High-Q torsional mode Si triangular beam resonators encapsulated using SiGe thin film

This paper reports on an SOI-based 20 MHz MEMS torsional resonator, wafer-level packaged using SiGe thin film and hermetically sealed using Al sputtering at 1Pa. The packaged resonators display a high quality factor (220,000) and a low motional resistance (12 k Ω) for low DC bias (1 V). The quality factor remains above 100,000 and the temperature coefficient of frequency (TCf) was measured to be -25ppm/°C and linear over the temperature range of -40 to +140 °C. Successful operation of a CMOS-based oscillator using the MEMS torsional resonator as the frequency determining element was demonstrated.