P1J-4 High-Q FBARs Using Epitaxial AlN Films

FBARs (Film Bulk Acoustic Resonators) are attractive candidates for RF filtering in radar phased array modules providing that their insertion loss can be reduced to 1 dB or less. One of the factors that contributes to the increased insertion loss of FBAR filters at X-band is the difficulty in achieving high crystalline quality in thin (<0.5 mum) sputtered films. We describe an FBAR fabrication process using single crystal AlN films that are deposited epitaxially on SiC substrates. It is intended that this process would ultimately be compatible with GaN wide-band-gap integrated circuits that would provide the switches required for a switched filterbank and the LNAs. The single crystal FBARs showed the expected resonator behavior but with lower Q and lower piezoelectric coupling coefficient (k²) than desired. Improvements to decrease film roughness, minimize electrode losses and improved fabrication process will result in the performance expected of single crystal films