CN112652709A - Seed layer forming method of magnetic tunnel junction - Google Patents
Seed layer forming method of magnetic tunnel junction Download PDFInfo
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- CN112652709A CN112652709A CN201910959679.XA CN201910959679A CN112652709A CN 112652709 A CN112652709 A CN 112652709A CN 201910959679 A CN201910959679 A CN 201910959679A CN 112652709 A CN112652709 A CN 112652709A
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- FQMNUIZEFUVPNU-UHFFFAOYSA-N cobalt iron Chemical compound [Fe].[Co].[Co] FQMNUIZEFUVPNU-UHFFFAOYSA-N 0.000 description 16
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- CPLXHLVBOLITMK-UHFFFAOYSA-N magnesium oxide Inorganic materials [Mg]=O CPLXHLVBOLITMK-UHFFFAOYSA-N 0.000 description 12
- AXZKOIWUVFPNLO-UHFFFAOYSA-N magnesium;oxygen(2-) Chemical compound [O-2].[Mg+2] AXZKOIWUVFPNLO-UHFFFAOYSA-N 0.000 description 12
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- PNHVEGMHOXTHMW-UHFFFAOYSA-N magnesium;zinc;oxygen(2-) Chemical compound [O-2].[O-2].[Mg+2].[Zn+2] PNHVEGMHOXTHMW-UHFFFAOYSA-N 0.000 description 4
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- H—ELECTRICITY
- H10—SEMICONDUCTOR DEVICES; ELECTRIC SOLID-STATE DEVICES NOT OTHERWISE PROVIDED FOR
- H10N—ELECTRIC SOLID-STATE DEVICES NOT OTHERWISE PROVIDED FOR
- H10N50/00—Galvanomagnetic devices
- H10N50/01—Manufacture or treatment
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- H—ELECTRICITY
- H10—SEMICONDUCTOR DEVICES; ELECTRIC SOLID-STATE DEVICES NOT OTHERWISE PROVIDED FOR
- H10N—ELECTRIC SOLID-STATE DEVICES NOT OTHERWISE PROVIDED FOR
- H10N50/00—Galvanomagnetic devices
- H10N50/10—Magnetoresistive devices
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Abstract
The seed layer of the magnetic tunnel junction structure is formed through multiple times of deposition or surface ion treatment, and the seed layer formed in the mode can guide the antiferromagnetic layer to form a face-centered cubic structure during generation, so that improvement of magnetism, electricity and yield of a magnetic tunnel junction unit and reduction of a device are facilitated.
Description
Technical Field
The invention relates to the technical field of memories, in particular to a seed layer forming method of a magnetic tunnel junction.
Background
Magnetic Random Access Memory (MRAM) in a Magnetic Tunnel Junction (MTJ) having Perpendicular Anisotropy (PMA), as a free layer for storing information, has two magnetization directions in a vertical direction, that is: upward and downward, respectively corresponding to "0" and "1" or "1" and "0" in binary, in practical application, the magnetization direction of the free layer will remain unchanged when reading information or leaving empty; during writing, if a signal different from the existing state is input, the magnetization direction of the free layer will be flipped by 180 degrees in the vertical direction. The ability of the mram to maintain the magnetization direction of the free Layer is called Data Retention or Thermal Stability (Thermal Stability), and is different in different application situations, and for a typical Non-volatile Memory (NVM), the requirement of Data Retention is to retain Data for 10 years at 125 ℃, and the Data Retention or Thermal Stability is reduced when external magnetic field flipping, Thermal disturbance, current disturbance or reading and writing are performed for many times, so that an Anti-ferromagnetic Layer (SyAF) superlattice is often used to pin the Reference Layer (RL). When the seed layer is manufactured, a heating coating technology is generally adopted to improve the uniformity and uniformity of the crystal orientation of the antiferromagnetic layer face-centered cubic FCC crystal, but the seed layer needs to have a certain thickness to obtain a high-quality crystal orientation, and relatively low surface roughness is not easy to obtain.
Disclosure of Invention
In order to solve the above-mentioned technical problems, an object of the present invention is to provide a method for forming a seed layer of a magnetic tunnel junction, which can guide the generation of crystal lattices of an antiferromagnetic layer by the formed seed layer, thereby realizing the pinning and lattice transformation of a reference layer and reducing/avoiding the "desferrimagnetic coupling".
