Analysis Method for the Influence of Parasitic Surface Conductivity on Silicon-Based Surface Acoustic Wave Devices

In this article, we studied the effect of radio frequency (RF) loss caused by parasitic surface conductivity (PSC) to surface acoustic wave (SAW) devices through a physical-model-based and universal method. First, through technology computer-aided design (TCAD) tools, the phenomenon of PSC attracting minority carriers to top part of Si to form an inversion layer was clearly displayed. Then, this influence was transformed into the reduction in the effective resistivity (
${R}_{\text {eff}}{)}$
of homogeneous Si substrate using equivalent circuit model. Finally,
${R}_{\text {eff}}$
was converted into the dielectric loss tangent, which can be conveniently introduced to ANSYS electromagnetics (EM) models. This method is first used for coplanar waveguide (CPW), which is an excellent device for characterizing substrate RF loss. Using a similar method, the specific impact of PSC on SAW resonators based on 42°YX-LiTaO3 (LT)/SiO2/PSi/Si and 42°YX-LT/SiO2/Si substrate was also studied. It has been verified that PSC causes a decrease in Bode-Q of SAW resonators and deterioration in insertion loss (IL). And by calculating the changes in Bode-Q, we successfully separated substrate RF loss from other losses, such as acoustic loss. Simulations for both CPW and SAW devices have achieved good agreement with measured results. This method provides a convenient approach for analyzing the impact of PSC that exist in all similar structures on the performance of RF devices.