Memory cells, methods of fabrication, and semiconductor devices
A magnetic cell includes an attracter material proximate to a magnetic region (e.g., a free region). The attracter material is formulated to have a higher chemical affinity for a diffusible species of a magnetic material, from which the magnetic region is formed, compared to a chemical affinity between the diffusible species and at least another species of the magnetic material. Thus, the diffusible species is removed from the magnetic material to the attracter material. The removal accommodates crystallization of the depleted magnetic material. The crystallized, depleted magnetic material enables a high tunnel magnetoresistance, high energy barrier, and high energy barrier ratio. The magnetic region may be formed as a continuous magnetic material, thus enabling a high exchange stiffness, and positioning the magnetic region between two magnetic anisotropy-inducing oxide regions enables a high magnetic anisotropy strength. Methods of fabrication and semiconductor devices are also disclosed.
1. A memory cell, comprising:
a magnetic cell core comprising:
a magnetic region exhibiting a switchable magnetic orientation and formed from a magnetic material comprising a diffusible species and at least one other species;
another magnetic region exhibiting a fixed magnetic orientation;
an intermediate oxide region between the magnetic region and the another magnetic region;
another oxide region spaced from the intermediate oxide region by the magnetic region; and
an attracter material directly between the another oxide region and the magnetic region, the magnetic region spaced from the another oxide region, the attracter material disposed external to magnetic regions of the magnetic cell core, the magnetic regions of the magnetic cell core including the magnetic region and the another magnetic region, a chemical affinity of the attracter material for the diffusible species being higher than a chemical affinity of the at least one other species for the diffusible species.
2. The memory cell of claim 1 , wherein the attracter material comprises at least one of tantalum, tungsten, hafnium, zirconium, a compound thereof, and a combination thereof.
3. The memory cell of claim 1 , wherein the magnetic material comprises a cobalt iron boron (CoFeB) material.
4. The memory cell of claim 1 , wherein the diffusible species comprises boron.
5. The memory cell of claim 1 , further comprising an attracter region directly between the another oxide region and the magnetic region and comprising the attracter material and the diffusible species, the diffusible species having diffused from the magnetic material from which the magnetic region was formed.
6. The memory cell of claim 1 , wherein the magnetic region has a bcc (001 ) crystalline structure.
7. The memory cell of claim 1 , wherein the memory cell has a tunnel magnetoresistance of greater than 100%.
8. A method of forming a magnetic memory cell, comprising:
forming a precursor structure comprising:
forming a magnetic material disposed vertically between a nonmagnetic oxide material and another nonmagnetic oxide material, the magnetic material exhibiting a switchable magnetic orientation, the magnetic material in direct physical contact with oxide material along only one of an upper surface and a lower surface of the magnetic material, the oxide material including the nonmagnetic oxide material and the another nonmagnetic oxide material;
forming an attracter material disposed vertically between the nonmagnetic oxide material and the another nonmagnetic oxide material, proximate to the magnetic material, and external to magnetic materials of the precursor structure including the magnetic material, the attracter material having a chemical affinity for a diffusible species of the magnetic material; and
transferring the diffusible species from the magnetic material to the attracter material; and
forming a magnetic cell core structure from the precursor structure.
9. The method of claim 8 , wherein:
forming a magnetic material disposed vertically between a nonmagnetic oxide material and another nonmagnetic oxide material comprises:
forming the nonmagnetic oxide material over a substrate;
forming the magnetic material over the nonmagnetic oxide material; and
forming the another nonmagnetic oxide material over the magnetic material; and
forming a magnetic cell core structure from the precursor structure comprises patterning the precursor structure to form a secondary oxide region from the nonmagnetic oxide material, a free region from the magnetic material, and an intermediate oxide region from the another nonmagnetic oxide material.
10. The method of claim 8 , wherein:
forming a magnetic material disposed vertically between a nonmagnetic oxide material and another nonmagnetic oxide material comprises:
forming the another nonmagnetic oxide material over another magnetic material exhibiting a fixed magnetic orientation;
forming the magnetic material over the another nonmagnetic oxide material; and
forming the nonmagnetic oxide material over the magnetic material; and
forming a magnetic cell core structure from the precursor structure comprises patterning the precursor structure to form a fixed region from the another magnetic material, an intermediate oxide region from the another nonmagnetic oxide material, a free region from the magnetic material, and a secondary oxide region from the nonmagnetic oxide material.
