Fast and slow transient charging of Oxide Semiconductor Transistors

Taeho Kim,Sanghun Jeon,Sungho Park

doi:10.1038/s41598-017-12155-3

Abstract

The comprehension of the governing mechanism which affects device instability is one of the most important requirements for the formation of reliable oxide-thin film transistors (TFTs). However, a quantitative analysis of the dominant mechanism of device instability, which stems from charge trapping induced by defects at the oxide semiconductor interface as well as in its bulk, has not yet been systematically performed. In this study, we examined subgap states, charge-transport dynamics, and various trap characteristics of oxide TFTs by multi-frequency C–V, pulse I–V, and transient current methods to achieve a comprehensive understanding of carrier transport and charge trapping mechanisms. We found that the charge trapping behavior of the tested amorphous InHfZnO (a-IHZO) TFT follows a multi-trapping mechanism, such as temperature-independent fast transient charge trapping by resonant drift of the injected electron and temperature-dependent slow transient charge trapping by charge transport from occupied to unoccupied traps. Understanding fast charging and slow charging described in this study can help to understand the root cause of device instability of oxide TFTs and ultimately improve stability and reliability characteristics.

Highlights

In recent times, amorphous oxide semiconductor-based thin film transistors (TFTs) have been attracting enormous attention for display applications[1,2,3,4,5], owing to their steep subthreshold slope (~0.2 V/decade), high field-effect mobility (5–100 cm2/ eV·s), and low-temperature fabrication process[6,7,8]
Schematics of a fabricated oxide TFT and a high annular transmission electron microscopy image are presented in Fig. 1(a) and (b), respectively
We found that tc increased with decreasing Hf content in the amorphous InHfZnO (a-IHZO)

Summary

Introduction

Amorphous oxide semiconductor-based TFTs have been attracting enormous attention for display applications[1,2,3,4,5], owing to their steep subthreshold slope (~0.2 V/decade), high field-effect mobility (5–100 cm2/ eV·s), and low-temperature fabrication process[6,7,8]. We investigated fast and slow transient charging behaviors in oxide TFTs and their effects on electrical characteristics To this end, we employed a multi-frequency measurement (MFM) technique to evaluate the subgap density of states (DOS)[32] as well as pulse I–V (PIV) and transient current methods to study time-dependent charge trapping phenomena[33,34,35,36,37,38,39,40,41,42]. As a result of this study, it was found that DOS through MFM measurement technique was exponentially distributed in the shallow energy state region, and fast & slow charge trapping occurred relatively shallow energy in range of less than 0.4 eV below the conduction band minimum through short and long pulse measurement technique This model enables comprehension of the dynamic charge trapping behavior of oxide TFTs43

Methods

Results

Conclusion