Development of an Electromagnetic Actuator based Translation Micromirror as a Movable Mirror in a Miniaturized FTIR Spectrometer

Abstract

Miniaturized FTIR spectrometer has been developed rapidly in recent years due to the increasing demands. MEMS micromirrors have been used to replace the movable mirror system, which is the largest part in conventional FTIRs. Electromagnetic actuators are suitable to drive the micromirrors because of their relatively large quasi-static translation range and high response speed. In addition, high surface quality is required for the micromirror. However, current MEMS based micromachining technologies cannot provide satisfactory surface quality. Therefore, a translation mircomirror with a large displacement, i.e., > 120 µm, and a novel magnetic field pulling-force assisted bonding technology are developed to bond a high surface quality (i.e., roughness of 2 nm and radius curvature over 15 m) mirror plate with a released microactuator using an adhesive. However, the touching points between the moving film and the substrate lead to a large starting position variation and low repeatability in operation. To solve these limitations, a repulsive force based translation micromirror utilizes a novel driving mechanism, i.e., permanent magnet ring above and electromagnet underneath the moving film, to lift and push the moving film away from the substrate for translation. As a result, the starting position of the repulsive force translating mirror is consistent and the repeatability is <1%. A maximum displacement of 144 µm can be achieved when a 140 mA current is applied. To eliminate the tilt of the translation micromirror during motion, a compensation system is developed which includes the translation mirror, a correcting mirror and a reflecting mirror. The correcting micromirror corrects the tilt by rotating the same angle as the translation micromirror with its rotating axis parallel to the tilting axis. The tilt of the attractive force translation micromirror can be reduced to 0.026° after compensation, so it can be used as a movable mirror in FTIRs to measure half of the midinfrared region between 13.6 µm an 25 µm. Therefore, the electromagnetic actuator based translation micromirror with large displacement, high surface quality can be successfully used as the movable mirror in the miniaturized FTIRs with the tilt compensation system.