Au maskless patterning for vacuum packaging using the electrochemical method
Citation
Xie, B., Chen, D., Wang, J., Chen, J., & Hong, W. (2018). Au maskless patterning for vacuum packaging using the electrochemical method. Nanotechnology and Precision Engineering, 1, 191–196. https://doi.org/10.1016/j.npe.2018.09.001
Keywords
- Vacuum Packaging
- Wire Interconnection
- SOI–Glass Anodic Bonding
- Au Maskless Patterning
- Electrochemical Etching
- Highly Uneven Surfaces
- Resonant Pressure Sensor
Brief
This article presents a novel method for wire interconnection in vacuum-packaged micro-electromechanical systems (MEMS) devices, employing a maskless electrochemical etching technique to selectively pattern gold films on uneven surfaces for reliable wire bonding and long-term vacuum sealing.
Summary
The article presents a method for wire interconnection in vacuum-packaged microelectromechanical systems (MEMS) devices where a silicon-on-insulator (SOI) wafer is anodically bonded to glass. The method involves etching via holes in the handle layer of the SOI wafer and selectively removing a deposited Cr/Au film on the handle layer using electrochemical dissolution in a chloride solution. This leaves behind the Au film on the device layer for wire bonding.
This method has several advantages over conventional methods:
- It is compatible with micro-fabrication processes.
- It avoids the complicated fabrication process and stress generation of thick metal electroplating by using thin metal film deposition.
- Maskless patterning simplifies the fabrication process on highly uneven surfaces.
The article details the principle, process, and optimization of the Au maskless patterning. The researchers addressed the problem of gold portion connection caused by Cr/Au film deposition by improving etching uniformity and using a switch-controlled setup. They demonstrated the feasibility and reliability of the method by fabricating and characterizing a vacuum-packaged resonant pressure sensor. The sensor maintained a high Q factor over a year, indicating reliable wafer bonding and wire interconnection.
While the method has limitations, such as pattern dependence and the requirement of electrical isolation and overhang structures, it is particularly suitable for resonant devices fabricated on SOI wafers. The authors believe this method offers a new approach to wire interconnection for vacuum-packaged devices based on SOI–glass anodic bonding.