Beyond 5 GHz excitation of a ZnO-based high-overtone bulk acoustic resonator on SiC substrate

Abstract: This work reports on the fabrication and characterization of an Au/ZnO/Pt-based high-overtone bulk acoustic resonator (HBAR) on SiC substrates. We evaluate its microwave characteristics comparing with Si substrates for micro-electromechanical applications. Dielectric magnetron sputtering and an electron beam evaporator are employed to develop highly c-axis-oriented ZnO films and metal electrodes. The crystal structure and surface morphology of post-growth layers have been characterized using X-ray diffraction, atomic force microscopy, and scanning electron microscopy techniques. HBAR on SiC substrate results in multiple longitudinal bulk acoustic wave resonances up to 7 GHz, with the strongest excited resonances emerging at 5.25 GHz. The value of f.Q (Resonance frequency * Quality factor) parameter obtained using a novel Q approach method for HBAR on SiC substrate is 4.1 * 10^13 Hz, which to the best of our knowledge, is the highest among all reported values for specified ZnO-based devices.