Subthermal switching with nanomechanical relays

TL;DR

This paper models electronic switching in nano-electromechanical transistors, highlighting how dipolar interactions and pull-in forces influence the steepness of switching curves and hysteresis effects.

Contribution

It introduces a physical model that explains the subthreshold swing and hysteresis in cantilever-based nano-electromechanical transistors, emphasizing the roles of dipolar and capacitive forces.

Findings

Subthreshold swing is governed by dipolar interactions and pull-in forces.

Capacitive energy dominates in longer cantilevers, enabling sharp switching.

Hysteresis arises from metastable and stable state interchange during voltage scans.

Abstract

We present a physical model for electronic switching in cantilever based nano-electro-mechanical field effect transistors, focusing on the steepness of its switching curve. We find that the subthreshold swing of the voltage transfer characteristic is governed by two separate considerations - the ability of the charges to correlate together through dipolar interactions and amplify the active torque, versus the active pull-in forces that drive an abrupt phase transition and close the air gap between the tip of the cantilever and the drain. For small sized relays, dipolar and short-range Van Der Waals 'sticking' forces dominate, while for longer cantilevers the capacitive energy acquires a major role. The individual pull-in and pull-out phases demonstrate a remarkably low subthreshold swing driven by the capacitive forces, sharpened further by dipolar correlation. The sharp switching, however, comes at the expense of strong hysteresis as the metastable and stable states interchange along the forward and reverse phases of the voltage scan.