自旋軌道矩已經被提出是下一個世代磁阻式隨機存取記憶體的寫入方式，除了寫入速度之外，記憶單元的自由層的熱穩定性也是非常重要的議題，因此以鈷鐵硼/嵌入層/鈷鐵硼為主的複合膜層結構開始被使用在自旋轉移矩的磁性記憶體中，因為這結構有較高的異相磁場和熱穩定性，在本實驗中我們將探討三種不同的複合膜層結構。
本文透過高真空鍍膜和退火製程，在矽/二氧化矽基板上製作鉭/鈷鐵硼/氧化鎂、鈀/鈷鐵硼/氧化鎂、鈀/鈷/鉭/鈷鐵硼三種複合膜層系統。並以振動樣品磁測儀量測所有試片都具有垂直異向性，利用飽和磁化量和鐵磁層厚度的乘積以及異相磁場的數值，可以證明當形成複合膜層後熱穩定性上升的現象。
元件製作上透過黃光微影製程和離子束蝕刻製作霍爾十字元件，以實驗室自行架設的磁矩簡諧運動量測和電子自旋翻轉量測來觀察電性。鉭/鈷鐵硼/氧化鎂系統中，複合膜層結構造成有效磁場變小，還有臨界翻轉電流變大的現象，但在嵌入的Ta層厚度超過1奈米之後，臨界翻轉電流又出現下降的趨勢。在鈀/鈷鐵硼/氧化鎂系統中，我們發現在嵌入鉭層厚度到2奈米之後，原先遵從下層鈀翻轉極性的情況突然改變，改為以中間鉭翻轉極性的表現。最後在鈀/鈷/鉭/鈷鐵硼系統中，我們發現當鈀或是鉭的極性想要使磁矩翻轉時，另一層會因為極性不同而阻止磁矩的翻轉，所以它們只能分別翻動它們上方的鐵磁層，導致磁矩無法完全翻轉。

Spin–orbit torque (SOT) switching has been proposed to be the most promising writing scheme for next-generation magnetic random access memory (MRAM). In addition to writing speed, the thermal stability of the free layer in MRAM cells is also quite critical; therefore, a composite free layer composed of CoFeB/interlayer/CoFeB has been used in the spin-transfer-torque (STT) MRAM to increase the anisotropy field Hk and thermal stability. In this experiment, we will investigate three kinds of composite layer structure.
All samples were deposited and then annealed in high vacuum. We fabricated Ta/CoFeB/MgO, Pd/CoFeB/MgO, Pd/Co/Ta/CoFeB three series of specimen on Si/SiO2 substrate. All samples were measure by vibrating sample magnetometer, and all of them revealed perpendicular anisotropy. We use Ms *t and HK value to prove that thermal stability increase after forming composite layer.
We used photolithography and ion beam etching to produce Hall-cross device. Then we measured electrical properties with magnetic harmonic measurement and spin–orbit torque switching measurement. In Ta/CoFeB/MgO system, forming composite layer cause effective field to decrease, and critical switching current density increased. However, when interlayer Ta is thicker than 1nm, critical switching current density begin to decrease. In Pd/CoFeB/MgO system, we observed when Ta interlayer is thicker than 2nm, the polarity of SOT switching switched from Pd to Ta. In Pd/Co/Ta/CoFeB system, we discovered the mechanism behind composite layer switching. Whenever Pd or Ta’s polarity want to switch magnetic moment, the other layer will tend to stop it because of the opposite polarity between two layers. So both of them can only switch the ferromagnetic layer above them, hence magnetic moments cannot fully switched.

1. 李明道, 各式記憶體簡介. 國家奈米元件實驗室奈米通訊, 2015. 22(4): p. 2-6.
2. Uhlenbeck, G.E. and S. Goudsmit, Spinning electrons and the structure of spectra. Nature, 1926. 117(2938): p. 264.
3. Johnson, M. and R.H. Silsbee, Interfacial charge-spin coupling: Injection and detection of spin magnetization in metals. Physical Review Letters, 1985. 55(17): p. 1790.
4. Slonczewski, J.C., Current-driven excitation of magnetic multilayers. Journal of Magnetism and Magnetic Materials, 1996. 159(1-2): p. L1-L7.
5. Wolf, S., et al., Spintronics: a spin-based electronics vision for the future. Science, 2001. 294(5546): p. 1488-1495.
6. Lakys, Y., et al., Self-enabled “error-free” switching circuit for spin transfer torque MRAM and logic. IEEE Transactions on Magnetics, 2012. 48(9): p. 2403-2406.
7. Chabi, D., et al., Design and analysis of radiation hardened sensing circuits for spin transfer torque magnetic memory and logic. IEEE Transactions on Nuclear Science, 2014. 61(6): p. 3258-3264.
8. Butler, W., et al., Spin-dependent tunneling conductance of Fe| MgO| Fe sandwiches. Physical Review B, 2001. 63(5): p. 054416.
