 MAGNETIC STACK, JUNCTION TUNNEL, MEMORY POINT AND SENSOR COMPRISING SUCH A STACK
专利摘要:
The subject of the present invention is a magnetic stack comprising: - A first element comprising a ferromagnetic layer; - A second element comprising a metallic layer capable of conferring on an assembly formed by the first and the second elements a magnetic anisotropy perpendicular to the plane of the layers, the magnetic stack being characterized in that the first element further comprises a refractory metallic material , the second element being arranged on the first element. 公开号:FR3077917A1 申请号:FR1851302 申请日:2018-02-15 公开日:2019-08-16 发明作者:Jyotirmoy Chatterjee；Paulo VELOSO COELHO；Bernard Dieny；Ricardo Sousa；Lucian Prejbeanu 申请人:Commissariat a lEnergie Atomique CEA；Universite Grenoble Alpes；Commissariat a lEnergie Atomique et aux Energies Alternatives CEA； IPC主号:
专利说明:
MAGNETIC STACK, TUNNEL JUNCTION, MEMORY POINT AND SENSOR COMPRISING SUCH A STACK TECHNICAL FIELD OF THE INVENTION The present invention relates to a magnetic stack with magnetization out of the plane. "Magnetic stack with magnetization out of the plane" is a magnetic stack which has a magnetization substantially perpendicular to the plane along which the stack or plane of the layers extends. An object of the present invention is to provide a magnetic stack not requiring to be deposited on a growth layer having a predetermined crystal symmetry to obtain a strong magnetic anisotropy outside the plane of the layers. This magnetic stack is advantageously able to withstand temperatures which may be high, such as in particular those of post-deposition annealing (generally at a temperature above 300 ° C.) without degradation of the magnetic properties which could take place as a result of phenomena of interdiffusion in the stack, at high temperatures. Another object of the present invention is a multilayer comprising such a magnetic stack. A third object of the invention is a magnetic tunnel junction comprising the magnetic stack or the multilayer according to the invention. The invention also relates to other spintronic devices with perpendicular magnetization comprising the magnetic stack or the multilayer according to the invention: - a memory point with at least two terminals for a memory cell and in particular three terminals in particular for a writing memory cell of the spin-orbit couple type (or "Spin-Orbit Tranfer" according to English terminology); - a double magnetic tunnel junction; - a magnetic tunnel junction for a multi-level memory cell; a memory point with at least two terminals for a memory cell with several levels and in particular three or even four terminals; - an external temperature and magnetic field sensor applied. STATE OF THE ART Magnetic tunnel junctions (or “Magnetic Tunnel Junctions” according to English terminology, MTJ) constitute a fundamental brick of spintronic devices. A magnetic tunnel junction is formed by two magnetic electrodes separated by a thin layer acting as a tunnel barrier. The tunnel layer is often made of MgO with a thickness of between 1 nm and 2 nm. One of the magnetic electrodes, called the reference layer, has a magnetization fixed thanks to a synthetic antiferromagnetic layer (or "Synthetic antiferromagnetic layer" according to English terminology, SAF). The second magnetic electrode, called the storage layer, has a magnetization which can be oriented either parallel or antiparallel to the direction of magnetization of the reference layer. The magnetization state of the MTJ can be read by measuring its electrical resistance which varies according to the magnetic configuration of the two magnetic electrodes due to the phenomenon of tunnel magnetoresistance. Thus, the configuration having the magnetizations of the two layers (storage and reference) oriented in parallel corresponds to a state of low resistance of the MTJ (Rmin). The configuration having the magnetizations of the two layers oriented antiparallel corresponds to a state of high resistance of the MTJ (Rmax). The relative resistance difference between the two configurations (Rmax-Rmin) / Rmin represents the amplitude of tunnel magnetoresistance which can exceed 200% at room temperature. These two magnetic states can be used to encode a "bit" of information. The magnetization of the storage layer is reversed by a current which crosses the stack in the direction perpendicular to the plane of the layers. This current is also called write current. For example, magnetic tunnel junctions are used as storage elements in magnetic memories of the "Spin Transfer Torque" or STTMRAM type. Or in magnetic memories of the "Thermally Assisted Switching" or TAS-MRAM type. A state-of-the-art magnetic tunnel junction is illustrated in Figure 1a. Such a magnetic tunnel junction comprises: - a layer of Sub substrate; - a lower electrode BE; - a growth layer S or "seed layer" according to English terminology; a hard layer HL antiferromagnetically coupled to a reference layer RL by a coupling layer AF to form a synthetic antiferromagnetic layer pSAF; - A reference layer RL formed by a pin trapping layer or "pinning layer" according to English terminology, a structural transition layer of TBL symmetry or "texture breaking layer" according to English terminology and a spin polarization layer PL; - A TB tunnel barrier layer; - A storage layer SL; - Cap protective layer; - A TE upper electrode. The function of these different layers is explained in the following. The two lower electrode BE and upper TE layers allow electrical contacts to be made to circulate a current normal to the layer plane, this current being able to be used to write or read the state of the magnetic tunnel junction. The growth layer S or "seed layer" is used to promote a predetermined crystal symmetry in the hard layer HL and in the trapping layer Pin. The crystal symmetry of the growth layer S makes it possible to obtain a trapping layer Pin and a hard layer HL having a high perpendicular magnetic anisotropy to obtain a magnetization of the reference layer stable over time. The tunnel barrier layer TB separates the storage layer SL, having a variable magnetization, and the reference layer RL, having a fixed magnetization, and makes it possible to obtain a tunnel magnetoresistance between the two electrodes. The hard layer HL is antiferromagnetically coupled to the reference layer RL by the AF layer, the antiferromagnetic coupling making it possible to increase the magnetic coercivity and therefore the magnetic stability of the pSAF stack and to reduce the parasitic field exerted by the reference layer on the storage layer. In most MTJs magnetic tunnel junctions, the magnetization is out of the plane, namely perpendicular to the plane of the layers. These stacks are also called perpendicular magnetic tunnel junctions or pMTJs. Such an orientation makes it possible to find a good compromise between the thermal stability of the magnetization of the storage layer which defines the retention of the memory and the intensity of the writing current. In the pMTJs the reference layer RL must have a strong perpendicular magnetic anisotropy, so as to keep a stable magnetization during the whole lifetime of the device. To this end, the reference layer RL comprises a polarization layer PL coupled to a trapping layer Pin having a strong perpendicular magnetic anisotropy, the coupling being carried out by a layer comprising boron. The pin trapping layer can be a multilayer formed by a repetition of FM / X type bilayers. FM is understood here to mean a ferromagnetic layer comprising for example one of the following materials Co, Fe, CoFe or an alloy of these materials. X means a magnetic or non-magnetic metallic layer comprising, for example, one of the following materials: Pt, Au, Ir, Pd, Ni, NiCo, NiFe, NiFeCo or an alloy of these materials. The notation [FM / X] n means a superposition of n FM / X bilayers. The PL polarization and Pin trapping layers can produce a parasitic field which disturbs the magnetization of the storage layer SL. To reduce this effect a layer with fixed magnetization or hard layer HL is used. The hard layer HL is characterized by a high value of coercive field. The HL hard layer is antiferromagnetically coupled to the Pin trapping layer. The antiferromagnetic coupling is carried out thanks to the coupling layer AF comprising one of the materials Ru, Re, Rh, Ir, Os or an alloy of these materials. As is well known to those skilled in the art, it is necessary to precisely control the thickness of this AF coupling layer in order to obtain an antiferromagnetic coupling. For example, for an antiferromagnetic coupling layer in Ru, a thickness between 0.3 and 0.9 nm must be used. The hard layer HL is also formed by a repetition of FM / X type bilayers, with a high perpendicular magnetic anisotropy. The set of layers formed by the hard layer, the antiferromagnetic coupling layer, the trapping layer, the structural transition layer of symmetry and the polarization layer is also called synthetic antiferromagnetic layer with perpendicular anisotropy pSAF. There are two types of tunnel magnetic junctions with perpendicular magnetization pMTJs illustrated in Figure 1. Figure 1a shows an example of pMTJs in which the synthetic antiferromagnetic element with perpendicular magnetization pSAF is located below the tunnel barrier. In this type of magnetic tunnel junction, the storage layer SL is located above the tunnel barrier, hence the name “top storage pMTJ” according to English terminology or TS-pMTJ. Figure 1b shows an example of pMTJs in which the synthetic antiferromagnetic element with perpendicular magnetization pSAF is located above the tunnel barrier. In this type of junction, the storage layer is located below the tunnel barrier TB, hence the name "bottom storage pMTJ" according to English terminology or BS-pMTJ. A BS-pMTJ type magnetic tunnel junction provides a more even surface for the growth of the storage layer and the tunnel barrier. In addition, a BS-pMTJ type magnetic tunnel junction can be used in the manufacture of magnetic random access memories of the spin-orbit couple or SOT-MRAM type according to the English terminology "Spin Orbit Torque Magnetic Random Access Memory". Indeed, in a SOT-MRAM type memory, the storage layer must be in contact with a metal strip placed below the magnetic tunnel junction. In a SOT-MRAM type tunnel junction, the storage