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High mobility field effect transistors of SnOx by reactive sputtering of Sn target on glass : 유리 위에 Sn 타겟을 이용하여 반응성 스퍼터로 증착한 높은 모빌리티 SnOx의 전계효과 트랜지스터 연구
| DC Field | Value | Language |
|---|---|---|
| dc.contributor.advisor | 차국린 | - |
| dc.contributor.author | 주찬종 | - |
| dc.date.accessioned | 2017-07-19T06:09:20Z | - |
| dc.date.available | 2017-07-19T06:09:20Z | - |
| dc.date.issued | 2015-08 | - |
| dc.identifier.other | 000000067476 | - |
| dc.identifier.uri | http://dcollection.snu.ac.kr:80/jsp/common/DcLoOrgPer.jsp?sItemId=000000067476 | - |
| dc.description | 학위논문(박사)--서울대학교 대학원 :자연과학대학 물리·천문학부,2015. 8. 차국린. | - |
| dc.description.abstract | Transparent oxide semiconductors (TOS) have attracted increasing interest recently. TOS can achieved high optical transparent and flexible electronics, such as large area panel display with ultra high definition and a high frame rate. Typical transparent oxide semiconductors such as ZnO, SnO2, In2O3-ZnO, In2O3?Ga2O3, In2O3?Ga2O3-ZnO (IGZO), ZnO?SnO2 (ZTO) have been widely researched.
Among them, the TOS based on Sn have received increasing attention because of the high thermal and chemical stability. The tin oxide have two stable phases : SnO and SnO2. In the case of SnO, the valence of Sn is +2, the crystal structure is based on corner shared SnO4 square pyramid, the bandgap is 2.8 eV, and SnO1+x appears to be a p-type semiconductor with extra oxygens. Ou et al. reported their tin oxide films grown by reactive evaporation method were p-type semiconductors with mobilities of ~0.01 cm2 V-1 s-1, which is likely due to formation of the SnO phase. Moreover, oxide semiconductor-based complementary metal-oxide-semiconductor (CMOS) inverters have been demonstrated by using IGZO as the n-type and SnOx as the p-type channel layers. The other phase of the tin oxides is SnO2, where the valence of Sn is +4, the crystal structure is a rutile based on corner and edge shared SnO6 octahedra, the bandgap is 3.6 eV, and SnO2-x becomes an n-type semiconductor with oxygen vacancies. More importantly, the SnO2 films are reported to exhibit the best thermal and chemical stability. In addition, they are inexpensive to make and have high mechanical durability. There have been several attempts to use SnO2 as the channel layer for thin film transistor (TFT), although the field effect mobility values were rather low in the range of 0.1~2.0 cm2 V-1 s-1. For example, Presley et al. reported a fully transparent SnO2-x TFT with a field effect mobility of 0.8~2.0 cm2 V-1 s-1. However, surprisingly, Sun et al. reported a field effect mobility of 158 cm2V-1s-1 in a Sb-doped SnO2 TFT. No such high field effect mobility have been reported ever since. In this paper, we report on the electrical and structural properties of SnOx thin films. We show our investigation that the electrical properties of SnOx films are very sensitive to changes in a total mixing gas (Ar + O2) pressure. Moreover fully transparent field-effect transistors of SnOx channel made by reactive sputtering of a Sn metal target with various gate insulator on glass substrates are investigated. Then we demonstrate FETs in an MIS heterostructure using Indium tin oxide (ITO) electrodes, Al2O3, HfOx and SiO2 as the gate dielectrics, and SnOx as the channel layer on insulating SnOx buffer layer. Key performance metrics including mobility, current on/off ratio, and subthreshold swing of the SnOx TFT devices fabricated on glass substrate with Sn metal target are better than those of conventional metal oxide TFTs. | - |
| dc.description.tableofcontents | Abstract
