Effect of indium low doping in ZnO based TFTs on electrical parameters and bias stress stability

Alexander B Cheremisin,Sergey N Kuznetsov,Genrikh B Stefanovich

doi:10.1063/1.4935789

Alexander B Cheremisin, Sergey N Kuznetsov + Show 1 more

Open Access

https://doi.org/10.1063/1.4935789

Copy DOI

Journal: AIP Advances	Publication Date: Nov 1, 2015
Citations: 10	License type: CC BY 3.0

Affiliation: Petrozavodsk State University

Abstract

Some applications of thin film transistors (TFTs) need the bottom-gate architecture and unpassivated channel backside. We propose a simple routine to fabricate indium doped ZnO-based TFT with satisfactory characteristics and acceptable stability against a bias stress in ambient room air. To this end, a channel layer of 15 nm in thickness was deposited on cold substrate by DC reactive magnetron co-sputtering of metal Zn-In target. It is demonstrated that the increase of In concentration in ZnO matrix up to 5% leads to negative threshold voltage (VT) shift and an increase of field effect mobility (μ) and a decrease of subthreshold swing (SS). When dopant concentration reaches the upper level of 5% the best TFT parameters are achieved such as VT = 3.6 V, μ = 15.2 cm2/V s, SS = 0.5 V/dec. The TFTs operate in enhancement mode exhibiting high turn on/turn off current ratio more than 106. It is shown that the oxidative post-fabrication annealing at 250oC in pure oxygen and next ageing in dry air for several hours provide highly stable operational characteristics under negative and positive bias stresses despite open channel backside. A possible cause of this effect is discussed.

Highlights

Recent progress in the industry of flat-panel active matrix displays has contributed to the research and technology development of thin film transistors (TFTs) fabrication with a channel made of oxide semiconductors such as IZO, IGZO and others
We propose a simple routine to fabricate indium doped zinc oxide-based (ZnO)-based TFT with satisfactory characteristics and acceptable stability against a bias stress in ambient room air
It is demonstrated that the increase of In concentration in ZnO matrix up to 5% leads to negative threshold voltage (VT) shift and an increase of field effect mobility (μ) and a decrease of subthreshold swing (SS)

Summary

INTRODUCTION

Recent progress in the industry of flat-panel active matrix displays has contributed to the research and technology development of TFTs fabrication with a channel made of oxide semiconductors such as IZO, IGZO and others. Transparency in the visible region, amorphous microstructure, low cost - all these advantages allow us to consider this class of oxides as a promising alternative to the existing semiconductors based on hydrogenated and polycrystalline silicon. Current understanding of the processes responsible for electrically induced drift of transistor parameters is based on the existence of traps on the dielectric/semiconductor interface and of capture centers in the semiconductor volume, as well as on the environment effect on the open backside of a channel. Variations of dielectric gate material, use of high temperatures treatments, passivation of the channel backside lead to considerable improvement of oxide transistors stability.[1,2,3] such solutions limit the area of their possible implementation. This paper presents comparative study of zinc oxide-based TFTs electric parameters with indium dopant variation. It is shown that small dopant concentration of 5% significantly improves parameters of ZnO:In-based transistors in comparison with ZnO-based TFTs

EXPERIMENTAL

RESULTS AND DISCUSSION

CONCLUSION