Demonstration of High-overtone Bulk Acoustic Resonators using an Epitaxial ε-Ga2O3 Piezoelectric Film on SiC

In this work, we developed novel high-overtone bulk acoustic resonators (HBARs) with only top electrodes using an epitaxial ε-Ga
2
O
3
piezoelectric film on conductive SiC substrates. The HBARs with different ε-Ga
2
O
3
film thicknesses and electrode spacings were fabricated and investigated. The device with a 300-nm thick ε-Ga
2
O
3
film showed a broad frequency response from 1 to 8 GHz, and the free spectral range (FSR) between adjacent modes was 18.3 MHz. Other critical metrics of the device include quality factor (Q) > 5000 and f•Q > 2.5×10
¹³
Hz for operating frequencies up to 5 GHz. By narrowing the electrode spacing, the Q value of the HBARs with a 1.2-μm thick ε-Ga
2
O
3
film was improved to over 8000. The results demonstrate the great potential of the epitaxial ε-Ga
2
O
3
piezoelectric film for developing novel RF acoustic devices.