Stability characterization of vacuum encapsulated MEMS resonators with Au–Sn solder bonding

This paper presents a vacuum encapsulation technique and stability characterization for MEMS resonator. Sn-rich Au–Sn solder bonding is used to achieve reliable hermetic packaging with high shear strength. Simple planar feedthrough structure is utilized to achieve electrical interconnection and low cost of packaging. The stabilities of the encapsulated resonator are systematically studied, including frequency stability, temperature stability, long-term hermeticity, and mechanical reliability. The short-term and medium-term frequency stability are ± 0.4 and ± 3 ppm, respectively. The temperature cycle test is introduced between − 20 and 80 °C, and the resonant-frequency drift of the packaged resonator is within ± 4 ppm between 40 temperature cycles. Furthermore, the packaged resonator is temperature compensated by micro-oven, which obtained a frequency stability range of ± 13 ppm between 20 and 100 °C. The packaged resonator shows favorable long-term stability of the Q-factor over 200 days and average shear strength of 43.93 MPa among 12 samples.