Effect of Drain Top Metal Overlap on the Current in Bottom-gate Thin Film Transistors

In this paper we analyze the effect of the top metal overlap associated to the drain contact, that can be present in thin film transistors (TFTs) with bottom-gate staggered configuration. It is shown that the effect of the top metal contact at the drain, overlapping the passivation or etch stopper layer (ESL), increases the drain current. Results from numerical simulations show that this top metal overlap acts as a second gate to the device, partially located near the drain contact. The overall effect on the device current will depend on the semiconductor doping, as well as on the thickness and dielectric constants of the gate dielectric and passivation/ESL layers. The effect is more significant as the channel length of the devices is reduced.