9. Yuasa, S., et al., Giant room-temperature magnetoresistance in single-crystal Fe/MgO/Fe magnetic tunnel junctions. Nature materials, 2004. 3(12): p. 868.
10. Yuasa, S. and D. Djayaprawira, Giant tunnel magnetoresistance in magnetic tunnel junctions with a crystalline MgO (0 0 1) barrier. Journal of Physics D: Applied Physics, 2007. 40(21): p. R337.
11. Djayaprawira, D.D., et al., 230% room-temperature magnetoresistance in CoFeB∕ MgO∕ CoFeB magnetic tunnel junctions. Applied Physics Letters, 2005. 86(9): p. 092502.
12. Ikeda, S., et al., A perpendicular-anisotropy CoFeB–MgO magnetic tunnel junction. Nature materials, 2010. 9(9): p. 721.
13. Qiu, X., et al., Spin–orbit-torque engineering via oxygen manipulation. Nature nanotechnology, 2015. 10(4): p. 333.
14. Naik, V., H. Meng, and R. Sbiaa, Thick CoFeB with perpendicular magnetic anisotropy in CoFeB-MgO based magnetic tunnel junction. Aip Advances, 2012. 2(4): p. 042182.
15. Prejbeanu, I., et al., Thermally assisted MRAMs: ultimate scalability and logic functionalities. Journal of Physics D: Applied Physics, 2013. 46(7): p. 074002.
16. Berger, L., Emission of spin waves by a magnetic multilayer traversed by a current. Physical Review B, 1996. 54(13): p. 9353.
17. Sun, J.Z., Spin-current interaction with a monodomain magnetic body: A model study. Physical Review B, 2000. 62(1): p. 570.
18. Oogane, M., et al., Magnetic damping in ferromagnetic thin films. Japanese journal of applied physics, 2006. 45(5R): p. 3889.
19. Wang, D.-S., et al., High thermal stability and low Gilbert damping constant of CoFeB/MgO bilayer with perpendicular magnetic anisotropy by Al capping and rapid thermal annealing. Applied Physics Letters, 2014. 104(14): p. 142402.
20. Bilzer, C., et al., Study of the dynamic magnetic properties of soft CoFeB films. Journal of Applied Physics, 2006. 100(5): p. 053903.
21. Inoue, J. and H. Ohno, Taking the Hall effect for a spin. Science, 2005. 309(5743): p. 2004-2005.
22. Miron, I.M., et al., Perpendicular switching of a single ferromagnetic layer induced by in-plane current injection. Nature, 2011. 476(7359): p. 189.
23. Liu, L., et al., Spin-torque switching with the giant spin Hall effect of tantalum. Science, 2012. 336(6081): p. 555-558.
24. Kim, J., et al., Layer thickness dependence of the current-induced effective field vector in Ta| CoFeB| MgO. Nature materials, 2013. 12(3): p. 240.
25. Kato, Y.K., et al., Observation of the spin Hall effect in semiconductors. science, 2004. 306(5703): p. 1910-1913.
26. Valenzuela, S.O. and M. Tinkham, Direct electronic measurement of the spin Hall effect. Nature, 2006. 442(7099): p. 176.
27. Dyakonov, M. and V. Perel, Current-induced spin orientation of electrons in semiconductors. Physics Letters A, 1971. 35(6): p. 459-460.
28. Hirsch, J., Spin hall effect. Physical Review Letters, 1999. 83(9): p. 1834.
29. Zhang, S., Spin Hall effect in the presence of spin diffusion. Physical review letters, 2000. 85(2): p. 393.
30. Niimi, Y. and Y. Otani, Reciprocal spin Hall effects in conductors with strong spin–orbit coupling: a review. Reports on progress in physics, 2015. 78(12): p. 124501.
31. Liu, L., et al., Current-induced switching of perpendicularly magnetized magnetic layers using spin torque from the spin Hall effect. Physical review letters, 2012. 109(9): p. 096602.
32. Crépieux, A. and P. Bruno, Theory of the anomalous Hall effect from the Kubo formula and the Dirac equation. Physical Review B, 2001. 64(1): p. 014416.
33. Guo, G.-Y., et al., Intrinsic spin Hall effect in platinum: First-principles calculations. Physical review letters, 2008. 100(9): p. 096401.
34. Rojas-Sánchez, J.-C., et al., Spin pumping and inverse spin Hall effect in platinum: the essential role of spin-memory loss at metallic interfaces. Physical review letters, 2014. 112(10): p. 106602.
35. Ando, K., et al., Electric manipulation of spin relaxation using the spin Hall effect. Physical review letters, 2008. 101(3): p. 036601.
36. Liu, L., et al., Spin-torque ferromagnetic resonance induced by the spin Hall effect. Physical review letters, 2011. 106(3): p. 036601.
37. Zhang, W., et al., Role of transparency of platinum–ferromagnet interfaces in determining the intrinsic magnitude of the spin Hall effect. Nature Physics, 2015. 11(6): p. 496.