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系統識別號 U0026-2707201003285300
論文名稱(中文) 應用雙層結構於介電及電極層對P型有機薄膜電晶體效能之改善
論文名稱(英文) Implementation of bilayer structure for dielectric and electrode layers to improve performance on p-type organic thin film transistors
校院名稱 成功大學
系所名稱(中) 電機工程學系專班
系所名稱(英) Department of Electrical Engineering (on the job class)
學年度 98
學期 2
出版年 99
研究生(中文) 黃耀族
研究生(英文) Yao-Tsu Huang
學號 n2796101
學位類別 碩士
語文別 英文
論文頁數 72頁
口試委員 指導教授-蘇炎坤
口試委員-許渭州
口試委員-黃俊元
口試委員-塗明隆
中文關鍵字 有機薄膜電晶體  五環素  雙層結構  金屬氧化物  三氧化鉬  三氧化鎢  五氧化二釩  線傳輸模型  奈米粒子  雙載子  電容  表面型態  遲滯效應 
英文關鍵字 organic thin film transistor  pentacene  bilayer  metal oxide  MoO3  WO3  V2O5  PMMA  TLM  nanoparticle  ambipolar  capacitance  surface morphology  hysteresis 
學科別分類
中文摘要 本論文中, 針對五環素有機薄膜電晶體,藉由應用雙層結構於介電層和電極層, 有效的改善元件的效能。
對於電極層的雙層結構,我們應用不同種類金屬氧化物(三氧化鉬, 三氧化鎢, 五氧化二釩)在金屬電極和半導體之間。這些金屬氧化物在有機薄膜電晶體主要的角色是充當載子注入層,藉由平衡半導體和金屬電極的能階的不對稱,同時在介面間形成歐姆接觸。特別是以低工作函數的金屬(鋁)當電極的元件, 電特性的改善尤其明顯,其中包括至少高兩級的輸出飽和電流和開關比,以及臨界電壓從 -24V下降到 -9 V。我們利用了線傳輸模型(TLM)來導出有機薄膜電晶體的接觸電阻,用以證實金屬氧化物在介面間歐姆機觸的確實形成。當元件使用MoO3當載子注入層,其接觸電阻從2.1 MΩ 下降到 0.1 MΩ。
在這份研究的另一部分,是利用奈米粒子和PMMA修飾表面所形成的雙層結構介電層,來提升絕緣層的電容值。進而我們探討了奈米粒子層和PMMA修飾層厚度的改變, 對電子特性的影響。在這份研究中,我們用了兩種不同的奈米粒子(SiO2, Al2O3)作為比較。當使用奈米粒子雙層結構的介電層時,兩種奈米粒子都可以發現雙載子(ambipolar)傳輸特性,這種特性在使用PMMA當單一層的絕緣層時,並無法產生進行n-type的操作。 其它絕緣層的一些特性像是電容、表面型態、遲滯效應等對元件特性的影響也在研究範圍內。和相似厚度的單層的高分子介電層的元件比較,奈米粒子雙層結構的元件主在效能改善在於電容值從5.6 nF/cm2上升到12 nF/cm2,因此輸出飽和電流有效的提昇至少一個等級。 最後,我們計算了雙層結構的奈米氧化矽在有機薄膜電晶體中,載子移動率在高電壓和低電壓應用方面,表現數值分別為0.78 cm2/Vs 和0.025 cm2/Vs。
英文摘要 In this thesis, the performances of pentacene-based OTFTs had been successfully improved by employing bilayer structure for electrode and dielectric layer.
The bilayer electrodes consists of a metal oxides(MoO3, WO3, V2O5) interlayer between semiconductor(pentacene) and metal electrodes such as Au and Al. The major roles of metal oxides in OTFT was to act as charge injection layer as a result of aligning mismatch of energy level between metal and semiconductor as well as formed ohmic contact at interface. Electrical performances improvement was particularly observed for device with low-work-function metal electrode such as Al, including at least two orders higher in saturation induced current and On/Off ratio as well as lower threshold voltage from -24 V to -9 V. The extraction of contact resistance (Rc) on top-contact OTFTs from TLM was used to characterize the surface property in order to prove the interface with metal oxide did ohmic, and contact resistance was reduced from 2.1 MΩ to 0.1 MΩ if device utilized MoO3 as interlayer.
