33 GHz Overmoded Bulk Acoustic Resonator

• Published in: IEEE microwave and wireless components letters Vol. 32; no. 6; pp. 656 - 659
• Main Authors: Schaffer, Zachary, Simeoni, Pietro, Piazza, Gianluca
• Format: Journal Article
• Language: English
• Published: IEEE 01.06.2022
• Subjects: acoustic filters; Acoustics; Aluminum nitride; Electrodes; Film bulk acoustic resonators; III-V semiconductor materials; MEMS; Metals; mm-wave; piezoelectric resonators; Resonant frequency
• ISSN: 1531-1309; 1558-1764
• DOI: 10.1109/LMWC.2022.3166682

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 <inline-formula> <tex-math notation="LaTeX">3\times </tex-math></inline-formula> thicker piezo layer and 5-<inline-formula> <tex-math notation="LaTeX">10\times </tex-math></inline-formula> 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 (<inline-formula> <tex-math notation="LaTeX">k_{t}^{2} </tex-math></inline-formula>) of 1.7%, and series resonance quality factor (<inline-formula> <tex-math notation="LaTeX">Q_{s} </tex-math></inline-formula>) of 110 at 33 GHz.