CoFe是一種廣泛用於自旋電子裝置的熱門磁性薄膜材料，如磁性隨機存取記憶體。在磁隧穿結構中，CoFe的結晶度被認為是獲得更高穿隧磁阻值的因素之一，此外，CoFe薄膜之磁性質表現又與應力高度相關，例如由熱收縮引起的介面應力，造成在可撓式基板樣品具有較大的矯頑力差異和更好的磁阻曲線方正性。本研究使用直流電磁控濺鍍將CoFe磊晶薄膜成長在可撓式雲母(Mica)基板和氧化鎂(MgO)基板上，生長溫度(Tg)分別為25°C、300°C、400°C和500°C，從X光繞射(XRD)結果來看，三個具有四重對稱的CoFe(002)晶域形成在雲母上，因此在chi角位於45°的phi角掃描結果中，出現十二個CoFe{101}繞射峰，而成長於MgO上的CoFe也同樣具有(002)優選取向，CoFe(200)在面上沿MgO(110)成長並呈現四重對稱。振動樣品磁力儀(VSM)量測結果顯示雲母上之CoFe方正性與矯頑力在彎曲時會隨著相對壓縮應變的提高而下降、隨著相對拉伸應變的提高而上升，其中成長溫度400°C的CoFe對於應力的敏感度最大，而500°C的CoFe對於應力的敏感度卻最小，推測是由CoFe顆粒間的空隙或是差排滑移，釋放掉部分的彎曲應力所導致，然而不論拉伸或是壓縮彎曲，方正性與矯頑力隨著應力的變化皆被證明為可逆的過程。雲母上CoFe磁滯曲線與在MgO上相似，但根據CoFe與MgO間晶格失配的計算結果，CoFe應受到來自MgO的拉伸應力，使成長於MgO上的CoFe磁滯曲線方正性表現較佳。
綜上所述，本研究表明CoFe磊晶薄膜可以形成在雲母基板之上，並且磁性質是可以藉由外部施加彎曲應力調整的。

CoFe is a popular material which is widely used in spintronic device like magnetic random access memory. In magnetic tunneling junction, the crystallinity of CoFe is considered as one of the factors to obtain higher tunneling magnetoresistance ratio. Besides, the magnetic property is highly related to the stress. Compare to rigid substrate, large coercivity difference and better squareness in magnetoresistance curve has been found in flexible substrate (Mica) samples because of the anisotropic strain which is caused by thermal contraction. In this work, we demonstrate the growth of epitaxial CoFe thin films on a flexible mica substrate and on MgO(001) substrate with growth temperature (T_g) 25°C, 300°C, 400°C and 500°C by DC sputtering. From the X-ray diffraction results, three CoFe(002) domains with four-folds symmetry are formed on mica. Therefore, there are twelve CoFe{101} diffraction peaks in phi scan results at chi = 45°. For CoFe grown on MgO, CoFe also has (002)-preferred orientation. CoFe(200) grows along MgO(110) in-plane and has four-folds symmetry. Vibrating sample magnetometry results revealed that the squareness and coercivity will decrease with the relative compressive strain and increase with relative tensile strain while bending. Furthermore, the CoFe with Tg : 400°C is most sensitive to stress. And CoFe with Tg : 500°C is the least sensitive to stress. It can be speculated that the voids between CoFe particles and dislocation slip release part of the bending stress. Regardless of tensile or compressive bending, the changes in squareness and coercivity with stress have been proved reversible. The hysteresis loop of CoFe are similar on mica and on MgO. But squareness of CoFe on MgO is better than on mica, the reason could be that CoFe is under tensile stress which is indicated by calculation of lattice mismatch between CoFe and MgO.
Overall, this study suggests that epitaxial CoFe thin films can be grown on mica substrate and magnetic properties can be tuned through bending.

