突起缺陷及應力對新型矽氧氮SiOxNy薄膜用於有機發光二極體之水氣阻障探討

Abstract

有機發光二極體（OLED）顯示器因其擁有自體發光之能力而不需背向光源之調節，以及快速的反應時間（<10 ms）、廣視角（170°以上）、色彩逼真、優良的對比與亮度、低操作電壓(3-10 V)以及省電等優點，故在過去幾年快速成長。然而，其有機物及電極對水氣及氧氣非常敏感，在無保護的情況下，水氣及氧氣會迅速降低OLED元件的性能。在此現況下，本研究動機在尋找低成本、製程簡單且高可靠性，用於OLED的氮氧化物或氮化物基底（oxynitride or nitride）之薄膜阻障層。我們利用一套新穎的蒸鍍系統(Ar ion beam evaporation technique)進行薄膜沉積，首先探討氮氧化矽阻障層之成分組成、微觀結構及表面形貌，並且改變其基材溫度及氣體流速來探討其SiOxNy/Al薄膜的表面形貌及薄膜應力之影響。此外，並調查水氣阻障與薄膜缺陷(突起缺陷及Al晶界)之關係。最後，探討突起密度以及其高度對於水氣阻障能力之影響。 從實驗的結果發現氮氧化矽薄膜呈現非晶結構，其Si: O: N成分比例為1: 2: 0.67。鋁薄膜呈現柱狀結構，其晶粒分布介於50到100奈米。吾人發現，Al突起缺陷是造成阻障層高水氣穿透的主要原因，同時並提出一套突起密度及其高度的可能機制。突起密度和鋁晶粒大小有關，而凸起高度和薄膜應力有正向關係。在高基材溫度、高氣體流速的情況下，其突起缺陷密度會較少但是其高度會較高;在低基材溫度、低氣體流速的情況下，其突起缺陷密度會較多但是其高度會較低。因此，如果使用一層阻障層的情況下，高溫高流速的阻氣能力會較低溫低流速的來的佳。但是，如果以層數為考量的話，低溫低流速因其缺限高度較低，所以只需要較少之阻障層數即可把缺陷完全癒合而高溫高流速則需較多的層數。總結來說，藉由改變鍍膜參數(氣體流量及基材溫度)來控制突起缺陷的形成，對於阻障層的阻氣能力有絕對的關係。

Organic light-emitting-diode displays (OLED) have gained momentum in the past few years because it was an emissive system creating its own light rather than relying on modulating a backlight. In addition, OLED possessed fast response time (<10ms, 100 times faster than TFT-LCD), wide view angle (>170°), true colors, excellent contrast ratio, brightness, low operating voltage and potentially less power consumption. However, its broad adoption has been hindered by the sensitivity of organic and electrode to the moisture and oxygen, which can quickly degrade the device performance if not properly protected. This motivated us to explore a simple, cheap, but reliable oxynitride-based thin film barrier for OLED in this study. The composition, microstructure and morphology of SiOxNy barrier layers deposited by a modified Ar ion beam evaporation system were first investigated. Then, the effects of substrate temperatures (60-90 oC) and gas flow rates (300-480 sccm) on the morphology and stress of SiOxNy/Al stack were examined. In addition, the roles of defects such as hillocks and grain sizes of Al films was studied and correlated with the moisture resistance of SiOxNy barrier films. Finally, the moisture barrier performance in terms of hillock density and hillock height was further discussed if multiple-layered passivation was warranted. In this study, SiOxNy layers were amorphous and the composition of Si: O: N was in the ratio of 1: 2: 0.67. Al films exhibited columnar structure with grain size distribution 50 to 100 nm after the deposition of SiOxNy. Al hillock was found to be the culprit of high moisture permeation in the passivation layer. A model of hillock formation in SiOxNy/Al was proposed in this thesis to illustrate the causes for their difference in hillock density and height. The hillock density was related to the initial Al grain size, while the hillock height was primarily derived by SiOxNy stress. The tallest height of hillock affected greatly on the numbers of barrier layers for complete sealing of defects. Therefore, high substrate temperature and high N2 gas flow rate deposition process yielded barrier films with less hillocks and improved moisture resistance if single layer of passivation was employed, while lower deposition temperature and low N2 gas flow rate were preferred for least number of layers if multiple-layer structure was adopted. In summary, defect control of Al hillocks was essential for controlling the moisture barrier performance in the practical OLED stack.