Nghiên cứu nâng cao tính chất sắt điện của màng mỏng PZT chế tạo bằng công nghệ sol gel

MINISTRY OF EDUCATION AND TRAINING HANOI UNIVERSITY OF TECHNOLOGY INTERNATIONAL TRAINING INSTITUTE FOR MATERIALS SCIENCE LE VAN MINH IMPROVEMENT IN FERROELECTRIC PROPERTY OF PZT THIN FILMS FABRICATED BY SOL-GEL METHOD MASTER THESIS OF MATERIALS SCIENCE BATCH ITIMS - 2006 Supervisor: Associate Prof Dr VU NGOC HUNG Hanoi - 2008 BỘ GIÁO DỤC VÀ ĐÀO TẠO TRƯỜNG ĐẠI HỌC BÁCH KHOA HÀ NỘI VIỆN ĐÀO TẠO QUỐC TẾ VỀ KHOA HỌC VẬT LIỆU LÊ VĂN MINH NGHIÊN CỨU NÂNG CAO TÍNH CHẤT SẮT ĐIỆN CỦA MÀNG MỎNG PZT CHẾ TẠO BẰNG CÔNG NGHỆ SOL-GEL LUẬN VĂN THẠC SĨ KHOA HỌC VẬT LIỆU KHOÁ ITIMS - 2006 Người hướng dẫn khoa học: PGS TS VŨ NGỌC HÙNG Hà Nội - 2008 ACKNOWLEDGMENTS My most sincere gratitude belongs to Associate Professor Vu Ngoc Hung for his continuous support and advice in my research efforts Moreover, besides expanding my breadth of ferroelectric knowledge, Prof Hung has made working at MEMS Group, International Training Institute for Materials Science (ITIMS), a true pleasure I’d also like to acknowledge IMS, Twente University, MESA+, the Netherlands, for analyzing and measuring experiment samples including XRD, AFM, FE-SEM, and TF2000 piezoelectric mode Special thanks go to PhD Nguyen Duc Minh, IMS, Twente, University, MESA+, the Netherlands for directly implementing these analyses and measurements I would also like to express my appreciation to the rest of the MEMS Group including, Dr Trinh Quang Thong, Nguyen Van Minh for their daily help and sincere friendship Special thanks go to Ms Bui Thi Huyen, an undergraduate student, for spending her time to take experiments along with me and Ms Vu Thu Hien, who investigated PZT thin film materials in 2007 and helped establish the scientific kernel and intrigue for completing this current work I would also like to thank ITIMS for making a scientific environment and facilities Special thanks go to Dr Nguyen Anh Tuan and Ms Le Thanh Hung for sputtering supports and Dr Pham Thanh Huy who gave me authority to use his group’s furnace system Finally, I would like to thank my family, especially Mom, Dad, my old brothers, Le Van Son and Le Van Quang, for their continual love and support as well as their forbearance of my scientific babble Without this link to family, I would become totally consumed by science, which would be a sad life indeed Hanoi, September, 2008 LE VAN MINH VIỆN ĐÀO TẠO QUỐC TẾ VỀ KHOA HỌC VẬT LIỆU ITIMS KHOÁ 2006 Tiêu đề luận văn: “Nghiên cứu nâng cao tính chất sắt điện màng mỏng PZT chế tạo công nghệ sol-gel” Tác giả: Lê Văn Minh Người hướng dẫn: PGS.TS Vũ Ngọc Hùng Người nhận xét: Tóm tắt: Màng mỏng PZT [(PbZrxTi1-x)O3], với tính chất sắt điện, áp điện, hoả điện bật vật liệu nghiên cứu ứng dụng lĩnh vực cơng nghệ MEMS, nhớ FeRAM, vv… Tại phịng thí nghiệm MEMS Viện ITIMS, màng mỏng PZT triển khai nghiên cứu thời gian vài năm trở lại Bước đầu xây dựng quy trình tổng hợp sol-gel chế tạo màng mỏng PZT, xong cịn số hạn chế tính chất màng màng rạn nứt, nhiều rosettes, độ phân cực điện dư (Pr) nhỏ điện trường khử phân cực (Ec) lớn Mục tiêu luận văn tiến hành nghiên cứu để tạo màng mỏng PZT có tính chất nâng cao nhằm định hướng ứng dụng nhóm MEMS Trong luận văn tập trung nghiên cứu nhằm nâng cao tính chất sắt điện, tránh việc nứt màng giảm thiểu rosettes màng mỏng PZT Bằng việc tối ưu hóa quy trình sử lý nhiệt, nghiên cứu ảnh hưởng vật liệu điện cực đế, đặc biệt nghiên cứu màng mỏng PZT dị lớp, tính chất màng nâng cao rõ rệt Màng mỏng PZT(53/47) đế Pt(111)/Ti/SiO2/Si có định hướng ưu tiên (100) chế tạo thành cơng có thơng số Pr Ec đạt giá trị tương ứng 12µC/cm2 Ec 80kV/cm Màng PZT(53/47) đế oxide SRO(110)/YSZ/Si có giá trị Pr Ec tương ứng 24µC/cm2 65kV/cm Màng PZT(47/53)/PZT(53/47) cấu trúc dị lớp đế SRO/YSZ/Si đạt giá trị Pr Ec tương ứng 