Au maskless patterning for vacuum packaging using the electrochemical method

The interconnection of wires is an important issue in vacuum-packaged microelectromechanical systems devices because of the difficulties of hermetical sealing and electrical insulation. This paper presents an approach of Au film selective patterning on highly uneven surfaces for wire interconnections of devices in which silicon-on-insulator (SOI) wafers are anodically bonded to glass. The Au film on the handle layer, functioned as an anode, was selectively removed with electrochemical dissolution in a chloride solution. The choice of etchant solution and etching conditions were optimized to improve the process efficiency, resulting in a high yield of gold portions within the via holes for wire interconnection. The proposed wire interconnection technology was employed to fabricate a vacuum-packaged resonant pressure sensor as a proof-of-concept demonstration. Reliable wire bonding and vacuum package were achieved as well as a Q factor that does not decrease over a year. As a platform technology, this method provides a new approach of wire interconnection for vacuum-packaged devices based on SOI–glass anodic bonding.