Title Page
Abstract
Contents
Chapter 1. Introduction 18
1.1. Needs for high-k 18
1.2. History of high-k 18
1.3. Comparison of high-k dielectrics 20
References 22
Chapter 2. Properties of BaHf₁₋xTixO₃ (BHTO)[이미지참조] 24
2.1. Research background 24
2.2. Dielectric properties of BaHf₁₋xTixO₃ (BHTO) system[이미지참조] 24
2.3. Structural properties of BaHf₁₋xTixO₃ (BHTO) system[이미지참조] 29
2.4. Optical properties of BaHf₁₋xTixO₃ (BHTO) system[이미지참조] 30
2.5. Field effect transistors using BaHf₀.₆Ti₀.₄O₃ 31
2.6. Conclusions 33
References 34
Chapter 3. Properties of BaHf₀.₆Ti₀.₄O₃ 35
3.1. Research background 35
3.2. Dielectric properties of BaHf₀.₆Ti₀.₄O₃ 35
3.3. Field effect transistors using BaHf₀.₆Ti₀.₄O₃ for modulation beyond 10¹⁴ cm⁻² 44
3.4. Structural properties of BaHf₀.₆Ti₀.₄O₃ 52
3.4.1. Scanning Transmission Electron Microscope (STEM) of BaHf₀.₆Ti₀.₄O₃ 52
3.4.2. High-resolution X-ray diffraction (HRXRD) of BaHf₀.₆Ti₀.₄O₃ 55
3.5. Optical bandgap of BaHf₀.₆Ti₀.₄O₃ 57
3.6. Percolation path formation model 58
3.7. Conclusion 59
References 61
Chapter 4. Size effect of BaHf₀.₆Ti₀.₄O₃ (BHTO) 62
4.1. Research background 62
4.2. Origins of size effect 63
4.3. Soft phonon propagation 65
4.4. Thickness dependence of dielectric constant of BHTO 67
4.5. Effect of top ITO electrode on interfacial capacitance 70
4.6. Effect of bottom SrRuO₃ electrode on interfacial capacitance 72
4.7. Conclusion 75
References 76
Chapter 5. Properties of SrHfO₃ 78
5.1. Research background 78
5.2. Dielectric properties of SrHfO₃ 80
5.3. Field-effect transistor using SrHfO₃ dielectric 87
5.4. Structural properties of SrHfO₃ 90
5.5. Future work 101
5.6. Conclusion 102
References 103
List of publications 107
List of presentations 107
국문초록 108
Chapter 1. 17
Table 1.1. Comparison of high-k materials. 21
Chapter 3. 17
Table 3.1. Calculated thickness of BHTO with different set of angles from Kiessig fringes. From the Bragg's law, 2dsinθ=nλ, thickness of film d is calculated for... 38
Table 3.2. Calculated dielectric constant of BHTO from different kinds of approximations. fBHO=0.6 and fBTO=0.4 were used.[이미지참조] 41
Chapter 4. 17
Table 4.1. Comparison of interfacial capacitance in various dielectric. 69
Chapter 2. 9
Figure 2.1. Dielectric constants of BaHf₁₋xTi-xO₃ system (a) BaHf₀.₈Ti₀.₂O₃ (b) BaHf₀.₆Ti₀.₄O₃ (c) BaHf₀.₄Ti₀.₆O₃ (d) BaHf₀.₂Ti₀.₈O₃.[이미지참조] 25
Figure 2.2. Breakdown field of BaHf₁₋xTi-xO₃ system (a) BaHf₀.₈Ti₀.₂O₃ (b) BaHf₀.₆Ti₀.₄O₃ (c) BaHf₀.₄Ti₀.₆O₃ (d) BaHf₀.₂Ti₀.₈O₃.[이미지참조] 26
Figure 2.3. Dielectric constants and breakdown fields of BHTO, 2-dimensional carrier density which BHTO can modulate with various alloying ratios. 27
Figure 2.4. Calculation of dielectric constants of BHTO as a function of the alloying ratio calculated by effective medium theory. 28
Figure 2.5. Statistical measurement data of (a) dielectric constant and (b) breakdown field of BaHf₀.₆Ti₀.₄O₃. 29
Figure 2.6. RSM of BHTO with various alloying ratios on BLSO (a) BaHf₀.₈Ti₀.₂O₃ (b) BaHf₀.₆Ti₀.₄O₃ (c) BaHf₀.₄Ti₀.₆O₃ (d) BaHf₀.₂Ti₀.₈O₃. 30
Figure 2.7. Lattice constant derived from RSM of BHTO with various alloying ratios on BLSO. 30
Figure 2.8. The optical bandgap of BHTO. (a) BaHf₀.₈Ti₀.₂O₃ (b) BaHf₀.₆Ti₀.₄O₃ (c) BaHf₀.₄Ti₀.₆O₃ (d) BaHf₀.₂Ti₀.₈O₃. 31
Figure 2.9. FET made with 0.3% BLSO channel layer and BaHf₀.₆Ti₀.₄O₃ gate oxide. (a) schematic of the device. (b) The top view of the device pictured by an optical... 33
Chapter 3. 9
Figure 3.1. X-ray diffraction measurement of BHTO capacitor and Kiessig fringes of BHTO peak. (a), (b), (c) X-ray diffraction data of BHTO MIM capacitor and... 37
