本論文之主要目的是探討運用微接觸壓印技術與旋轉塗佈法沉積量子點(QDs)薄膜於有機光記憶體薄膜電晶體之研究。量子點在元件中扮演載子捕獲的重要角色，比較利用此兩種方法沉積量子點之元件在光照下之電流變化量與臨界電壓偏移幅度，並從中探討適合做為光記憶體薄膜電晶體之元件結構。
在本研究中的壓印方式上，運用聚二甲基矽氧烷(PDMS)製作壓印所需之印章，將量子點旋轉塗佈於PDMS印章上，隨後利用砝碼以及浸鍍機兩種方式將其轉印於介電層材料上，而浸鍍機壓出之量子點具有良好之分佈及均勻性，因此選用此方式轉印量子點並製作出元件。我們採用n+型矽(閘極電極)/氧化矽(介電層)/並五苯(通道層)/金(源極及汲極電極)為基礎，於介電層與通道層中壓印量子點，發現當元件具量子點結構時，其輸出及轉移特性曲線量測上之電流在照光下增加幅度較基礎結構明顯，臨界電壓偏移幅度亦較大。在磁滯測試中，記憶空窗從傳統結構的9 V提升至101 V，顯示出利用壓印法轉印量子點於介電層上之結構具有做為一般記憶體元件之潛力。然而此兩種元件於白光或特定波長照射下，其電流並無增加之趨勢，並逐步減少，甚至低於初始狀態。因此我們採用浮動閘極之結構，進而改善以上缺點。
於本研究中之旋轉塗佈法上，其結構為n+型矽(閘極電壓)/氧化矽(介電層)/量子點與聚甲基丙烯酸甲酯混合層(浮動閘極)/聚甲基丙烯酸甲酯(穿隧層)/並五苯(通道層)/金(源極及汲極層)，其中浮動閘極層與穿隧層皆使用旋轉塗佈法形成薄膜。電性量測上，元件之電流增加幅度與臨界電壓偏移量於照光後，皆隨著元件之量子點濃度增加而變大，記憶空窗以及動態響應(dynamic response)亦具有相同趨勢。尤其白光下動態響應的電流在濃度為20 mg/ml 量子點與聚甲基丙烯酸甲酯混合層為浮動閘極之元件時上升134.7 倍，不同光波長照射下電流也有明顯上升之情形，並且此濃度之元件亦具備「照光寫入，偏壓做抹除」的特性，可被視為光記憶體薄膜電晶體。由於有聚甲基丙烯酸甲酯做為阻擋層，使得關燈後被量子點捕捉的電子不易回到通道層與電洞復合，因此電流得以維持一段時間不回到初始狀態。根據原子力顯微鏡量測的結果，表面粗糙度在旋轉塗佈聚甲基丙烯酸甲酯後大幅度減少至1.5 nm 以下，對於之後並五苯的成長及元件特性具有正面影響。

The main purpose of this thesis was focused on the deposition of quantum dots (QDs) thin film in organic optical memory thin film transistors by micro-contact printing technique and spin coating method. The QDs plays an important role in capturing the charge carriers in the transistor device. We compared the current increment and threshold voltage shift under illumination condition of the devices which were deposited QDs by these two methods. And investigated which of these device structures is more suitable for optical memory thin film transistors application.
In the study of contact printing method, we used polydimethylsiloxane (PDMS) as the stamps. After spin coating the QDs on the PDMS stamp, the QDs were transfer onto the dielectric layer by means of using counterweight and dip coater, respectively. Because of the better distribution and uniformity of QDs monolayers which were printed by dip coater, we chose contact printing technique to transfer QDs by using dip coater to fabricate the devices. The basic structure was composed by n+-Si (gate electrode) / SiO2 (dielectric later) / pentacene (channel layer) / Au (source and drain electrodes). After transferring QDs between dielectric layer and channel layer, the device with QDs showed more obvious current increment and threshold voltage shift under illumination than conventional structure in the measurements of output and transfer characteristics. For the hysteresis test, the memory window could be increased from 9 V of conventional structure to 101 V of the device with QDs. This large memory window indicated that the structure using contact printing technique to transfer QDs on dielectric layer had the potential to be used for memory devices application. However, both structures showed poor characteristics, i.e. under illumination of white light or different wavelengths of light, the currents didn’t increase as expected but declined to even lower than the initial state. As the result, we investigated floating gate structure to improve this disadvantage.
