CN112310272B - Magnetic tunnel junction structure of magnetic random access memory - Google Patents
Magnetic tunnel junction structure of magnetic random access memory Download PDFInfo
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Abstract
The utility model provides a magnetic tunnel junction structure of magnetic random access memory, magnetic tunnel junction structure includes multilayer lattice conversion layer, realizes having the anti-ferromagnetic layer of face-centered cubic crystal structure to having the lattice conversion and strong ferromagnetic coupling between the reference layer is piled up to the body-centered cube, is favorable to magnetic tunnel junction unit in magnetism, electricity and the promotion of yield and the microminiaturization of device.
Description
Technical Field
The invention relates to the technical field of memories, in particular to a magnetic tunnel junction structure of a magnetic random access memory.
Background
Magnetic random access memory (Magnetic random access memory, MRAM) has, in a magnetic tunnel junction (Magnetic tunnel junction; MTJ) with perpendicular anisotropy (Perpendicular Magnetic Anisotropy; PMA), as a free layer for storing information, two magnetization directions in the perpendicular direction, namely: up and down, 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 being empty; during writing, if a signal different from the existing state is input, the magnetization direction of the free layer will be inverted 180 degrees in the vertical direction. The ability of the free Layer magnetization direction of the mram to remain unchanged is called Data Retention (Data Retention) or thermal stability (Thermal Stability), which is different in different applications, and for a typical Non-volatile Memory (NVM), the Data Retention is required to be able to store Data for 10 years under the condition of 125 ℃, and the Data Retention or thermal stability is reduced during external magnetic field flipping, thermal perturbation, current perturbation or multiple operations, so that the pinning of the Reference Layer (RL) is often implemented by using an antiferromagnetic Layer (Synthetic Anti-Ferrimagnet Layer, syAF) superlattice. Current manufacturers use various techniques to achieve lattice matching of the antiferromagnetic layer to the reference layer, but the "antiferromagnetic coupling" situation still occurs.
Disclosure of Invention
In order to solve the above technical problems, an object of the present application is to provide a magnetic tunnel junction structure of a magnetic random access memory, which realizes reference layer pinning, lattice conversion, and reduces/avoids the situation of "demagnetizing magnetic coupling".
The aim and the technical problems of the application are achieved by adopting the following technical scheme.
According to the magnetic tunnel junction structure of the magnetic random access memory provided by the application, the magnetic tunnel junction structure comprises a Covering Layer (CL), a Free Layer (FL), a barrier Layer (Tunneling Barrier Layer, TBL), a Reference Layer (RL), a lattice conversion Layer (Crystal Transfer Layer, CTL), an antiferromagnetic Layer (SyAF) and a Seed Layer (Seed Layer; SL), wherein the lattice conversion Layer comprises: the first conversion sub-layer, i.e., the exchange coupling maintaining layer, is formed of a transition metal material having a high electronegativity and a face-centered crystal structure; a second conversion sublayer, i.e., a discontinuous barrier layer, disposed on the first conversion sublayer, formed of a low electronegativity metallic material, or an oxide or nitride thereof, having a thickness insufficient to form a continuous atomic layer; a third conversion sub-layer, i.e., an intermediate magnetic coupling layer, disposed on the second conversion sub-layer, formed of a ferromagnetic material; and a fourth conversion sublayer, namely a body-centered lattice promoting layer, disposed on the third conversion sublayer, formed of a transition metal having a body-centered crystal structure with high electronegativity; wherein the magnetic tunnel junction comprises four lattice-switching sublayers that perform lattice switching and strong ferromagnetic coupling between the antiferromagnetic layer and the reference layer.
The technical problem of the application can be further solved by adopting the following technical measures.
In an embodiment of the present application, the material of the first conversion sub-layer is one selected from iridium, platinum, palladium, rhodium, nickel, gold or silver, and the thickness of the first conversion sub-layer is between 0.1 nm and 0.4 nm, preferably between 0.15nm and 0.2 nm.