28µC/cm2 60kV/cm Từ khố: Màng mỏng PZT; Sol-gel; Màng mỏng sắt điện; PZT cấu trúc dị lớp; Điện cực đế SRO; Điện cực đế Platinum INTERNATIONAL TRAINING INSTITUTE FOR MATERIALS SCIENCE BATCH -2006 Title of Msc Thesis: “Improvement in Ferroelectric Property of PZT Thin Films Fabricated by Sol-gel Method” Author: Le Van Minh Supervisor: Associate Prof Dr Vu Ngoc Hung Referees: Abstract: PZT [(PbZrxTi1-x)O3]thin films having prominent ferroelectric, piezoelectric, and pyroelectric properties have researched and applied in numerous technological fields, such as MEMS technology and nonvolatile FeRAM and so on In recent years, PZT thin films have been studied and fabricated at MEMS Group, International Training Institute for Materials Science (ITIMS) At the first stage, the PZT thin films were synthesized and fabricated There were, however, some disadvantages of these thin films, such as, cracked films, many rosettes, small remanent polarization Pr, and high coercive field Ec This thesis is the next study with the aim of fabricating high quality PZT thin films for oriented applications of MEMS Group Thus, eliminating crack, reducing rosettes, and improving ferroelectric property were studied By optimizing the thermal process and studying the influence of electrode materials and the heterolayered PZT thin films, the properties of the PZT thin films have improved significantly The PZT thin films on Pt(111)/Ti/SiO2/Si substrates had highly preferred-(001) orientation and the values of remanent polarization and coercive filed were 12µC/cm2 and 80kV/cm, respectively The remanent polarization and the coercive field of the PZT thin films on SRO(110)/YSZ/Si substrates were 24µC/cm2 and 60kV/cm, respectively These values of the heterolayered PZT(47/53)/PZT(53/47) thin films with SRO bottom electrodes were 28µC/cm2 and 60kV/cm, respectively Keywords: PZT thin films; Sol-gel method; Ferroelectric thin films; Heterolayered PZT thin films; SRO electrode; Platinum electrode i CONTENTS List of Tables iv List of Figures v Abbreviations x Chapter 1: FUNDAMENTAL THEORIES OF PZT THIN FILM 1.1 Description of Ferroelectricity 1.1.1 Description of the Ferroelectric Phase Transition 1.1.2 Ferroelectricity in Perovskite Crystals 1.1.3 Origin of Spontaneous Polarization 1.2 Ferroelectric Domains 1.2.1 Domain Walls 1.2.2 Field-Induced Strain Mechanism and Domain Configurations 1.2.3 in Ferroelectric Ceramics 10 Extrinsic Contribution to Ferroelectric Properties 12 1.3 PZT thin films 14 1.3.1 Effects of Stress in PZT thin films 16 1.3.2 Effects of Crystalline Orientation on PZT thin films 17 1.4 Ferroelectric Aging 18 1.5 Ferroelectric Fatigue 21 1.5.1 General Discussion of Fatigue Mechanisms 22 1.5.2 Fatigue – Domain Wall Pinning Hypothesis 23 1.5.3 Fatigue- Seed Inhibition Hypothesis 24 ii 1.6 Ferroelectric thin film applications References: Chapter 2: 28 31 EXPERIMENTS 36 2.1 General PZT thin film fabrication methods 36 2.1.1 Sputtering 36 2.1.2 PLD: Pulsed Laser Ablation 37 2.1.3 Sol-gel: Solution-Gel 37 2.2 The Sol-Gel Process 39 2.2.1 Sol-gel Route 39 2.2.2 2-MOE based PZT solution preparation 41 2.2.3 Thermal analysis 43 2.3 PZT thin film Fabrication and Processing 46 2.3.1 Substrate Preparation 46 2.3.2 Deposition 50 2.3.3 Thermal Processing 52 References: Chapter 3: 54 RESULTS AND DISCUSSION 3.1 PZT (53/47) thin films on Pt/Ti/SiO2/Si substrates 55 55 3.1.1 Effect of thermal process 55 3.1.2 Microstructure and XRD patterns 57 3.1.3 Electrical Properties 61 3.2 PZT(53/47) thin films on SRO bottom electrode 3.2.1 Microstructure and XRD patterns 64 66 iii 3.2.2 Electrical properties of PZT(53/47) on SRO/YSZ/Si substrate 68 3.2.3 C-V characteristics 3.3 Heterolayered PZT(47/53)/PZT(53/47) Thin Films 70 71 References: 76 CONCLUSIONS 78 iv List of Tables Table 2.1: Advantages and disadvantages