Impact of transient currents caused by alternating drain stress in oxide semiconductors

Hyeon-Jun Lee,Sung Haeng Cho,Myoung-Jae Lee,Katsumi Abe,Minkyung Jung

doi:10.1038/s41598-017-10285-2

Hyeon-Jun Lee, Sung Haeng Cho + Show 3 more

Open Access

https://doi.org/10.1038/s41598-017-10285-2

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Abstract

Reliability issues associated with driving metal-oxide semiconductor thin film transistors (TFTs), which may arise from various sequential drain/gate pulse voltage stresses and/or certain environmental parameters, have not received much attention due to the competing desire to characterise the shift in the transistor characteristics caused by gate charging. In this paper, we report on the reliability of these devices under AC bias stress conditions because this is one of the major sources of failure. In our analysis, we investigate the effects of the driving frequency, pulse shape, strength of the applied electric field, and channel current, and the results are compared with those from a general reliability test in which the devices were subjected to negative/positive bias, temperature, and illumination stresses, which are known to cause the most stress to oxide semiconductor TFTs. We also report on the key factors that affect the sub-gap defect states, and suggest a possible origin of the current degradation observed with an AC drive. Circuit designers should apply a similar discovery and analysis method to ensure the reliable design of integrated circuits with oxide semiconductor devices, such as the gate driver circuits used in display devices.

Highlights

From the time since Nomura et al proposed[1, 2] metal-oxide semiconductor thin film transistors as replacements for silicon-based devices in active matrix displays a decade ago, numerous studies have been conducted to investigate a variety of applications, as well as to understand the nature of the defects in these devices[3,4,5]
We reported on the degradation of the drive capability and the asymmetric degradation caused by hot electrons when driving pulse signals were applied between the source and drain in oxide semiconductor thin film transistors (TFTs)
There is a series of phenomena that arise when driving oxide semiconductor TFTs such that the trap states close to the conduction band minimum (CBM) and the leakage current in the channel when the gate is in the off-state supply electrons that are transformed into hot electrons when subjected to a pulsed high electric field on the drain

Summary

Introduction

From the time since Nomura et al proposed[1, 2] metal-oxide semiconductor thin film transistors as replacements for silicon-based devices in active matrix displays a decade ago, numerous studies have been conducted to investigate a variety of applications, as well as to understand the nature of the defects in these devices[3,4,5]. There have been reports detailing the influence of gate[12] and/or drain[13] voltage stress dependence (applied direct current (DC)) and on the influence of alternating stress signals[14], our understanding of the stresses induced by alternating high voltage and periodic pulses on the drain side remains incomplete because the drain voltage and frame rate (frequency) affect both the electrical properties and performance of oxide semiconductors. A complete understanding of the effects of the hot carriers and frame rates caused by alternating current drives on the electrical properties of amorphous oxide semiconductors is important to ensure the success of future electronics applications that leverage this technology. The transient properties caused by hot electrons were characterised using a device simulation

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