臺灣博碩士論文加值系統

本論文中，低溫(25℃-250℃)濺鍍氮化鋁(AlN)薄膜被沉積當作有機薄膜電晶體(OTFTs)上的閘極絕緣層。不同於傳統的高介電常數的材料，氮化鋁擁有低的閘極漏電以及高的疏水性。在實驗中發現氮化鋁的表面能比五環素(pentacene)還低而且近似於用自組裝單層膜(SAM)處理過後的介電層。在實驗中，嘗試調整氮化鋁的製程條件，我們發現當製程溫度降低時，氮化鋁可獲得平整的表面(表面粗糙度小0.2nm)以及很低的閘極漏電(在1MV/cm，漏電流小於1×10-9A/cm2)。並且觀察到崩潰電場大於5MV/cm以及量測到的氮化鋁介電常數為7。除了降低溫度外，當增加氮氣流率比時，氮化鋁漏電也獲得抑制。更近一步分析漏電行為，發現氮化鋁在低電場時，由歐姆(Ohmic)定律主導。在高電場時，由普爾-夫倫克爾(Poole-Frenkel)過程來主導。因此當增加氮氣流率時，氮相關之缺陷可能獲得補償，漏電因此而降低。
根據最佳製程條件，我們實現了低電壓操作的氮化鋁有機薄膜電晶體。當氮化鋁的厚度降低到70nm以下，氮化鋁有機薄膜電晶體可以被操作在5伏特以下。並且可以獲得高的電流開/關比值(大於10^6)以及高的載子移動率(約1.67cm2/V-sec)。而且也可得到極低的次臨界擺幅(約130mV/decadec)和臨界電壓(約-1.5伏特)。然而由於氮化鋁擁有低的表面能，可能導致低的介面捕獲電荷密度和極小的次臨界擺幅。這些顯著的電晶體特性論證了氮化鋁有機薄膜電晶體擁有極大的潛力，可以應用在低操作電壓以及快速開關的有機電晶體上。

In this thesis, the low-temperature (25℃-250℃) sputtered aluminum nitride (AlN) film was deposited as the gate insulator in organic thin film transistors (OTFTs). In contrary to the conventional high-k dielectrics, the AlN film has a very low dielectric leakage and hydrophobic. The surface free energy is lower than the pentacene film and similar to the self-assembled monolayer (SAM) treated dielectrics. By adjusting the AlN sputtering process, it was found that the smooth (surface roughness <0.2nm) and very low leakage (less than 1×10-9A/cm2 at 1MV/cm) AlN film was obtained by lowering down the process temperature. The dielectric breakdown field is larger than 5MV/cm and the relative electrical permittivity is 7 in the AlN film. With the increasing of nitrogen gas flow rate, the dielectric leakage of AlN film is suppressed. Moreover, the leakage-current in AlN film obeys the Ohmic-conduction and the Poole-Frenkel transport in low and high electric field, respectively. It is suggested that the nitrogen-related defects are compensated, with the increasing of nitrogen flow rate in sputtering process, thus the leakage is decreased.
Accordingly to the optimized sputtering conditions, the low-voltage AlN-OTFTs is realized. With the thin AlN gate-dielectric (thickness less than 70nm), the AlN-OTFTs are operated at a very low voltage (less than 5V). It is founded that the high on/off current ratio more than 10^6, and the high mobility about 1.67cm2/V-sec are achievable. The lowest subthreshold swing is 130mV/decade and the threshold voltage is -1.5V. The low interface-trap-density and the steep subthreshold swing for AlN-OTFTs may be attributed to the low surface energy of the AlN film. The remarkable transistor properties demonstrate that the AlN-OTFT has potential application in low-voltage and rapid-switching organic transistors.

