Micromechanical reliability evaluation of mirror devices through applying accelerated electrostatic force
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We describe the reliability evaluation for MEMS devices, especially designed for DVD (Digital Video Disk) and CD compatible application module. These MEMS devices are fabricated as a mirror plane (shutter plane) used in DVD or CD data picking up. This micromachined annular shutter mirror (ASM) acts as an adjusting means of the numerical aperture. The electrostatic force can drive the upper plane up and down for focusing or defocusing of incident laser beam to the selected recording plane. So we need to evaluate the micromechanical properties of thin film structural materials to ensure the reliability of those MEMS devices. For those, we perform the fatigue tests onto the devices in the conditions of much accelerated than those of normal driving. The applied electrostatic force can induce the change of the thin film properties, and those are observed by direct and indirect methods. And then, we compare the fatigue effects with electrical, optical data from the intentionally-fatigue- applied specimen and as-fabricated one under accelerated conditions. Microstructure changes are able to explain the fatigue effects through observing the crack initiation, propagation, and its size around stress concentration region of metal mirror plane. Consequently, we can estimate the structural reliability and will provide the effective suggestion data for the fabrication of stable mirror material before commercialization.
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