Wafer level hermetic bonding and packaging using recrystallized parylene

This work reports a wafer-level vacuum packaging technique for microelectromechanical system (MEMS) using recrystallized parylene material as a bonding layer. The effect of thermal annealing on the crystallinity of the parylene surface was demonstrated. The low-temperature, stable, homogeneous, and defect-free recrystallized parylene is found as an excellent bonding material for hermetic packages, suitable for the packaging of MEMS sensors. The material's recrystallization improves its capabilities as a moisture and air barrier. The mechanical stability of the bond interface was also investigated by measuring the package's tensile and shear strength. In the absence of a vacuum bonding tool, a Ti getter was integrated into the cavity of the glass capping wafer to create the vacuum and test the hermeticity. The MEMS silicon Pirani gauge was used to monitor the pressure changes inside the sealed cavity. After the getter activation, it was observed that there was a decrease in the pressure from atmospheric pressure to 0.2 mbar for the first few days; after that, no noticeable change was observed. The hermeticity of the packaged device was examined, and the vacuum level inside the package remained the same for the last 70 d. The recrystallized parylene bonded micro package shows better hermeticity than the non-recrystallized parylene micro package.