摘要 i
Abstract ii
致謝 iv
目錄 v
圖目錄 vii
表目錄 xi
第一章 、緒論 1
1.1 前言 1
1.2 文獻回顧 2
1.2.1 外加應力對磁性薄膜之影響 2
1.2.2 雲母之結構與特性 11
1.2.3 雲母上的凡德瓦異質磊晶 12
1.2.4 研究動機 14
第二章 、儀器原理與實驗方法 16
2.1 磁控濺鍍(magnetron sputtering) 16
2.1.1 直流濺鍍(Direct Current Sputtering, DC) 17
2.1.2 射頻濺鍍(Radio Frequency Sputtering, RF) 18
2.2 X光繞射儀(X-Ray Diffractometer, XRD) 18
2.2.1 掠角X光粉末繞射法(Grazing Incidence X-Ray Diffraction, GIXRD) 19
2.2.2 外全反射繞射法(Total External Reflection Diffraction, TERD) 21
2.3 X光反射率(X-Ray Reflectivity, XRR) 22
2.3.1 臨界角(Critical angle) 22
2.3.2 薄膜厚度(Thickness) 25
2.4 震動樣品磁力儀(Vibrating Sample Magnetometer, VSM) 26
2.5 掃描式電子顯微鏡(Scanning Electron Microscope, SEM) 27
2.5.1 二次電子影像(Secondary electron image, SEI) 28
2.5.2 背向散射電子影像(Backscattered electron image, BEI) 28
2.6 實驗步驟 28
2.6.1 基板清洗流程 28
2.6.2 樣品製備流程 29
2.6.3 樣品分析量測 29
第三章 、結果與討論 31
3.1 CoFe薄膜成長於Mica(001)單晶基板 31
3.1.1 X光繞射之結果 31
3.1.2 X光反射率之結果 50
3.1.3 掃描式電子顯微鏡之結果 54
3.1.4 震動樣品磁力儀之結果 56
3.1.5 拉伸彎曲應力下的CoFe磊晶磁性質 60
3.2 CoFe薄膜成長於MgO(001)單晶基板 74
3.2.1 X光繞射之結果 74
3.2.2 X光反射率之結果 81
3.2.3 掃描式電子顯微鏡之結果 85
3.2.4 震動樣品磁力儀之結果 88
3.3 雲母與MgO上之CoFe薄膜結構與磁性質比較 92
第四章 、結論 95
第五章 、未來展望 97
參考文獻 99
附錄A 磁阻式隨機存取記憶體 106
附錄B 異常散射之結果 110
附錄C XRR擬合之各層詳細參數 111
附錄D 期刊草稿 113

[1] C. Du, R. Adur, H. Wang, A. J. Hauser, F. Yang, and P. C. Hammel, "Control of magnetocrystalline anisotropy by epitaxial strain in double perovskite Sr(2)FeMoO(6) films," Phys Rev Lett, vol. 110, no. 14, p. 147204, Apr 5 2013, doi: 10.1103/PhysRevLett.110.147204.
[2] N. Moutis, D. Suarez-Sandoval, and D. Niarchos, "Voltage-induced modification in magnetic coercivity of patterned Co50Fe50 thin film on piezoelectric substrate," J. Magn. Magn. Mater., vol. 320, no. 6, pp. 1050-1055, 2008, doi: 10.1016/j.jmmm.2007.10.018.
[3] Y. Li, W. Luo, L. Zhu, J. Zhao, and K. Wang, "Voltage manipulation of the magnetization reversal in Fe/n-GaAs/piezoelectric heterostructure," J. Magn. Magn. Mater., vol. 375, pp. 148-152, 2015, doi: 10.1016/j.jmmm.2014.09.074.
[4] S. Isogami and T. Taniyama, "Strain Mediated in-Plane Uniaxial Magnetic Anisotropy in Amorphous CoFeB Films Based on Structural Phase Transitions of BaTiO3 Single-Crystal Substrates," physica status solidi (a), vol. 215, no. 6, 2018, doi: 10.1002/pssa.201700762.
[5] G. Dai et al., "Mechanically tunable magnetic properties of Fe81Ga19 films grown on flexible substrates," Appl. Phys. Lett., vol. 100, no. 12, 2012, doi: 10.1063/1.3696887.
[6] H. Zhang et al., "Tuning the magnetic anisotropy of CoFeB grown on flexible substrates," Chinese Physics B, vol. 24, no. 7, 2015, doi: 10.1088/1674-1056/24/7/077501.
[7] D. Hunter et al., "Giant magnetostriction in annealed Co(1-x)Fe(x) thin-films," Nat Commun, vol. 2, p. 518, Nov 1 2011, doi: 10.1038/ncomms1529.
