Development of wafer level packaged scanning micromirrors

Abstract

This paper presents design, simulation and fabrication of a wafer level packaged Microelectromechanical Systems (MEMS) scanning mirror. In particular we emphasize on the process development and materials characterization of In- Ag solder for a new wafer level hermetic/vacuum package using low temperature wafer bonding technology. The micromirror is actuated with an electrostatic comb actuator and operates in resonant torsional mode. The mirror plate size is 1.0 mm × 1.0 mm. The dynamic vibration characteristics have been analyzed by using FEM tools. With a single rectangular torsion bar, the scanning frequency is 20 KHz. Besides, the hermetically sealed packaged is favored by commercial applications. The wafer level package is successfully carried out at process temperature of 180°C. With proper process design, we may lead the form a single phase of Ag2In at the bonding interface, in which it is an intermetallic compound of high melting temperature. This new wafer level packaging approach allows us to have high temperature stability of wafer level packaged scanning mirror devices. The wafer level packaged devices are able to withstand the peak temperature in SMT (surface mount technology) manufacturing lines. It is a promising technology for commercializing MEMS devices.