Design and fabrication of one and two axis nickel electroplated micromirror array

Abstract

[ACCESS RESTRICTED TO THE UNIVERSITY OF MISSOURI AT AUTHOR'S REQUEST.] MEMS based micromirror devices are gaining importance at a steady pace in the applications related to optical communications and display technology. This research work describes the design, simulation and fabrication of a new micromachined metallic micromirror array. The work focuses on improved design for reducing actuation voltage and increasing the glass transition temperature for the high temperature applications. The goal is to develop micromirror array for switches and cross connects in optical communications. The micromirror utilizes primarily electroplated nickel, a mechanically durable material with a high glass transition temperature and with controllable residual stress as the main structural material. It also provides high reflectivity to obtain high resolution display. Micromirror arrays with 5x5 pixels were designed with an area between 0.1x0.1 mm2 and 0.5x0.5 mm2 to provide high fill factor and uniform stress distribution. The realization of fabrication of micromirrors was discussed. The micromirror fabrication process can be performed by surface micromachining technologies with a thick photoresist sacrificial layer. The torsion beams were designed with a serpentine shape in order to optimize the voltage necessary to tilt the micromirror by [plus or minus] 10o. Micromirror devices with different beam designs were designed and simulated. The results indicated significant reduction of actuation voltage. The micromirrors were simulated by coupling the mechanical and electrostatic parameters using Coventor, a finite element tool, in order to determine their geometries and electrostatic performance. A voltage of 20 volts was required to rotate the mirror with a diameter of 0.5 mm by 7.680 with resonance frequency of 221.52 Hz. In addition, the 0.5 mm mirror was able to achieve a resonant frequency of 2 kHz with 8.390 tilt angle for 202 V.