Fabrication of suspended thin film resonator for application of RF bandpass filter

Characteristics of AlN thin film and thin film resonator for RF bandpass filter have been studied. AlN thin films were deposited by RF magnetron sputter system. Deposition parameters such as N₂ contents, Ar and N ₂ partial pressures, and the distance between metal target and substrate were found to affect the piezoelectric response. To fabricate the suspended thin film resonator (STFR) using the piezoelectric AlN thin film, the etching of AlN and the surface micromachining process were conducted. The thickness of AlN film and membrane for the STFR are 2 and 15 μm, respectively. This membrane was fabricated by SOI technology. The device with the dimension of 160×160 μm² has a resonant frequency of 1.653 GHz, a K_eff² of 2.4%, a bandwidth of 17 MHz, and a quality factor of 91.7. The device with the dimension of 200×200 μm² has a resonant frequency of 1.641 GHz, a K_eff ² of 1.2%, and a bandwidth of 9 MHz, and a quality factor of 50.2.