MAGNETIC STORAGE UNIT WITH RESONANT SYNTHETIC ANTIFERROMAGNETIC REFERENCE LAYER STRUCTURE

Abstract

Magnetic storage unit comprising: a magnetic tunnel contact column comprising a tunnel barrier layer (22) arranged between a synthetic antiferromagnetic reference layer structure (10) and a magnetic free layer (24), wherein the synthetic antiferromagnetic reference layer structure comprises a polarizing magnetic layer (20) magnetically interacting with a stack of magnetic reference layers comprising a first magnetic reference layer (16) and a second magnetic reference layer (12), wherein the polarizing magnetic layer (20) forms an interface with the tunnel barrier layer (22) and has a ferromagnetic resonant frequency peak substantially overlapping a ferromagnetic resonant frequency peak of at least the first magnetic reference layer (16).

Description

BACKGROUNDThe present invention relates generally to magnetic memories and, more particularly, to a magnetic memory device comprising a magnetic tunnel junction (MTJ) having a stable resonant synthetic antiferromagnetic (SAF) reference layered structure.Magnetic tunnel junction (MTJ) pillars are a potential approach for nonvolatile memory applications. Units comprising an MTJ column store information about the magnetization of a magnetic free layer. State switching and readout is accomplished by passing a current through an MTJ column that includes a magnetic free layer (MRI), a tunnel barrier layer (MRI), and a polarizing magnetic layer (MRI). The stronger the current passed through, the faster the bit changes take place. However, if the current level in writing is too high, the polarizing magnetic layer may also change, resulting in a "back and forth" motion between the free magnetic layer and the top surface of the polarizing magnetic layer, thereby creating writing errors.To stabilize the polarizing magnetic layer, the polarizing magnetic layer is interacting with a stack of magnetic reference layers (magnetic reference layer) having high anisotropy to attempt to support the polarizing magnetic layer; such a structure may be referred to as a synthetic antiferromagnetic (SAF) reference layer structure. In static tests, such a structure can increase the stability. However, in the previous embodiments of SAF reference layer structures, oscillations due to the unwanted excitation of the magnetic reference layer by the spin current that has an exclusive effect on the polarizing magnetic layer often occur under the effect of a large spin current (e.g. when the MTJ column is biased with a high voltage).US 2018 / 0 248 110 A1 relates to a magneto-resistive random access memory (MRAM). The MRAM device includes a magnetic tunnel junction stack that has significantly improved free layer performance in the magnetic tunnel junction structure. The MRAM device uses a precessional spin current (PSC) magnetic structure in conjunction with a perpendicular MTJ, whereby the magnetization direction of the PSC magnetic layer can freely rotate in the plane. The precessional spin magnetic layer includes first and second precessional spin ferromagnetic layers separated by a non-magnetic precessional spin insertion layer.US 2019 / 0 165 255 A1 relates to a memory device having a plurality of layers forming a stack. The plurality of layers includes a spin polarization layer having a magnetic anisotropy approximately perpendicular to a plane of the spin polarization layer, an antiferromagnetic layer having an antiferromagnetic material, a ferromagnetic layer exchange-coupled to the antiferromagnetic layer, the antiferromagnetic layer being located between the ferromagnetic layer and the spin polarization layer, and a storage layer having a magnetization direction indicating a storage state of the storage layer. The storage state is switched by the current through the stack. The spin polarization layer, the ferromagnetic layer, and the antiferromagnetic layer are configured to reduce current through the stack for switching the magnetization direction of the storage layer relative to current through a storage device without the spin polarization layer, the ferromagnetic layer, and the antiferromagnetic layer.US 2018 / 0 211 996 A1 relates to a semiconductor device comprising: a substrate, a first insulating layer on a logic region and a memory region of the substrate, a second insulating layer on the first insulating layer, a base insulating layer between the first insulating layer and the second insulating layer over the logic region and the memory region, first connection structures running through the first insulating layer, second connection structures running through the second insulating layer, a base connection structure running through the base insulating layer over the logic region, and a variable resistor structure in the base insulating layer over the memory region. The variable resistor structure includes a lower electrode, a magnetoresistive unit, and an upper electrode stacked one after another. The lower electrode and the upper electrode are electrically connected to one of the first connection patterns and one of the second connection patterns, respectively, over the storage region.US 2018 / 0 083 067 A1 relates to a magneto-resistive random access memory device comprising: a free layer, a tunnel barrier layer, an isolation barrier layer, a pinned layer and a vertical polarizer structure. The tunnel barrier layer and the insulation barrier layer are in direct contact with different surfaces of the free layer. The pinned layer structure is in contact with the tunnel barrier layer and includes at least one pinned layer. The vertical polarizer structure is in contact with the isolation barrier layer and includes a plurality of sequentially stacked