本論文研究光致有機薄膜電晶體的電流增益效應，與光寫入非揮發性有機薄膜記憶體之應用。本研究所使用n型有機薄膜電晶體(Organic thin-film transistors, OTFT)是以自行合成的十三烷基駢苯衍生物(N,N’-ditridecyl-3,4,9,10-perylene tetracarboxylic diimide, PTCDI-C13H27)作為半導體主動層材料，並使用聚4-乙烯基吡啶[Poly(4-vinylphenol), PVP]與聚(三聚氰胺-co-甲醛)甲醇[Poly(melamine-co-formaldehude), PMF]濃度比例為12:4 wt%的交聯聚4-乙基苯酚[Cross-Linked poly(4-vinylphenol), C-PVP]當作介電層，量測元件通道照射雷射前後OTFT的電特性變化及研究光寫入有機記憶體元件的特性。
本實驗分為兩部分，第一部分的研究為比較532 nm綠光雷射及633 nm紅光雷射照射元件通道時，對具C-PVP/SiO2介電層與僅具SiO2介電層OTFT元件電特性的差異。結果顯示532 nm綠光雷射對具C-PVP/SiO2介電層的OTFT元件具有電流增益效應。在進一步比較元件通道未照光與照射532 nm綠光雷射的OTFT元件電特性後發現，元件通道照射532 nm綠光雷射後會使元件Ion電流上升、次臨界擺幅(Subthreshold swing, S.S.)變大、臨界電壓(Threshold voltage, VT)變小及載子遷移率(Mobility, µ)上升，且可維持長時間的電流增益效應，此效應直到1至3天左右的時間才回復至初始電特性，而元件通道照射633 nm紅光雷射則無此效果。此外，實驗發現無使用C-PVP為介電層(亦即只使用SiO2為介電層)的OTFT元件，不論元件通道照射532 nm綠光雷射或633 nm紅光雷射均無電流增益的效果。這個結果是因為PTCDI-C13H27的吸收光譜主要吸收帶在532 nm附近，而633 nm吸收效果較差；經推測532 nm綠光雷射可使具C-PVP/SiO2介電層的OTFT元件在PTCDI-C13H27與C-PVP的界面因物理或化學環境的改變造成長時間的緩遲效應產生暫穩態(Metastable)的激發能階，而這能階是屬於長生命週期的能階致使電流增益能維持極長的時間，若僅具SiO2介電層的OTFT元件則無法產生暫穩態(Metastable)的激發能階，因此無電流增益的現象，故具C-PVP/SiO2介電層的OTFT元件照射532 nm綠光雷射後可提升元件電特性。而軟性電子為目前有機電子研究趨勢，因此本研究亦製作OTFT元件於polyether sulfone (PES)軟性基板上，再比較不同半導體層膜厚的元件其通道照射532 nm綠光雷射之電性變化，經研究發現半導體層膜厚為60 nm的元件，其通道在照光後電流增益量為最大，推測是因為半導體厚度增加使電阻率提高造成IDS電流下降及厚度增加使光吸收效率提高造成IDS電流上升的平衡結果。
第二部分將本研究第一部分具C-PVP介電層OTFT元件應用於光記憶體元件，並觀察元件通道照射532 nm綠光雷射以不同光強度及不同照射時間下的電特性差異。本研究發現隨著光強度愈大、照射時間愈久，半導體層內產生的電子電洞對愈多，使元件VT變愈小、VT位移愈大及Ion電流上升愈多、S.S.變化愈大等。在532 nm綠光雷射強度為15.29 mW/cm2照射元件通道兩分鐘，光寫入的載子使VT變小3到5 V，而記憶體的清除是以施加偏壓應力的方式將被寫入的載子清除，因此本實驗發現施加偏壓150 V時間持續10秒可完全清除光寫入的載子達到記憶體之功效。

Photo-induced current enhancement in organic thin-film transistors (OTFTs) and the application of OTFTs in optical writing for non-volatile memory were studied. The OTFT comprises organic semiconductor N,N’-ditridecyl-3,4,9,10-perylene tetracarboxylic diimide (PTCDI-C13H27) and organic dielectric cross-linked poly(4-vinylphenol) (C-PVP) in which the PVP blends with poly(melamine-co-formaldehyde) (PMF) at a weight ratio of 12:4. The electrical characteristics of OTFTs with and without light illumination and the optical assistant memory were measured.