The purpose of the application and the technical problem to be solved are realized by adopting the following technical scheme.
According to the Seed Layer forming method of the magnetic tunnel junction, the magnetic tunnel junction is arranged in a magnetic random access memory unit, and the structure of the magnetic tunnel junction comprises a Buffer Layer (BL), a Seed Layer (Seed Layer; SL), an Anti-ferromagnetic Layer (SyAF), a Crystal Breaking Layer (CBL), a Reference Layer (RL), a Barrier Layer (Tunnel Barrier, TBL) and a Free Layer (FL) from bottom to top. The seed layer forming method comprises the following steps: forming a plurality of seed sub-layers on the buffer layer in an environment without vacuum interruption, wherein each seed sub-layer is formed by deposition and further combined with subsequent surface ion treatment.
The technical problem solved by the application can be further realized by adopting the following technical measures.
In one embodiment of the present application, heating, preferably at a temperature between 150 ℃ and 400 ℃, may optionally be applied during each deposition of the seed sub-layer or surface ion treatment.
In one embodiment of the present application, the seed sub-layer is sputter deposited with neon, argon, krypton, or xenon at a pressure of 0.1mTorr to 20.0mTorr, preferably 1.0mTorr or 2.0mTorr, and then the surface is subjected to low energy surface plasma etching.
In one embodiment of the present application, after the deposition or surface ion treatment, natural cooling to room temperature or ultra-low temperature cooling, preferably 100K or 200K, is performed.
In an embodiment of the present application, the seed layer has n seed sub-layers, where n is greater than or equal to 2 and less than or equal to 20, and a thickness a of each sub-layer is: a is more than or equal to 0.25nm and less than or equal to 1.50 nm.
In an embodiment of the present application, the structure of the seed layer is platinum or platinum/ruthenium.
In an embodiment of the present application, the buffer layer is made of tantalum, titanium nitride, tantalum nitride, tungsten nitride, carbon, silicon, gallium, cobalt carbon compound, cobalt iron carbon compound, nickel, chromium, cobalt boron compound, iron boron compound, cobalt iron boron compound, or a combination thereof. Preferably, the buffer layer is formed of a two-layer structure of cofeb/ta or ta/cofeb.
In one embodiment of the present application, the antiferromagnetic layer has a structure of [ Co/Pt ]]nCobalt or [ platinum/cobalt ]]nTwo-layer structure of sequentially overlying ruthenium and/or iridium, or [ cobalt/platinum ]]nCobalt or [ platinum/cobalt ]]nRuthenium and/or iridium, cobalt [ platinum/cobalt ]]mWherein n > m is greater than or equal to 0, preferably, the thickness of the single layer of cobalt, platinum, ruthenium and/or iridium is less than 1 nanometer, preferably, the thickness of the single layer of cobalt and platinum is 0.5 nanometerThe following is a description.
In an embodiment of the present application, the thickness of each layer structure of the antiferromagnetic layer is the same or different.
In an embodiment of the present application, a capping layer is disposed on the free layer, and a material of the capping layer is a double-layer structure selected from (one of magnesium, magnesium oxide, magnesium zinc oxide, magnesium boron oxide or magnesium aluminum oxide)/(one of tungsten, molybdenum, magnesium, niobium, ruthenium, hafnium, vanadium, chromium or platinum), or a three-layer structure of magnesium oxide/(one of tungsten, molybdenum or hafnium)/ruthenium, or a four-layer structure of magnesium oxide/platinum/(one of tungsten, molybdenum or hafnium)/ruthenium.
In an embodiment of the present application, the material of the free layer is selected from a single layer structure of cobalt boride, iron boride, cobalt iron boron, or a double layer structure of cobalt boride/cobalt iron boron, iron/cobalt iron boron, or a triple layer structure of cobalt iron boron/(one of tantalum, tungsten, molybdenum, or hafnium)/cobalt boride, or a four-layer structure of iron/cobalt iron boron/(one of tantalum, tungsten, molybdenum, or hafnium)/cobalt iron boron, or cobalt/cobalt iron boron/(one of tungsten, molybdenum, or hafnium)/cobalt iron boron, or cobalt boride/cobalt iron boron/(one of tungsten, molybdenum, or hafnium)/cobalt iron boron, and the thickness of the free layer is between 1.2 nm and 3.0 nm.
