A curved multimorph based electrothermal micromirror with large scan range and low drive voltage

We report a circular micromirror with a 1 mm aperture that has an optical scan range of 60° at 0.68 V applied voltage and 11 mW power input. The mirror is actuated by a semicircular aluminum (Al)-tungsten (W) electrothermal multimorph that bends and twists upon controlled Joule heating. W acts as an active layer of the multimorph and a resistive heater. The curved actuator design not only maximizes the efficiency of chip area usage, but also achieves high resonant frequency due to torsional stiffness encountered during beam deformation. The first three resonant modes of the micromirror are at 104 Hz, 400 Hz and 416 Hz, respectively. Two-dimensional (2D) optical scanning is demonstrated by using the second resonant mode. The low power consumption may be attributed to the use of a single actuator beam. Mirror-center shift produced by actuator bending and twisting partially compensate each other and this results in 1.6 times lower center-shift compared to previously reported straight multimorph based designs. Device fabrication involves surface and bulk micromachining on an SOI wafer.