In an embodiment of the present application, the low electronegativity metallic material of the second conversion sublayer is X, XY or XZ, wherein X is one or a combination of rare earth elements selected from calcium, scandium, yttrium, titanium, zirconium, hafnium, vanadium, niobium, tantalum, chromium, aluminum, lanthanide rare earth elements, actinide rare earth elements; y is nitrogen, Z is oxygen, and the thickness of the second conversion sub-layer is not more than 0.15 nm.
In an embodiment of the present application, the material of the second conversion sub-layer is one of tantalum, zirconium, hafnium and niobium, and the thickness of the second conversion sub-layer is not greater than 0.10nm, preferably between 0.05 and 0.08 nm.
In an embodiment of the present application, the material of the third conversion sub-layer is one or a combination of cobalt, iron and nickel, and the thickness of the third conversion sub-layer is between 0.3 nm and 1.0 nm.
In an embodiment of the present application, the material of the fourth conversion sub-layer is one selected from tungsten, molybdenum, rhenium and technetium, and the thickness of the fourth conversion sub-layer is between 0.1 nm and 0.5 nm.
In an embodiment of the present application, the material of the covering layer is a double layer structure selected from (one of magnesium, magnesium oxide, magnesium zinc oxide, magnesium boron oxide, and magnesium aluminum oxide)/(one of tungsten, molybdenum, magnesium, niobium, ruthenium, hafnium, vanadium, chromium, or platinum), or a double 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 a single-layer structure selected from cobalt boride, iron boride, cobalt-iron-boron, or a double-layer structure of cobalt boride/cobalt-iron-boron, or cobalt-iron-boron/(tantalum, tungsten, molybdenum, or hafnium)/cobalt-iron-boron, or a three-layer structure of cobalt-iron-boron/(tungsten, molybdenum, or hafnium)/cobalt-iron-boron, or iron/cobalt-iron-boron/(tungsten, molybdenum, or hafnium)/cobalt-iron-boron, or one of four-layer structures of cobalt-iron-boron/(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 one selected from 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, the material of the reference layer is selected from 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-carbon alloy, and the thickness of the reference layer is between 0.5nm and 2.0 nm.
In one embodiment of the present application, the antiferromagnetic layer of the magnetic tunnel junction is made of [ cobalt/(palladium, platinum or nickel)] n Cobalt/(ruthenium, iridium or rhodium)/cobalt [ (palladium, platinum or nickel)/cobalt] m Wherein n is greater than or equal to 1, m is greater than or equal to 0, and the thickness of the single layer of cobalt, palladium, platinum, nickel, ruthenium, iridium or rhodium is less than 1.0 nm.
In an embodiment of the present application, the material of the seed layer of the magnetic tunnel junction is one or a combination of titanium, titanium nitride, tantalum nitride, tungsten nitride, ruthenium, palladium, chromium, oxygen, nitrogen, chromium cobalt, chromium nickel, cobalt boride, iron boride, cobalt iron boron, or the like, or one of the multi-layer structures selected from cobalt iron boron/tantalum/platinum, tantalum/ruthenium, tantalum/platinum/ruthenium, cobalt iron boron/tantalum/platinum/ruthenium, or the like.
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 template of a face-centered cubic crystal structure barrier layer.
The magnetic tunnel junction unit structure with the four lattice conversion layers can realize lattice conversion and ferromagnetic coupling between an antiferromagnetic layer with a face-centered cubic crystal structure and a reference layer with a body-centered cubic stack, and is favorable for improvement of magnetism, electricity and yield of the magnetic tunnel junction unit and miniaturization of devices.
Drawings
FIG. 1 is a schematic diagram of a magnetic memory cell of a magnetic random access memory according to an embodiment of the present application;
FIG. 2 is a schematic diagram of a multi-layer conversion layer structure of a lattice conversion layer according to an embodiment of the present disclosure;
FIG. 3 is a schematic diagram of a memory cell according to an embodiment of the present disclosure;
FIG. 4 is a schematic diagram illustrating a memory cell reading operation according to an embodiment of the present disclosure;
FIG. 5 is a schematic diagram showing the magnetization direction of the free layer being flipped during writing of a memory cell according to an embodiment of the present application;
FIG. 6 is a schematic diagram showing the magnetization reversal of the free layer during writing of a memory cell according to an embodiment of the present application.
