臺灣博碩士論文加值系統

本論文主要以系統化的方式來探討高溫超導晶界接面(grain boundary)約瑟分結之電性傳輸機制(electric transport property)及晶界接面結構之間的相互關聯。
利用原子力顯微鏡(Atomic Force Microscope)所得出的表面檢測結果，我們證實了釔鋇銅氧(YBCO)薄膜島狀成長的機制是造成晶界接面漫步(meandering)現象的主要原因。另外，晶界接面上大尺度的漫遊結構則是由於雙晶基座接面內隱藏的缺陷造成的，這些缺陷可利用高倍率顯微鏡檢測出來。從研究成果我們可得出雙晶基座品質和薄膜成長機制及其特性都是決定晶界接面均勻性的重要因素。
由於原子力顯微鏡的非破壞檢測特性，其對薄膜上的晶界接面的檢測程序，皆不會影響後續製程的元件品質。如此一來，量測出的約瑟分結之電性傳輸性質，皆能與先前表面檢測所得到的晶界接面結構作一對一的相關對應。由約瑟分結在微波調變下顯示的半整數Shapiro階梯，臨界電流對磁場(Ic-versus-B)的關係圖以及製作之高溫超導量子干涉元件(High-Tc SQUID)的不良操作結果，皆與晶界接面的漫步現象造成之結構不均情形有關。另外，約瑟分結的零界電壓對溫度(IcRn-versus-T)的關係圖顯示其為一超導-金屬-超導之弱聯結。
我們發現，雙晶基座晶界接面由於熱處理造成的溝槽(groove)是以隱藏在其內缺陷之尺度向下延伸。我們利用已形成溝槽結構的雙晶基座來探討其特徵對其上成長之薄膜晶界接面性質的影響。當溝槽越深或越陡，沿著晶界接面成長的螺旋狀結構隨之增加。另外，晶界接面的漫步特徵也跟著改變。由在其上製成之約瑟分結之電性量測結果，溝槽結構已被證實它確實對晶界接面約瑟分結有顯著之影響。此外，由量測製作在其上之超導量子干涉元件訊號所得之結果，我們發現在有限的程度上，雙晶基座接面上的溝槽結構可以增進晶界接面的均勻度。

A systematical study of the relation between the transport and structure property of YBa2Cu3Oy (YBCO) grain boundaries (GBs) has been performed.
Using the atomic force microscope (AFM), the island growth mechanism of the YBCO film is found to be responsible for the common meandering characteristic observed in the GB. Besides, the strikingly wandering of the GB is related to the defects embedded in the bicrystal fusion bicrystal substrate detected by the optical microscope. The spatial properties of the GB are correlated to the film properties, film growth mechanism and the quality of the bicrystal substrate.
Because of the nondestructivity of the AFM investigation, the electrical property of junction devices fabricated across the film GB can be correlated to the structure property directly. The half integer Shapiro steps, Ic-versus-B curves and the poor performance of the SQUID show evidence of the inhomogeneous current distribution along the grain boundary junction due to the meandering behavior. The IcRn-versus-T curve exhibits the character of superconductor-normal-material- superconductor (SNS) junction.
It is observed that the formation of the groove is substantially developing along the boundary interface with a width as the magnitude of the defects embedded in the bicrystal fusion. Grooved bicrystal substrates are used to study the correlation between the characteristics of the grooved fusion line and the properties of the film GB. It is found that the density of spirals growth along the boundary and the meandering configuration change, depending on the depth and steepness of the groove. Experimental characteristics of the junction devices show strikingly evidence that the grooved substrates affect the behavior of GB junction essentially. Besides, from the measured signals of the SQUIDs, it is concluded that, to a certain extent, the homogeneity of the GB can be improved by the underlying grooved substrate.

Cover
Contents
Chapter 1 Introduction
Chapter 2 Experimental Details
2.1 Substrate preparation
2.2 Thin film deposition
2.3 Device Patterning
2.4 Electrical measurement
2.5 Surface morphology analysis
Chapter 3 Characteristics of bicrystal substrates and Y1Ba2Cu3O7 films
3.1 Characteristics of the bicrystal substrate
3.2 Characteristics of the YBCO film
Chapter 4 Characteristics of the grain boundary Y1Ba2Cu3O7 junction
4.1 Characteristics of the grain boundary structure
4.1.1 Surface morphology of the meandering grain boundary
4.1.2 Predicted influence of the meandering configuration on the transport preperties
4.2 Electrical properties of the grain boundary junction
4.2.1 Microwave response
4.2.2 Effectof the magnetic field
4.2.3 Temperature dependence of the critical current
Chapter 5 Influence of the groved SrTiO3 bicrystal line on the YBa2Cu3O7 grain boundary
5.1 Influence on the resistance measurement
5.2 Effect of thermal annealing on the development of the groove and the thickness depression of films
5.3 Correlation between the characteristics of grooved bicrystal line and the GB microstructure of the YBCO film
5.4 Influence on the IcRn product
5.5 Influence on the V-Φ characteristics
Chapter 6 Conclusion
Appendix
Reference

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