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Comparison of Electrical Characteristic of Graphene FETs and Pentacene FETs for Flexible Electronics

최보식 (Choi Bosik, 포항공과대학교)

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Synthesis of high-quality of monolayer graphene using chemical vapor deposing (CVD) method and fabrication of the graphene FET to measure electrical characteristic have been demonstrated. In the CVD synthesis mechanism, copper foils were used as catalyst to grow graphene. To find optimized synthesi...
Synthesis of high-quality of monolayer graphene using chemical vapor deposing (CVD) method and fabrication of the graphene FET to measure electrical characteristic have been demonstrated. In the CVD synthesis mechanism, copper foils were used as catalyst to grow graphene. To find optimized synthesis conditions such as reaction time, reaction gas ratio, and cooling time have been investigated. The number of graphene layer was analyzed using the raman spectrum and AFM measurement. To measure electrical properties of graphene, graphene FET was fabricated. Gold was evaporated to form source and drain electrode. As 1mV drain voltage is applied, drain current was modulated by gate voltage. Field effect mobility of hole and electron was extracted as 4200cm2/V·s, 2500cm2/V·s, respectively. On/off current ratio are 6. Due to its outstanding characteristic and flexible property of graphene, it is one of the most outstanding materials that can be applied to flexible and RF devices. To make flexible devices, Stainless steel (STS) was used. It has higher mechanical and chemical stability than plastic substrate. Organic material, pentacene, was used as organic semiconductor to make organic field effect transistor. STS was polished and spin-coated as Polyvinylpynolidone(PVP) to reduce substrate roughness. Al was evaporated as bottom gate and oxidized to form gate dielectric. Tetradecylphosphonic acid(TPA) was self-assembled to reduce interfacial trap states and to increase the crystallinity of organic semiconductor layer. Fabricated pentacene FET shows 102 on/off ratio and 0.02 cm2/V·s field effect mobility. More works for flexible FETs on STS substrate will be needed to improve the performance of flexible DC and RF performance.
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Contents
Abstract…………………………………………………………………………………… ⅰ
Contents…………………………………………………………………………………… ⅲ
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Contents
Abstract…………………………………………………………………………………… ⅰ
Contents…………………………………………………………………………………… ⅲ
List of Figures ………………………………………………………………………… ⅴ
Chapter 1 Graphene FET Fabrication
I. Introduction………………………………………………………………………………1
II. Graphene …………………………………………………………………………………2
2.1 Graphene Structure ……………………………………………………………………3
2.2 Electron Properties of Graphene……………………………………………………4
2.3 Microscopy Analysis of Graphene……………………………………………………6
2.3.1 Raman Analysis ………………………………………………………………………6
2.3.2 Transmittance…………………………………………………………………………7
2.4 Graphene Synthesis Method……………………………………………………………8
2.4.1 Mechanical Exfoliation ……………………………………………………………8
2.4.2 Chemical Exfoliation ………………………………………………………………9
2.4.3 Chemical Vapor Deposition…………………………………………………………9
2.4.4 Expitaxial Growth on Silicon Carbide…………………………………………10
2.5 Graphene Applications ………………………………………………………………10
III. Experiment and Analysis……………………………………………………………11
3.1 Graphene Synthesis……………………………………………………………………12
3.2 Graphene Transfer ……………………………………………………………………13
3.3 Graphene Synthesis Condition………………………………………………………16
3.3.1 Change H2 ratio ……………………………………………………………………16
3.3.2 Change H2 and CH4 ratio …………………………………………………………16
iv
3.3.3 Change reaction time………………………………………………………………17
3.3.4 Change cooling time ………………………………………………………………17
3.3.5 Conclusion……………………………………………………………………………17
3.4 AFM analysis……………………………………………………………………………24
3.5 Device fabrication……………………………………………………………………25
3.5.1 Characterization of Back Gate Devices ………………………………………26
3.5.2 Mobility Extraction ………………………………………………………………27
Ⅳ. Conclusion………………………………………………………………………………29
Reference ……………………………………………………………………………………30
Chapter 2 Organic FET fabrication
I. Introduction ……………………………………………………………………………33
II. Organic FET ……………………………………………………………………………34
2.1 Operating Mechanism of Organic Field Effect Transistor……………………34
III. Fabrication of Pentacene FET on STS……………………………………………36
Ⅳ. Electrical Characteristics of OFET on STS ……………………………………39
3.1 On/off ratio……………………………………………………………………………41
3.2 Threshold voltage ……………………………………………………………………41
3.3 Mobility…………………………………………………………………………………41
Ⅴ. Conclusion………………………………………………………………………………42
Reference ……………………………………………………………………………………43