Frequency stability of wafer-scale encapsulated MEMS resonators

This paper presents an investigation of the long-term frequency stability of wafer-scale encapsulated silicon MEMS resonators. Two aspects of stability were examined: long-term stability over time and temperature-related hysteresis. Encapsulated resonators were tested over a period of 8,000 hours in constant environmental temperature of 25/spl deg/C /spl plusmn/ 0.1/spl deg/C. No measurable drift, burn-in time, or other changes in resonant frequencies were detected. Another experiment was performed to investigate the stability of the resonators with temperature cycling. The resonant frequency was measured between each cycle for more than 450 temperature cycles from -50/spl deg/C to +80/spl deg/C. Additional data is presented for short-term hysteresis measurements -10/spl deg/C to +80/spl deg/C temperature cycle. No detectable hysteresis was observed in either of the temperature cycle experiments. These series of experiments demonstrate resonant frequency stability of wafer-scale silicon based MEMS resonators.