Contents List of Tables List of Figures Chapter 1 Introduction…………………………………………………………………………………13 Chapter 2 Description of experiment……………………………………………………………32 2.1 DC magnetron sputtering system………………………………………………………32 2.1.1 Basic concept of DC magnetron sputtering system………………………32 2.1.2 Part of DC magnetron sputtering system I : Chamber…………………35 2.1.3 Part of DC magnetron sputtering system II : Gun & target……………37 2.2 Pulsed laser deposition system and Tube furnance……………………………38 2.3 Atomic layer deposition system…………………………………………41 Chapter 3 Properties of SnOx films…………………………………………………………………44 3.1 Structure of SnO2 and SnO…………………………………………………………………44 3.2 Surface properties of SnOx films…………………………………………………………46 3.3 Phase analysis of SnOx films…………………………………………………………………49 3.3.1 Amorphous phase before post-deposition annealing……………………49 3.3.2 Polycrystalline phase after post-deposition annealing…………………52 3.4 Electrical properties of polycrystalline SnOx films………………………………54 3.5 Buffer effect of polycrystalline SnOx films ……………………………………………56 Chapter 4 Properties of field effect transistors with SiO2 gate insulator………58 4.1 Structure of SnOx FET with SiO2 gate insulator ……………………………………58 4.2 Output characteristics IDS-VDS curves……………………………………………………60 4.3 Transfer characteristics IDS-VGS curves…………………………………………………61 Chapter 5 Investigation of Al2O3 and HfOx gate insulators……………………………63 5.1 Reported properties of Al2O3 and HfOx………………………………………………64 5.2 Properties of Al2O3 and HfOx gate insulators………………………………………66 5.2.1 Preparation of masks……………………………………………………………………66 5.2.2 AFM and SEM images of Al2O3………………………………………………………68 5.2.3 AFM and SEM images of HfOx………………………………………………………70 5.2.4 Dielectric constant of Al2O3 and HfOx……………………………………………71 Chapter 6 Properties of field effect transistors with Al2O3 or HfOx gate insulators……………………………………………………………………………………74 6.1 Process of field effect transistor …………………………………………………………74 6.2 Structure of field effect transistor ………………………………………………………76 6.3 Hydrogen effect of ALD process…………………………………………………………78 6.4 Theory of Field effect transistor…………………………………………………………80 6.5 Polycrystalline SnOx field effect transistor with Al2O3 gate insulator …84 6.5.1 Output characteristics IDS-VDS curves……………………………………84 6.5.2 Transfer characteristics IDS-VGS curves ……………………………………86 6.6 Polycrystalline SnOx field effect transistor with HfOx gate insulator …88 6.6.1 Output characteristics IDS-VDS curves………………………………………88 6.6.2 Transfer characteristics IDS-VGS curves………………………………………90 Chapter 7 Analysis of high off current……………………………………………………………93 7.1 The conceptual diagram of off current path………………………………………93 7.2 Analysis of Ioff current from gating effect …………………………………………95 7.3 Analysis of Ioff current from leakage current of gate Insulator……………96 7.4 Analysis of interface trapped charge by subthreshold swing………………92 7.5 Analysis of Interface trapped charge by capacitance and conductance ? frequency characteristics …………………………………………………………………99 7.5.1 SnOx/HfOx interface trapped charge……………………………………………99 7.6 Analysis of Interface trapped charge in depletion region …………………101 7.7 Summary of analysis…………………………………………………………………………102 Chapter 8 Summary……………………………………………………………………………………104 Abstract (In Korean) …………………………………………………………………………………106 List of Tables Table 1. Summary of physical properties of the transparent conducting oxides, In2O3, ZnO and SnO2 ……………………………………………………………………………………………………………………………14 Table 2. Comparison the pros and cons between oxide semiconductor TFTs …………………19 Table 3. The condition of pulsed laser deposition for Indium tin oxide (ITO) and electrical properties of ITO grown by pulsed laser deposition system……………………………………………39 Table 4. Properties of high-k gate insulator Al2O3 and HfOx ..............................................65 Table 5. Properties of field effect transistors with SnOx channels…………………………………91 List of Figures Figure 1.1. Decrease of the resistivity achieved for TCO materials over the last 30 years…15 Figure 1.2. Band structure calculations for (a) SnO2, (b) Sb doped SnO2 and for (c) In2O3 and (d) Sn doped In2O3 (ITO)……………………………………………………………………………………………………17 Figure 1.3. Schematic of the broadening of the optical band gap due to the Burstein-Moss effect…………………………………………………………………………………………………………………………………18 Figure 1.4. Initial patents of field effect devices submitted by Lilienfeld in 1925………………20 Figure 1.5. (a) The photograph and (b) Output characteristics of the CdS TFTs reported by Weimer in 1962………………………………………………………………………………………………………………20 Figure 1.6. Cross-sectional view of the SnO2 thin film transistor reported by Klaseus and Koelmams in 1964……………………………………………………………………………………………………………21 Figure 1.7. Output characteristics of Li doped ZnO reported by Boesen and Jacobs in 1968…………………………………………………………………………………………………………………………………21 