Symbol description
1, word line; 2, source electrode line; 3, a transistor; 4, bit line; 10, a bottom electrode; a magnetic tunnel junction; a seed layer 21; an antiferromagnetic layer 22; a lattice conversion layer 23; 24, a reference layer; 25, a barrier layer; 26, a free layer; a cover layer 27; 30, a top electrode; 231 a first conversion sublayer; a second conversion sublayer 232; 233, a third conversion sublayer; 234 a fourth conversion sublayer;
Detailed Description
The following description of the embodiments refers to the accompanying drawings, which illustrate specific embodiments in which the invention may be practiced. The terms of directions used in the present invention, such as "up", "down", "front", "back", "left", "right", "inside", "outside", "side", etc., refer only to the directions of the attached drawings. Accordingly, directional terminology is used to describe and understand the invention and is not limiting of the invention.
The drawings and description are to be regarded as illustrative in nature, and not as restrictive. In the drawings, like structural elements are denoted by like reference numerals. In addition, for the sake of understanding and convenience of description, the size and thickness of each component shown in the drawings are arbitrarily shown, but the present invention is not limited thereto.
In the drawings, the scope of the arrangement of devices, systems, components, circuits, etc. is exaggerated for clarity, understanding, and convenience 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 "comprising" will be understood to mean comprising the recited component, but not excluding any other components. Further, in the specification, "above" means above or below the target assembly, and does not mean necessarily on top based on the direction of gravity.
In order to further describe the technical means and effects adopted for achieving the preset aim of the present invention, the following description refers to the specific structure, the characteristics and the effects of a magnetic tunnel junction structure of a magnetic random access memory according to the present invention with reference to the accompanying drawings and the specific embodiments.
FIG. 1 is a schematic diagram of a magnetic memory cell of an embodiment of the present application. Fig. 2 is a schematic diagram of a four-layer lattice conversion layer of a magnetic tunnel junction cell structure according to an embodiment of the present application. The magnetic memory cell structure comprises at least a multilayer structure formed by a bottom electrode 10, a magnetic tunnel junction 20 and a top electrode 30. The magnetic tunnel junction 20 includes, from top to bottom, a Capping Layer (CL) 27, a Free Layer (FL) 26, a barrier Layer (Tunneling Barrier Layer, TBL) 25, a Reference Layer (RL) 24, a lattice conversion Layer (Crystal Transfer Layer, CTL) 23, an antiferromagnetic Layer (SyAF) 22, and a Seed Layer (BL) 21 (Buffer Layer, BL).
In an embodiment of the present application, the lattice conversion layer 23 is a stacked multi-layer structure, and is regarded as a first conversion sub-layer 231, a second conversion sub-layer 232, a third conversion sub-layer 233, and a fourth conversion sub-layer 234 from bottom to top.
In some embodiments, the first conversion sublayer 231, the exchange coupling maintaining layer, is formed of a transition metal material having a high electronegativity and a face-centered crystal structure; the second conversion sublayer 232, i.e., a discontinuous barrier layer, is disposed on the first conversion sublayer and is formed of a low electronegativity metallic material, or an oxide or nitride thereof, and is not thick enough to form a continuous atomic layer; the third conversion sub-layer, namely the middle magnetic coupling layer, is arranged on the second conversion sub-layer and is formed by ferromagnetic materials; the fourth conversion sublayer, i.e., the body-centered lattice promoting layer, is disposed on the third conversion sublayer and is formed of a transition metal having a body-centered crystal structure with high electronegativity.
In some embodiments, antiferromagnetic layer 22 is a face centered cubic crystal structure and interfaces with the first switching sublayer 231; reference layer 24 is of a body centered cubic lattice structure and interfaces with the fourth conversion sublayer 234.
In some embodiments, the magnetic tunnel junction 20 includes four lattice-switching sublayers that perform lattice switching and strong ferromagnetic coupling between the antiferromagnetic layer 22 and the reference layer 24 during the read or write operation of the magnetic random access memory cell.
