Bistable planar polysilicon microactuator with shallow arch-shaped leaf springs

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Abstract
Bi-stable microactuators are necessary to implement optical switch and microrelay with low power and high reliability. In this work, we analyzed the buckling and vibration characteristics of a planar microactuators with shallow arch- shaped leaf springs. To investigate elastic stability of the proposed microactuator, we derived static buckling modes. A concentrated force of 0.35 muN at the center of beam was required for the snap-through motion for the beam length of 1600 micrometer, thickness of 3 micrometer, beam width of 6.5 micrometer and initial rise of 15 micrometer considering only the first buckling mode. We also analyzed vibration characteristics of arch-shaped leaf spring. The resonant frequencies of the first modes across over the second mode and keeps constant resonant frequencies over the cross point. On the contrary, the resonant frequencies of second modes become almost constant regardless of initial rise. The planar microactuator with shallow arch-shaped leaf springs at both sides were fabricated using silicon micromachining technology. The vertical structure of the planar microactuator features simplicity and consists of p-doped polysilicon as a structural layer and LTO (Low Temperature Oxide) as a sacrificial layer. The polysilicon was annealed for the relaxation of residual stress and HF GPE (gas-phase etching) process was finally employed in order to release the microactuators. These bi- stable planar microactuators with shallow arch-shaped leaf springs showed a high stiffness against external disturbance, and would be very useful for the stable operation of micro optical switch and microrelay.

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