本實驗室過去於製作有機場效電晶體（organic field-effect transistors, OFETs）時發現，以豬精液蛋白（porcine seminal plasma, PSP）作為閘極介電層時，即使薄膜厚度相較於一般高分子介電層較厚，元件仍可呈現較低之臨界電壓（threshold voltage, Vth）。由於介電層厚度增加通常會使單位面積電容降低，進而提高元件操作電壓，因此 PSP 介電層所展現之低臨界電壓行為，顯示其可能具有不同於傳統高分子介電層之電性與界面調控機制。因此，本論文主要探討 PSP 介電層應用於低臨界電壓 OFET 之原因，並與常見高分子介電層進行比較分析。
本研究首先由元件電性表現進行比較，確認 PSP 介電層元件相較於其他高分子介電層具有較低之臨界電壓。接著透過電容量測與次臨界擺幅分析，發現 PSP 具有較高之單位面積電容與較低之介面陷阱密度，表示其可能具有較佳的閘極調控能力與介面品質。此外，AFM 表面形貌分析顯示，不同介電層之表面粗糙度並無明顯差異，說明 PSP 造成低臨界電壓的主要原因並非來自表面形貌差異。PFM 表面電位分析顯示，PSP 具有較高且較穩定之表面電位，推測其表面可能存在極性官能基、界面偶極或固定電荷效應。進一步於 PSP 表面覆蓋薄層高分子材料後，元件臨界電壓產生位移，而單位面積電容並未明顯改變，顯示 PSP 表面特性對低臨界電壓行為具有重要影響。綜合上述結果，本研究認為 PSP 介電層所造成之低臨界電壓並非單一因素所致，而是與較高的單位面積電容、較低的介面陷阱密度以及較高且穩定的表面電位共同相關。

In previous studies conducted in our laboratory, it was found that organic field-effect transistors (OFETs) using porcine seminal plasma (PSP) as the gate dielectric layer could still exhibit a low threshold voltage (Vth), even though the PSP dielectric film was thicker than conventional polymer dielectric layers. Since an increase in dielectric thickness generally leads to a decrease in areal capacitance and consequently increases the operating voltage of the device, the low Vth behavior observed in devices suggests that PSP may possess electrical properties and interfacial modulation mechanisms different from those of traditional polymer dielectrics. Therefore, this thesis investigates the origin of the low Vth in devices and compares PSP with commonly used polymer dielectric layers.
This study first compares the electrical characteristics of devices with different dielectric layers and confirms that devices exhibit a lower Vth than those using other polymer dielectrics. Capacitance measurements and subthreshold swing analysis further reveal that PSP possesses a higher areal capacitance and a lower interfacial trap density, indicating that it may provide better gate modulation capability and improved interface quality. In addition, atomic force microscopy (AFM) analysis shows no significant difference in surface roughness among the different dielectric layers, suggesting that the low Vth of PSP devices is not mainly caused by differences in surface morphology. Kelvin probe force microscopy (KPFM) surface potential analysis shows that PSP exhibits a higher and more stable surface potential, implying the possible presence of polar functional groups, interfacial dipoles, or fixed charge effects on the PSP surface. Furthermore, after covering the PSP surface with a thin polymer layer, the Vth shifts while the areal capacitance remains nearly unchanged, indicating that the surface properties of PSP play an important role in the low Vth behavior. Overall, the low Vth induced by the PSP dielectric layer is not attributed to a single factor, but is collectively associated with its higher areal capacitance, lower interfacial trap density, and higher and more stable surface potential.

[1] M. Pope and C. E. Swenberg, Electronic Processes in Organic Crystals and Polymers, 2nd ed. New York, NY, USA: Oxford University Press, 1999.
[2] K. Nomoto, N. Hirai, N. Yoneya, N. Kawashima, M. Noda, M. Wada, and J. Kasahara, “A high-performance short-channel bottom-contact OTFT and its application to AM-TN-LCD,” IEEE Transactions on Electron Devices, vol. 52, no. 7, pp. 1519–1526, 2005.
[3] H. Shirakawa, E. J. Louis, A. G. MacDiarmid, C. K. Chiang, and A. J. Heeger, “Synthesis of electrically conducting organic polymers: Halogen derivatives of polyacetylene, (CH)x,” Journal of the Chemical Society, Chemical Communications, no. 16, pp. 578–580, 1977.
[4] F. Ebisawa, T. Kurokawa, and S. Nara, “Electrical properties of polyacetylene/polysiloxane interface,” Journal of Applied Physics, vol. 54, no. 6, pp. 3255–3259, 1983.
[5] A. Assadi, C. Svensson, M. Willander, and O. Inganäs, “Field-effect mobility of poly (3-hexylthiophene),” Applied Physics Letters, vol. 53, no. 3, pp. 195–197, 1988.
