Simulation and experiment of high-overtone bulk acoustic resonators

In this paper, the influence of the thickness and materials of layers (top electrode, piezoelectric film and substrate) on the resonant characteristics (resonant frequency, effective electromechanical coupling coefficient K_eff² and quality factor Q) of HBAR is investigated using the four-layer thickness extension mode composite resonator model. Some adjustment can be made to obtain the desired resonance and performance. HBAR based on Al/ZnO/Al sandwich layers on c-axis sapphire substrate is measured to obtain its resonant characteristics, and compared with those derived from numerical simulation. The experiment shows that the spacing of resonance frequency Δf and center frequency f₀ are almost agreed with the numerical simulation, which is about 14MHz and 1.9GHz, respectively, while the maximum of K_eff² and Q is less than the simulation.