtered c-axis inclined piezoelectric film and shear wave resonators,” in Proceedings of the 37th IEEE Frequency Control Symposium, pp. 144–146, Philadelphia, Pa, USA, 1983.
[20]
J. Weber, W. M. Albers, J. Tuppurainen et al., “Shear mode FBARs as highly sensitive liquid biosensors,” Sensors and Actuators A, vol. 128, no. 1, pp. 84–88, 2006.
[21]
M. Link, J. Weber, M. Schreiter, W. Wersing, O. Elmazria, and P. Alnot, “Sensing characteristics of high-frequency shear mode resonators in glycerol solutions,” Sensors and Actuators B, vol. 121, no. 2, pp. 372–378, 2007.
[22]
G. Wingqvist, J. Bjurstr？m, L. Liljeholm, V. Yantchev, and I. Katardjiev, “Shear mode AlN thin film electro-acoustic resonant sensor operation in viscous media,” Sensors and Actuators B, vol. 123, no. 1, pp. 466–473, 2007.
[23]
G. Wingqvist, “AlN-based sputter-deposited shear mode thin film bulk acoustic resonator (FBAR) for biosensor applications—a review,” Surface and Coatings Technology, vol. 205, no. 5, pp. 1279–1286, 2010.
[24]
G. Wingqvist, H. Anderson, C. Lennartsson, T. Weissbach, V. Yantchev, and A. L. Spetz, “On the applicability of high frequency acoustic shear mode biosensing in view of thickness limitations set by the film resonance,” Biosensors and Bioelectronics, vol. 24, no. 11, pp. 3387–3390, 2009.
[25]
M. Akiyama, K. Nagao, N. Ueno, H. Tateyama, and T. Yamada, “Influence of metal electrodes on crystal orientation of aluminum nitride thin films,” Vacuum, vol. 74, no. 3-4, pp. 699–703, 2004.
[26]
K. Biswas and S. Kal, “Etch characteristics of KOH, TMAH and dual doped TMAH for bulk micromachining of silicon,” Microelectronics Journal, vol. 37, no. 6, pp. 519–525, 2006.
[27]
C. M. Horowitz, R. A. Monetti, and E. V. Albano, “Competitive growth model involving random deposition and random deposition with surface relaxation,” Physical Review E, vol. 63, no. 6, Article ID 066132, 2001.
[28]
I. Petrov, P. B. Barna, L. Hultman, and J. E. Greene, “Microstructural evolution during film growth,” Journal of Vacuum Science and Technology A, vol. 21, pp. S117–S128, 2003.
[29]
L. Qin, Q. Chen, H. Cheng, and Q.-M. Wang, “Analytical study of dual-mode thin film bulk acoustic resonators (FBARs) based on ZnO and AlN films with tilted c-axis orientation,” IEEE Transactions on Ultrasonics, Ferroelectrics, and Frequency Control, vol. 57, no. 8, pp. 1840–1853, 2010.
[30]
G. Sauerbrey, “Verwendung von schwingquarzen zur w？gung dünner schichten und zur mikrow？gung,” Zeitschrift für Physik, vol. 155, pp. 206–222, 1959.
[31]
J. Bjurstr？m, D. Rosén, I. Katardjiev, V. M. Yanchev, and I. Petrov, “Dependence of the electromechanical coupling on the degree of orientation of c-textured thin AlN films,” IEEE Transactions on Ultrasonics, Ferroelectrics, and Frequency Control, vol. 51, no. 10, pp. 1347–1353, 2004.
[32]
C.-L. Wei, Y.-C. Chen, C.-C. Cheng, and K.-S. Kao, “Solidly mounted resonators consisting of a molybdenum and titanium Bragg reflector,” Applied Physics A, vol. 90, no. 3, pp. 501–506, 2008.
