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研究生：	王伯彰 Wang, Po-Cheng
論文名稱：	探討以「聚甲基丙烯酸甲酯」為介電材質之有機薄膜電晶體的特性 Study of the characteristics of Pentacene-OTFTs with PMMA as dielectric layer
指導教授：	蘇炎坤 Su, Yan-Kuin
學位類別：	碩士 Master
系所名稱：	電機資訊學院 - 電機工程學系 Department of Electrical Engineering
論文出版年：	2007
畢業學年度：	95
語文別：	英文
論文頁數：	84
中文關鍵詞：	五環素、有機薄膜電晶體、聚甲基丙烯酸甲酯
外文關鍵詞：	Pentacene, PMMA, Organic thin-film transistors, OTFTs
相關次數：	點閱：113 下載：1
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有機薄膜式電晶體是近年來被廣泛研究的電子元件。他具有低成本以及低製程溫度的優點，這些優點使得它可以選擇使用不同種類的基板，甚至可以成長在可撓式的基板上。同時有機薄膜電晶體也可以和有機發光二極體整合當作有機發光二極體顯示器的驅動元件。
本論文主要著重於期許使用高分子材料「聚甲基丙烯酸甲酯」取代二氧化矽，探討其元件特性。
第一部分是關於高分子材料「聚甲基丙烯酸甲酯」特性研究。了其此材料的介電值，及膜厚。
第二部份是關於不同厚度之Pentacene的差異性。並且設定之後實驗有機層之最佳厚度。
第三部分是關於分別使用以二氧化矽及高分子材料「聚甲基丙烯酸甲酯」作為有機薄膜電晶體之絕緣層，並且分析其元件特性。
第四部分是藉由幾種量測方式，進而分析元件特性之差異性與介電材料不同之關聯性。
在這個研究當中，成功利用高分子材料作為有機薄膜電晶體之絕緣層，最大載子遷移率為0.241 cm2 /V.s。同時，在未來有機會發展成可撓式元件。

Thin film transistors (TFTs) based on conjugated organic materials, both small molecules and polymers have emerged recently due to their potential in low-cost, low-temperature fabrication and, the possibility of producing flexible devices. Several groups have proposed or reported successful integration of such devices with organic light-emitting diodes.
In our study, we investigated the dielectric layer of pentacene-OTFTs using PMMA of polymer material to replace conventions device with SiO2. The characteristic of pentacene-OTFTs with PMMA dielectric layer was also studied.
In the first part, we observed that the characteristics of PMMA were the same as the dielectric layer. The major property of PMMA was about dielectric constant and thickness.
In the second part, we investigated the characteristics of pentacene-OTFTs dependence of different thickness. The optimum thickness of pentacene-OTFTs in my experiment was found.
In the third part, we study the characteristics of Pentacene-OTFTs insulator layer using PMMA and SiO2. The performance of the device in my experiment was investigated.
In the final part, we analyze the difference of characteristics of device with different materials of dielectric layer.
In this study, the pentacene organic thin-film transistor with PMMA as insulator was fabricated successfully. The maximum saturation field-effect mobility was 0.241 cm2 /Vs. In the future, flexible device by using PMMA can be tried and fabricated.

Abstract (in Chinese)………………………………………………………………………..I
Abstract (in English)………………………………………………………………………III
Acknowledgements………………………………………………………………………...V
Contents……………………………………………………………….………………….VI
List of Table………………………………….......………………………………………..IX
Figure Captions…………………………………………………………………………….X

Chapter 1 Introduction……………………………………………………………….1
  1-1 The Development of Organic Thin-film Transistors…………………………………1
1-2 Advantages of Organic Thin-film Transistors………………………………………..2
1-3 Comparison with Inorganic Thin-film Transistors…………………………………...3
  1-4 Aim of this Research…………………………………………………………………4
Chapter 2 Organic Semiconductor………………………………………………...5
2-1 Organic Semiconductor Materials…………………………………………………...5
2-2 Conduction Mechanisms of Organic Semiconductors……………………….………6
Chapter 3 Principle of Organic Thin-film Transistor…………………………8
3-1 Structure and Operation of Organic Thin Film Transistor…………………………...8
  3-2 Important Parameter of Organic Thin Film Transistor………………………………9
    3-2-1 Field Effect Carrier Mobility………………….…………….…………………..9
    3-2-2 Threshold Voltage……………………………………………………………...10
    3-2-3 Sub-threshold Slope……………………………………………………………13
    3-2-4 On/Off Current Ratio…………………………………………………………..14
Chapter 4 Experimental Procedures and Equipment……………………….15
  4-1 Material preparation………………………………………………………………...15
4-1-1 Substrate…………………………………………………………………….....15
	4-1-2 Organic material……………………………………………………………….15
	4-1-3 Insulator material……………………………………………………………....16
	4-1-4 Electrode……………………………………………………………………….16
4-2 Fabrication Equipment……………………………………………………………...17
    4-2-1 Thermal Evaporation System………………………………………………….17
    4-2-2 Spin Coater…………………………………………………………………….18
  4-3 Fabrication Procedures…………………………………………………...…………18
	4-3-1 Pre-Processing Cleaning……………………………………………………….18
	4-3-2 Insulator………………………………………………………………………..19
	4-3-3 Active Layer……………………………………………………………………19
	4-3-4 Electrode…………………………………………………….…………………19
  4-4 Measurement………………………………………………………………………..20
	4-4-1 I-V Characteristics……………………………………………………………..20
	4-4-2 Surface Free Energy...……………………………………………………….....20
	4-4-3 X-Ray Diffraction……………………………………………………………...22
	4-4-4 Crystal Size…………………………………………………………………….25
	4-4-5 AFM……………………………………………………………………………26
Chapter 5 Experimental Results and Discussions…………………………….30
  5-1 Study of PMMA Insulator…………………………………………………………..30
  5-2 The Effect of Thickness of Pentacene…………..………………………..…………31
  5-3 Effect of Thickness of PMMA film in the Characteristic of OTFT………………...32
5-3-1 Surface Free Energy…………………………………………………………...33
5-3-2 AFM………………………………………………………………….………...33
5-3-3 X-ray……………………………………………………………………...……33
  5-4 Surface Effect of PMMA…………………………………………………………...34
Chapter 6 Conclusions and Future Work……………………………………….35
  6-1 Conclusions…………………………………………………………………………35
  6-2 Future work…………………………………………………………………………36
References………………………………………………………………………………37


