Co/Ni multilayers with improved out-of-plane anisotropy for magnetic device applications
View Patent ↗A MTJ for a spintronic device includes a thin seed layer that enhances perpendicular magnetic anisotropy (PMA) in an overlying laminated layer with a (Co/Ni) n composition or the like where n is from 2 to 30. 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. There may be a Ta insertion layer between the CoFeB layer and laminated layer to promote (100) crystallization in the CoFeB layer. The laminated layer may be used as a reference layer in a MTJ. Annealing between 300° C. and 400° C. may be used to further enhance PMA in the laminated layer.
1. A magnetic tunnel junction (MTJ), comprising:
(a) a seed layer formed on a substrate and comprising one or more of Hf, NiFeCr, and NiCr that enhances PMA in an overlying laminated layer;
(b) a composite reference layer comprising the laminated layer that contacts a top surface of the seed layer, the laminated layer has intrinsic PMA and comprises a multilayer stack that inclpdes two magnetic elements, a magnetic element and alloy, or two alloys represented by (A 1 /A 2 ) n or (A 1 /C/A 2 ) where A 1 is a first metal or alloy, A 2 is a second metal or alloy, C is a non-magnetic spacer, and n is the number of laminates in the laminated layer, the composite reference layer also includes an upper magnetic layer that has PMA with a magnetization in the same direction as the PMA in the laminated layer;
(c) a tunnel barrier layer contacting a top surface of the upper magnetic layer;
(d) a free layer formed on the tunnel barrier layer; and
(e) a capping layer as the uppermost layer in the MTJ.
2. The MTJ of claim 1 wherein the seed layer is Hf, NiFeCr, or NiCr, or a composite with a Hf/NiCr, Hf/NiFeCr, NiFeCr, or NiCr/Hf configuration and having a thickness between about 10 and 300 Angstroms.
3. The MTJ of claim 1 wherein the upper magnetic layer is CoFeB, CoFe, or combinations thereof with a thickness from about 6 to 14 Angstroms.
4. The MTJ of claim 1 wherein the upper magnetic layer consists of CoFeB and the composite reference layer is further comprised of a Ta layer about 0.5 to 3 Angstroms thick formed between the laminated layer and the upper magnetic layer.
5. The MTJ of claim 1 wherein n is from 2 to 30, A 1 is a first metal or alloy selected from one or more of Co, Ni, and Fe that may be doped with boron up to about 50 atomic%, A 2 is a second metal or alloy selected from one or more of Co, Fe, Ni, Pt, and Pd, and A 1 is unequal to A 2 .
6. The MTJ of claim 1 wherein the laminated layer has a (111) crystal texture, the tunnel barrier layer has a (100) crystal orientation, and the upper magnetic layer has a (100) portion adjoining the tunnel barrier layer and a (111) crystalline or amorphous portion that interfaces with the laminated layer.
7. The MTJ of claim 1 wherein C is a Ru layer with a thickness from about 5 to 20 Angstroms.