Study on the effectiveness of protective methods for AlN film during SAW resonator fabrication

AlN is a new kind of piezoelectric material with promising application prospects in harsh working environment. Though its outstanding thermal and mechanical stability has been proven, AlN is sensitive to alkaline substances including most of the developer solution in common use, so extra methods are required to protect the material from corrosion in photolithography process afterwards. We have succeeded in examining the effectiveness of SiO2 protective layer to achieve a rigid ‘sandwich’ structure of an AlN-based SAW resonator. Evident from the results showed an overall modification with subsequent upper structure manufacturing because the adopted protective layer has guaranteed good quality of the AlN substrate. This work reported a simple methodology to enable a MEMS-compatible fabrication process of SAW resonator, which makes further improvement on the characterization of AlN devices possible.