Another section in this thesis is to increase capacitance by utilizing nanoparticles and smooth by PMMA polymer to form bilayer gate dielectric. The influence of thickness for PMMA modified layer and nanoparticles layer to electrical properties had been investigated. Two types of nanoparticles(SiO2, Al2O3) were used for comparison in this work. Ambipolar behavior in output characteristics was observed for both nanoparticle used as bilayer gate dielectric, pentacene-based OTFT did not exhibit n-channel transport as using PMMA for single layer dielectric. The device properties influenced by gate dielectric such as capacitance, surface morphology, hysteresis behavior had been characterized. Comparing with the single layer polymeric dielectric, the major improvement for bi-layer dielectric structure were higher capacitance from 5.6 (nF/cm2) to 12 (nF/cm2) with similar gate dielectric thickness, therefore electrical properties such as induced current was increased at least one order. Mobility in saturate regime for OTFTs with nano-SiO2 bilayer gate dielectric was calculated, which was 0.78 (cm2/Vs) and 0.025 (cm2/Vs) for high-voltage and low-voltage applications respectively.
論文目次 Abstract (in Chinese) .....................................I
Abstract (in Engilsh) ...................................III
Acknowledgement ...........................................V
Content...................................................VI
Table Captions .........................................VIII
Figure Captions..........................................XII

Chapter 1 Introduction....................................1
1-1 Application of organic thin-film transistors...1
1-2 OTFT Structures................................1
1-3 Pentacene-based organic thin film transistors..2
1-4 Organic thin-film transistors with polymeric gate dielectric ...........................................2
1-5 Influence factors to performances of OTFT .....3
Chapter 2 Principles of Organic Thin-Film Transistors .....6
2.1 Charge carriers transport in organic semiconductor .............................................6
2.2 Organic TFT operation .........................6
2.3 Electrical properties of organic TFTs .........7
Chapter 3 Experiment procedure and Measurement ...........14
3-1 Materials.....................................14
3-2 OTFT device fabrication procedure ............15
3-3 Measurement ..................................16
Chapter 4 Results and Discussions.........................25
4-1 Metal-Oxide carriers injection layers between Electrodes/Semiconductor .................................26
4-1-1 Fixed thickness of Metal oxide interlayer with Au electrodes ............................26
4-1-2 Fixed thickness of Metal oxide interlayer with Al electrodes ............................28
4-1-3 Contact resistance(Rc) extracted by Transmission Line Model ..................................29
4-1-4 Thickness of metal oxides interlayers ..........................................................30
4-2 Nanoparticles bi-layer gate dielectrics ......31
4-2-1 Thickness changing of PMMA modified layer ....................................................31
4-2-2 Thickness changing of SiO2 nanoparticles layer ......................................33
4-2-3 Comparison between different nanoparticles dielectric materials .......................34
4-2-3(a) Output characteristics and ambipolar behavior .......................................34
4-2-3(b) Transfer characteristics and hysteresis ..........................................35
4-2-3(c) Surface morphology ......36
4-2-3(d) Capacitance and dielectric constant .................................................36
Chapter 5 Conclusions and Future Prospect ................64
5-1 Conclusions ..................................64
5-2 Future Prospect ..............................65
Reference ................................................67

Figure 1-1. Schematic view of top-contact and bottom-contact ...................................................5
Figure 1-2. Output characteristics for ambipolar OTFT......5
Figure 2-1. Hopping model for carriers conduction ........11
Figure 2-2. π-orbital overlap in Benzene ................11
Figure 2-3. P-type operation in OTFT .....................12
Figure2-4. Typical electrical behaviors for OTFT .........13
Figure 3-1. Chemical structure of PMMA ...................18
Figure 3-2. Chemical structure of Pentacene ..............18
Figure 3-3. Device Structure .............................19
Figure 3-4. Process Flow to fabricate OTFT ...............19
Figure 3-5. Thermal vacuum evaporation system ............20
Figure 3-6. Masks designed for thermal evaporation a) mask for pentacene deposit b) mask to define source/drain......21
Figure 3-7. Top view of top-contact Pentacene-based OTFTs ..........................................................21
Figure 3-8. Configuration of two 2400 sourcemeters for electrical characteristics measurement....................22
Figure 3-9. AFM for morphology characterization ..........23
