Electrostatic actuation is most commonly used because of low-power consump-
tion and ease of control. Early devices used parallel-plate actuators, which have
high actuation voltage and limited scan angle due to pull-in instability [49]. The
mirror angle beyond 1/3 of the maximum mechanical angle is not stable because
the electrostatic force can no longer be balanced by the spring force. The mirror
will continue to rotate until it hits a mechanical stop. Although the pull-in effect
can be mitigated by nonlinear controllers, it increases the complexity of the
electronics [50]. Micromirrors with vertical combdrive actuators reported first by
Conant et al. [51] offer many advantages. They have much larger torque, which
one can use to reduce the operating ...