Figure 1.8. (a) Structure and (b) Photograph of flexible TFT reported by Nomura in 2004……………………………………………………………………………………………………………………………………23 Figure 1.9. Number of oxide TFTs related papers published per year. In the legend, S means solution processed…………………………………………………………………………………………………………24 Figure 1.10. (a) Structure and (b) Output characteristics of a top gate TFT reported by Ogo in 2008……………………………………………………………………………………………………………………………………25 Figure 1.11. (a) Output characteristics and (b) Transfer characteristics of the top gate SnO2 TFTs reported by Ou in 2008………………………………………………………………………………………………26 Figure 1.12. (a) Transfer characteristic of SnO TFTs reported by Lee in 2010 and (b) Transfer characteristic of SnO TFTs reported by Liang in 2010………………………………………………………27 Figure 1.13. Structure and transfer characteristic of SnO TFTs reported by Fortunato in 2011 …………………………………………………………………………………………………………………………………………28 Figure 2.1. Photograph of plasma. The color of plasma depends on target, inserting gas, and working power………………………………………34 Figure 2.2. The diagram of sample growth process in DC magnetron sputter …………………34 Figure 2.3. DC magnetron sputtering system…………………………………………………………………36 Figure 2.4. Mass flow controller ………………………………………………………………………………………36 Figure 2.5. Sn metal target in sputter chamber…………………………………………………………………37 Figure 2.6. Pulsed laser deposition system………………………………………………………………………39 Figure 2.7. Tube furnance…………………………………………………………………………………………………40 Figure 2.8. Atomic layer deposition …………………………………………………………………………………42 Figure 2.9. Schematic diagram depicting a completed ALD cycle………………………………………42 Figure 3.1. Unit cell of the crystal structure of SnO2 and SnO……………………………………………45 Figure 3.2. Schematic of the chemical bond between oxide anions and tin cations in SnO2 and SnO……………………………………………………………………………………………………………………………45 Figure 3.3. Transparency of polycrystalline 100 nm SnOx thin film……………………………………47 Figure 3.4. The surface morphologies of polycrystalline 100 nm SnOx thin film grown with 1.2 mTorr and 3.3 mTorr oxygen partial pressure………………………………………………………………47 Figure 3.5. The images of polycrystalline 100 nm SnOx thin films grown with various oxygen partial pressures…………………………………………………………………………………………………………………48 Figure 3.6. The X-ray diffraction patterns of amorphous 100 nm SnOx thin films grown with 1.2 mTorr (red) and 3.3 mTorr (black) oxygen partial pressure. Inset : Fast Fourier transform of amorphous 100 nm SnOx thin film grown 3.3 mTorr oxygen partial pressure…………………50 Figure 3.7. The X-ray diffraction patterns of amorphous 100 nm SnOx thin films grown with 1.2 mTorr (red) and 3.3 mTorr (black) oxygen partial pressure. Inset : Fast Fourier transform of amorphous 100 nm SnOx thin film grown 3.3 mTorr oxygen partial pressure…………………52 Figure 3.8. The electrical properties of 100 nm polycrystalline SnOx thin films after post- deposition annealing at 400 ℃ as a function of oxygen partial pressure(mTorr)………………54 Figure 3.9. The 100 nm polycrystalline SnOx thin films electrical comparison between with and without buffer layer as a function of oxygen partial pressure (mTorr)…………………………55 Figure 4.1. Structure of the bottom gate FET with SiO2 gate insulator. (a) Our FET has been fabricated, employing ITO as the source, drain, and SiO2 as the gate insulator, and SnOx as channel. (b) The top view image of our device is presented………………………………………………59 Figure 4.2. Comparison of the 1.2 mTorr and 2.1 mTorr SnOx top-gate FET devices with SiO2 gate insulator (a) Output characteristics, IDS-VDS curves of SnOx channel grown at 1.2 mTorr oxygen partial pressure for various gate bias VGS at room temperature, (b) Output characteristics, IDS-VDS curves of SnOx channel grown at 2.1 mTorr oxygen partial pressure for various gate bias VGS at room temperature …………………………………………………………………61 Figure 4.3. Comparison of the 1.2 mTorr and 2.1 mTorr SnOx top-gate FET devices with SiO2 gate insulator (a) the transfer characteristics, IDS-VGS curves of SnOx channel grown at 1.2 mTorr oxygen partial pressure, (b) the transfer characteristics, IDS-VGS curves of SnOx channel grown at 2.1 mTorr oxygen partial pressure..