Abstract
Surface acoustic wave (SAW) resonators have been the core RF filtering technology for mobile communication due to their inherent high quality-factor (Q) and small physical size. This paper investigates the effect of the substrate resistivity on the performance of the SAW resonators. For this study, the RF performance of SAW resonators, fabricated on 1 μm thick C-axis Scandium (Sc)-doped AlN (AlScN) thin-film with 6% Sc on alternative wafer stack-ups with Low Resistivity (LR) and High Resistivity (HR) Silicon (Si) substrates are analyzed. To capture the effect of the substrates on the AlScN-based SAW resonator performances, the Figure of Merit (FoM) per unit of Sc percentage (i.e., FoMSc% or FoM/Sc) is introduced in this work. The FoM / Sc% of the SAW resonators with 400 nm and 450 nm IDT width on LR Si substrate with 1 μm Tox are found to be 68 and 55 respectively. The same are 100 and 128 for the SAW devices with similar design built on HR Si without oxide and 102 and 120 for the SAW devices on HR Si with 2 μm oxide. The observed enhanced performance using HR Silicon substrates is attributed to the reduction of substrate RF losses.