Characterization of frequency tuning using focused ion beam platinum deposition

This paper presents and characterizes focused ion beam (FIB) platinum (Pt) deposition as a novel frequency tuning method for micromechanical resonators. FIB Pt deposited tuning was performed at room temperature and in contrast to other reported methods, frequency changes were achieved without any device failure. To perform the tuning, Pt was deposited on a 13 mu m x 5 mu m surface area at the free end of 3C silicon carbide (SiC) and polysilicon cantilever resonators in thicknesses ranging from 0.5 mu m to 2.6 mu m. To determine the amount of tuning, the resonant frequency of SiC and polysilicon devices was measured before and after Pt deposition. Frequency measurements performed before Pt deposition found that SiC resonators operated at higher resonant frequencies and quality (Q)-factors than their polysilicon counterparts. Measurements after Pt deposition on SiC and polysilicon resonators confirmed the predicted maximum frequency change of -15.5% made by FEM simulations and analytical modelling. Due to their lower mass, polysilicon resonators showed a larger frequency change than their SiC counterparts. A Q-factor decrease was observed for SiC and polysilicon resonators due to thermoelastic damping associated with the deposited Pt and surface contamination.