CN112635654A - Magnetic tunnel junction structure and magnetic random access memory - Google Patents

Magnetic tunnel junction structure and magnetic random access memory Download PDF

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CN112635654A
CN112635654A CN201910951256.3A CN201910951256A CN112635654A CN 112635654 A CN112635654 A CN 112635654A CN 201910951256 A CN201910951256 A CN 201910951256A CN 112635654 A CN112635654 A CN 112635654A
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oxide
cobalt
layer
iron
magnetic
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张云森
郭一民
陈峻
肖荣福
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Shanghai Ciyu Information Technologies Co Ltd
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Abstract

The application provides a magnetic tunnel junction structure and a magnetic random access memory, the magnetic tunnel junction structure comprises a free layer with a double-layer structure, a vertical anisotropy enhancement layer formed by non-magnetic metal oxide between the two free layers, and a magnetic damping barrier layer arranged above the free layer. The magnetic tunnel junction structure unit with the double free layers and the magnetic damping barrier layers enhances the thermal stability of the device, reduces the damping coefficient and is beneficial to reducing the writing current.

Description

Magnetic tunnel junction structure and magnetic random access memory
Technical Field
The present invention relates to the field of memory technologies, and in particular, to a magnetic tunnel junction structure and a magnetic random access memory.
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 one hundred and eighty 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 Factor (v), and is required to be different in different application situations, and for a typical Non-volatile Memory (NVM), the ability of Data Retention is required to be able to retain Data for ten years at 125 ℃, and the Data Retention or Thermal Stability is reduced when external magnetic field flipping, Thermal disturbance, current disturbance or multiple read/write operations are performed.
In order to increase the storage density of the magnetic random access memory, the Critical Dimension (Critical Dimension) of the magnetic tunnel junction has become smaller in recent years. When the size is further reduced, it is found that the thermal stability factor (v) of the magnetic tunnel junction is drastically deteriorated. In order to increase the thermal stability factor (v) of the ultra-small MRAM cell device, the effective perpendicular effective anisotropy energy density may be increased by reducing the thickness of the free layer, adding or changing the free layer to a material with a low saturation magnetic susceptibility, and the like, so as to maintain a higher thermal stability factor (v), but the Tunneling Magnetoresistance Ratio (TMR) of the magnetic Tunnel junction may be reduced, thereby increasing the error rate of the memory read operation.
Disclosure of Invention
In order to solve the above technical problems, an object of the present invention is to provide a magnetic tunnel junction structure and a magnetic random access memory using a dual free layer design and a nonmagnetic perpendicular anisotropy enhancement layer.
The purpose of the application and the technical problem to be solved are realized by adopting the following technical scheme.
According to the present application, a magnetic tunnel junction structure comprises, from top to bottom, a Capping Layer (CL), a magnetic damping Barrier Layer, a Free Layer (FL), a Barrier Layer (TBL), a Reference Layer (RL), a lattice Breaking Layer (CBL), an Anti-ferromagnetic Layer (SyAF), and a Seed Layer (Seed Layer; SL), wherein the Free Layer comprises: a first free layer which is a variable magnetic polarization layer and is formed by a magnetic metal alloy; a vertical anisotropy enhancement layer disposed on the first free layer, the vertical anisotropy enhancement layer being formed of a non-magnetic metal oxide; a second free layer disposed on the vertical anisotropy enhancement layer, the second free layer being a variable magnetic polarization layer formed of a non-magnetic doped elemental metal alloy or a compound thereof; the magnetic damping blocking layer is arranged on the second free layer and is formed by non-magnetic metal or oxide thereof; wherein the perpendicular anisotropy enhancement layer is to enable magnetic coupling of the first free layer with a second free layer; the magnetic damping barrier layer is beneficial to adjusting and reducing the damping coefficient of the whole film structure.
The technical problem solved by the application can be further realized by adopting the following technical measures.
In an embodiment of the present application, the material of the first free layer is a single-layer structure selected from cobalt boride, iron boride, cobalt-iron-boron alloy, or a double-layer structure of cobalt boride/cobalt-iron-boron alloy, iron/cobalt-iron-boron alloy, or a three-layer structure of iron boride/(tungsten, molybdenum, vanadium, niobium, hafnium, titanium, zirconium, tantalum, scandium, yttrium, zinc, ruthenium, osmium, rhodium, iridium, palladium, and/or platinum)/cobalt-iron-boron alloy, cobalt-iron-boron alloy/(tungsten, molybdenum, vanadium, niobium, chromium, hafnium, titanium, zirconium, scandium, yttrium, zinc, osmium, rhodium, iridium, palladium, and/or platinum)/cobalt-iron-boron alloy, or a three-layer structure of iron/cobalt-iron-boron alloy/(tungsten, molybdenum, vanadium, niobium, chromium, hafnium, titanium, zirconium, scandium, tantalum, yttrium, zinc, ruthenium, osmium, rhodium, iridium, palladium, and/or platinum)/cobalt-iron-boron alloy, A four-layer structure of cobalt ferrite/cobalt iron boron alloy/(tungsten, molybdenum, vanadium, niobium, chromium, hafnium, titanium, zirconium, tantalum, scandium, yttrium, zinc, ruthenium, osmium, rhodium, iridium, palladium and/or platinum)/cobalt iron boron alloy; the thickness of the first free layer is between 1.2 nanometers and 3.0 nanometers.