In an embodiment of the present application, the material of the barrier layer is selected from one of magnesium oxide, magnesium zinc oxide, magnesium boron oxide, or magnesium aluminum oxide, and the thickness of the barrier layer is between 0.6 nm and 1.5 nm.
In an embodiment of the present application, a material of the reference layer of the magnetic tunnel junction is one or a combination of cobalt, iron, nickel, iron-cobalt alloy, cobalt boride, iron boride, cobalt-iron-boron alloy, cobalt-iron-carbon alloy, and cobalt-iron-boron alloy, and a thickness of the reference layer is between 0.5 nm and 1.5 nm.
In an embodiment of the present application, the material of the lattice partition layer of the magnetic tunnel junction is one or a combination of tungsten, molybdenum, tantalum, hafnium, zirconium, magnesium, titanium and ruthenium, and the thickness of the reference layer is between 0.1 nm and 0.5 nm.
In one embodiment of the present application, an annealing process is performed on the magnetic tunnel junction to cause the reference layer and the free layer to transform from an amorphous structure to a body-centered cubic stacked crystal structure under the templating action of a face-centered cubic crystal structure barrier layer.
According to the magnetic tunnel junction unit structure, the seed layer growth process is adopted after the buffer layer is deposited and before the antiferromagnetic layer is deposited, so that the grain structure and the surface roughness of the formed seed layer can be greatly improved, the antiferromagnetic layer can be guided to form a strong face-centered cubic structure and vertical anisotropy, the lattice conversion and ferromagnetic coupling from the antiferromagnetic layer with the face-centered cubic crystal structure to the body-centered cubic stacking reference layer are facilitated, and the magnetic tunnel junction unit structure is beneficial to the improvement of magnetism, electricity and yield and the miniaturization of devices.
Drawings
FIG. 1 is a schematic diagram of a magnetic memory cell of an embodiment of the present application;
fig. 2a and fig. 2b are schematic diagrams of a layer structure of a seed layer of a magnetic tunnel junction according to an embodiment of the present disclosure.
Detailed Description
The following description of the embodiments refers to the accompanying drawings for illustrating the specific embodiments in which the invention may be practiced. In the present invention, directional terms such as "up", "down", "front", "back", "left", "right", "inner", "outer", "side", etc. refer to directions of the attached drawings. Accordingly, the directional terms used are used for explanation and understanding of the present invention, and are not used for limiting the present invention.
The drawings and description are to be regarded as illustrative in nature, and not as restrictive. In the drawings, elements having similar structures are denoted by the same reference numerals. In addition, the size and thickness of each component shown in the drawings are arbitrarily illustrated for understanding and ease of description, but the present invention is not limited thereto.
In the drawings, the range of configurations of devices, systems, components, circuits is exaggerated for clarity, understanding, and ease of description. It will be understood that when an element is referred to as being "on" another element, it can be directly on the other element or intervening elements may also be present.
In addition, in the description, unless explicitly described to the contrary, the word "comprise" will be understood to mean that the recited components are included, but not to exclude any other components. Further, in the specification, "on.
To further illustrate the technical means and effects of the present invention for achieving the predetermined objects, the following detailed description is provided with reference to the accompanying drawings and embodiments for a seed layer forming method of a magnetic tunnel junction according to the present invention, and its specific structure, features and effects.
FIG. 1 is a diagram illustrating a magnetic memory cell structure of a magnetic random access memory according to an embodiment of the present invention. Fig. 2a and fig. 2b are schematic diagrams of a layer structure of a seed layer of a magnetic tunnel junction according to an embodiment of the present disclosure. The magnetic memory cell structure includes at least a Bottom Electrode (BE) 10, a Magnetic Tunnel Junction (MTJ)20, and a Top Electrode (Top Electrode) 29 forming a multi-layer structure.
In some embodiments, the bottom electrode 10 is titanium (Ti), titanium nitride (TiN), tantalum (Ta), tantalum nitride (TaN), ruthenium (Ru), tungsten (W), tungsten nitride (WN), or a combination thereof, and is typically implemented by Physical Vapor Deposition (PVD), and is typically planarized after deposition to achieve surface flatness for fabricating the magnetic tunnel junction; the top electrode 29 is made of titanium (Ti), titanium nitride (TiN), tantalum (Ta), tantalum nitride (TaN), tungsten (W), tungsten nitride (WN), or a combination thereof.