Abstract (Chinese) Ι
Abstract (English) III
Acknowledgement V
Contents VI
Table Captions VIII
Figure Captions IX

Chapter 1. Introduction
1-1 Introduction of Organic Thin Film Transistors (OTFTs)1
1-2 Deposition Methods of AlN 2
1-3 Motivation 3
1-4 Thesis Organization 4

Chapter 2. Theoretical Background of OTFTs
2-1 Introduction 5
2-2 Transportation Mechanisms of Organic Semiconductor 5
2-3 Operation of OTFTs 7
2-4 Parameter Extraction 9
2-4-1 Mobility 9
2-4-2 Threshold voltage 9
2-4-3 On/Off current ratio 10
2-4-4 Subthreshod swing 10
2-4-5 Maximum interface trap density 10
2-4-6 Surface free energy 11
2-4-7 Poole-Frenkel (P-F) mechanism 11

Chapter 3. Experiments
3-1 AlN Deposition 12
3-2 OTFTs Fabrication 12
3-3 Capacitance Structure Fabrication 14

Chapter 4. Result and Discussion
4-1 Electrical Properties of AlN Dielectric 16
4-1-1 Dependence of dielectric leakage on substrate temperature 16
4-1-2 Dependence of dielectric leakage on nitrogen gas flow rate 18
4-2 Effects of AlN Dielectric Roughness 20
4-3 Surface Polarity of AlN Film 22
4-4 Low-Voltage OTFTs with AlN Dielectric 23
4-5 High-Performance AlN-OTFTs 25
4-5-1 AlN dielectric with higher Ar/N2 ratio 25
4-5-2 Room temperature AlN dielectric 26
4-6 Summary 28

