Displacement and Thermal Performance of Laser-Heated Asymmetric MEMS Actuators

Optical actuators are fundamental building blocks in the development of all-optical microelectromechanical devices. Photothermally actuated devices are inevitably limited by overheating and device damage resulting from the absorption of laser power. Optimal actuator design requires an efficient use of the applied laser power while minimizing the susceptibility of device damage. Surface micromachined polycrystalline silicon flexure-style optical actuators, which are powered using an 808-nm continuous-wave laser, were evaluated for displacement performance and susceptibility to damage. Actuator displacement is linear with incident power for laser powers below those that cause damage to the irradiated surface, up to a maximum displacement of 7-9 mum. Damage of the irradiated surface causes viscous relaxation of the polysilicon film and leads to recession of the displacement during the heating and additional recession after the optical power is removed. The first spatially resolved temperature measurements during device operation were obtained using micro-Raman thermometry. The temperature measurements revealed the influence of temperature-dependent optical properties in the thermal behavior of the irradiated devices.