Atomic Layer-Deposited Al-Doped ZnO Thin Films for Display Applications

Dimitre Dimitrov,Stefan Petrov,Velichka Strijkova,Blagovest Napoleonov,Ken Yuh Hsu,Blagoy Blagoev,Che-Liang Tsai,Shiuan Huei Lin,Vera Marinova,Dimitrina Petrova

doi:10.3390/coatings10060539

Abstract

The integration of high uniformity, conformal and compact transparent conductive layers into next generation indium tin oxide (ITO)-free optoelectronics, including wearable and bendable structures, is a huge challenge. In this study, we demonstrate the transparent and conductive functionality of aluminum-doped zinc oxide (AZO) thin films deposited on glass as well as on polyethylene terephthalate (PET) flexible substrates by using an atomic layer deposition (ALD) technique. AZO thin films possess high optical transmittance at visible and near-infrared spectral range and electrical properties competitive to commercial ITO layers. AZO layers deposited on flexible PET substrates demonstrate stable sheet resistance over 1000 bending cycles. Based on the performed optical and electrical characterizations, several applications of ALD AZO as transparent conductive layers are shown—AZO/glass-supported liquid crystal (LC) display and AZO/PET-based flexible polymer-dispersed liquid crystal (PDLC) devices.

Highlights

Transparent conducting materials (TCMs) possess simultaneously high electrical conductivity and optical transparency, with these particular characteristics being achieved on processing the materials as thin films on transparent substrates.This specific combination of properties makes TCMs very interesting both from a fundamental viewpoint and for a large variety of applications
In liquid crystal displays (LCDs), light-emitting diodes (LEDs), or transparent displays, these films are used as electrodes, while they are used as touch sensors for resistive and capacitive touch panels
We demonstrate the application of aluminum-doped zinc oxide (AZO) thin films as a substitute for indium tin oxide (ITO) electrodes in LC and polymer-dispersed liquid crystal (PDLC) display devices

Summary

Introduction

Transparent conducting materials (TCMs) possess simultaneously high electrical conductivity and optical transparency (i.e., effective transmission of light in the visible spectrum), with these particular characteristics being achieved on processing the materials as thin films on transparent substrates. This specific combination of properties makes TCMs very interesting both from a fundamental viewpoint and for a large variety of applications. The basic TCO materials include indium oxide (In2 O3 ), tin oxide (SnO2 ), and zinc oxide (ZnO) They can be degenerately n-type doped with tin (In2 O3 :Sn, known as ITO), fluorine (SnO2 :F) or Al (ZnO:Al), as popular examples. The most relevant properties for all these applications are their high conductivity combined with high transparency in the visible spectral region

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