In an embodiment of the present application, the material of the first conversion sub-layer 231 may be one of iridium (Ir), platinum (Pt) or palladium (Pd), rhodium (Rh), nickel (Ni), gold (Au) or silver (Ag), and the thickness of the first conversion sub-layer 231 is between 0.1 nm and 0.4 nm, preferably between 0.15nm and 0.2 nm.
In an embodiment of the present application, the material of the second conversion sublayer 232 is X, XY or XZ, where X may be selected from one or a combination of calcium (Ca), scandium (Sc), yttrium (Y), titanium (Ti), zirconium (Zr), hafnium (Hf), vanadium (V), niobium (Nb), tantalum (Ta), chromium (Cr), aluminum (Al), lanthanide rare earth elements, actinide rare earth elements, Y is nitrogen (N), Z is oxygen (O), and the thickness of the second conversion sublayer 232 is not greater than 0.15 nm.
In an embodiment of the present application, the material of the second conversion sublayer 232 is one of tantalum (Ta), zirconium (Zr), hafnium (Hf) and niobium (Nb), and the thickness of the second conversion sublayer 232 is not greater than 0.10nm, preferably between 0.05 and 0.08 nm.
In an embodiment of the present application, the material of the third conversion sublayer 233 may be selected from one or a combination of metals such as cobalt (Co), iron (Fe) or nickel (Ni), for example, cobalt iron (CoFe), cobalt nickel (CoNi), iron nickel (FeNi) or cobalt iron nickel (CoFeNi). The thickness of the third conversion sub-layer 233 is between 0.3 nm and 1.0 nm, for example: 0.4 nm, 0.5nm or 0.6 nm, but not limited thereto, depending on the design requirements.
In an embodiment of the present application, the material of the fourth conversion sublayer 234 may be selected from one of metals such as tungsten (W), molybdenum (Mo), rhenium (Re) and technetium (Tc), and the thickness of the fourth conversion sublayer 234 is between 0.1 nm and 0.5 nm.
In an embodiment of the present application, the material of the seed layer 21 of the magnetic tunnel junction 20 is one or a combination of titanium, titanium nitride, tantalum nitride, tungsten nitride, ruthenium, palladium, chromium, oxygen, nitrogen, chromium cobalt, chromium nickel, cobalt boride, iron boride, cobalt iron boron, and the like. In some embodiments, the seed layer 21 may be selected from one of cobalt-iron-boron/tantalum/platinum, tantalum/ruthenium, tantalum/platinum/ruthenium, cobalt-iron-boron/tantalum/platinum/ruthenium, etc. multilayer structures for optimizing the crystal structure formed by the synthetic ferromagnetic layer (SyAF) 22.
In one embodiment of the present application, the antiferromagnetic layer 22 of the magnetic tunnel junction 20 is made of [ cobalt/(palladium, platinum, or nickel)] n Cobalt/(ruthenium, iridium or rhodium)/cobalt [ (palladium, platinum or nickel)/cobalt] m And a multilayer structure, wherein m is more than or equal to 0, and the thickness of single-layer cobalt, palladium, platinum, nickel, ruthenium, iridium or rhodium is less than 1.0 nm. In some embodiments, a monolayer of any of cobalt, palladium, platinum, nickel, ruthenium, iridium, or rhodium may be formed to a thickness below 0.5nm, such as: 0.10nm,0.15nm,0.20nm,0.25nm,0.30nm,0.35nm,0.40nm,0.45nm or 0.50nm, etc., but are not limited thereto, as determined by design requirements.
In an embodiment of the present application, the material of the reference layer 24 of the magnetic tunnel junction 20 is selected from 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-carbon alloy, and has a thickness of 0.5nm to 2.0 nm.
In an embodiment of the present application, the material of the barrier layer 25 of the magnetic tunnel junction 20 is a non-magnetic metal oxide, which is one of magnesium oxide, magnesium zinc oxide, magnesium boron oxide or magnesium aluminum oxide, and has a thickness of 0.6 nm to 1.5 nm.