[8] Z. Tang et al., "Magneto-mechanical coupling effect in amorphous Co40Fe40B20 films grown on flexible substrates," Appl. Phys. Lett., vol. 105, no. 10, 2014, doi: 10.1063/1.4895628.
[9] M. Gueye et al., "Bending strain-tunable magnetic anisotropy in Co2FeAl Heusler thin film on Kapton®," Appl. Phys. Lett., vol. 105, no. 6, 2014, doi: 10.1063/1.4893157.
[10] S. Ota, A. Ando, T. Sekitani, T. Koyama, and D. Chiba, "Flexible CoFeB/MgO-based magnetic tunnel junctions annealed at high temperature (≥350 °C)," Appl. Phys. Lett., vol. 115, no. 20, 2019, doi: 10.1063/1.5128952.
[11] C. Barraud et al., "Magnetoresistance in magnetic tunnel junctions grown on flexible organic substrates," Appl. Phys. Lett., vol. 96, no. 7, 2010, doi: 10.1063/1.3300717.
[12] J. H. Kwon, W. Y. Kwak, and B. K. Cho, "Magnetization Manipulation of a Flexible Magnetic Sensor by Controlled Stress Application," Sci Rep, vol. 8, no. 1, p. 15765, Oct 25 2018, doi: 10.1038/s41598-018-34036-z.
[13] X. Qiao et al., "Enhanced stress-invariance of magnetization direction in magnetic thin films," Appl. Phys. Lett., vol. 111, no. 13, 2017, doi: 10.1063/1.4990571.
[14] H. Li et al., "Stretchable Spin Valve with Stable Magnetic Field Sensitivity by Ribbon-Patterned Periodic Wrinkles," ACS Nano, vol. 10, no. 4, pp. 4403-9, Apr 26 2016, doi: 10.1021/acsnano.6b00034.
[15] M. Yen, Y. Bitla, and Y.-H. Chu, "van der Waals heteroepitaxy on muscovite," Materials Chemistry and Physics, vol. 234, pp. 185-195, 2019, doi: 10.1016/j.matchemphys.2019.05.053.
[16] T. Amrillah et al., "Flexible Epsilon Iron Oxide Thin Films," ACS Appl Mater Interfaces, vol. 13, no. 14, pp. 17006-17012, Apr 14 2021, doi: 10.1021/acsami.0c23104.
[17] H. Tanaka and M. Taniguchi, "Atomically flat platinum films grown on synthetic mica," Japanese Journal of Applied Physics, vol. 57, no. 4, 2018, doi: 10.7567/jjap.57.048001.
[18] D.-A. Luh, C.-W. Liu, C.-M. Cheng, K.-D. Tsuei, C.-H. Wang, and Y.-W. Yang, "Single-crystalline silver films on mica," Thin Solid Films, vol. 645, pp. 215-221, 2018, doi: 10.1016/j.tsf.2017.10.051.
[19] S. Mukherjee et al., "Role of boron diffusion in CoFeB/MgO magnetic tunnel junctions," Physical Review B, vol. 91, no. 8, 2015, doi: 10.1103/PhysRevB.91.085311.
[20] Z. Bai et al., "Boron diffusion induced symmetry reduction and scattering in CoFeB/MgO/CoFeB magnetic tunnel junctions," Physical Review B, vol. 87, no. 1, 2013, doi: 10.1103/PhysRevB.87.014114.
[21] Z.-P. Li et al., "The study of origin of interfacial perpendicular magnetic anisotropy in ultra-thin CoFeB layer on the top of MgO based magnetic tunnel junction," Appl. Phys. Lett., vol. 109, no. 18, 2016, doi: 10.1063/1.4966891.
[22] S. S. Parkin et al., "Giant tunnelling magnetoresistance at room temperature with MgO (100) tunnel barriers," Nat Mater, vol. 3, no. 12, pp. 862-7, Dec 2004, doi: 10.1038/nmat1256.
[23] T. Takeuchi et al., "Crystallization of Amorphous CoFeB Ferromagnetic Layers in CoFeB/MgO/CoFeB Magnetic Tunnel Junctions," Japanese Journal of Applied Physics, vol. 46, no. No. 25, pp. L623-L626, 2007, doi: 10.1143/jjap.46.L623.