In one embodiment of the present application, the second free layer has a structure of [ (cobalt)1-xIronx)1-yBorony]1-zMz[ (cobalt)1-xIronx)1-yBorony]1-zMzCobalt1-wIronwCobalt, cobalt1-vIronv[ (cobalt)1-xIronx)1-yBorony]1-zMzOr cobalt1-vIronv[ (cobalt)1-xIronx)1-yBorony]1- zMzCobalt1-wIronw[ (cobalt)1-xIronx)1-yCy]1-zMz[ (cobalt)1-xIronx)1-yCy]1-zMzCobalt1-wIronwCobalt (II)1-vIronv[ (cobalt)1-xIronx)1- yCy]1-zMzOr cobalt1-vIronv[ (cobalt)1-xIronx)1-yCy]1-zMzCobalt1-wIronw(ii) a Wherein M is molybdenum, tungsten, chromium, tantalum, hafnium, vanadium, nitrogen, boron, zirconium, zinc, magnesium, aluminum or a combination thereof, x is 0% to 100%, y is 5% to 30%, z is 2% to 20%, w is 0% to 100%, v is 0% to 100%, preferably M is Mo, x is 20% to 100%, y is 7% to 17%, z is 5% to 15%.
In one embodiment of the present application, [ (cobalt)1-xIronx)1-yBorony]1-zMzThe forming mode is realized by codeposition of a cobalt-iron-boron, cobalt-iron-carbon, iron-carbon or cobalt-carbon alloy target and a doped metal M target in a PVD process cavity.
Further, the total thickness of the second free layer is between 0.5 nm and 3.0 nm.
In an embodiment of the present application, the perpendicular anisotropy enhancing layer is made of a non-magnetic metal oxide, the non-magnetic metal oxide includes a metal oxide selected from magnesium oxide, zirconium oxide, zinc oxide, aluminum oxide, gallium oxide, yttrium oxide, strontium oxide, scandium oxide, titanium oxide, hafnium oxide, vanadium oxide, niobium oxide, tantalum oxide, chromium oxide, molybdenum oxide, tungsten oxide, ruthenium oxide, osmium oxide, technetium oxide, rhenium oxide, rhodium oxide, iridium oxide, tin oxide, antimony oxide, magnesium zinc oxide, magnesium boron oxide, magnesium aluminum oxide, or a combination thereof, preferably, the non-magnetic metal oxide is magnesium oxide; the total thickness of the perpendicular anisotropy enhancing layer is between 0.3 nm and 1.5 nm.
In an embodiment of the present application, the material of the magnetic damping barrier layer is selected from magnesium, zirconium, zinc, aluminum, gallium, yttrium, strontium, scandium, titanium, vanadium, niobium, chromium, osmium, technetium, rhenium, rhodium, iridium, tin, antimony, magnesium oxide, zirconium oxide, zinc oxide, aluminum oxide, gallium oxide, yttrium oxide, strontium oxide, scandium oxide, titanium oxide, hafnium oxide, vanadium oxide, niobium oxide, tantalum oxide, chromium oxide, molybdenum oxide, tungsten oxide, ruthenium oxide, osmium oxide, technetium oxide, rhenium oxide, rhodium oxide, iridium oxide, tin oxide, antimony oxide, magnesium zinc oxide, magnesium boron oxide, magnesium aluminum oxide, or a combination thereof, preferably, the material of the magnetic damping barrier layer is magnesium oxide, and the thickness of the magnetic damping barrier layer is between 0.5 nm and 3.0 nm.
In an embodiment of the present application, the structure of the capping layer is at least one of cofeb, w, mo, mg, nb, ru, hf, v, cr, and pt, preferably, the structure of the capping layer is (w, mo, or hf)/ru, or the structure of the capping layer is pt/(w, mo, or hf)/ru.
It is another objective of the present invention to provide a magnetic random access memory, wherein the storage unit comprises any one of the foregoing magnetic tunnel junction structures, a top electrode disposed above the magnetic tunnel junction structure, and a bottom electrode disposed below the magnetic tunnel junction structure.