of different deposition techniques Table 2.2: 39 Recipe for 0.01mol 2-methoxyethanol (2-MOE) based PZT (53/47) solution (0.4M) 41 Table 2.2: Flow diagram for the synthesis of the PZT solution[11-12] 43 Table 3.1: Remnant polarization and coercive field of PZT thin films on Pt/Ti/SiO2/Si substrates under different thermal processes 62 v List of Figures Figure 1-1: Typical hysteresis loops from various ferroelectric ceramics: paraelectric (a), ferroelectric (b), relaxor (c), antiferroelectric (d) Figure 1-2: Soft Mode Description of the Ferroelectric Phase Transition Figure 1-3: Illustration of the Perovskite Unit Cell Figure 1-4: Energy explanation of the origin of spontaneous polarization Figure 1-5: Formation of 180o Ferroelectric Domain Walls Figure 1-6: Strain Energy Relief by 90o Domain Wall Motion Figure 1-7: Schematic explanation of the strain change in a ferroelectric ceramic associated with the 10 domain reorientation [11] Figure 1-8: Illustration of Dielectric Tunability in Ferroelectric Materials Figure 1-9: 13 Phase Diagram of the PbZrO3/PbTiO3 Solid Solution System Figure 1-10: 13 15 Illustration of stress induced domain structure in PZT thin films 17 Figure 1-11: Aging in Poled Ferroelectric Materials 20 Figure 1-12: Effect of Aging in Unpoled Ferroelectrics 20 Figure 1-13: Change in P-E Response as a result of ferroelectric fatigue 21 Figure 1-14: Domain Wall Pinning Model of Ferroelectric Fatigue 24 64 Figure 3-11: The P-E and C-V characteristics of PZT(53/47)/Pt/Ti/SiO2/Si 3.2 PZT(53/47) thin films on SRO bottom electrode Ferroelectric lead zirconate titanate (PZT) thin film capacitors have been studied with great interest in the last decade because of their potential applicability in piezoelectric sensors, actuators, power generators and nonvolatile memory devices [6, 7, 9] Electrode materials can play a significant role in determining the quality of ferroelectric thin films Among the materials, Platinum presents very attractive properties as bottom electrode material for ferroelectric thin films due to its high electrical conductivity, good stability in oxidation at high electrical conductivity, good stability in oxidation at high temperatures and a high Schottky barrier, which gives the leakage currents to low values However, when using Pt film as a ferroelectric device electrode, the Pt electrode cannot be used for more than 106 switching cycles because of the fatigue On the contrast, conductive metal oxide such as SrRuO3(SRO), YBa2CuO7-x, IrO2, RuO2, LaNiO3(LNO), and La0.5Sr0.5CoO3(LSCO) were found to be effective candidates to improve the fatigue property for PZT thin films All these materials possess relatively 65 good electrical conductivity The lattice-matched hetero-structures of PZT/oxide electrode ferroelectric thin films can be expected to improve the electrical properties, especially for the fatigue property Perovskite-type oxide electrode such as LNO and SRO are promising candidates because of their similar lattice parameters (the lattice parameters for a PZT of a morphotropic phase boundary: a=4.036 , c=4.146 and the pseudocubic lattice parameter of a SRO: at=3.928 ) Recently, great efforts have been taken to research in the interfaces between the ferroelectric film and electrode to optimize the properties of ferroelectric devices In this section, the results on the fabrication of PZT thin films having SRO bottom electrodes are presented The SRO conducting oxide electrodes significantly affected the microstructure and ferroelectric properties of PZT thin films fabricated by sol-gel method The PZT solution was deposited on SRO/YSZ/Si substrates and after that, the PZT thin films were thermally treated by using thermal process (figure 3-1b) Figure 3-12 shows micrograph of PZT thin films with SRO bottom electrode There were no