In the first part, wavelength 532 and 633 nm lasers were used to irradiate OTFTs with and without a C-PVP dielectric layer. For devices with a C-PVP dielectric layer, the light-on current (Ion), subthreshold swing, and carrier mobility increased under irradiating wavelength 532 nm light, whereas the threshold voltage (VT) decreased. This irradiation effect can be sustained for 1 to 3 days and then recovered its initial state, indicating that a metastable state existed at the interface of PTCDI-C13H27 and C-PVP. The metastable excitation energy level would enhance the Ion of the devices and had a long lifetime to maintain Ion for a long time. In contrast, the electrical characteristics of the devices were almost unchanged at the condition of illumination with light of wavelength 633 nm. On the other hand, the effect of the current enhancement was not observed for devices without a C-PVP dielectric layer irradiated with the both lights. This is due to the main absorbance of PTCDI-C13H27 located at the neighbor of 532 nm band; however, the 633 nm wavelength of exciting light is in the tail of the absorption spectrum. Accordingly, the electrical characteristics of OTFTs can be improved by irradiating with a 532 nm light. Moreover, the OTFTs are the potential canidates in flexible electronics. Our organic devices were fabricated on polyether sulfone substrate to investigate the electrical characteristics for various semiconductor layer thicknesses under irradiating with the 532 nm laser. The device with a semiconductor layer thickness of 60 nm shows the highest current gain at illuminating condition. Although the absorption increases with increasing the thickness of active layer, the drain current decreases owing to the increase of resistance.
In the second part, OTFT devices with a C-PVP dielectric layer were applied in the field of optical memory. The light-on electrical characteristics at various light intensities and exposure times were studied. The semiconductor layer generated more electron-hole pairs when increasing the light intensity and the exposure time. The more electron-hole pairs would lead to the negative VT shift. For a laser irradiation intensity of 15.29 mW/cm2 and an exposure time of two minutes, optic-induced writing carriers generated a VT in the range between 3 and 5 V. The optical carriers can be erased by abias stress. of 150V for 10 seconds. This work shows that our OTFT can be used as a memory device.

[1]. M. H. Choi, B. S. Kim, and J. Jang, “High-Performance Flexible TFT Circuits Using TIPS Pentacene and Polymer Blend on Plastic”, IEEE Electron, 33, 11 (2012)
[2]. F. Yakuphanoglu,W. A. Farooq, “Flexible pentacene organic field-effect phototransistor ”, Org. Electronic, 161, 379 (2011)
[3]. P. Cosseddu, G. Tiddia, S. Milita, A. Bonfiglio, “Continuous tuning of the mechanical sensitivity of Pentacene OTFTs on flexible substrates: From strain sensors to deformable transistors”, Org. Electronic, 14, 206 (2013)
[4]. G. Horowitz, “Organic Field-Effect Transistors”, Adv. Mater., 10, 368 (1998)
[5]. H. Yan, Y. Zheng, R. Blache, C. Newman, S. Lu, J. Woerle, and A. Facchetti, “Solution Processed Top-Gate n-Channel Transistors and Complementary Circuits on Plastics Operating in Ambient Conditions”, Adv. Mater., 20, 3393 (2008)
