Title Page
ABSTRACT
국문 초록
Contents
Abbreviations 16
1. Introduction 17
1.1. Motivation 18
1.2. Materials 19
1.2.1. Perovskite oxides 19
1.2.2. STO and LAO 21
1.2.3. STO/LAO bilayer 24
1.3. Oxide deposition 36
1.3.1. Surface treatment of STO substrate 36
1.3.2. Deposition of perovskite oxides 40
1.3.3. Device fabrication 48
2. Results 56
2.1. Experimental setup 56
2.2. Electronic properties of the trilayer thin film 61
2.2.1. Difference between bilayer and trilayer system 62
2.2.2. Thickness dependence of the electric properties 64
2.2.3. Magnetoresistance 72
2.2.4. Superconductivity 81
2.3. Quantum coherence effect in trilayer ring structure 86
2.3.1. Quantum coherence effect 86
2.3.2. Device fabrication 87
2.3.3. Little park oscillation 91
2.3.4. Aharonov-Bhom oscillation 96
2.3.5. Altshuler-Aronov-Spivak oscillation 97
2.4. Band calculation 99
2.5. Resistance change by light 101
3. Discussion 105
3.1. Critical thickness of STO/LAO/STO trilayer system 106
3.2. Little park oscillation 106
3.3. Magnetoresistance 108
4. Summary and Outlook 112
4.1. Summary 112
4.2. Outlook 114
Bibliography 117
Figure 1.1. Perovskite structure of ABO₃ 20
Figure 1.2. STO structure that changes with temperature 23
Figure 1.3. LAO deposited on STO substrate 25
Figure 1.4. Electrical properties of LAO/STO bilayer according to LAO thickness 26
Figure 1.5. Graph measuring (a) conductivity and (b) carrier density using... 28
Figure 1.6. Resistance-temperature graph according to oxygen partial... 30
Figure 1.7. Illustration of polar catastrophe theory 32
Figure 1.8. TMR (tunneling magnetoresistance) in LAO/STO bilayer samples 33
Figure 1.9. Superconductivity in LAO/STO bilayer 35
Figure 1.10. Process of etching STO substrate 38
Figure 1.11. Terrace change of STO substrate according to etching time 39
Figure 1.12. AFM picture of STO substrate (a) before and (b) after annealing 40
Figure 1.13. Photo of pulsed laser deposition in KRISS 42
Figure 1.14. Schematic illustration of pulsed laser deposition 44
Figure 1.15. (a) The path of the RHEED beam hitting the substrate and (b) a... 45
Figure 1.16. Oscillation graph of RHEED beam intensity during oxide thin... 46
Figure 1.17. A cross-sectional TEM image of a sample in which 1 UC of LAO... 47
Figure 1.18. The process of lithography of patterns using SEM 48
Figure 1.19. Photo taken with an optical microscope of the dose test to... 50
Figure 1.20. The process of fabricating a device using the amorphous LAO technique 51
Figure 1.21. The process of fabricating a device using the etching technique 53
Figure 1.22. AFM image of ring device fabricated by (a) amorphous LAO... 54
Figure 2.1. Measurement of a square conductivity sample in the Van der Pauw 58
Figure 2.2. Schematic of a van der Pauw configuration used in the... 59
Figure 2.3. Photo of the Physical Properties Measurement System 60
Figure 2.4. (a) Sheet resistance and (b) Hall coefficient (RH/H) as a function of...[이미지참조] 63
Figure 2.5. Distribution of conductivity of each sample at room temperature 65
Figure 2.6. Electrical properties when the sum of the thicknesses of LAO and... 68
Figure 2.7. Electrical properties according to the thickness of deposited STO... 71
Figure 2.8. Magnetoresistance as a function of the angle θ and φ of... 73
Figure 2.9. Resistance graph that changes with angle at each temperature... 74
Figure 2.10. Resistance graph that changes with angle at each magnetic field... 76
Figure 2.11. A graph plotting the resistance according to the rotation angle... 79
Figure 2.12. Magnetoresistance as a function of temperature when magnetic... 80
Figure 2.13. Magnetoresistance as a function of temperature when magnetic... 81
Figure 2.14. (a) Critical magnetic field at 20 mK and (b) Critical temperature... 84
Figure 2.15. Critical current according to sweep direction of magnetic field at... 85
Figure 2.16. Schematic of the ring pattern 88
Figure 2.17. AFM image of the fabricated ring pattern 90
Figure 2.18. Optical micrograph and AFM image of the ring device. The inner... 92
Figure 2.19. Critical current depending on temperature of ring device 93
Figure 2.20. Measured oscillation as a function of the back gate voltage in a... 95
Figure 2.21. Bandgap according to thickness of LAO and STO confirmed by calculation 100
Figure 2.22. Time-dependent resistance of resistance to light when the total... 103
Figure 3.1. 2D map graph of dV/dI according to current with changing... 107
Figure 3.2. Angular resistance as a function of angle at the temperature is 2 K... 110