In the study of spin coating technique, the structure was n+-Si (gate electrode) / SiO2 (dielectric layer) / QDs-PMMA blends (floating gate) / PMMA (tunneling layer) / pentacene (channel layer) / Au (source and drain electrodes). Among the device structure, the films of floating gate and tunneling layer were formed by spin coating method. In electrical measurement, the current increment and threshold voltage shift under illumination were increased by the increasing concentrations of QDs of the devices. Memory windows and dynamic responses also showed identical tendencies, especially for the dynamic response under white light illumination, the current increased by 134.7 times for the device using QDs-PMMA blends (with 20 mg/ml QDs)as floating gate. And current under illumination of different wavelengths of lights also had obvious increments. In addition, the device with QDs-PMMA blends (with 20 mg/ml QDs) demonstrated the properties of “optical-writing” and “electrical-erasing”, as a result, it can be viewed as an optical memory thin film transistor. Due to the PMMA layer was used as blocking layer, after turning off the light, electrons were trapped by QDs and difficult to be transferred to the active layer and recombined with holes. Therefore, the current could maintain for a period of time and didn’t decline to the initial state. According to the results of atomic force microscopy (AFM) measurement, after spinning PMMA as modified layer, the Rrms could be reduced under 1.5 nm which was benefit to the growth of pentacene layer and device performance.

[1] Q. D. Linga, D. J. Liawb, C. X. Zhuc, Daniel S. H. Chanc, E. T. Kanga, K. G. Neoh, “Polymer electronic memories: Materials, devices and mechanisms”, Progress in Polymer Science, 33, 917-978 (2008)
[2] A. Tsumura, H. Koezuka and T. Ando, “Macromolecular electronic device: Field‐effect transistor with a polythiophene thin film”, Appl. Phys. Lett., 49, 1210 (1986)
[3] Rogers, J. A., et al., “Paper-like electronic displays: Large-area rubber-stamped plastic sheets of electronics and microencapsulated electrophoretic inks”, Proc. Nat. Acad. Sci. USA, 98, 4835 (2001)
[4] Gelinck, G. H., et al., “Flexible active-matrix displays and shift registers based on solution-processed organic transistors”, Nat. Mater. 3, 106 (2004)
[5] Sheraw, C. D., et al., “Organic Thin-Film Transistor-Driven Polymer-Dispersed Liquid Crystal Displays on Flexible Polymeric Substrates”, Appl. Phys. Lett. 80, 1088 (2002)
[6] Zhu, Z.-T., et al., “Humidity sensors based on pentacene thin-film transistors”, Appl. Phys. Lett. 81, 4643 (2002)
[7] Crone, B. K., et al., “Organic oscillator and adaptive amplifier circuits for chemical vapor sensing”, J . Appl. Phys. 91 (12), 10140 (2002)
[8] Voss, D., “Cheap and cheerful circuits”, Nature 407, 442 (2000)
[9] Baude, P. F., et al., “Pentacene-based radio-frequency identification circuitry”, Appl. Phys. Lett. 82, 3964 (2003)
[10] (a) https://www.itri.org.tw/chi/content/search/Search.aspx?SiteID=1&keyword=e+pa
per
(b) http://harryshpauto.com/2012/08/flat-screen-tv-giveaway/
(c) http://www.answers.com/Q/What_is_a_tft_sensor
(d) http://nanotechweb.org/cws/article/tech/35130
(e) http://www.linkasia.com.tw/RFID-1.html
[11] Colin Reese, Mark Roberts, Mang-mang Ling, Zhenan Bao,”Organic thin film transistors”, materialstoday
[12] M. Debucquoy, S. Verlaak, S. Steudel, K. Myny, J. Genoe, ,P. Heremans, “Correlation between bias stress instability and phototransistor operation of pentacene thin-film transistors,” Appl. Phys. Lett., 91, 103-508 (2007)
[13] Y. Guo, C. Du, C.-A. Di, J. Zheng, X. Sun, Y. Wen, L. Zhang, W. Wu, G. Yu, Y. Liu, “Field dependent and high light sensitive organic phototransistors based on linear asymmetric organic semiconductor,” Appl. Phys. Lett., 94, 143303 (2009).
