Electrostatic scanning micromirrors using localized plastic deformation of silicon

Electrostatic scanning micromirrors made of single-crystal silicon from a SOI (silicon-on-insulator) wafer using self-aligned and localized plastic deformation of silicon have been demonstrated. Localized plastic deformation is achieved by selective Joule heating of silicon structures while the whole substrate is kept at low temperature. Novel designs for torsional springs to prevent the buckling problem due to the non-uniform thermal expansion by localized heating are presented and the optimal range of electric power for successful Joule heating is discussed. The prototype micromirror is actuated by self-aligned vertical comb sets at a measured resonant frequency of 4.13 kHz with optical scanning angles up to 50.9° under driving voltages of 30 Vdc plus 14 Vac. After continuous operation of 20 billion cycles (56 days) at the maximum scanning angle, the device shows no observable signs of degradation or fatigue.