In some embodiments, the magnetic tunnel junction 20 includes, from bottom to top, a Buffer Layer (BL) 21, a Seed Layer (Seed Layer; SL)22, an antiferromagnetic Layer (SyAF) 23, a lattice Breaking Layer (CBL)24, a Reference Layer (RL) 25, a Barrier Layer (tunnel Barrier) 26, and a Free Layer (Free Layer; FL) 27. The seed layer forming method comprises the following steps: forming a plurality of seed sub-layers (22-1 to 22-n) in an environment without vacuum interruption to form the seed layer 22 on the buffer layer 21, wherein each seed sub-layer (22-1 to 22-n) is formed by deposition and further combined with a subsequent surface ion treatment.
In some embodiments, the seed layer is provided with n seed sublayers, where 2 ≦ n ≦ 20, and the thickness a of each sublayer is: 0.25nm < a < 1.50nm, the structure of the seed layer is platinum (Pt) or platinum (Pt)/ruthenium (Ru), that is, the composition of the seed layer is such that all the sub-layers are formed by platinum (Pt), or the front seed sub-layer is formed by platinum (Pt) and the back seed sub-layer is formed by ruthenium (Ru), that is: so-called platinum (Pt)/ruthenium (Ru) structure.
In some embodiments, the various sub-sublayer depositions are generally performed in a PVD process chamber by sputter deposition. The sputtering gas is typically neon (Ne), argon (Ar), krypton (Kr), or xenon (Xe) at a pressure of 0.1mTorr to 20.0mTorr, preferably 1.0mTorr or 2.0mTorr, during each seed sublayer deposition process. In each deposition process of the seed sub-layer (22-1-22-n), heating or non-heating can be selectively carried out, and the heating temperature is preferably between 150 ℃ and 400 ℃. The superior effect of high temperature deposition is that grains of platinum (Pt) or ruthenium (Ru) can grow larger.
In some embodiments, after deposition of each sublayer, the various sublayer surfaces are plasma treated without breaking vacuum, and the surface plasma treatment may be performed in situ in the PVD process chamber, or in other process chambers, such as: reactive Ion Etching (RIE) or Ion Beam Etching (IBE) process chambers. The process temperature is generally room temperature, and further, the temperature can be 150 ℃ to 400 ℃. The high temperature treatment has the advantage of enhancing the activation energy of surface atoms, so that the surface atoms can be removed from the original positions for surface migration. The surface treatment is generally carried out using a He +, Ne +, Ar +, Kr + or Xe + plasma source at a working gas pressure of 0.5mTorr to 50.0 mTorr. During the surface plasma treatment, some atoms on the surface of each sublayer are separated from the surface of each sublayer by means of re-sputtering, and some atoms are migrated again until the nucleation point with the lowest energy. In this case, the surface roughness of seed layer 22 can be effectively reduced, as shown in fig. 2 b.
In one embodiment of the present application, after the deposition and/or surface ion treatment, natural cooling to room temperature or ultra-low temperature cooling, preferably 100K or 200K, is performed.
In an embodiment of the present application, a layer of platinum (Pt) or palladium (Pd) is added on the surface of the crystalline seed layer 22, and the thickness is 0.15 nm to 2 nm.
In an embodiment of the present application, the seed layer 22 guides the growth of the antiferromagnetic layer 23 to form a face-centered cubic structure.
Preferably, the magnetic tunnel junction 20 includes a lattice-partitioning layer (CBL)24 that effects lattice-switching and strong ferromagnetic coupling of the antiferromagnetic layer with the reference layer.
In an embodiment of the present application, the buffer layer 21 is made of tantalum (Ta), titanium (Ti), titanium nitride (TiN), tantalum nitride (TaN), tungsten (W), tungsten nitride (WN), carbon (C), silicon (Si), gallium (Ga), cobalt carbon compound (CoC), cobalt iron carbon compound (CoFeC), nickel (Ni), chromium (Cr), cobalt boron compound (CoB), iron boron compound (FeB), cobalt iron boron compound (CoFeB) or a combination thereof. Preferably, the buffer layer 21 is formed of a two-layer structure of cobalt iron boron (CoFeB)/tantalum (Ta) or tantalum (Ta)/cobalt iron boron (CoFeB). In some embodiments, the buffer layer 21 is amorphous.
