Torsional stress, fatigue and fracture strength in silicon hinges of a micro scanning mirror

Special micro scanning mirrors have been designed for the investigation of torsional stress in micro-scale hinges made of crystalline silicon. The setup with precise logging of resonant frequency and deflection amplitude of the MEMS-scanners is described. First results on fatigue and fracture strenght are presented. Fracture of torsion beams with 6.6 µm x 30 µm cross-section occured at 2.0 GPa to 2.4 GPa. No sign of fatigue was observed in operation for 512 h at 1.4 GPa torsional stress in resonance at 2260.7 Hz oscillation frequency. Measured frequency variation was 0.06 % without any trend.