A 2-AXIS SI/AL Bimorph-Based Electrothermal Micromirror Integrated with Piezoresistors for High Resolution Position Sensing

In this work, single-crystal silicon (SCS) is employed to replace fragile SiO2 to construct robust 2-axis electrothermal micromirrors with piezoresistors for position sensing. A lateral shift-free (LSF) SCS/Al bimorph electrothermal bimorph actuator is proposed, and a two-axis LSF SCS/Al electrothermal micromirror with piezoresistors was designed, fabricated and characterized. Each actuator was composed of six segments of bimorph and a thin silicon layer with the thickness of 2 μm. The dimensions of the square mirror plate are 1800 μm × 1800 μm × 30 μm. The fabricated micromirror achieved a tip-tilt angle of 7.2 ° and piston displacement of 240 μm under a voltage of 5 V. The performance of the angular shift of the proposed micromirror was improved about one order of magnitude with the value decreasing from 0.035 ° under open-loop control to 0.0062 ° under closed-loop control. Compared with SiO2-based bimorphs, the fabrication process is not only simplified, but also provides a method for integrating piezoresistive sensors on the bimorph actuator and realizing feedback control.