Bidirectional and location-dependent frequency tuning of single crystal 4H-SiC micromechanical cantilevers

In this paper, bidirectional and location-dependent frequency tuning of single crystal 4H silicon carbide (4H-SiC) cantilever resonators was investigated. 4H-SiC is a superior material platform for MEMS devices operated in harsh environments. A passive tuning method was employed using focused ion beam (FIB) deposition of platinum (Pt) and milling of Pt and SiC material at different locations on cantilever beams. Linear downward shifts in resonant frequency were observed with Pt films deposited at the free end of cantilever, which is attributed to the increase in effective mass. Subsequent FIB milling reduced Pt mass and therefore restored the resonant frequency to previous values, showing the advantage of FIB for fine-tuning of frequency by precise adjustment of Pt mass. Location dependence of frequency tuning was investigated by measuring frequency shifts when removing SiC material at different locations by FIB milling, which leads to changes in effective mass and effective stiffness. Results show that resonant frequency increases when removing SiC at the free end, and decreases when close to the fixed anchor. These results demonstrate the capability of bidirectional frequency tuning of SiC cantilever resonators.