In the magnetic tunnel junction unit structure, firstly, the double-layer free layer needs to provide energy larger than the energy barrier of the double-layer free layer to turn over the magnetization vector of the free layer under the condition of thermal disturbance or an external magnetic field, so that the thermal stability is improved; secondly, an interface anisotropy source can be additionally provided through the vertical anisotropy enhancement layer made of the non-magnetic material, so that the thermal stability is enhanced; thirdly, the damping coefficient of the whole film structure is reduced through the magnetic damping barrier layer, so that the reduction of reading and writing current is facilitated; fourthly, the tunneling magnetic resistance rate is not influenced by the addition of the second free layer; fifthly, through the design of the double-layer free layer, the whole thickness of the free layer can be increased or maintained, the reduction of the damping coefficient is facilitated, and therefore the critical write current cannot be increased.
Drawings
FIG. 1 is a diagram illustrating an exemplary MRAM cell structure;
FIG. 2 is a diagram illustrating a magnetic memory cell structure of a magnetic random access memory according to an embodiment of the present invention.
Detailed Description
Refer to the drawings wherein like reference numbers refer to like elements throughout. The following description is based on illustrated embodiments of the application and should not be taken as limiting the application with respect to other embodiments that are not detailed herein.
The following description of the various embodiments refers to the accompanying drawings, which illustrate specific embodiments that can be used to practice the present application. In the present application, directional terms such as "up", "down", "front", "back", "left", "right", "inner", "outer", "side", and the like are merely referring to the directions of the attached drawings. Accordingly, the directional terminology is used for purposes of illustration and understanding, and is in no way limiting.
The terms "first," "second," "third," and the like in the description and in the claims of the present application and in the above-described drawings, if any, are used for distinguishing between similar elements and not necessarily for describing a particular sequential or chronological order. It should be understood that the objects so described are interchangeable under appropriate circumstances. Furthermore, the terms "comprising" and "having," as well as variations thereof, such as, for example, are intended to cover non-exclusive inclusions.
The terminology used in the description of the present application is for the purpose of describing particular embodiments only and is not intended to be limiting of the concepts of the present application. Unless the context clearly dictates otherwise, expressions used in the singular form encompass expressions in the plural form. In the present specification, it will be understood that terms such as "including," "having," and "containing" are intended to specify the presence of the features, integers, steps, acts, or combinations thereof disclosed in the specification, and are not intended to preclude the presence or addition of one or more other features, integers, steps, acts, or combinations thereof. Like reference symbols in the various drawings indicate like elements.
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 application 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 adopted to achieve the predetermined objects, the following detailed description of the magnetic tunnel junction structure and the magnetic random access memory according to the present invention with reference to the accompanying drawings and the specific embodiments will be made as follows.
FIG. 1 is a diagram of an exemplary MRAM cell structure. The magnetic memory cell structure includes a multi-layer structure formed by at least a Bottom Electrode (BE) 110, a Magnetic Tunnel Junction (MTJ)200, and a Top Electrode (Top Electrode) 310.
In some embodiments, the bottom electrode 110 is titanium (Ti), titanium nitride (TiN), tantalum (Ta), tantalum nitride (TaN), ruthenium (Ru), tungsten (W), tungsten nitride (WN), or combinations thereof; the top electrode 310 is made of titanium (Ti), titanium nitride (TiN), tantalum (Ta), tantalum nitride (TaN), tungsten (W), tungsten nitride (WN), or a combination thereof. The magnetic memory cell structure is typically implemented by Physical Vapor Deposition (PVD), and is typically planarized after the bottom electrode 110 is deposited to achieve surface flatness for the magnetic tunnel junction 200.
In some embodiments, the magnetic tunnel junction 200 includes, from top to bottom, a Capping Layer (CL) 290, a Free Layer (FL) 260, a Barrier Layer (Tunnel Barrier, TBL)250, a Reference Layer (RL) 240, a lattice Breaking Layer (CBL) 230, an antiferromagnetic Anti-ferromagnetic Layer (SyAF) 220, and a Seed Layer (Seed Layer; SL) 210.
As shown in fig. 1, in some embodiments, the free layer 260 is composed of a single layer or a multi-layer structure of cofeb, fe/cofeb, or cofeb/(one of ta, w, mo, or hf)/cofeb. To increase the density of the magnetic random access memory, the Critical Dimension (Critical Dimension) of the magnetic tunnel junction 200 is made smaller and smaller. When the size is further reduced, it is found that the Thermal Stability (Thermal Stability Factor) of the magnetic tunnel junction 200 is drastically deteriorated. For ultra-small sized MRAM magnetic memory cells, to improve thermal stability, the thickness of the free layer 260 may typically be reduced, the saturation susceptibility of the free layer 260 may be reduced, or the interfacial anisotropy may be increased. If the thickness of the free layer 260 is reduced, the Tunneling Magnetoresistance Ratio (TMR) is reduced, which increases the error rate in the read operation; under the condition of constant thickness, the addition or change of the free layer 260 into a material with low saturation magnetic susceptibility in the free layer 260 also reduces the tunneling magnetic resistivity, which is not beneficial to the read/write operation of the device.
