隨著自動化製造需求的增加，對精確位置控制的要求也越來越高。線性定位系統通常用於工具機和機器人應用。大多數定位系統為光學或磁性原理。光學定位系統雖然具有較高的解析度，但在油污、灰塵等惡劣的環境下，其精度和穩定性等性能會嚴重下降。同時，還需要考慮更高的能耗和價格。相比之下，隨著精度的提高，磁定位系統由於其高環境耐受性而變得更具競爭力。磁性定位系統可忍受嚴苛環境，在粉塵油汙等雜質存在的情況下仍能保持其性能。此外，磁定位系統具有更低的價格、更低的功耗和可微縮性，使磁性編碼器系統更受關注。在這項研究中，我們開發了多種自旋電子學感測器，全面性地提高不同類型磁編碼器之性能。
在第一章節，我們開發了以多層膜式巨磁阻（ML GMR）和自旋閥穿隧磁阻（SV TMR）為感測原理的增量型編碼器感測器。通過材料選擇，我們發現在Cu/NiFeCo介面插入NiFe之膜層結構可有效降低磁滯現象以及提高多層膜式巨磁阻感測器之定位精度。為了進一步提高靈敏度，我們利用自旋閥式穿隧磁阻，成功開發具高靈敏度的高精度感測器。此外，我們進一步研究不同工作高度時影響定位精度之因子。為了增加可工作區間，被釘扎層和感測層之間的層間耦合必須被盡可能被降低。
在第二章節，為了解決絕對-增量整合式磁性編碼器系統的對準誤差和安裝問題，我們提出利用具垂直異向性之磁穿隧結的感測模組。透過此新穎的感測模組，絕對列和增量列中所需的所有感測器可被製造在同一基板上，且能符合兩列所需之訊號輸出。因為感測器的相對位置在黃光微影階段已定義完成，因此感測模組能完全消弭對準誤差和安裝問題。此外，我們還研究如何進一步提高定位精度，膜層設計同時必須考慮水平磁場之干擾，以抵抗crossed-effect。
在最後一章節，我們提出了一種新方法來實現 Nonius 絕對編碼器的自由極距之感測器 (Free Pitch Sensor)。透過利用鐵磁環中的渦旋磁態，我們可以在相鄰的反鐵磁層建立渦漩交換偏壓。如此一來，透過蝕刻製程將環分成四區，就可得到了相差90°的四個交換偏壓方向。若能成功與 MTJ 整合，將大大簡化傳統上穿隧磁阻式惠斯通電橋感測器的製程，並能應用於穿隧磁阻式自由極距感測器以解決現有商用產品問題。此概念亦可用於角度感測器、雙軸磁場感測器和任何其他自旋閥式穿隧磁阻感測器。

As the demands for automated manufacturing rises, the requirement for precise position control is enhanced. Linear positioning systems are often used in machine tools and robotic applications. Most of the positioning systems are based on optical or magnetic sensing principle. Although the optical position systems have higher resolution, the performance such as accuracy and the stability are strongly degraded in the un-clean environment with the presence of oil and dust. Meanwhile, the higher energy consumption and price also need to be considered. In contrast, as the accuracy enhances, the magnetic positioning systems become more competitive due to the high environmental endurance. The magnetic positioning systems stand for hazardous environment, maintaining its performance with the presence of impurities. In addition, the magnetic positioning systems have lower price, lower power consumption and the scalability, making the system draw more attentions.
In this work, we develop several spintronic sensors to comprehensively enhance the performance for different types of magnetic encoder. In first chapter, we develop the sensors based on multilayer giant magnetoresistance (ML GMR) and spin valve tunneling magnetoresistance (SV TMR) for incremental type encoder. Through material selections, we find that NiFeCo with NiFe dusting layer is suitable for ML GMR sensor. In order to further increase the sensitivity, we also utilize the SV TMR. A high accuracy sensor with high sensitivity is obtained. In addition, the factors that influence the accuracy at different air gaps are studied. In order to increase the air gap, the interlayer coupling between the pinned layer and sensing layer should be reduced.
In second part, in order to solve the alignment error and installation problem in absolute (ABS)-incremental (INC) integrated magnetic encoder system, an alignment-free sensing module based on magnetic tunnel junction (MTJ) with perpendicular anisotropy (PMA) is proposed. With the novel sensing scheme, all the required sensors in ABS and INC tracks are able to be fabricated on a single substrate, which totally excludes the alignment error and the installation problem since the relative position of the sensors are well-defined in patterning stage. The ways to improve the accuracy are also investigated. The layer design should also consider the effect of the Hx biasing field, which causes the cross-field effect.
Finally, we propose a novel method to realize the TMR free pitch sensor for Nonius absolute encoder. By utilizing the vortex magnetic state in ferromagnetic ring, we are able to set the exchange bias of the adjacent antiferromagnetic layer into vortex as well. In this way, by dividing the ring into four segments, four exchange bias directions with 90°difference are obtained. If the integration with MTJ can be realized, it would strongly simplify the fabrication of TMR Wheatstone bridge sensor compared with conventional methods and the TMR free-pitch sensor can be achieved. The proposed method may also be used as angular sensors, dual axis magnetic field sensors and any other spin valve based TMR sensors.

