Improvement of the Bias Stress Stability in 2D MoS2 and WS2 Transistors with a TiO2 Interfacial Layer.

Woojin Park,Tae Hyeon Kim,Sung Mook Choi,Hye Yeon Jang,Yusin Pak,Seyoung Oh,Byungjin Cho,Yonghun Kim,Jae Hyeon Nam

doi:10.3390/nano9081155

Abstract

The fermi-level pinning phenomenon, which occurs at the metal–semiconductor interface, not only obstructs the achievement of high-performance field effect transistors (FETs) but also results in poor long-term stability. This paper reports on the improvement in gate-bias stress stability in two-dimensional (2D) transition metal dichalcogenide (TMD) FETs with a titanium dioxide (TiO2) interfacial layer inserted between the 2D TMDs (MoS2 or WS2) and metal electrodes. Compared to the control MoS2, the device without the TiO2 layer, the TiO2 interfacial layer deposited on 2D TMDs could lead to more effective carrier modulation by simply changing the contact metal, thereby improving the performance of the Schottky-barrier-modulated FET device. The TiO2 layer could also suppress the Fermi-level pinning phenomenon usually fixed to the metal–semiconductor interface, resulting in an improvement in transistor performance. Especially, the introduction of the TiO2 layer contributed to achieving stable device performance. Threshold voltage variation of MoS2 and WS2 FETs with the TiO2 interfacial layer was ~2 V and ~3.6 V, respectively. The theoretical result of the density function theory validated that mid-gap energy states created within the bandgap of 2D MoS2 can cause a doping effect. The simple approach of introducing a thin interfacial oxide layer offers a promising way toward the implementation of high-performance 2D TMD-based logic circuits.

Highlights

The process of extreme scaling-down to reach a physical channel length limit of sub-100 nm has caused critical problems, such as a short channel effect and increased leakage current
To identify the existence of the 2D transition metal dichalcogenide (TMD), MoS2 was mechanically exfoliated from the bulk mineral, and the multilayer MoS2 was characterized using Raman spectroscopy (Figure 1a)
To unveil how the TiO2 layer electronically influences the MoS2 semiconductor, we explored a theoretical simulation of electronic states for free-standing MoS2 and MoS2/TiO2 materials via a density functional theory (DFT) calculation (Figure 5)

Summary

Introduction

The process of extreme scaling-down to reach a physical channel length limit of sub-100 nm has caused critical problems, such as a short channel effect and increased leakage current. To address these limitations, efforts have recently been made to scrutinize promising semiconducting materials. Atomically thin layered transition metal dichalcogenides (TMDs) have attracted great attention due to their extraordinary electrical, optical, and mechanical properties [1,2,3,4,5,6,7,8,9] One of their most attractive properties is the existence of a band-gap and its facile engineering. The effect of the interfacial buffer layer at the metal/2D TMD (MoS2 and WS2) contact on transistor performance was experimentally and theoretically investigated. It can be highlighted that we suggested a facile approach to achieve both higher transistor performance and stability at the same time

Materials and Methods

Findings

Conclusions