臺灣博碩士論文加值系統

近幾年來，有機薄膜電晶體 (organic thin film transistors, OTFTs ) 因為其較傳統矽半導體技術更為簡單及更為便宜的製程方式而受到廣大的注目。有機薄膜電晶體可利用印刷 (printing) 方式製作於可撓曲的基板上，如金屬薄膜及塑膠基板。由於它輕、薄、可撓曲和耐衝擊的特性，相當適合應用於可攜式或需要撓曲的電子產品上。因此，如何製作有機薄膜電晶體於塑膠基板上及撓曲所產生的應力對有機薄膜電晶體電性的影響已成為相當重的研究課題。
本實驗研究關於有機薄膜電晶體的製作方式及有機薄膜電晶體經由不同曲率半徑的撓曲對其電性的影響。我們選擇聚醚砜 (polyethersulphone, PES) 為塑膠基板，利用真空熱蒸鍍的金為導電極，以旋塗方式 (spin coating) 製成的聚亞醯胺 (polyimide, PI) 為介電層，搭配真空熱蒸鍍五苯環 pentacene 作為主動層，製成可撓曲的有機薄膜電晶體。之後，我們利用兩種方法去改善有機薄膜電晶體的特性。一種是利用雙面膠將塑膠基板貼合於玻璃基板上，再以此為基材製作有機薄膜電晶體。以此方式作成的元件，其載子移動率為3.19 × 10-1 cm2/Vs，而汲極電流比為3.8 × 105。另一種方式是利用自組裝單分子膜層 (self-assembled monolayers, SAMs) 對金閘極表面作改質。經此步驟所製成的有機薄膜電晶體其載子移動率為2.26 × 10-1 cm2/Vs，而汲極電流比為3.22 × 106。
在撓曲量測實驗方面，將上述的可撓曲有機薄膜電晶體依照不同的曲率半徑彎曲後，量測其電性並與未撓曲前的電性作比較。所限定的曲率半徑分別25毫米、15毫米、10毫米、5毫米和2.5毫米。實驗結果顯示，有機薄膜電晶體的電性在最小曲率半徑2.5毫米時會有超過80 %的衰減。且從 SEM (scanning electron microscope) 的圖片可明顯看到 pentacene 薄膜表面已有破裂的現象

In recent years, organic thin-film transistors (OTFTs) have become very attractive for their fabrication processes are much uncomplicated compared with conventional Si technology. OTFTs can be utilized for flexible electronic applications by using flexible substrate. So the fabrication techniques of OTFTs on plastic substrates and the effects of bending stress on the electronic properties have been the most important research topics.
This thesis presents the results of research about manufacturing methods and bending experiment of OTFTs on plastic substrates. We used polyethersulphone (PES) as flexible substrate, Au as conductive electrode, polyimide (PI) as dielectric layer, and pentacene as active semiconductor for devices fabrication. Then we utilized double-coated tape and self-assembled monolayers (SAMs) to improve the electrical properties of devices on plastic substrates. Using double-coated tape to prepare the base substrates, the devices were obtained with a mobility of 3.19 × 10-1 cm2/Vs and ION/IOFF of 3.8 × 105. Moreover, we manufactured flexible devices by using SAMs surface treatment with a mobility of 2.26 × 10-1 cm2/Vs and ION/IOFF of 3.22 × 106.
In bending experiment, the flexible devices were bent with bending radii of 25mm, 15 mm, 10 mm, 5 mm, and 2.5 mm. The experimental results presented the mobility decrease by over 80 % in the smallest bending radius in both outward and inward bending. We can see the distinct cracks on surface of pentacene thin film which may cause the worse electrical performances after critical bending stress from scanning electron microscope (SEM) image.

Abstract (Chinese) I
Abstract (English) II
Acknowledgements III
Contents IV
List of Figures VII
List of Tables X

Chapter 1 Introduction 1
1.1 Overview 1
1.2 Research motivation 4
1.3 Literature review 5
1.3.1 OTFT on plastic substrate 5
1.3.2 Bending experiment 7
1.4 Structure of thesis 10

Chapter 2 Theory and Fabrication Needs for OTFT 12
2.1 OTFT structure 12
2.2 Conduction mechanisms 14
2.3 Modeling of the electrical characteristics 17
2.4 Materials 21
2.4.1 Substrate 21
2.4.2 Electrode 23
2.4.3 Dielectric layer 24
2.4.4 Active layer 27
2.5 Fabrication methods 31
2.5.1 Vacuum thermal evaporation 32
2.5.2 Spin coating 35

