隨著科技的進步，顯示器由傳統的陰極射線管CRT進步到液晶顯示器LCD，非晶矽薄膜電晶體與多晶矽薄膜電晶體已用於製造液晶顯示器的畫素開關，其中非晶矽薄膜電晶體已大量用於製造大尺寸的顯示面板。
目前由a-Si作為主動層的薄膜電晶體，有嚴重的光漏電問題，由於a-Si的光導係數較高，因此在光照下容易有較大的漏電現象，當電晶體處於面板應用時，便是以強背光照射，如多媒體顯示器、液晶電視等，而光漏電現象會造成顏色顯示上的問題。
在TFT導通時，電荷會經由TFT儲存於液晶電容及輔助電容中，在TFT關閉後利用上述兩個電容所產生的電壓使液晶轉動，由於電視每秒顯示30張畫素，而電容的電壓須維持定值至少1/30秒，而光漏電流過大會造成TFT在關閉狀態下仍有通道使電荷可以通過，電容中的電荷就會由此通道流失，令所提供的電壓降低，造成液晶旋轉角度不足，導致顏色不準確。
因此，本論文將研究薄膜電晶體在背光源照射下，所產生的電性變化，並探討不同的電晶體構造使否會對物理機制的影響，以及在光照下漏電流所產生的變化。

Thin-film transistor uses a-Si as active layer so far, but it has serious problems about light leakage. Due to the high photoconductivity of a-Si, it is easy to have a large leakage under light. When the transistor is in a panel application, it is lighted by strong power. In multimedia monitors, LCD TVs, etc. Light leakage can cause color display problems.
When TFT turns on, the charge is stored in the liquid crystal capacitor and the auxiliary capacitor via the TFT. The light leakage current is too large to cause the TFT to have a channel in the off state so that the charge can pass through, and the charge in the capacitor is lost through this channel. As a result, the voltage supplied is reduced, causing the liquid crystal to rotate at a short angle, resulting in inaccurate colors.
This paper will investigate the problem in thin-film transistors under backlight illumination, and discuss whether different transistor configurations will affect light leakage current, and the mechanism of the deterioration.

論文審定書.................................................................................................................................... i
論文公開授權書........................................................................................................................... ii
誌謝...............................................................................................................................................iv
中文要摘....................................................................................................................................... v
Abstract.........................................................................................................................................vi
第一章 序論................................................................................................................................. 3
1.1.前言..................................................................................................................................... 3
1.2.摻雜氫的非晶矽(a-Si:H)..................................................................................................... 3
1.3.原子結構與電子能態密度................................................................................................. 4
1.4.光漏電流機制[7] ................................................................................................................ 5
第二章 結構............................................................................................................................... 10
2.1 化學氣相沉積法沉積摻氫非晶矽.................................................................................. 10
2.2 PECVD 沉積氮化矽(SiNx) .................................................................................................. 11
2.3 化學氣相沉積法沉積 n
+ a-Si:H ....................................................................................... 12
2.4 元件結構.......................................................................................................................... 13
第三章 儀器與參數................................................................................................................... 14
3.1 儀器設備.......................................................................................................................... 14
3.2 參數萃取.......................................................................................................................... 14
3.3 場效遷移率...................................................................................................................... 15
第四章 非晶矽薄膜電晶體的基本特性分析........................................................................... 18
4.1 基本電性分析.................................................................................................................. 18
4.1.1 載子遷移率............................................................................................................... 18
4.1.2 接觸電阻在低溫下的變化....................................................................................... 18
4.1.3 傳輸機制................................................................................................................... 19
4.2 傳輸機制模型的驗證...................................................................................................... 20
4.2.1 改變閘極起始掃描電壓........................................................................................... 20
4.2.2 改變量測溫度........................................................................................................... 20
3
4.2.3 改變主動層厚度....................................................................................................... 21
4.2.4 不同的閘極與汲極重疊面積................................................................................... 21
4.3 結果與討論...................................................................................................................... 22
第五章 長時間操作的劣化....................................................................................................... 28
5.1 閘極正偏壓長時間操作.................................................................................................. 28
5.2 閘極負偏壓長時間操作.................................................................................................. 29
5.3 結果與討論...................................................................................................................... 29
第六章 背光源對元件的影響................................................................................................... 33
6.1 增加背光源與暗態下的差異.......................................................................................... 33
6.2 不同結構設計在光照下的影響...................................................................................... 33
6.3 空乏區與光漏電流........................................................................................................... 34
6.4 不同的閘極覆蓋主動層面積.......................................................................................... 34
6.5 結果與討論....................................................................................................................... 35
第七章 結論............................................................................................................................. 39
7.1 結果與討論...................................................................................................................... 39
7.2 改良元件.......................................................................................................................... 39
7.2.1 使用較厚的主動層................................................................................................... 39
7.2.2 使用較小的關閉閘極電壓....................................................................................... 40
7.2.3 閘極與汲極重疊面積要小....................................................................................... 40
7.2.4 確保汲極端的主動層有完整被閘極所覆蓋............................................................ 40
參考文獻..................................................................................................................................... 41