List of Table

Table 1-1       Comparison of organic and inorganic TFTs……………………………43
Table 2-1       Performance of different polymers…………………………………….43
Table 2-2       Performance of different oligomers……………………………………44
Table 5-1       The grain size and disorder of Pentacene film…………………………45
Table 5-2       The characteristic of OTFT with different spin speed of PMMA……...45
Table 5-3       The surface free energy of different materials…………………………46
Table 5-4       The crystal size and disorder of Pentacene film grown on PMMA and SiO2…….…………………………………………………………….46
Table 5-5       PMMA surface roughness of different spin speed………..……………47








Figure Captions

Fig. 1-1      The highest field-effect mobility reported for OTFTs from 1986 to 2000………………………………………………………………………48
Fig. 2-1      Prominent (a) n- and (b) p-type organic semiconductor materials………..49
Fig. 2-2      Carriers transport in organic semiconductors……………………………..50
Fig. 2-3      Conduction mechanism in organic materials……………………………...50
Fig. 3-1      (a) Top Contact (TC) and (b) Bottom contact (BC) OTFT architectures
			 …..………………………………………………………………………..51
Fig. 3-2      Schematic energy-level diagrams for p-type OTFTs with bias voltage
	……………………………………………………………………………52
Fig. 4-1      The molecule structure of (a) Pentacene and (b) PMMA…………………53
Fig. 4-2      The schematic diagram of thermal evaporation system…………………..54
Fig. 4-3      Evaporation sources: (a) Quartz crucible source
            (b) Resistance-heated source……………………………………………..55
Fig. 4-4      The schematic diagram of spin coating system…………………………...56
Fig. 4-5      Cross section of OTFTs with (a) SiO2 and (b) PMMA layer
The device channel width and length is 1mm and 100um, respectively
	..………………………………………………………………………….57
Fig. 4-6      Fabrication procedures……………………………………………….……58
Fig. 4-7      Contact angle θ of a sessile drop……………………………………….....59
Fig. 4-8      The effect of crystal size on diffraction…………………………………...60
Fig. 4-9      Effect of fine particle size on diffraction curves…………………………..61
Fig. 4-10     Schematic illustration of an atomic force microscope (AFM)……………62
Fig. 5-1      The molecule structure of different solvent…………………………..…...63
Fig. 5-2      The IDS-VDS characteristics of OTFTs with PMMA were dissolved in 
(a)	Toluene (b) p-xylene (c) o-Dichlorobenzene and (d) Chloroform.
…………………………………………………………………….…. 64-65
Fig.5-3     The LogID – VGS characteristics of OTFTs with PMMA were
dissolved in different solvent………..……………………………..……...66
Fig. 5-4      The AFM image of Pentacene grown on PMMA for different solvent
             …………………………………………………………..…………..67-68
Fig. 5-5      The thickness-spin speed (rpm) curves for PMMA thin film………..……69
Fig. 5-6      The dielectric constant-spin speed of PMMA………………………..…...70
Fig. 5-7      The IDS-VDS characteristics of OTFTs was with different thickness of
             Pentacene. The thicknesses of Pentacene are (a) 300Å (b) 600 Å and (c) 1200 Å……………………………...…………………………………71-72
Fig. 5-8      The IDS-VDS curves at VGS=-50V…………..……………………...………73
Fig. 5-9       The square root of drain current-gate voltage curves……………………73
Fig. 5-10      X-ray spectra of Pentacene films (a) 300Å (b) 600 Å and (c) 1200 Å.
             ……………………………………………………………………………74
Fig. 5-11      The AFM image of Pentacene thickness is(a) 300Å (b) 600 Å and (c)1200Å…………………………………………………..………….75-76
Fig. 5-12      The IDS-VDS curves with different spin speed of PMMA………………..77
Fig. 5-13      The Log IDS-VGS curves with different spin speed of PMMA…………...77
Fig. 5-14      Transfer characteristics with different spin speed of PMMA……………78
Fig. 5-15      The image of the (a) Diiodomethane and (b) water are drop on                substrate…………………………………………………………..…….79
Fig. 5-16      The AFM image of Pentacene grown on (a) SiO2 and (b) PMMA...80
Fig. 5-17      X-ray spectra of Pentacene film were grown on PMMA and SiO2
              ………………………………………………………………..…………81
Fig. 5-18      The surface of PMMA for different spin speed.
             The spin sped of PMMA were (a) 2000rpm (b) 3000rpm (c) 4000rpm
             (d)5000rpm and (e)6000rpm…………………………….……………82-84
                                    

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