[6] 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 Letters, vol. 18, no. 12, pp. 606–608, 1997.
[7] M. P. Hong, B. S. Kim, Y. U. Lee, K. K. Song, S. Y. Lee, B. W. Koo, J. H. Shin, E. J. Jeong, and L. S. Pu, “3.5: Invited paper: Recent progress in large sized & high performance organic TFT array,” SID Symposium Digest of Technical Papers, vol. 36, no. 1, pp. 23–25, 2005.
[8] H. Klauk, M. Halik, U. Zschieschang, G. Schmid, W. Radlik, and W. Weber, “High-mobility polymer gate dielectric pentacene thin film transistors,” Journal of Applied Physics, vol. 92, no. 9, pp. 5259–5263, 2002.
[9] R. Schroeder, L. A. Majewski, and M. Grell, “A study of the threshold voltage in pentacene organic field-effect transistors,” Applied Physics Letters, vol. 83, no. 15, pp. 3201–3203, 2003.
[10] T. B. Singh, T. Meghdadi, S. Günes, N. Marjanovic, G. Horowitz, P. Lang, S. Bauer, and N. S. Sariciftci, “High-performance ambipolar pentacene organic field-effect transistors on poly(vinyl alcohol) organic gate dielectric,” Advanced Materials, vol. 17, no. 19, pp. 2315–2320, 2005.
[11] B. Singh, N. S. Sariciftci, J. G. Grote, and F. K. Hopkins, “Bio-organic-semiconductor-field-effect-transistor based on deoxyribonucleic acid gate dielectric,” Journal of Applied Physics, vol. 100, no. 2, 024514, 2006.
[12] C.-H. Wang, C.-Y. Hsieh, and J.-C. Hwang, “Flexible organic thin-film transistors with silk fibroin as the gate dielectric,” Advanced Materials, vol. 23, no. 14, pp. 1630–1634, 2011.
[13] C. W. Tang and S. A. VanSlyke, “Organic electroluminescent diodes,” Applied Physics Letters, vol. 51, no. 12, pp. 913–915, 1987.
[14] L. Abu-Sen, Environmental Stability Studies of an Organic Semiconductor, Ph.D. dissertation, The University of Manchester, Manchester, U.K., 2013.
[15] A. Tsumura, H. Koezuka, and T. Ando, “Macromolecular electronic device: Field-effect transistor with a polythiophene thin film,” Applied Physics Letters, vol. 49, no. 18, pp. 1210–1212, 1986.
[16] A. Facchetti, “Semiconductors for organic transistors,” Materials Today, vol. 10, no. 3, pp. 28–37, 2007.
[17] Z. Bao, A. J. Lovinger, and J. Brown, “New air-stable n-channel organic thin film transistors,” Journal of the American Chemical Society, vol. 120, no. 1, pp. 207–208, 1998.
[18] F. Ruiz Simões, G. Martins de Araújo, and M. A. Cardoso, “Conducting polymers and carbon-based materials in biosensor applications,” in Advances in Bioelectrochemistry, Volume 2: Biomimetic, Bioelectrocatalysis and Materials Interfaces. Cham, Switzerland: Springer, 2022, pp. 101–119.
[19] L. Luo, W. Huang, C. Yang, J. Zhang, and Q. Zhang, “Recent advances on π-conjugated polymers as active elements in high performance organic field-effect transistors,” Frontiers of Physics, vol. 16, no. 3, 33500, 2021.
[20] J. Edberg, Flexible and Cellulose-Based Organic Electronics, Ph.D. dissertation, Linköping University, Linköping, Sweden, 2017.
[21] H. Sirringhaus, N. Tessler, and R. H. Friend, “Integrated optoelectronic devices based on conjugated polymers,” Science, vol. 280, no. 5370, pp. 1741–1744, 1998.
[22] S. Han, Thermoelectric Polymer-Cellulose Composite Aerogels. Ph.D. dissertation, Linköping University, Linköping, Sweden, 2019.
[23] A. J. Heeger, S. Kivelson, J. R. Schrieffer, and W.-P. Su, “Solitons in conducting polymers,” Reviews of Modern Physics, vol. 60, no. 3, pp. 781–850, 1988.
[24] S. Stafström and K. Chao, “Soliton states in polyacetylene,” Physical Review B, vol. 29, no. 4, pp. 2255–2258, 1984.
[25] K. Wijeratne, Conducting Polymer Electrodes for Thermogalvanic Cells, Ph.D. dissertation, Linköping University, Linköping, Sweden, 2018.
[26] J. L. Brédas and G. B. Street, “Polarons, bipolarons, and solitons in conducting polymers,” Accounts of Chemical Research, vol. 18, no. 10, pp. 309–315, 1985.
