High-Quality Film Bulk Acoustic Resonators Fabricated on AlN Films Grown by a New Two-Step Method

The quality enhancement of sputtering AlN has hampered a bottleneck that limits the further development and deployment of film bulk acoustic resonator (FBAR) filters. To address this bottleneck, a new two-step growth process integrating metal-organic chemical vapor deposition (MOCVD) and physical vapor deposition (PVD) technologies was carefully constructed to grow AlN films on Si substrates. It was found that both the crystallinity and the surface roughness were increased by more than double that of the one-step produced PVD AlN because of the MOCVD AlN buffer layer with smaller dislocations and grain boundaries. Afterward, using our 4-inch MEMS wafer process, high-quality AlN-based FBARs wafers were obtained accordingly with small full-width at half-maximums for two-step grown AlN(0002) X-ray rocking curves of 0.68 degrees, showing that the Q-factor of FBARs with two-step grown AlN precedes FBARs with one-step grown PVD AlN by 57.6%.

Automated summary

A new two-step growth process integrating MOCVD and PVD technologies was developed to enhance the quality of sputtering AlN films for FBAR filters. The process resulted in higher crystallinity and surface roughness compared to the one-step PVD AlN growth method, leading to improved Q-factor for FBARs. The research demonstrates the importance of optimizing the growth process to achieve high-quality AlN-based FBAR wafers.