Co/X and CoX multilayers with improved out-of-plane anisotropy for magnetic device applications
View Patent ↗A MTJ for a spintronic device is disclosed and includes a thin seed layer that enhances perpendicular magnetic anisotropy (PMA) in an overlying laminated layer with a (Co/X) n or (CoX) n composition where n is from 2 to 30, X is one of V, Rh, Ir, Os, Ru, Au, Cr, Mo, Cu, Ti, Re, Mg, or Si, and CoX is a disordered alloy. The seed layer is preferably NiCr, NiFeCr, Hf, or a composite thereof with a thickness from 10 to 100 Angstroms. Furthermore, a magnetic layer such as CoFeB may be formed between the laminated layer and a tunnel barrier layer to serve as a transitional layer between a (111) laminate and (100) MgO tunnel barrier. The laminated layer may be used as a reference layer, dipole layer, or free layer in a MTJ. Annealing between 300° C. and 400° C. may be used to further enhance PMA in the laminated layer.
1. A method of forming a magnetic tunnel junction (MTJ); comprising:
(a) forming a seed layer on a substrate, the seed layer consists of one or more of Hf, NiCr, and NiFeCr, and enhances perpendicular magnetic anisotropy (PMA) in an overlying laminated layer; and
(b) forming the laminated layer having instrinsic PMA that contacts a top surface of the seed layer, the laminated layer has a (Co/Mg) n or (CoMg) n structure, CoMg is a disordered alloy, and n is the number of laminates wherein n is from 2 to 30.
2. The method of claim 1 wherein the MTJ has a bottom spin valve configuration in which the seed layer, a composite reference layer, a tunnel barrier layer, and a free layer are sequentially formed on the substrate, and the laminated layer is part of the composite reference layer, the composite reference layer is further comprised of a magnetic layer formed between the laminated layer and the tunnel barrier layer, the magnetic layer has PMA aligned in the same direction as the PMA in the laminated layer.
3. The method of claim 1 wherein the MTJ has a top spin valve configuration in which the seed layer, a composite free layer, a tunnel barrier layer, and a reference layer are sequentially formed on the substrate, and the laminated layer is part of the composite free layer, the composite free layer is further comprised of a magnetic layer formed between the laminated layer and the tunnel barrier layer, the magnetic layer has PMA aligned in the same direction as the PMA in the laminated layer.
4. The method of claim 1 wherein the MTJ has a bottom spin valve configuration in which a reference layer, a tunnel barrier layer, a free layer, a non-magnetic spacer, and a dipole layer are sequentially formed on a substrate, the seed layer and laminated layer are part of the dipole layer.
5. The method of claim 1 wherein the seed layer consists of Hf, NiCr, NiFeCr, Hf/NiCr, Hf/NiFeCr, NiCr/Hf, or NiFeCr/Hf.
6. The method of claim 5 wherein the seed layer is a composite with a Hf/NNiCr, Hf/NiFeCr, NiCr/Hf, NiFe/Hf configuration and the NiCr or NiFeCr layer in the composite has a greater thickness than the Hf layer.
7. The method of claim 1 wherein each Co layer in the (Co/Mg) n laminated layer has a thickness from about 1.5 to 4 Angstroms, and each Mg layer has a thickness from about 4 to 10 Angstroms.