layer must therefore be at the base of the junction. As illustrated in FIG. 1b, the manufacture of a magnetic tunnel junction of the SOT-MRAM type requires the growth of a synthetic antiferromagnetic element pSAF having a high perpendicular magnetic anisotropy directly above the tunnel barrier. In other words, the growth of the pSAF element cannot be carried out above a growth layer having a symmetry suitably chosen to favor a high perpendicular magnetic anisotropy. In a BS-pMTJ type tunnel junction, it is therefore impossible to obtain the desired crystal structure using a growth layer having a given symmetry. On the contrary, the perpendicular synthetic antiferromagnetic element pSAF must be produced directly in contact with the tunnel barrier in order to be able to produce the effect of tunnel magnetoresistance allowing the reading of the magnetic state of the junction. These difficulties greatly limit the production of memories of the SOT-MRAM type having a high perpendicular magnetic anisotropy and their use in spintronic devices. According to patent application FR 2976396, it is possible to increase the perpendicular magnetic anisotropy of a stack of FM / X type thanks to the addition of a layer I intermediate between the ferromagnetic layer FM and the layer not ferromagnetic X, I being a material little miscible with the FM layer. However, these known magnetic stacks have a thermal stability which is not satisfactory. Indeed, they can lose their anisotropy perpendicular to annealing temperatures of the order of 300 ° C. which are too low compared to those required for integration into a CMOS (Complementary Metal Oxide Semiconductor) technology which requires annealing at 400 ° C. Furthermore, the materials I disclosed in document FR2976396 do not allow interfaces between the different layers of the FM / I / X stack to be sufficiently smooth and regular. Furthermore, these materials do not make it possible to avoid interfacial defects, in particular those created during the growth of the X layers, often composed of heavy metals such as Pt or Pd. TECHNICAL PROBLEM Magnetic stacks having a strong perpendicular magnetic anisotropy are today mainly obtained by depositing above a growth layer having a crystalline structure suitably chosen to favor the perpendicular magnetic anisotropy. In certain applications, such as magnetic tunnel junctions of the BSpMTJ type, it is not possible to use such a growth layer because the magnetic stack must be deposited above the tunnel barrier. In such cases, it is impossible to obtain magnetic stacks having a strong perpendicular magnetic anisotropy using the stacks known in the state of the art. SUMMARY OF THE INVENTION To at least partially solve the problems mentioned above, an object of the present invention is a magnetic stack having a strong perpendicular magnetic anisotropy and which does not require to be deposited on a growth layer having a predefined crystal structure. To this end, an object of the invention is a magnetic stack comprising: - A first element comprising a ferromagnetic layer; - A second element comprising a metal layer capable of imparting to an assembly formed by the first and the second elements a magnetic anisotropy perpendicular to the plane of the layers, the magnetic stack being characterized in that the first element further comprises a refractory metallic material , the second element being disposed on the first element. By magnetic stack is meant a stack of layers, with at least one layer having magnetic properties. The term “first element” comprising a ferromagnetic layer is understood to mean an element of the magnetic stack comprising a layer or two superposed layers, at least one of the two layers being ferromagnetic. The second element made up of a metallic layer will be indifferently called second element or second layer or simply metallic layer. The term refractory metallic material means a metal having a melting temperature greater than 1600 ° C. and preferably greater than 1900 ° C. at the pressure of 1 bar. In general, the magnetic stack according to the invention is of the ferromagnetic layer FM / metal layer X type in the presence of a refractory metallic material. The metallic layer consists of a metallic material capable of giving the assembly formed by the first magnetic element and the second layer a perpendicular magnetic anisotropy of interfacial origin. For example, the first element comprises one or more materials taken from a first group of materials, said first group of materials being constituted by the following materials: cobalt, iron, nickel and the magnetic alloys based on these materials. The second element comprises one or more materials taken from a second group of materials, said second group of materials consisting of the following materials: platinum, gold, iridium, palladium, nickel, NiCo, NiFe, NiFeCo and the alloys based on these materials. The refractory metallic material may take the form of an insertion layer I separating the ferromagnetic layer and the second metallic layer, the magnetic stack according to the invention then having the form of ferromagnetic layer FM / insertion layer I / second layer metallic X or FM / I / X. Alternatively, the first element may comprise a single layer formed by an alloy of one of the materials of the first group and of a refractory metallic material. The magnetic stack according to the invention makes it possible to obtain thermal stability and a higher perpendicular magnetic anisotropy than the stacks known in the state of the art. This is possible thanks to the use, in the first element of the magnetic stack, of a refractory metallic material having a high melting temperature. Such a high melting temperature reflects the fact that the atoms of the refractory material have strong chemical bonds which resist during the deposition step of the second element or second layer X. Thanks to the use of the refractory metal it is therefore possible to reduce the interface defects created during the growth of the second layer. When used as an insertion layer, the refractory material also smooths the interfaces between the first layer and the second layer so as to increase the magnetic anisotropy perpendicular to the interface. Furthermore, the insertion of refractory metal layers mechanically stiffens the entire stack, which has the effect of increasing its stability during possible annealing at high temperature such as 400 ° C. In addition, the insertion layer can reduce the magnetization of the stack and therefore reduce the demagnetizing energy. This produces an effective increase in perpendicular magnetic anisotropy. Thanks to this set of properties, the magnetic stack according to the invention makes it possible to obtain good perpendicular magnetic anisotropy without the need for a growth layer having a texture conveniently chosen to promote perpendicular magnetic anisotropy. The magnetic stack according to the invention can therefore be placed on several types of support layers. It follows that the magnetic stack according to the invention can be used in spintronic devices which are not compatible with the presence of a growth layer having a defined texture, for example a magnetic tunnel junction of the BS-pMTJ type. . In addition, thanks to the use of a refractory metallic material having a high melting temperature, the magnetic stack according to the invention has greater thermal stability. In particular, thanks to the mechanical rigidity of the refractory materials, the magnetic stack remains stable up to 425 ° C. The magnetic stack according to the invention may also have one or more of the following characteristics, taken individually or in any technically possible combination: - The ferromagnetic layer of the first element comprises one or more materials taken from a first group of materials, said first group of materials consisting of the following materials: cobalt, iron, nickel and the magnetic alloys based on these materials; the metal layer of the second element comprises one or more materials taken from a second group of materials, said second group of materials being constituted by the following materials: platinum, gold, iridium, palladium, nickel, NiCo, NiFe, NiFeCo and the alloys based on these materials; the ferromagnetic layer of the first element comprises an alloy of one or more materials taken from the first group of materials and of a refractory metallic material; the first element comprises a first layer of the first element and a second layer of the first element, the first layer of the first element comprising one or more materials taken from the first group of materials and the second layer of the first element consisting of the refractory metallic material ; - the refractory metallic material is taken from the following group: tantalum, tungsten, molybdenum, ruthenium, zirconium, vanadium, niobium; - the refractory metallic material has a melting temperature above 1600 ° C, said melting temperature being measured at a pressure of 1 bar; - The second layer of the first element has a thickness between 0.1 and 0.6 nm; - The second layer of the first element has a thickness between 0.2 and 0.4 nm. Another object of the present invention is a multilayer comprising at least a first and a second magnetic stack according to the invention, the multilayer having magnetization out of the plane, the first element of the second magnetic stack being disposed on the second element or second layer. of the first magnetic stack. Another object of the invention is a magnetic tunnel junction comprising: - A first magnetic multilayer called the reference layer; - A second magnetic multilayer known as a storage layer; - A tunnel barrier layer which separates the reference layer and the storage layer the reference layer comprising a magnetic stack or a multilayer according to the invention. By reference layer is meant a magnetic multilayer comprising a trapping layer, a structural transition layer of symmetry and a spin polarization layer. The magnetization of the reference layer is fixed and perpendicular to the plane of the layers. The term storage layer is understood to mean a magnetic monolayer or multilayer having a magnetization perpendicular to the layer plane, the orientation of the magnetization of the storage layer being modifiable by a writing method conveniently chosen. According to a variant, in the magnetic tunnel