Mems Resonator Vacuum-Sealed by Silicon Migration and Hydrogen Outdiffusion

Abstract

MEMS resonators were vacuum-encapsulated at lower than 1 Pa by Silicon Migration Sealing (SMS) technology. The tuning-fork resonators were fabricated on a 6-inch SOI wafer and capped with a cap wafer with submicron release holes by direct bonding. After SMS, the encapsulated device was capacitively driven and sensed. The Q factor showed 18823 after 430℃ 27 h baking in nitrogen and improved to 36756 after leaving the device in air at 145℃for a long time, showing hydrogen out-diffusion from the sealed cavity. Vacuum baking was also tested and showed faster hydrogen out-diffusion. The Q factor reached 54712 after 24 h baking at 220°C and 1 Pa.