Effects of capping layers on the properties of CoFeB｜國立清華大學博碩士論文庫

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研究生：	宋京瑾 Jing-Jin Song
論文名稱：	Effects of capping layers on the properties of CoFeB 覆蓋層對鈷鐵硼性質之影響效應
指導教授：	賴志煌 Chih-Huang Lai
口試委員:
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：	2008
畢業學年度：	96
語文別：	英文
論文頁數：	86
中文關鍵詞：	鈷鐵硼、阻尼係數、覆蓋層
外文關鍵詞：	CoFeB, damping constant, capping layer
相關次數：	點閱：64 下載：0
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To confront the limitation of development of field-switching devices in nanometer scale is inevitable. Spintronic devices with current-induced switching can solve the difficult of the field-switching devices, and then have attracted a lot of attention.
In this study, we have focused on the capping effects on the CoFeB, which is the potential candidate of ferromagnet for the current-induced switching devices, including Gilbert damping constant and the magnetic properties of CoFeB. Gilbert damping is an important factor for the critical switching current density of spin-transfer devices. To investigate the dynamic behavior of CoFeB film, we have carried out the angle dependent FMR measurement and extracted the damping constant.
Different capping layers of Ta, Cu, MgO inserted into the interface of the half MTJ structure with various heat treatment have brought about interesting effects on the CoFeB. We apply Vibrating Sample Magnetometer (VSM), Magneto-Optical Kerr Effect Meter (MOKE), and X-ray magnetic circular dichroism (XMCD) to analyze magnetic properties. In addition, we investigate the micro-structure and composition analysis by Transmission Electron Microscope (TEM) and secondary ion mass spectrometer (SIMS).
Finally, we would get the lower damping constant at the case of Co60Fe20B20/MgO/Ta and it is also found that the capping effect is relative to the phase transition and interface oxidation.

本論文致力於自旋傳輸記憶體中鈷鐵硼自由層阻尼係數之研究，並探討不同覆蓋層及退火處理對鈷鐵硼自由層磁性質與阻尼係數所造成之影響。除欲以降低阻尼係數來解決自旋穿隧電流過高的難題，更希望能分析出覆蓋層與鈷鐵硼自由層相變之間的關聯性。
我們藉由電子自旋共振儀所量得的不同外加場夾角下之鐵磁共振訊號並配合數值上的計算，進而獲得鐵磁材料的阻尼係數值。初步得到自旋幫浦效應以及介面混合是額外造成阻尼係數增加的原因之一。此外，我們利用振動樣品測磁力計(VSM)、磁光柯爾效應儀(MOKE)等來分析磁性質，並利用穿透式電子顯微鏡(TEM)、二次離子質譜儀(SIMS)來進行成分以及微結構分析。
最後，在雙氧化鎂阻絕層的結構中，我們調節上層氧化鎂厚度及退火處理溫度，來獲得相當低的阻尼係數，並歸納出上層覆蓋層對鈷鐵硼相變的引導作用對自由層的表現有莫大影響。

Contents
Abstract    III
Contents    V
Chapter 1 Introduction    1
Chapter 2 Background    3
1 Principles of Current-Induced Magnetization Switching    3
1.1 Introduction    3
1.2 Basic Concepts of Current-Induced Magnetization Switching    4
1.3 A model of CIMS    5
1.4 Reduction of CIMS switching current density    6
1.4.1 Single AlOx-based structure    6
1.4.2 Dual structure    7
1.4.3 Single MgO barrier    7
1.4.4 Dual MgO barrier    7
2 Characteristics of MgO-based TMR    8
2.1 Spin Dependent Tunneling    8
2.2 Materials of free layer of MgO-based MTJ    8
2.2.1 Fe    8
2.2.2 CoFe    9
2.2.3 Co    9
2.2.4 Amorphous CoFeSiB and NiFeSiB    11
2.2.5 Full-Heusler Alloy    12
3 Properties of amorphous CoFeB    14
3.1 Growth and Crystallization Processes    14
3.2 Annealing Effect vs. TMR    16
3.3 Chemical Composition vs. Microstructure    18
3.4 Chemical Composition vs. Magnetostriction    19
3.5 Chemical Composition vs. Gilbert Damping Constant    20
4 Gilbert damping    21
4.1 Introduction    21
4.2 Gilbert damping vs. flux rise time of write head fields    22
4.3 Damping constant in spin torque driven perpendicular MRAM    23
4.4 Influence of eddy currents on the effective damping parameter    25
4.5 Enhancement of the Gilbert damping due to spin pumping    26
5 Methods for extracting damping constant    26
5.1 Ferromagnetic Resonance    26
5.1.1 Out-of-plane FMR    27
5.1.2 Frequency dependent FMR    30
5.2 Ultrafast optical excitation/ pump-probe    31
5.3 Complex susceptibility measurement    32
6 Investigation of ferromagnetic resonance    33
6.1 Introduction    33
6.2 FMR in ultrathin ferromagnets    33
6.2.1 FMR in single ultrathin films    33
6.2.2 FMR in coupled ultrthin films    34
Chapter 3 Experimental and Analysis Technique    36
1 Experimental Flow Chart    36
2 Post Field-Annealing System    37
3 Vibrating Sample Magnetometer (VSM)    38
4 Magneto-Optical Kerr Effect Meter (MOKE)    39
5 Electron Paramagnetic Resonance (EPR)    41
6 Secondary Ion Mass Spectrometry (SIMS)    42
7 X-ray Magnetic Circular Dichroism (XMCD)    44
Chapter 4 Results and Discussion    45
1 Effects of different capping layers    45
1.1 Experimental Procedures    45
1.2 Magnetic Properties    46
1.3 Gilbert Damping Constant    48
1.4 Depth profile by SIMS    56
1.5 Magnetic properties from XMCD    59
2 The thickness-dependent effects of MgO capping    65
2.1 Introduction    65
2.2 Magnetic properties    65
(a)    MgO＜10Å    67
(b)    MgO≧10Å    68
2.3 Effective demagnetization and perpendicular anisotropy    69
(a)    MgO＜10Å    69
(b)    MgO≧10Å    71
2.4 g factor    72
(a)    MgO＜10Å    72
(b)    MgO≧10Å    73
2.5 Damping constant vs. deviation of g-factor    74
(a)    MgO＜10Å    74
(b)    MgO≧10Å    75
2.6 Damping constant    76
(a)    Discontinuous MgO    76
(b)    Transition between discontinuous and continuous    78
(c)    Continuous MgO capping    78
(d)    Extremely thick MgO capping    80
Chapter 5 Conclusions    81
References    83

                                

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