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

Abstract

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

Comb-Actuated Resonant Torsional Microscanner With Mechanical Amplification

“…At the torsional mode, the capacitance varies with the angular deflection, and the ES torque depends on the displacement as well as the excitation voltage [28]. The actuation torque's dependence on displacement creates time-varying torsional stiffness, and the system is described by an equation of motion in the form of parametric nonlinear ordinary differential equations [27]- [29]. As seen in Figs.…”

“…The largest amplitude is obtained at n = 1, and it decreases with higher values of n, i.e., for maximum scan angle, the drive signal should be chosen as twice the mechanical resonance frequency [27].…”

“…The presented device is designed to achieve 72 • TOSA at its coupling frequency, and the parameters are adjusted to keep the maximum stress below 1.4 GPa [27] for the required deflection angle. As shown in Fig.…”

Design and fabrication of a MEMS mirror for miniature laser projection

“…Thermal issues are negligible because power dissipation will be in the μWatt range and only 1 type of material is used. Scan angle can be very large, only limited by mechanical stress in the hinges 15 and electrical breakdown in the comb fingers.…”

An Overview of Reliability and Failure Mode Analysis of Microelectromechanical Systems (MEMS)

“…Stress and shock are recognized as the two factors that induce fracture. It has been investigated that stress induced fracture is due to three ways things: bending stress [35], [36], shearing stress [37], [38] and torsional stress [39].…”