……………………………………………………………………63 Figure 5.1. Silicon channel 4 lines mask………………………………………………………………………………67 Figure 5.2. SUS source-drain mask……………………………………………………………………………………67 Figure 5.3. Top gate contact mask………………………………………………………………………………………67 Figure 5.4. (a) Surface morphologies and (b) Cross-section view of SEM of 90 nm Al2O3 thin film on glass ………………………………………………………………………………………………………………………69 Figure 5.5. (a) Surface morphologies and (b) Cross-section view of SEM of 90 nm HfOx thin film on glass………………………………………………………………………………………………………………………70 Figure 5.6. Capacitance-frequency characteristics of (a) Al2O3 and (b) HfOx gate insulators..72 Figure 6.1. Progress of SnOx field effect transistor………………………………………………………………75 Figure 6.2. Structure of the top gate FET device and the dielectric properties of Al2O3 or HfOx. (a) Our FET has been fabricated, employing ITO as the source, drain, and gate electrode, Al2O3 or HfOx as the gate insulator, and SnOx channel. The channel length and the width of the FET device were 140 μm and 60 μm, respectively. (b) The top view image of our device is presented…………………………………………………………………………………………………………………………77 Figure 6.3. Hydrogen effect in progress of SnOx field effect transistor………………………………79 Figure 6.4. Comparison of the 1.2 mTorr and 2.1 mTorr SnOx top-gate FET devices with Al2O3 gate insulator (a) Output characteristics, IDS-VDS curves of SnOx channel grown at 1.2 mTorr oxygen partial pressure for various gate bias VGS at room temperature and (b) Output characteristics, IDS-VDS curves of SnOx channel grown at 2.1 mTorr oxygen partial pressure for various gate bias VGS at room temperature…………………………………………………………………85 Figure 6.5. Comparison of the 1.2 mTorr and 2.1 mTorr SnOx top-gate FET devices with Al2O3 gate insulator. The transfer characteristics, IDS-VGS and IGS-VGS of the FET devices with SnOx channel grown at 1.2 mTorr and 2.1 mTorr oxygen partial pressure…………………………………87 Figure 6.6. Comparison of the 1.2 mTorr 1.5 mTorr and 2.1 mTorr SnOx top-gate FET devices with HfOx gate insulator (a) Output characteristics, IDS-VDS curves of SnOx channel grown at 1.2 mTorr oxygen partial pressure for various gate bias VGS at room temperature, (b) Output characteristics, IDS-VDS curves of SnOx channel grown at 1.5 mTorr oxygen partial pressure for various gate bias VGS at room temperature and (c) Output characteristics, IDS-VDS curves of SnOx channel grown at 2.1 mTorr oxygen partial pressure for various gate bias VGS at room temperature……………………………………………………………………………………………………………89 Figure 6.7. Comparison of the 1.2 mTorr, 1.5 mTorr and 2.1 mTorr SnOx top-gate FET devices with HfOx gate insulator. The transfer characteristics, IDS-VGS and IGS-VGS of the FET devices with SnOx channel grown at 1.2 mTorr, 1.5 mTorr and 2.1 mTorr oxygen partial pressure …91 Figure 7.1. The conceptual diagram of off current path……………………………………………………94 Figure 7.2. The conceptual diagram of depletion by gate insulator………………………………95 Figure 7.3. The breakdown field and the structure of HfOx junction…………………………………96 Figure 7.4. The conceptual diagram of subthreshold swing in IDS-VGS curve……………………98 Figure 7.5. Measured capacitance (C, black line) and normalized conductance (G/ω, red line) per unit area as a function of frequency ω for SnOx/HfOx interface. The sample was held at room temperature with a dc bias of -6 V……………………………………………100 Figure 7.6. The scheme of band structure of FET in depletion………………………………………101 | - |
| dc.format.extent | 109 | - |
| dc.language.iso | eng | - |
| dc.publisher | 서울대학교 대학원 | - |
| dc.subject | Reactive sputtering system, Transparent oxide semiconductor, Tin monoxide, SnO, Tin dioxide, SnO2, SnOx, n-type semiconductor, Thin film, Transparent field effect transistor, Al2O3, HfOx, SiO2, High mobility | - |
| dc.subject.ddc | 523 | - |
| dc.title | High mobility field effect transistors of SnOx by reactive sputtering of Sn target on glass | - |
| dc.title.alternative | 유리 위에 Sn 타겟을 이용하여 반응성 스퍼터로 증착한 높은 모빌리티 SnOx의 전계효과 트랜지스터 연구 | - |
| dc.type | Thesis | - |
| dc.type | Dissertation | - |
| dc.contributor.department | 자연과학대학 물리·천문학부 | - |
| dc.description.degree | Doctor | - |
| dc.date.awarded | 2015-08 | - |
| dc.identifier.holdings | 000000000023▲000000000025▲000000067476▲ | - |
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