臺灣博碩士論文加值系統

本論文主要探討以Ta/CoFeB為磁性層之MgO垂直式磁穿隧接面結構（pMTJ）的研究，首先第一部份是探討在FM1/Ta/FM2磁性結構中Ta薄層對垂直磁異向性的貢獻，其中FM1代表MgO/CoFeB，FM2為[Co/Pd]6多層膜。結果顯示若不以Ta為間隔層，此結構會失去垂直異向性。只要在CoFeB薄層和[Co/Pd]多層膜間夾入Ta層，便可再現其垂直異向性。為證實此一發現，研究中乃循序的變化Ta厚度來探討CoFeB/Ta(x)/[Co/Pd]結構之磁特性，由磁滯曲線顯示這些結構之磁方正性皆接近於1，指出Ta的夾入確實可使其具完美的垂直異向性。磁滯曲線中也顯示其敏銳的翻轉特性，明確顯示MgO/CoFeB雙層和[Co/Pd]多層膜間為鐵磁性耦合在一起。其矯頑場強度是隨Ta膜厚增加而提昇，結果顯示Ta層對結合MgO/CoFeB和[Co/Pd]6結構具備垂直異向性是不可或缺的。
第二部份是探討將人工反鐵磁層（SAF）導入垂直式磁穿隧接面結構（pMTJ），其中pMTJ的結構為下電極/自由層CoFeB (1.0)/MgO (1)/固定層CoFeB (1.0)/Ta間隔層/SAF/Ru/上電極。而人工反鐵磁層(SAF)是以一個薄的Ru層夾於兩層[Co/Pd]n多層膜之間而成，當 [Co/Pd]n多層膜的層數n>2以及改變Ru的厚度，可以增加垂直異向性與反鐵磁層的耦合。其中之一的重要發現是層間交換耦合強度Jiec可透過改變Ru厚度來控制。此外，亦發現Jiec對應Ru厚度曲線呈現一簡單的指數衰減。本研究也探討了具人工反鐵磁層（SAF）之全結構pMTJ的電特性，顯示其具有低電阻－面積乘積值（RA）約44.7Ωµm2，TMR比值約達10.2%。這些結果已成功將[Co/Pd] n多層膜應用於具垂直磁異向性的MTJ結構中。

MgO-based perpendicular magnetic tunnel junctions (p-MTJ) with Ta/CoFeB magnetic electrodes was studied in this dissertation. In the first part, I investigated the effect of a thin Ta layer on the perpendicular magnetic anisotropy (PMA) of composite FM1/Ta/FM2 magnetic structures, where FM1 represents the subsystem MgO/CoFeB, and FM2 denotes a [Co/Pd]6 multilayer. I found that the stack structure without a Ta spacer layer shows no PMA. However, once a Ta layer is inserted between the thin CoFeB layer and the [Co/Pd]6 multilayer, PMA is observed. To corroborate this observation, I systematically studied the magnetic properties of CoFeB/Ta(x)/[Co/Pd]6 structures using different Ta thicknesses x. The perpendicular magnetization loops of these structures show squareness ratios close to unity, indicating the presence of almost complete perpendicular anisotropy when the Ta was inserted. These hysteresis loops also show sharp switching characteristics, indicating that the MgO/CoFeB bilayer and the [Co/Pd]6 multilayer are ferromagnetically coupled together. The coercive field Hc of the composite structure increases as Ta thickness increases. My results show that Ta layer is essential for integrating MgO/CoFeB and [Co/Pd]6 into a composite magnetic structure with perpendicular anisotropy.
