Frequency stability of wafer-scale film encapsulated silicon based MEMS resonators

The stability of resonant frequency for single wafer, thin-film encapsulated silicon MEMS resonators was investigated for both long-term operation and temperature cycling. The resonant frequencies of encapsulated resonators were periodically measured at 25 ± 0.1 °C for >9000 h, and the resonant frequency variation remained within the measurement uncertainty of 3.1 ppm and 3.8 ppm for the two designs of resonators measured. Also, the resonators were temperature cycled for 680 cycles between -50 °C and 80 °C, measuring the resonant frequency each time the temperature reached 30 °C. Again, the change in resonant frequency was seen to remain within the measurement uncertainty. This demonstrates stability of resonant frequency for both long-term operation of more than a year and large number of temperature cycles, emphasizing the stability of both the resonator and the package.