Characterization of a Multilayered SAW Pressure Sensor with Low Temperature Variability

Abstract

A method to reduce temperature effects in SAW pressure sensors is presented. A layer of SiO2 is deposited on the surface of 128YX LiNbO3 in order to achieve a high coupling coefficient (κ2) as well as a low temperature coefficient of delay (TCD). The FEM tool COMSOL Multiphysics is used to estimate the phase velocity and frequency of the input RF signal using an eigenfrequency analysis. Then by using a time domain analysis, a surface acoustic wave (SAW) is generated by IDTs and its wave propagation characteristics are obtained. During this process, the boundary reflection is removed by adding a perfectly matched layer (PML). The reflected signal on the IDT can be detected; as such the phase angle is calculated. By applying different pressures to the sensor, a relationship between pressure and phase angle is determined. Using frequency domain analysis, the coupling coefficient is computed with high accuracy. The TCD is calculated at different SiO2 thicknesses and the SiO2 thickness corresponding to a zero TCD and high coupling coefficient is obtained. A prototype is tested to validate these values.