Versatile wafer-level hermetic packaging technology using anodically-bondable LTCC wafer with compliant porous gold bumps spontaneously formed in wet-etched cavities

This paper reports simple and versatile technology for hermetically capping MEMS with a wet-etched LTCC (low temperature cofired ceramic) wafer by standard anodic bonding process, in which the MEMS and Au vias in the LTCC wafer are electrically connected by porous Au bumps. The porous Au bump is spontaneously formed from a part of the Au via by wet-etching the LTCC wafer, because glass-based filler in the Au via is etched away and leaves pores. Excellent compliance of the porous Au bump absorbs error in the height of the electrodes etc. The wet-etched LTCC wafer was anodically bonded with an SOI wafer with diaphragms and Au electrodes under a standard condition. 100% yield of both hermetic sealing and electrical connection was confirmed. A thermal shock test was performed, and no significant change of sealing pressure and the resistance of electrical connections was observed at least up to 3000 cycles.