Tailoring Subthreshold Swing in A‐IGZO Thin‐Film Transistors for Amoled Displays: Impact of Conversion Mechanism on Peald Deposition Sequences

Abstract

Amorphous IGZO (a‐IGZO) thin‐film transistors (TFTs) are standard backplane electronics to power active‐matrix organic light‐emitting diode (AMOLED) televisions due to their high carrier mobility and negligible low leakage characteristics. Despite their advantages, limitations in color depth arise from a steep subthreshold swing (SS) (≤ 0.1 V/decade), necessitating costly external compensation for IGZO transistors. For mid‐size mobile applications such as OLED tablets and notebooks, it is important to ensure controllable SS value (≥ 0.3 V/decade). In this study, a conversion mechanism during plasma‐enhanced atomic layer deposition (PEALD) is proposed as a feasible route to control the SS. When a pulse of a diethylzinc (DEZn) precursor is exposed to the M2O3 (M = In or Ga) surface layer, partial conversion of the underlying M2O3 to ZnO is predicted on the basis of density function theory calculations. Notably, significant distinctions between In‐Ga‐Zn (Case I) and In‐Zn‐Ga (Case II) films are observed: Case II exhibits a lower growth rate and larger Ga/In ratio. Case II TFTs with a‐IGZO (subcycle ratio of In:Ga:Zn = 3:1:1) show reasonable SS values (313 mV decade−1) and high mobility (µFE) of 29.3 cm2 Vs−1 (Case I: 84 mV decade−1 and 33.4 cm2 Vs−1). The rationale for Case II's reasonable SS values is discussed, attributing it to the plausible formation of In‐Zn defects, supported by technology computer‐aided design (TCAD) simulations.