[14] 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, 074-505 (2005)
[15] Hu, Yan, Dong, Guifang ; Liu, Chen ; Wang, Liduo ; Qiu, Yong, ”Dependency of organic phototransistor properties on the dielectric layers”, Appl. Phys. Lett., 89, 072108 (2006)
[16] Y. Guo, C. Du, C.-A. Di, J. Zheng, X. Sun, Y. Wen, L. Zhang, W. Wu, G. Yu, Y. Liu, “Field dependent and high light sensitive organic phototransistors based on linear asymmetric organic semiconductor,” Appl. Phys. Lett., 94, 143303 (2009).
[17] Wei Wang, Dongge Ma,” Light response characteristics of organic thin-film transistors with and without a P(MMA–GMA) modification layer,” Semicond. Sci. Technol., 25, 115009 (2010)
[18] Hsiao-Wen Zan, Shih-Chin Kao, Shiang-Ruei Ouyang,” Pentacene-Based Organic Phototransistor With High Sensitivity to Weak Light and Wide Dynamic Range,” IEEE ELECTRON DEVICE LETTERS, 31, (2010)
[19] (a) http://www.bizrice.com/products/Digital-Optical-Audio.html
(b) http://www.made-in-china.com/showroom/appletn/product-detailPboxBMvhZTUq
/China-Infrared-Sensor-Double-.html
(c) http://www.testo.com.au/en/home/products_1/product_details.jsp?productNo=05
60+0540
[20] Khairul Anuar Mohamad, Keisuke Goto, Katsuhiro Uesugi, Hisashi Fukuda, “Poly(3-hexylthiophene)/Fullerene Organic Thin-Film Transistors: Investigation of Photoresponse and Memory Effects,” Jpn. J. Appl. Phys., 49, (2010)
[21] T. H. Kim, K. S. Cho, E. K. Lee, S. J. Lee, J. W. Kim, D. H. Kim, J. Y. Kwon, G. Amaratunga, S. Y. Lee, B. L. Choi, Y. Kuk, J. M. Kim, and K. Kim, “Full-color quantum dot displays fabricated by transfer printing”, Nature Photonics, 5 (2011)
[22] Ugo Russo, Deepak Kamalanathan, Daniele Ielmini, Andrea L. Lacaita, and Michael N. Kozicki, “Study of Multilevel Programming in Programmable Metallization Cell (PMC) Memory”, IEEE TRANSACTIONS ON ELECTRON DEVICES, 56, MAY (2009)
[23] https://quimicosonador.wordpress.com/tag/qd/
[24] Sheung Man Mok, Feng Yan, and Helen L. W. Chan, ” Organic phototransistor based on poly(3-hexylthiophene)/TiO2nanoparticle composite”, Appl. Phys. Lett., 93, 023310 (2008)
[25] Michael C. Hamilton, Sandrine Martin, and Jerzy Kanicki, “Thin-Film Organic Polymer Phototransistors”, IEEE TRANSACTIONS ON ELECTRON DEVICES, 51, JUNE (2004)
[26] K. S. Narayan and N. Kumar, “Light responsive polymer field-effect transistor”, Appl. Phys. Lett. 79, 1891 (2001)
[27] N. Marjanovic, T. B. Singh, G. Dennler, S. Gunes, H. Neugebauer, N. S.Sariciftci, R. Schwodiauer, and S. Bauer, ” Photoresponse of organic field-effect transistors based on conjugated polymer/fullerene blends”, Org. Electron. 7, 188 (2007)
[28] Yamada I, Takagi K, Hayashi Y, Soga T, Shibata N, Toru T, “Poly[(3-hexylthiophene)-block-(3-semifluoroalkylthiophene)] for Polymer Solar Cells”, Int J Mol Sci (2010)
[29] Dan Kolb “Pentacene-based organic transistors”
[30] G. Horowitz, “Organic Field-Effect Transistor,” Adv. Mater., 10, 365377, January (1998)