Chapter 5. Conclusion and Future Work
5-1 Conclusion 29
5-2 Future Work 30

References 31
Tables 39
Figures 41
Profile 63

[1] A. Tsumura, K. Koezuka, and T. Ando, “Macromolecular electronic devices: Field-effect transistor with a polythiophene thin film”, Appl. Phys. Lett. vol.49, pp. 1210, (1986).
[2] J. H. Burroughes, C. A. Jones, and R. H. Friend, “Polymer diodes and transistors: new semiconductor device physics”, Nature, vol. 335, pp.137, (1988).
[3] Y. Y. Lin, D. J. Gundlach, S. F. Nelson, and T. N. Jackson, “Pentacene organic thin-film transistors-molecular ordering and mobility”, IEEE Electron Device Lett. vol. 18, pp. 87, (1997).
[4] C. D. Dimitrakopoulos and P. R. L. Malenfant, ”Organic thin film transistors for large area electronics”, Adv. Mater. (Weinheim, Ger.) 14, No. 2, pp.99, (2002).
[5] H. Klauk, M. Halik, U. Zschieschang, F. Eder, D. Rohde, G. Schmid, and C. Dehm, “Flexible organic complementary circuits”, IEEE Trans. Electron Devices, vol. 52, pp. 618, (2005).
[6] C. D. Dimitrakopoulos, S. Purushothaman, J. Kymissis, A. Callefari, J. M. Shaw, “Low-voltage organic transistors on plastic comprising high-dielectric-constant gate insulator”, Science, vol. 283, pp. 822, (1999).
[7] Sang Yoon Yang, Se Hyun Kim, Kwonwoo Shin, Hayoung Jeon, and Chan Eon Park, “Low-voltage pentacene field-effect transistors with ultrathin polymer gate dielectrics”, Appl. Phys. Lett., vol. 88, pp. 173507, (2006).
[8] Guangming Wang, Daniel Moses, Alan J. Heeger, Hong-Mei Zhang, Mux Narasimhan, and R. E. Demaray, “Poly(3-hexylthiophene) field-effect transistors with high dielectric constant gate insulator”, J. Appl. Phys.,vol. 95, pp. 316, (2004).
[9] G. Nunes Jr., S. G. Zane, and J. S. Meth, “Styrenic polymers as gate dielectrics for pentacene field-effect transistors”, J. Appl. Phys., vol. 98, pp. 104503, (2005).
[10] M. McDowell, I. G. Hill, J. E. McDermott, S. L. Bernasek, and J. Schwartz, “Improved organic thin-film transistor performance using novel self-assembled monolayers”, Appl. Phys. Lett., vol. 88, pp. 073505, (2006).
[11] Sandra. E. Fritz, Tommie Wilson Kelley, and C. Daniel Frisbie, ”Effect of Dielectric Roughness on Performance of Pentacene TFTs and Restoration of Performance with a Polymeric Smoothing Layer”, J. Phys. Chem. B, vol.109, pp.10574, (2005).
[12] H. Harima, T. Inoue, S. Nakashima, H. Okumura, Y. Ishida, S. Yoshida, T. Koizumi, H. Grille, and F. Bechstedt, “Raman studies on phonon modes in cubic AlGaN alloy”, Appl. Phys. Lett., vol. 74, pp. 191, (1999).
[13] L. Chen, B. J. Skromme, R. F. Dalmau, R. Schlesser, Z. Sitar C. Chen, W. Sun, J. Yang, M. A. Khan, M. L. Nakarmi, J. Y. Lin, and H.-X. Jiang, “Band-edge exciton states in AlN single crystals and epitaxial layers”, Appl. Phys. Lett., vol. 85, pp. 4334, (2004).
[14] K. K. Harris, B. P. Gila, J. Deroaches, K. N. Lee, J. D. MacKenzie, C. R. Abernathy, F. Ren, and S. J. Pearton, “Microstructure and Thermal Stability of Aluminum Nitride Thin Films Deposited at Low Temperature on Silicon”, J. Electrochem. Soc., vol. 149, pp. G128, (2002).
[15] Laurie Valbin, Laure Sevely, and Serge Spirkovitch, “Low temperature piezoelectric aluminum nitride thin film”, Proceeding of SPIE, vol. 4174, pp.154, (2000).
[16] Yanming Sun, Yunqi Liu, and Daoben Zhu, “Advances in organic field-effect transistors”, J. Mater. Chem., vol. 15, pp. 53, (2005).
[17] R. A. Street, D. Knipp, and A. R. Völkel, “Hole transport in polycrystalline pentacene transistors”, Appl. Phys. Lett., vol. 80, pp. 1658, (2002).
[18] G. Horowitz, “Organic field-effect transistors”, Adv. Mater., vol. 10, pp. 365, (1998).
[19] Y.-Y. Lin, D. J. Gundlach, S. F. Nelson, and T. N. Jackson, “Stacked pentacene layer organic thin-film transistors with improved characteristics”, IEEE Electron Device Lett, vol. 18, pp 606, (2000).
[20] S. F. Nelson, Y.-Y. Lin, D. J. Gundlach, and T. N. Jackson, “Temperature-independent transport in high-mobility pentacene transistors”, Appl. Phys. Lett., vol. 72, pp. 1854, (1998).
[21] W. Warta, and N. Karl, “Hot holes in naphthalene: High, electric-field-dependent mobilities”, Phys. Rev. B, vol. 32, pp. 1172, (1985).