[27] T.-H. Le, Y. Kim, and H. Yoon, “Electrical and electrochemical properties of conducting polymers,” Polymers, vol. 9, no. 4, 150, 2017.
[28] H. Sirringhaus, M. Bird, and N. Zhao, “Charge transport physics of conjugated polymer field-effect transistors,” Advanced Materials, vol. 22, no. 34, pp. 3893–3898, 2010.
[29] Y. Yamashita, J. Tsurumi, F. Hinkel, Y. Okada, J. Soeda, W. Zajączkowski, M. Baumgarten, W. Pisula, H. Matsui, K. Müllen, and J. Takeya, “Transition between band and hopping transport in polymer field-effect transistors,” Advanced Materials, vol. 26, no. 48, pp. 8169–8173, 2014.
[30] M. Kim, G. Tarsoly, D. Kwon, and S. Pyo, “Interfacial spreading for rapid formation of uniform gate dielectric layers on flat and curved substrates for organic devices,” Journal of Materials Chemistry C, vol. 13, no. 26, pp. 13206–13213, 2025.
[31] C. P. Pokhrel, Crystal Growth and Charge Carrier Transport in Liquid Crystals and Other Novel Organic Semiconductors, Ph.D. dissertation, Kent State University, Kent, OH, USA, 2009.
[32] J. Urbančič, “Perspective chapter: Charge transport in organic semiconductors－fundamentals and improvement methods,” in Organic Electronics－From Fundamentals to Applications. London, U.K.: IntechOpen, 2025.
[33] Y. Luo and A. J. Flewitt, “Revisiting multiple trapping and release charge transport in amorphous semiconductors exemplified by hydrogenated amorphous silicon,” Journal of Non-Crystalline Solids, vol. 654, 123436, 2025.
[34] A. Salleo, T. W. Chen, A. R. Völkel, Y. Wu, P. Liu, B. S. Ong, and R. A. Street, “Intrinsic hole mobility and trapping in a regioregular poly(thiophene),” Physical Review B, vol. 70, no. 11, 115311, 2004.
[35] W. Li and H. Kwok, “Conduction mechanisms in organic semiconductors,” in Encyclopedia of Nanotechnology. Dordrecht, The Netherlands: Springer, 2012, pp. 493–500.
[36] C. D. Dimitrakopoulos and P. R. L. Malenfant, “Organic thin film transistors for large area electronics,” Advanced Materials, vol. 14, no. 2, pp. 99–117, 2002.
[37] C. Reese, M. Roberts, M.-M. Ling, and Z. Bao, “Organic thin film transistors,” Materials Today, vol. 7, no. 9, pp. 20–27, 2004.
[38] B. Kumar, B. K. Kaushik, and Y. S. Negi, “Organic thin film transistors: Structures, models, materials, fabrication, and applications: A review,” Polymer Reviews, vol. 54, no. 1, pp. 33–111, 2014.
[39] M. Waldrip, O. D. Jurchescu, D. J. Gundlach, and E. G. Bittle, “Contact resistance in organic field-effect transistors: Conquering the barrier,” Advanced Functional Materials, vol. 30, no. 20, 1904576, 2020.
[40] C. Liu, Y. Xu, Y. Li, W. Scheideler, and T. Minari, “Critical impact of gate dielectric interfaces on the contact resistance of high-performance organic field-effect transistors,” The Journal of Physical Chemistry C, vol. 117, no. 23, pp. 12337–12345, 2013.
[41] Y. Shi, J. Liu, Y. Hu, W. Hu, and L. Jiang, “Effect of contact resistance in organic field-effect transistors,” Nano Select, vol. 2, no. 9, pp. 1661–1681, 2021.
[42] Y. Yamashita, “Organic semiconductors for organic field-effect transistors,” Science and Technology of Advanced Materials, vol. 10, no. 2, Art. no. 024313, 2009.
[43] J. Veres, S. Ogier, G. Lloyd, and D. de Leeuw, “Gate insulators in organic field-effect transistors,” Chemistry of Materials, vol. 16, no. 23, pp. 4543–4555, 2004.
[44] C.-A. Di, Y. Liu, G. Yu, and D. Zhu, “Interface engineering: An effective approach toward high-performance organic field-effect transistors,” Accounts of Chemical Research, vol. 42, no. 10, pp. 1573–1583, 2009.
[45] S. M. Sze and K. K. Ng, “Metal-semiconductor contacts,” in Physics of Semiconductor Devices, 3rd ed. Hoboken, NJ, USA: Wiley, 2007, ch. 3, pp. 134–196.
[46] W. L. Kalb and B. Batlogg, “Calculating the trap density of states in organic field-effect transistors from experiment: A comparison of different methods,” Physical Review B, vol. 81, no. 3, 035327, 2010.
