Electrical Properties of Inhomogeneous Pb(Zr0.52Ti0.48)O3 Thin Films
- 주제(키워드) ferroelectric , PZT , x-ray , C-V , I-V , interface
- 발행기관 서강대학교 일반대학원
- 지도교수 박광서
- 발행년도 2009
- 학위수여년월 2009. 2
- 학위명 석사
- 실제URI http://www.dcollection.net/handler/sogang/000000044866
- 본문언어 영어
초록/요약
비균질한 Pb(Zr0.52Ti0.48)O3 (PZT) 박막의 구조 및 전기적 특성에 대해 연구하였다. PZT 박막의 결정구조를 확인하기 위해 고분해능 x-ray 회절 (high resolution x-ray diffraction)을 이용하였고, 계면의 거칠기 및 각 PZT층의 전자밀도를 확인하기 위하여 x-ray 반사율 (x-ray specular reflectivity) 측정을 하였다. Pt 기판위에 화학 용액 증착법 (chemical solution deposition)으로 성장한 PZT 박막 내에서 두 개의 PZT층과 한 개의 계면층을 관찰하였고, 상부 PZT층은 하부 PZT층에 비하여 낮은 전자밀도를 가지고 있음을 확인하였다. 전기적 특성을 측정하기 위하여 Pt/PZT/Pt 축전기를 구성하고 그의 전기적 특성을 알아보았다. 그 결과 PZT 축전기는 C-V와 I-V에서 극성에 따른 강한 비대칭성을 보였다. 이러한 전기적 특성의 비대칭성은 도핑농도 (doping concentration)와 내부전위 (built-in potential)의 차이를 줄 수 있는 계면 근처의 거칠기에 기인한다는 것을 확인하였다. 또한 이는 전도특성 (conduction mechanism) 분석을 통해 상부 PZT층과 하부 PZT층 내의 서로 다른 산소 및 Pb 빈자리 (vacancy) 분포에 기인함을 알 수 있다.
more초록/요약
We have studied the structural and electrical properties of inhomogeneous Pb(Zr0.52Ti0.48)O3 (PZT) thin films. The high resolution x-ray diffraction θ-2θ scan and the x-ray specular reflectivity techniques were employed in order to examine its crystal structure, the roughness of the interfacial layer, and the electron density of the constituent layers. We found two sublayers and an interfacial layer in the PZT thin films on Pt substrate deposited by chemical solution deposition. The PZT top and bottom sublayers had a lower and a higher electron density, respectively. Pt/PZT/Pt capacitor showed strong asymmetry on its electrical properties of I-V and C-V characteristics. It was proved that these asymmetries originate from the difference of doping concentration between two sublayers and the configuration of the roughness, giving rise to the different built-in potential near the top and bottom electrodes, which could be well explained by structural inhomogeneity. In addition, the difference of conduction mechanism at the region of the positive and negative bias could be understood by the different distribution of oxygen and lead vacancies in the PZT thin films.
more목차
1. Introduction = 1
2. Theories = 6
2.1. X-ray specular reflectivity (XRR) = 6
2.2. Metal-semiconductor contacts = 10
3. Experiments = 17
3.1. Sample preparations = 17
3.2. Structural investigations: X-ray diffraction (XRD), reflectivity, and Raman spectroscopy = 19
3.3. Electrical analyses = 21
3.3.1. Polarization vs. voltage (P-V) = 21
3.3.2. Capacitance vs. voltage (C-V) and current vs. voltage (I-V) = 22
4. Results and Discussion = 23
4.1. Structural properties of inhomogeneous Pb(Zr_(0.52)Ti_(0.48))O₃ (PZT) thin films = 23
4.2. Electrical properties of Pt/PZT/Pt heterostructures = 29
5. Summary = 42
6. References = 44
Figure
Figure 1-1. Crystal structure of the ABO3 ideal cubic perovskite structure [3] = 2
Figure 1-2. (a) In-plane diffuse x-ray scattering indicates that the ferroelectric phase is stable for thicknesses down to 3 unit cells at room temperature [4]. (b) The P - E hysteresis loop of 5 nm thick BTO thin film has been shown [5] = 2
Figure 1-3. In-depth analysis of oxygen concentration in PZT thin films by using AES [9] = 4
Figure 2-1. Energy-band diagrams of metal on n-type (left) and on p-type (right) semiconductors under different biasing conditions: (a) Thermal equilibrium, (b) Forward bias, (c) Reverse bias [17] = 12
Figure 2-2. Energy-band diagrams showing conduction mechanisms of (a) direct tunneling, (b) Fowler-Nordheim tunneling, (c) thermionic emission, and (d) Poole-Frenkel emission [17] = 16
Figure 3-1. (a) Schematic diagram of the Pt / PZT / Pt heterostructure and (b) top-view of that = 18
Figure 3-2. Geometry of a diffractometer for XRD and XRR measurement = 19
Figure 3-3. Back-scattering geometry for Raman spectra = 20
Figure 4-1. Experimental XRRs of the three PZT samples having different thicknesses (open symbols), and best fits of them (solid lines) = 24
Figure 4-2. EDPs calculated by the fits showing three regions clearly in the PZT thin films = 24
Figure 4-3. XRD curves of three PZT samples indicating (00l) preferred orientation = 26
Figure 4-4. Deconvolution of the (001) / (100) PZT peaks obtained from XRD = 26
Figure 4-5. (a) Raman spectra of the PZT thin films annealed at different temperatures [27], and (b) those of our PZT thin films = 28
Figure 4-6. P-V hysteresis curves of the (a) 460, (b) 865, and (c) 1365 A thick PZT thin films at different sampling frequencies, and (d) that of the three films at a sampling frequency of 1 kHz = 30
Figure 4-7. (a) C-V curves of the three PZT thin films at a sampling Frequency of 1 kHz, and (b) differential capacitance of them = 32
Figure 4-8. (a) Non-polarization reversal C - V curves of the PZT thin films (solid lines) and normal C-V curves (cross), and (b) those 1/C² - V curves and their linear fits = 34
Figure 4-9. An asymmetric band diagrams for the Pt/PZT/Pt heterostructure of sample (a) #1 (460 A), (b) #2 (865 A), and (c) #3 (1365 A) = 35
Figure 4-10. Current density vs. electric field (J - E) characteristics of the PZT thin films = 37
Figure 4-11. Positive bias J - E of the sample #2 and #3, fitted to Schottky thermionic emission model = 37
Figure 4-12. Positive bias J - E of the sample #2 and #3, fitted to Poole-Frenkel emission model at the intermediate region = 39
Figure 4-13. Positive bias data of the sample #2 and #3, showing a very good fit to the SCLC model at the high voltage region = 39
Figure 4-14. Negative bias data of the three samples, fitted to the Schottky thermionic emission = 40
Figure 4-15. Negative bias data of the sample #2 and #3, showing a good fit to the Fowler-Nordheim tunneling at the high field region = 40
Table
Table 4-1. Electron density (ρ), thickness (d) and roughness (σ) of the constituent layers in the PZT thin films obtained from the fits = 25
