  In this paper, we report the advantage of using AC actuating signal for
driving MEMS actuators instead of DC voltages. The study is based upon micro
mirror devices used in digital mode for optical switching operation. When the
pull-in effect is used, charge injection occurs when the micro mirror is
maintained in the deflected position. To avoid this effect, a geometrical
solution is to realize grounded landing electrodes which are electro-statically
separated from the control electrodes. Another solution is the use of AC signal
which eliminates charge injection particularly if a bipolar signal is used.
Long term experiments have demonstrated the reliability of such a signal
command to avoid injection of electric charges.
