Metal-Air-Piezoelectric (MAP) mmWave Resonator

Abstract

Piezoelectric MEMS resonator is one of the key components in acousto-optic modulators, and different types of acoustic resonators have been utilized to realize acousto-optic modulation. However, current acoustic resonators cannot support the high-frequency scenario as high-frequency acoustic waves are hard to propagate coupling with light waves for large modal overlap. To eliminate mechanical and optical losses from metal, this study introduces a novel structure featuring suspended electrodes above the suspended piezoelectric thin film. By utilizing metal-air-piezoelectric (MAP) thin film structures, these resonators enable the propagation of light waves into the acoustic resonator, thus facilitating acousto-optic interaction while minimizing light wave absorption by the metal. The fabrication process involves the removal of two sacrificial layers to suspend the stacked electrodes and piezoelectric film, resulting in the successful excitation of the antisymmetric Lamb waves (A-modes). The fabricated device demonstrates the A1 mode at 10.38 GHz, exhibiting an extracted ${K}_{\textit {mat}}^{{2}}$ of 28% and an extracted ${Q}_{\textit {MBVD}}$ of 380. Additionally, the A3 mode is achieved at 31 GHz, with a ${K}_{\textit {mat}}^{{2}}$ of 5% and a ${Q}_{\textit {MBVD}}$ of 280. Through further optimization and investigation, this innovative structure is expected to enable acousto-optic modulation at mmWave frequencies.