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

TL;DR

This paper demonstrates high-Q millimeter wave thin-film bulk acoustic resonators using sputtered scandium aluminum nitride with platinum electrodes, achieving significant electromechanical coupling at frequencies up to 61.6 GHz.

Contribution

It introduces the use of platinum electrodes in ScAlN FBARs for mmWave applications, showing improved performance and high Q factors at frequencies around 60 GHz.

Findings

Achieved Q of 116 at 13.7 GHz with Pt electrodes.

Demonstrated Q of 94 at 61.6 GHz for third-order mode.

Confirmed potential of ScAlN FBARs for mmWave applications.

Abstract

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 on mmWave FBARs. The demonstrated FBAR with Pt top and bottom electrodes achieve electromechanical coupling (k2) of 4.0% and Q of 116 for the first-order symmetric (S1) mode at 13.7 GHz, and k2 of 1.8% and Q of 94 for third-order symmetric (S3) mode at 61.6 GHz. Through these results, we confirmed that even in the frequency band of approximately 60 GHz, ScAlN FBAR can achieve a Q factor approaching 100 with optimized fabrication and acoustic/EM design. Further development calls for stacks with better quality in piezoelectric and metallic layers.