Staggered Torsional Electrostatic Combdrive (STEC) Micromirror
High-aspect-ratio micromachining processes have been developed over the past few years, especially enabled by new deep-trench silicon etchers that use the Bosch process (65]. This process enables etching of trenches in silicon with aspect ratios up to 100:1. This deep-trench-etching process provides a hybrid between surface micromachining, as described in Chapter 3, and traditional bulk micromachining, where wet chemical etching is used to make structures from single-crystal silicon. High-aspect ratio micromachining using deep-trench silicon etching has been applied to a number of MEMS mirror designs. The work we present in this chapter shows that high-aspect-ratio micromachined mirrors can deliver significant performance improvements over surface-micromachined mirrors because: a) the thicker mirrors reduce dynamic deformation; b) the process allows designs without hinges that reduce the accuracy and repeatability of the mirror scan; and c) combtooth thicknesses are increased to provide higher-torque actuators. Section 1 describes the Staggered Torsional Electrostatic Combdrive (STEC) micromirror used to make high-speed, high-resolution scanning mirrors, and section 2 describes the Tensile Optical Surface (TOS) process modification that allows lighter-weight mirrors for higher-speed, steady-state beam steering.
KeywordsResonant Frequency Dynamic Deformation Optical Resolution Actuator Torque Fabrication Process Flow
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