Continuous bending fatigue test of cantilever hinge for digital micromirror devices

This study investigates the fatigue life of cantilever-style hinges in digital micromirror devices (DMD), which are critical for their optical switching function. The hinges, which facilitate the rotation of reflective mirrors, are subjected to significant mechanical stress due to repetitive flexing, posing a risk of device failure. Prior to the main continuous bending fatigue test, a preliminary resonance-based fatigue experiment was conducted using microscopic laser Doppler vibrometry. The amplitude-frequency response of the cantilever-hinged micromirrors was measured, identifying a resonant frequency through Gaussian curve fitting. Operating at this resonant frequency, the micromirrors achieved stable performance more than 2 x 1010 oscillation cycles, with frequency stability throughout, affirming the reliability of the hinge structure under low-stress, high-cycle fatigue conditions. To further assess fatigue resistance, atomic force microscopy was subsequently employed to conduct continuous bending fatigue tests, in which cyclic stress loading was applied to induce continuous bending in the cantilever hinges. Force-displacement curves obtained during the loading process were analyzed to determine the deflection and spring constants of the hinges at different stages of bending. Experimental results reveal that after 5 x 105 continuous bending cycles, plastic deformation occurred in the hinges along the bending axis, with the end morphology of the hinge exhibiting a significant residual plastic deformation of 417.18 nm compared to its initial state. This research provides valuable insights into the high-stress, low-cycle fatigue behavior of nanoscale devices, contributing to the understanding and improvement of DMD reliability.