rosettes, no cracks even at the edges of the substrates Figure 3-12: Micrograph of PZT thin films on the SRO/YSZ/Si substrates 66 3.2.1 Microstructure and XRD patterns Microstructure of the film affects its electrical properties, therefore, the surface morphology of the resultant films was observed by AFM Figure 3-13 shows the AFM images of the PZT/SRO/YSZ/Si film The average roughness values of the PZT/SRO/YSZ/Si film and the PZT/Pt/Ti/SiO2/Si film were 1.1 nm and 7.5 nm, respectively It was confirmed that the surface of PZT/SRO/YSZ/Si was smoother than that of PZT/Pt/Ti/SiO2/Si The average particle size of the PZT on SRO/YSZ/Si (60-100nm) was smaller than that on Pt/Ti/SiO2/Si (100-300nm) Figure 3-13: AFM images of four-layer PZT (53/47)thin film on SRO/YSZ/Si substrate Figure 3-14 shows the cross-section SEM of PZT thin film on the SRO/YSZ/Si substrate It was shown that the microstructure of PZT thin film on the SRO/YSZ/Si had columnar structure Therefore, the PZT column became anisotropic geometry along the c-axis on the SRO/YSZ/Si substrate film 67 Figure 3-14: SEM of four-layer PZT(53/47) thin film on SRO/YSZ/Si substrate Figure 3-15: XRD pattern of four-layer PZT(53/47) thin film on SRO/YSZ/Si substrate Figure 3-15 illustrates the XRD pattern for the PZT/SRO/YSZ/Si thin film This XRD explained the crystal structure of SRO/YSZ/Si substrate 68 Peaks, (002) and (004), were YSZ crystal orientation phases and peak (110) was SRO electrode material Obviously, the crystal orientation of SRO was rotated 45o compared to the crystal orientation of YSZ In addition, the SRO bottom electrode had the highly (110) crystal orientation and similar lattice parameter with PZT materials PZT (53/47) thin film, therefore, grew easily along the crystal orientation of SRO electrode material The highest intensity of (110) perovskite phase of PZT thin film is shown on XRD pattern in figure 3-15 Moreover, pyrochlore phase and other perovskite phases with very small intensity, such as (001) and (111) prove that the PZT thin film had highly textured (110) orientation This result was very different from the PZT (53/47) deposited on Pt/Ti/SiO2/Si substrate (figure 3-7) 3.2.2 Electrical properties of PZT(53/47) on SRO/YSZ/Si substrate Figure 3-16a and b show the hysteresis loops for the PZT/SRO/YSZ/Si film depending on various frequencies and voltages, respectively These P-E loops were measured at different frequencies, 100Hz, 1kHz and 10kHz In addition, these P-E loops of PZT thin films were examined at three different voltages, 5V, 10V and 20V Both the loops had good symmetries and imprint was not observed These figures indicate that the SRO electrode has improved the ferroelectric property of the PZT thin films on the SRO/YSZ/Si substrate In figure 3-17, the remanent and saturated polarization of the PZT films were larger than that of (001)-oriented PZT thin film on the traditionally used substrate of a Pt/Ti/SiO2/Si Thus, the remanent polarization and the saturation polarization of the PZT/SRO/YSZ/Si film were 22µC/cm2 and 46µC/cm2, and those of the PZT/Pt/Ti/SiO2/Si film were 12µC/cm2 and 39µC/cm2, respectively (figure 3-17) In addition, coercive field of the PZT films was also reduced by using the SRO electrode because of the better 69 contact of the interface between electrode and the ferroelectric PZT thin film The coercive field for the PZT/SRO and the PZT/Pt capacitor was 65kV/cm and 80kV/cm, respectively (figure 3-17) (a) (b) Figure 3-16: Ferroelectric hysteresis loops of PZT/SRO/YSZ/Si thin films: (a) at different frequencies (b) at different applied voltages 5V, 10V, and 20V with a frequency 1kHz Figure 3-17: P-E loops of PZT on SRO/YSZ/Si and Pt/Ti/SiO2/Si substrates, at applied voltage 20V, and frequency 1kHz 70 3.2.3 C-V characteristics The C-V curve (figure 3-18) reveals the