In an embodiment of the present application, the free layer 26 of the magnetic tunnel junction has a variable magnetic polarization characteristic, and the material of the free layer 26 is selected from a single-layer structure of cobalt boride, iron boride, cobalt-iron-boron, or the like, or a four-layer structure of cobalt-iron-boron/(tantalum, tungsten, molybdenum, or hafnium, or the like)/cobalt-iron-boron, cobalt-iron-boron/(tungsten, molybdenum, or hafnium, or the like)/cobalt-iron-boron, or the like, or a three-layer structure of iron/cobalt-iron-boron/(tungsten, molybdenum, or hafnium, or the like)/cobalt-iron-boron, or the like, or the material of the cobalt-iron-boron/(tungsten, molybdenum, or hafnium, or the like)/cobalt-iron-boron, or the material of the like, and the thickness thereof is 1.2 nm to 3.0 nm.
In an embodiment of the present application, the material of the capping layer 27 of the magnetic tunnel junction 20 is a double layer structure selected from (one of magnesium, magnesium oxide, magnesium zinc oxide, magnesium boron oxide, magnesium aluminum oxide, etc./(one of tungsten, molybdenum, magnesium, niobium, ruthenium, hafnium, vanadium, chromium, platinum, etc.), or a three-layer structure of magnesium oxide/(one of tungsten, molybdenum, hafnium, etc./ruthenium), or a four-layer structure of magnesium oxide/platinum/(one of tungsten, molybdenum, hafnium, etc./ruthenium). In some embodiments, the choice of magnesium oxide (MgO) can provide an additional source of interfacial anisotropy for the Free Layer (FL) 26, thereby increasing thermal stability.
In one embodiment of the present application, an annealing process is performed on the magnetic tunnel junction 20 at a temperature between 350 ℃ and 400 ℃ to cause the reference layer 24 and the free layer 26 to be transformed from an amorphous structure to a body-centered cubic stacked crystal structure by the template of a sodium chloride (NaCl) type-centered cubic crystal structure barrier layer 25.
Fig. 3 is a schematic structural diagram of a memory cell according to an embodiment of the present application. In one embodiment of the present application, the memory cell is disposed at a portion where a Bit Line (BL) 4 intersects a Word Line (WL) 1. The memory cell comprises a magnetic tunnel junction 20 and a transistor 3. The Source of the transistor 3 is connected to a Source Line (SL), the drain is connected to the bottom of the magnetic tunnel junction 20, and the Gate (Gate) is connected to the word Line 1. The top of the magnetic tunnel junction 20 is connected to the bit line 4. In the memory cell, the Magnetic Tunnel Junction (MTJ) 20 acts as a Resistor (Resistor) when the magnetization vector of the Free Layer (FL) 26 and the magnetization vector of the Reference Layer (RL) 24 are antiparallel, the Magnetic Tunnel Junction (MTJ) 20 assumes a "high resistance state", corresponding to "1" in binary; when the magnetization vector of the Free Layer (FL) 26 and the magnetization vector of the Reference Layer (RL) 24 are parallel, the Magnetic Tunnel Junction (MTJ) 20 assumes a "low resistance state," corresponding to a "0" in binary.
FIG. 4 is a schematic diagram illustrating a memory cell reading operation according to an embodiment of the present disclosure. When less than the critical current (I c0 ) Is a read current (I) READ ) When passing through the Magnetic Tunnel Junction (MTJ) 20, it can be determined whether the memory cell holds a "1" signal or a "0" signal by the resistance value of the Magnetic Tunnel Junction (MTJ) 20.
Fig. 5 and 6 are schematic diagrams illustrating magnetization directions of the free layer when writing values in the memory cell according to the embodiment of the present disclosure. To effect a transition from "1" to "0" or from "0" to "1", only a specific direction of passage into the Magnetic Tunnel Junction (MTJ) 20 is required and greater than the critical current (I c0 ) Write current (I) WRITE ) And (3) obtaining the product. The current flowing through the Magnetic Tunnel Junction (MTJ) 20 is Spin-excited to become Spin-excited current (Spin-polarized Current, SPC), and the Spin-excited current generates a Spin transfer torque (Spin Transfer Torque, STT) through the Free Layer (FL) 26 to flip the magnetization vector of the Free Layer (FL) 26 by 180 degrees.