[24] N. K. Jain, M. Sawant, S. H. Nikam, and S. Jhavar, "Metal Deposition: Plasma-Based Processes," in Encyclopedia of Plasma Technology, 2016, pp. 722-740.
[25] 汪建民, 材料分析 Materials Analysis. 中國材料科學學會, 2014.
[26] A. J. Littlejohn, Y. Xiang, E. Rauch, T. M. Lu, and G. C. Wang, "van der Waals epitaxy of Ge films on mica," Journal of Applied Physics, vol. 122, no. 18, 2017, doi: 10.1063/1.5000502.
[27] Y. Bitla and Y.-H. Chu, "MICAtronics: A new platform for flexible X-tronics," FlatChem, vol. 3, pp. 26-42, 2017, doi: 10.1016/j.flatc.2017.06.003.
[28] A. Castellanos-Gomez et al., "Mechanical properties of freely suspended atomically thin dielectric layers of mica," Nano Research, vol. 5, no. 8, pp. 550-557, 2012, doi: 10.1007/s12274-012-0240-3.
[29] H. Asano, Y. Bando, N. Nakanishi, and S. Kachi, "Order-Disorder Transformation of Fe-Co Alloys in Fine Particles," Transactions of the Japan Institute of Metals, vol. 8, pp. 180-185, 1967.
[30] A. Khort, S. Roslyakov, and P. Loginov, "Solution combustion synthesis of single-phase bimetallic nanomaterials," Nano-Structures & Nano-Objects, vol. 26, 2021, doi: 10.1016/j.nanoso.2021.100727.
[31] P. Bayliss, "Revised unit-cell dimensions, space group, and chemical formula of some metallic minerals," Canadian Mineralogist, vol. 28, pp. 751-755, 1990.
[32] I. Ohnuma et al., "Phase equilibria in the Fe–Co binary system," Acta Materialia, vol. 50, pp. 379–393, 2002.
[33] A. Kumar and P. C. Srivastava, "Magnetic, morphological and structural investigations of CoFe/Si interfacial structures," Journal of Experimental Nanoscience, vol. 10, no. 10, pp. 803-818, 2014, doi: 10.1080/17458080.2014.902543.
[34] A. Kumar and P. C. Srivastava, "A study on CoFe/p-Si interfacial structures before and after swift heavy ion irradiation," Radiation Effects and Defects in Solids, vol. 170, no. 6, pp. 461-476, 2015, doi: 10.1080/10420150.2015.1036428.
[35] A. K. Kaveev et al., "Laser MBE-grown CoFeB epitaxial layers on MgO: Surface morphology, crystal structure, and magnetic properties," Physical Review Materials, vol. 2, no. 1, 2018, doi: 10.1103/PhysRevMaterials.2.014411.
[36] B. J. H. Stadler, "Vapor Processes," in Materials Processing, 2016, pp. 513-588.
[37] S. Ikeda et al., "Tunnel magnetoresistance of 604% at 300K by suppression of Ta diffusion in CoFeB∕MgO∕CoFeB pseudo-spin-valves annealed at high temperature," Appl. Phys. Lett., vol. 93, no. 8, 2008, doi: 10.1063/1.2976435.
[38] P. D. Kulkarni, J. Khan, P. Predeep, and P. Chowdhury, "Thermally induced perpendicular magnetic anisotropy in CoFeB/MgO/CoFeB based magnetic tunnel junction," 2016.
[39] P. Sharma, H. Kimura, A. Inoue, E. Arenholz, and J. H. Guo, "Temperature and thickness driven spin-reorientation transition in amorphous Co-Fe-Ta-B thin films," Physical Review B, vol. 73, no. 5, 2006, doi: 10.1103/PhysRevB.73.052401.
[40] G. Q. Gao, C. Jin, W. C. Zheng, X. Pang, D. X. Zheng, and H. L. Bai, "Strain-mediated magnetic properties of epitaxial cobalt ferrite thin films on flexible muscovite," EPL (Europhysics Letters), vol. 123, no. 1, 2018, doi: 10.1209/0295-5075/123/17002.
[41] G. Yu et al., "Strain-induced modulation of perpendicular magnetic anisotropy in Ta/CoFeB/MgO structures investigated by ferromagnetic resonance," Appl. Phys. Lett., vol. 106, no. 7, 2015, doi: 10.1063/1.4907677.