FIG. 2 is a diagram illustrating a magnetic memory cell structure of a magnetic random access memory according to an embodiment of the present invention. The prior art also refers to fig. 1 to facilitate understanding.
As shown in fig. 2, in an embodiment of the present application, a magnetic tunnel junction structure 200 includes a Capping Layer (CL) 290, a magnetic damping Barrier Layer 280, a Free Layer (FL) 260, a Barrier Layer (Tunneling Barrier, TBL)250, a Reference Layer (RL) 240, a lattice Breaking Layer (CBL) 230, an antiferromagnetic Anti-ferromagnetic Layer (SyAF) 220, and a Seed Layer (Seed Layer; SL)210 from top to bottom, wherein the Free Layer includes: a first free layer 260a which is a variable magnetic polarization layer, wherein the first free layer 260a is formed of a magnetic metal alloy; a vertical anisotropy enhancing layer 270 disposed on the first free layer 260a, the vertical anisotropy enhancing layer 270 being formed of a non-magnetic metal oxide; a second free layer 260b disposed on the vertical anisotropy enhancing layer 270, the second free layer 260b being a variable magnetic polarization layer formed of a non-magnetic doped elemental magnetic metal alloy or a compound thereof; the magnetic damping barrier layer 280 is disposed on the second free layer 260b, and the magnetic damping barrier layer 280 is formed of a non-magnetic metal or an oxide thereof; wherein the perpendicular anisotropy enhancement layer is to enable magnetic coupling of the first free layer with a second free layer; the magnetic damping barrier layer reduces the damping coefficient of the entire film structure.
In some embodiments, the magnetization vector in the second free layer 260b is always perpendicular to the first free layer 260a interface and parallel to the magnetization vector in the first free layer 260 a.
In an embodiment of the present application, the material of the first free layer 260a is a single layer structure selected from cobalt boride CoB, iron boride FeB, cobalt iron boron alloy CoFeB, or a double layer structure of cobalt boride CoFe/cobalt iron boron alloy CoFeB, iron Fe/cobalt iron boron alloy CoFeB, or a three layer structure of iron boride FeB/(tungsten W, molybdenum Mo, vanadium V, niobium Nb, chromium Cr, hafnium Hf, titanium Ti, zirconium Zr, tantalum Ta, scandium Sc, yttrium Y, zinc Zn, ruthenium Ru, Os, rhodium Rh, iridium Ir, palladium Pd and/or platinum Pt)/cobalt iron boron alloy CoFeB, cobalt iron boron alloy CoFeB/(tungsten W, molybdenum Mo, vanadium V, niobium Nb, chromium, hafnium Hf, titanium Ti, zirconium Zr, Ta, tantalum Sc, yttrium Y, zinc Zn, ruthenium, osmium Os, rhodium, Ir, palladium and/or platinum)/cobalt iron boron alloy, or a three layer structure of iron tungsten/cobalt iron boron/(tungsten W/Pt)/cobalt iron boron alloy, A four-layer structure of molybdenum Mo, vanadium V, niobium Nb, chromium Cr, hafnium Hf, titanium Ti, zirconium Zr, tantalum Ta, scandium Sc, yttrium Y, zinc Zn, ruthenium Ru, osmium Os, rhodium Rh, iridium Ir, palladium Pd and/or platinum Pt)/cobalt iron boron alloy, cobalt iron/cobalt iron boron alloy/(tungsten W, molybdenum Mo, vanadium V, niobium Nb, chromium Cr, hafnium Hf, titanium Ti, zirconium Zr, tantalum Ta, scandium Sc, yttrium Y, zinc Zn, ruthenium Ru, osmium Os, rhodium Rh, iridium, palladium Pd and/or platinum Pt)/cobalt iron boron alloy; the thickness of the first free layer 260a is between 1.2 nm and 3.0 nm.
In one embodiment of the present application, the second free layer has a structure of [ (cobalt Co)1-xFex)1-yBoron By]1-zMz[ (cobalt Co)1-xFex)1-yBoron By]1-zMzCobalt Co1-wFewCobalt Co1-vFev/[ (cobalt Co)1-xFex)1-yBoron By]1-zMzOr cobalt Co1-vFev/[ (cobalt Co)1-xFex)1-yBoron By]1-zMzCobalt Co1-wFew[ (cobalt Co)1-xFex)1-yCy]1-zMz[ (cobalt Co)1-xFex)1-yCy]1-zMzCobalt Co1-wFewCobalt Co1-vFev/[ (cobalt Co)1-xFex)1-yCy]1-zMzOr cobalt Co1-vFev/[ (cobalt Co)1-xFex)1-yCy]1-zMzCobalt Co1-wFew(ii) a Wherein M is molybdenum Mo, tungsten W, chromium Cr, tantalum Ta, hafnium Hf, vanadium V, nitrogen N, boron B, zirconium Zr, zinc Zn, magnesium Mg, aluminum Al or a combination thereof, x is 0% to 100%, y is 5% to 30%, z is 2% to 20%, W is 0% to 100%, V is 0% to 100%, preferably M is molybdenum Mo, 20% to 100%%≤x≤100%,7%≤y≤17%,5%≤z≤15%。
In some embodiments, [ (cobalt Co)1-xFex)1-yBoron By]1-zMzThe forming mode is realized by codeposition of CoFeB, FeB, CoB, CoFeC, FeC or CoC alloy target and doped metal M target in a PVD process cavity.
