Zero-Group-Velocity acoustic waveguides for high-frequency resonators

TL;DR

This paper explores zero group velocity acoustic waveguides in SOI/AlN structures for high-frequency resonators, demonstrating their potential for gas sensing and stable operation without metal gratings.

Contribution

It introduces the design and theoretical analysis of ZGV acoustic resonators in SOI/AlN structures, highlighting their thermal stability and gas sensing capabilities.

Findings

Identified ZGV points in SOI/AlN plates up to 1900 MHz.

Estimated temperature coefficients of ZGV frequencies.

Theoretically demonstrated gas sensor sensitivity using ZGV resonators.

Abstract

The propagation of the Lamb-like modes along a silicon-on-insulator (SOI)/AlN thin supported structure was theoretically studied in order to exploit the intrinsic zero group velocity (ZGV) features to design electroacoustic resonators that do not require metal strip gratings or suspended edges to confine the acoustic energy. The ZGV resonant conditions in the SOI/AlN composite plate, i.e. the frequencies where the mode group velocity vanishes while the phase velocity remains finite, were investigated in the frequency range from few hundreds of MHz up to 1900 MHz. Some ZGV points were found that show up mostly in low-order modes. The thermal behaviour of these points was studied in the -30 to 220 {\deg}C temperature range and the temperature coefficients of the ZGV resonant frequencies (TCF) were estimated. The behaviour of the ZGV resonators operating as gas sensors was studied under the hypothesis that the surface of the device is covered with a thin polyisobutylene (PIB) film able to selectively adsorb dichloromethane (CH2Cl2), trichloromethane (CHCl3), carbontetrachloride (CCl4), tetrachloroethylene (C2Cl4), and trichloroethylene (C2HCl3). at atmospheric pressure and room temperature. The sensor sensitivity to gas concentration in air was theoretically estimated for the first four ZGV points of the inhomogeneous plate. The feasibility of high-frequency, low TCF electroacoustic micro-resonator based on SOI and piezoelectric thin film technology was demonstrated theoretically.