A silicon optical bench with vertically-oriented micromirrors for active beam steering

This paper reports a Silicon Optical Bench (SiOB) integrated with two vertically-oriented tip-tilt micromirrors that can perform active beam steering. The curling of W/SiO₂ bimorphs is utilized to bend microstructures out of plane. The vertical orientation is realized by using a combination of curling W/SiO₂ bimorphs and stoppers. W is employed as one of the bimorph materials to increase the bimorph stiffness, attributed to its much higher Young's modulus than other materials. At the same time, the stress of the W layer is tuned to maximize the bending angle range of the W/SiO₂ bimorphs. The fabrication process of making this new SiOB platform has been developed. Particularly, two electrothermal bimorph-based MEMS mirrors are successfully fabricated and stand upright on an SiOB. The two upright micromirrors are parallel to each other and can perform 2-axis forward-view optical scanning. The mirror plate is made of a 20 μm-thick silicon layer coated with aluminum and its diameter is 0.72 mm. The mirror can rotate ±8° at 4.5 V. This MEMS scanner has potential applications in miniature LiDAR for Micro Air Vehicles (MAVs).