Figure 2.

In (a) the cantilever is in unadjusted state. When the bias voltage $V_{\mathrm{DC}}$ is applied, the cantilever will start bending towards the electrode; When the bias voltage is bigger than the pull-in voltage, the cantilever will pull-in towards the electrode (b). The cantilever will hit the electrode (dashed line) and will be in a stable state. When the voltage is further increased, the cantilever will finally be in the adjusted state. The effective length $L_{\mathrm{eff}}$ of the cantilever has decreased, and the stiffness is increased.