Design of a 2D Electrostatic-Thermal Actuated MEMS Mirror

Abstract

MOEMS (Micro-Opto-Electro-Mechanical System) are MEMS in which the optical part plays a dominant role. MOEMS are usually used to deflect and/or focus light from/on a given spot thus acting as optical switches. Now, imagine to have a 2D array of optical switches (e.g. a CCD) and to rotate the MOEMS so that the incoming light is focused subsequently on each of these switches. What you have designed is a 2D scanner. If you reverse the process (i.e. one light source and the MOEMS projecting on a screen) you have designed a projector. The main advantage of a MOEMS projector and/or scanner are the reduced dimensions/weight with respect to traditional projectors and scanners and the fact that the necessity of optical lenses is greatly reduced thus reducing the cost of the system. In the present paper, a 2D MOEMS projector/scanner is designed. The peculiarity of the system is that the MOEMS mirror is able to rotate around two perpendicular axes having only one excitation point instead of two thus allowing to design a system that can be produced from a planar surface. This is achieved by applying the excitation to the micro-mirror indirectly through a supporting frame that is free to rotate around an eccentric vertical axis. The micro-mirror, instead, is free to rotate around an eccentric horizontal axis with respect to such supporting frame (figure 3). To be able to excite the motion of the micro-mirror along two perpendicular axes, the actuation force has to be applied in a point that is not nodal for any of the two rigid vibration modes of the system, has to be biharmonic and, to increase displacements, has to have frequencies that correspond to the two rigid eigenfrequencies of the micro-mirror.