Fabrication of 5GHz band film bulk acoustic wave resonators using ZnO thin film

We successfully fabricated 5GHz band thin film bulk acoustic wave (BAW) resonators using ZnO thin film. Two types of BAW resonators utilizing fundamental resonance and secondary harmonics, were examined. In the fundamental mode resonator, the quality factor (Q factor) and the effective electromechanical coupling coefficient (k(teff)(2)) were realized at 1000 and 6.7%, respectively. These values for the secondary mode resonator were 700 and 4.7%, respectively. Combining four fundamental mode resonators as a ladder type piezoelectric filter, the bandwidth at 3dB was achieved to be 191MHz at 4.9GHz. Even with the filter using the secondary mode resonator, the bandwidth was 130MHz at 5.2GHz.