Effect of Key Technological Parameters on GaN/Si SAW Resonators Operating Above 5 GHz

This paper presents the experimental investigation results of the technological dispersion effect on the response of Surface Acoustic Wave Resonators (SAW-R) fabricated on GaN/Si. Two types of SAW-R test structures with interdigital transducers having the digit/interdigit widths of 200 nm were processed on a quarter of a 3 inch wafer. The fabricated structures were investigated using SEM, AFM and ellipsometry techniques. The structures were measured on-wafer and the resonance frequencies around 5.4 GHz were recorded. The resonant frequency deviation as a function of the position on the wafer was analyzed. A numerical model was developed in COMSOL software and multiphysics analyses were performed. The main technological parameters that can influence the resonance frequency of the SAW-R (GaN layer thickness, the metallization thickness, the electrode width, the variation of the elastic constants due to the thermal strain) were varied around the nominal values. It is shown that the thermal strain variation has the highest influence on the resonant frequency deviation of the SAW-Rs. The other possible influences have only a small effect that cannot explain the total measured variation of the series resonance frequency of about 100 MHz. The results lead to the conclusion that the position on the wafer and frequency shift compensation techniques need to be taken into account for narrow band SAW-R based applications designed for this technological approach.