Polarization Gradient Effect of Negative Capacitance LTFET.

Hao Zhang,Dong Wang,Chen Chong,Chenyu Yin,Shupeng Chen,Shulong Wang,Hongxia Liu,Tianzhi Gao,Xiaoyang Fan

doi:10.3390/mi13030344

Abstract

In this paper, an L-shaped tunneling field effect transistor (LTFET) with ferroelectric gate oxide layer (Si: HfO2) is proposed. The electric characteristic of NC-LTFET is analyzed using Synopsys Sentaurus TCAD. Compared with the conventional LTFET, a steeper subthreshold swing (SS = 18.4 mV/dec) of NC-LTFET is obtained by the mechanism of line tunneling at low gate voltage instead of diagonal tunneling, which is caused by the non-uniform voltage across the gate oxide layer. In addition, we report the polarization gradient effect in a negative capacitance TFET for the first time. It is noted that the polarization gradient effect should not be ignored in TFET. When the polarization gradient parameter g grows larger, the dominant tunneling mechanism that affects the SS is the diagonal tunneling. The on-state current (Ion) and SS of NC-LTFET become worse.

Highlights

Due to the limitation of SS (60 mV/dec) at room temperature, detrimental effects, such as short channel effect, higher off-state current (Ioff ) and subthreshold swing, would appear in the continuous miniaturization of complementary MOS technology [1,2]
In order to intuitively display the change of transfer characteristic curve, the NC-L-shaped tunneling field effect transistor (LTFET)
The SS of NC-LTFET and LTFET is 18.3 mV/dec and 33 mV/dec at the range of drain current from 4 × 10−17 to 1 × 10−9 A/μm, respectively

Summary

Introduction

Due to the limitation of SS (60 mV/dec) at room temperature, detrimental effects, such as short channel effect, higher off-state current (Ioff ) and subthreshold swing, would appear in the continuous miniaturization of complementary MOS technology [1,2]. It is no longer feasible to reduce power consumption by lowering the supply voltage [3,4]. The TFET with a gate-controlled reverse biased p-i-n diode structure is one of candidates for the generation of low-power devices because of its lower Ioff and steep subthreshold slope [5,6,7,8]. Some structures with overlapping gate/channel/source are proposed to increase the Ion and improve the subthreshold characteristic by increasing the effective tunneling area. Others use hetero-materials such as Si/Gex Si1−x to form a shorter tunneling path to achieve steeper SS and greater Ion [9,10,11,12]. All the above methods are based on the band-to-band tunneling mechanism to change the n factor of SS to obtain better subthreshold characteristics. The expression of SS is as follows [13]: published maps and institutional affiliations

Methods

Results

Conclusion