[31] C. D. Dimitrakopoulos, P. R. L. Malenfant, “Organic Thin-Film Transistors for Large Area Electronics,” Adv. Mater., 14, 99117, January (2002)
[32] Kline, R. J. McGehee, M. D. Kadnikova, E. N. Liu, J. Frechet, J. M. J., “Controlling the field‐effect mobility of regioregular polythiophene by changing the molecular weight,” Adv. Mater. 15, 1519 (2003)
[33] Sirringhaus, H. Brown, P. J. Friend, R. H. Nielsen, M. M. Bechgaard, K.; Langeveld-Voss, B. M. W. Spiering, A. J. H. Janssen, R. A. J.; Meijer, E. W. Herwig, P. De Leeuw, D. M., “Two-dimensional charge transport in self-organized, high-mobility conjugated polymers,” Nature (London) 401, 685 (1999)
[34] Bao, Z., Dodabalapur, A, Lovinger, A. J., “Soluble and processable regioregular poly (3‐hexylthiophene) for thin film field‐effect transistor applications with high mobility,” Appl. Phys. Lett. 69, 4108 (1996)
[35] Sirringhaus, H.; Tessler, N.; Friend, R. H., “Integrated optoelectronic devices based on conjugated polymers,” Science 280, 1741 (1998)
[36] Wang, G.; Swensen, J.; Moses, D.; Heeger, A. J., “Increased mobility from regioregular poly (3-hexylthiophene) field-effect transistors,” J. Appl. Phys. 93, 6137 (2003)
[37] Chen-Chia Chen, Mao-Yuan Chiu, Jeng-Tzong Sheu, and Kung-Hwa Wei, ” Photoresponses and memory effects in organic thin film transistors incorporating poly (3-hexylthiophene)/CdSe quantum dots”, Appl. Phys. Lett. 92, 143105 (2008)
[38] Rozalina Zakaria, Woon Kai Lin, and Chua Chong Lim, ” Plasmonic Enhancement of Gold Nanoparticles in Poly(3-hexylthiophene) Organic Phototransistor”, Applied Physics Express, 5, 082002 (2012)
[39] A. S. Sedra, & K. C. Smith. “Microelectronic Circuit” 4th edition (354-366), Oxford University Press. (1997)
[40] Brijesh Kumar, B. K. Kaushik, Y. S. Negi and Poornima Mittal, “Characteristics and Applications of Polymeric Thin Film Transistor: Prospects and Challenges”, Proceedings of ICETECT (2011)
[41] K. P. Pernstich, S. Haas, D. Oberhoff, C. Goldmann, D. J. Gundlach, B. Batlogg, A. N. Rashid, G. Schitter, “ Threshold voltage shift in organic field effect transistors by dipole monolayers on the gate insulator”, Journal of Applied Physics, 96, 11 (2004)
[42] Y. L. Guo, Y. Q. Liu, C. A. Di, G. Yu, W. P. Wu, S. H. Ye, Y. Wang, X. J. Xu, Y. M. Sun, “Tuning the threshold voltage by inserting a thin molybdenum oxide layer into organic field-effect transistors”, Applied Physics Letter, 91, 263502 (2007)
[43] D. J. Gundlach, L. L. Jia, and T. N. Jackson, “Pentacene TFT with improved linear region characteristics using chemically modified source and drain electrodes”, IEEE Electron Device Letters, 22, 12 (2001)
[44] S. T. Han, Y. Zhou, Z. X. Xu, L. B. Huang, X. B. Yang and V. A. L. Roy, “Microcontact printing of ultrahigh density gold nanoparticle monolayer for flexible flash memories”, Adv. Mater., 24, 3556 (2012)