[47] J. F. Martínez Hardigree and H. E. Katz, “Through thick and thin: Tuning the threshold voltage in organic field-effect transistors,” Accounts of Chemical Research, vol. 47, no. 4, pp. 1369–1377, 2014.
[48] A. Boubaker, B. Hafsi, K. Lmimouni, and A. Kalboussi, “A comparative TCAD simulations of a p- and n-type organic field effect transistors: Field-dependent mobility, bulk and interface traps models,” Journal of Materials Science: Materials in Electronics, vol. 28, no. 11, pp. 7834–7843, 2017.
[49] J. Zaumseil and H. Sirringhaus, “Electron and ambipolar transport in organic field-effect transistors,” Chemical Reviews, vol. 107, no. 4, pp. 1296–1323, 2007.
[50] Z. A. Lamport, H. F. Haneef, S. Anand, M. Waldrip, and O. D. Jurchescu, “Tutorial: Organic field-effect transistors: Materials, structure and operation,” Journal of Applied Physics, vol. 124, no. 7, 071101, 2018.
[51] H. Klauk, Ed., Organic Electronics: Materials, Manufacturing, and Applications. Weinheim, Germany: Wiley-VCH, 2006.
[52] J. Hwang, A. Wan, and A. Kahn, “Energetics of metal–organic interfaces: New experiments and assessment of the field,” Materials Science and Engineering: R: Reports, vol. 64, no. 1–2, pp. 1–31, 2009.
[53] S. Jakher and R. Yadav, “Organic thin film transistor review based on their structures, materials, performance parameters, operating principle, and applications,” Microelectronic Engineering, vol. 290, 112193, 2024.
[54] H. Ishii, K. Sugiyama, E. Ito, and K. Seki, “Energy level alignment and interfacial electronic structures at organic/metal and organic/organic interfaces,” Advanced Materials, vol. 11, no. 8, pp. 605–625, 1999.
[55] J. C. Scott and G. G. Malliaras, “Charge injection and recombination at the metal–organic interface,” Chemical Physics Letters, vol. 299, no. 2, pp. 115–119, 1999.
[56] J. Huang, Y. Mo, and Y. Yao, “Unified dynamic approach for simulating quantum tunneling and thermionic emission at metal-organic interfaces,” Physical Review Applied, vol. 15, no. 1, 014021, 2021.
[57] C. Liu, Y. Xu, and Y.-Y. Noh, “Contact engineering in organic field-effect transistors,” Materials Today, vol. 18, no. 2, pp. 79–96, 2015.
[58] M. Aghamohammadi, R. Rödel, U. Zschieschang, C. Ocal, H. Boschker, R. T. Weitz, E. Barrena, and H. Klauk, “Threshold-voltage shifts in organic transistors due to self-assembled monolayers at the dielectric: Evidence for electronic coupling and dipolar effects,” ACS Applied Materials & Interfaces, vol. 7, no. 41, pp. 22775–22785, 2015.
[59] C. Wang, W.-Y. Lee, D. Kong, R. Pfattner, G. Schweicher, R. Nakajima, C. Lu, J. Mei, T.-H. Lee, H.-C. Wu, J. Lopez, Y. Diao, X. Gu, S. Himmelberger, W. Niu, J. R. Matthews, M. He, A. Salleo, Y. Nishi, and Z. Bao, “Significance of the double-layer capacitor effect in polar rubbery dielectrics and exceptionally stable low-voltage high transconductance organic transistors,” Scientific Reports, vol. 5, 17849, 2015.
[60] J. Wu, “Understanding the electric double-layer structure, capacitance, and charging dynamics,” Chemical Reviews, vol. 122, no. 12, pp. 10821–10859, 2022.
[61] M. Kitamura and Y. Arakawa, “pentacene-based organic field-effect transistors,” Journal of Physics: Condensed Matter, vol. 20, no. 18, 184011, 2008.
[62] H. Klauk, “Organic thin-film transistors,” Chemical Society Reviews, vol. 39, no. 7, pp. 2643–2666, 2010.
[63] C. Celle, C. Suspène, M. Ternisien, S. Lenfant, D. Guérin, K. Smaali, K. Lmimouni, J. P. Simonato, and D. Vuillaume, “Interface dipole: Effects on threshold voltage and mobility for both amorphous and poly-crystalline organic field effect transistors,” Organic Electronics, vol. 15, no. 3, pp. 729–737, 2014.
[64] T. D. Tsai, J. W. Chang, T. C. Wen, and T. F. Guo, “Manipulating the hysteresis in poly(vinyl alcohol)-dielectric organic field-effect transistors toward memory elements,” Advanced Functional Materials, vol. 23, no. 34, pp. 4206–4214, 2013.