Once the PMA was demonstrated in the above structures, I fabricated p-MTJs with synthetic antiferromagnetic (SAF) pinned layers. The p-MTJs stack has the structure bottom contact/Free Layer CoFeB (1.0)/MgO (1)/Pinned Layer CoFeB (1.0)/Ta Spacer layer/ SAF/Ru Cap Layer/Top Contact (the units in parenthesis are in nanometers). The SAF pinned layer consisted of two Co/Pd multilayers separated by a thin Ru spacer layer. I optimized the SAF by changing the repetition period n in one of the Co/Pd multilayers as well as varying the Ru thickness in order to produce PMA with AFM coupling. The magnetic studies show that all magnetic films, including the Ta/CoFeB layers, are perpendicularly magnetized. The two Co/Pd MLs in the SAF are AFM coupled when n > 2. One of the important results I found was that the interlayer exchange coupling (IEC) strength Jiec can be tailored by controlling the Ru thickness. In addition, I found that the Jiec vs. Ru thickness curve exhibits a simple exponential decay. The electrical properties of the full p-MTJ with SAF were also investigated, showing a low RA value of 44.7 Ωµm2 and a TMR ratio of 10.2%. These results demonstrate the successful integration of Co/Pd MLs into MTJ with perpendicular anisotropy.

摘要 i
Abstract------ii
誌謝------iv
Contents------v
List of Figure------vi
Chapter 1 Introduction------1
Chapter 2 Experimental Equipment and Procedure------7
2-1 High Vacuum Sputtering System------8
2-2 Alternating Grandient Magnetometer, AGM------11
2-3 Current In-Plane Tunneling, CIPT------13
2-4 Conducting Atomic Force Microscopy, CAFM------16
Chapter 3 Results and Discussion------18
3-1 Effect of Ta Thickness on the MgO/ CoFeB/Ta/ [Co/Pd]n structures------18
3-1-1 Selecting the [Co/Pd] thin film multilayer------18
3-1-2 Study of Ta on the MgO/CoFeB/Ta/[Co/Pd]n structures------22
3-2 Preparation of SAF pinned layers based on multilayers------31
3-3 pMTJ with SAF pinned layers based on multilayers------34
Chapter 4 Conclusion------42
Reference------44
Appendices------48

[1]S. Ikeda, K. Miura, H. Yamamoto, K. Mizunuma, H.D. Gan, M. Endo, S. Kanai, J. Hayakawa, F. Matsukura, and H. Ohno, Nature Mater. 9, 721 (2010).
[2]D.C. Worledge, G. Hu, D.W. Abraham, J.Z. Sun, P.L. Trouilloud, J. Nowak, S. Brown, M. C. Gaidis, E. J. O’Sullivan, and R. P. Robertazzi, Appl. Phys. Lett. 98, 022501 (2011).
[3]F.-T. Yuan, Y.-H. Lin, J.K. Mei, J.-H. Hsu, P.C. Kuo, J. Appl. Phys. 111, 07C111 (2012).
[4]S. S. P. Parkin, Phys. Rev. Lett. 67, 3598 (1991).
[5]E. E. Shalygina, A. A. Rozhnovskaya, and A. N. Shalygin, Tech. Phys. Lett. 37, 980 (2011).
[6]H. Sato, M. Yamanouchi, S. Ikeda, S. Fukami, F. Matsukura, H. Ohno, Appl. Phys. Lett. 101, 022414 (2012).
[7]V. Sokalski, M.T. Moneck, E. Yang, J.-G. Zhu, Appl. Phys. Lett. 101, 072411 (2012).
[8]C.-W. Cheng, C.H. Shiue, T.-I. Cheng, G. Chern, J. Appl. Phys. 112, 033917 (2012).
[9]V.B. Naik, H. Meng, R. Sbiaa, AIP Advances. 2, 042182 (2012).
[10]S. Mangin, D. Ravelosona, J. A. Katine, M. J. Carey, B. D. Terris, and E. E. Fullerton, Nature Mater. 5, 210 (2006).
[11]H. Meng, J.-P. Wang, Appl. Phys. Lett. 88, 172506 (2006).
[12]M. Nakayama, T. Kai, N. Shimomura, M. Amano, E. Kitagawa, T. Nagase, M. Yoshikawa, T. Kishi, S. Ikegawa, and H. Yoda, J. Appl. Phys. 103, 07A710 (2008).
[13]S. Mangin, Y. Henry, D. Ravelosona, J. A. Katine, and E. E. Fullerton, Appl. Phys. Lett. 94, 012502 (2009).
[14]L. Liu, T. Moriyama, D. C. Ralph, and R. A. Buhrman, Appl. Phys. Lett. 94, 122508 (2009).
