Investigation of heat transfer in micromirrors

Heat transfer mechanisms in electrostatically actuated torsion mirrors are dominated by heat conduction in the torsion springs and the air gap between mirror plate and driving electrodes and by convection above the mirror. The maximum optical power rate capability of micromirrors strongly depends on the reflectivity of the mirror surface and of the heat transfer out of the mirror plate. The results provide important knowledge since increased mirror temperature influences its optical parameters like flatness and roughness, the dynamical system behavior or even damages the reflective layer. This paper deals with investigations of the heat transfer by conduction and convection. The cumulative heat resistance of micromirrors is calculated using analytical formulas and by means of finite element modeling. Theoretical results are compared with experimental data. A thermographic imaging system and electrical heating is used to measure the thermal decay function which evaluates the resistance at known capacitance. It can be deduced that an optical power of several Watt can be steered by micromirrors.