Nanoelectromechanical switches work by using electrostatic forces to mechanically deflect an active element into physical contact with an opposing electrode, thus changing the state of the device.
The electrostatic forces scale inversely with the square of the gap between the active element and the electrode, making them increasingly effective as devices get smaller. As the voltage applied across the active element and the electrode is increased, the resulting electrostatic forces are balanced by elastic restoring forces in the active element. When a critical ‘pull-in’ voltage is reached, the electrostatic forces overwhelm the restoring force: this causes the active element to accelerate towards the electrode, which closes the switch and leads to a sharp rise in the current through the device.
After the switch has closed, elastic restoring forces in the deformed active element act to pull the switch open. Adhesive forces at the contact between the active element and electrode counteract this, holding the switch closed. If the elastic restoring forces are insufficient to break the adhesion when the electrical bias is fully removed, the switch will behave in a non-volatile manner, remaining in the closed state even when no input is applied (Fig.2a).
However, if the switch is designed such that the elastic forces of the deformed active element are sufficient to overcome the adhesive forces, the switch will be volatile and re-open when the applied bias is sufficiently reduced (Fig.2b).