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研究生: 李盈欣
Li, Ying-Hsin
論文名稱: 介電層結構對五環素薄膜電晶體電性的影響
Effects of the PVP Dielectric Layer Structures on the Performance of Pentacene-based Organic Thin-Film Transistors
指導教授: 王永和
Wang, Yeong-Her
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: 2008
畢業學年度: 96
語文別: 英文
論文頁數: 49
中文關鍵詞: 未交聯的PVPPVP介電層遲滯現象OH官能基有機薄膜電晶體
外文關鍵詞: PVP dielectric layer, Organic-Thin-Film-Transistor, OH groups, Hysteresis phenomenon, Un-cross-linked PVP
相關次數: 點閱:113下載:1
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  • 在論文中,主要探討的部分為介電層的處理方式對五環素薄膜電晶體電性的影響。單層PVP介電層的電晶體一般會有明顯的遲滯現象,但我們在原本的介電層上再疊加第二層PVP介電層上去形成雙層PVP介電層,發現電晶體的遲滯現象有明顯的改善,遲滯電壓從9V減少到1V,我們推論是由於第一層的PVP烘烤的時間拉長所導致。實驗發現,PVP烘烤的時間長短的確會對遲滯有重大的影響。PVP中OH官能基的多寡是影響遲滯的一個因素,我們使用FTIR去量測在各種不同的烘烤時間下所含的OH多寡,得知在最佳烘烤時間下,會使得OH官能基含量變少,其遲滯也相對的降低了許多,進而改善了電晶體的遲滯現象。值得一提的是,我們意外發現,比較單層跟雙層PVP介電層,在相同單位電場下其漏電流可從10-6Acm-2改善至10-8Acm-2,這樣的漏電流改善將會使得雙層的PVP介電層有著更優越的電容特性。
    我們使用未交聯的PVP當作原本PVP介電層(已交聯)的修飾層,期待電五環素薄膜晶體的電性能夠有所提升。當我們比較有交聯和未交聯的PVP修飾層電晶體,則最大飽和電流可從27.6μA增加至83.1μA;且mobility可從0.19改善至0.61cm2V-1s-1。這可以歸於未交聯PVP介電層的表面較平坦。另外,未交聯PVP的表面能和Pentacene薄膜表面能較為接近,這表示未交聯PVP介電層是比較有利於Pentacene薄膜的成長。

    The treatments of the poly(4-vinylphenol) (PVP) dielectrics on the performance of Pentacene-based organic thin-film transistor (OTFT) will be investigated. Generally, OTFTs suffer from the hysteresis phenomenon while using the single PVP dielectric. However, the OTFTs based on the double PVP dielectrics, which deposit on the gate electrode sequentially, could show lower levels of hysteresis. Comparing the device with single- and double-PVP dielectrics, hysteresis decreased from 9 V to 1 V. We supposed that the decreased hysteresis was due to the longer curing time of the double-PVP dielectrics. The experimental results showed that the curing time of PVP dielectrics significantly affected hysteresis, and as such, the hydroxyl groups existing inside the PVP bulk resulted in hysteresis. From Fourier Transform Infrared Spectroscopy (FTIR) measurement, the hydroxyl group’s amount inside the PVP dielectric decreased as the curing time increased, thereby further decreasing the hysteresis phenomenon of OTFTs. By the way, comparing the single and double PVP dielectric layer structures, the leakage current can be greatly improved from 10-6 Acm-2 to 10-8 Acm-2.It indicates the double PVP dielectrics are more suitable for MOS capacitor.
    Using the PVP dielectrics without cross-linked agent to modify the surface of PVP dielectrics is found to improve the transistor performance significantly. Compared the transistors without and with cross-linked agent, the maximum saturation current can be improved from 27.6 μA to 83.1 μA while the mobility can be enhanced from 0.19 to 0.61 cm2V-1s-1. This can be partly attributed to the smoother surface of the un-cross-linked dielectrics. In addition, the surface wetting property of un-cross-linked PVP dielectrics is closer to that of Pentacene layer. It indicated the un-cross-linked PVP dielectrics are suitable for the buffer layer to improve the Pentacene-based thin film transistor performance.

    English Abstract................................................................................I Chinese Abstract..............................................................................III Acknowledgement................................................................................IV Table Captions................................................................................VII Figure Captions..............................................................................VIII Chapter 1 Introduction..........................................................................1 1.1 Overview of Organic Thin Film Transistors (OTFTs)...........................................1 1.2 Operation of Organic Thin Film Transistors (OTFTs)..........................................2 1.2.1 Mobility..................................................................................3 1.2.2 Threshold Voltage.........................................................................4 1.2.3 On/off Ratio..............................................................................4 1.3 Motivation and Objective....................................................................4 1.4 Thesis Organization.........................................................................5 Chapter 2 The effect of PVP dielectric layer curing time........................................9 2.1 Experimental materials......................................................................9 2.1.1 Pentacene................................................................................10 2.1.2 ITO......................................................................................10 2.1.3 PVP......................................................................................10 2.2 Experimental Process.......................................................................11 2.2.1 Cleaning procedure.......................................................................11 2.2.2 ITO transparent film as a gate electrode.................................................11 2.2.3 Fabrication procedures...................................................................12 2.2.3.1 OTFTs with a single PVP dielectric (Top contact):......................................12 2.2.3.2 OTFTs with double PVP dielectrics......................................................13 2.3 Results and discussion.....................................................................14 2.3.1 Electrical characteristics of OTFTs......................................................14 2.3.2 Fourier Transform Infrared Spectroscopy (FTIR)...........................................15 2.4 Summary....................................................................................16 Chapter 3 The effect of surface modification layer on the electrical characteristics of OTFTs..........................................................................................27 3.1 Experimental Process.......................................................................27 3.1.1 Cleaning procedure:......................................................................27 3.1.2 ITO transparent film as a gate electrode.................................................28 3.1.3 Fabrication procedures...................................................................29 3.2 Results and discussion.....................................................................30 3.2.1 Electrical characteristics of OTFTs......................................................30 3.2.2 Surface morphology (SEM) measurement.....................................................31 3.2.3 Surface roughness (AFM) measurement......................................................31 3.2.4 X-ray diffraction (XRD) measurement......................................................32 3.3 Summary....................................................................................34 Chapter 4 Conclusions..........................................................................44 Chapter 5 Future work..........................................................................45 References.....................................................................................46

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