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 °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 10¹¹ 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. (paper)