junction according to the invention the tunnel barrier layer is placed above the storage layer to produce a magnetic tunnel junction of the BS-pMTJ type. Advantageously, this type of magnetic tunnel junction is particularly suitable for a SOT-MRAM type memory cell. Another object of the invention is a memory point with two or three terminals comprising: - An upper electrode in contact with a first terminal; - A magnetic multilayer called reference layer comprising at least one magnetic stack or a multilayer according to the invention; - A magnetic multilayer called storage layer; - A tunnel barrier layer separating the reference layer and the storage layer; - A second terminal in electrical contact with the storage layer or A metal line electrically connected to a second and third terminals, placed below the storage layer and in electrical contact with the storage layer. Such a memory point with three terminals is particularly suitable for memory cells of the SOT-MRAM type or for memories known as “racetrack” or shift registers. According to a variant of the memory point with three terminals according to the invention, the metallic line is an antiferromagnetic metallic line, the writing of the storage layer then being carried out by propagation of the walls of the magnetic domains. According to a variant of the memory point with three terminals, the storage layer has a geometry of the “racetrack” or shift register type. Another object of the invention is a memory point with three terminals comprising: - An upper electrode connected to a first terminal; - A first magnetic multilayer called reference layer comprising at least one magnetic stack according to the invention or a multilayer according to the invention; - A magnetic multilayer called storage layer, a second and a third terminal being connected to said storage layer; - A tunnel barrier layer separating the reference layer and the storage layer. In this case the electrical contacts are directly connected to the storage layer. Another object of the invention is a double magnetic tunnel junction comprising: - A first magnetic multilayer called the first reference layer; - A second magnetic multilayer called the first storage layer; - A third magnetic multilayer called the second reference layer comprising a magnetic stack or a magnetic multilayer according to the invention; - A first tunnel barrier layer separating the first reference layer and the storage layer; - A second tunnel barrier layer separating the second reference layer and the storage layer. Another object of the invention is a magnetic tunnel junction for a multi-level memory cell comprising: - A first magnetic multilayer called the first storage layer; - A second magnetic multilayer called first reference layer comprising a magnetic stack or a magnetic multilayer according to the invention; - A first tunnel barrier layer separating the first reference layer and the first storage layer; - A third magnetic multilayer called the second reference layer; - A fourth magnetic multilayer called the second storage layer; - A second tunnel barrier layer separating the second reference layer and the second storage layer. Another object of the invention is a memory point with three terminals for a memory cell with several levels comprising: - A metal line connected to a second and a third terminal; - A first magnetic multilayer called first storage layer placed above the metal line and in contact with said metal line; - A second magnetic multilayer called first reference layer comprising a magnetic stack or a magnetic multilayer according to the invention; - A third magnetic multilayer called the second reference layer; - A fourth magnetic multilayer called the second storage layer; - An upper electrode connected to a first terminal. Another object of the invention is a memory point with four terminals for a memory cell with several levels comprising: - A first metal line connected to a first and a second terminal; - A first magnetic multilayer called first storage layer placed above the first metal line and in contact with said first metal line; - A second magnetic multilayer called first reference layer comprising a magnetic stack or a magnetic multilayer according to the invention; - A first tunnel barrier layer separating the first storage layer and the first reference layer; - A third magnetic multilayer called the second reference layer; - A fourth magnetic multilayer called the second storage layer; - A second metal line connected to a third and a fourth terminal, said second metal line being placed above the second storage layer and in contact with said second storage layer; - A second tunnel barrier layer separating the second storage layer and the second reference layer. Another object of the invention is a sensor for measuring an applied magnetic field comprising: - An upper electrode connected to a first terminal; - A first magnetic multilayer called reference layer comprising a magnetic stack or a magnetic multilayer according to the invention; - A second magnetic multilayer known as the detection layer having a magnetization oriented parallel to the plane of the layers in the absence of an applied magnetic field; - A tunnel barrier layer separating the detection layer (Sen) and the reference layer; - At least one second terminal connected to the detection layer. According to a variant, the sensor according to the invention is suitable for measuring an applied magnetic field and the temperature and further comprises a metal line connected to a second and to a third terminal, said metal line being below the layer detection and in contact with said detection layer. LIST OF FIGURES Other characteristics and advantages of the invention will emerge on reading the description which follows, with reference to the appended figures, which illustrate: - Figure 1a and Figure 1b show two magnetic stacks according to the state of the art and corresponding to a magnetic tunnel junction with a reference layer respectively below and above the tunnel barrier; - Figure 2a shows a magnetic stack according to the invention; - Figure 2b shows a multilayer according to the invention comprising at least two stacks according to Figure 2a; - Figure 3a shows a magnetic tunnel junction comprising a multilayer according to Figure 2b; - Figure 3b shows a second embodiment of the magnetic tunnel junction according to Figure 3a; - Figure 4 shows the perpendicular magnetic anisotropy for magnetic stacks according to the invention having different insertion layers; - Figures 5a and 5b show the magnetization curves measured for stacks whose perpendicular magnetic anisotropy is shown in Figure 4; - Figure 6 shows the saturation magnetization of magnetic stacks whose perpendicular magnetic anisotropy is shown in Figure 4; - Figure 7 shows the perpendicular magnetic anisotropy for different types of magnetic stacks according to the invention; - Figure 8 shows the magnetization curve of a magnetic tunnel junction according to the invention; - Figures 9a to 9d show different types of memory point according to the invention; - Figure 10 shows a double magnetic tunnel junction comprising a composite storage layer and comprising at least one multilayer according to the invention; - Figure 11 shows a magnetic tunnel junction comprising two storage layers and at least one multilayer according to the invention; - Figure 12 shows a memory point with three terminals obtained from the double tunnel junction illustrated in Figure 11; - Figure 13 shows a memory point with four terminals comprising at least one magnetic stack or a multilayer according to the invention; - Figure 14 shows an example of a temperature and magnetic field sensor comprising a multilayer according to the invention; - Figure 15 shows the electrical resistance measured across a metal line in Pt as a function of temperature. DETAILED DESCRIPTION OF THE INVENTION FIG. 2a shows an example of magnetic stack E according to the invention. The magnetic stack E according to the invention comprises a first element E1 and a second element or second layer X, the second layer X being placed above the first element E1. The first element E1 can be a bilayer as illustrated in FIG. 2a. In this case the first element E1 comprises a first FM layer and a second layer I of the first element. The first FM layer of the first element E1 is a ferromagnetic layer comprising at least one of the materials belonging to the first group of materials. The first group of materials includes the following materials: cobalt, iron, nickel and the magnetic alloys based on these materials. The second layer I of the first element E1, also called insertion layer I, is a layer made of a refractory metal. The melting temperature of the second layer I of the first element E1 is greater than 1600 ° C. and preferably greater than 1900 ° C. According to another embodiment not shown in FIG. 2a, the first element E1 comprises a single layer consisting of an alloy of a material included in the first group of materials and of a refractory metal. The magnetic stack E according to the invention further comprises a second element or second layer X deposited on the first element E1. The second layer X comprises at least one of the materials belonging to the second group of materials. The second group of materials includes the following materials: Pt, Au, Ir, Pa, Ni, NiCo, NiFe, NiFeCo and the alloys based on these materials. The second layer I of the first magnetic element is a layer having several purposes: • avoid the formation of defects in the FM layer during the deposition of the X layer often made of heavy materials such as Pt or Pd; • to obtain a low roughness interface between the FM layer and X which has the effect of increasing the perpendicular anisotropy of the stack E; • reduce the saturation magnetization of the layer of FM material which contributes to increasing the effective perpendicular anisotropy; • improve the structural stability of the entire stack during possible high temperature anneals such as 400 ° C thanks to the mechanical stiffening introduced by the insertion of the refractory layer I. Examples of refractory metals for the second layer I of the first element E1 are: tantalum, tungsten, molybdenum, ruthenium, zirconium, vanadium, niobium. According to the embodiment illustrated in FIG. 2a, the magnetic stack according to the invention has a structure of the