Development of double layered thickness-shear resonator using langasite-type piezoelectric single crystal

A novel device structure "double layered thickness-shear resonator" was proposed to improve the temperature characteristics of a bulk acoustic wave resonator. In order to design the double layered resonator, optimal combination of cut angles and thickness ratio of the substrates were determined from calculations using material constants and their temperature coefficients measured for a Ca3TaGa3Si2O14 (CTGS) single crystal. Based on the results, a double layered resonator was fabricated by directly bonding two CTGS substrates with cut angles of 122 degrees Y and 171 degrees Y under the thickness ratio of 0.248. As a result, the double layered resonator operated successfully at a fundamental mode of around 7.5 MHz like a normal resonator exhibiting temperature compensation effect. The mechanism of the deviation from the expected value observed in the measured temperature dependence of the frequency changes was discussed using the model of the wave propagation and the electric field generated in the double layer structure. (C) 2020 The Japan Society of Applied Physics.