One-axis metallic electrostatic micromirror array

Abstract

A new micromachined one dimensional (1-D) micromirror array structure is presented that utilizes primarily electroplated nickel, a mechanically durable material with a high glass transition temperature and with controllable residual stress as the main structural material. The goal of this research is to develop custom micromirror array for use in epitaxial growth systems to define the device structure and hence eliminate the need for etching and lithography, the same micromirror can be used for switches and optical cross-connects. The high glass transition temperature of nickel allows it to be used at high temperature without causing any contamination to the epitaxial systems or to the deposited materials. Micromirror arrays with 5×5 and 1×5 pixels were designed with square shape with an area of 500 μm2 to provide high fill factor and uniform stress distribution. The focus of this paper is on improved design for reducing actuation voltage and increasing the rotation angle. The micromirror was previously fabricated using surface micromachining technologies with a thick photoresist sacrificial layer [1]. The torsion beams were designed with a serpentine shape in order to optimize the voltage necessary to tilt the micromirror by ± 10°. The micromirrors were simulated using Coventor finite element tool in order to determine their geometries and performance. A voltage of 20 volts was required to rotate the mirror with a pixel pitch of 500 μm by 7.68° with resonance frequency of 221.52 Hz.