[1]K.S. Karim, A. Nathan, J.A. Rowlands, and S.O. kasap, “X-ray detector with on-pixel amplification for large area diagnostic medical image,”IEE Proc. Circuits, Devices and Systems, vol. 150.no.4, pp267-273 Aug 2003.
[2] B. G. Streetman, Solid State Electronic Devices, Chapter 1.3, London: Prentice Hall, 1990.
[3] J. Mort and F. Jansen, “Plasma-Deposited Thin Films,” p.28-33 (CRC Press, Boca Raton, FL, 1986).
[4] T. Globus, H. C. Slade, M. S. Shur, and M. Hack, “Density of deep bandgap states in amorphous silicon from the temperature dependence of thin film transistor current ”, Mat. Res. Soc. Proc., vol.336,pp.823,1994.
[5] Dosi Dosev, Josep Pallares and Joaquim Puigdollers, “Fabrication, Characterisation and Modelling of Nanocrystalline Silicon Thin-Film Transistors Obtained by Hot-Wire Chemical Vapour Deposition”, p. 64.
[6] R. Ishihara, H. Kanoh, Y. Uchida, O. Sugiura, and M. Matsumura, “Low-temperature chemical vapor deposition of silicon nitride from tetrasilane and hydrogen azide,” Mat. Res. Soc. Symp. Proc., vol.284, pp.3-8, 1992.
[7] S.Martin, J.Kanicki, N.Szydlo, and A.Rolland. Analysis of the amorphous silicon thin-film transistors behavior under illumination. Proceedings of the AMLCD '97
[8] W. M. M. Kessels, A. H. M. Smets, D. C. Marra, E. S. Aydil, D. C. Schram, and M.C. M. van de Sanden, “ On the growth mechanism of a-Si:H,” Thin Solid Films, vol.383, pp. 154-160, 2000
[9] K. Nomoto, Y. Urano, J. L. Guizot, G.. Ganguly, and A. Matsuda. “ Role of hydrogen atoms in the formation process of hydrogenated microcrystalline silicon, ” Jpn. J. Appl. Phys., vol.29, pp. L1372-L1375, 1990.
[10]A. Asano, “Effects of hydrogen atoms on the network structure of hydrogenated amorphous and microcrystalline silicon thin films,” Appl. Phys. Lett., vol.56, pp.533-535, 1990.
[11]C. C. Tasi, G. B. Anderson, and R. Thompson, “ Growth of amorphous, microcrystalline, and epitaxial silicon in low-temperature plasma deposition, ” Mat. Res. Soc. Symp. Proc., vol.192, pp.475-480, 1990.
[12]J. Mort and F. Jansen, “Plasma-Deposited Thin Films,” p.28-33 (CRC Press, Boca Raton, FL, 1986).
[13]F. J. Kampas and R. W. Griffith, “ Hydrogen elimination during the glow- discharge deposition of a-Si:H alloys,” Appl. Phys. Lett., vol.39, pp.407-409,1981
[14]P. A. Longeway, “Semiconductors and Semimetals 21A, ” pp.179-193 (In: J. I. Pankove, ed., Academic Press, New York, 1984).
[15] F. Giorgis, C. F. Pirri, and E. Tresso, “Structural properties of a-Si1-xNx:H films grown by plasma-enhanced chemical vapor deposition by SiH4 + NH3 + H2 gas mixtures,” Thin Solid Films, vol.307, pp.298-305, 1997
[16]R. Ishihara, H. Kanoh, Y. Uchida, O. Sugiura, and M. Matsumura, “Low-temperature chemical vapor deposition of silicon nitride from tetrasilane and hydrogen azide,” Mat. Res. Soc. Symp. Proc., vol.284, pp.3-8, 1992.
[17] S. Yamakawa, S. Yabuta, A. Ban, M. Okamoto, M. Katayama, Y. Ishii, and M. Hijikigawa, “The effect of plasma treatment on the off-current characteristics of a-Si TFTs,” SID 98 Digest, pp.443-446, 1998.
[18] K. Takechi, H. Uchida, and S. Kaneko, “Mobility- improvement mechanism in a-Si:H TFTs with Smooth a-Si:H/SiN x Interface,” Mat. Res. Soc. Symp. Proc., vol.258, pp.955-960, 1992.
[19] C. R. Kagan, P. Andry, The Film Transistors, p52-p57, IBM T. J. Watson Research Center, Yorktown Heights, New York, U.S.A. 2003.