11. The method of claim 8 , wherein forming a magnetic material disposed vertically between a nonmagnetic oxide material and another nonmagnetic oxide material comprises:
forming a metal over a substrate; and
oxidizing the metal to form the nonmagnetic oxide material.
12. The method of claim 8 , wherein transferring the diffusible species from the magnetic material to the attracter material comprises annealing the magnetic material, the nonmagnetic oxide material, and the attracter material.
13. The method of claim 8 , wherein transferring the diffusible species from the magnetic material to the attracter material comprises transferring boron from the magnetic material to the attracter material.
14. The method of claim 8 :
wherein transferring the diffusible species from the magnetic material to the attracter material converts the magnetic material to a depleted magnetic material; and
further comprising crystallizing the depleted magnetic material.
15. The method of claim 9 , further comprising forming another magnetic material over the another nonmagnetic oxide material, the another magnetic material exhibiting a fixed magnetic orientation.
16. The method of claim 11 , wherein:
forming a metal over a substrate comprises forming magnesium over the substrate; and
oxidizing the metal to form the nonmagnetic oxide material comprises oxidizing the magnesium to form magnesium oxide.
17. A semiconductor device, comprising:
a spin torque transfer magnetic random access memory (STT-MRAM) array comprising:
STT-MRAM cells, at least one STT-MRAM cell of the STT-MRAM cells comprising:
a nonmagnetic, secondary oxide region over a substrate;
a free region over the nonmagnetic, secondary oxide region;
an attracter region in contact with the free region and spacing the free region from the nonmagnetic, secondary oxide region, the attracter region comprising an attracter material and a species diffused from the free region, the attracter material having a chemical affinity for the species, an oxide of the species inducing magnetic anisotropy in the free region;
an intermediate oxide region over the free region; and
a fixed region over the intermediate oxide region,
the attracter region being external to magnetic regions of the at least one STT-MRAM cell, including the free region and the fixed region.
18. The semiconductor device of claim 17 , wherein the attracter material consists of a metal or a metal compound.
19. The semiconductor device of claim 17 , wherein the attracter region is physically isolated from the fixed region.
20. A semiconductor device, comprising:
a spin torque transfer magnetic random access memory (STT-MRAIVI) array comprising:
STT-MRAM cells, at least one STT-MRAM cell of the STT-MRAM cells comprising:
a magnetic cell core disposed between an upper electrode and a lower electrode, the magnetic cell core comprising:
a nonmagnetic oxide region over a substrate;
a crystalline magnetic region over the nonmagnetic oxide region, the crystalline magnetic region formed from a magnetic material;
an attracter material proximate to the crystalline magnetic region and directly between the nonmagnetic oxide region and the crystalline magnetic region, the crystalline magnetic region spaced from the nonmagnetic oxide region, a chemical affinity of the attracter material for a diffused species from the magnetic material being higher than a chemical affinity of at least one other species of the magnetic material for the diffused species;
an intermediate nonmagnetic oxide region over the crystalline magnetic region; and
another magnetic region over the intermediate nonmagnetic oxide region,
the attracter material being external to magnetic regions of the at least one STT-MRAM cell, including the crystalline magnetic region and the another magnetic region.
21. The semiconductor device of claim 20 , wherein:
the diffused species comprises boron; and
the attracter material is chemically bonded to the boron.
22. A semiconductor device, comprising:
an array of magnetic memory cells, at least one magnetic memory cell of the array of magnetic memory cells comprising:
at least two magnetic regions over an oxide region over a substrate, one of the at least two magnetic regions exhibiting a switchable magnetic orientation;
an attracter material external to magnetic material of the at least one magnetic memory cell, the attracter material disposed directly between the oxide region and the one of the at least two magnetic regions, the attracter material spacing the oxide region from the one of the at least two magnetic regions, the attracter material chemically bonded to a species diffused from the one of the at least two magnetic regions exhibiting the switchable magnetic orientation; and
an intermediate oxide region between the at least two magnetic regions.
23. The semiconductor device of claim 22 , wherein the one of the at least two magnetic regions exhibits a perpendicular switchable magnetic orientation.