Voltage tunable surface acoustic wave phase shifter using semiconducting/piezoelectric ZnO dual layers grown on r-Al2O3

A voltage tunable surface acoustic wave phase shifter is made of a ZnO based semiconducting/piezoelectric dual-layer structure on an r-Al2O3 substrate by using a hybrid growth technology. Piezoelectric and semiconducting ZnO layers are used for acoustic wave excitation and n-type conducting channel, while SiO2 serves as the gate insulator. The acoustic velocity of the device is tuned by changing the n-channel conductance with a dc bias. The in-plane anisotropy of the piezoelectric ZnO∕r-Al2O3 structure enables multimode operations. Sezawa and Love wave modes are used to get high effective coupling coefficients, which result in large phase shifts.