FM / I / X type. It is important to note that the materials used for the insertion layer I according to the invention have higher melting temperatures than the other metal insertion layers known in the state of the art. For example, the metals disclosed in patent application FR 2 976 396 have melting temperatures on the order of 1000 ° C. or lower. Such materials are not considered refractory materials within the meaning of the present application. FIG. 2b shows a multilayer comprising: - A layer of Sub substrate; - A layer of adhesion A; - a multilayer nE formed by magnetic stacks E according to FIG. 2a; - Cap protective layer. The multilayer nE is obtained by superimposing at least two stacks E according to the invention. During the superposition, the first element E1 of a second magnetic stack E according to the invention is deposited on the second layer X of a first stack E according to the invention. In the example illustrated in FIG. 2b, the multilayer nE is deposited on an adhesion conductive layer A. The adhesion conductive layer A can be made of Ta with a thickness of between 3 and 5 nm. The Ta can be replaced by any other material capable of providing good adhesion with the Sub substrate and keeping an upper interface of low roughness. Layer A can also have the role of a lower electrode to make electrical contact at the base of the structure. Alternatively, such a lower electrode can be made of CuN, TiN, TaN or Ru. The lower electrode can also be a multilayer formed by the repetition of a CuN / Ta bilayer. To improve the magnetic properties of the multilayer nE according to the invention, the roughness of the surface of this layer can be reduced by mechanochemical polishing followed by low etching of the surface layer. Layer A or the lower electrode can be placed on a Sub substrate layer. To prevent oxidation of the multilayer nE according to the invention, a protective layer Cap is deposited on the second layer X. The protective layer Cap can also be used as an upper electrical contact. According to one embodiment, the ferromagnetic layer of the first element E1 is made of Cu. However, the Fm layer can also comprise CoFe, Fe, Ni or an alloy of these materials. The FM layer can also include a non-magnetic element such as CR, V, B or Zr. The second layer X of the magnetic stack E according to the invention may comprise one of the following materials: Pt, Pd, Ru, Au, Ir, Ni, NiCo, NiFe or a combination of these materials. The second layer I of the first element E1 consists of a refractory metal such as Ta, W, Ru, Mo, Nb, V, Zr or a combination of these materials. The melting temperatures of these materials are 3020 ° C, 3422 ° C, 2334 ° C, 2623 ° C, 2469 ° C, 1910 ° C, 1855 ° C, respectively. These melting temperatures are measured at a pressure of 1 bar. When the first element E1 is a monolayer, it is an alloy composed of one of the ferromagnetic materials given above and of a refractory metal such as Ta, Mo, W, Ru, Nb, Vou Zr. FIG. 3a shows an MTJ1 magnetic tunnel junction according to the invention comprising: - A layer of Sub substrate; - A lower electrode layer BE; - A growth layer S; - A storage layer SL; - A TB tunnel barrier layer, preferably made of MgO; - A spin polarization layer PL, preferably made of FeCoB; - A structural transition layer of symmetry, TBL; - A multilayer nE according to the invention; - Cap protective layer. The spin polarization layer PL, the structural transition layer of symmetry TBL and the multilayer nE according to the invention form the reference layer RL. The reference layer RL can also be considered as an upper magnetic electrode. The tunnel barrier layer separates the reference layer RL and the storage layer SL. The storage layer SL can be a monolayer or a magnetic multilayer. The storage layer SL is preferably made of CoFeA, A being an amorphizing element for example B, Zr or Nb. The storage layer SL is located above the growth layer S, which absorbs the amorphous element A during annealing at a temperature between 250 ° C and 450 ° C. When a BT MgO tunnel barrier is used, annealing induces recrystallization of the storage layer SL. Because of this recrystallization the storage layer in amorphous CoFeA transforms into CoFe having a centered cubic symmetry (bcc). Placed above the tunnel barrier, the upper magnetic electrode or reference layer RL is formed by a spin polarization layer PL made of CoFeB, a structural transition layer of TBL symmetry and the multilayer nE according to the invention. As is known in the prior art, the TBL symmetry structural transition layer ensures the structural transition between the crystalline structure bcc of the polarization layer PL after annealing and the crystalline structure fcc of the multilayer nE according to the invention. In particular, the multilayer nE does not need to be in contact with a growth layer S to keep a stable magnetization oriented out of the plane of the layers throughout the lifetime of the device. This is possible thanks to the strong perpendicular magnetic anisotropy inherent in the multilayer nE according to the invention. The multilayer nE can therefore be inserted into a reference layer above the tunnel barrier BT and used in a magnetic tunnel junction of the "bottom storage" or BS-pMTJ type such as that illustrated in FIG. 3a. Advantageously, a magnetic tunnel junction BS-pMTJ can be used to make a memory point of the SOT-MRAM type, in which the storage layer SL must be close to the lower electrode. According to a variant of the magnetic tunnel junction MTJ1 according to the invention, the reference layer RL can be inserted into a perpendicular synthetic antiferromagnetic element pSAF as illustrated in FIG. 3b. In this case, an AF antiferromagnetic coupling layer such as that shown in FIG. 3b is used. This AF coupling layer can be in Ru with a thickness between 0.3nm and 0.9nm. A second nE type (FM / I / X) m stack according to the invention is placed above the coupling layer and covered by a protective layer Cap. A TE top electrode layer is deposited over the Cap protective layer. In a magnetic tunnel junction of BS-pMTJ type according to the invention, the trapping layer can be constituted by a multilayer nE according to the invention, for example of the type (FM / I / X) n , namely n repetitions of l FM / I / X stack or E stack according to the invention. The hard layer HL can be constituted by a simple multilayer of the type (FM / X) m, with m and n being adjusted taking into account the thicknesses of the layers FM in the two multilayers nE and HL to minimize the parasitic field exerted by the layer synthetic antiferromagnetic pSAF on the SL storage layer. Alternatively, the hard layer can also consist of a multilayer according to the invention of the (FM / I / X) n type . Indeed, the use of a multilayer according to the invention for the hard layer makes it possible to increase the perpendicular magnetic anisotropy. Alternatively, the hard layer HL can be made of a bulk material having a perpendicular magnetic anisotropy. Examples of such materials are alloys with L1o type symmetry such as Fe-Pt, Fe-Pd and Co-Pt. Alternatively, it is possible to use materials with L11 symmetry such as CoPt, CoPd or Co-Ni-Pt. The HL hard layer can also be produced using an alloy of a rare earth and a RE-TM transition metal. Among the rare earths, one can particularly choose an element from the group formed by Tb, Dy, Ho, Er or a mixture of these elements. The term transition metal is understood to mean an element such as Fe, Co or a mixture of these elements. Alternatively, a Heusler type alloy with perpendicular anisotropy can be used, for example Mn2.7Coo.3Ga. The hard layer HL and the reference layer RL are antiferromagnetically coupled by an AF coupling layer, by RKKY interaction. The AF coupling layer can be produced in Ru, Re, Rh, Ir, Os or a mixture of these elements. The TB tunnel barrier is made of MgO. However, other metal oxides can also be used, such as AIOx, TaOx, T1O2, HfOx, ZrOx, GaOx, SrTiO3. FIG. 4 shows the perpendicular magnetic anisotropy Keff of a multilayer nE according to the invention formed by the repetition of five magnetic stacks E according to the invention. Each of the five stacks includes: - a first ferromagnetic layer FM of the first element E1 in Co and having a thickness of 0.6 nm; a second layer I of the first element E1 made of refractory metallic material, each point of the graph in FIG. 4 corresponding to a different material; - a second layer X in Pt and having a thickness of 1.7 nm. In other words, the multilayer nE studied in FIG. 4 has the structure (Co / I / Pt) s. The five stacks are inserted into the upper part of an MTJ1 magnetic tunnel junction like the one illustrated in Figure 3. The magnetic tunnel junction was annealed at 400 ° C. The graph in FIG. 4 shows on the ordinate the perpendicular magnetic anisotropy and on the abscissa the different materials chosen for the insertion layer I, as well as the thickness in de of the insertion layer I. Each point of the graph in the figure 4 represents the perpendicular magnetic anisotropy of a magnetic stack of the Sub type / Adhesion layer in Ta / Polarization layer in CoFeB / Tunnel barrier in MgO / Layer in FeCoB / Structural transition layer of symmetry TBL / (Co / I / Pt) s / Protective layer Cap. As is known to those skilled in the art, Keff is calculated from the area between the hysteresis curves M (H) measured respectively with the field applied perpendicular to the plane of the layers and parallel to the plane of the layers. By hysteresis curve M (H) is meant a measure of the magnetization M of the layers as a function of an applied external magnetic field H. The magnetization curve M (H) relative to the magnetization perpendicular to the layer plane is illustrated in FIG. 5a. The magnetization curve M (H) relating to the magnetization parallel to the plane of the layers is illustrated in FIG. 5b. The graph in FIG. 4 shows that the perpendicular magnetic anisotropy Keff measured in the presence of an Al, Cu or Ta insertion layer is higher than that measured without an insertion layer. In particular, the use of the refractory metal Ta gives the highest perpendicular magnetic anisotropy Keff. The perpendicular magnetic anisotropy per unit of volume Keff for a multilayer of the type (Co / I / Pt) n can be calculated using the following equation: rz _ ^ FeCoB K eff - 7 L FeCoB + (η - 1) Kpt-Co tco-Pt Kço-I-Pt tco-Pt - 2nM s 2 In this equation, in CGS units: - n is the number of superimposed stacks (Co / I / Pt); - Kri -Co and Kco-i-pt are the interface anisotropy constants at the Pt-Co and Co-I-Pt interfaces respectively; these constants are expressed in surface energy density; - KFeCoB is the interface anisotropy at the interface between MgO and FeCoB; - Ms is the saturation magnetization; - tco-pt is the total thickness of the layers in Pt and Co. The high value of Keff obtained for a layer I of Cu is explained by the low miscibility of Cu with Co, as it was explained in the document FR 2976396. However, the use of an insertion layer in Ta subsequently increases the perpendicular magnetic anisotropy, as illustrated in FIG. 4. This is explained by the high rigidity of the refractory element Ta and the presence of very strong chemical bonds which prevent the creation of surface defects during deposition. of the heavy metal layer, for example Pt. FIG. 5a shows that the perpendicular magnetization curve M (H) of the multilayer comprising a Ta layer has more abrupt transitions than the curve relating to a multilayer comprising a layer of Cu or another non-refractory metal. In addition, FIG. 5b shows that the planar magnetization curve M (H) relative to the stack comprising a layer of Ta is almost linear. Such a linear behavior of M (H) when the field is applied perpendicular to the easy axis of magnetization suggests that the anisotropy is of uniaxial character (anisotropy of order 2) as it is known to the man of the art. On the other hand, for the other materials used, the curves M (H) measured with the field applied in the plane of the layers have a pronounced curvature. This suggests that the perpendicular anisotropy has terms of anisotropy of order higher than the uniaxial order (in particular terms of anisotropy of order 4). According to the equation given above, the perpendicular magnetic anisotropy Keff increases when the demagnetizing energy 2πΜ 3 2 is weak. FIG. 6 shows the saturation magnetization Ms for different insertion layers I in a multilayer of the Co / I / Pt type. It appears that for an insertion layer I in Ta, a contribution to the high Keff value is due to the reduction of the magnetization Ms of saturation. We can summarize the four technical effects obtained by adding an insertion layer I between a first ferromagnetic layer FM of the first element E1 and a second layer X of the magnetic stack E according to the invention: - the mixture between the atoms of the first element E1 and the atoms of the second metallic layer X is reduced; - reduction in the magnetization of stack E; - smoothing of the interface between the first element E1 and the second metal layer X. - Increase in the structural stability of the entire stack E during possible annealing at high temperature such as 400 ° C thanks to the mechanical stiffening introduced by the insertion of the refractory layer I. These technical effects are also present when the first magnetic element is a monolayer comprising an alloy of one or more materials taken from the first group of materials and a refractory metal. These technical effects make it possible to obtain a higher perpendicular magnetic anisotropy than in known stacks. It is important to note that if the layer order is reversed and the FM ferromagnetic layer is deposited above the second layer X, the introduction of an insertion layer I above the layer X would reduce the perpendicular magnetic anisotropy Keff. For this reason the technical effects mentioned above are also found in the case of a multilayer nE obtained by superposition of several magnetic stacks E. The BTL symmetry structural transition layer also plays a role in increasing the perpendicular magnetic anisotropy. FIG. 7 shows the perpendicular magnetic anisotropy Keff measured for three different types of stacks, each stack being produced in two variants: a variant with a structural transition layer of symmetry in Ta and a variant with a structural transition layer of symmetry in W. The graph in Figure 7 clearly shows that a structural transition layer of symmetry in W systematically has higher Keff values. Other possible materials for the TBL symmetry structural transition layer are W, Mo, Hf, Zr, Nb. Advantageously, the multilayer nE according to the invention can be used for the production of a magnetic tunnel junction with perpendicular magnetization MTJ1 according to the invention. The multilayer nE makes it possible to obtain a high perpendicular magnetic anisotropy, even in the absence of a growth layer S having a predetermined symmetry. FIG. 8 shows the magnetization curve M as a function of the external magnetic field H applied for a magnetic tunnel junction of the BS-pMTJ type. In particular, the magnetic tunnel junction studied in FIG. 8 is of the type illustrated in FIG. 3b, in which the trapping layer included in the reference layer RL is a multilayer nE of type (FM / X / I) n according to the invention. Starting from a positive and high value of H and gradually decreasing H, we observe the reversal of the magnetization of the reference layer for H = 3kOe. Successively, the reversal of the magnetization of the storage layer is observed for a slightly negative value of H. For a field H = -1.5kOe we observe the simultaneous inversion of the magnetization of the reference layer and the hard layer. The magnetization of the reference layer is oriented according to the negative H field for H = -3.35kOe. The insert in FIG. 8 shows in detail the reversal of the magnetization of the storage layer SL for an applied magnetic field H close to zero. FIGS. 9a to 9d show memory points at three terminals for a magnetic memory cell with random access of the “spin orbit couple” or SOT-MRAM type. These memory points can also be used for a racetrack type memory. These memory points are obtained from a magnetic tunnel junction of the BS-pMTJ type according to the invention. The device of FIG. 9a comprises: - an upper TE electrode placed above a protective layer Cap of the tunnel junction; - a hard layer HL; - an AF antiferromagnetic coupling layer; a reference layer RL comprising a multilayer nE according to the invention, a structural transition layer of symmetry TBL, a spin polarization layer PL; - a TB tunnel barrier; - a storage layer SL; - a conductive metallic line ML placed below the storage layer SL; - a layer of Sub substrate placed below the metallic line ML; - a first terminal T1 in contact with the upper electrode; - a second T2 and a third T3 terminal in contact with the metal line. Unlike STT-MRAM type magnetic memories, which include two terminals, SOT-MRAM type memories include three or four terminals for separating the read and write current paths. For a SOT-MRAM type memory, the writing operation is carried out by a current pulse flowing in the metallic line ML which therefore has the role of lower electrode of the magnetic tunnel junction. The write operation can use the Rashba effect or the Spin Hall Effect (SHE, or Spin Hall Effect, according to English terminology). If the Hall spin effect is used, the metallic line ML comprises a heavy metal such as Pt, Ta or W. When an electron current flows through this metallic line between the terminals T2 and T3, a spin current is injected by the metallic line ML in the storage layer because of the Hall spin effect. This spin current exerts a spin-orbit couple on the magnetization of the storage layer SL. If the torque exerted by the spin current is high enough, the magnetization of the storage layer SL is reversed. Thanks to the fact that the write current does not cross the tunnel barrier TB, the endurance at writing of a memory point of the SOT-MRAM type is higher than that of a memory point of the STT-MRAM type, especially for current pulses of duration less than a few ns. By writing endurance is meant the number of writing cycles that the device can endure before its properties are degraded, in particular due to the dielectric breakdown of the tunnel barrier. By reversing the direction of the current flow between the terminals T2 and T3, the direction of the torque exerted on the magnetization of the storage layer SL is also reversed. It is therefore possible to reverse the magnetization of the storage layer SL again. The metal chosen for the metallic line ML is a metal characterized by a high Hall angle of spin, for example Ta, W, Pd, Pt, Au, Ir, Bi or an alloy of the Leather, CuBi, CuAu, AuW, IrMn type. . The metallic line ML can also be a bilayer or a multilayer formed by a stack of these materials. According to an embodiment of the device illustrated in FIG. 9a, the hard layer HL can also comprise a multilayer nE according to the invention. The writing of the memory point illustrated in FIG. 9a is based on the use of current pulses flowing between the second T2 and the third terminal T3. This method is suitable for a memory point having two possible states of the storage layer SL. Alternatively, the magnetization of the storage layer SL can be inverted gradually by passing through a series of states having intermediate resistance values. This embodiment of the memory point according to the invention is illustrated in FIG. 9b. The device of FIG. 9b differs from the device of FIG. 9a in that the metallic line is an AF-ML antiferromagnetic metallic line. The material of which the antiferromagnetic metallic line is made is for example IrMn or PtMn. At the interface between the ferromagnetic material of which the AF-ML metallic line is made and the TB tunnel barrier, the Hall spin effect is combined with an exchange anisotropy effect. Thanks to the combined effect of SHE and anisotropy of exchange at the metal line / storage layer interface, the magnetization of the storage layer is not reversed abruptly but by creation of small inverted domains and by propagation of the walls of these areas. The exchange anisotropy also increases the coercive field of the storage layer and the reversal of the magnetization becomes progressive. See for example S. Fukami et al. “Magnetization switching by spin-orbit torque in an antiferromagnet-ferromagnet bilayer System”, published in Nature Materials, vol. 15, pages 535-541,2016. By controlling the amplitude and duration of the current pulses flowing in the AF-ML antiferromagnetic metal line, it is possible to obtain several states with intermediate magnetoresistance