Investigation of the high-vacuum Au/Si eutectic wafer bonding process for MEMS resonators

This study demonstrates a reliable wafer-level Au/Si eutectic bonding technique suitable for hermetic packaging of MEMS resonators with small cavities (≤ 0.01 mm3). By optimizating the Au-Si eutectic bonding process, including outgassing/bonding time, heating/cooling rates, and the incorporation of a Pt barrier layer, significant improvements in bonding quality was achieved. The hermetically sealed cavities exhibited a vacuum level below 2 Pa, a shear strength exceeding 56.4 MPa, and an average helium leak rate of 2.85 × 10-9 atm·cc/s. Furthermore, the quality factors (Q factors) of packaged cantilevers increased substantially from 400 to over 60,000, indicating effective mitigation of air damping. These results suggest that this bonding technique holds considerable promise for the development of high-performance, small-volume, and cost-effective MEMS devices.