Ultra-Short Pulsed Laser Annealing Effects on MoS2 Transistors with Asymmetric and Symmetric Contacts

Hyeokjin Kwon,Jaewon Jang,Jae Jang,Costas Grigoropoulos,Hyuk-Jun Kwon,Sunkook Kim,Seunghun Baik

doi:10.3390/electronics8020222

Abstract

The ultra-short pulsed laser annealing process enhances the performance of MoS2 thin film transistors (TFTs) without thermal damage on plastic substrates. However, there has been insufficient investigation into how much improvement can be brought about by the laser process. In this paper, we observed how the parameters of TFTs, i.e., mobility, subthreshold swing, Ion/Ioff ratio, and Vth, changed as the TFTs’ contacts were (1) not annealed, (2) annealed on one side, or (3) annealed on both sides. The results showed that the linear effective mobility (μeff_lin) increased from 13.14 [cm2/Vs] (not annealed) to 18.84 (one side annealed) to 24.91 (both sides annealed). Also, Ion/Ioff ratio increased from 2.27 × 10 5 (not annealed) to 3.14 × 10 5 (one side annealed) to 4.81 × 10 5 (both sides annealed), with Vth shifting to negative direction. Analyzing the main reason for the improvement through the Y function method (YFM), we found that both the contact resistance (Rc) and the channel interface resistance (Rch) improves after the pulsed laser annealings under different conditions. Moreover, the Rc enhances more dramatically than the Rch does. In conclusion, our picosecond laser annealing improves the performance of TFTs (especially, the Rc) in direct proportion to the number of annealings applied. The results will contribute to the investigation about correlations between the laser annealing process and the performance of devices.

Highlights

Flexible electronics have the potential to be applied in various fields due to advantages such as better durability, lighter weight, higher space efficiency, and improved comfort that conventional form factor cannot have [1]
We mainly focused on showing the possibility of obtaining highly improved performance through a laser annealing process, and revealed that selective and localized laser annealing can lower the effective contact barrier of the metal-MoS2 junction [17]
In this paper, we examine the degree of improvement in one-side annealing where only one of the source or the drain is annealed and the contacts thereby becoming asymmetric (“asymmetric contacts”) and in both-side annealing where both of the source and the drain are annealed and contacts becoming symmetric (“symmetric contacts”)

Summary

Introduction

Flexible electronics have the potential to be applied in various fields due to advantages such as better durability, lighter weight, higher space efficiency, and improved comfort that conventional form factor cannot have [1]. In spite of the potential, there are some obstacles to applying conventional thin-film transistors (TFTs) to a flexible device: process temperature, electrical properties in stress and strain, and deformation. New approaches in terms of the material and process are required to overcome previous drawbacks. Two-dimensional (2D) layered semiconductor materials (vertically stacked structure in layers consisted of MX2 (transition metal dichalcogenides (TMDs)) by weak van der Waals force) can be a good candidate for solving these problems due to their properties.

Methods

Results

Conclusion