氧化物薄膜電晶體載子遷移率和穩定性提升之研究

Study on Mobility and Stability Enhancement for Oxide based Thin Film Transistor Technology

倪希(Nidhi, Tiwari)

指導教授 ： 謝漢萍 ； 劉柏村

國立交通大學/電機學院/電機資訊國際學位學程/博士(2016年)

摘要

近幾年以透明非晶氧化物半導體取代矽材料作為薄膜電晶體的通道受到許多的關
注，以金屬氧化物為通道的薄膜電晶體有潛力地作為驅動主動矩陣液晶螢幕及有機發光
二極體顯示器的開關。近期非晶銦鎵鋅氧化物薄膜受到極高的關注，由於它有高載子遷
移率、對於可見光的高透明率並對現今固態半導體製程技術相容性像是高清顯示器製程，
然而非晶銦鎵鋅氧化物薄膜電晶體有高密度的缺陷導致高臨界電壓、高次臨界擺幅及薄
膜電晶體在負偏壓照光下的不穩定性，當然缺陷劣化氧化物薄膜電晶體的電性是一個關
鍵問題。本篇的論文研究三種不同的通道材料，包含氧化鋅、銦鋅氧化物及銦鎵鋅氧化
物，並著重於探討對於未來大尺寸面板的電子產品的各方面影響。在此主要是研究藉由
雙主動層及共濺鍍結構來提升氧化物薄膜的遷移率和穩定性，並探討雙主動層及共濺鍍
結構的非晶銦鎵鋅氧化物薄膜電晶體的電性相對於其餘薄膜電晶體的比較。首先在結構
上及光照影響下，氧化鋅及銦鎵鋅氧化物雙層結構相對於單一的銦鎵鋅氧化物層都突顯
出較少的缺陷，由於雙層結構薄膜電晶體有較低次臨界擺幅及臨界電壓，但是此雙層通
道結構因為含有多晶矽氧化鋅而導致低場效載子遷移率和高次臨界漏電流。接著探討以
高遷移率銦鋅氧化物來取代氧化鋅進而改善薄膜電晶體電性，並鍍一層非常薄的氧化鋅
在銦鋅氧化物和銦鎵鋅氧化物雙層結構中，降低銦鋅氧化物本質上的缺陷。另外研究氧
化鋅和銦鎵鋅氧化物共濺鍍為一種可代替和低價非晶態氧化物半導體材料進而優化電
ii
晶體，此材料會減少接面問題不像一般雙層結構。藉由在氧化鋅和銦鎵鋅氧化物共濺鍍
下維持鋅陽離子的摩爾比改善此結構的粗糙度和電性。最後，氧化鋅和銦鎵鋅氧化物共
濺鍍的薄膜電晶體相對於一般銦鎵鋅氧化物薄膜電晶體有較佳的電性和負面壓照光下
的穩定性，適用於低電壓和大面積的顯示器。

關鍵字

以透明非晶氧化物半導體 ； 以金屬氧化物為通道的薄膜電晶體

並列摘要

In recent years, the transparent amorphous oxide semiconductor (TAOS) has attracted a lot of
attention to replace the silicon material as the channel layer of thin film transistors (TFTs).
Metal oxide based TFTs are potential candidate for switching or driving the active matrix
liquid crystal displays (AMLCD) and organic light emitting diode displays (AMOLED).
Recently, amorphous InGaZnO (a-IGZO) thin films have received considerable attention
owing to high carrier mobility, transparency for visible light, high process compatibility with
present solid-state semiconductor technologies such as high definition displays. However,
a-IGZO thin films contain large density of defects – leading higher threshold voltage (Vth),
sub-threshold swing (SS) and instability of the TFTs under negatively biased light
illumination stress (NBIS) test. The defects play a crucial role to degrade the electrical
characteristics of oxide TFTs. In this dissertation work, various aspects of the a-IGZO TFTs
by choosing three different materials, zinc oxide (ZnO), indium zinc oxide (IZO), and indium
gallium zinc oxide (IGZO) have been detailed studied to shed light further on potential
application of such technology to future large area electronics. Present study aims to enhance
mobility and stability in the oxide based thin films by adopting their bilayer and co-sputtered
structures. Also, the bilayer and co-sputtered thin film qualities vis-à-vis their thin film
iv
transistors characteristics are compared with a-IGZO TFTs. First, structural, optical, and
photoluminescence study of ZnO/IGZO thin films has been investigated to show fewer
structural defects in comparison to single layer pure a-IGZO. The bilayer TFTs thus showed
better sub-threshold swing and threshold voltage than the a-IGZO TFTs. However, the
ZnO/IGZO TFT displayed lower field effect mobility and large subthreshold leakage owing to
channel formation by polycrystalline ZnO. Further, the channel is substituted by high mobility
indium zinc oxide (IZO) to enhance the electrical characteristics of IZO/IGZO TFT. A very
thin layer of ZnO is used as interlayer of IZO/IGZO to reduce the intrinsic defects within the
IZO channel for the development of reliable IZO/IGZO bilayer thin film transistors. To
further optimize the device performance of IGZO based material, ZnO co-sputtered IGZO is
investigated as a possible alternative and cost effective amorphous oxide semiconductor
(AOS), leading less interfacial problems unlike in the bilayer case. The performance of ZnO
co-sputtered IGZO TFTs is optimized by maintaining the molar ratio of zinc cation in ZnO
co-sputtered IGZO, which is able to improve structure, roughness and electrical performance.
ZnO co-sputtered IGZO TFT performs a better electrical transfer characteristic and NBIS
stability than a-IGZO TFTs- leading a potential candidate for low voltage and large area
displays applications.

並列關鍵字

A transparent amorphous oxide semiconductor ； Metal oxide channel thin film transistor

參考文獻

[1] H. D. Kim, et.al, “Technological Challenges for Large-Size AMOLED Display”, SID 08 DIGEST, pp. 291-294, 2008.

[2] J. K. Jeong, et.al, “WXGA AMOLED display driven by InGaZnO thin-film transistors”, Journal of the SID 17/2, pp.95-100, 2009.

[3] J. F. Wager, et. al, “An amorphous oxide semiconductor thin-film transistor route to oxide electronics”, Curr. Opin. Solid State Mater. Sci. 18, pp. 53–61, 2014.

[4] S. Jeong, et.al, “Role of Gallium Doping in Dramatically Lowering Amorphous-Oxide Processing Temperatures for Solution-Derived Indium Zinc Oxide Thin-Film Transistors”, Adv. Mater., 22, pp.1346–1350, 2010.

[5] K. Ellmer,” Magnetron sputtering of transparent conductive zinc oxide: relation between the sputtering parameters and the electronic properties”, J. Phys. D: Appl. Phys. 33, pp. R17–R32, 2000.