Fatigue Characteristics of Silicon Micromechanism for Micromachine

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A fatigue-testing machine based on four-point bending was developed for micromaterials and micromechanisms. Cyclic loads were applied to a specimen by means of a piezo-electric actuator, which can control the displacement of the specimen with high resolution and frequency. Displacement of the specimen was measured by the optical interferometer combined with the computer image processing technique. A microscope and a CCD TV camera were used to obtain interference fringes, and the shutter of the camera was synchronized to the loading signal for the real-time processing of the cyclic displacement of the specimen. Basic tests were conducted with a smoothed specimen fabricated by dicing from a silicon wafer, and it was confirmed that the fatigue-testing machine satisfies the specifications needed. Two types of specimens were prepared to be used in the micromaterial fatigue testing, one was a notched type specimen and another was a smoothed film type one. These specimens were fabricated from silicon wafers by micromachining, such as PVD and the photo-etching process. In order to evaluate the key process of micromachining, the anisotropic etching process for a single silicon crystal was studied to determine the etching condition, so that the specimens with accurate geometry and dimensions could be performed.