Exploiting Within-Channel Tunneling in a Nanoscale Tunnel Field-Effect Transistor

Shelly Garg,Sneh Saurabh

doi:10.1109/ojnano.2020.3031633

Abstract

In this paper, using device simulations, we investigate electrical characteristics of a tunnel field-effect transistor (TFET) in which band-to-band tunneling (BTBT) occurs dominantly within the channel, rather than at source-channel junction. The within-channel BTBT is enabled by sharp band-bending induced by the dual material gate (DMG). The work-functions of two metal gates are chosen, such that the surface potential profile exhibits a distinct step at the DMG interface. Consequently, even under equilibrium condition, a high lateral electric field and an abrupt tunneling junction exist at the DMG interface. When a small gate voltage is applied, the inherent lateral electric field aids in creating an abrupt band alignment and obtaining a small tunneling width. As a result, an excellent average subthreshold swing is obtained in the proposed device. We have also investigated scaling of channel lengths in the proposed device and have demonstrated that within-channel tunneling can be exploited for channel lengths of 40nm and above. Furthermore, low drain threshold voltage and suppressed drain-induced barrier lowering can be obtained in the proposed device. Moreover, in contrast to conventional TFETs, electrical characteristics of the proposed device are less susceptible to source doping variations and shift in gate-edge with respect to the source-channel junction.

Highlights

Tunnel field-effect transistor (TFET) is one of the most promising alternatives to metal-oxide semiconductor FET (MOSFET) for futuristic low-power applications [1]–[3]
In this paper, using device simulations, we investigate electrical characteristics of a tunnel fieldeffect transistor (TFET) in which band-to-band tunneling (BTBT) occurs dominantly within the channel, rather than at source-channel junction
Though we have demonstrated the technique of exploiting within-channel tunneling in a silicon-based TFET, with proper device optimization, the concept can be extended to TFETs based on other materials as well

Summary

INTRODUCTION

Tunnel field-effect transistor (TFET) is one of the most promising alternatives to metal-oxide semiconductor FET (MOSFET) for futuristic low-power applications [1]–[3]. TFETs exhibit exponential onset in the output characteristics because of the dependence of the BTBT on the gate-to-source voltage VGS and drain-to-source voltage VDS, in contrast to the conventional MOSFET [13], [14]. Due to the existence of an inherent lateral electric field, a strong gate control over the BTBT region and the shift of BTBT region from the source–channel junction towards the drain, several electrical parameters improve in the proposed TFET. It is demonstrated that in contrast to the conventional TFETs, the proposed device is less susceptible to variations in source doping and shift in the gate-edge with respect to the source-channel junction. A high inherent lateral electric field at the BTBT junction in the proposed device suppresses the further impact of drain-induced electric field leading to a smaller DIBL effect. Though the total ON-state gate capacitance is similar in both the conventional and the proposed devices, the decreased CGD in the proposed device can ameliorate this problem

SCALING OF GATE LENGTH

EFFECT OF SOURCE DOPING PROFILE

EFFECT OF SHIFT IN GATE-EDGE WITH RESPECT TO

EFFECT OF INTERFACE TRAP CHARGES

Findings

CONCLUSION