How slender can comb-drive fingers be?

In this work, the electromechanical stability of individual comb-drive fingers is considered. Previous studies have shown that optimal design of elastic suspensions can prevent the side pull-in instability of comb-drive rotors. In this work it is shown that side pull-in can nevertheless occur in individual comb fingers, if they are exceedingly slender. To this end, the critical electromechanical state of individual comb fingers is analytically solved. This solution is in good agreement with finite elements simulations. The analytic solution can be used to design comb-drives in which side pull-in of individual fingers is avoided.