Chapter 3 Device Fabrication and Parameters Measurement 37
3.1 Device fabrication 37
3.1.1 Preparation of PES plastic substrate 39
3.1.2 Au deposition 39
3.1.3 Polyimide dielectric coating 41
3.1.4 Pentacene deposition 43
3.2 OTFT characteristics comparison 46
3.3 Characteristics improvement 55
3.3.1 Plastic flatness by double-coated tape 55
3.3.2 Surface treatment by SAMs 57

Chapter 4 Bending Experiment 66
4.1 Experimental setup 66
4.2 Experimental results 69
4.3 Experimental analysis 73

Chapter 5 Conclusions and Future work 79
5.1 Conclusions 79
5.2 Future work 81

Reference 83

Appendix 1 87
Appendix 2 98

[1]H. Lebrun, F. Maurice, J. Magarino, and N. Szydlo, 1995, “AMLCD with Integrated Drivers Made with Amorphous-silicon TFTs,” Journal of SID, pp. 177-180, April.
[2]Thomas N. Jackson, Yen-Yi Lin, David J. Gundlach, and Hagen Klauk, 1998, “Organic thin-film Transistors for Organic Light-emitting Flat-panel Display Backplanes,” IEEE Journal of Selected Topics in Quantum Electronics, Vol. 4, No. 1, pp. 100-104, January/February.
[3]Colin Reese, Mark Roberts, Mang-Mang Ling, and Zhenan Bao, 2004, “Organic Thin Film Transistors,’’ Materials Today, Vol. 7, Issue 9, pp. 20-27, September.
[4]C. D. Sheraw, J. A. Nichols, D. J. Gundlach, J. R. Huang, C.C. Kuo, H. Klauk, T. N. Jackson, M. G. Kane, J. cCampi, F. P. Cuomo, and B. K. Greening, 2000, “An Organic Thin Film Transistor Backplane for Flexible Liquid Crystal Displays, ” 58th Device Research Conference Digest, USA, pp. 107-108, June.
[5]Taehyoung Zyung, Seong Hyun Kim, Hye Yong Chu, Jung Hun Lee, Sang Chul Kim, Jeong-in Lee, and Jiyoung Oh, 2005, “Flexible Organic LED and Organic thin-film Transistor,” Proceedings of the IEEE, Vol. 93, No. 7, pp. 1265-1272, July.
[6]C. D. Sheraw, L. Zhou, J. R. Huang, D. J. Gundlach, and T. N. Jackson, 2002, “Oranic thin-film Transistor-Driven Polymer-dispersed Liquid Crystal Displays on Flexible Polymeric Substrates,” Applied Physics Letters., Vol. 80, No. 6, pp. 1088, February.
[7]Takao Someya, Tsuyoshi Sekitani, Shingo Iba, Yusaku Kato, Hiroshi Kawaguchi, and Takayasu Sakurai, 2004, “A Large-area, Flexible Pressure Sensor Matrix with Organic field-effect Transistors for Artificial Skin Applications,” PNAS of the USA, Vol. 101, No.27, pp. 9966-9970, July.
[8]Melissa Mushrush, Antonio Facchetti, Michael Lefenfeld, Howard E. Katz, and Tobin J.Marks, 2003, “Easily Processable Phenylene-Thiophene based Organic field-effect Transistors and Solution-fabricated Nonvolatile Transistor Memory Elements,” J. AM. CHEM. SOC., Vol. 125, pp. 9414-9423, March.
[9]N. Camaioni, G. Ridolfi, G. Casalbore-Miceli, G. Possamai, L. Garlaschelli, and M. Maggini, 2003, “A stabilization Effect of [60] Fullerene in Donor-acceptor Organic Solar Cells,” Solar Energy Materials & Solar Cells, Vol. 76, pp. 107-113, May.
[10]Y. J. Chan, C. P. Kung, and Z. Pei, 2005, “Printed RFID: Technology and Application,” IEEE International on Radio Frequency Integration Technology, Singapore, pp. 139-141, November.
[11]Zhenan Bao, Yi Feng, Ananth Dodabalapur, V. R. Raju, and Andrew J. Lovinger, 1997, “High-performance Plastic Transistors Fabricated by Printing Techniques,” Chemical Materials, Vol. 9, PP. 1299-1301, February.
[12]Thomas N. Jackson, 2001, “Organic Thin Film Transistors- Electronics anywhere,” International Semiconductor Device Research Symposium, USA, pp. 340-343, December.
[13]Sung Hun Jin, Jae Sung Yu, Chun An Lee, Jin Wook Kim, Byung-Gook Park, and Duk Lee, 2004, “Pentacene OTFTs with PVA Gate Insulators on a Flexible Substrate,” Journal of the Korean Physical Society, Vol. 44, No. 1, pp. 181-184, January.