Abstract i
摘要 iv
致謝 vi
Contents vii
List of Figures xi
List of Tables xviii
Chapter 1. Introduction 1
1.1 Introduction 1
Chapter 2. Background 3
2.1 Magnetoresistance 3
2.2 Anisotropic Magnetoresistance (AMR) 4
2.3 Giant Magnetoresistance (GMR) 5
2.3.1 Spin-Dependent Scattering 7
2.3.2 GMR Structures 9
2.3.3 Multilayer Structure 10
2.3.3.1 RKKY Coupling 11
2.3.3.2 Ferromagnetic Materials 12
2.3.4 Spin Valve Structure 14
2.3.4.1 Exchange Bias 17
2.3.4.2 Synthetic Antiferromagnetic Pinned Spin Valve 19
2.4 Tunneling Magnetoresistance (TMR) and Magnetic Tunnel Junction (MTJ) 22
2.4.1 Spin-Dependent Tunneling 23
2.4.2 Coherent Tunneling and MgO-Based Magnetic Tunnel Junction 24
2.4.3 CoFeB/MgO/CoFeB Structure 26
2.4.4 Perpendicular Anisotropy 26
2.5 Magnetoresistive Sensors 29
2.5.1 Characteristics of MR Sensors 29
2.5.2 Linearization Methods 30
2.5.2.1 Crossed Anisotropy 32
2.5.3 Wheatstone Bridge Configurations 34
2.5.3.1 AMR Wheatstone Bridge 35
2.5.3.2 Spin Valve Wheatstone Bridge 36
2.6 Magnetic Encoders 39
2.6.1 Incremental Type Encoder 40
2.6.2 Non-Repeated Absolute Type Encoder 41
2.6.3 Non-Repeated Absolute-Incremental-Integrated Encoder 41
2.6.4 Nonius Absolute Encoder 43
Chapter 3. Experimental and Analysis Techniques 44
3.1 Sample Preparation 44
3.1.1 Ultrahigh Vacuum Magnetron Sputtering Systems 44
3.1.2 Field Annealing System 44
3.1.3 Rapid Thermal Annealing System 45
3.2 Device Fabrication 45
3.2.1 Photolithography 45
3.2.2 E-Beam Lithography 46
3.2.3 Ion-Beam Etching 47
3.2.4 Inductively Coupled Plasma Reactive Ion Etching (ICP-RIE) 48
3.3 Analysis Technique 49
3.3.1 Vibrating Sample Magnetometer (VSM) 49
3.3.2 Magneto-Optical Kerr Effect Microscope 50
3.3.3 Atomic Force Microscope (AFM) and Magnetic Force Microscope (MFM) 51
3.3.4 X-Ray Diffraction (XRD) 52
3.3.5 Transmission Electron Microscope (TEM) 53
3.3.6 Scanning Electron Microscope (SEM) 53
3.3.7 Four Point Probe 54
3.4 Scale Measurement 55
3.4.1 Measurement Platform 55
Chapter 4. Development of Magnetoresistive Sensors for Incremental Type Magnetic Encoder 56
4.1 Introduction 56
4.2 Experimental Details 57
4.3 Results and Discussions 60
4.3.1 Multilayer GMR-Based Sensor 60
4.3.1.1 Non-magnetic Spacer 60
4.3.1.2 Buffer Layers 62
4.3.1.3 Ferromagnetic Layers 63
4.3.1.4 Device Fabrication 65
4.3.1.5 Scale Measurements 68
4.3.1.6 Accuracy Improvement 71
4.3.2 Spin Valve TMR-Based Sensor 74
4.3.2.1 TMR Incremental Sensor Design 75
4.3.2.2 TMR Sensors for Incremental Scale 77
4.3.2.3 Factors Influence Accuracy 79
4.3.2.4 Repeatability 84
4.4 Summary 85
Chapter 5. Alignment-Free Sensing Module for Absolute and Incremental Lines in the Magnetic Encoder System Based on Tunneling Magnetoresistance Sensors 86
5.1 Introduction 86
5.2 Experimental Details 87
5.2.1 Existing Integrated System 87
5.2.2 Proposed Integrated System 88
5.2.3 Sensor Design 89
5.3 Results and Discussions 91
5.3.1 Sensor Layer Design 91
5.3.2 Co/Pd-Based Pinned Layer and Ta-Capped MTJ 94
5.3.2.1 MgO Crystallinity 95
5.3.2.2 Perpendicular CoFeB Pinned Layer 96
5.3.2.3 Co/Pd Pinning Layer 97
5.3.2.4 Ta Bridge Layer 98
5.3.2.5 CoFeB Sensing Layer 99
5.3.2.6 Full Structure and MR Measurements 100
5.3.2.7 Scale Measurements 102
5.3.3 Co/Pt SAF-Based Pinned Layer and Mo-Capped MTJ 104
5.3.3.1 Mo Capping Layer 104
5.3.3.2 Co/Pt SAF-Pinned MTJ 105
5.3.3.3 MR Measurements 106
5.3.3.4 Scale Measurements 107
5.3.4 Further Investigations for Improvement 109
5.3.4.1 Pinned Layer Improvement 109
5.3.4.2 Sensing Layer Improvement 110
5.4 Summary 112
Chapter 6. Novel Design for Free Pitch Magnetic Encoder Sensor through Vortex Exchange Bias 114
6.1 Introduction 114
6.2 Experimental Details 115
6.2.1 Analysis for AMR Free Pitch Sensor 115
6.2.2 Vortex Exchange Bias 119
6.3 Results and Discussions 120
6.3.1 C-Ring Structure 120
6.3.2 PtMn/Co System 122
6.3.2.1 Single Co Layer 122
6.3.2.2 PtMn/Co Exchange Bias 124
6.3.2.3 PtMn/Co Rings 126
6.3.3 IrMn/NiFe System 130
6.3.2.1 Single NiFe Layer 130
6.3.2.2 IrMn/NiFe Exchange Bias 131
6.3.2.3 IrMn/NiFe Rings 133
6.3.2.4 Multiple Exchange Bias Directions 134
6.4 Material Selections 135
6.5 Summary 137
Chapter 7. Conclusion 138
Reference 141

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