臺灣博碩士論文加值系統

本實驗使用脈衝雷射鍍膜法製作鈦酸鍶鉛(Pb0.6Sr0.4TiO3, PSrT)鐵電薄膜於白金、單層和雙層混合型鈷酸鍶鑭(La0.5Sr0.5CoO3, LSCO)和錳酸鍶鑭(La0.5Sr0.5MnO3, LSMO)電極，並分析不同電極種類對鐵電性的影響。
經X-ray繞射儀分析，在製程控制上成長LSCO與LSMO薄膜均可得 c－軸結晶取向的薄膜，將鈦酸鍶鉛薄膜成長於此二種不同緩衝層之矽基板上，而且控制適當的雷射鍍膜條件亦可得到相同結晶取向的薄膜。另外，由於PSrT成長於白金基材有嚴重的擴散現象，故其上之鐵電薄膜電性較低劣。相對的，在使用氧化物電極成長鐵電薄膜的優點為降低鈣鈦礦的結晶溫度，而且PSrT的介電常數也較成長於白金電極高。然而，單層氧化物電極因具較高的電阻，使得PSrT薄膜未能得到較佳鐵電電性，而使用雙層混合型電極的優點在於不但可增加鐵電薄膜的結晶性而且可改善氧化物本身高電阻性的缺點。
在考慮鐵電電容的長時間操作上，氧化物電極的應用使得發生在白金基材上得電性疲勞現象得以改善。此外，由於PSrT/LSCO晶格參數匹配較PSrT/LSMO差，經由疲勞測試後的電滯曲線變化中發現造成鐵電電性的退化。為此，實驗亦以改良型的LSMC55(La0.5Sr0.5Mn0.5Co0.5O3) 作為電極層確定此項結果，同時二次離子質譜儀分析數據中，發現薄膜製作過程中有些許的Mn原子擴散到鐵電材料中，這個結果造成了PSrT/LSMO或PSrT/LSMC55薄膜介電常數增加，並且經疲勞測試鐵電特性亦不易產生劣化。

Ferroelectric Pb0.6Sr0.4TiO3 (PSrT) thin films were deposited on various electrodes with different architectures by pulsed laser deposition, and electrical properties before and after polarization switching up to 1 × 1010 times were investigated. In this study, the ferroelectric PSrT films were fabricated with following architectures, 1.Au/PSrT/Pt(Si) refers to Metal-Ferroelectric-Metal (MFM), 2.Au/PSrT/LSMO/Si and Au/PSrT/LSCO/Si refers to Metal-Ferroelectric-Oxide (MFO), and 3.Au/PSrT/LSMO/Pt(Si) and Au/PSrT/LSCO/Pt(Si) refers to Metal-Ferroelectric-Oxide-Metal (MFOM) (Pt(Si) is used as an abbreviation of Pt/Ti/SiO2/Si).
The experimental results reveal that the PSrT films grown on Pt(Si) show less crystallinity and serious interdiffusion occurs between the PSrT and Pt layers. Moreover, the PSrT/Pt(Si) films degraded seriously at an applied electric field of 400 kV/cm for 1 ×1010 switching cycles. Deterioration of electrical properties, such as, increasing leakage current density, decreasing dielectric constant, and serious decreasing the remanent polarization, occurred after repeated polarization reversals.
The PSrT films on LSMO/Si and LSCO/Si with MFO architectures show less ferroelectric property degradation after polarization. The benefit of application of the perovskite oxides is to enhance the growth kinetics of the PSrT films. Therefore, the crystallinity of PSrT on the oxide electrodes is higher than that of PSrT/Pt(Si). Although polarization did not significantly change after switching, relatively high resistance of the electrodes leads to small field-induced polarization.
PSrT films on the LSCO/Pt(Si) or LSMO/Pt(Si) electrodes with MFOM architectures show the benefit of application of the hybrid electrodes. Ferroelectric properties of the MFOM architectures show the best results such as, highest dielectric constant, largest remanent polarization and storage charge density among all the film architectures. Meanwhile, PSrT films on LSMO/Pt(Si) electrodes show several results superior to those of LSCO/Pt(Si), namely, higher dielectric constant, larger magnitude of storage charge density, larger magnitude of remanent polarization and better fatigue-resistance.
By observing the relative coercive field (REc) as a function of the switching cycles, the REc of PSrT/LSCO/Pt(Si) films increases more significantly than that of PSrT/LSMO/Pt(Si) as the switching cycle increases. The change of REc might be attributed to the interfacial conditions due to lattice mismatches and atomic interdiffusion among the films.
The secondary ions mass spectroscopic results indicate that the diffusion of Ti ions from both the PSrT and the Pt/Ti layer into LSCO layer is significant. In contrast, smaller amount of Ti ions diffuse into LSMO layer in the PSrT/LSMO/Pt(Si) layers. Moreover, it is clearly observed that large proportion of Mn ions than that of Co ions outward diffuse from LSMO or LSCO layer into PSrT films. It appears that Mn ions diffuse into the PSrT layers resulting in an enhancement of the polarization switchability. Therefore, the remanent polarization of PSrT/LSMO/Pt(Si) films show increasing tendency after repeated polarization reversals.

