非晶質氧化銦鋅鋁(IAZO)之材料特性分析

Characterization of Amorphous Indium-Aluminium-Zinc Oxide

莊英駿(Ying-Chun Chuang)

指導教授 ： 甘炯耀

國立清華大學/工學院/材料科學工程學系/碩士(2010年)

摘要

薄膜電晶體是電子電路中基本的元件，隨著科技的發展，其不僅有縮小化的需求，也已朝向可撓式與透光式元件邁進。而在其中，通道層之特性也是影響整個元件表現之重要因素之一，其基本需求在於低載子濃度與高載子遷移率，而為鍍製於可撓式基板上，其製程之溫度需在低溫下進行(因為基板無法承受高溫)；再者，為了使整個元件能夠透光，此層材料也需為透明。目前最為廣為運用之材料為非晶矽，也有人使用有機材料與非晶質氧化物半導體當作此層材料。而非晶質氧化物之優勢在於第一、其可在低溫下鍍製，第二、其載子遷移率不會因為晶格扭曲(非晶質狀態)而大幅下降(相較於非晶矽而言)，第三、由於能隙約在3 eV附近，因此其還有在可見光範圍下為透明這附加優點。目前最被廣為研究為非晶質氧化銦鎵鋅(IGZO)，這是由於其高載子遷移率(來自於銦)與低載子濃度(來自於鎵)，而且還有良好之熱穩定性(結晶溫度~6000C)。
由於鋁與鎵同屬一族且較易取得，在本研究中欲以鋁取代鎵摻入氧化銦鋅(IZO)，探討非晶質氧化銦鋅鋁(IAZO)中之非晶結構穩定性以及其相關特性，希望能在通道層之材料選擇中提供更大之選擇。
眼前的材料之能隙寬度是影響其電性行為之一重要參數，在此我們利用橢圓偏振技術分析非晶質氧化銦鋅鋁(IAZO, In：Al：Zn=2：<<1：1)之材料特性。在實驗中發現，氧化銦鋅鋁在室溫鍍製的結果為非晶狀態，而在退火溫度上升至約8500C時才會結晶。隨著退火溫度上升，非晶質氧化銦鋅鋁之載子濃度會由5.99×1018 cm-3先下降至2×1017 cm-3再上升至5.94×1018 cm-3，而載子遷移率會隨著溫度的上升而由2.48 cm2V-1s-1上升至14.9 cm2V-1s-1；再來，其材料之折射率會隨著退火溫度上升而有上升之現象，而且在退火結晶後，材料之能隙也會由3.122 eV上升至3.516 eV。

關鍵字

非晶質 ； 氧化銦鋅鋁

並列摘要

Thin film transistor(TFTs) is the most crucial active component in flat-panel displays. With the development of display industry, there are not only the demands for miniaturization of devices, but also toward the flexible and light transmission type devices. Within these, the characteristics of channel layer such as low concentration and high mobility of carriers, are important to the performance of overall devices. Furthermore, in order to deposit on flexible substrates, the process should under low temperature because the substrates could not afford the high temperature. Although materials like amorphous silicon and also organic materials have been intensively studied in the past decades, amorphous oxide semiconductors (AOSs) made with In-Zn composite oxide has recently caught a great attention. The later has the advantages including low process temperature, relatively higher carrier mobility, and good thermal stability (Tc~6000C).
In order to suppress the carrier density of the In-Zn composite oxide films, they are commonly doped with Ga. It is suspected that the role of Ga may be replaced with Al, which is obviously abundant and cheap compared to Ga. In this work, a detail electrical and optical characterization on the co-sputtered amorphous indium-aluminium-zinc oxide(IAZO) has been performed.
The bandgap of materials is one of the important parameters for affecting the electrical behavior of them. Here we utilized the spectroscopic ellipsometry to analyze the properties of IAZO(In:Al:Zn=2:<<1:1) in different annealing temperatures. In this study, we found that IAZOs were amorphous when be deposited under room temperature, and would be crystallized after the post-annealing about 8500C. During the increase of annealing temperature, the carrier concentration would first decrease from 5.99×1018 cm-3 to 2×1017 cm-3 and then increase to 5.94×1018 cm-3, and the carrier mobility would raise to 14.9 cm2V-1s-1 from 2.48 cm2V-1s-1. Furthermore, the index of refractive would increase during the increase of annealing temperature, and the bandgap of materials would increase from 3.122 eV to 3.516 eV when they were crystallized.

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