ZnO-on-Diamond Resonators with Notched Thin-Film Piezoelectric Interdigital Transducer for Enhanced Signal-to-Noise Ratio and Feedthrough Suppression

Abstract

This paper presents an innovative and convenient postprocessing methodology to improve the signal-to-noise ratio (SNR) by 3 dB or more than that of the original two-port piezoelectric MEMS resonator by introducing notched air cavities in the thin-film piezo-transducer layer between interdigital transducer (IDT) electrodes. Meanwhile, this strategy also effectively lowers the broadband feedthrough levels by more than 10 dB by substituting piezoelectric layer with the air cavities in the notched regions. This postprocessing technique also does not negatively impact the electromechanical coupling coefficients (signal strength) or the quality factors of the MEMS resonators. In addition, several spurious modes are adequately suppressed because of the modified distribution of electric fields and strain fields in the piezoelectric thin-film transducer adjacent to IDT electrodes. The equivalent circuit models that combine the motional current signal and the electronic feedthrough parasitics, while considering the notched IDT transducer design, have been developed and verified that match well with the measured frequency characteristics.