[6]. B. Crone, A. Dodabalapur, Y.-Y. Lin, R. W. Filas, Z. Bao, A. LaDuca, R. Sarpeshkar, H. E. Katz and W. Li, “Large-scale complementary integrated circuits based on organic transistors”, Nature, 403, 521 (2000)
[7]. C.-F. Sung, D. Kekuda, L. F. Chu, F.-C. Chen, S.-S. Cheng, Y.-Z. Lee, M.-C. Wu, C.-W. Chu, “Hybrid TiOx/fluoropolymer bi-layer dielectrics for low-voltage complementary inverters”, Org. Electronic, 11, 154 (2010)
[8]. S. Ju, J. Li, J. Liu, P.-C. Chen, Y.-G. Ha, F. Ishikawa, H. Chang, C. Zhou, A. Facchetti, D. B. Janes and T. J. Marks, “Transparent Active Matrix Organic Light-Emitting Diode Displays Driven by Nanowire Transistor Circuitry”, Nano Lett., 8, 997 (2008)
[9]. T. W. Kelley, P. F. Baude, C. Gerlach, D. E. Ender, D. Muyres, M. A. Haase, D. E. Vogel and S. D. Theiss, “Recent Progress in Organic Electronics: Materials, Devices, and Processes”, Chem. Mater., 16, 4413 (2004)
[10]. C. D. Dimitrakopoulos and P. R. L. Malenfant, “Organic Thin Film Transistors for Large Area Electronics”, Adv. Mater., 14, 99 (2002)
[11]. G. Guillaud, M. A. Sadound, M. Maitrot, “Field-effect transistors based on intrinsic molecular semiconductors”, Chem. Phys. Lett., 167, 503 (1990)
[12]. D. Shukla, S. F. Nelson, D. C. Freeman, M. Rajeswaran, W. G. Ahearn, D. M. Meyer, and J. T. Carey, “Thin-Film Morphology Control in Naphthalene-Diimide-Based Semiconductors: High Mobility n-Type Semiconductor for Organic Thin-Film Transistors”, Chem. Mater., 20, 7486 (2008)
[13]. A. R. Brown, D. M. de Leeuw, E. J. Lous, E. E. Havinga, “Organic N-Type Field-Effect Transistor”, Synth. Met., 66, 257 (1994)
[14]. A. Facchetti, J. Letizia, M.-H. Yoon, M. Mushrush, H. E. Katz, and T. J. Marks, “Synthesis and Characterization of Diperfluorooctyl-Substituted Phenylene-Thiophene Oligomers as n-Type Semiconductors. Molecular Structure-Film Microstructure-Mobility Relationships,Organic Field-Effect Transistors, and Transistor Nonvolatile Memory Elements”, Chem. Mater., 16, 4715 (2004)
[15]. J. G. Laquindanum, H. E. Katz, A. Dodabalapur, and A. J. Lovinger, “n-Channel Organic Transistor Materials Based on Naphthalene Frameworks”, J. Am. Chem. Soc., 118, 11331 (1996)
[16]. J. R. Ostrick, A. Dodabalapur, L. Torsi, A. J. Lovinger, E. W. Kwock, T. M. Miller, M. Galvin, M. Berggren, and H. E. Katz, “Conductivity-type anisotropy in molecular solids ” , J. Appl. Phys., 81, 6804 (1997)
[17]. R. J. Chesterfield, J. C. McKeen, C. R. Newman, P. C. Ewbank, D. A. da S. Filho, J.-L. Brédas, L. L. Miller, K. R. Mann, C. D. Frisbie, “Organic thin film transistors based on N-alkyl perylene diimides: Charge transport kinetics as a function of gate voltage and temperature”, J. Phys. Chem. B., 108, 19281 (2004)
[18]. S. Tatermichi, M. Ichikawa, T. Koyama, Y. Taniguchi, “High mobility n-type thin-film transistors based on N,N’-ditridecyl perylene diimide with thermal treatments”, Appl. Phys. Lett., 89, 112108 (2006)
[19]. J. H. Oh, S. Liu, Z. Bao, R. Schmidt, F. Wurthner, “Air-stable n-channel organic thin-film transistors with high field-effect mobility based on N,N’-bis(heptafluorobutyl) 3,4:9,10-perylene diimide”, Appl. Phys. Lett., 91, 212107 (2007)
[20]. H. G. Jeon, et al. , “Thermal treatment effects on N-alkyl perylene diimide thin-film transistors with different alkyl chain”, J. Appl. Phys., 108, 124512 (2010)
