Introduction of a metal strip in oxide region of junctionless tunnel field-effect transistor to improve DC and RF performance

Abstract

Achieving steeper subthreshold slope and high ON–OFF current ratio (\(I_{\mathrm{ON}}/I_{\mathrm{OFF}}\)) is essential for use of semiconductor devices in switching applications. It is well known that tunnel field-effect transistors face serious issues related to low ON-state current and poor radio frequency (RF) response. We report herein a unique method for realizing a sharp tunneling junction in a charge plasma-based junctionless tunnel field-effect transistor by embedding a metal strip in the oxide region near to the source–channel connection. This modulates the carrier concentration profile at the source–channel interface, making it abrupt. This steeper source–channel tunneling junction results in a reduced tunneling barrier and increased flow of charge carriers at the junction. Furthermore, electron transfer along the channel is accounted for using postprocessing based on the drift–diffusion equations as well as the band-to-band tunneling current. This phenomenon contributes to the improved direct-current (DC) characteristics of the device. Selection of a metal with an appropriate work function for the strip can improve the subthreshold swing and threshold voltage (\(V_{\mathrm{th}}\)) of the device. The increased charge carrier tunneling rate at the junction also results in a huge improvement in RF parameters of the device, including cutoff frequency (\(f_{T}\)), gain–bandwidth product, and transit time (\(\tau \)).