Modeling of thermal actuation in a bulk-micromachined CMOS micromirror

In this paper, the thermal actuation characteristics of a novel Micro-Electro-Mechanical mirror fabricated in a standard CMOS process is presented. The micromirror consists of a plate suspended over a hulk-etched pit by four cantilever flexures, two of which are vertical thermal actuators. The thermal actuators consist in part of stacked layers of aluminum, silicon dioxide and polysilicon. The differences in thermal expansion coefficient (CTE) of these materials cause the flexures to curl when an ohmic heating from an input electrical power is applied. Due to a complex geometry, the actuators are not complete bimorphs, rendering use of bimorph theory alone inadequate in predicting the deflection. Analytical and finite element models verified by experiments were developed to predict and model the static deflection of the thermal actuator. The temperature distribution throughout the actuator and the mirror warpage were investigated. (C) 2000 Elsevier Science Ltd. All rights reserved.