BAW RF Filter Based on Single Crystal AlN-on-SiC Resonator

This Letter reports a new bulk acoustic wave (BAW) filter based on single crystal AlN piezoelectric film which has the potential application in 5G wireless communication. The single crystal AlN is deposited on SiC substrate by MOCVD and the air-cavity structure BAW device is fabricated. Testing results show that the fabricated resonators have Q-factor up to 837 and electromechanical coupling coefficient up to 7.2% with resonant frequency 3.2 GHz. The ladder-type filters are also developed on the same wafer, which have a center frequency of 3.38 GHz and 3 dB bandwidth 160 MHz, minimum insertion loss of 1.5 dB, and out-of-band rejection above 31dB. High performance of the filters comes from low defects of the single crystal AlN film, which demonstrates promising potential of single crystal AlN filters in 5G and future 6G applications.