Abstract (in English) IV
Abstract (in Chinese) VI
Acknowledgements VII
List of Figures VIII
List of Tables XI
Chapter 1 Introduction 1
Chapter 2 Literature Review 4
2-1 Ferroelectrics 4
2-2 History and Fundamentals of Pulsed Laser Deposition 6
2-3 Ferroelectric Thin Films for Electronic Applications 7
2-3-1 Ferroelectric Nonvolatile Random Access Memory 8
2-3-2 Surface Acoustic Wave Devices 9
2-3-3 Sensors and Actuators 11
2-3-4 Degradation of Ferroelectric Thin Films for Electronic Applications 13
2-4 Materials 13
2-4-1 Ferroelectric (Pb0.6Sr0.4)TiO3 (PSrT) 13
2-4-2 Electrode Material (La0.5Sr0.5)CoO3 (LSCO) 15
2-4-3 Electrode Material (La0.5Sr0.5)MnO3 (LSMO) 17
2-5 Contributions of Electrodes to Electrical Properties of Ferroelectric Thin Films 19
2-5-1 Metal Electrodes 20
2-5-2 Oxide Electrodes 21
Chapter 3 Experimental Procedures and Measurement Methods 22
3-1 Experimental Procedures 22
3-1-1 Preparation of Targets 24
3-1-2 Pre-treatment of substrate 25
3-1-3 Film deposition system 26
3-1-4 Au Top Electrode 28
3-2 Measurements and Analyses 30
3-2-1 Crystal and Compositional Analyses 30
3-2-2 Electrical Properties 31
Chapter 4 Results and Discussion 35
4-1 Contributions of Electrode to Electric Properties of PSrT Thin Films on various electrodes 35
4-1-1 Crystal and Structural Analysis 35
4-1-2 Ferroelectric Hysteresis Loops of PSrT Films 44
4-1-3 Ferroelectric fatigue characteristics of PSrT Films 48
(a) P－E curves and fatigue behavior 48
(b) J－E curves and fatigue behavior 55
(c) C－E curves and fatigue behavior 57
(d) V－t curves and fatigue behavior 60
4-2 Ferroelectric PSrT Thin Films on Modification of
(La0.5Sr0.5)(CoxMn1-x)O3 Electrodes 64
4-2-1 Crystal and Structural Analysis of the
(La0.5Sr0.5)(Co0.5Mn0.5)O3 (LSMC55) Electrode 64
4-2-2 Ferroelectric fatigue characteristics of
PSrT/LSMC55/Pt(Si) 68
(a) P－E curves and fatigue behavior 68
(b) J－E, C－E, and V－t curves and fatigue behavior 71
Chapter 5 Conclusions 74
References 76
Vita 83
Publications 84

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