[42] Y. A. Yurakov, Y. A. Peshkov, S. A. Ivkov, S. V. Kannykin, A. V. Sitnikov, and E. P. Domashevskaya, "The state of individual layers and interfaces in multilayer nanostructures [(Co40Fe40B20)34(SiO2)66/ZnO/C]46," Surface and Interface Analysis, vol. 53, no. 2, pp. 244-249, 2020, doi: 10.1002/sia.6908.
[43] W. H. Butler, X. G. Zhang, T. C. Schulthess, and J. M. MacLaren, "Spin-dependent tunneling conductance ofFe|MgO|Fesandwiches," Physical Review B, vol. 63, no. 5, 2001, doi: 10.1103/PhysRevB.63.054416.
[44] S. Ikeda et al., "A perpendicular-anisotropy CoFeB-MgO magnetic tunnel junction," Nat Mater, vol. 9, no. 9, pp. 721-4, Sep 2010, doi: 10.1038/nmat2804.
[45] Y. Wu et al., "Perpendicular magnetic anisotropy and magnetization process of ferrimagnetic CoFeB/Tb multilayer films," Japanese Journal of Applied Physics, vol. 59, no. 8, 2020, doi: 10.35848/1347-4065/aba793.
[46] W. Lin et al., "Perpendicular Magnetic Anisotropy and Dzyaloshinskii-Moriya Interaction at an Oxide/Ferromagnetic Metal Interface," Phys Rev Lett, vol. 124, no. 21, p. 217202, May 29 2020, doi: 10.1103/PhysRevLett.124.217202.
[47] M. Akyol, "Origin of Interfacial Magnetic Anisotropy in Ta/CoFeB/MgO and Pt/CoFeB/MgO Multilayer Thin Film Stacks," Journal of Superconductivity and Novel Magnetism, vol. 32, no. 3, pp. 457-462, 2019, doi: 10.1007/s10948-019-5005-8.
[48] B. Lüssem, S. Karthäuser, H. Haselier, and R. Waser, "The origin of faceting of ultraflat gold films epitaxially grown on mica," Applied Surface Science, vol. 249, no. 1-4, pp. 197-202, 2005, doi: 10.1016/j.apsusc.2004.11.082.
[49] T. D. Ha et al., "Mechanically tunable exchange coupling of Co/CoO bilayers on flexible muscovite substrates," Nanoscale, vol. 12, no. 5, pp. 3284-3291, Feb 7 2020, doi: 10.1039/c9nr08810e.
[50] R. Koch and H. Poppa, "The influence of the mica surface composition on the growth morphology of discontinuous epitaxial palladium vapor deposits," Journal of Vacuum Science & Technology A: Vacuum, Surfaces, and Films, vol. 5, no. 4, pp. 1845-1848, 1987, doi: 10.1116/1.574512.
[51] L. Kipgen, H. Fulara, M. Raju, and S. Chaudhary, "In-plane magnetic anisotropy and coercive field dependence upon thickness of CoFeB," J. Magn. Magn. Mater., vol. 324, no. 19, pp. 3118-3121, 2012, doi: 10.1016/j.jmmm.2012.05.012.
[52] Y. C. Chen et al., "Heteroepitaxy of Co-Based Heusler Compound/Muscovite for Flexible Spintronics," ACS Appl Mater Interfaces, vol. 11, no. 38, pp. 35162-35168, Sep 25 2019, doi: 10.1021/acsami.9b12219.
[53] M. Yen et al., "Giant Resistivity Change of Transparent ZnO/Muscovite Heteroepitaxy," ACS Appl Mater Interfaces, vol. 12, no. 19, pp. 21818-21826, May 13 2020, doi: 10.1021/acsami.0c02275.
[54] H. J. Liu et al., "Flexible Heteroepitaxy of CoFe2O4/Muscovite Bimorph with Large Magnetostriction," ACS Appl Mater Interfaces, vol. 9, no. 8, pp. 7297-7304, Mar 1 2017, doi: 10.1021/acsami.6b16485.
[55] E. Grünbaum and R. Schwarz, "Epitaxial Growth of Titanium Films on Mica," Journal of Applied Physics, vol. 40, no. 8, pp. 3364-3369, 1969, doi: 10.1063/1.1658189.