values. This type of device can also be used for memristor type applications. FIGS. 9c and 9d show memory points at three terminals for memories of the racetrack type. For a description of this type of memory, see for example "Magnetic domain-wall racetrack memory" by S.S. Parkin et al., Published in Science, vol 320.5873, pages 190-194, 2008. The memory point of FIG. 9c has a structure similar to that of the device of FIG. 9b, unlike the storage layer SL which has an elongated shape according to a geometry of the racetrack type. The storage layer of the memory point of FIG. 9c has a larger surface area than the tunnel barrier layer TB. The AF-ML metallic line is made of antiferromagnetic material as in the device in FIG. 9b. The material chosen for the AF-ML line is based on heavy metal such as IrMn or PtMn so that it generates Dzyaloshinski Moriya interactions in the adjacent storage layer. As is known to those skilled in the art, this makes it possible to obtain in the layer SL chiral magnetic walls (CD), that is to say all having the same direction of rotation. The variation of the magnetization of the storage layer SL is then carried out by translation of the domain walls along the racetrack. The walls are translated using the Hall spin effect. In the device of FIG. 9d, the metal line has been eliminated. The second T2 and third terminal T3 are connected directly to the storage layer SL. The magnetization variation of the storage layer SL is done by translation of the domain walls along the racetrack. The translation of the walls of the domains is done by spin transfer as in the device of FIG. 9b. In the devices of FIGS. 9c and 9d the direction of translation of the walls depends on the polarity of the current pulses flowing between the second and third terminals. FIG. 10 illustrates a double magnetic tunnel junction DMTJ comprising a multilayer nE according to the invention. The DMTJ double magnetic tunnel junction according to the invention comprises: - a layer of Sub substrate; - a lower electrode BE; - a growth layer S; - a hard layer HL; - an AF antiferromagnetic coupling layer; - a first Pin trapping layer; - a first structural transition layer of TBL symmetry; - a first spin polarization layer PL; - a first TB tunnel barrier; - a storage layer SL; - a second TB2 tunnel barrier; - a second PL2 spin polarization layer; - a second structural transition layer of symmetry TBL2; - a multilayer according to the invention nE acting as a second trapping layer; - a second antiferromagnetic coupling layer AF2; - a second hard layer HL2; - a protective cap layer; - a TE upper electrode. The first reference layer RL is formed by the first trapping layer Pin, the first structural transition layer of symmetry TBL and the first spin polarization layer PL. The first reference layer RL is coupled to the first hard layer HL using a first antiferromagnetic coupling layer AF to form a first synthetic antiferromagnetic layer pSAF with perpendicular magnetization. The second reference layer RL2 is formed by the second polarization layer PL2, the second structural transition layer of symmetry TBL2 and a multilayer nE according to the invention acting as a second trapping layer. The second reference layer RL2 is coupled to the second hard layer HL2 using a second antiferromagnetic coupling layer AF2 to form a second synthetic antiferromagnetic layer pSAF2 with perpendicular magnetization. The use of the two synthetic ferromagnetic layers pSAF and pSAF2 makes it possible to strengthen the coercivity of the layers PL and PL2 and to reduce the magnetostatic coupling between the reference layers and the storage layer SL. The storage layer SL can be a composite layer comprising a ferromagnetic layer / non-magnetic layer / ferromagnetic layer in which the magnetizations of the two ferromagnetic layers are strongly coupled by the non-magnetic layer. The thickness of the non-magnetic layer determines the type of ferromagnetic or antiferromagnetic coupling between the two ferromagnetic layers. The non-magnetic coupling layer can be in Ta, W or Mo with a thickness between 0.1 nm and 1 nm. Thanks to the presence of the two polarization layers of spin PL and PL2 of magnetization oriented antiparallel to each other, the spin transfer torque acting on the magnetization of the storage layer SL is more efficient. In particular, the efficiency of the spin transfer torque is more than doubled compared to a magnetic tunnel junction of the BS-pMTJ or TS-pMTJ type. When the storage layer is a composite ferromagnetic layer, the magnetization of the first reference layer must be oriented antiparallel to the magnetization of the second reference layer to be able to obtain a spin transfer effect (or Spin T ransfer T orque STT according to English terminology) effective. On the contrary, if the storage layer SL is a synthetic antiferromagnetic layer, that is to say comprising two ferromagnetic layers coupled in an antiferromagnetic manner, the magnetization of the first reference layer RL must be parallel to the magnetization of the second RL2 reference layer to maximize the spin transfer effect. The parallel or antiparallel orientation of the two magnetizations can be obtained by making hysteresis loops and by exploiting the difference between the coercive fields of the two reference layers. According to the variant of double magnetic tunnel junction DJTM illustrated in FIG. 10, the second trapping layer, placed above the storage layer SL, is produced using the multilayer nE according to the invention and in particular a multilayer of the type (FM / I / X) n . The first pin trapping layer and the two hard layers HL and HL2 are produced using a standard multilayer of type (FM / X) n , m. In the (FM / X) n configuration for hard layers, the FM layer consists of a material taken from the group of materials comprising: Co, CoFe, Fe, Ni or a mixture of these materials. The FM layer can also include a non-magnetic element such as Cr, V, B or Zr. Layer X consists of a material taken from the group of materials comprising: Pt, Pd, Ru, Au, Ir, Ni, NiCo, NiFe or a mixture of these materials. According to a variant of double magnetic tunnel junction DJTM not shown, the hard layers HL and HL2 can be produced using a multilayer nE according to the invention of the type (FM / I / X) m and the first trapping layer Pin can also be produced using an nE multilayer according to the invention of type (FM / I / X) n . In all the variants of the DMTJ double magnetic tunnel junction according to the invention, the first and second tunnel barriers, TB and TB2, must have different resistance * surface products. Indeed, the tunnel magnetoresistance of the first barrier is opposite to that of the second barrier. A difference between the two tunnel barriers is therefore necessary so that the effective value of magnetoresistance is not less than that obtained for a simple tunnel junction. Figure 11 shows a multi-level magnetic tunnel junction M-pMTJ for the creation of a memory point with a higher information density than a standard memory point. The multilevel magnetic tunnel junction M-pMTJ of FIG. 11 comprises: - a layer of Sub substrate; - a lower electrode BE; - a growth layer S; - a first storage layer SL; - a first TB tunnel barrier; - a first spin polarization layer PL; - a first structural transition layer of TBL symmetry; - A first trapping layer produced using an nE multilayer according to the invention; - a first antiferromagnetic coupling layer AF; - a first hard layer HL; - a second antiferromagnetic coupling layer AF2; - a second Pin2 trapping layer; - a second structural transition layer of symmetry TBL2; - a second PL2 spin polarization layer; - a second TB2 tunnel barrier; - a second storage layer SL2; - a Cap protective layer; - a TE upper electrode. The first polarization layer PL, the first structural transition layer of symmetry TBL and the multilayer according to the invention nE acting as the first trapping layer constitute the first reference layer RL. The second polarization layer PL2, the second structural transition layer of symmetry TBL and the second trapping layer Pin2 constitute the second reference layer RL2. The hard layer HL is antiferromagnetically coupled to the two reference layers RL and RL2. According to a variant of the device of FIG. 11, the second trapping layer Pin2 can also comprise a multilayer nE according to the invention. The M-pMTJ multi-level magnetic tunnel junction includes two storage layers. The first storage layer SL is below the first tunnel barrier BT, the second storage layer SL2 is above the second tunnel barrier TB2. By choosing two tunnel barrier layers having two different values of their resistance * surface product, it is possible to obtain four resistance values corresponding to the four different configurations of the magnetizations of the storage layers. The four configurations correspond to the parallel / parallel, parallel / antiparallel, antiparallel / parallel, antiparallel / antiparallel orientations. The critical magnetization reversal current must be different for the two storage layers to be able to selectively write one or the other of the storage layers. During the writing of the storage layer having the highest coercive field, the storage layer having the lowest coercive field can also be found with its reverse magnetization. So after writing the hardest layer magnetically, it is necessary to write the layer with the weakest coercive field. FIG. 12 shows a memory point with three terminals for a multilevel memory cell M-pMTJ2 having two storage layers SL and SL2. The M-pMTJ2 multi-level magnetic tunnel junction consists of the following layers: - a layer of Sub substrate; - A metallic line ML comprising a material having a high Hall angle of spin; - A second T2 and third T3 terminal connected to the metallic line ML; - A first layer of SL storage; - A first TB tunnel barrier; - A first structural transition layer of TBL symmetry; - A multilayer according to the invention nE having the role of first trapping layer; - A first AF antiferromagnetic coupling layer; - A hard layer HL; - A second antiferromagnetic coupling layer AF2; - A second Pin2 trapping layer; - A second structural transition layer of symmetry TBL2; - A second layer of PL2 spin polarization; - A second structural transition layer of symmetry TBL2; - A protective cap layer; - A TE upper