Analysis of frequency-temperature behavior of X-cut LiTaO3 strip resonators

We numerically study the frequency-temperature (f-T) behavior of a partially plated X-cut LiTaO3 strip resonator operating in the fundamental thickness-shear fast mode. The plate orientation is designated by (XZt)ψ based on the IEEE standard notation. The f-T curves are calculated as functions of the electrode length and the plate-orientation angle ψ. The results confirm that the turnover temperature of the f-T curve decreases with increasing electrode length. Furthermore, we find that the turnover temperature changes depending on the coupling between thickness shear and thickness width flexure through c56, and that it therefore depends on ψ. An angle ψ = 40° that yields a turnover temperature in the range of 33-6.5°C is optimal for the material constants of [J. Appl. Phys. 42 (1971) 2219] because c56 is zero. We also show that the external loading of both series and parallel capacitances can make the adjustment of turnover temperature of high electro-mechanical coupling resonators very simple.