  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.
