非晶矽薄膜電晶體及多晶矽薄膜電晶體已經用於製造液晶顯示器的畫素開關，尤其以非晶矽薄膜電晶體更是已經大量的運用在製造大面積的顯示面板。而因使用上的方便性，傳統的平面顯示器預估將被可曲撓式顯示器所取代。在製作非晶矽薄膜電晶體時，有兩個主要的目標需要改善：在元件開的狀態下，增加其導通電流及在元件關的狀態下，降低背光源照射下的光漏電流。增加其導通電流是為了用於大面積高解析度的面板；另一方面是因為非晶矽的光吸收係數較高，因此在光照射下會有較大的漏電流。若面板應用於需高強度背光照射的產品如多媒體顯示器、液晶電視時，光漏電的問題就極為嚴重。有鑑於此，本論文將研究非晶矽薄膜電晶體應用於可曲撓式顯示器之光漏電特性分析。
在量測方面，由於非晶矽之對光的吸收與其費米能階所在的位置相關，因此可以利用不同溫度量測粹取出的元件活化能(Ea)。由於其活化能會因不同曲撓狀態下的非晶矽薄膜電晶體而有所不同，因為非晶矽薄膜電晶體的費米能階會受到非晶矽能隙內的缺陷密度(DOS)分佈而改變。而缺陷密度亦為一重要的參數，其和元件的起始電壓(threshold voltage)、次臨界擺幅(subthreshold swing)、載子移動率及元件可靠度有關。根據實驗結果顯示，在張應力下的非晶矽薄膜電晶體受到背光照射下所造成的影響較不受應力的非晶矽薄膜電晶體小，因此也具有在背光照射下較少的起始電壓(threshold voltage)和次臨界擺幅(subthreshold swing)的偏移現象，源由於非晶矽通道材料的活化能較小所影響。

The off-state leakage current under back light illumination is, in particular, a serious problem in the multimedia displays that require high intensity backlight illumination. The photo leakage current characteristic of flexible a-Si:H TFTs has been measured in this study .
The device activation energy (Ea) of a-Si:H TFTs extracted from various temperature measurements are different from those of typical a-Si:H TFTs, because the Fermi level of a-Si:H TFTs are modulate by the density of states (DOS) in the a-Si:H band gap. The information on DOS is important for understanding the physical mechanisms responsible for the device behavior. It’s related to the threshold voltage,iii
subthreshold slope, field effect mobility and the stability of the TFTs.
Experimental results show the photo leakage currents of a-Si:H TFTs under tensile stress are less than that of flattened a-Si:H TFTs stemmed the weak light intensity. In addition, the small shifts of threshold voltage and subthreshold swing are resulted from the smaller Ea in a-Si:H channel material.

Chinese Abstract……………………………………………...i
English Abstract……………………………………………..iii
Tables Captions………………………………………………v
Figures Caotions…………………………………………….vi
Chapter One
1.1 Introduction…………………………………………………1
1.1.1 Introduction……………………………………………………....1
1.1.2 Hydrogenated Amorphous Silicon…………………………………..2
1.2 Substrate Material…………………………………………..3
1.2.1 Plastic Substrate………………………………………………………3
1.2.2 Metal Substrate…………………………………………………..…...4
1.2.3 Thin Glass Substrate………………………………………….……..6
1.3 Photo leakage current mechanism…………………….......7
1.4 Motivation………………………………………………....12
Chapter Two
2.1 Apparatus………………………………………………....14
2.2 Setup instruments for I-V…………………………….….15
2.3 Method of Device Parameter Extraction………….……16
2.3.1 Determination of the threshold voltage……………………..…….16
2.3.2 Determonation of the subthreshold swing……………………….16
2.3.3 Determination of the field-effect mobility……………………….17
2.4 Density of States……………………………………………19
2.5 Defined Bending Direction………………………………..21
Chapter Three
3.1 Deposition of Hydrogenated Amorphous Silicon by PECVD
………………………………………………………………22
3.2 Deposition of SiNx by PECVD…………………………….26
3.3 Deposition of n+ Hydrogenated Amorphous Silicon by PECVD
………………………………………………………………28
3.4 Process Flow………………………………………………..29
Chapter Four
4.1 Bending experiment……………………………………….32
4.1.1 Results…………………………………………………………………32
4.1.2 Discussion………………………………………………………33
4.2 Bending and Back Light Illumination Experiment……..39
4.2.1 Results………………………………………………………………….39
4.2.2 Discussion………………………………………………………40
Chapter Five
5.1 Electrical characteristic under mechanical strain………43
5.2 Electrical characteristic with back light illumination……….44
References…………………………………………………...45
Tables………………………………………………………..53
Figures………………………………………………………54

