Pre-stresses Influence on a Micro Mirror Structure

Introduction The purpose of the model is to exemplify the use of pre- stresses in plated metal layers in order to create a desired lift-off of a MEMS structure The model shows the use of the Initial Stresses feature in the Structural Mechanics Module

Model Geometry Cantilever beams as support Two-layers of plating Mirror

Problem Definition Loads: –Pre-stresses of different signs but equal in magnitude for the upper and lower layer of the cantilevers Constraints: –Cantilevers constrained in all directions at the free end surfaces Materials –Alternative 1: Aluminum for both mirror and beams –Alternative 2: Aluminum for beams, stainless steel for mirror

Results, Aluminum for Both Mirror and Beams

Results, Stainless Steel for Mirror

Conclusions The model shows that the curvature of the mirror and the lift-off from the substrate is substantially larger for aluminum Steel gives a flatter mirror surface The model can be quickly set-up and solve the COMSOL Multiphysics’ Structural Mechanics Module