Effect of Wavelength and Intensity of Light on a-InGaZnO TFTs under Negative Bias Illumination Stress

Woo-Sic Kim,Byeong-Koo Kim,Kyung Tae Park,Yeol-Hyeong Lee,Yong-Jung Cho,Ohyun Kim

doi:10.1149/2.0021701jss

Abstract

We investigated degradation mechanism of a-IGZO TFTs under NBIS with different wavelengths λ and intensities IL of light. Negative gate bias was applied for 4000 s while drain and source were grounded, and illuminations with λ = 450, 530, or 700 nm were applied. Illumination with photon energy exceeding ∼2.3 eV (530 nm) induced noticeable change in threshold voltage shift ΔVth, which can be interpreted in terms of ionization of oxygen vacancies VO. In addition, IL of blue illumination (450 nm) was varied from 6 to 200 lux and saturation in ΔVth was observed after exceeding a certain IL. We suggest that the saturation occurs because VO-ionization rate is saturated by outward relaxation of metal atoms in the a-IGZO film.

Highlights

Metal oxide-based materials have high carrier mobility, low offcurrent, and good transparency, so they are promising candidates for the channel material of thin film transistors (TFTs).[1]
A-IGZO TFTs remain stable under negative bias stress (NBS), their electrical characteristics degrade when it is combined with illumination,[7,8] i.e., negative bias illumination stress (NBIS)
Transfer characteristics were measured after NBS and NBIS with negative gate voltage of −40 V were applied at 90◦C (Fig. 2)

Summary

Introduction

Metal oxide-based materials have high carrier mobility, low offcurrent, and good transparency, so they are promising candidates for the channel material of thin film transistors (TFTs).[1]. Stability of a-IGZO TFTs is affected by several factors including bias/current stress, temperature, light illumination and passivation conditions.[2,3,4,5] Among several factors, bias stress is most widely studied because bias is always applied to TFTs in practical display applications. Instability of a-IGZO TFTs under NBIS has been widely investigated and reported.[7,8,9,10,11] Though some papers dealt with the effect of light intensity on reliability of the TFT,[12,13] the effects of wavelength λ and intensity IL of light during NBIS have not been fully explained yet, especially in terms of oxygen vacancy which is crucial factor affecting reliability of a-IGZO TFTs. In this paper, we investigated degradation mechanism of a-IGZO TFTs under NBIS with light of various λ and IL. We propose that the saturation phenomenon can be explained by restriction in the ionization rate of oxygen vacancy VO due to their effect on the structure of a-IGZO

Methods

Results

Conclusion