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A high-quality factor piezoelectric-on-substrate phononic crystal micromechanical resonator

In this paper phononic crystal (PnC) micromechanical structures with phononic band gaps (PnBGs) are used to effectively confine acoustic modes in a resonator. Two different types of resonant modes are obtained at ∼130 MHz with measured quality factors (Qs) of ∼3,600 and ∼10,000 in air. The PnC resonator is fabricated on a silicon on isolator (SOI) substrate with silicon (Si) layer thickness of 15 µm. The modes in the resonator are excited by a thin piezoelectric zinc oxide (ZnO) layer sputtered and patterned on the Si slab. The ZnO layer is sandwiched between two metallic electrodes. The shape of the top electrode and the design of the resonator result in the excitation of an anti-symmetric and a symmetric resonant mode. The mode shapes and resonance frequencies of these two modes are obtained using finite element method and the results are in a very good agreement with the experimental data. The electrical characteristics of the resonant modes are extracted by fitting a Buttherworth-Van-Dyke model. The measured results verify the effectiveness of these PnC structures in confining different types of modes in a resonant region and show their potential in realizing resonators with better performance over their conventional counterparts.