Effect of Si substrate conductivity on surface acoustic wave resonator

Abstract

A surface acoustic wave (SAW) filter’s bandwidth and quality are determined by its resonators’ electromechanical coupling coefficient (k2) and impedance ratio (IR). Research commonly focuses on the effects of piezoelectric material and cutting direction on these parameters. This paper investigates the effect of the conductivity of the Si substrate on k2 and IR through finite element method (FEM) simulations. A new model based on the modified Butterworth-van-Dyke (MBVD) model is presented. This new model takes into account the substrate parasitic capacitance and resistance to predict resonator performance on low resistivity (LR) Si piezoelectric on insulator (POI) substrates. Both high resistivity (HR) Si and LR-Si are utilized to fabricate POI SAW resonators, which are subsequently tested. The high conductivity of the Si support layer leads to a decrease in both k2 and IR. By employing Si substrates with different resistances during fabrication, it becomes possible to manufacture resonators with varying k2 values, thus meeting diverse bandwidth requirements for filters.