Study on Threshold Voltage Control of Tunnel Field-Effect Transistors Using <i>V<sub>T</sub></i>-Control Doping Region

Abstract

Although the Tunnel Field-Effect Transistor (TFET) is a promising device for ultra-low power CMOS technology due to the ability to reduce power supply voltage and very small off-current, there have been few reports on the control of VT for TFETs. Unfortunately, the TFET needs a different technique to adjust VT than the MOSFET by channel doping because most of TFETs are fabricated on SOI substrates. In this paper, we propose a technique to control VT of the TFET by putting an additional VT-control doping region (VDR) between source and channel. We examine how much VT is changed by doping concentration of VDR. The change of doping concentration modulates VT because it changes the semiconductor work function difference, φs,channel-φs,source, at off-state. Also, the effect of the size of VDR is investigated. The region can be confined to the silicon surface because most of tunneling occurs at the surface. At the same time, we study the optimum width of this region while considering the mobility degradation by doping. Finally, the effect of the SOI thickness on the VDR adjusted VT of TFET is also investigated.