Figure 3.2. Dielectric properties of BHTO. (a) Frequency-dependent capacitance curve of a BaHf₀.₆Ti₀.₄O₃ metal-insulator-metal device. The inset shows the layer... 38
Figure 3.3. Fowler-Nordheim analysis and comparison of band diagrams. (a) J-E characteristic of BHTO capacitor. (b) ln(J E⁻²) vs E⁻¹ curve for Fowler-Nordheim... 39
Figure 3.4. Statistical measurement data of 21 MIM devices. (a) Dielectric constant. (b) Breakdown field of BaHf₀.₆Ti₀.₄O₃. The symbol ± denotes standard deviations. 40
Figure 3.5. I-V characteristics of several BaHf₀.₆Ti₀.₄O₃ capacitors. The current measurement in (b) is limited by the compliance current, and the EBD is located...[이미지참조] 42
Figure 3.6. Comparison of dielectric constant, breakdown field of dielectric materials including well-known high-k materials. Each colored lines denotes... 43
Figure 3.7. FET in an n-type accumulation mode made with 0.1% BLSO channel layer and BaHf₀.₆Ti₀.₄O₃ gate oxide. (a) Schematic of the device. (b) The top view... 44
Figure 3.8. Detailed geometry for the channel length and width and the gate length for the accumulation mode FET. 46
Figure 3.9. √ID vs VGS plot in linear scale for determining threshold voltage (VT) of device.[이미지참조] 47
Figure 3.10. Thickness profile of 0.4% BLSO channel by AFM measurement. 48
Figure 3.11. Hall measurement of a 20 nm thick 0.4% La-doped BSO film. (A) Schematic of the film. (B) Geometry of 4-probe Hall measurement. (C) Hall... 49
Figure 3.12. FET in an n-type depletion mode made with 0.4 % La-doped BSO channel layer and Hf₀.₆Ti₀.₄O₃ gate oxide. (a) Schematic of the device. (b) The top... 50
Figure 3.13. Detailed geometry for the channel width and length and the gate length of the depletion mode FET. 51
Figure 3.14. Capacitance of a BHTO depletion mode FET with 0.4% BLSO channel (A) Capacitance-frequency curve of depletion mode FET with zero dc bias... 52
Figure 3.15. STEM image of BaHf₀.₆Ti₀.₄O₃. (a) HAADF-STEM of various magnification scales. (b) LAADF-STEM of various magnification scales. 54
Figure 3.16. EELS of BHTO. (a) EELS element mapping image of BaHf₀.₆Ti₀.₄O₃. (b) Region of EELS line scan. Red arrows denote scan directions. (c) Line profile... 54
Figure 3.17. RSM of BHTO. (a) Reciprocal space mapping (RSM) of BaHf₀.₆Ti₀.₄O₃ (103) peak. (b) (002) peaks and corresponding rocking curves. Black... 55
Figure 3.18. Rocking curves of BaHf₀.₆Ti₀.₄O₃ capacitor from XRD measurements. 56
Figure 3.19. Optical band gap of BaHf₀.₆Ti₀.₄O₃. Bandgap fitting is performed assuming direct bandgap. 57
Figure 3.20. Percolation path formation model in heterogeneous BaHf₀.₆Ti₀.₄O₃ system. In Ti-rich regions, defects are more easily generated compared to Hf-rich... 59
Chapter 4. 12
Figure 4.1. Interfacial low-k capacitance model between dielectric and electrodes. 62
Figure 4.2. Soft phonon density propagation model depending on interfacial bonding. 66
Figure 4.3. Thickness dependent dielectric constant of BHTO. 67
Figure 4.4. Inverse capacitance per area of BHTO depending on the dielectric thickness. 68
Figure 4.5. (a) Thickness dependent dielectric constant of BSHO (b) Inverse capacitance per area of BSHO depending on the dielectric thickness. 70
Figure 4.6. Schematic of BHTO MIM capacitors. Top electrode is replaced to ITO. 71
Figure 4.7. Comparison of BHTO MIM capacitors with top 4% BLSO electrodes and ITO electrodes. (a) Dielectric constants (b) Interfacial capacitance. 71
Figure 4.8. Comparison of BHTO MIM capacitors with top SRO electrodes and ITO electrodes. (a) Average dielectric constants (b) Interfacial capacitance when... 73