non-linearity and hysteresis in ferroelectric thin films The two maxima, which are due to ferroelectric polarization reversals, can be regarded as the double coercive field (Ec) From the figure 3-18 the Ec value is estimated of about 60kV/cm Generally, the coercive field determined by bias-dielectric constant measurements is somewhat smaller than that determined from the P-E hysteresis loop measurements due to dependence of Ec on the applied voltage and frequency The dependence of the dielectric constant on the electric field could be explained by the combination of two kinds of domain notion process: the reversal of the 180o domain and the rotation of the 90o domain Figure 3-18: C-V and P-E characteristics of PZT (53/47) thin film on SRO/YSZ/Si substrate at frequency 10kHz and at voltage 10V Figure 3-19 shows the dielectric constant vs applied voltage for these PZT thin films on SRO/YSZ/Si and Pt/Ti/SiO2/Si substrates The dielectric 71 constant of highly preferred (110) PZT thin film on SRO bottom electroded at 10kHZ was about 580 (figure 3-19) On the other hand, the dielectric constant for the (001)-preferred PZT thin film on a Pt/Ti/SiO2/Si substrate at 10kHz was about 310 (figure 3-19), which was smaller than that of the PZT film on the SRO/YSZ/Si substrate Figure 3-19: The dielectric constant of PZT thin films on SRO and Pt bottom electrodes depend on applied voltages 3.3 Heterolayered PZT(47/53)/PZT(53/47) Thin Films Ferroelectric thin films have attracted much attention in recent years because of their practical or potential applications in various fields, such as ferroelectric nonvolatile random access memories, microelectromechanical systems (MEMS), and so on Among the researches lead zirconate tintanate [Pb(Zr1-xTix)O3 (PZT)] thin films have been one of the most extensively studied materials for nonvolatile random access memory (FeRAM) application due to large remnant polarization and low coercive field The multilayered PZT thin films are a promising material for applications in MEMS and nonvolatile FeRAM The coupling and interactions among the layers in the multilayered structures can strongly 72 influence the film’s growth and electrical properties An appropriate combination of the layers with different compositions can improve functional properties These studies suggest that the design of the multilayered films with tetragonal and rhombohedral phases should be an effective way to enhance the dielectric and ferroelectric properties Electrical properties of ferroelectric films are strongly dependent on many parameters including the composition and orientation of the films The orientation control of the films is important for obtaining good properties The objective of this research is to investigate the effect of the ratio of the layer thicknesses of rhombohedral phase and tetragonal phase in one periodicity on the dielectric and ferroelectric properties of the PZT thin films However, the mechanism behind the enhancement of the ferroelectric properties is still unclear and needs to be further studied J G Wu et al [4] have reported the enhanced remnant polarization and dielectric constant in Pb(Zr20Ti80)O3/Pb(Zr80Ti20)O3 multilayers by rf magnetron sputtering And, three possible reasons were given for the enhancement The first is the formation of MPB region around the interface; the second is the stress and interaction of the electric dipoles in the interfaces between the tetragonal and rhombohedral layer; and the thirds is the improved crystallinity of the multilayered films F M Pontes et al [2] have also reported the enhancement of the remnant polarization and dielectric constant in sol-gel derived Pb(Zr40Ti60)O3/Pb(Zr60Ti40)O3 multilayered films, and ascribed the enhancement to the MPB effect Giant polarization at high electric field has been observed