A full nonlinear model based on modified couple stress theory is developed for cantilevered microbeams under electrical force.
The geometric nonlinearities slightly affect the static pull-in voltages.
The presence of geometric and inertial nonlinearities may change the frequency-response curves from a softening-type nonlinear behavior to a hardening-type one.
The effect of small length scale parameter on the dynamic pull-in band of frequencies may be pronounced.