Search

A composite free layer (CFL) consisting of a soft layer and a hard layer exchange coupled in parallel is proposed. The experimental results showed that the critical current density (Jc) can be reduced from 7.05×106 A/cm2 of strong coupled CoFeB(12.5 Å)/Ru(4 Å)/NiFe(17.5 Å) CFL to 2.65×106 A/cm2 of weak coupled CoFeB(12.5 Å)/Ru(15 Å)/NiFe(17.5 Å) CFL. The macrospin simulations showed that the soft layer of CFL can assist the hard layer of CFL to switch at a lower Jc. These results suggest that by using CFL, it is possible to reduce the Jc of spin torque transfer switching without compromising the thermal stability. [ABSTRACT FROM AUTHOR]

The capping effects on the properties of magnetic tunneling junctions (MTJs) have been investigated to improve the magitetoresistive (MR) ratio [Nagamine et al. Applied Physics, vol. 99, p. 08K703, 2006] and thermal stability [Fukumoto et al. Japanese Journal of Applied Physics, vol. 45, p. 3829, 2006. In this paper, MgO/Mg and MgO capping layers for MTJs were used to replace our previously used Ta and Ru capping layer [Yen et al., IEEE Transactions on Magnetics, vol. 42, no. 10, p. 862, 2004]. The MTJs with NiFe and CoFeB free layers were patterned to ellipses of 0.36 µm × 0.72 µm. The MR ratios of the MTJs with an NiFe free layer were enhanced from 26% to about 33% by capping MgO/Mg bilayers. A great improvement was also found on the MTJs with the CoFeB free layer, where the MR ratio was 50.4% with the MgO cap layer enhanced from 44.7% of Ru-capped MTJs. In addition, the influences of those capping layers included Ta, Ru, MgO, and MgO/Mg on thermal stability were also discussed. [ABSTRACT FROM AUTHOR]

The writing probability of toggle magnetic random access memory (MRAM) at built-in bias field is studied by micromagnetic simulation and a dual polarity write pulse scheme has been proposed to enhance the toggle probability at low writing field. The critical writing field can be reduced to 19 Oe at strong built-in bias field from CoFe(1.0 nm)/CoFeB(2.0 nm)/Ru/CoFe(5.0 nm) pinned layer structure. From the simulation and experimental results, it is proven that the toggle MRAM can be operated at lower writing field by dual polarity write pulse scheme. [ABSTRACT FROM AUTHOR]

A Ru/Ta capping layer for magnetic tunneling juctions (MTJs) was used to replace the routinely used Ta capping layer. The MTJs with CoFeB used as the free layer were shaped to ellipses of 0.36 × 0.60 μm. The magnetoresistive (MR) ratio of Ru/Ta capped MTJs was found to be 47.3%, slightly lower than the value of 52.8% of Ta capped MTJs. In the meantime, the switching field of Ru/Ta capped MTJs with 30Å of Ru was found to be 37.7 Oe, greatly reduced from 63 Oe of Ta capped MTJs. The switching field varition of Ru/Ta capped MTJ5 was 6 Oe, also better than the value of 11 Oe of Ta capped MTJs. The different switching behaviors of Ru/Ta and Ta capped MTJs were discussed from the aspects of oxygen diffusion, intermixing, and magnetostriction. [ABSTRACT FROM AUTHOR]

In this work, a writing scheme with preceding negative pulse wave form for toggle magnetic random access memory (MRAM) is proposed to enhance the switching yield and enable a low current switching. The failure mechanism of toggle switching is studied by micromagnetic analysis. As a result of broadened operation window and reduced switching current, the scalability of MRAM is feasible with the robust toggle operation. [ABSTRACT FROM AUTHOR]