Chapter One – Introduction
1. J. H. Choi, C. S. Kim, B. C. Lim, and J. Jang, IEEE TRANSACTION ON ELECTRON DEVICES, Vol. 45, No. 9, September 1998.
2. Y. Yamaji, M. Ikeda, M. Akiyama, and T. Endo, J. J. Appl. Phys. Vol. 38 (1999) pp.6202-6206
3. M. C. Wang ,T. C. Chang, P. T. Liu, S. W. Tsao, and J. R. Chen, Electrochemical and Solid-State Letters, 10 (3) J49-J51 (2007)
4. B. G. Streetman, Solid State Electronic Devices, Chapter 1.3, London: Prentice Hall, 1990
5. Powell, “ The Physics of Amorphous-silicon Thin-film Transistors, IEEE Trans. Electron. Devices, 36, 2753 (1989).
6. Y. Kuo, The Film Transistors – Material and Processes, vol. 1, p17, Texas A&M University, U.S.A. 2004.
7. Y. Kuo, The Film Transistors – Material and Processes, vol. 1, p428, Texas A&M University, U.S.A. 2004
8. Y. Kuo, The Film Transistors – Material and Processes, vol. 1, p430, Texas A&M University, U.S.A. 2004.
9. A. Weber, S. Deutschbein, A. Plichta, and A. Habeck, Society of InformationDisplay, Digest of Technical Papers, 200th International Symposium at Boston, Ma, 53-55, May 2002.
10. Y. Kuo, The Film Transistors – Material and Processes, vol. 2, p430, Texas
A&M University, U.S.A. 2004.
11. Sandrine Martin, Jerzy Kanicki, Nicolas Szydlo, Alain Rolland “Analysis of the amorphous silicon thin film transistors behavior under illumination” AM-LCD ‘97
12. H.Gleskova and S. Wagner, Appl. Phys. Letts. 79 (2001)
13. H.Gleskova, S. Wagner, W. Soboyejo, and Z. Suo, J. Appl. Phys., 92,6224(2004)
14. F. B. Ellis, Jr., R. G. Gordon, W. Paul, and B. G. Yacobi, “Properties of hydrogenated amorphous silicon prepared by chemical vapor deposition,” J. Appl. Phys., vol. 55, pp. 4309-4317, 1984.
15. Jong Hyun Choi, Chang Soo Kim, Byung Cheon Lim, and Jin Jang, IEEE TRANSACTIONS ON ELECTRON DEVICE, VOL. 45, NO. 9, SEPTEMBER 1998
Chapter Two – Apparatus and Parameters
1. R. A. Street, Hydrogenated Amorphous Silicon, Cambridge University Press, 1991.
2. W. E. Spear and P. G. Le Comber, “Investigation of the Localized State Distribution in Amorphous Si Film, ” J. Non-Cryst. Solids, 8-10, 727-738 (1972).
3. M. J. Powell, “Analysis of Field-effect-conductance Measurements on Amorphous Semiconductors, ” Phil. Mag. B, 43 (1), 93 (1981).
4. C. Y. Huang, S. Guha, and S. J. Hudgen, “Study of Gap States in Hydrogenated Amorphous Silicon by Transient and Steady-state Photoconductivity Measurement, ” Phys. Rev. B, 27 (12), 7460 (1983)
5. J. D. Cohen, D. V. Lang, and J. P. Harbison, “Direct Measurement of the Bulk Density of Gap States in n-type Hydrogenated Amorphous Silicon, ” Phys. Rev. Lett., 45 (3), 197 (1980).