[22] L. B. Schein, C. B. Duke, and A. R. McGhie, “Observation of the Band-Hopping Transition for Electrons in Naphthalene”, Phys. Rev. Lett., vol 40, pp. 197, (1978).
[23] E. A. Silinsh, A. Klimkans, S. Larsson, and V. Cápek, “Molecular polaron states in polyacene crystals. Formation and transfer processes”, Chem. Phys., vol 198, pp. 311 (1995).
[24] O. Ostroverkhova, D. G. Cooke, S. Shcherbyna, R. F. Egerton, F. A. Hegmann, R. R. Tykwinski, and J. E. Anthony, “Bandlike transport in pentacene and functionalized pentacene thin films revealed by subpicosecond transient photoconductivity measurements”, Phys. Rev. B, vol. 71, pp. 035204, (2005).
[25] A. R. Brown, C. P. Jarrett, D. M. de Leeuw, and M. Matters, “Field-effect transistors made from solution-processed organic semiconductors”, Synth. Met., vol. 88, pp. 37, (1997).
[26] K N Narayanan Unni, Sylvie Dabos-Seignon, and Jean-Michel Nunzi, “Improved performance of pentacene field-effect transistors using a polyimide gate dielectric layer”, J. Phys. D: Appl. Phys.,vol. 38, pp. 1148, (2005).
[27] A. Rolland, J. Richard, J. P. Kleider, and D. Mencaraglia, “Electrical properties of amorphous silicon transistors and MIS-devices: Comparative study of top nitride and bottom nitride configurations”, J. Electrochem. Soc., vol. 140, pp. 3679, (1993).
[28] Kui-Xiang Ma, Chee-Hin Ho, Furong Zhu, and Tai-Shung Chung, “Investigation of surface energy for organic light emitting polymers and indium tin oxide”, Thin Solid Films, vol. 371, pp. 140, (2000).
[29] S. M. Sze, Physics of Semiconductor Devices, Chap. 7, pp. 402, Wiley, New York, (1981).
[30] Po-Tsun Liu, Ting-Chang Chang, Ya-Liang Yang, Yi-Fang Cheng, Jae-Kyun Lee, Fu-Yung Shih, Eric Tsai, Grace Chen, and Simon M. Sze, “Improvement on intrinsic electrical properties of low-k hydrogen silsesquioxane/copper interconnects employing deuterium plasma treatment”, J. Electrochem. Soc., vol. 147, pp. 1186, (2000).
[31] C.-M. Yeh, C.H. Chen, J.-Y. Gan, C.S. Kou, and J. Hwang, “Enhancement of the c-axis texture of aluminum nitride by an inductively coupled plasma reactive sputtering process”, Thin Solid Films, vol. 483, pp. 6, (2005).
[32] C. D. Dimitrakopoulos, A. R. Brown, and A. Pomp, “Molecular beam deposited thin films of pentacene for organic field effect transistor applications”, J. Appl. Phys.,vol. 80, pp. 2501, (1996).
[33] Chih-Wei Chu, Sheng-Han Li, Chieh-Wei Chen, Vishal Shrotriya, and Yang Yang, “High-performance organic thin-film transistors with metal oxide/metal bilayer electrode”, Appl. Phys. Lett., vol. 87, pp. 193508, (2005).
[34] R. W. I. de Boer, N. N. Iosad, A. F. Stassen, T. M. Klapwijk, and A. F. Morpurgo, “Influence of the gate leakage current on the stability of organic single-crystal field-effect transistors”, Appl. Phys. Lett., vol. 86, pp. 032103, (2005).
[35] Jun Wang, Xuanjun Yan, Yanxia Xu, Jian Zhang, and Donghang Yan, “Organic thin-film transistors having inorganic/organic double gate insulators”, Appl. Phys. Lett., vol. 85, pp. 5424, (2004).
[36] Wenfeng Xiang, Huibin Lü, Lei Yan, Haizhong Guo, Lifeng Liu, Yueliang Zhou,
Guozhen Yang, Jinchun Jiang, Huansheng Cheng, and Zhenghao Chen,
“Characteristics of LaAlO3/Si(100) deposited under various oxygen pressures”, J. Appl. Phys.,vol. 93, pp. 533, (2003).
[37] Yi-Hsien Lee, Jenn-Ming Wu, Yu-Lun Chueh, and Li-Jen Chou, “Low-temperature growth and interface characterization of BiFeO3 thin films with reduced leakage current”, Appl. Phys. Lett., vol. 87, pp. 172901, (2005).
[38] Yun-Hi Lee, Young-Sik Kim, Byeong-Kwon Ju, and Myung-Hwan Oh, “Roughness of ZnS:Pr,Ce/Ta2O5 interface and its effects on electrical performance of alternating current thin-film electroluminescent devices”, IEEE Trans. Electron Devices, vol. 46, pp. 892, (1999).
[39] H. Klauk, M. Halik, U. Zschieschang, G. Schmid, W. Radlik, and W. Weber, “High-mobility polymer gate dielectric pentacene thin film transistors”, J. Appl. Phys., vol. 92, pp.5259, (2002).
