臺灣博碩士論文加值系統

本研究使用溶液式高介電材料鋯鈦酸鋇於五環素有機薄膜電晶體，相較於金屬遮罩，透過黃光微影能夠有效將元件面積縮減。為了降低臨界電壓，電晶體的閘極使用兩種不同功函數金屬，分別為較高與較低於五環素的HOMO，發現藉由利用較高的功函數金屬，臨界電壓有效從-4.6V下降至-2.6V。並且使用紫外光/臭氧處理元件之源極與汲極表面，進而改善五環素分子於金屬表面失序成長之現象，增強電流注入能力，同時降低電晶體之總電阻。並且透過AFM與XRD分析，得知五環素分子成長於紫外光/臭氧處理之金屬表面之晶粒與晶相明顯得到改善，因此得到良好之電晶體特性：高場效載子移動率（4.5 cm2V-1s-1)、低次臨界效應（260 mV/decade)、高電流開關比（1.4 × 105)以及低驅動電壓(-5V)。

The solution-processed high-k barium zirconate titanate (BZT) as gate dielectric for pentacene-based organic thin film transistor (OTFT) applications is presented. As compared to the conventional metal mask, the fabricated transistors by photolithography process can effectively reduce the device dimension, especially for the bottom gate contact structures. To reduce the transistor threshold voltage, higher work function metals (Au) is used as the gate electrodes. The threshold voltage is efficiently decreased from -4.6 to -2.6 V as compared to that of Al. In addition, the UV/ozone was employed to treat the Au(source/drain) surface to improve the poor crystalline of pentacene grown on Au. Moreover, the surface morphologies and orientations of pentacene films were analyzed through atomic force microscopy (AFM) and X-ray diffraction. As the results show, the stack of pentacene molecules from disorder changed to vertical growth on the Au surface. Thus, the electrical properties of pentacene-based thin film transistors show high field-effect mobility of 4.5 cm2V-1s-1, low subthreshold swing of 260 mV/decade, high on/off ratio of 1.4× 105 and low operation voltage of -5 V. These results are better than the reported data using bottom contact pentacene OTFTs.

Contents
摘要 I
Abstract II
誌謝 IV
Figure Captions VII
Table Captions IX
Chapter 1 Introduction 1
1-1 Introduction to the development of OTFTs 1
1-2 Advantages of organic thin film transistors 2
1-3 Background and motivation 4
1-4 Organization of thesis 6
Chapter 2 Organic Semiconductor 7
2-1 Organic semiconductor Materials 7
2-2 Physics of organic semiconductors 9
Chapter 3 Principle of OTFT 13
3-1 Thin-film transistor architecture 13
3-2 Operating mode 15
3-3 Important parameters of OTFTs 17
3-3-1 Field-effect mobility 17
3-3-2 Threshold voltage 18
3-3-3 Subthreshold Swing 19
3-3-4 On/off current ratio 19
3-4 Oxide charges 22
3-4-1 Interface tapped charge (Qit) 22
3-4-2 Fixed oxide charge (Qf) 22
3-4-3 Oxide trapped charge (Qot) 22
3-4-4 Mobile ionic charge (Qm) 22
Chapter 4 Experiment 24
4-1 Experimental materials 24
4-2 Experimental instruments 28
4-2-1 Sputter 28
4-2-2 Thermal Evaporator 31
4-2-3 Spin coater 32
4-2-4 UV-ozone cleaner 34
4-3 Experimental procedure 35
4-3-1 Substrate cleaning 35
4-3-2 Gate electrode 36
4-4-3 Insulator layer 39
4-3-3-1 BZT solution preparation 39
4-3-3-2 Experiment of insulator 39
4-3-4 Etching of insulator 41
4-3-5 Source and Drain electrodes 44
4-3-6 UV/ozone treatment 47
4-3-7 Active layer 47
4-4 Measurement System 50
4-4-1 Current-Voltage (I-V) measurement 50
4-4-2 Capacitance-Voltage (C-V) measurement 50
4-4-3 Atomic Force Microscope (AFM) 50
4-4-4 X-ray photoelectron spectroscopy (XPS) 51
4-4-5 X-ray Diffraction (XRD) 51
Chapter 5 Results and Discussion 53
5-1 Analysis of insulator film 53
5-1-1 X-ray photoelectron spectroscopy (XPS) 53
5-1-2 Physical properties of BZT 55
5-1-3 MIM measurement 57
5-2 Electrical properties 59
5-2-1 Different deposition rates of active layer 59
5-2-2 Different metal of gate electrodes 65
5-3 Surface treatment with UV/ozone 70
5-3-1 AFM analysis 70
5-3-2 XRD analysis 76
5-3-3 Energy level 78
5-3-4 MSM measurement 80
5-3-5 Electrical properties 82
Chapter 6 Conclusions and Future Works 91
6-1 Conclusions 91
6-2 Future works 92
References 94

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