硼參雜控制電流生成自旋軌道力矩效率之研究

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研究生：	楊博元 Yang, Bo Yuan
論文名稱：	硼參雜控制電流生成自旋軌道力矩效率之研究 Study of current induced spin orbital torque efficiency manipulation by Boron doping
指導教授：	賴志煌 Lai, Chih-Huang
口試委員:	林秀豪 Lin, Hsiu-Hau 郭光宇 Guo, Guang-Yu
學位類別：	碩士 Master
系所名稱：	工學院 - 材料科學工程學系 Materials Science and Engineering
論文出版年：	2016
畢業學年度：	104
語文別：	英文
論文頁數：	76
中文關鍵詞：	自旋軌道力矩效率、硼參雜、自旋霍爾角、阻尼型有效場
外文關鍵詞：	Spin orbital torque efficiency, B doping, Spin hall angle, damping-like effective field
相關次數：	點閱：4 下載：0
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在本研究中，我們製備鉑/鈷鎳多層膜結構來研究硼參雜對電流生成自旋軌道力矩效率之影響，利用鉑及硼靶共濺鍍以及在鉑膜層中插入硼膜層的方式來進行硼雜質的參雜。在確保硼雜質不影響鐵磁層的異向性及飽和磁化量的狀況之下，用異常霍爾效應的原理量測元件，取得因電流生成自旋軌道矩而產生的有效磁場(Effective magnetic field)。此有效磁場能轉換成自旋霍爾角(Spin hall angle)，作為評價電流生成自旋軌道力矩效率的依據。實驗結果顯示插入硼膜層相較共濺鍍能更有效的增加因阻尼型(damping-like)力矩誘發的有效磁場，並且此有效場能隨著硼膜厚度增厚而增大至1.8倍，佐以相關的實驗分析，我們推論硼雜質在膜內擴散或是硼層與鉑層介面因濺鍍混合造成的電子散射，貢獻了額外的自旋霍爾效應，因而造成阻尼型有效場的提升，而另一方面，因為膜層結構不改變，Rashba effect 所造成的場型(field-like)力矩誘發有效場並沒有因硼參雜而有明顯變化。最後我們利用磁光柯爾效應儀及電流脈衝產生器對元件進行電流翻轉磁矩的測試，證明硼膜層厚度增加，亦能使得相鄰鐵磁層的臨界翻轉電流減小，與有效場的量測結果相互印證。
我們能從這一系列的實驗結果了解到硼參雜能額外的提升電流通過鉑層產生的自旋軌道力矩效率，使得阻尼型(damping-like)力矩誘發的有效磁場增大，並且也展示了元件磁矩的臨界翻轉電流能隨著硼膜層的增厚而降低。相關原理具有應用於提升未來自旋電子元件效能，以及降低下一代SOT-MRAM驅動電流之潛力。

B doping effect on the spin orbital torque efficiency has been investigated in this work. The Ti (5nm)/ Pt (5nm, B doped)/ [Co (0.2nm)/ Ni (0.6nm)]2/ Ti (5nm) structures were prepared, and we directly doped B into Pt layer by co-sputtering and by inserting B dusting layer into Pt layer. Under the premise that the anisotropy field (H_k) and the saturation magnetization (M_s) of the Co/Ni multilayers are barely affected by the B doping, we analyze the spin orbital torque induced magnetic effective field by locking measurement. The results show that dusting layer can be more effective than the co-sputtering method in increasing the damping-like torque induced longitudinal effective field (〖ΔH〗_L), which may also due to different amount of the B dopants. Furthermore, by changing the dusting layer insert position in Pt and the dusting layer thickness, we found that setting the dusting layer at the middle of the Pt layer gain the largest 〖ΔH〗_L and it increase with the B dusting layer thickness, which can be 67% larger than the non-doped sample. Finally, we apply the magnetization switching test and realize that the critical switching current density also reduced with the increasing dusting layer thickness.
It can be inferred that additional spin orbital torque can be induced by the B impurity in the Pt layer. Furthermore, we also clearly demonstrate that the critical current for magnetization switching can be reduced by setting the B dusting layer, which shows potential for improving performance of future spintronic devices .

Chapter 1 Introduction    1
1 Foreword    1
2 Motivation    2
3 Outline    3
Chapter 2 Background    4
1 Multilayers with perpendicular magnetic anisotropy  4
1.1 Origin of the perpendicular magnetic anisotropy in Co/Ni    5
1.2 Structural dependent magnetic properties of Co/Ni multilayers    6
1.3 Application of Co/Ni multilayers    9
2 Introduction to spin orbital torque    11
2.1 Rashba effect on spin orbital torque    12
2.2 Spin Hall Effect on spin orbital torque    15
2.3 Field-like and damping-like torque    17
2.4 SOT induced magnetization switching    19
3 Impurity and resistivity effect on the spin orbital torque    23
3.1 Origin of extrinsic Spin Hall effect in metallic systems    24
3.2 Impurity effect on the Spin Hall effect    25
3.3 Resistivity and spin orbital torque efficiency   29
Chapter 3 Experimental Techniques    34
1 Sample preparations    34
1.1 Magnetron sputtering    34
1.2 Annealing process    35
2 Device fabrication    36
2.1 Photolithography    36
2.2 Lift-off process    37
2.3 Inductively coupled plasma enhanced ion etching (ICP-RIE)    38
3 Structural characterization    39
3.1 X-ray diffraction (XRD)    39
3.2 Atomic force microscopy (AFM)    40
4 Magnetic analyses    41
4.1 Vibration sample magnetometer (VSM)    41
4.2 Focused polar magneto-optical Kerr effect    42
4.3 Anomalous Hall effect (AHE) measurement    43
Chapter 4 Experimental results    44
1 Introduction    44
2 Experimental procedure    46
3 Result and discussion    49
3.1 Properties of co-sputtered B doped samples    49
3.2 Harmonic measurement for samples with B dusting layers    58
3.3 SOT efficiency with respect to B dusting layer thickness    62
Chapter 5 Conclusion and future work    69
1 Conclusion    69
2 Future works    71
Reference  72

                                

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