Mems Resonator Vacuum-Sealed by Silicon Migration and Hydrogen Outdiffusion

MEMS resonators were vacuum-encapsulated by Silicon Migration Seal (SMS) technology. SMS is new wafer-level vacuum packaging technology, which utilizes silicon reflow phenomena to close release holes in hydrogen (H
2
) environment at high temperature (>1000°C). In this study, we first demonstrated the encapsulation of a MEMS resonator made on an SOI wafer, which is one of the most standard structures for inertial sensors and timing devices. After the encapsulation, hydrogen trapped in the sealed cavity was diffused out by annealing at 430ºC in nitrogen (N
2
) environment for 27 hours. The resonator was capacitively driven and sensed, and the Q factor reached 6000. The sample after successful packaging was penetrated by focused ion beam (FIB) out of the resonating element area. Judging from the Q factor, the vacuum level of the sealed cavity is much better than that of the hydrogen annealing (10 kPa) and estimated ~60 Pa.