Co/Ni multilayers with improved out-of-plane anisotropy for magnetic device applications
View Patent ↗A method for forming a MTJ in 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/Ni) n composition. The seed layer is preferably NiCr, NiFeCr, Hf, or a composite thereof. 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, 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 a Hf/NiCr, Hf/NiFeCr, NiFeCr/Hf, or NiCr/Hf configuration and a thickness of the NiCr layer or the NiFeCr layer is greater than a thickness of the Hf layer, the seed layer 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 includes two metals, a metal and alloy, or two alloys represented by (A1/A2) n where A1 is a first metal or alloy, A2 is a second metal or alloy, and n is the number of laminates in the laminated layer.
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 n is from 2 to 30, A1 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 %, A2 is a second metal or alloy selected from one or more of Co, Fe, Ni, Pt, and Pd, and A1 is unequal to A2.
5. The method of claim 1 wherein the seed layer has a thickness from about 10 to 300 Angstroms.
6. The method of claim 1 further including an annealing step comprising a temperature between about 300° C. and 400° C. for a period of about 30 minutes to 5 hours after all layers in the MTJ have been formed.
7. A method of forming a magnetic tunnel junction (MTJ); comprising:
(a) forming a seed layer on a substrate, the seed layer has a Hf/NiCr, Hf/NiFeCr, NiFeCr/Hf, or NiCr/Hf configuration and a thickness of the NiCr layer or the NiFeCr layer is greater than a thickness of the Hf layer, 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 includes two metals, a metal and alloy, or two alloys represented by (A1/C/A2) where A1 is a first metal or alloy, A2 is a second metal or alloy, and C is a non-magnetic spacer.
8. The method of claim 7 wherein A1 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 %, A2 is a second metal or alloy selected from one or more of Co, Fe, Ni, Pt, and Pd, and A1 is unequal to A2.
9. The method of claim 7 wherein the seed layer has a thickness from about 10 to 300 Angstroms.
10. A method of forming a magnetic tunnel junction (MTJ); comprising:
(a) forming a first 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 includes two metals, a metal and alloy, or two alloys represented by (A1/A2) n where A1 is a first metal or alloy, A2 is a second metal or alloy, and n is the number of laminates in the laminated layer;
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 second seed layer, the first seed layer and the laminated layer are part of the dipole layer.
11. The method of claim 10 wherein the seed layer has a Hf/NiCr, Hf/NiFeCr, NiFeCr/Hf, or NiCr/Hf configuration and a thickness of the NiCr layer or the NiFeCr layer is greater than a thickness of the Hf layer.