Millimeter Wave Thin-Film Bulk Acoustic Resonator in Sputtered Scandium Aluminum Nitride Using Platinum Electrodes

This work describes sputtered scandium aluminum nitride (ScAlN) thin-film bulk acoustic resonators (FBAR) at millimeter wave (mmWave) with high quality factor (Q) using platinum (Pt) electrodes. FBARs with combinations of Pt and aluminum (Al) electrodes, i.e., Al top – Al bottom, Pt top – Al bottom, Al top – Pt bottom, and Pt top – Pt bottom, are built to study the impact of electrodes. The FBAR with Pt top – Pt bottom achieves electromechanical coupling (k²) of 1.8% and Q of 94 for third-order symmetric (S3) mode at 61.6 GHz, confirming FBAR can achieve a Q approaching 100 with optimized fabrication and acoustic design.