Figure 3-10. (a) The conducting path between source and drain, total resistance is divided into a series of five resistive elements b) Rc extracted from TLM at various gate voltages .................................................24
Figure 4-1. Contact angles on surface on PMMA ............39
Figure 4-2. Contact angles on surface on pentacene .......39
Figure 4-3. Device structure of OTFT with metal oxide interlayer ...............................................40
Figure 4-4. Work function of Au and Al as well as energy band diagram for metal oxide and Pentacene ...............40
Figure 4-5. Output characteristics for the devices with Au electrode (a) Control sample without metal oxide interlayer (b) sample with 6 nm thickness of MoO3 interlayer (c) sample with 6 nm thickness of V2O5 interlayer (d) sample with 6 nm thickness of WO3 interlayer ....................41
Figure 4-6. Transfer characteristics for the devices with Au electrode (a) Sub-threshold Swing and On/OFF Ratio (b) Threshold Voltage ........................................42
Figure 4-7. Output characteristics for the devices with Al electrode (a) control sample without metal oxide interlayer (b) sample with 6 nm thickness of MoO3 interlayer (c) sample with 6 nm thickness of V2O5 interlayer (d) sample with 6 nm thickness of WO3 interlayer ....................43
Figure 4-8. Transfer characteristics for the devices with Al electrodes (a) Sub-threshold Swing and On/OFF Ratio (b) Threshold Voltage ........................................44
Figure 4-9. (a) The computed RT vs. drain voltage for devices with/without MoO3 interlayer. (b) The RT for different channel lengths at same drain and gate voltage. The strain line fit to y-intercept is representing Rc ....46
Figure 4-10. Output characteristics in various thicknesses for different metal oxides interlayers a) MoO3 b) V2O5 c) WO3 ......................................................48
Figure 4-11. Transfer characteristics in various thicknesses for different metal oxides interlayers a) MoO3 b) V2O5 c) WO3 ..........................................50
Figure 4-12. Device structure for a) control sample with PMMA insulator and b) bi-layer dielectrics ...............51
Figure 4-13. TEM image: 20nm SiO2 nanoparticles dispersing in Ethylene Glycol solvent ...............................51
Figure 4-14. Output characteristics for bilayer structure by 530nm thickness of SiO2 nanoparticles with PMMA modified layer a) 5% PMMA (260nm) b) 5% PMMA (240nm) c) 3% PMMA (200nm) d) 3% PMMA(120nm) ...............................52
Figure 4-15. Transfer characteristics for bilayer structure by 530nm thickness of SiO2 nanoparticles with various thicknesses of PMMA modified layer .......................53
Figure 4-16. Hysteresis behaviors of OTFTs with bilayer dielectric by 530nm thickness of SiO2 nanoparticles with PMMA modified layer a) 5% PMMA (260nm) b) 5% PMMA (240nm) c) 3% PMMA (200nm) d) 3% PMMA (120nm) ...................54
Figure 4-17. Output characteristics for bilayer structure by various thickness of SiO2 nanoparticles with fixed 120nm thickness PMMA modified layer a) SiO2: 340nm b) SiO2: 220nm ..........................................................55
Figure 4-18. Transfer characteristics for bilayer structure by various thickness of SiO2 nanoparticles with fixed 120nm thickness PMMA modified layer ............................56
Figure 4-19. Hysteresis behaviors for bilayer structure by various thickness of SiO2 nanoparticles with fixed 120nm thickness PMMA modified layer a) SiO2: 340nm b) SiO2: 220nm ..........................................................56
Figure 4-20. Output characteristics for different dielectric layers structure: a) PMMA only b) PMMA/nano-SiO2 c) PMMA/nano-Al2O3 .......................................57
Figure 4-21. Output characteristics in N-channel for bilayer structure a) PMMA/nano-SiO2 b) PMMA/nano-Al2O3 ...58
Figure 4-22. Transfer characteristics for different dielectric layers structure ..............................59
Figure 4-23. Hysteresis behavior for different dielectric layers structure: a) PMMA only b) PMMA/nano-SiO2 c) PMMA/nano-Al2O3 ..........................................60
Figure 4-24. Surface morphology of bilayer dielectric by AFM a) PMMA/nano-SiO2 b) PMMA/nano-Al2O3 ...............61
Figure 4-25. AFM images of pentacene films deposited on a) PMMA/nano-SiO2 b) PMMA/nano-Al2O3 ........................61
Figure 4-26. Capacitances-Voltage curve at 1k Hz for single-layer/bilayer gate dielectrics ...........................62

Table 4-1. Summary of electric properties for devices with Au / Metal-Oxides and Al / Metal-Oxides contact...........45
Table 4-2. Comparison of Pentacene-based OTFTs with single-layer / bilayer gate dielectric extracted from IDS-VGS at VDS=-40 V and VGS=-40V ........................63
Table 4-3. Electric properties for Pentacene-based OTFTs with bilayer nano-SiO2 gate dielectric extracted from IDS-VGS at VDS=-10 V and VGS=-10V ........................63
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