Polysilicon vibrating gyroscope vacuum-encapsulated in an on-chip micro chamber

Abstract A new polysilicon vibrating gyroscope whose resonator is vacuum-encapsulated in an on-chip micro chamber was developed. A micro chamber that is large enough to encapsulate a thin film vertical gyroscope in vacuum was successfully fabricated using a polysilicon multilayer process, an HF permeable polysilicon film, and a new chamber suspension structure. The suspension structure consists from pillars arranged in the mass part of micro chamber. The pillars keep the resonator from coming into contact with the chamber shell film, which is deformed by atmospheric pressure. The mass of the gyroscope in the micro chamber is a 240-μm-square; the four straight suspension beams are 2 μm wide and 250–300 μm long. The lower and upper gaps are 2 μm each. The angular rate resolution of the current device is about 5°/s at 300 Pa of encapsulation pressure. The long-term stability of the vacuum packaged structure was evaluated by the quality-factor ( Q -factor) of the resonator, and the pressure in the micro chamber was estimated to be below 400 Pa at more than 20 months after vacuum encapsulation.