Temperature coefficient of elastic constants of SiO2 over-layer on LiNbO3 for a temperature stable SAW device

Abstract

The influence of sputtered SiO2 over-layer on the SAW propagation characteristics of a 128° rotated Y-cut X-propagating lithium niobate SAW filter has been studied. Experimentally measured SAW phase velocity and temperature coefficient of delay (TCD), with varying SiO2 over-layer thickness, show a significant deviation from the theoretically calculated values using the bulk material parameters of SiO2. The observed deviation is attributed to the differences in the material parameters (density, elastic and dielectric constants and their temperature coefficient) of the deposited SiO2 over-layer. The density and the dielectric constant of the deposited SiO2 layer were determined separately, and the elastic constants and their temperature coefficients were estimated by fitting the experimental velocity and TCD data, respectively. The deviation in the dielectric constant and the density in comparison to the bulk was insignificant, and the estimated values of the elastic constants (C11 = 0.75×1011 N m−2 and C44 = 0.225×1011 N m−2) were found to be lower, and the respective temperature coefficients (5.0×10−4 °C−1 and 2.0×10−4 °C−1) were high in comparison to the bulk material parameters.