[21]. J. Kastner, J. Paloheimo, H. Kuzmany, “Conduction mechanisms in doped thin film of C60 and C60/70”, Science Metals, 55, 3185 (1993)
[22]. R. C. Haddon, A. S. Perel, R. C. Morris, T. T. M. Palstra, A. F. Herbard, R. M. Fleming, “C-60 Thin-Film Transistors”, Appl. Phys. Lett., 67, 121 (1995)
[23]. G. Horowitz, F. Kouki, P. Spearman, D. Fichou, C. Nogues, X. Pan and F. Garnier, “Evidence for n-Type Conduction in a Perylene Tetracarboxylic Diimide Derivative” , Adv. Mater., 8, 242 (1996)
[24]. E. Karmann, J.-P. Meyer, D. Schlettwein, N. I. Jaeger, M. Anderson,A. Schmidt, N. R. Armstrong, “Photoelectrochemical effects and (photo)conductivity of 'N-type' phthalocyanines”, Mol. Cryst. Liq. Cryst., 283, 283 (1996)
[25]. H. E. Katz, J. Johnson, A. J. Lovinger, and W. Li, “Naphthalenetetracarboxylic Diimide-Based n-Channel Transistor Semiconductors: Structural Variation and Thiol-Enhanced Gold Contacts”, J. Am. Chem. Soc., 122, 7877 (2000)
[26]. Z. Wei, H. Xi, H. Dong, L. Wang, W. Xu, W. Hu, D. Zhu, “Blending induced stack-ordering and performance improvement in a solution-processed n-type organic field-effect transistor ” , J. Mater. Chem., 20, 1203 (2009)
[27]. J. Youn, G. R. Dholakia, H. Huang, J. W. Hennek, A. Facchetti, and T. J. Marks, “Infl uence of Thiol Self-Assembled Monolayer Processing on Bottom-Contact Thin-Film Transistors Based on n-Type Organic Semiconductors”, Adv. Funct. Mater., 22, 1856 (2012)
[28]. Z. Yan, B. Sun and Y. Li, “Novel stable (3E,7E)-3,7-bis(2-oxoindolin-3-ylidene)-benzo[1,2-b:4,5-b0]difuran-2,6(3H,7H)-dione based donor–acceptor polymer semiconductors for n-type organic thin film transistors”, Chem. Commun., (2013)
[29]. A. Facchetti, M. H. Yoon, T. J. Marks, “Gate Dielectrics for Organic Field-Effect Transistors: New Opportunities for Organic Electronics”, Adv. Mater., 17, 1705 (2005)
[30]. C. R. Newman, C. D. Frisbie, D. A. da Silva Filho, J.-L.
Bredas, P. C. Ewbank, K. R. Mann, “Introduction to Organic Thin
Film Transistors and Design of n-Channel Organic Semiconductors”, Chem. Mater., 16, 4436 (2004)
[31]. D. R.T. Zahn, T. U. Kampen, H. Me´ndez, “Transport gap of organic semiconductors in organic modified Schottky contacts”, Applied Surface Science, 212-213, 423 (2003)
[32].林益生，以烷基駢苯衍生物作為主動層之有機薄膜電晶體，國立成功大學碩士論文 (2008)
[33].郭凌伶，可撓式n型有機薄膜電晶體於光偵測器之應用，國立成功大學碩士論文(2012)
[34]. C. Rolin, K. Vasseur, S. Schols, M. Jouk, G. Duhoux, “High mobility electron-conducting thin-film transistor by organic vapor phase deposition”, Appl. Phys. Lett., 93, 033305 (2008)
[35]. L. Resendiz, M. Estrada, A. Cerdeira, B. Iniguez c, M.J. Deen, “Effect of active layer thickness on the electrical characteristics
of polymer thin film transistors”, Org. Electronic, 11, 1920 (2010)
[36]. Y.-Y. Noh, D.-Y. Kim, and K. Yase, “Highly sensitive thin-film organic phototransistors: Effect of wavelength of light source on device performance”, J. Appl. Phys., 98, 074505 (2005)
[37]. C. Feng, T. Mei, X. Hu, N. Pavel, “A pentacene field-effect transistor with light-programmable threshold voltage”, Org. Electronic, 11, 1713 (2010)
[38]. C. H. Kim, S. H. Kim, S. H. Lee, S. H. Han, M. H. Choi, “Bimolecular recombination in solution-processed 6, 13- bis(pentylphenylethynyl) pentacene thin-film transistor”, Appl. Phys. Lett., 94, 083308 (2009)