Wafer-Level Vacuum-Packaged 2-Axes MEMS Gyroscope with High Yield Rate
Authors: ChungMo Yang, JongCheol Park, TaeHyun Kim, KilSon No, ChangHo Seo, NamSu Park, GapSeop Shim, SungKyu Lim, HeeYeoun Kim Company: National NanoFab Center Date Published: 10/18/2016
IWLPC (Wafer-Level Packaging)
Abstract: MEMS devices such as a gyroscope often suffer from a lower yield rate due to external stress. Our team reports on a novel design and architecture for realizing high yield rate gyroscope based on Micro-Electro-Mechanical Systems (MEMS) technology. The proposed device is suitable for high-precision and yield rate Gyroscopes. The design has been investigated analytically and numerically by means of CoventorWare of the low stress structure shapes and resonant frequencies. MEMS gyroscope was fabricated with triple stacked 8 inch SOG (Si on Glass) substrate. For high device performance of MEMS gyroscope. The wafer level hermetic packaging was a method of sealing micro-devices containing movable parts with a capping Glass wafer in high vacuum under 10-6mbar. The capping Glass wafer was etched to form a cavity with sand blast method which will cover over the MEMS devices. In this process flow a cap wafer, usually a thermally matched glass (Boro33) is aligned with the silicon based MEMS wafer (Device wafer). The anodic bonding was applied upto 1000V under tightly controlled pressure in vacuum with 5000N of force at 400°C temperature for 10 minutes. This processing method gives cost advantages due to the process time reduction and hermetic seal over the wafer level packaging (WLP). To improve the yield rate we propose a packaged SOG (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 SOG 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.