A high yield rate MEMS gyroscope with a packaged SiOG process

MEMS devices such as a vibratory gyroscope often suffer from a lower yield rate due to fabrication errors and external stress. In the decoupled vibratory gyroscope, the main factor that determines the yield rate is the frequency difference between the sensing and driving modes. The gyroscope, fabricated with a SOI (silicon-on-insulator) wafer and packaged using anodic bonding, has a large wafer bowing caused by thermal expansion mismatch as well as non-uniform surfaces of the structures caused by the notching effect. These effects result in a large distribution in the frequency difference, and thereby a lower yield rate. To improve the yield rate we propose a packaged SiOG (silicon-on-glass) technology. It uses a silicon wafer and two glass wafers to minimize the wafer bowing and a metallic membrane to avoid the notching. In the packaged SiOG gyroscope, the notching effect is eliminated and the warpage of the wafer is greatly reduced. Consequently, the frequency difference is more uniformly distributed and its variation is greatly improved. Therefore, we can achieve a more robust vibratory MEMS gyroscope with a higher yield rate.