You have to deposit thick ZnO films, and the thickness should be accordingly to the frequency of operation.

The deposited ZnO films need to be deposited on metallic electrodes. (gold-Cr) electrodes are the best.

The ZnO films of piezoelectric quality should have a preferred c-axis orientation, and should be insulating in nature.  Posess high resistivity, and low dielectric loss.

There is a lot of literature on ZnU films deposition by sputtering methods, and many kinds of bulk resonators devices have been developed.

K. Sreenivas

Maybe you can email to Prof. Zhonglin Wang for the best.