臺灣博碩士論文加值系統

相較於準自旋閥系統，自旋閥系統的穿隧磁電阻接面提供了一個較明確且對比較好的反平行自旋組態。本實驗中，我們製作了以鐵錳為反鐵磁層的自旋閥穿隧磁電阻接面（包括頂自旋閥與底自旋閥結構），並研究這些元件的磁性性質與穿隧磁電阻。藉由研究數個製程上的關鍵步驟（比如交換偏偶合的強度，緩衝層的作用以及加熱退火的效應）來得到高品質的自旋閥穿隧磁電阻接面。
利用高解析度穿透式電子顯微鏡的截面影像，能量散佈Ｘ光光譜儀以及電子能量損失能譜儀來得到穿隧接面的空間結構與成分分佈的訊息，同時也證實了已發展的準自旋閥穿隧磁電阻接面擁有良好的接面品質。
自旋閥穿隧磁電阻接面的磁性與電性量測分別利用磁光柯爾效應以及四點量測法來完成。在底自旋閥的實驗中發現，釘扎層的厚度直接影響到交換偏偶合場的大小，而經由X光繞射的實驗證實了緩衝層提供一個有利於鎳鐵/鐵錳多晶結構成長的條件。
適當的溫度下，加熱退火效應提升了層間介面與絕緣位壘的品質，因此也提高了穿隧磁電阻率。在頂自旋閥的實驗中，我們同時研究在不同停留溫度下的加熱退火效應。本實驗中的頂自旋閥穿隧磁電阻接面，其磁電阻率可達42%。

Comparing to the pseudo spin valve magnetic tunnel junction (MTJ), the spin valve MTJ provides a better spin configuration for clearer and more definite antiparallel state. In this work, the FeMn-based spin valve MTJs (top spin valve & bottom spin valve) are prepared to investigate the magnetic properties and the tunnel magnetoresistance. We discuss several critical factors for fabricating high quality spin valve MTJ, for example: bias field, buffer layer, annealing effect, and etc.
The structure and composition of MTJs are examined with cross-sectional images generated by high-resolution transmission electron microscopy, energy dispersive X-ray spectrometer, and electron energy loss spectrometer. The microscopic images prove that we already have high quality pseudo spin valve MTJs.
The magnetic and electric properties of the spin valve MTJ are measured by magneto-optical Kerr effect and four-probe method, respectively. In the bottom spin valve experiment, the thickness of pinned layer affects the bias field directly, and buffer layer provides a texture, which is determined by x-ray diffraction, for NiFe/FeMn growth.
For proper annealing temperature, the post annealing effect improves the interface condition and barrier quality, resulting in a higher tunnel magnetoresistance ratio. In the top spin valve experiment, we discuss the post annealing effect at different dwelling temperatures. A value of 42% was achieved for the tunnel magnetoresistance ratio in the top spin valve structure.

Chapter 1 Introduction……………………………………………1
Chapter 2 Basic Concepts and Theories…………………………3
2-1 Magnetoresistance…………………………………………………3
2-1-1 Ordinary magnetoresistance effect………………………4
2-1-2 Anisotropic magnetoresistance effect…………………5
2-1-3 Colossal magnetoresistance eff…………………………6
2-1-4 Giant magnetoresistance effect……………………………8
2-1-5 Tunneling magnetoresistance effect………………………10
2-2 Spin-dependent Tunnel Models…………………………………11
2-3 Exchange bias coupling…………………………………………13
2-4 Magnetic tunnel junctions……………………………………18
2-4-1 Pseudo spin valve……………………………………………18
2-4-2 Spin valve……………………………………………………19
2-4-3 Synthetic spin valve………………………………………20
2-5 Applications of the MR effect……………………………21
Chapter 3 Experimental Principles…………………………………23
3-1 Ultra-high vacuum system………………………………………23
3-1-1 Pumping system………………………………………………26
3-1-2 Gauges…………………………………………………………26
3-2 Sputtering system……………………………………………29
3-2-1 DC and RF sputtering……………………………………29
3-2-2 Magnetron sputtering……………………………………31
3-3 Sample fabrication…………………………………………32
3-4 Sample measurement…………………………………………34
3-4-1 Four-probe method………………………………………34
3-4-2 Magneto-optical Kerr effect…………………………35
3-5 Material and structure measurements…………………36
3-5-1 High-resolution transmission electron microscopy……36
3-5-2 Electron energy loss spectroscopy………………………36
3-5-3 Energy dispersive x-ray spectroscopy……………………37
3-5-4 Parallel beam powder method………………………………37
Chapter 4 Results and Discussion………………………………39
4-1 Structural characterization of PSV.………………………39
4-2 Bottom spin valve………………………………………………42
4-2-1 Preparation and results……………………………………42
4-2-2 Effect of Ta buffer layer…………………………………47
4-3 Top spin valve…………………………………………………50
4-3-1 Preparation for spin-valve MTJ…………………………50
4-3-2 Consideration of shape anisotropy……………………52
4-3-3 Post annealing effect……………………………………55
4-3-4 Angular dependent measurement…………………………61
Chapter 5 Conclusion……………………………………………65
Reference……………………………………………………………67

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