磁性穿隧元件之鈷鐵硼自由層的阻尼係數之研究

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研究生：	王致喨 Chih-Liang Wang
論文名稱：	磁性穿隧元件之鈷鐵硼自由層的阻尼係數之研究 Study of CoFeB Gilbert damping constant on Magnetic Tunnel Junction
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：	2007
畢業學年度：	95
語文別：	英文
論文頁數：	77
中文關鍵詞：	阻尼常數、鈷鐵硼薄膜、磁性穿隧元件、磁性薄膜、自旋傳輸效應、磁阻式隨機存取記憶體
外文關鍵詞：	Damping constant, CoFeB thin film, Magnetic tunnel junction, Magnetic thin film, Spin transfer, Magnetic Random Access Memory (MRAM)
相關次數：	點閱：3 下載：0
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本論文致力於應用在次世代自旋傳輸記憶體之鈷鐵硼自由層阻尼係數之研究，以期能突破目前自旋翻轉電流過高而不能商用化的窘境。藉由電子自旋共振儀而量得的鐵磁共振訊號、改變試片膜面與外加場夾角並配合數值上的計算，進而獲得鐵磁材料的阻尼係數值。
運用鐵磁共振分析技術，除了進行不同成份之鈷鐵硼自由層研究外，並探討實際應用於自旋傳輸效應上，元件中覆蓋層對鈷鐵硼自由層阻尼係數之影響。此外根據自旋幫浦理論，插入不同厚度之銀、鉭、以及銅來研究鈷鐵硼自由層阻尼係數之變化，並發現界面的混合效應亦是額外造成阻尼係數增加的原因之一，且以鉭當為覆蓋層格外明顯。
最後，由於銅的插入在阻尼係數上的表現明顯優於銀與鉭覆蓋層，因此探討退火條件下，銅對於鈷鐵硼自由層磁性質上的影響，並藉由硼的擴散來解釋退火後磁性質的變化。

In this thesis, we studied the effect of capping layers on the CoFeB Gilbert damping constant, which was an important factor for the critical current density of spin-transfer. To investigate the dynamic magnetic property of CoFeB films, the ferromagnetic resonance technique (FMR) was carried out and the angular dependence of FMR was numerically calculated to obtain the Gilbert damping constant.
The different metals of Cu, Ta and Ag inserted into the Co72Fe8B20/Ta interface were prepared by ion beam deposition to study the capping effect on the effective damping constant. It is found that there are two sources, the intermixing effect and the spin-pumping effect, to enhance the effective damping constant, especially within the thinner ferromagnetic film. Besides, it is also observed that the 2.5 nm Co60Fe20B20/Ta (0.012) possess the lower effective damping constant than 2.5 nm Co72Fe8B20/Ta (0.016).
Finally, the lower effective damping constant of Co60Fe20B20/Cu/Ta is used to study the annealing effect on magnetic properties including of Ms, , HC, and HK. It is also found that magnetic properties during the annealing are strongly affected by the boron diffusion.

Chapter 1 Introduction ---------------------------------------------------------1
Chapter 2 Background ---------------------------------------------------------2
2-1 Introduction of Current-induced Magnetization Switching ----------------------2
2-1-1 What is CIMS ------------------------------------------------------------------------2
2-1-2 A Model Study of CIMS ------------------------------------------------------------3
2-1-3 Reduction of Switching Current Density ---------------------------------------5
2-1-3-1 Single AlOx-based Structure ----------------------------------------------5
2-1-3-2 Dual Structure ---------------------------------------------------------------5
2-1-3-3 MgO Tunneling Barrier ----------------------------------------------------5
2-2 Introduction of MgO-based TMR -----------------------------------------------------6
2-2-1 Spin Dependent Tunneling ---------------------------------------------------------6
2-2-2 Free layer of MgO-based MTJ ----------------------------------------------------6
2-2-2-1 Fe -------------------------------------------------------------------------------6
2-2-2-2 CoFe ---------------------------------------------------------------------------7
2-2-2-3 Co ------------------------------------------------------------------------------8
2-2-2-4 Amorpous CoFeSiB and NiFeSiB ----------------------------------------9
2-2-2-5 Hull-Heusler Alloys -------------------------------------------------------10
2-2-2-6 CoFeB ------------------------------------------------------------------------11
2-2-2-6-(a) Growth and Crystallization Processes -------------------11
2-2-2-6-(b) Annealing Effect vs. TMR ----------------------------------14
2-2-2-6-(c) Chemical Composition vs. TMR --------------------------16
2-2-2-6-(d) Chemical Composition vs. Microstructure -------------17
2-2-2-6-(e) Chemical Composition vs. Magnetostriction -----------19
2-2-2-6-(f) Chemical Composition vs. Damping Constant ---------20
2-3 Ferromagnetic Resonance -------------------------------------------------------------22
2-3-1 Angular Dependence of FMR ----------------------------------------------------23
2-3-2 Spin Pumping -----------------------------------------------------------------------28
Chapter 3 Experiment Procedure ------------------------------------------29
3-1 Experiment Flow Chart ----------------------------------------------------------------29
3-2 Dual Ion Beam Deposition System ---------------------------------------------------30
3-3 Field-Annealing System ----------------------------------------------------------------31
3-4 Electron Paramagnetic Resonance (EPR) ------------------------------------------32
3-5 Vibrating Sample Magnetometer (VSM) -------------------------------------------34
3-6 X-Ray Diffraction (XRD) --------------------------------------------------------------35
3-7 Atomic Force Microscopy (AFM) ----------------------------------------------------36
Chapter 4 Results and Discussion ------------------------------------------38
4-1 Introduction ------------------------------------------------------------------------------38
4-2 Free Layer of Co72Fe8B20 ---------------------------------------------------------------38
4-2-1 Experimental Procedures --------------------------------------------------------38
4-2-2 Magnetic Properties ---------------------------------------------------------------40
4-2-3 Gilbert Damping Constant -------------------------------------------------------46
  4-2-3-1 Capping Layer Effect --------------------------------------------------------53
  4-2-3-1-(a) Cu(x nm)/Ta(5 nm) ------------------------------------------------------53
  4-2-3-1-(b) Ta(x nm) -------------------------------------------------------------------57
  4-2-3-1-(c) Ag(5 nm)/Ta(5 nm) -------------------------------------------------------58
  4-2-3-1-(d) Mg(5 nm)/Ta(5 nm) ------------------------------------------------------61
4-2-4 X-Ray Diffraction ------------------------------------------------------------------62
4-3 Free Layer of Co60Fe20B20 --------------------------------------------------------------63
4-3-1 Experimental Procedures --------------------------------------------------------63
4-3-2 Gilbert Damping Constant -------------------------------------------------------64
  4-3-2-1 Capping Layer Effect --------------------------------------------------------64
  4-3-2-1-(a) Ta(5nm) --------------------------------------------------------------------64
  4-3-2-2-(b) Cu(5 nm)/Ta(5 nm) ------------------------------------------------------65
  4-3-2-1-(c) Annealing Effect ----------------------------------------------------------66
4-4 Free Layer of Co40Fe40B20 --------------------------------------------------------------70
4-4-1 Experimental Procedures --------------------------------------------------------70
4-4-2 Magnetic Properties ---------------------------------------------------------------70
Chapter 5 Conclusions --------------------------------------------------------74
References -----------------------------------------------------------------------76

                                

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