Lamb wave dispersion in gallium nitride micromechanical resonators

In this paper, we explore the phase velocity dispersion of Lamb wave in gallium nitride (GaN) thin film. For this study, ultra-high-frequency (UHF) GaN micromechanical resonators with various electrode pitch distances are designed as test vehicles. Fabricated by a process compatible with commercial monolithic microwave integrated circuit (MMIC) technology, our GaN resonators demonstrate promising performance (e.g. high quality factor of 1200 at 1GHz) and can be monolithically integrated with active (i.e. HEMTs) devices in an all-GaN platform. The zero-order symmetric (S0) and antisymmetric (A0) Lamb wave modes are observed in our measurements. The experimentally extracted phase velocity dispersion relations of GaN for both S0 and A0 modes are in good agreement with the theoretical data. Out results indicate that S0 mode is a better choice than A0 mode for high frequency GaN Lamb wave resonators because of its high phase velocity and low dispersion characteristics.