High-quality temperature-complementary bulk acoustic wave resonators fabricated with strippable single-crystalline AlN films grown on sapphire

To satisfy the strict demands of 5G radio frequency communication, we propose high-quality, flexible temperature-compensated single-crystalline AlN film bulk acoustic wave resonators (TC-SABARs) based on a 6-inch sapphire substrate. An AlGaN sacrificial layer and a 600-nm-thick single-crystalline AlN epitaxial layer are deposited on a sapphire substrate by metal organic chemical vapor deposition (MOCVD). Two types of TC-SABARs are fabricated and their performances are compared with published results. The results indicate that one of the TC-SABARs has a maximum Bode Q of 3406, an effective coefficient ( Keff2) of 6.21%, and a temperature coefficient of frequency (TCF) of −9.5 ppm/°C. The other TC-SABAR exhibits a maximum Bode Q of 3022, a Keff2 of 5.99%, and a TCF of +0.7 ppm/°C. This performance can be attributed to the high-quality single-crystalline AlN film and the temperature-compensation structure with nonmetallic flip-chip bonding film transfer process and a thick SiO2 layer.