6. M. Hirose, T, Suzuki, and G. H. Döhler, “Electronic Density of States in Discharge-produced Amorphous Silicon, ” Appl. Phys. Lett., 34 (3), 234 (1979).
7. P. Viktorovitch and G. Moddel, “Interpretation of the Conductance and Capacitance Frequency Dependence of Hydrogenated Amorphous Silicon Schottky Barrier Diodes, ” J. Appl. Phys., 51 (9), 4847 (1980).
8. M. Shur and M. Hack, “Physics of Amorphous Silicon Based Alloy Field-effect Transistors, ” J. Appl. Phys., 55 (10), 3831 (1984).
9. S. Kishida, Y. Naruke, Y. Uchida, and M. Matsumura, “Theoretical Analysis of Amorphous-silicon Field-effect-transistors, ” Jpn. J. Appl. Phys., 22 (3), 511 (1983).
10. J. G. Shaw and M. Hack, “An Analytical Model for Calculating Trapped Charge in Amorphous Silicon, ” J. Appl. Phys., 64 (9), 4562 (1988).
11. M. S. Shur, M. D. Jacunski, H. C. Slade, and M. Hack, “Analytical Models for Amorphous-silicon and Poly-silicon Thin-film Transistors for High-definition-display Technology, ” J. of the SID, 3-4, 223 (1995)
12. Y. Kuo, The Film Transistors – Material and Processes, vol. 1, p83, Texas A&M University, U.S.A. 2004.
13. S. H. Won, J. K. Chung, C. B. Lee, H. C. Nam, J. H. Hur, and J. Jang, Journal of Electrochemical Society, 151 (3), G167-G170 (2004).
Chapter Three – Fabrication
1. 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.
2. 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.
3. 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.
4. 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.
5. J. Mort and F. Jansen, “Plasma-Deposited Thin Films,” p.28-33 (CRC Press, Boca Raton, FL, 1986).
6. 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
7. F. J. Kampas, “Reactions of atomic hydrogen in the deposition of hydrogenated amorphous silicon by glow discharge and reactive sputtering,” J. Appl. Phys., vol. 53, pp.6408-6412, 1982.
8. P. A. Longeway, “Semiconductors and Semimetals 21A,” pp.179-193 (In: J. I. Pankove, ed., Academic Press, New York, 1984).
9. 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.
10. 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.
11. 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.
12. K. Takechi, H. Uchida, and S. Kaneko, “Mobility-improvement mechanism in a-Si:H TFTs with Smooth a-Si:H/SiNx Interface,” Mat. Res. Soc. Symp. Proc., vol.258, pp.955-960, 1992.
13. C. R. Kagan, P. Andry, The Film Transistors, p52-p57, IBM T. J. Watson Research Center, Yorktown Heights, New York, U.S.A. 2003.
14. M. C. Wang ,T. C. Chang, P. T. Liu, S. W. Tsao, and J. R. Chen, Electrochemical and Solid-State Letters, 10 (3) J49-J51 (2007)
Chapter Four – Bending Experiment
1. S. Luana and G. W. Neudeck, J. Appl. Phys, 72,766 (1992)
2. S. H. Won, J. K. Chung, C. B. Lee, H. C. Nam, J. H. Hur, and J. Jang, J. Electrochem.Soc., 151, G167 (2004)
3. Sazonov and C. McArthur, J. Vac. Sci. Technol. A, 22,2052 (2004)
4. M. J. Powell, C. Glasse, P. W.Green, I. D. French, and I. J. Stemp, IEEE Electron Device Lett., 21, 104 (2000)
5. S. H. Won, J. K. Chung, C. B. Lee, H. C. Nam, J. H. Hur, and J. Jang, J. Electrochem.Soc., 151, G167 (2004)
6. H. Gleskova, P. I. Hsu, Z. Xi, J. C. Sturm, Z. Suo, and S. Wagner, J. Non-Cryst.
Solids, 338–340, 732 (2004)
7. G. D. Cody, C. R. Wronski, B. Abeles, R. B. Stephens, and B. Brooks, Sol. Cells, 2, 227 (1980)
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