In one embodiment of the present application, the antiferromagnetic layer 23 has a structure of [ Co/Pt]nCobalt Co or [ platinum Pt/cobalt Co]nTwo-layer structure of ruthenium (Ru) and/or iridium (Ir) stacked up in sequence, or [ cobalt Co/platinum Pt ]]nCobalt Co or [ platinum Pt/cobalt Co]nRuthenium (Ru) and/or iridium (Ir), cobalt (Co) [ platinum Pt/cobalt Co]mWhere n > m ≧ 0, preferably, the individual layers of cobalt (Co), platinum (Pt), ruthenium (Ru) and/or iridium (Ir) are less than 1 nm thick, preferably, the individual layers of cobalt (Co) and platinum (Pt) are below 0.5 nm thick, such as: 0.10 nm, 0.15 nm, 0.20 nm, 0.25nm, 0.30 nm, 0.35 nm, 0.40 nm, 0.45 nm, or 0.50 nm …. In some embodiments, the antiferromagnetic layer23 are the same or different in thickness.
In an embodiment of the present application, a capping layer 28 is disposed on the free layer 27, and a material of the capping layer 28 is a double-layer structure selected from (one of magnesium Mg, magnesium oxide MgO, magnesium zinc oxide MgZnO, magnesium boron oxide MgBO or magnesium aluminum oxide MgAlO)/(one of tungsten W, molybdenum Mo, magnesium Mg, niobium Nb, ruthenium Ru, hafnium Hf, vanadium V, chromium Cr or platinum Pt), or a three-layer structure of magnesium oxide MgO/(one of tungsten W, molybdenum Mo or hafnium Hf)/ruthenium Ru, or a four-layer structure of magnesium oxide/platinum/(one of tungsten, molybdenum or hafnium)/ruthenium.
In an embodiment of the present application, the material of the free layer 27 is selected from a single layer structure of cobalt boride (CoB), iron boride (FeB), cobalt iron boron (CoFeB), or a double layer structure of cobalt ferrite (CoFe)/cobalt iron boron (CoFeB), iron (Fe)/cobalt iron boron (CoFeB), or a three-layer structure of cobalt iron boron (CoFeB)/(one of tantalum Ta, tungsten W, molybdenum Mo, or hafnium Hf)/cobalt boride (CoB), iron boride (FeB)/(one of tantalum Ta, tungsten W, molybdenum Mo, or hafnium Hf)/cobalt iron boron (CoFeB), cobalt iron boron (CoFeB)/(tantalum Ta, tungsten W, one of molybdenum Mo, or hafnium Hf)/cobalt iron boron (CoFeB), or iron (Fe)/cobalt iron boron (CoFeB)/(one of tungsten W, molybdenum Mo, or hafnium Hf)/cobalt iron boron (CoFeB), or cobalt iron boron (CoFe)/cobalt iron boron (CoFeB)/(cobalt tungsten W, one of four-layer structure of Mo or Hf/CoFeB (CoFeB), the thickness of the free layer 27 is between 1.2 nm and 3.0 nm.
In an embodiment of the present application, the material of the barrier layer 26 is one selected from magnesium oxide (MgO), magnesium zinc oxide (MgZnO), magnesium boron oxide (MgB), or magnesium aluminum oxide (MgAlO). Preferably, magnesium oxide may be used. The thickness of the barrier layer is between 0.6 nm and 1.5 nm.
In an embodiment of the present application, a material of the reference layer 25 of the magnetic tunnel junction 20 is one or a combination of cobalt (Co), iron (Fe), nickel (Ni), iron-cobalt alloy (CoFe), cobalt boride (CoB), iron boride (FeB), cobalt-iron-boron alloy (CoFeB), cobalt-iron-carbon alloy (CoFeC) and cobalt-iron-boron alloy (CoFeB), and the reference layer 25 has a thickness of 0.5 nm to 1.5 nm.
In an embodiment of the present application, the material of the lattice-blocking layer 24 of the magnetic tunnel junction 20 is one or a combination of tungsten (W), molybdenum (Mo), tantalum (Ta), hafnium (Hf), zirconium (Zr), magnesium (Mg), titanium (Ti) and ruthenium (Ru), and the thickness of the reference layer 25 is between 0.1 nm and 0.5 nm.
