Temperature coefficient of elastic constants of SiO2over-layer on LiNbO3for a temperature stable SAW device

The influence of sputtered SiO 2 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 SiO 2 over-layer thickness, show a significant deviation from the theoretically calculated values using the bulk material parameters of SiO 2 . The observed deviation is attributed to the differences in the material parameters (density, elastic and dielectric constants and their temperature coefficient) of the deposited SiO 2 over-layer. The density and the dielectric constant of the deposited SiO 2 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 ( C 11 = 0.75×10 11 N m −2 and C 44 = 0.225×10 11 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.