electrode; - A first terminal connected to the upper TE electrode. The first polarization layer PL, the first structural transition layer of symmetry TBL and the multilayer according to the invention nE constitute the first reference layer RL. In the memory point for a multi-level memory cell M-pMTJ2, each storage layer can be written independently of the other. When a current pulse flows along the metallic line ML between the terminals T2 and T3, a spin-polarized current generated by the Hall spin effect is injected into the first storage layer SL. This spin-polarized current exerts a spin-orbit couple on the magnetization of the storage layer which can be reversed if the torque is sufficient. To reverse the magnetization in the opposite direction, reverse the direction of flow of the current pulse along the metallic line ML. The writing of the second storage layer SL2 is carried out by spin transfer thanks to a current pulse flowing perpendicular to the plane of the layers through the stack. In order to be able to carry out the writing operations of the two storage layers SL and SL2 independently, the first storage layer SL has a higher coercive field than that of the second storage layer SL2. This allows the magnetization of the first storage layer SL to be left unchanged when the magnetization of the second storage layer SL2 is reversed. If on the contrary the coercive field of the first storage layer SL is weaker than that of the second storage layer SL2, each parallel antiparallel inversion of the magnetization of the second storage layer SL2 will cause an antiparallel-parallel inversion of the first storage layer SL, if the latter was initially in the antiparallel state. To overcome this problem it is necessary to rewrite the first SL storage layer, as has also been discussed with reference to Figure 11. The problem of the double writing of the storage layer having the weakest coercive field is solved by another memory point according to the invention and represented in the figure. 13. FIG. 13 represents a memory point with four terminals for a memory cell with several levels M4-pMTJ. The memory point with four terminals M4-pMTJ according to FIG. 13 comprises: - A layer of Sub substrate; - A first metallic line ML comprising a material having a high Hall angle of spin; - Two terminals T3 and T4 connected to the first metallic line ML; - A first storage layer SL deposited in contact with the first metallic line ML; - A first TB tunnel barrier; - A first polarization layer PL; - A first structural transition layer of TBL symmetry; - A multilayer nE according to the invention having the role of first trapping layer; - A first AF antiferromagnetic coupling layer; - A hard layer HL; - A second antiferromagnetic coupling layer AF2; - A second Pin2 trapping layer; - A second structural transition layer of symmetry TBL2; - A second polarization layer PL2; - A second TB2 tunnel barrier; - A second storage layer SL2; - A second metallic line ML2 comprising a material having a high spin angle, the second metallic line being deposited in contact with the second storage layer SL2; - Two terminals T1 and T2 placed in contact with the second metallic line ML2. The first spin polarization layer PL, the first structural transition layer of symmetry TBL and the multilayer nE according to the invention acting as the first trapping layer constitute a first reference layer RL. The second trapping layer Pin2, the second structural transition layer of symmetry TBL2 and the second polarization layer PL2 constitute a second reference layer RL2. In the configuration illustrated in FIG. 13, the two storage layers SL and SL2 are written by spin-orbit couple. The magnetization of the first storage layer SL is reversed by means of a current pulse flowing along the first metal line ML between the two terminals T3 and T4. In the same way, the writing of the second storage layer SL2 is carried out thanks to a current pulse flowing along the second metallic line ML2 between the two terminals T1 and T2. No writing error is possible in the configuration of FIG. 13 and this independently of the values of the coercive fields of the two storage layers SL and SL1. The memory point with four terminals M4-pMTJ according to FIG. 13 has four distinct resistance states. Reading the resistance value is possible using a vertical current, for example by choosing one of the terminals of the first metallic line ML and one of the terminals of the second metallic line ML2. Alternatively, the writing of the two storage layers SL and SL2 can be carried out by nucleation of magnetic domains or by propagation of the walls of magnetic domains, as has been described in relation to FIG. 9b. In this case, the two metallic lines ML and ML2 are made of an antiferromagnetic material having a high Hall angle of spin. Examples of such a material are IrMn or PtMn. These writing methods are applicable not only for memory points at several levels of the SOT-MRAM type but also for memristor type devices. FIG. 14 illustrates a temperature and magnetic field sensor comprising an nE multilayer according to the invention. The sensor illustrated in Figure 14 includes: - A layer of Sub substrate; - A metallic line ML, typically in Pt; - A Sen detection layer placed above and in contact with the metallic line ML; - A TB tunnel barrier; - A spin polarization layer PL; - A structural transition layer of TBL symmetry; - A multilayer nE according to the invention having the role of a trapping layer; - An AF antiferromagnetic coupling layer; - A hard layer HL; - Cap protective layer; - A TE upper electrode. A first electrical terminal T1 is connected to the upper electrode. A second T2 and a third terminal T3 are connected to the metallic line ML. The polarization layer PL, the structural transition layer of symmetry TBL and the multilayer nE according to the invention form a reference layer RL. According to a variant, the hard layer HL can also comprise a multilayer nE according to the invention of the type (FM / X / I) n . The detection layer has a magnetization in the plane in the absence of an applied external magnetic field. The magnetic field to be measured is oriented in the direction normal to the layers. Under the action of the magnetic field to be measured, the magnetization of the detection layer is pulled out of the plane and is oriented parallel or antiparallel to the magnetization of the reference layer according to the direction of the magnetic field to be measured. It is therefore possible to measure a resistance which depends on the magnetic field to be measured due to the tunnel magnetoresistance of the stack. To read the resistance value, it is possible to measure the electrical voltage between the first terminal T1 and one of the terminals T2 or T3 of the metallic line ML by circulating a current of determined intensity through the stack between terminals T1 and T2 or T3. The detection layer can be a single layer or a stack of layers forming a synthetic antiferromagnetic layer. Advantageously, in the second case it is possible to reduce the stray field of magnetostatic origin between the detection layer and the trapping layers. The perpendicular magnetic susceptibility of the detection layer can be modified by varying the thickness of the detection layer, which makes it possible to modify the sensitivity of the magnetic field sensor. Generally, the resistance of the layers, the magnetoresistance and the sensitivity of the sensor according to FIG. 14 depend on the temperature. It is therefore necessary to measure the temperature of the sensor in order to be able to go back to the value of the magnetic field starting from a measured value of magnetoresistance. The temperature can be measured by measuring the resistance of the metallic line ML between terminals T2 and T3. This measurement of the resistance of the line ML must be carried out at sufficiently low current so that the influence of a possible torque of orbit spin induced by the circulation of the current in the line ML on the magnetization of the Sen layer does not come disturb the reading of the magnetoresistance signal between terminals T1 and T2 or T3. In practice, it may be preferable to carry out the two electrical resistance measurements between the terminals T1 and T2 or T3 (measurement of the magnetic field) and between the terminals T2 and T3 (measurement of the temperature) at two separate time intervals and consecutive. When choosing a metal such as Pt, the resistance measured depends almost linearly on the temperature, as illustrated in Figure 15. The device according to FIG. 14 can therefore be used to measure the temperature and an external magnetic field perpendicular to the plane of the layers.
权利要求:
Claims (20) [1" id="c-fr-0001] 1. Magnetic stack (E) comprising: - A first element (E1) comprising a ferromagnetic layer; - A second element (X) comprising a metallic layer capable of imparting to an assembly formed by the first and the second elements a magnetic anisotropy perpendicular to the plane of the layers, the magnetic stack (E) being characterized in that the first element ( E1) further comprises a refractory metallic material, the second element (X) being disposed on the first element. [2" id="c-fr-0002] 2. Magnetic stack (E) according to the preceding claim, characterized in that: - The ferromagnetic layer of the first element (E1) comprises one or more materials taken from a first group of materials, said first group of materials consisting of the following materials: cobalt, iron, nickel and the magnetic alloys based on these materials; and or - The metal layer of the second element (X) comprises one or more materials taken from a second group of materials, said second group of materials consisting of the following materials: platinum, gold, iridium, palladium, nickel, NiCo, NiFe, NiFeCo and the alloys based on these materials. [3" id="c-fr-0003] 3. Magnetic stack (E) according to the preceding claim characterized in that the ferromagnetic layer of the first element (E1) comprises an alloy based on one or more materials taken from the first group of materials and the refractory metallic material. [4" id="c-fr-0004] 4. Magnetic stack (E) according to claim 1 and claim 2 characterized in that the first element (E1) comprises a first layer (FM) of the first element and a second layer (I) of the first element, the first layer ( FM) of the first element (E1) comprising one or more materials taken from the first group of materials and the second layer of the first magnetic element (I) (E1) consisting of the refractory metallic material. [5" id="c-fr-0005] 5. Magnetic stack (E) according to one of the preceding claims characterized in that the refractory metallic material is taken from the following group: tantalum, tungsten, molybdenum, ruthenium, zirconium, vanadium, niobium. [6" id="c-fr-0006] 6. Magnetic stack (E) according to one of the preceding claims, characterized in that the refractory metallic material has a melting temperature above 1600 ° C, said melting temperature being measured at a pressure of 1 bar. [7" id="c-fr-0007] 7. Magnetic stack (E) according to one of the preceding claims 4 to 6 characterized in that the second layer of the first magnetic element (I) has a thickness between 0.1 and 0.6 nm and preferably between 0.2 and 0.4 nm. [8" id="c-fr-0008] 8. Multilayer (nE) comprising at least a first and a second magnetic stack according to any one of the preceding claims, the multilayer having magnetization out of the plane, the first element of the second magnetic stack being disposed on the second element of the first stack magnetic. [9" id="c-fr-0009] 9. Magnetic tunnel junction (MTJ1) comprising: - A first magnetic multilayer called the reference layer (RL); - A second magnetic multilayer called storage layer (SL); - A tunnel barrier layer (TB) which separates the reference layer (RL) and the storage layer (SL); said magnetic tunnel junction being characterized in that the reference layer (RL) comprises a magnetic stack (E) according to one of claims 1 to 7 or a multilayer (nE) according to claim 8. [10" id="c-fr-0010] 10. Magnetic tunnel junction (MTJ1) according to the preceding claim characterized in that the tunnel barrier layer (TB) is placed above the storage layer (SL). [11" id="c-fr-0011] 11. Memory point (PM) at two or three terminals including: - An upper electrode (TE) in contact with a first terminal (T1); - A magnetic multilayer called reference layer (RL) comprising at least one magnetic stack (E) according to one of claims 1 to 7 or a multilayer (nE) according to claim 8; - A magnetic multilayer called storage layer (SL); - A tunnel barrier layer (TB) separating the reference layer and the storage layer; - A second terminal in electrical contact with the storage layer (SL) or a metal line (ML) electrically connected to a second (T2) and third terminals (T3), placed below the storage layer (SL) and in electrical contact with the storage layer (SL). [12" id="c-fr-0012] 12. Memory point according to the preceding claim characterized in that the conductive metal line is an antiferromagnetic conductive metal line (AF-ML). [13" id="c-fr-0013] 13. Memory point at three terminals including: - An upper electrode (TE) connected to a first terminal (T1); - A first magnetic multilayer called reference layer (RL) comprising at least one magnetic stack (E) according to one of claims 1 to 7 or a multilayer (nE) according to claim 8; - A magnetic multilayer called storage layer (SL), a second (T2) and a third (T3) terminals being connected to said storage layer (SL); - A tunnel barrier layer (TB) separating the reference layer and the storage layer. [14" id="c-fr-0014] 14. Memory point according to any one of claims 12 or 13 characterized in that the storage layer (SL) has a geometry of the "racetrack" type. [15" id="c-fr-0015] 15. Double magnetic tunnel junction (DMTJ) comprising: - A first magnetic multilayer called first reference layer (RL); - A second magnetic multilayer called storage layer (SL); - A third magnetic multilayer called the second reference layer (RL2) comprising a magnetic stack (E) according to one of claims 1 to 7 or a magnetic multilayer (nE) according to claim 8; - A first tunnel barrier layer (TB) separating the first reference layer (RL) and the storage layer (SL); - A second tunnel barrier layer (TB2) separating the second reference layer (RL2) and the storage layer (SL). [16" id="c-fr-0016] 16. Magnetic tunnel junction for a multi-level memory cell (MpMTJ) comprising: - A first magnetic multilayer called the first storage layer (SL); - A second magnetic multilayer called first reference layer (RL) comprising a magnetic stack (E) according to one of claims 1 to 7 or a magnetic multilayer (nE) according to claim 8; - A first tunnel barrier layer (TB) separating the first reference layer (RL) and the first storage layer; - A third magnetic multilayer called the second reference layer (RL2); - A fourth magnetic multilayer called the second storage layer (SL2); - A second tunnel barrier layer (TB) separating the second reference layer (RL2) and the second storage layer (SL2). [17" id="c-fr-0017] 17. Three-terminal memory point for a multi-level memory cell (M-pMTJ2) comprising: - A metal line (ML) connected to a second (T2) and a third (T3) terminal; - A first magnetic multilayer called first storage layer (SL) placed above the metallic line (ML) and in contact with said metallic line (ML); - A second magnetic multilayer called first reference layer (RL) comprising a magnetic stack (E) according to one of claims 1 to 7 or a magnetic multilayer (nE) according to claim 8; - A third magnetic multilayer called the second reference layer (RL2); - A fourth magnetic multilayer called the second storage layer (SL2). - An upper electrode (TE) connected to a first terminal (T 1). [18" id="c-fr-0018] 18. Four-terminal memory point for a multi-level memory cell (M4-pMTJ2) comprising: - A first metallic line (ML) connected to a first (T1) and to a second (T2) terminal; - A first magnetic multilayer called first storage layer (SL) placed above the first metallic line (ML) and in contact with said first metallic line (ML); - A second magnetic multilayer called first reference layer (RL) comprising a magnetic stack (E) according to one of claims 1 to 7 or a magnetic multilayer (nE) according to claim 8; - A first tunnel barrier layer (TB) separating the first storage layer (SL) and the first reference layer (RL); - A third magnetic multilayer called the second reference layer (RL2); - A fourth magnetic multilayer called the second storage layer (SL2); - A second metallic line (ML2) connected to a third (T3) and to a fourth (T4) terminal, said second metallic line (ML2) being placed above the second storage layer (SL2) and in contact with said second storage layer (ML2); - A second tunnel barrier layer (TB2) separating the second storage layer (SL2) and the second reference layer (RL2). [19" id="c-fr-0019] 19. Sensor for measuring an applied magnetic field comprising: - An upper electrode (TE) connected to a first terminal (T1); - A first magnetic multilayer called reference layer (RL) comprising a magnetic stack (E) according to one of claims 1 to 7 or a magnetic multilayer (nE) according to claim 8; - A second magnetic multilayer called the detection layer (Sen) having a magnetization oriented parallel to the plane of the layers in the absence of an applied magnetic field; - A tunnel barrier layer (TB) separating the detection layer (Sen) and the reference layer (RL); - At least one second terminal electrically connected to the detection layer. [20" id="c-fr-0020] 20. Sensor for measuring an applied magnetic field according to the preceding claim characterized in that it is configured to measure the temperature and in that it comprises a metal line connected to a second (T2) and to a third ( T3) terminal, said metal line being below the detection layer (Sen) and in electrical contact with said detection layer (Sen).
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同族专利:
公开号 | 公开日 FR3077917B1|2022-02-04| US20190252601A1|2019-08-15| US10978234B2|2021-04-13| EP3528256A1|2019-08-21|
引用文献:
公开号 | 申请日 | 公开日 | 申请人 | 专利标题 WO2017052606A1|2015-09-25|2017-03-30|Intel Corporation|Psttm device with free magnetic layers coupled through a metal layer having high temperature stability| JP2012043967A|2010-08-19|2012-03-01|Sony Corp|Magnetic memory element| FR2976396B1|2011-06-07|2013-07-12|Commissariat Energie Atomique|MAGNETIC STACK AND MEMORY POINT COMPRISING SUCH A STACK| JP5862242B2|2011-11-30|2016-02-16|ソニー株式会社|Memory element and memory device| US9858975B1|2016-08-24|2018-01-02|Samsung Electronics Co., Ltd.|Zero transistor transverse current bi-directional bitcell| US10229723B1|2017-09-12|2019-03-12|Sandisk Technologies Llc|Spin orbit torque magnetoresistive random access memory containing composite spin hall effect layer including beta phase tungsten|US10658021B1|2018-12-17|2020-05-19|Spin Memory, Inc.|Scalable spin-orbit torquemagnetic memory| US10930843B2|2018-12-17|2021-02-23|Spin Memory, Inc.|Process for manufacturing scalable spin-orbit torquemagnetic memory| US11081154B1|2020-01-27|2021-08-03|Rongfu Xiao|Synthetic magnetic pinning element having strong antiferromagnetic coupling| US11088200B1|2020-02-10|2021-08-10|Rongfu Xiao|Lattice matched seed layer to improve PMA for perpendicular magnetic pinning| US11217289B1|2020-07-31|2022-01-04|Western Digital Technologies, Inc.|Spinel containing magnetic tunnel junction and method of making the same| WO2022026057A1|2020-07-31|2022-02-03|Western Digital Technologies, Inc.|Spinel containing magnetic tunnel junction and method of making the same| FR3113519A1|2020-08-24|2022-02-25|Commissariat A L'energie Atomique Et Aux Energies Alternatives|Method for measuring an external magnetic field by at least one magnetic memory point|
法律状态:
2019-02-28| PLFP| Fee payment|Year of fee payment: 2 | 2019-08-16| PLSC| Publication of the preliminary search report|Effective date: 20190816 | 2020-02-28| PLFP| Fee payment|Year of fee payment: 3 | 2021-02-26| PLFP| Fee payment|Year of fee payment: 4 |
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申请号 | 申请日 | 专利标题 FR1851302A|FR3077917B1|2018-02-15|2018-02-15|MAGNETIC STACK, TUNNEL JUNCTION, MEMORY POINT AND SENSOR COMPRISING SUCH STACK| FR1851302|2018-02-15|FR1851302A| FR3077917B1|2018-02-15|2018-02-15|MAGNETIC STACK, TUNNEL JUNCTION, MEMORY POINT AND SENSOR COMPRISING SUCH STACK| US16/277,260| US10978234B2|2018-02-15|2019-02-15|Magnetic stack, multilayer, tunnel junction, memory point and sensor comprising such a stack| EP19157406.0A| EP3528256A1|2018-02-15|2019-02-15|Multilayer magnetic stack, tunnel junction, memory point and sensor comprising such a stack| 相关专利
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