[45] M. Y. Chiua, C. C. Chen, J. T. Sheub and K. H. Wei, “An optical programming/electrical erasing memory device : Organic thin film transistors incorporating core/shell CdSe@ZnSe quantum dots and poly(3-hexylthiophene)”, Org. Electron., 10, 769 (2009)
[46] W. Wang and D. G. Ma, “Nonvolatile memory effect in Organic Thin-Film Transistors based on aluminum nanoparticle floating gate”, Chinese Physics Letters, 27, 018503 (2010)
[47] X. C. Ren, S. M. Wang, C. W. Leung, F. Yan and P. K. L. Chan, “Thermal anneling and temperature dependences of memory effect in organic memory transistor”, Appl. Phys. Lett., 99, 043303 (2011)
[48] M. F. Mabrook, Y. Yun, C. Pearson, D. A. Zeze, and M. C. Petty, “A pentacene-based organic thin film memory transistor”, Appl. Phys. Lett., 94, 173302 (2009)
[49] Z. Liu, F. Xue, Y. Su, Y. M. Lvov and K. Varahramyan, “Memory Effect of a Polymer Thin-Film Transistor With Self-Assembled Gold Nanoparticles in the Gate Dielectric”, IEEE Transactions on Nanotechnology, 5, 379 (2006)
[50] S. Paul, C. Pearson, A. Molloy, M. A. Cousins, M. Green, S. Kolliopoulou, P. Dimitrakis, P. Normand, D. Tsoukalas and M. C. Petty, “Langmuir-Blodgett Film Deposition of Metallic Nanoparticles and Their Application to Electronic Memory Structures”, Nano Letters, 3, 533 (2003)
[51] Marko Marinkovic, Dagmawi Belaineh, Veit Wagner and Dietmar Knipp, “On the Origin of Contact Resistances of Organic Thin Film Transistors”, Adv. Mater., 24, 40054009 (2012)
[52] J. Jang, S.H. Han, “Lifetime of organic thin-film transistors with organic passivation layers”, Current Applied Physics, 6S1, e17–e21 (2006)
[53] P.V. Necliudov, M.S. Shur, D.J. Gundlach, T.N. Jackson, “Contact resistance extraction in pentacene thin film transistors”, Solid State Electron., 47, 259 (2003)
[54] L. A. Kim, P. O. Anikeeva, S. A. Coe-Sullivan, J. S. Steckel, M. G. Bawendi and V. Bulovic, “Contact Printing of Quantum Dot Light-Emitting Devices”, Nano. Letters, 8, 4513 (2008)
[55] Y. Yun, C. Pearson, and M. C. Petty, “ Pentacene thin film transistors with a poly,,methyl methacrylate gate dielectric : Optimization of device performance”, Journal of Applied Physics, 105, 034508 (2009)
[56] B. M. Dhar, R. Ozgun, T. Dawidczyk, A. Andreou, H. E. Katz, “Threshold voltage shifting for memory and turning in printed transistor circuits”, Materials Science and Engineering R, 72, 49 (2011)
[57] Y. C. Chen, C. Y. Huang, H. C. Yu, and Y. K. Su, ” Nonvolatile memory thin film transistors using CdSe/ZnS quantum dotpoly(methyl methacrylate) composite layer formed by a two-step spin coating technique”, J. Appl. Phys., 112, 034518 (2012)
[58] 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., 80, 2501 (1996)
[59] L Piot, D Bonifazi, P Samori, “Organic reactivity in confined spaces under scanning tunneling microscopy control: tailoring the nanoscale world”, Adv. Funct. Mater., 17, 3693 (2007)