Relation Between Thickness and TFTs Properties of HfO2 Dielectric Layer Synthesized by Plasma-Enhanced Atomic Layer Deposition

TL;DR

This paper studies how the thickness of HfO2 dielectric layers affects the performance of a-IGZO thin film transistors used in OLED displays.

Contribution

The study systematically investigates the relationship between HfO2 thickness and a-IGZO TFT performance using plasma-enhanced atomic layer deposition.

Findings

A 40 nm HfO2 layer achieved a threshold voltage of −0.9 V and a saturation mobility of 6.76 cm²/Vs.

The subthreshold swing was 0.084 V/decade with an Ion/Ioff ratio of 1.35 × 10⁹.

PEALD-based HfO2 gate insulators improve the electrical performance of a-IGZO TFTs.

Abstract

The advancement of portable high-definition organic light-emitting diode (OLED) displays necessitates thin film transistors (TFTs) with low power consumption and high pixel density. Amorphous indium gallium zinc oxide (a-IGZO) TFTs are promising candidates to meet these requirements. However, conventional silicon dioxide gate insulators provide limited channel modulation due to their low dielectric constant, while alternative high-k dielectrics often suffer from high leakage currents and poor surface quality. Plasma-enhanced atomic layer deposition (PEALD) enables the atomic-level control of film thickness, resulting in high-quality films with superior conformality and uniformity. In this work, a systematic investigation was conducted on the properties of HfO2 films and the electrical characteristics of a-IGZO TFTs with different HfO2 thicknesses. A Vth of −0.9 V, μsat of 6.76 cm2/Vs, SS of 0.084 V/decade, and Ion/Ioff of 1.35 × 109 are obtained for IGZO TFTs with 40 nm HfO2. It is believed that the IGZO TFTs based on a HfO2 gate insulating layer and prepared by PEALD can improve electrical performance.

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