The effect of Ta on the magnetic thickness of permalloy (Ni81Fe19) films

Abstract

The effect of Ta and Ta/Cu seed layers, and Ta and Cu cap layers on the effective magnetic thickness of ultrathin permalloy (Ni81Fe19) was investigated for MRAM applications. The films were deposited by Ion Beam Deposition. The magnetic moment of each as-deposited permalloy film was measured using a B-H looper and a SQUID magnetometer. The films were further annealed at either 525 K for 1/2 h or 600 K for 1 h to study the effect of thermally driven interdiffusion on the magnetic moment of the permalloy film. Our theoretical calculations showed that the presence of 12% intermixing at the interface reduces the Ni moments to zero. Experimentally, it was shown that the tantalum rather than the copper interfaces are primarily responsible for the magnetically dead layers. The Ta seed layer interface produces a loss of moment equivalent to a magnetically dead layer of thickness 0.6±0.2 nm. The Ta metal in the cap layer results in a loss of moment equivalent to a dead layer of thickness 1.0±0.2 nm. Upon annealing, thermally driven interdiffusion is concluded to have a strong effect on the Ta(seed)/ Ni81Fe19 as-deposited interface, based on the doubling of the magnetically dead layer to 1.2±0.2 nm. The Ni81Fe19/Ta(cap) as-deposited interface slightly increases its equivalent magnetically dead layer upon annealing to 1.2±0.2 nm. As-deposited interfaces of Ta(seed)/permalloy and permalloy/Ta(cap) are not chemically equivalent and result in different magnetically dead layers, whereas after annealing to 600 K both interfaces attain comparable intermixing and magnetically dead layers. It was also shown that a half-hour anneal at the lower 525 K annealing temperature, which is closer to the actual processing temperature, results in only slight increase of the magnetically dead layer at both interfaces.

Effect of interface intermixing on the magnetoresistive and the exchange coupling in bottom‐ and top‐spin valves

“…2), and previously, we speculated that differences in the deposition sequence play a key role in formation of the interfacial structure and interlayer diffusion during annealing [3]. For instance, CoFe has a larger surface free energy than IrMn, which results in blending of CoFe with the IrMn layer during deposition, thereby creating relatively thick, magnetically dead layers [10][11][12]. A comparison of the interfaces of CoFe/IrMn in the B-SV and IrMn/CoFe in the T-SV in the as-deposited state shows that the two interfaces differ energetically.…”

Switching-Field Stabilization against Effects of High-Temperature Annealing in Magnetic Tunnel Junctions using Thermally Reliable NixFe100-x/Al-Oxide/Ta Free Layer

“…(10), where X indicates the Ni composition in NiFe and d indicates the deposition thickness of NiFe. Three kinds of capping layers were prepared: Ta(5), Al(0.7)-oxide/Ta(5), and Ru(3)/ Ta (5). We named the samples according to the capping layers, i.e., ''Ta cap'', ''AlO cap'', and ''Ru cap'', respectively.…”

“…[1][2][3][4] Although attention should be given to MRAM write operations, the thermal robustness of the switching field (H sw ) in the MTJs of MRAM cell structures has not been adequately studied. The magnetic properties of ultrathin NiFe layers sandwiched between Ta or Cu under and capping layers have been investigated and the reaction at the NiFe/Ta interface was shown to create a thick magnetic dead layer, 5,6) which can interfere with the H sw of MTJs after high-temperature treatments. On the other hand, we have already reported that a thin Al-oxide (AlO) layer can prevent interdiffusion between the NiFe and CoFe layers even after annealing at 400 C, 4) and we briefly demonstrated the same effect for AlO between NiFe and Ta layers, leading to a large improvement in the magnetic properties of NiFe after annealing at 400 C. 7) However, to date, the overall effect of capping layer materials with magnetoresistive properties in MTJ devices has not been reported.…”

Advantages of Prefabricated Tunnel Junction-Based Molecular Spintronics Devices

“…A bilayer of 2 nm tantalum (Ta) and 10 nm NiFe was sputter deposited on an oxidized Si wafer with $ 300 nm thick SiO 2 . Hence, Ta only served as a the seed layer 70,71 to increase the adhesion of NiFe to the substrate. Electrochemical Au deposition occurred on NiFe aged for more than one month at room temperature.…”