Design, Modeling and Characterization of High-Performance Bulk-Mode Piezoelectric MEMS Resonators

Abstract

In this paper, the design, modeling and characterization of width-extensional (WE) mode piezoelectric microelectromechanical systems (MEMS) resonators are presented. The resonators consist of piezoelectric stacked layers for transductions, highly doped single crystal silicon (HDS) device layer as vibrating structures, and oxide layers on top and bottom surfaces for passive temperature compensation. Dependencies of quality factors ( <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$Q\text{s}$ </tex-math></inline-formula> ) of the WE mode resonators on structure designs, such as device length, thickness as well as crystal orientation of the HDS device layer are investigated. Effects of crystal orientation of the HDS device layer and oxide thickness on the temperature stability of resonant frequency of the WE mode resonators are also analyzed. Both aluminum nitride (AlN) and scandium-doped aluminum nitride (Sc <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><i>x</i></sub> Al <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">1−<i>x</i></sub> N, <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$x=9.5\%$ </tex-math></inline-formula> ) are adopted as the piezoelectric transduction layer in this work, in order to investigate the performance improvements by Sc doping. The designed WE mode MEMS resonators are fabricated based on a piezoelectric on cavity-silicon-on-insulator (CSOI) platform. A fabricated ScAlN-based MEMS resonator exhibits a <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$Q$ </tex-math></inline-formula> of 11086 and motional impedance as low as 28 <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\Omega $ </tex-math></inline-formula> at its series resonant frequency of 25.044 MHz. [2021-0222]