Figure 4.9. Comparison of BHTO MIM capacitors with top SRO electrodes and ITO electrodes. (a) Average dielectric constants (b) Interfacial capacitance when... 74
Figure 4.10. RSM of SRO/BHTO/ITO capacitors and derived lattice parameters. 74
Chapter 5. 13
Figure 5.1. Dielectric properties of SrHfO₃. (a) Frequency-dependent capacitance curve of SHO capacitors deposited in 30 mTorr. The inset shows the structure of... 81
Figure 5.2. DC electric field dependence of dielectric constant for SHO dielectric deposited in various oxygen partial pressures. Significant dependence of dielectric... 81
Figure 5.3. Leakage current density vs. electric field measured in two different modes. In a slow and quiet mode, the tens of pA current level dropped to a few pA. 82
Figure 5.4. Comparison of leakage current density of SrHfO₃ capacitors. (a-c) Leakage current density vs. electric field for SrHfO₃ capacitors deposited in 1, 10,... 83
Figure 5.5. Dielectric properties of SrHfO₃ capacitors deposited at various oxygen partial pressures. The leakage current densities are measured at 2 MV cm⁻¹. 83
Figure 5.6. Analysis of Fowler-Nordheim tunneling and comparison of band levels. (a) ln(J E⁻²) vs. E⁻¹ plot for Fowler-Nordheim analysis of BHO, LSO, LIO and... 86
Figure 5.7. Optical band gap of SHO thin films grown on MgO (001) substrate. Tauc's plot for (a) direct band gap and (b) indirect band gap for SHO thin films... 86
Figure 5.8. Comparison of leakage current density for binary and ternary gate oxides. High-k SrHfO₃ perovskite dielectric has ultra-low leakage current density... 87
Figure 5.9. FET in an n-type accumulation mode made with 0.3% La-doped BaSnO₃ channel layer and SrHfO₃ gate oxide. (a) A schematic of the device. (b)... 89
Figure 5.10. X-ray diffraction (XRD) of SHO FET. (a) θ-2θ scan and (b) rocking curves for FET with SHO gate oxide deposited in 30 mTorr. 89
Figure 5.11. Threshold voltage (Vth) of the device in the saturation region. Vth extracted by the linear extrapolation of √ID vs VGS plot is estimated to be 6 V.[이미지참조] 90
Figure 5.12. Reciprocal space mapping (RSM) measurement. (a) RSM (013) images for SHO capacitors deposited in 1, 10, 30, and 100 mTorr. The red, green,... 91
Figure 5.13. RSM (013) measurement for SHO capacitors deposited in 30 mTorr. (a) The RSM (013) images measured by rotating the devices 0°, 90°, 180°, and 270°... 92
Figure 5.14. X-ray reflectivity (XRR) measurement for SHO thin films. The experimental data of SHO thin films grown at 1, 10, 20, 30, 50, and 100 mTorr.... 93
Figure 5.15. Reciprocal space mapping (RSM) measurement. (a) RSM (013) images for SHO thin films deposited in 1, 10, 30, and 100 mTorr on STO substrates.... 93
Figure 5.16. X-ray diffraction measurement. (a) θ-2θ scan and rocking curves for SrHfO₃ thin films grown in various oxygen partial pressures. The energy fluence... 95
Figure 5.17. (a, b) The XPS spectra of Sr 3d and Hf 4f region for SHO thin films deposited in various oxygen partial pressures. (c) Cation stoichiometric ratio in... 96
Figure 5.18. X-ray diffraction (XRD) measurement for SHO thin films. (a) θ-2θ scan and rocking curves for SrHfO₃ thin films on SrTiO₃ (001) substrate grown at... 96
Figure 5.19. Deconvolution of rocking curves for SHO (002). (a-f) The rocking curves for SHO thin films on STO substrate grown in 1, 10, 20, 30, 50 and 100... 98
Figure 5.20. The results of deconvolution of the 2θ peak for SHO by using the Voigt functions (black and red line). Symmetric 2θ peak for SHO deposited in 30... 99
Figure 5.21. (a) Cross-sectional STEM images of the SHO capacitors grown in 30 mTorr. Magnified HAADF-STEM image of the SHO-BLSO interface (yellow box)... 101