原子層沉積技術成長透明導電氧化物薄膜：氧化鋅鉿應用於軟性電子之研究

Abstract

本篇研究運用原子層沉積技術(ALD)來成長氧化鋅鉿薄膜，以應用於軟性電子元件之透明電極。原子層沉積技術成長的氧化鋅鉿薄膜之導電度會受限於氧化鋅與二氧化鉿組成之層狀堆疊結構，這種層狀堆疊結構會妨礙二氧化鉿層中的部分分子發揮其完全的摻雜效應，由於載子穿過氧化鋅層的傳導受到妨礙，導致多餘的二氧化鉿分子僅貢獻了極少量地載子。為了克服這個問題，我們提出了一種新穎的原子層沉積製程的步驟來使薄膜的層狀堆疊改變成均勻混摻的結構，經由這個改變我們令氧化鋅鉿薄膜的電阻率從2.0 E-03Ω-cm降低至8.5 E-04 Ω-cm。執行此新穎的製程是在同一次原子層沉積的週期中連續通入兩種有機氧化前驅物，只需要少量的二氧化鉿分子就能達到高摻雜濃度的效果，少量的雜質摻雜也同時保持了氧化鋅鉿薄膜中氧化鋅的載子遷移率。而氧化鋅鉿薄膜的均勻性可經由穿透式電子顯微鏡(TEM)配合能量散布光譜儀(EDX)的元素分析來證明。 至於光學透明度，透明導電薄膜的可見光的穿透率超過了85%，足以和常用的氧化銦錫薄膜相比，另外，由於製程溫度低(約150℃)，此方法適用於高分子基板，且沉積於高分子基板的薄膜導電率可維持和在玻璃基板上差不多。此外，原子層沉積技術成長的氧化鋅鉿薄膜也具有不錯的阻氣性。整體而言，本篇研究之原子層沉積氧化鋅鉿薄膜具備高導電度、高穿透率、低溫製程和低的氣體滲透率等優點，相當適合使用於軟性電子的應用。

This study utilizes atomic layer deposition (ALD) to develop Hf:ZnO films for use as transparent conductive electrodes of flexible electronics. The conductivity of the ALD Hf:ZnO film was found to be limited by the layer-by-layer nature of the HfO2 and ZnO constituents, which prevented some HfO2 molecules in the HfO2 layers from applying their full doping effects, resulting in redundant HfO2 molecules that contributed little carriers while hindering conduction of carriers across the ZnO layers. To overcome this issue, we developed a novel ALD process to change the layer-by-layer HfO2/ZnO structure to a more homogeneous mixture, and as a result we improved the resistivity of the ALD Hf:ZnO film from 2.0 E-03 to 8.5 E-04 Ω-cm. Using the novel ALD process, which involved exposing the substrate consecutively with the two organometallic precursors within the same ALD cycle, high doping concentration could be obtained with low HfO2 content; meanwhile, with low HfO2 content, the carrier mobility of ZnO could be better preserved in the Hf:ZnO film. The homogeneity of the Hf:ZnO film deposited with the novel process was confirmed with TEM and energy-dispersive X-ray spectroscopy (EDX). In terms of optical transparency, the ALD Hf:ZnO film showed >85% transmittance throughout the visible wavelengths, exceeding that of the widely used indium tin oxide (ITO). With its low deposition temperature (150 ºC), the novel ALD process was applicable to polymer substrates, and the resulted Hf:ZnO films largely retained the conductivity of those deposited on glass substrates. Additionally, the ALD Hf:ZnO film was found to be effective gas-diffusion barriers for the polymer substrates： Its helium transmission rate was lower than sputtered films by more than 1 orders of magnitude. With its high conductivity, high optical transparency, low deposition temperature, and low gas permeability, the ALD Hf:ZnO film developed in this study will offer many advantages for flexible electronics applications.