in sol-gel derived Pb(Zr20Ti80)O3/Pb(Zr80Ti20)O3 multiayers, and explained as the improvement of film orientation and the coupling and interactions between the rhombohedral and tetragonal layers, instead of a MPB effect [3, 10, 12, 14] 73 Figure 3-20: Illustrate the heterolayers between PZT(47/53)(tetragonal) and PZT(53/47) (rhombohedral) (a) (b) Figure 3-21: Cross section SEM images of PZT thin film on SRO/YSZ/Si substrates: four-layer PZT (53/47) (a) and four-layer PZT(47/53)/PZT( 53/47) heterolayer structure (b) In this thesis, the heterolayered PZT thin films were studied by using sol-gel method The heterolayered PZT thin film consists of four-layers of alternating PZT (47/53) and PZT (53/47) Figure 3-20 illustrates the heterolayered PZT thin film on the SRO/YSZ/Si substrate SEM micrographs in figure 3-21b show the cross section and texture of PZT film consisting of four alternative layers of PZT(47/53) and PZT(53/47) 74 Although the PZT thin film consists of alternative layers of PZT(47/53) and PZT(53/47), it did not occur discrete layers The total thickness of the four layers is approximate 420nm In figure 3-21, it is shown that the four-layer PZT (53/47) thin film (figure 3-21a) and the heterolayered PZT thin film of four alternative layers of PZT(47/53) and PZT(53/47) (figure 3-21b) had granular structure, but the later was clearer and had more high aspect ratio than the former In addition, the later has grain size in the range of 40-60nm, which is smaller than the former, 60-100nm (see section 3.2.1) Figure 3-22 shows the AFM images of the heterolayered PZT thin film According to these images, the heterolayered PZT thin film has homogenous grains compared to four-layer PZT (53/47) (figure 3-13) Furthermore, the average roughness of the heterolayered PZT thin film was approximate 0.75nm compared to 1.1nm average roughness of the PZT (53/47) (figure313) Figure 3-22: AFM images of heterolayered PZT thin film consisting of alternating PZT(47/53) and PZT(53/47)layers Heterolayered PZT thin films demonstrated remarkably unique electrical properties in comparison to the conventional PZT thin films As 75 shown in figure 3-24, a remanent polarization, Pr, of 28µC/cm2 and a coercive field, Ec of 50kV/cm were measured for the four-layer PZT thin film (a) (b) Figure 3-23: P-E hysteresis for PZT thin film on SRO/YSZ/Si substrates: PZT(53/47) (a), PZT(47/53)/PZT(53/47) (b) 76 References: Vũ Thu Hiền, Lê Văn Minh, Nguyễn Đức Minh, Vũ Ngọc Hùng, “Tính chất điện màng mỏng PZT(53/47)/Pt chế tạo sở phương pháp sol-gel”, HNVLCR toàn quốc lần thứ 5, Vũng Tàu, 12-14/11/2007 [2] F.M Pontes, E Longo, and E R Leite; “Improvement of the dielectric and ferroelectric properties in superlattice structure of Pb(Zr,Ti)O3 thin films grown by a chemical solution route”, Appl Phys Lett., Vol 84, No 26, 28 June 2004, 5470-5472 [3] Fengang Zheng, Jianping Chen, XinwanLi, Mingrong Shen; “Morphotropic phase boundary (MPB) effect in Pb(Zr,Ti)O3 rhombohedral/Tetragonal multilayered films”; Materials Letters 60 (2006) 2733–2737 [4] G.A.C.M Spierings, G.J.M Dormans, W.G.J Moors, M.J.E Ulenaers, P.K Larsen, “Stresses in Pt/Pb(Zr,Ti)O3/Pt thin-film stacks for integrated ferroelectric capacitors”, J Appl Phys 78 (1995) 1926– 1933 [5] J G Wu, D Q Xiao, J G Zhu, J L Zhu, J Z Tan, and Q L Zhang; “Enhanced dielectric and ferroelectric properties of Pb(Zr0.8Ti0.2)O3/Pb(Zr0.2Ti0.8)O3 multilayered thin films prepared by rf magnetron sputtering”; Appl Phys Lett 90, 082902-(2007)-1-3 [6] Jian Lu, Yi Zhang, Takeshi Kobayashi, Ryutaro Maeda, Takashi Mihara, “Preparation and characterization of wafer scale lead ziconate titanate film for MEMS application” Sensor and Actuators A 139 (2007) 152-157 [7] Jian Lua, Yi Zhang, Takeshi Kobayashi, Ryutaro Maeda, Takashi Mihara, “Preparation and characterization of