Piezoelectric Disk Resonators Based on Epitaxial AlGaAs Films

A new design for anisotropic piezoelectric disk resonators is demonstrated using single-crystal Al_0.3Ga_0.7As films. The shape of the disk resonator is based on the velocity propagation profile of the elastic wave in the plane of the piezoelectric film, with lateral dimensions scaled to the half wavelength of the desired resonance frequency. The resonators are designed with supports which emulate free-free boundary conditions. Prototype resonators are fabricated using a three-layer Al_0.3Ga_0.7As heterostructure containing silicon-doped electrodes and an undoped piezoelectric Al_0.3Ga _0.7As layer. Quality factors as high as 11 200 are measured in air for a 23.25 MHz fundamental resonant mode, with a corresponding motional resistance of 1.67 kOmega. A finite-element model for the resonator design is also described. Simulation results agree well with both theoretical calculations and experimental data