33 GHz Overmoded Bulk Acoustic Resonator

In this work, we present a new class of thickness extensional microelectromechanical resonator, the overmoded bulk acoustic resonator (OBAR) for filtering applications in the 5G millimeter wave (mm-wave) spectrum. This resonator operates in a second overtone thickness mode with approximately equal thickness electrodes and piezoelectric layer so that acoustic energy is distributed evenly between the different layers. Compared to a fundamental mode at a fixed frequency, the OBAR possess a 3x thicker piezo layer and 5-10x thicker metal electrodes, enabling manufacturable 30-60 GHz devices. We demonstrate the OBAR experimentally through fabrication of a Pt-AlN-Al device with electromechanical-coupling coefficient ( $k_{t}(2))$ of 1.7%, and series resonance quality factor (Q $_{s}$ ) of 110 at 33 GHz.

Automated summary

In this work, a new class of thickness extensional microelectromechanical resonator called overmoded bulk acoustic resonator (OBAR) is proposed for filtering applications in the 5G millimeter wave spectrum. The OBAR operates in a second overtone thickness mode, distributing acoustic energy evenly between layers. Compared to traditional resonators, the OBAR has thicker piezo and metal layers, enabling higher frequency devices.