[40] Keiji Ueno, Shigeomi Abe, Ryo Onoki, and Koichiro Saiki, “Anodization of electrolytically polished Ta surface for enhancement of carrier injection into organic field-effect transistors,” J. Apply. Phys., vol.98, pp.114503-1, (2005).
[41] Y. S. Kim, M. Y. Sung, Y. H. Lee, B. K. Ju, and M. H. Oh, “The influence of surface roughness on the electric conduction process in amorphous Ta2O5 thin films”, J. Electrochem. Soc., vol. 146, pp. 3398, (1999).
[42] Chang Su Kim, Woo Jin Kim, Sung Jin Jo, Sung Won Lee, Se Jong Lee, and Hong Koo Baik, “Influence of the oxygen concentration of YSZ gate dielectric layer on the low voltage operating pentacene thin film transistor”, Electrochem. Solid-State Lett., vol. 9, pp. G96, (2006).
[43] KyongTae Kang, Mi-Hwa Lim, Ho-Gi Kim, YongWoo Choi, Harry L. Tuller, II-Doo Kim, and Jae-Min Hong, “Mn-doped Ba0.6Sr0.4TiO3 high-K gate dielectrics for low voltage organic transistor on polymer substrate”, Apply. Phys. Lett., vol. 87, pp. 242908, (2005).
[44] X. Li, T. L. Tansley and V. W. L. Chin, “Dielectric properties of AlN films prepared by laser-induced chemical vapour deposition”, Thin Solid Films, vol. 250, pp. 263, (1994).
[45] T. L. Tansley and R. J. Egan, “Point-defect energies in the nitrides of aluminum, gallium, and indium”, Phys. Rev. B, vol. 45, pp. 10942, (1992).
[46] Kwonwoo Shin, Chanwoo Yang, Sang Yoon Yang, Hayoung Jeon, and Chan Eon Park, “Effects of polymer gate dielectrics roughness on pentacene field-effect transistors”, Appl. Phys. Lett., vol. 88, pp. 072109, (2006).
[47] Hagen Klauk, David J. Gundlach, Jonathan A. Nichols and Thomas N. Jackson, ”Pentacene Organic Thin-Film Transistors for Circuit and Display Applications”, IEEE Trans. Electron Device, vol. 46, pp. 1258, (1999).
[48] D. Knipp, R. A. Street, A. Volkel, and J. Ho, “Pentacene thin film transistors on inorganic dielectrics: Morphology, structural properties, and electronic transport”, J. Apply. Phys., vol. 93, pp. 347, (2003).
[49] Sang Chul Lim, Seong Hyun Kim, Jung Hun Lee, Mi Kyung Kim, Do Jin Kim, and Taehyoung Zyung, “Surface-treatment effects on organic thin-film transistors”, Synth. Met., vol. 148, pp. 75, (2005).
[50] Yunseok Jang, Do Hwan Kim, Yeong Don Park, Jeong Ho Cho, Minkyu Hwang, and Kilwon Cho, “Influence of the dielectric constant of a polyvinyl phenol insulator on the field-effect mobility of a pentacene-based thin-film transistor”, Appl. Phys. Lett., vol. 87, pp. 152105, (2005).
[51] M. Yoshida, S. Uemura, T. Kodzasa, T. Kamata, M. Matsuzawa, and T. Kawai, “Surface potential control of an insulator layer for the high performance organic FET”, Synth. Met., vol. 137, pp. 967, (2003).
[52] Sang Yoon Kwonwoo, Kwonwoo Shin, and Chan Eon Park, “The Effect of Gate-Dielectric Surface Energy on Pentacene Morphology and Organic Field-Effect Transistor Characteristics”, Adv. Funct. Mater., vol. 15, pp. 1806, (2005).
[53] L. A. Majewski, R. Schroeder, and M. Grell, “Low-voltage, high-performance organic field-effect transistors with an ultra-thin TiO2 layer as gate insulator”, Adv. Funct. Mater., vol. 15, pp. 1017, (2005).
[54] Florian Eder, Hagen Klauk, Marcus Halik, Ute Zschieschang, Günter Schmid, and Christine Dehm, “Organic electronics on paper”, Appl. Phys. Lett., vol. 84, pp. 2673, (2004).
[55] Christopher R. Newman, C. Daniel Frisbie, Demetrio A. da Silva Filho, Jean-Luc Bredas, Paul C. Ewbank, and Kent R. Mann, “Introduction to organic thin film transistors and design of n-channel organic semiconductors”, Chem. Mater., vol. 16, pp. 4436, (2004).
[56] Yunseok Jang, Do Hwan Kim, Yeong Don Park, Jeong Ho Cho,Minkyu Hwang,and Kilwon Cho, “Low-voltage and high-field-effect mobility organic transistors with a polymer insulator”, Appl. Phys. Lett., vol. 88, pp. 072101, (2006).
[57] Flavio de Paula Santos, Elson de Campos, Marcelo Costa, Francisco Cristovao Lourenco Melo, Roberto Yzumi Honda, and Rogerio Pinto Mota, “Superficial modifications in TiO2 and Al2O3 ceramics”, Materials Research, vol. 6, pp. 353, (2003).
[58] Myung. M. Sung, G. Jonathan Kluth, and Roya Maboudian, “Formation of alkylsiloxane self-assembled monolayers on Si3N4”, J. Vac. Sci. Technol. A, vol. 17(2), pp. 540, (1999).