More specifically, as shown in FIG. 5, when the Magnetic Tunnel Junction (MTJ) 20 stores a signal of "1", a signal greater than the critical current (I) is introduced into the top of the free layer (26) for the purpose of writing a "0 c0 ) The current of (3) is required; as shown in FIG. 6, when the Magnetic Tunnel Junction (MTJ) 20 stores a signal of "0", a signal greater than the critical current (I) is introduced into the top of the free layer (26) for the purpose of writing a "1 c0 ) Is sufficient.
In connection with the previous description of the structure of the lattice conversion layer, the second conversion sublayer 232 mainly serves to interrupt the lattice growth of the antiferromagnetic layer 22, and the third conversion sublayer 233 mainly serves to effect a lattice transition between the synthetic antiferromagnetic layer 22 and the reference layer 24. However, the second switching sublayer 232, if deposited too thick, tends to cause "demagnetizing coupling" between the antiferromagnetic layer 22 and the third switching sublayer 233. In an embodiment of the present application, the fourth conversion sublayer 234 mainly functions to achieve magnetic coupling between the third conversion sublayer 233 and the reference layer 24.
Another object of the present application is a mram architecture, comprising a plurality of memory cells, each memory cell being disposed at a location where a bit line 4 intersects a word line 1, each memory cell comprising: a magnetic tunnel junction 20 as any one of the preceding; a bottom electrode located below the magnetic tunnel junction 20; and a top electrode located above the magnetic tunnel junction 20.
In one embodiment of the present application, the bottom electrode 10, the magnetic tunnel junction 20, and the top electrode 30 are all completed using a physical vapor deposition process.
In an embodiment of the present application, the material of the bottom electrode 10 is one or a combination of titanium, titanium nitride, tantalum nitride, ruthenium, tungsten nitride, and the like.
In an embodiment of the present application, the material of the top electrode 30 is one or a combination of titanium, titanium nitride, tantalum nitride, tungsten nitride, and the like.
In some embodiments, the bottom electrode 10 is planarized after deposition modeling to achieve surface flatness for fabricating the magnetic tunnel junction 20.
In a preferred embodiment of the present application, iridium (Ir), platinum (Pt) or palladium (Pd) may be deposited directly over the last cobalt (Co) layer of the antiferromagnetic layer (SyAF) 22, which may provide an additional source of interfacial energy anisotropy, thereby enhancing the overall perpendicular anisotropy of the magnetic tunnel junction 20.
In an embodiment of the present application, the second conversion sublayer 232 may be accomplished in a PVD deposition process chamber.
The magnetic tunnel junction unit structure with the four lattice conversion layers can realize lattice conversion and ferromagnetic coupling between an antiferromagnetic layer with a face-centered cubic crystal structure and a reference layer with a body-centered cubic stack, and is favorable for improvement of magnetism, electricity and yield and miniaturization of devices.
The terms "in an embodiment" and "in various embodiments" and the like are used repeatedly. This phrase generally does not refer to the same embodiment; but it may also refer to the same embodiment. The terms "comprising," "having," "including," and the like are synonymous, unless the context clearly dictates otherwise.
The foregoing description is only illustrative of the present application and is not intended to be limiting, since the present application is described in terms of specific embodiments, but rather is not intended to be limited to the details of the embodiments disclosed herein, and any and all modifications, equivalent to the above-described embodiments, may be made without departing from the scope of the present application, as long as the equivalent changes and modifications are within the scope of the present application.
