Wafer level vacuum packaged resonator with in-situ Au-Al eutectic Re-Distribution layer

In this paper, a wafer level vacuum packaged resonator with in-situ Au-Al eutectic Re-Distribution layer is demonstrated. A cap wafer with silicon bumps and electrical feedthroughs is bonded together with a MEMS resonator wafer using wafer level glass frit bonding technology. The silicon bumps provide close contact for the aluminum layer on the cap wafer and the gold layer on the device wafer, on which a gold-aluminum (Au-Al) eutectic is formed. The in-situ Au-Al eutectic layer achieve electrical interconnections between the cap wafer and the device wafer, which realizes the redistribution of the electrical feedthroughs of the MEMS resonator on the cap wafer. The formation mechanism of the Au-Al eutectic is illustrated. The Au-Al eutectic is observed through the FD3/SEM and IR images and is analyzed using EDX. The measured dynamic performance of the packaged MEMS resonator is presented in this paper. Experimental results show that the wafer-level vacuum packaged MEMS resonator results in over 100× higher quality factor (Q) than the resonator vibrating in atmosphere pressure. The experimental results indicate that vacuum about 3 mbar can be sealed in this approach.