In one embodiment of the present application, an annealing process is performed on the magnetic tunnel junction 20 to cause the reference layer 25 and the free layer 26 to transform from an amorphous structure to a body-centered cubic stacked crystal structure under the templating action of the face-centered cubic crystal structure barrier layer 26.
According to the magnetic tunnel junction unit structure, the seed layer growth process is adopted after the buffer layer is deposited and before the antiferromagnetic layer is deposited, so that the grain structure and the surface roughness of the formed seed layer can be greatly improved, the antiferromagnetic layer can be guided to form a strong face-centered cubic structure and vertical anisotropy, the lattice conversion and ferromagnetic coupling from the antiferromagnetic layer with the face-centered cubic crystal structure to the body-centered cubic stacking reference layer are facilitated, and the magnetic tunnel junction unit structure is beneficial to the improvement of magnetism, electricity and yield and the miniaturization of devices.
The terms "in one embodiment of the present application" and "in various embodiments" are used repeatedly. This phrase generally does not refer to the same embodiment; it may also refer to the same embodiment. The terms "comprising," "having," and "including" are synonymous, unless the context dictates otherwise.
Although the present application has been described with reference to specific embodiments, it should be understood that various changes, substitutions and alterations can be made herein without departing from the spirit and scope of the application, and all changes, substitutions and alterations that fall within the spirit and scope of the application are to be understood as being covered by the following claims.
Claims (10)
1. A seed layer forming method of a magnetic tunnel junction is provided, the magnetic tunnel junction is arranged in a magnetic random access memory unit, and the structure of the magnetic tunnel junction comprises a buffer layer, a seed layer, an antiferromagnetic layer, a lattice partition layer, a reference layer, a barrier layer and a free layer from bottom to top, and is characterized by comprising the following steps:
forming a plurality of seed sub-layers on the buffer layer in an environment without vacuum interruption, wherein each seed sub-layer is formed by deposition and subsequent surface ion treatment.
2. The method for forming a seed layer of a magnetic tunnel junction according to claim 1, wherein heating or not heating is optionally performed during each deposition of the seed sub-layer or the surface ion treatment, and the heating temperature is preferably 150 ℃ to 400 ℃.
3. The method of claim 2, wherein the seed layer is deposited by sputtering with neon, argon, krypton or xenon at a pressure of 0.1mTorr to 20.0mTorr, preferably 1.0mTorr or 2.0mTorr, and then low energy surface plasma etching is performed to form the seed sub-layer.
4. The method for forming a seed layer of a magnetic tunnel junction according to claim 2, wherein the deposition or surface ion treatment is followed by natural cooling to room temperature or ultra-low temperature cooling, preferably 100K or 200K.
5. The method of forming a seed layer for a magnetic tunnel junction of claim 1 wherein the seed layer comprises n seed sublayers, wherein n is 2. ltoreq. n.ltoreq.20, and wherein a, the thickness of each sublayer is: a is more than or equal to 0.25nm and less than or equal to 1.50 nm.
6. The method for forming a seed layer for a magnetic tunnel junction of claim 1 wherein the seed layer is platinum or platinum/ruthenium.
7. The method of forming a seed layer for a magnetic tunnel junction of claim 1 wherein the buffer layer is comprised of tantalum, titanium nitride, tantalum nitride, tungsten nitride, carbon, silicon, gallium, cobalt carbon compound, cobalt iron carbon compound, nickel, chromium, cobalt boron compound, iron boron compound, cobalt iron boron compound, or combinations thereof.
8. The method for forming a seed layer for a magnetic tunnel junction according to claim 1, wherein the buffer layer is formed of a two-layer structure of cofeb/ta or ta/cofeb.
9. The method of forming a seed layer for a magnetic tunnel junction of claim 1 wherein said antiferromagnetic layer has a structure of [ cobalt/platinum ]]nCobalt or [ platinum/cobalt ]]nTwo-layer structure of ruthenium and/or iridium or of [ cobalt/platinum ]]nCobalt or [ platinum/cobalt ]]nRuthenium and/or iridium, cobalt [ platinum/cobalt ]]mThe three layers of structures are sequentially and upwards superposed, wherein n is more than m and is more than or equal to 0.
10. The method of claim 9, wherein the thickness of the cobalt, platinum, ruthenium and/or iridium is less than 1 nm, and preferably the thickness of the cobalt and platinum is less than 0.5 nm.
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Application publication date: 20210413 |