Role of Self-Assembled Monolayers on Improved Electrical Stability of Amorphous In-Ga-Zn-O Thin-Film Transistors

TL;DR

This paper demonstrates that self-assembled monolayers (SAMs) on IGZO thin-film transistors significantly enhance electrical stability by reducing bias stress effects through surface energy modification and contaminant adsorption prevention.

Contribution

It introduces the use of specific SAMs (HPA and FPA) to improve the bias-stress stability of IGZO TFTs, highlighting the role of surface chemistry in device reliability.

Findings

FPA SAMs reduce bias stress voltage shifts more effectively than HPA.

Lower surface energy of FPA correlates with improved stability.

SAMs decrease contaminant adsorption and trap states on IGZO surfaces.

Abstract

Self-assembled monolayers (SAMs) have been used to improve both the positive and negative bias-stress stability of amorphous indium gallium zinc oxide (IGZO) bottom gate thin film transistors (TFTs). N-hexylphosphonic acid (HPA) and fluorinated hexylphosphonic acid (FPA) SAMs adsorbed on IGZO back channel surfaces were shown to significantly reduce bias stress turn-on voltage shifts compared to IGZO back channel surfaces with no SAMs. FPA was found to have a lower surface energy and lower packing density than HPA, as well as lower bias stress turn-on voltage shifts. The improved stability of IGZO TFTs with SAMs can be primarily attributed to a reduction in molecular adsorption of contaminants on the IGZO back channel surface and minimal trapping states present with phosphonic acid binding to the IGZO surface.