wafer scale lead zirconate titanate film for MEMS application”; Sensors and Actuators A 139 (2007) 152–157 [8] K Yao, S Yu, F.E-H Tay, “Residual stress analysis in ferroelectric Pb(Zr0.52Ti0.48)O3 thin films fabricated by a sol–gel process”, Appl Phys Lett 82 (2003) 4540–4542 [9] Kyoung-Tae Kim, Chang-Il Kim, Sung-Gap Lee; “Ferroelectric properties of Pb(Zr,Ti)O3 heterolayered thin films for FRAM applications”; Microelectronic Engineering 66 (2003) 662–669 [10] Lee Sung- Gap, Shim Young- Jae, Kim Cheol Jin, Chung Jun- Ki, “ Structural and dielectric properties of Pb(Zr, Ti)O3 heterolayered thick films” Jounal of Alloys and Compounds(2006) [11] P C Juan, J D Jiang, W C Shih, J Y M Lee, Effect of annealing temperature on electrical properties of metal-ferroelectric (PbZr0.53Ti0.47O3)- insulator (ZrO2)- semiconductor (MFIS) thin-film [1] 77 [12] [13] [14] [15] capacitors, Microelectron Eng., 84 (2007), pp 2014- 2017 Sung-Gap Lee, Kyoung-Tae Kim, Young-Hie Lee, “Characterization of lead zirconate titanate heterolayered thin films prepared on Pt/Ti/SiO2/Si substrate by the sol-gel method”, Thin Solid Films 372 (2000) 45-49 Sung-Gap Lee, Young-Hie Lee; “Dielectric properties of sol-gel derived PZT (40/60)/PZT(60/40) heterolayered thin films”; Thin Solid Films 353 (1999)244-248 Z H Zhou, J M Xue, W.Z Li, J Wang, H Zhu, and J M Miao; “Heterolayered lead zirconate titanate thin films of giant polarization”; J Appl Phys., Vol 96, No 10, 15 November 2004, 5706-5711 Zhu Chen, Chentao Yang, Bo Li, Mingxia Sun, Bangchao Yang,” Preferred orientation controlling of PZT (52-48) thin films prepared by sol- gel process” Journal of Crystal Growth 258 (2005) 627-632 78 CONCLUSIONS In this thesis, we have focused on optimizing thermal process, effect of electrode materials, and heterolayered structures to fabricate PZT thin films by sol-gel method With two-step pyrolysis, 300 oC for 30min and 4000C for 10min, the PZT (53/47) thin films on Pt/Ti/SiO2/Si substrates were fabricated successfully with highly preferred-(001) crystal orientation The ferroelectric property of the PZT thin films, the remanent polarization, Pr and the coercive field, Ec were 12µC/cm2 and 80kV/cm, respectively, was improved in comparison to that of the previous study Moreover, the effect of electrode materials was also studied PZT(53/57) thin films on SRO/YSZ/Si substrates had highly preferred (110) and columnar structure The remanent polarization and coercive field of the PZT thin films on SRO bottom electrodes were 24µC/cm2 and 65kV/cm, respectively Thus, the ferroelectric property of the PZT thin films on SRO electrodes were improved on comparison to that of the PZT thin films on Pt bottom electrodes than PZT(001) thin films on Pt/Ti/SiO2/Si substrates The heterolayered PZT (47/53)/PZT(53/47) thin films had been successfully fabricated In microstructure, the heterolayered thin films had average roughness, 0.75nm and grain size, 40-60nm In electrical property, this film had Pr, 28µC/cm2, and Ec, 60kV/cm Based on the obtained results, the following issues would be considered: • Study of these influences of seed layer on the ferroelectric property of PZT thin films • Development of some MEMS devices using the PZT thin films ... DỤC VÀ ĐÀO TẠO TRƯỜNG ĐẠI HỌC BÁCH KHOA HÀ NỘI VIỆN ĐÀO TẠO QUỐC TẾ VỀ KHOA HỌC VẬT LIỆU LÊ VĂN MINH NGHIÊN CỨU NÂNG CAO TÍNH CHẤT SẮT ĐIỆN CỦA MÀNG MỎNG PZT CHẾ TẠO BẰNG CÔNG NGHỆ SOL- GEL LUẬN... 2008 LE VAN MINH VIỆN ĐÀO TẠO QUỐC TẾ VỀ KHOA HỌC VẬT LIỆU ITIMS KHOÁ 2006 Tiêu đề luận văn: ? ?Nghiên cứu nâng cao tính chất sắt điện màng mỏng PZT chế tạo công nghệ sol- gel? ?? Tác giả: Lê Văn Minh... tập trung nghiên cứu nhằm nâng cao tính chất sắt điện, tránh việc nứt màng giảm thiểu rosettes màng mỏng PZT Bằng việc tối ưu hóa quy trình sử lý nhiệt, nghiên cứu ảnh hưởng vật liệu điện cực