[15]T. Kishi, H. Yoda, T. Kai, T. Nagase, E. Kitagawa, M. Yoshikawa, K. Nishiyama, T. Daibou, M. Nagamine, M. Amano, S. Takahashi, M. Nakayama, N. Shimomura, H. Aikawa, S. Ikegawa, S. Yuasa, K. Yakushiji, H. Kubota, A. Fukushima, M. Oogane, T. Miyazaki, and K. Ando: IEDM Tech Dig., p. 309 (2008).
[16]H. Yoda, T. Kishi, T. Nagase, M. Yoshikawa, K. Nishiyama, E. Kitagawa, T. Daibou, M. Amano, N. Shimomura, S. Takahashi, T. Kai, M. Na- kayama, H. Aikawa, S. Ikegawa, M. Nagamine, J. Ozeki, S. Mizukami, M. Oogane, Y. Ando, S. Yuasa, K. Yakushiji, H. Kubota, Y. Suzuki, Y. Nakatani, T. Miyazaki, and K. Ando, Curr. Appl. Phys. 10, e87 (2010).
[17]R. Sbiaa, H. Meng, S.N. Piramanayagam, Phys. Status Solidi RRL. 5, 413–419 (2011).
[18]M. T. Johnson, P. J. H. Bloemen, F. J. A. den Broeder, and J. J. de Vries, Rep. Prog. Phys. 59, 1409 (1996).
[19]P.F. Carcia, A.D. Meinhaldt, A.Suna, App. Phys. Let. 47, 178 (1985).
[20]P. F. Carcia, J. Appl. Phys. 63, 5066 (1988).
[21]Li-Xiu Ye, Ching-Ming Lee, Jhin-Wei Syu, Yi-Rung Wang, Kun-Wei Lin, Yu-Hsiu Chang, and Te-ho Wu, IEEE Trans. Mag. 44, 3601–3604 (2008).
[22]Z. Tadisina, A. Natarajarathinam, B. Clark, A. Highsmith, T. Mewes, S. Gupta, E. Chen, and S. Wang, J. App. Phys. 107, 09C703 (2010).
[23]Z.R. Tadisina, A. Natarajarathinam, S. Gupta, J. Vac. Sci. Technol. A. 28, 973 (2010).
[24]K. Yakushiji, T. Saruya, H. Kubota, A. Fukushima, T. Nagahama, S. Yuasa, and K. Ando, Appl. Phys. Lett. 97, 232508 (2010).
[25]Z. Kugler, V. Drewello, M. Schäfers, J. Schmalhorst, G. Reiss, A. Thomas, J. Mag. Mag. Mat. 323, 198–201 (2011).
[26]M.T. Rahman, A. Lyle, G. Hu, W.J. Gallagher, J.-P. Wang, J. Appl. Phys. 109, 07C709 (2011).
[27]A. Natarajarathinam, R. Zhu, P.B. Visscher, S. Gupta, J. Appl. Phys. 111, 07C918 (2012).
[28]S. S. P. Parkin et al., Phys. Rev. Lett. 64, 2304 (1990).
[29]J. A. Katine and E. E. Fullerton, J. Magn. Magn. Mater. 320, 1217 (2008).
[30]O. Hellwig, T.L. Kirk, J.B. Kortright, A. Berger, E.E. Fullerton, Nature Mater. 2, 112 (2003).
[31]O. Hellwig, A. Berger, J.B. Kortright, E.E. Fullerton, J. Mag. Mag. Mat. 319, 13 (2007).
[32]P. Grünberg, R. Schreiber, Y. Pang, M. B. Brodsky, and H. Sowers, Phys. Rev. Lett. 57, 2442 (1986).
[33]W. X. Wang, Y. Yang, H. Naganuma, Y. Ando, R. C. Yu, and X. F. Han, Appl. Phys. Lett. 99, 012502 (2011).
[34]MPS-4000-C6 Sputtering System Instruction Manual, ULVAC, Inc (2007)
[35]MicroMag 2900 AGM Magnetometer Instruction Manual, Princetion Measurements Corporation , Inc(2004)
[36]http://www.smarttip.nl/products/cipt/cipt-method , SmartTip, Inc
[37]NanoScope Dimension 3100 Controller Instruction Manual, Veeco,Inc(2004)
[38]F.-T. Yuan, Y.-H. Lin, J.K. Mei, J.-H. Hsu, P.C. Kuo, J. Appl. Phys. 111, 07C111 (2012).
