A low-drift, open-loop controlled, single crystalline silicon micromirror with floating field-limiting shields

Abstract

This paper describes the design, fabrication and testing of a one-axis micromirror in order to suppress the electric charging problem related to its actuation. The electrostatically-actuated torsional micromirror is of the parallel-plate type. Since the dielectric around the electrodes below the mirror plates is highly exposed, we installed gold shields in the floating state around the electrodes, so as to cover the exposed dielectric surface. The gold shields played a leading role in limiting the electric field between the electrodes. This effect was characterized and the tilting angle stability was measured by observing the micromirror performance with and without the floating field-limiting shields. Drift measurements of these two types of micromirrors were made using a position-sensing detector (PSD). The micromirror with the field-limiting shields, namely micromirror type A, showed a tilting angle drift of 0.005° at 83% of the pull-in voltage, while a tilting angle drift of 0.5° was measured at the same percentage of the pull-in voltage for the micromirror without the field-limiting shields, namely micromirror type B. At 97.7% of the pull-in voltage, the pull-in phenomenon occurred after 220 s for micromirror type B due to the charging effect. On the other hand, micromirror type A showed no pull-in phenomena with elapsed time at a bias of 97.7% of the pull-in voltage due to the resolution of the charging effect. © 2008 IOP Publishing Ltd.