Claims (10)
1. A magnetic tunnel junction structure of a magnetic random access memory, disposed in a magnetic random access memory cell, the magnetic tunnel junction comprising, from top to bottom, a capping layer, a free layer, a barrier layer, a reference layer, a lattice conversion layer, an antiferromagnetic layer and a seed layer, wherein the lattice conversion layer comprises:
the first conversion sub-layer, i.e., the exchange coupling maintaining layer, is formed of a transition metal material having a high electronegativity and a face-centered crystal structure;
a second conversion sublayer, i.e., a discontinuous barrier layer, disposed on the first conversion sublayer, formed of a low electronegativity metallic material, or an oxide or nitride thereof, having a thickness insufficient to form a continuous atomic layer;
a third conversion sub-layer, i.e., an intermediate magnetic coupling layer, disposed on the second conversion sub-layer, formed of a ferromagnetic material; and
a fourth conversion sublayer, namely a body-centered lattice promoting layer, disposed on the third conversion sublayer, formed of a transition metal having a body-centered crystalline structure with high electronegativity;
wherein the magnetic tunnel junction comprises four lattice-switching sublayers that perform lattice switching and strong ferromagnetic coupling between the antiferromagnetic layer and the reference layer;
the low electronegativity metal material of the second conversion sublayer is X, XY or XZ, wherein X is one or a combination of rare earth elements selected from calcium, scandium, yttrium, titanium, zirconium, hafnium, vanadium, niobium, tantalum, chromium, aluminum, lanthanide rare earth elements, actinide rare earth elements; y is nitrogen, Z is oxygen, and the thickness of the second conversion sub-layer is not more than 0.15 nm.
2. The magnetic tunnel junction structure of claim 1 wherein the first conversion sublayer is made of a material selected from the group consisting of iridium, platinum, palladium, rhodium, nickel, gold, and silver, and the first conversion sublayer has a thickness of between 0.1 nm and 0.4 nm.
3. The magnetic tunnel junction structure of claim 2 wherein said first switching sub-layer has a thickness of between 0.15nm and 0.2 nm.
4. The magnetic tunnel junction structure of claim 1 wherein the material of the second conversion sublayer is one of tantalum, zirconium, hafnium and niobium, and the thickness of the second conversion sublayer is no greater than 0.10 nm.
5. The magnetic tunnel junction structure of claim 4 wherein said second conversion sublayer has a thickness of between 0.05 and 0.08 nm.
6. The magnetic tunnel junction structure of claim 1 wherein the third conversion sublayer is made of a material selected from the group consisting of cobalt, iron and nickel, and has a thickness of between 0.3 nm and 1.0 nm.
7. The magnetic tunnel junction structure of claim 1 wherein said fourth conversion sublayer is formed of a material selected from the group consisting of tungsten, molybdenum, rhenium and technetium and has a thickness of between 0.1 nm and 0.5 nm.
8. The magnetic tunnel junction structure of claim 1 wherein the reference layer of the magnetic tunnel junction is formed of a material selected from the group consisting of cobalt, iron, nickel, iron-cobalt alloy, cobalt boride, iron boride, cobalt-iron-boron alloy, cobalt-iron-carbon alloy, and cobalt-iron-boron-carbon alloy, or a combination thereof, and has a thickness of between 0.5nm and 2.0 nm.
9. The magnetic tunnel junction structure of claim 1 wherein the antiferromagnetic layer of the magnetic tunnel junction is a multi-layer structure of [ cobalt/(palladium, platinum, or nickel) ] ncobalt/(ruthenium, iridium, or rhodium)/cobalt [ (palladium, platinum, or nickel)/cobalt ] m, wherein n is 1, m is 0, and the thickness of the single layer of cobalt, palladium, platinum, nickel, ruthenium, iridium, or rhodium is less than 1.0 nm.
10. The magnetic tunnel junction structure of claim 1 wherein the seed layer of the magnetic tunnel junction is of a material selected from the group consisting of titanium, titanium nitride, tantalum nitride, tungsten nitride, ruthenium, palladium, chromium, oxygen, nitrogen, chromium cobalt, chromium nickel, cobalt boride, iron boride, cobalt iron boron, or a combination thereof, or of a multilayer structure selected from the group consisting of cobalt iron boron/tantalum/platinum, tantalum/ruthenium, tantalum/platinum/ruthenium, cobalt iron boron/tantalum/platinum/ruthenium.
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