Design and Fabrication of Si-Diaphragm, ZnO Piezoelectric Film-Based MEMS Acoustic Sensor Using SOI Wafers

This paper reports a simpler technique for fabricating an microelectromechanical system acoustic sensor based on a piezoelectric zinc oxide (ZnO) thin film, utilizing silicon-on-insulator wafers. A highly c-axis-oriented ZnO film of thickness 2.4 μm, which is covered with 0.2-μm-thick PECVD SiO2, is sandwiched between two aluminum electrodes on a 25- μm-thick silicon diaphragm. This diaphragm thickness has been optimized to withstand sound pressure level range of 120-160 dB. Stress distribution studies using ANSYS have been performed to determine the locations for placement of capacitor electrodes. This paper also reports a technique for the creation of a positive slope of the ZnO step to ensure proper coverage during Al metallization. In order to maximize yield, process steps have been developed to avoid the microtunnel blockage by silicon/glass particles. The packaged sensor is found to exhibit a sensitivity of 382 μV/Pa (RMS) in the frequency range from 30 to 8000 Hz, under varying acoustic pressure.

[1]  D. Blackstock.  Fundamentals of Physical Acoustics , 2000 .

[2]  M. Royer,et al.  ZnO on Si integrated acoustic sensor , 1983 .

[3]  P. Muralt,et al.  Thickness dependence of the properties of highly c-axis textured AlN thin films , 2004 .

[4]  Richard M. White,et al.  Piezoelectric cantilever microphone and microspeaker , 1996 .

[5]  Yilong Hao,et al.  The compatibility of ZnO piezoelectric film with micromachining process , 2003 .

[6]  Anil Arora,et al.  Zinc oxide thin film-based MEMS acoustic sensor with tunnel for pressure compensation , 2008 .

[7]  W. Janna,et al.  Introduction to Fluid Mechanics , 2012 .

[8]  Richard S. Muller,et al.  Piezoelectric microphone with on-chip CMOS circuits , 1993 .

[9]  Jan Mehner,et al.  Computer Aided Design for Microelectromechanical Systems , 2001 .

[10]  B. Khuri-Yakub,et al.  Surface micromachined capacitive ultrasonic transducers , 1998, IEEE Transactions on Ultrasonics, Ferroelectrics and Frequency Control.

[11]  Xiaoming Wu,et al.  A Micromachined Piezoelectric Ultrasonic Transducer Operating in ${\rm d}_{33}$ Mode Using Square Interdigital Electrodes , 2007, IEEE Sensors Journal.

[12]  Masanori Okuyama,et al.  Ultrasonic micro array sensors using piezoelectric thin films and resonant frequency tuning , 2004 .

[13]  Man-Soon Yoon,et al.  Piezoelectric microspeakers with high compressive ZnO film and floating electrode , 2009 .

[14]  Madan Dubey,et al.  Design and Fabrication of a Lead Zirconate Titanate (PZT) Thin Film Acoustic Sensor , 2003 .

[15]  Wouter Olthuis,et al.  A review of silicon microphones , 1994 .

[16]  Yu Wang,et al.  Design, fabrication, and measurement of high-sensitivity piezoelectric microelectromechanical systems accelerometers , 2003 .

[17]  Reza Abdolvand,et al.  Voltage-tunable piezoelectrically-transduced single-crystal silicon micromechanical resonators , 2004 .

[18]  Seung S. Lee,et al.  Piezoelectric microphone built on circular diaphragm , 2008 .

[19]  Patrick Richard Scheeper,et al.  A piezoelectric triaxial accelerometer , 1996 .

[20]  A. Barzegar,et al.  Piezoelectric micromachined ultrasonic transducers based on PZT thin films , 2005, IEEE Transactions on Ultrasonics, Ferroelectrics and Frequency Control.

[21]  Zheyao Wang,et al.  Design and analysis of a PZT-based micromachined acoustic sensor with increased sensitivity , 2005, IEEE Transactions on Ultrasonics, Ferroelectrics and Frequency Control.

[22]  Emmanuel Defay,et al.  PZT thin films integration for the realisation of a high sensitivity pressure microsensor based on a vibrating membrane , 2002 .

[23]  Chen Chao,et al.  Piezoelectric micromachined ultrasonic transducer based on dome-shaped piezoelectric single layer , 2010 .

[24]  Sang Choon Ko,et al.  Micromachined piezoelectric membrane acoustic device , 2003 .