[56] M. Higo, K. Fujita, M. Mitsushio, T. Yoshidome, and T. Kakoi, "Epitaxial growth and surface morphology of aluminum films deposited on mica studied by transmission electron microscopy and atomic force microscopy," Thin Solid Films, vol. 516, no. 1, pp. 17-24, 2007, doi: 10.1016/j.tsf.2007.04.046.
[57] S. Königshofen, F. Matthes, D. E. Bürgler, C. M. Schneider, E. Dirksen, and T. J. J. Müller, "Epitaxial and contamination-free Co(0001) electrodes on insulating substrates for molecular spintronic devices," Thin Solid Films, vol. 680, pp. 67-74, 2019, doi: 10.1016/j.tsf.2019.04.021.
[58] F.-T. Yuan, Y.-H. Lin, J. K. Mei, J.-H. Hsu, and P. C. Kuo, "Effect of thickness of MgO, Co-Fe-B, and Ta layers on perpendicular magnetic anisotropy of [Ta/Co60Fe20B20/MgO]5 multilayered films," Journal of Applied Physics, vol. 111, no. 7, 2012, doi: 10.1063/1.3673408.
[59] M. Akyol, B. Kıvrak, K. U. Tümen, and A. Ekicibil, "Effect of Ta insertion between Pt and CoFeB on interfacial magnetic anisotropy in Pt/CoFeB/MgO multilayer thin-film stack," Journal of Materials Science: Materials in Electronics, vol. 31, no. 24, pp. 23037-23043, 2020, doi: 10.1007/s10854-020-04831-4.
[60] X. Zhang et al., "Effect of mechanical strain on magnetic properties of flexible exchange biased FeGa/IrMn heterostructures," Appl. Phys. Lett., vol. 102, no. 2, 2013, doi: 10.1063/1.4776661.
[61] A. K. Singh and J.-H. Hsu, "Effect of heat treatment on interface driven magnetic properties of CoFe films," J. Magn. Magn. Mater., vol. 432, pp. 96-101, 2017, doi: 10.1016/j.jmmm.2017.01.070.
[62] V. B. Naik et al., "Effect of electric-field on the perpendicular magnetic anisotropy and strain properties in CoFeB/MgO magnetic tunnel junctions," Appl. Phys. Lett., vol. 105, no. 5, 2014, doi: 10.1063/1.4892410.
[63] J. Cao, J. Kanak, T. Stobiecki, P. Wisniowski, and P. P. Freitas, "Effect of Buffer Layer Texture on the Crystallization of CoFeB and on the Tunnel Magnetoresistance in MgO Based Magnetic Tunnel Junctions," IEEE Trans. Magn., vol. 45, no. 10, pp. 3464-3466, 2009, doi: 10.1109/tmag.2009.2025382.
[64] X. Zhang et al., "Effect of buffer layer and external stress on magnetic properties of flexible FeGa films," Journal of Applied Physics, vol. 113, no. 17, 2013, doi: 10.1063/1.4793602.
[65] D.-T. Quach, T.-D. Chu, D.-T. Ngo, and D.-H. Kim, "Correlation of hysteresis loop and domain structure of CoFeB/Pd multilayer at various temperatures," Physica B: Condensed Matter, vol. 577, 2020, doi: 10.1016/j.physb.2019.411822.
[66] C. Y. Yang et al., "Competing Anisotropy-Tunneling Correlation of the CoFeB/MgO Perpendicular Magnetic Tunnel Junction: An Electronic Approach," Sci Rep, vol. 5, p. 17169, Nov 24 2015, doi: 10.1038/srep17169.
[67] Z. Wang et al., "Atomic-Scale Structure and Local Chemistry of CoFeB-MgO Magnetic Tunnel Junctions," Nano Lett, vol. 16, no. 3, pp. 1530-6, Mar 9 2016, doi: 10.1021/acs.nanolett.5b03627.
[68] B. Jinnai, K. Watanabe, S. Fukami, and H. Ohno, "Scaling magnetic tunnel junction down to single-digit nanometers—Challenges and prospects," Appl. Phys. Lett., vol. 116, no. 16, 2020, doi: 10.1063/5.0004434.