Further, the total thickness of the second free layer is between 0.5 nm and 3.0 nm.
Further, after the second free layer 260b is deposited, a plasma process may be selected to perform surface modification or selective component removal.
As previously described, the perpendicular anisotropy enhancement layer 270 is disposed between the first and second free layers 260a, 260b for enabling magnetic coupling of the first and second free layers 260a, 260 b.
In an embodiment of the present application, the perpendicular anisotropy-enhanced layer 270 is made of a non-magnetic metal oxide including magnesium oxide MgO, zirconium oxide ZrO2Zinc oxide ZnO and aluminum oxide Al2O3Gallium oxide GaO, yttrium oxide Y2O3Strontium oxide SrO and scandium oxide Sc2O3Titanium oxide TiO2Hafnium oxide HfO2Vanadium oxide V2O5Niobium oxide Nb2O5Tantalum oxide Ta2O5Chromium oxide CrO3Molybdenum oxide MoO3Tungsten oxide WO3Ruthenium oxide RuO2Osmium oxide OsO2Technetium oxide TcO, rhenium oxide ReO, rhodium oxide RhO, iridium oxide IrO, tin oxide SnO, antimony oxide SbO, magnesium zinc oxide MgZnO, magnesium boron oxide MgBO, magnesium aluminum oxide MgAlO, or a combination thereof, preferably, the non-magnetic metal oxide is magnesium oxide MgO.
In some embodiments, the perpendicular anisotropy enhancement layer 270 has a thickness between 0.3 nm and 1.5 nm.
The vertical anisotropy enhancement layer 270 is deposited prior to the deposition of the second free layer 260b, providing a source of interfacial anisotropy, thereby increasing thermal stability.
In an embodiment of the present application, the material of the magnetic damping barrier layer 280 is selected from Mg, Zr, Zn, Al, Ga, Y, Sr, Sc, Ti, V, Nb, Cr, Os, technetium Tc, Re, Rh, Ir, Sn, Sb, MgO, ZrO, Zr, Y, Sr, Sc, Ti, V, Nb, Cr, Os, technetium Tc, Re, Rh, Ir, Sn, Sb, MgO, ZrO2Zinc oxide ZnO and aluminum oxide Al2O3Gallium oxide GaO, yttrium oxide Y2O3Strontium oxide SrO and scandium oxide Sc2O3Titanium oxide TiO2Hafnium oxide HfO2Vanadium oxide V2O5Niobium oxide Nb2O5Tantalum oxide Ta2O5Chromium oxide CrO3Molybdenum oxide MoO3Tungsten oxide WO3Ruthenium oxide RuO2Osmium oxide OsO2Technetium oxide TcO, rhenium oxide ReO, rhodium oxide RhO, iridium oxide IrO, tin oxide SnO, antimony oxide SbO, magnesium zinc oxide MgZnO, magnesium boron oxide MgBO, magnesium aluminum oxide MgAlO, or a combination thereof, preferably, the material of the magnetic damping barrier layer 280 is magnesium oxide MgO, and the thickness of the magnetic damping barrier layer 280 is between 0.5 nm and 3.0 nm. Further, due to the addition of the magnetic damping barrier layer 280 on the second free layer 260b, the damping coefficient of the whole film structure is effectively reduced, which is beneficial to reducing the write current.
In an embodiment of the present application, the structure of the capping layer 290 is at least one of CoFeB, CoFeC, W, Mo, Mg, Nb, Ru, Hf, V, Cr, and Pt, preferably, the structure of the capping layer 290 is (W, Mo, or Hf)/Ru, or the structure of the capping layer 290 is Pt/(W, Mo, or Hf)/Ru.
Referring to fig. 2, in an embodiment of the present application, a memory cell of a magnetic random access memory includes any one of the magnetic tunnel junction 200 structures described above, a top electrode 310 disposed above the magnetic tunnel junction 200 structure, and a bottom electrode 110 disposed below the magnetic tunnel junction 200 structure.
In an embodiment of the present application, the material of the seed layer 210 of the magnetic tunnel junction 200 is one or a combination of Ti, TiN, Ta, TaN, W, WN, Ru, Pt, Cr, CrCo, Ni, CrNi, CoB, FeB, CoFeB, etc. In some embodiments, the seed layer 21 may be selected from one of tantalum Ta/ruthenium Ru, tantalum Ta/platinum Pt/ruthenium Ru, and the like. The seed layer 21 is used to optimize the crystal structure of the subsequent antiferromagnetic layer 220.
