Measurements of Doubly-Rotated-Cuts of Langasite Isomorph

Abstract

In this paper, we report the measured properties of doubly-rotated cuts of bulk-acoustic-wave resonators made of a langasite isomorph material. Test resonators with planoconvex blanks (14 mm diameter, 2 diopter, nominal 10 MHz 5th OT) were fabricated for four different cuts: (thetas = 10deg, phi = 10deg), (thetas = 10deg, phi = 20deg), (thetas = 20deg, phi = 10deg), (thetas = 20deg, phi = 20deg). Using an impedance analyzer, we were able to measure strongly excited fundamental and 3rd overtones of the c- and b-modes, along with their anharmonic modes, as evidenced by their low motional resistances. The a-modes were weakly excited but could also be measured. The theoretical values of eigenmode velocities and piezoelectric coupling coefficients of the doubly-rotated cuts were obtained by solving Christoffel equations. The theoretical values were compared to the measured ones. The frequency-temperature (f-t) characteristics were also measured in the temperature range of -55 degC to 85 degC. The f-t curves of the c- and b-modes showed parabolic characteristics