Reliability and stability of thin-film amorphous silicon MEMS resonators

The stability of the resonance frequency (f(res)) characteristics of MEMS resonators upon long-term cycling is crucial for many applications. Thin-film silicon MEMS have been developed to take advantage of their low-temperature processing and large area deposition characteristics. A reliability and stability study of thin-film-doped hydrogenated amorphous silicon (n(+)-a-Si:H)-aluminum MEMS resonators fabricated on glass substrates at a maximum processing temperature of 110 degrees C is presented. Long-term cycling of thin-film silicon microbridge resonators with different top electrode configurations was performed in vacuum and in air using electrostatic actuation. The number of cycles to failure, the f(res) stability, the quality factor (Q) stability and the effect of measurement temperature are studied. The resonant bridges withstand the industry standard of 10(11) continuous cycles at high load with no failure reported both in vacuum and air with f(res) shifts which depend on the resonator top electrode configuration. No Q degradation was observed. Frequency stability better than +/- 20 ppm was observed in vacuum after long-term cycling.