(A) study on high mechanically reliable digital micromirror with interdigitated cantilevers

Abstract

In this thesis, we have proposed and developed a new electrostatic digital micromirror structure based on a new actuator called interdigitated cantilevers. In contrast to conventional micromirrors that rotate through the twisting actuation of a hinge, this micromirror has a symmetric bidirectional rotation through a bending actuation of interdigitated cantilevers hidden under a mirror plate. For the static and dynamic characteristics of the micromirror, analytical models were first developed on the basis of the Euler-Bernoulli beam equation as well as distributed-parameter and lumped-parameter models. The results of the developed analytical models are in good agreement with those of a finite element method (FEM) simulation, having just a 10 % deviation. On the basis of these analytical models, we successfully designed, fabricated and evaluated a micromirror with a mirror size of $16 \mum \times 16 \mum$. The fabricated micromirror has a mechanical rotation angle of $\plusmm 10\deg$, a pull-in voltage of 54 V, a resonant frequency of 350 kHz, and a switching response time of 15 $\mu s$. The measurement results compare favorably with those of analytical models and FEM simulations, with a deviation of less than 15 % and 10 %, respectively. Also, this research reports for the first time the analytical studies and the experimental results about the mechanical reliability of the micromirror with interdigitated cantilevers. Through analytical calculations, FEM simulations, and experiments, we have presented that the mechanical reliability of the micromirror can be improved by a new spring structure of interdigitated cantilevers without any help of mechanically reliable materials and any control of operation condition. To quantitatively demonstrate that, we have compared the maximum Von Mises stress exerted in the two micromirror types which have two different springs. The micromirror with interdigitated cantilever has been subjected to 2 times lower maximum Vo...