Temperature and Coupling Behavior of Resonators and Transducers of LithiumTetraborate Driven by Lateral and Thickness Fields

摘要

Lithium tetraborate is a tetragonal material of considerable promise for signalprocessing, transducer, and frequency control applications. It exhibits piezoelectric coupling values that fall between those of lithium niobate and quartz, but possesses orientations for which the temperature coefficient of frequency or delay time is zero for both bulk and surface acoustic waves. Calculations have previously been made for rotated y-cut, bulk wave plates, including the regions where the quasi-extensional and quasi-shear thickness modes have zero temperature coefficients of frequency. In this report we extend the calculations to doubly rotated bulk wave resonators, and compute the coupling factors for the three simple thickness modes driven by (TE) and lateral (LE) quasistatic electric fields as a function of the orientation angles phi and theta, and the direction of the applied lateral field psi. Because of the temperature coefficients of the piezoelectric coupling factors, the temperature coefficient of a resonator will depend not only upon orientation, but also upon harmonic number and location of the resonator operating point on the immittance circle. It is found that two unique orientations exist in lithium tetraborate for which plate resonators have zero temperature coefficients of frequency of both