Instability of electrical property in metal oxide transistor : adsorption/desorption and trapping/detrapping effects
- 주제(키워드) surface reaction , metal oxide nanowire , n-type , p-type , metal oxide film , electron-beam , electrical hysteresis , Spice modeling
- 발행기관 고려대학교 대학원
- 지도교수 김규태
- 발행년도 2012
- 학위수여년월 2012. 8
- 학위구분 박사
- 학과 일반대학원 전기공학과
- 세부전공 마이크로 소자 및 초전도
- 원문페이지 206 p
- 실제URI http://www.dcollection.net/handler/korea/000000034991
- 본문언어 영어
- 제출원본 000045717768
초록/요약
Abstract It is raising the interests in nano-scaled devices owing to the limitation for scaling down of the bulk silicon semiconducting devices by the process limit. The researches and experiments for realization of the extreme scales of silicon based semiconducting devices have been implemented up to now as based on the silicon-silicon dioxide structures using the conventional semiconducting process flows, however, it has been reported from the research or industrial worlds that the limit will come soon in scaling down just by using the structural or process improvements for the dimension of several nanometers active area (<10nm). So it is required that the newly applied materials for active area (such as Ge or SiGe, etc) or nano-structured materials such as nanowires, nanotubes or nanoribbons, etc. Representatively, the reliability or reproducibility in device application using nano-materials has always been considered as the problems to be solved or further improved. It is quite needed that not only the technical controls for nanostructures but also the deep understanding about the real carriers behaviors or electro-chemical reaction in the nano-materials channel or in their active surface. In this paper, firstly it was shown that the fabrication methods for nano-materials devices especially based on metal oxide nanowires such as CuOX, SnO2, and ZnO nanowires. The devicecs was realized which are including the three electrodes of a gate, a source, and a drain electrode in the configuration of the transistor with the back-side gate as applying the photo-lithography and the electron-beam lithography techniques. At that time, it was also explained in detail that the optimization of the device fabrication such as the substrate cleaning and the post treatments with based on the several experiments. And it was also considered that the nanowires aligning method using the dielectrophoresis. Roughly two kinds of researches were implemented here for investigating the electrical properties in metal oxide nanowires, one is analyses of the changes of the electrical conductance in nanowire transistors under various circumstances like the air or the vacuum and also under the electron beam irradiation. The nanowires were categorized to n-type and p-type semiconductors for comparative analysis. Though this experiment, it was tried to enhance the understanding about the detailed behaviors of electrons, holes, and ions in active channel or on their surface as studying about the distinguishable electrical properties of each type of semiconducting nanowire device and as suggesting the consistent mechanisms. Secondly, it was suggested that the microscopic mechanisms according to the common and different electrical properties in between metal oxide nanowire devices and metal oxide thin film transistors as analyzing combatively their electrical hysteresis characteristics. It was also shown that the changes of the electrical hysteresis under various environments and the pulsed bias application methods were provided to reduce or control the electrical properties in devices. Accordingly, it was analyzed and summarized that the electrical properties and consistent mechanism of the surface ionic reactions related water molecules or oxygen in metal oxide nano-materials which has to be mainly considered and studied. The industrial device applications with metal oxide film have being gradually realized for a mass production due to its advantages such as the transparency or the high carrier mobility recently, so simultaneously the improved device simulation method for characterization has also been appeared as modifying several parts away from the existed silicon film characterization. As considering the amorphous film structure in metal oxide, it could be applied the modeling from organic thin film transistors which were established in spice modeling as the amorphous silicon transistor modeling with some modifications. So this modified spice modeling was applied in both of metal oxide film transistors and metal oxide nanowire devices comparatively. The experimental results, analyses and researches described above provide the direction of the device application realization in the extreme scaling down in semiconducting devices, especially by using the metal oxide nano-materials for the improved reliability and the reproducibility. Key words : surface reaction, metal oxide nanowire, n-type, p-type, metal oxide film, electron-beam, electrical hysteresis, Spice modeling
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Contents
Abstract …………………………............................................................................. i
Chapter 1 Introduction …………............................................................................. 1
Chapter 2 Theoretical background........................................................................... 3
2.1 Ionic reactive conduction in metal oxides ......................................................... 3
2.1.1 Oxygen on oxides ................................................................................... 3
2.1.2 Ionic reaction on semiconducting metal oxides ...................................... 4
2.1.3 Photo-assisted adsorption and desorption ............................................. 10
2.2 Si-SiO2 system ................................................................................................ 12
2.2.1 Interfacial defect structures ...................................................................... 12
2.2.2 Interface tarps .......................................................................................... 14
2.3 Metal oxide semiconductor field effect transistors ......................................... 17
2.3.1 Basic MOSFET theory............................................................................. 17
2.4 Amorphous silicon TFTs ................................................................................. 18
2.5 References ........................................................................................................ 23
Chapter 3 Experimental background...................................................................... 26
3.1 Introduction ...................................................................................................... 26
3.2 Nano-device fabrication ................................................................................... 26
3.2.1 Photolithography ................................................................................... 26
3.2.2 Electron beam lithography .................................................................... 27
3.2.3 Fabrication of nanowire devices ............................................................ 34
3.2.4 Dielectrophoresis ................................................................................... 40
3.2.5 Wet etching process ............................................................................... 46
3.2.6 Rapid thermal anneal (RTA) .................................................................. 51
3.3 Electrical measurement .................................................................................... 53
3.4 References ........................................................................................................ 55
Chapter 4 The Change of carrier concentrations in oxide nanowires by electron beam exposure ......................................................................................................... 57
4.1 Introduction...................................................................................................... 57
4.2 Ionic reaction on metal-oxide surface ............................................................. 60
4.2.1 Adsorption and desorption of oxygen and water related species .......... 60
4.3 The preparation of nanowire devices and the measuring system .................... 62
4.3.1 The Synthesis of Nanowires ................................................................. 62
4.3.2 The Fabrication of Devices ................................................................... 63
4.3.3 Electrical Measurement in the SEM ..................................................... 63
4.4 The carrier tuning by E-beam and their mechanism ....................................... 65
4.4.1 Preliminary in network device .............................................................. 65
4.4.2 Metal oxide nanowire FETs .................................................................. 69
4.4.3 Ionic Reaction and Mechanism............................................................. 72
4.4.4 Secondary Phenomenon and Mechanism ............................................. 79
4.4.5 Repetitive on/off and I-t property ......................................................... 81
4.4.6 Electrical hysteresis in nanowire FET ................................................ 85
4.5 Conclusions ..................................................................................................... 87
4.6 References ....................................................................................................... 88
Chapter 5 Electrical hysteresis in transistor .......................................................... 93
5.1 Introduction ..................................................................................................... 93
5.2 a-IGZO thin film transistor ....................................................................... 94
5.2.1 Fabrication of devices .......................................................................... 94
5.2.2 Background theory ............................................................................... 95
5.2.3 Electrical property .............................................................................. 101
5.2.4 Proposed equivalent circuit and its calculation .................................. 116
5.3 ZnO nanowire field effect transistor ...................................................... 133
5.3.1 Electrical property ............................................................................. 134
5.3.2 Calculation ......................................................................................... 148
5.4 Conclusions ............................................................................................. 153
5.5 References ............................................................................................... 154
Chapter 6 Conclusions………………….......................................................... 159
Appendix
