Fabrication of vertical comb electrodes using selective anodic bonding

This paper presents a new fabrication technology for forming vertical comb (VC) electrodes used in sensors and actuators. The main feature of VC electrodes is that they are positioned above and below the plane of a moving microstructure that is used as the sensing or actuating plate, thus enabling one to either measure or create out-of-plane motion. In our method, VC electrodes and the moving microstructure are first fabricated using the silicon-on-glass (SOG) process. Next, the VC electrodes are moved into position by selectively displacing them up or down using electrostatic force applied during an anodic bonding step specifically utilized for this purpose. Three different VC electrode designs and analytic approaches to determine mechanical stiffness and required pull-down force are presented. VC structures with both 8mum and 4.6mum gaps to glass wafers are successfully fabricated. VC electrodes with vertical (out of plane) displacement of as large as 45mum in 100mum-thick structure have been realized.