[39]H. Sato, M. Yamanouchi, S. Ikeda, S. Fukami, F. Matsukura, H. Ohno, Appl. Phys. Lett. 101, 022414 (2012).
[40]D.C. Worledge, G. Hu, D.W. Abraham, J.Z. Sun, P.L. Trouilloud, J. Nowak, S. Brown, M. C. Gaidis, E. J. O’Sullivan, and R. P. Robertazzi, Appl. Phys. Lett. 98, 022501 (2011).
[41]S. Ikeda, K. Miura, H. Yamamoto, K. Mizunuma, H.D. Gan, M. Endo, S. Kanai, J. Hayakawa, F. Matsukura, and H. Ohno, Nature Mater. 9, 721 (2010).
[42]V.B. Naik, H. Meng, R. Sbiaa, AIP Advances. 2, 042182 (2012).
[43]B.M. Lairson, J. Perez, C. Baldwin, IEEE Trans. Magn. 30, 4014 (1994).
[44]S.Y. Jang, S.H. Lim, S.R. Lee, J. Appl. Phys. 107, 09C707 (2010).
[45]S. Kim, S. Lee, J. Kim, J. Kang, J. Hong, J. Appl. Phys. 109, 07B766 (2011).
[46]K. Kyuno, J.G. Ha, and R. Yamamoto, S. Asano, Phys. Rev. B 54, 1092 (1996).
[47]A. Natarajarathinam, R. Zhu, P.B. Visscher, S. Gupta, J. Appl. Phys. 111, 07C918 (2012).
[48]M. Johnson, P. Bloemen, F.J.A. Broeder, J.J. Vries, Rep. Prog. Phys. 59, 1409 (1996).
[49]T. Miyajima, T. Ibusuki, S. Umehara, M. Sato, S. Eguchi, M. Tsukada, and Y. Kataoka, Appl. Phys. Lett, 94, 122501 (2009).
[50]S. V. Karthick, Y. K. Takahashi, T. Ohkubo, K. Hono, S. Ikeda, and H. Ohno, J. Appl. Phys. 106, 023920 (2009).
[51]V. Sokalski, M.T. Moneck, E. Yang, J.-G. Zhu, Appl. Phys. Lett. 101, 072411 (2012).
[52]C.-W. Cheng, T.-I. Cheng, C.H. Shiue, C.-L. Weng, Y.-C. Tsai, G. Chern, IEEE Trans. Mag. 49, 4433 (2013).
[53]Y. Nagamine, H. Maehara, K. Tsunekawa, D. D. Djayaprawira, N. Watanabe, S. Yuasa, and K. Ando: Appl. Phys. Lett. 89, 162507 (2006).
[54]Y. S. Choi, Y. Nagamine, K. Tsunekawa, H. Maehara, D. D. Djayaprawira, S. Yuasa, and K. Ando: Appl. Phys. Lett. 90, 012505 (2007).
[55]A. Natarajarathinam, R. Zhu, P.B. Visscher, S. Gupta, J. Appl. Phys. 111, 07C918 (2012).
[56]S. Ikeda, K. Miura, H. Yamamoto, K. Mizunuma, H. D. Gan, M. Endo, S. Kanai, J. Hayakawa, F. Matsukura, and H. Ohno, Nature Mater. 9, 721 (2010).
[57]D.C. Worledge, G. Hu, D.W. Abraham, J.Z. Sun, P.L. Trouilloud, J. Nowak, S. Brown, M.C. Gaidis, E.J. O’Sullivan, and R.P. Robertazzi, Appl. Phys. Lett. 98, 022501 (2011).
[58]F.-T. Yuan, Y.-H. Lin, J.K. Mei, J.-H. Hsu, P.C. Kuo, J. Appl. Phys. 111, 07C111 (2012).
[59]Y.-J. Chang, A. Canizo-Cabrera, V. Garcia-Vazquez, Y.-H. Chang, and Te-ho Wu, J. Appl. Phys. 114, 184303 (2013).