The antiferromagnetic layer 220, formally known as an antiparallel ferromagnetic super-lattice (Anti-Parallel ferromagnetic super-lattice) layer 220 is also known as a Synthetic antiferromagnetic-ferromagnetic (SyAF) layer. Typically from [ cobalt Co/platinum Pt ]]nCo/(Ru, Ir, Rh) and Co/Pt]nCo/(Ru, Ir, Rh)/(Co, Co [ Co/Pt ] Co]m) [ cobalt Co/palladium Pd ]]nCo/(Ru, Ir, Rh) and Co/Pt]nCo/(Ru, Ir, Rh)/(Co, Co [ Co/Pt ] Co]m) [ cobalt Co/nickel Ni ]]nCo/(Ru, Ir, Rh) or [ Co/Ni ]]nCo/(Ru, Ir, Rh)/(Co, Co [ Ni/Co ]]m) Superlattice compositions, where n ≧ m ≧ 0, preferably, individual thicknesses of cobalt (Co) and platinum (Pt) are below 0.5 nm, such as: 0.10 nm, 0.15 nm, 0.20 nm, 0.25 nm, 0.30 nm, 0.35 nm, 0.40 nm, 0.45 nm or 0.50 nm …. In some embodiments, the thickness of each layer structure of the antiferromagnetic layer 220 is the same or different. The antiferromagnetic layer 220 has a strong perpendicular anisotropy (PMA).
In an embodiment of the present application, the reference layer 240 has a magnetic polarization invariance under ferromagnetic coupling of the antiferromagnetic layer 220. The reference layer 240 is made of one or a combination of cobalt Co, iron Fe, nickel Ni, cobalt ferrite CoFe, cobalt boride CoB, iron boride FeB, cobalt iron carbon CoFeC and cobalt iron boron alloy CoFeB, and the thickness of the reference layer 25 is 0.5 to 1.5 nanometers.
Since the antiferromagnetic layer 220 has a Face Centered Cubic (FCC) crystal structure and the crystal structure of the reference layer 240 is Body Centered Cubic (BCC) and the lattices are not matched, in order to realize the transition and ferromagnetic coupling from the antiferromagnetic layer 220 to the reference layer 240, a lattice-blocking layer 230 is generally added between two layers of materials, the material of the lattice-blocking layer 230 is one or a combination of Ta, W, Mo, Hf, Fe, Co, and the thickness of the reference layer 240 is between 0.1 nm and 0.5 nm.
In some embodiments, barrier layer 250 is formed of a non-magnetic metal oxide having a thickness between 0.6 nanometers and 1.5 nanometers, including magnesium oxide, MgO, magnesium zinc oxide, MgZnO, zinc oxide, aluminum oxide, Al2O3MgN, Mg boron oxide, Mg3B2O6Or MgAl2O4. Preferably, magnesium oxide MgO may be used.
In one embodiment of the present application, after deposition of all layers, an annealing process is performed on the magnetic tunnel junction 200 at a temperature between 350 ℃ and 400 ℃ for 90 minutes to change the reference layer 240, the first free layer 260a, and the second free layer 260b from an amorphous phase to a Body Centered Cubic (BCC) crystal structure.
In the magnetic tunnel junction cell structure of the present application, the magnetization vector of the second free layer 260b is always perpendicular to the interface of the first free layer 260a and parallel to the magnetization vector of the first free layer 260a, and since the second free layer 260b and the first free layer 260a exhibit ferromagnetic coupling, under the condition of thermal disturbance or external magnetic field, in order to make the magnetization vector of the first free layer 260a turn, energy larger than the sum of the energy barrier of the first free layer 260a and the energy barrier of the second free layer 260b must be provided. Further, the addition of the second free layer 260b does not affect the tunneling magnetoresistance ratio.
Further, the design of the second free layer 260b maintains or increases the overall thickness of the free layer 260, which is advantageous in reducing the damping constant (α). Also, when selecting the materials of the coupling layer and the capping layer of the first free layer 260 a/the second free layer 260b, a material having a low damping coefficient may be preferable, so that the damping coefficient may be further reduced. When writing to the device, the critical write current does not increase due to the reduced damping coefficient, despite the increased thermal stability factor.
The ability of the free layer 260 of the magnetic random access memory to maintain a constant magnetization direction is called Data Retention (Data Retention) or Thermal Stability (Thermal Stability). The data retention capacity can be calculated using the following formula:
Figure DEST_PATH_IMAGE001
wherein tau is the time when the magnetization vector is unchanged under the condition of thermal disturbance, tau0For the trial time (typically 1ns), E is the energy barrier of the free layer, kBBoltzmann constant, T is the operating temperature.
