Wafer-Level Vacuum Packaging for Microsystems Using Glass Frit Bonding

Wafer-level glass frit bonding is an important technology for the hermetic encapsulation of microsystems. In this paper, the sintering characteristic of the glass frit material is investigated based on thermogravimetry/differential scanning calorimetry (TG/DSC) thermal analysis techniques. TG/DSC measurement results illustrate that the organic binder burnout temperature and glass transition temperature for the glass frit used in this paper are 300 ^°C and 331 ^°C, respectively. With the TG/DSC measured results, a wafer-level vacuum packaging approach for microsystems using glass frit bonding is developed through experimental analysis. The glass frit is presintered at 300 ^°C for 30 min to completely remove the organic binder and fired at 430 ^°C to seal the bonded wafers. The cross-sectional observation shows no void or gap is formed in the bonded layer. The average shear stress of the bonded devices is 6.2 kgf, which satisfies military standard-883E. Application of the glass frit bonding approach for a thermocouple vacuum gauge is demonstrated, which is employed to illustrate the feasibility of this process, and also to measure the vacuum degree in the packaged cavity. The measured results show that a vacuum of about 100-300 Pa can be sealed using this approach.