Pressure sensing with Zero Group Velocity Lamb modes in self-supported a-SiC/c-ZnO membranes

Abstract

The propagation of the Lamb modes along a-SiC/ZnO thin supported composite structures was simulated for different ZnO and a-SiC layer thicknesses and electrical boundary conditions. The phase and group velocity, the field profile and the electroacoustic coupling coefficient dispersion curves of the Lamb modes travelling along the composite plate were calculated for different layers thicknesses. Zero group velocity (ZGV) points were identified which group velocity vanishes while the phase velocity remains finite, at specific layers thickness values. ZGV resonators (ZGVRs) were designed that consist in only one interdigital transducer (IDT) and no grating reflectors at its sides. The finite element method analysis was performed to investigate the strain, stress and internal pressure the a-SiC/ZnO plate experiences when subjected to an external uniform differential pressure in the 1 to 10 kPa range. The ZGVR pressure sensitivity, i.e. the relative frequency shift per unit pressure change, was found to be mostly affected by the change in the membrane thickness induced by the pressure. A pressure sensitivity of 9 ppm/kPa, in the 4 to 10 kPa range, was predicted for the a-SiC(1μm)/ZnO(1μm) ZGV-based pressure sensor. The feasibility of high-frequency micro-pressure sensors based on a-SiC and ZnO thin film technology was demonstrated by the present simulation study.