[14]Yusaku Kato, Shingo Iba, Ryohei Teramoto, Tsuyoshi Sekitani, and Takao Someya, 2004, “High Mobility of Pentacene field-effect Transistors with Polyimide Gate Dielectric Layers,” Applied Physics Letters, Vol. 84, No. 19, pp. 3789-3791, May.
[15]Seungmoon Pyo, Hyunsam Son, Kil-Yeong Choi, and Mi Hye Yi, 2005, “Low-temperature Processable Inherently Photosensitive Polyimide as A Gate Insulator for Organic thin-film Transistors,” Applied Physics Letters, Vol. 86, No. 133508, pp. 1-3, March.
[16]H. Gleskova, S. Wagner, W. Soboyejo and Suo, 2002, “Electrical Response of Amorphous Silicon thin-film Transistors under Mechanical Train,” Journal of Applied Physics, Vol. 92, No. 10, pp. 6224-6229, November.
[17]Sung Hwan Won, Jang Kyun Chung, Chang Bin Lee, Hyun Chul Nam, Ji Ho Hur, and Jin Jang, 2004, “Effect of Mechanical and Electrical Stresses on the Performance of An a-Si:H TFT on Plastic Substrate,” Journal of the Electrochemical Society, Vol. 151, No. 3, pp. G167-G170, January.
[18]Tsuyoshi Sekitani, Shingo Iba, Yusaku Kato and Takao Someya, 2005, “Bending Effect of Organic field-effect Transistors with Polyimide Gate Dielectric Layers,” Japanese Journal of Applied Physics, Vol. 44, No. 4B, pp. 2841-2843, April.
[19]Tsuyoshi Sekitani, Yusaku Kato, Shingo Iba, Hiroshi Shinaoka, Takao Someya, Takayasu Sakurai, and Shinichi Takagi, 2005, “Bending Experiment on Pentacene field-effect Transistors on Plastic Films,” Applied Physics Letters, Vol. 86, No. 073511, pp. 1-3, February.
[20]Tsuyoshi Sekitani, Shingo Iba, Yusaku Kato, Yoshiaki Noguchi, Takao Someya, and Takayasu Sakurai, 2005, “Ultraflexible Organic field-effect Transistors Embedded At a Neutral Strain Position,” Applied Physics Letters, Vol. 87, No. 173502, pp. 1-3, October.
[21]Tsuyoshi Sekitani, Shingo Iba, Yusaku Kato, Yoshiaki Noguchi, Takayasu Sakurai, and Takao Someya, 2006, “Submillimeter Radius Bendable Organic field-effect Transistors,” Journal of Non-Crystalline Solids, Vol. 352, pp. 1769-1773, March.
[22]C. D. Dimitrakopoulos, and D. J. Mascaro, 2001, “Organic thin-film Transistors: A Review of Recent Advances,” IBM J. RES. & DEV., Vol. 45, No. 1, pp.11-27, January.
[23]Y. Roichman, and N. Tessler, 2002, “Structures of Polymer field-effect Transistor: Experimental and Numerical Analyses,” Applied Physics Letters, Vol. 80, No, 1, pp. 151-153, January.
[24]G. Horowitz, R. Hajlaoui, R. Bourguiga, and M. Hajlaoui, 1999, “Theory of the Organic field-effect Transistor,” Synthetic Matals, Vol. 101, pp. 401-404.
[25]Christos D., Dimitrakopoulos, and Patrick R. L. Malenfant, 2002, “Organic Thin Film Transistors for Large Area Electronics,” Advanced Materials, Vol. 14, No. 2, pp. 99-117, January.
[26]Antonio Facchetti, Myung-Han Yoon, and Tobin J. Marks, 2005, “Gate Dielectrics for Organic Field-Effect Transistors: New Opportunities for Organic Electronics,” Advanced Materials, Vol. 17 pp. 1705-1725, March.
[27]Yen-Yi Lin, David J. Gundlach, Shelby F. Nelson, and Tomas N. Jackson, 1997, “Pentacene-based Organic thin-film Transistors,” IEEE Transactions on Electron Devices, Vol. 44, No. 8, pp. 1325-1331, August.
[28]David J. Gundlach, LiLi Jia, and Thomas N. Jackson, 2001, “Pentacene TFT with Improved Linear Region Characteristics Using Chemically Modified Source and Drain Electrodes,” IEEE Electron Device Letters, Vol. 22, No. 12, pp. 571-573, December.
[29]J. H. Schon and B. Batlogg, 2001, “Trapping in Organic field-effect Transistors,” Journal of Applied Physics, Vol. 89, No. 1, pp. 336-342, January.