The thermal stability factor (v) can then be expressed as the following equation:
Figure 1
wherein, KeffIs the effective isotropic energy density of the free layer 260, V is the volume of the free layer, KVConstant of bulk anisotropy MsSaturation susceptibility of the free layer, demagnetization constant in the direction perpendicular to Nz, t thickness of the free layer, KiCD is the critical dimension of the magnetic random access memory (i.e., the diameter of the free layer), A, as the interfacial anisotropy constantsK is the critical dimension of the free layer 260 switching mode transition from domain switching (i.e., Magnetization switching processed by "macro-spin" switching) to inverse domain nucleation/growth (i.e., Magnetization switching by nuclear of a reversed domain and propagation of a domain wall) for stiffness integrating exchange constants. Experiments have shown that the free layer 260 exhibits in-plane anisotropy when it is thick and perpendicular anisotropy when it is thin, KVGenerally negligible, while the contribution of demagnetization energy to the perpendicular anisotropy is negative, so the perpendicular anisotropy comes entirely fromInterfacial effect (K)i)。
In some embodiments, the thermal stability factor is also affected by the static magnetic Field, particularly the leakage magnetic Field (Stray Field) from the reference layer 240, in combination with the difference in the magnetization direction applied by the static magnetic Field on the free layer 260 to produce an enhancement or reduction effect.
In addition, as the volume of the magnetic free layer is reduced, the smaller the spin polarization current to be injected for writing or switching operation, and the critical current I for writing operationC0The relationship between the compound and the thermal stability is strongly related, and can be expressed as the following formula:
Figure BDA0002225849420000101
wherein alpha is a damping constant,
Figure BDA0002225849420000102
η is the spin polarizability, which is the approximate planck constant. As can be understood from the above equations, the addition of the second free layer 260b does not affect the tunneling magnetoresistance ratio. Even if the thickness of the free layer 260 is increased, the thermal stability factor can be increased by selecting a material with a low damping coefficient to lower the damping coefficient, and the critical write current will not increase.
In the magnetic tunnel junction unit structure, firstly, the double-layer free layer needs to provide energy larger than the sum of energy barriers of the double-layer free layer to overturn the magnetization vector of the free layer under the condition of thermal disturbance or an external magnetic field, so that the thermal stability is improved; secondly, the vertical anisotropy enhancement layer can additionally provide an interface anisotropy source, so that the thermal stability is enhanced; thirdly, the damping coefficient of the whole film structure is reduced through the magnetic damping barrier layer, so that the reduction of writing current is facilitated; fourthly, the tunneling magnetic resistance rate is not influenced by the addition of the second free layer; fifthly, through the design of the double-layer free layer, the whole thickness of the free layer can be increased or maintained, the reduction of the damping coefficient is facilitated, and therefore the critical write current cannot be increased.
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 (9)

1. A magnetic tunnel junction structure of a magnetic random access memory is arranged in a magnetic random access memory unit, the magnetic tunnel junction structure comprises a covering layer, a magnetic damping barrier layer, a free layer, a barrier layer, a reference layer, a lattice partition layer, an antiferromagnetic layer and a seed layer from top to bottom, and the free layer comprises:
a first free layer which is a variable magnetic polarization layer and is formed by a magnetic metal alloy;
a vertical anisotropy enhancement layer disposed on the first free layer, the vertical anisotropy enhancement layer being formed of a non-magnetic metal oxide; and
a second free layer disposed on the vertical anisotropy enhancing layer, the second free layer being a variable magnetic polarization layer formed of a magnetic metal alloy containing a non-magnetic doping element or a compound thereof;
wherein the perpendicular anisotropy enhancement layer is to enable magnetic coupling of the first free layer with a second free layer.
2. The magnetic tunnel junction structure of claim 1, wherein the material of the first free layer is a single layer structure selected from cobalt boride, iron boride, cobalt iron boron alloy, or a double layer structure of cobalt boride/cobalt iron boron alloy, iron/cobalt iron boron alloy, or a three-layer structure of iron boride/(tungsten, molybdenum, vanadium, niobium, chromium, hafnium, titanium, zirconium, tantalum, scandium, yttrium, zinc, ruthenium, osmium, rhodium, iridium, palladium and/or platinum)/cobalt iron boron alloy, cobalt iron boron alloy/(tungsten, molybdenum, vanadium, niobium, chromium, hafnium, titanium, zirconium, tantalum, scandium, yttrium, zinc, ruthenium, osmium, rhodium, iridium, palladium and/or platinum)/cobalt iron boron alloy, or a three-layer structure of iron/cobalt iron boron alloy/(tungsten, molybdenum, vanadium, niobium, chromium, hafnium, titanium, zirconium, tantalum, scandium, yttrium, zinc, ruthenium, osmium, cobalt, and cobalt iron boron alloy, Rhodium, iridium, palladium and/or platinum)/cofeb alloys, cobalt ferrite/cofeb alloys/(tungsten, molybdenum, vanadium, niobium, chromium, hafnium, titanium, zirconium, tantalum, scandium, yttrium, zinc, ruthenium, osmium, rhodium, iridium, palladium and/or platinum)/cofeb alloys; the thickness of the first free layer is between 1.2 nanometers and 3.0 nanometers.
