Temperature stability of electro-thermally and piezoelectrically actuated silicon carbide MEMS resonators

The influence of temperature between 10 °C and 100 °C on the frequency shift of electro-thermally actuated silicon carbide (SiC) clamped–clamped beams and piezoelectrically actuated SiC cantilevers has been studied. For electro-thermally actuated beams, it has been found that the rate of change of frequency varies from around ±530 ppm/°C to around ±20 ppm/°C. The differential stress of the different materials has been found to play an important role in the temperature stability of the resonators. The shifts in frequency have been shown to decrease as the temperature increases above 40 °C, attributable to the converging coefficients of thermal expansion (TCEs) of Si and SiC, resulting in reduced stress at the anchors, confirmed by simulations. Platinum, rather than aluminium, has been found to be a superior material for use as actuation electrodes because the TCEs of platinum and SiC are better matched, and converge as the temperature increases, leading to less induced stress. A larger electrode area on top of the structure can result in the thermal stress being more evenly distributed, which can improve the temperature stability, as measured with devices with a larger area of Pt electrodes as well as piezoelectrically actuated cantilevers with the electrodes covering the entire length, rather than half the length, of the cantilevers.