Oxidation structure/method to fabricate a high-performance magnetic tunneling junction MRAM
View Patent ↗An MTJ (magnetic tunneling junction) MRAM (magnetic random access memory) has a tunneling barrier layer of substantially uniform and homogeneous Al 2 O 3 stoichiometry. The barrier layer is formed by depositing Al on a CoFe layer or a CoFe—NiFe bilayer having an oxygen surfactant layer formed thereon, then oxidizing the Al by radical oxidation. The underlying surfactant layer contributes oxygen to the bottom surface of the Al, forming an initial amorphous Al 2 O 3 layer. This layer produces small, uniform grains in the remaining Al layer, which promotes a uniform oxidation of the Al between its upper and lower surfaces by the subsequent radical oxidation. A final annealing process to set a pinned layer magnetization enhances the homogeneous oxidation of the layer.
1. A magnetic tunneling junction (MTJ) device in an MRAM configuration comprising:
a substrate;
a conducting lead layer formed on said substrate, the layer including a Ta capping layer having a sputter-etched upper surface;
an NiCr seed layer formed on said sputter-etched upper surface;
a bottom electrode formed on said seed layer, said bottom electrode further comprising:
a pinning layer of antiferromagnetic material;
an SyAP pinned layer formed on said pinning layer, said SyAP layer including lower and upper ferromagnetic layers magnetized in antiparallel directions, said upper and lower layers separated by a coupling layer;
an oxygen surfactant layer having been formed on said upper ferromagnetic layer;
a smooth, stoichiometrically homogeneous, tunneling barrier layer of oxidized aluminum having uniformly small grain size, formed on said oxygen surfactant layer and having absorbed the oxygen thereof;
a ferromagnetic free layer formed on said barrier layer;
a capping layer formed on said ferromagnetic free layer.
2. The device of claim 1 wherein said NiCr seed layer is formed of NiCr with there being between approximately 35%–45% Cr by number of atoms.
3. The device of claim 1 wherein the antiferromagnetic pinning layer is a layer of MnPt formed to a thickness of between approximately 100 and 200 angstroms or a layer of IrMn formed to a thickness between approximately 50 and 100 angstroms.
4. The device of claim 1 wherein the SyAP layer comprises a lower and upper layer of CoFe separated by a coupling layer of Ru, wherein at least the upper layer of CoFe, which is adjacent to the tunnel barrier layer, is CoFe(25%).
5. The device of claim 1 wherein the SyAP layer comprises a lower layer of CoFe and an upper composite layer of CoFe(10%)—NiFe(60%) separated by a coupling layer of Ru, wherein the upper composite layer is adjacent to the tunnel barrier layer.
6. The device of claim 4 wherein the lower layer of CoFe is between approximately 18 and 25 angstroms thick, the upper layer of CoFe is between approximately 15 to 20 angstroms thick and the Ru layer is 7 to 8 angstroms thick.
7. The device of claim 5 wherein the lower layer of CoFe is between approximately 18 and 25 angstroms thick, the upper composite layer of CoFe(10%)—NiFe(60%) is between approximately 5 and 10 angstroms thick, giving said composite layer a total magnetic thickness equivalent to 15 to 20 angstroms of CoFe(25%) and the Ru layer is 7 to 8 angstroms thick.
8. The device of claim 1 wherein the oxygen surfactant layer is less than a monolayer of oxygen adsorbed on the surface of said upper ferromagnetic layer.
9. The device of claim 4 wherein said upper ferromagnetic layer is CoFe(25%) and wherein the oxygen in said oxygen surfactant layer formed on said CoFe(25%) has been incorporated into said tunnel barrier layer.
10. The device of claim 5 wherein said upper ferromagnetic layer is a composite layer of CoFe(10%)—NiFe(60%) and wherein the oxygen in said oxygen surfactant layer has been incorporated into said tunnel barrier layer.
11. The device of claim 1 wherein the tunneling barrier layer is a layer of oxidized Al, formed by PVD deposition on an oxygen surfactant layer to a thickness between approximately 7 and 10 angstroms and oxidized by radical oxidation to a homogeneous Al 2 O 3 stoichiometry.
12. The device of claim 1 wherein the ferromagnetic free layer is a bilayer of CoFe(25%)—NiFe(20%) in which the CoFe(25%) is formed to a thickness between approximately 5 and 10 angstroms and the NiFe(20%) is formed to a thickness between approximately 25 and 50 angstroms.
13. The device of claim 1 wherein the ferromagnetic free layer is a bilayer of NiFe(60%)—NiFe(20%) in which the NiFe(60%) is formed to a thickness between approximately 5 and 10 angstroms and the NiFe(20%) is formed to a thickness between approximately 25 and 50 angstroms.