3. The magnetic tunnel junction structure of claim 1 wherein the second free layer has a structure of [ (cobalt) cobalt ]1-xIronx)1-yBorony]1-zMz[ (cobalt)1-xIronx)1-yBorony]1-zMzCobalt1-wIronwCobalt, cobalt1-vIronv[ (cobalt)1-xIronx)1-yBorony]1-zMzOr cobalt1-vIronv[ (cobalt)1-xIronx)1-yBorony]1-zMzCobalt1-wIronw[ (cobalt)1-xIronx)1-yCy]1-zMz[ (cobalt)1-xIronx)1- yCy]1-zMzCobalt1-wIronwCobalt (II)1-vIronv[ (cobalt)1-xIronx)1-yCy]1-zMzOr cobalt1-vIronv[ (cobalt)1-xIronx)1-yCy]1-zMzCobalt1-wIronw(ii) a Wherein, the non-magnetic doping element M is molybdenum, tungsten, chromium, tantalum, hafnium, vanadium, nitrogen, boron, zirconium, zinc, magnesium, aluminum or the combination thereof, x is more than or equal to 0% and less than or equal to 100%, y is more than or equal to 5% and less than or equal to 30%, z is more than or equal to 2% and less than or equal to 20%, w is more than or equal to 0% and less than or equal to 100%, v is more than or equal to 0% and less than or equal to 100%, preferably, M is Mo, x is more than or equal to 20% and less than or equal to 100%, y is more than or equal to 7% and less than.
4. The magnetic tunnel junction structure of claim 3 in which [ (cobalt) is present1-xIronx)1-yBorony]1-zMzThe forming mode is realized by codeposition of a cobalt-iron-boron, cobalt-iron-carbon, iron-carbon or cobalt-carbon alloy target and a doped metal M target in a PVD process cavity.
5. The magnetic tunnel junction structure of claim 3 wherein the thickness of the second free layer is between 0.5 nm and 3.0 nm.
6. The magnetic tunnel junction structure of magnetic random access memory of claim 1 wherein the perpendicular anisotropy enhancing layer is made of a non-magnetic metal oxide comprising a metal oxide selected from the group consisting of magnesium oxide, zirconium oxide, zinc oxide, aluminum oxide, gallium oxide, yttrium oxide, strontium oxide, scandium oxide, titanium oxide, hafnium oxide, vanadium oxide, niobium oxide, tantalum oxide, chromium oxide, molybdenum oxide, tungsten oxide, ruthenium oxide, osmium oxide, rhenium oxide, rhodium oxide, iridium oxide, tin oxide, antimony oxide, magnesium zinc oxide, magnesium boron oxide, magnesium aluminum oxide, or combinations thereof, preferably the non-magnetic metal oxide is magnesium oxide; the total thickness of the perpendicular anisotropy enhancing layer is between 0.3 nm and 1.5 nm.
7. The magnetic tunnel junction structure of claim 1, wherein the material of the magnetic damping barrier layer is selected from magnesium, zirconium, zinc, aluminum, gallium, yttrium, strontium, scandium, titanium, vanadium, niobium, chromium, osmium, technetium, rhenium, rhodium, iridium, tin, antimony, magnesium oxide, zirconium oxide, zinc oxide, aluminum oxide, gallium oxide, yttrium oxide, strontium oxide, scandium oxide, titanium oxide, hafnium oxide, vanadium oxide, niobium oxide, tantalum oxide, chromium oxide, molybdenum oxide, tungsten oxide, ruthenium oxide, osmium oxide, technetium oxide, rhenium oxide, rhodium oxide, iridium oxide, tin oxide, antimony oxide, magnesium zinc oxide, magnesium boron oxide, magnesium aluminum oxide, or a combination thereof, preferably the material of the magnetic damping barrier layer is magnesium oxide, and the thickness of the magnetic damping barrier layer is between 0.5 nm and 3.0 nm.
8. The magnetic tunnel junction structure of claim 1, wherein the structure of the capping layer is at least one of cofeb, w, mo, mg, nb, ru, hf, v, cr and pt, preferably (w, mo or hf)/ru, or pt/(w, mo or hf)/ru.
9. A magnetic random access memory comprising the magnetic tunnel junction structure of any of claims 1-8, a top electrode disposed above the magnetic tunnel junction structure, and a bottom electrode disposed below the magnetic tunnel junction structure.
CN201910951256.3A 2019-10-08 2019-10-08 Magnetic tunnel junction structure and magnetic random access memory Pending CN112635654A (en)

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