magnetized multilayer structures. Each magnetic multilayer structure includes a non-magnetic layer and a magnetic layer stacked one after another. The pinned layer and the magnetic layer have mutually antiparallel magnetization directions. The object is to improve corresponding magnetic storage units.SUMMARYThe object is achieved by the magnetic storage unit according to claim 1. Further embodiments of the invention are specified in the dependent claims.A magnetic storage device is provided that includes a magnetic tunnel junction (MTJ) pillar including a stable resonant synthetic antiferromagnetic (SAF) reference layered structure in which the ferromagnetic resonant characteristics of a polarizing magnetic layer of the SAF reference layered structure are substantially matched to at least a first magnetic reference layer within the SAF reference layered structure. The "first reference magnetic layer" of the SAF reference layer structure is the reference magnetic layer directly connected to the polarizing magnetic layer via a first connection layer. By substantially matching the ferromagnetic resonance properties of the polarizing magnetic layer to at least the first reference magnetic layer, an MTJ column is provided in which the dynamic stability of the polarizing magnetic layer can be improved and undesirable write errors associated with the instability of the reference magnetic layer can be reduced.In one aspect, the magnetic storage device comprises an MTJ column having a tunnel barrier layer disposed between a synthetic antiferromagnetic (SAF) reference layer structure and a magnetic free layer. The SAF reference layer structure comprises a polarising magnetic layer that is interactive with a stack of reference magnetic layers comprising a first reference magnetic layer and a second reference magnetic layer. The polarizing magnetic layer interfaces with the tunnel barrier layer and has a resonant frequency peak substantially overlapping a resonant frequency peak of at least the first reference magnetic layer. In some embodiments, the resonant frequency peak of the polarizing magnetic layer may overlap the resonant frequency peaks of both the first and second reference magnetic layers.In another aspect, the magnetic storage device comprises an MTJ column having a tunnel barrier layer disposed between a synthetic antiferromagnetic (SAF) reference layer structure and a magnetic free layer. The SAF reference layer structure comprises a polarising magnetic layer that is interactive with a stack of reference magnetic layers comprising a first reference magnetic layer and a second reference magnetic layer. According to the present application, both the polarizing magnetic layer and the first reference magnetic layer have spin current excitations therein. In some embodiments, the polarizing magnetic layer and the first and second reference magnetic layers have spin current excitations therein.In embodiments of the two aspects of the present application, the first magnetic reference layer is antiferromagnetically interactively bonded to the second magnetic reference layer. In the present application, a first bonding layer separates the polarizing magnetic layer from the first reference magnetic layer, and a second bonding layer separates the first reference magnetic layer from the second reference magnetic layer.In some embodiments, the MTJ column is a top pinned MTJ column in which the magnetic free layer is disposed above the SAF reference layer structure, while in other embodiments, the MTJ column is a bottom pinned MTJ column in which the magnetic free layer is disposed below the SAF reference layer structure.In some embodiments of the present application, the polarizing magnetic layer is made of an alloy of cobalt-iron-boron (Co-Fe-B), an alloy of cobalt-iron (Co-Fe), iron (Fe), cobalt (Co), or multilayer stacks thereof, and has a thickness of 0.5 nm to 3 nm. In some cases, the polarizing magnetic layer has perpendicular anisotropy, H k, of -0.1 T to 1 T.In some embodiments of the present application, the first magnetic reference layer and the second magnetic reference layer are made of cobalt / nickel (Co / Ni), cobalt / platinum (Co / Pt), cobalt / palladium (Co / Pd), cobalt (Co), nickel (Ni), platinum (Pt), palladium (Pd), or multilayer stacks thereof, and have a thickness of 0.2 nm to 1 nm. In some cases, the first reference magnetic layer has a perpendicular anisotropy, H k, of 0 T to 1 T, and the perpendicular anisotropy of the first reference magnetic layer substantially matches the perpendicular anisotropy of the polarizing magnetic layer.In some embodiments, and to increase the overlap of the resonant frequency peaks of the polarizing magnetic layer and the first reference magnetic layer, the first reference magnetic layer comprises a rare earth element introduced therein. In such an embodiment, the first magnetic reference layer containing the incorporated rare earth element has an attenuation value, α, of 0.0001 to 1.BRIEF DESCRIPTION OF THE DRAWINGSFIG. 1A shows a cross-sectional view of an MTJ pillar according to an embodiment of the present application. FIG. 1B shows a cross-sectional view of an MTJ pillar according to another embodiment of the present application. FIG. 2A shows the precession of the magnetic momentum vector about the axis of rest when the resonant frequency of the polarizing magnetic layer (PL) (ω PL) is not equal to the resonant frequency of the first magnetic reference layer (RL) (ω RL). FIG. 2B shows the precession of the magnetic momentum vector about the axis of rest when the resonant frequency of the polarizing magnetic layer (ω PL) is substantially equal to the resonant frequency of the first magnetic reference layer (ω RL). FIG. 3A shows a plot of the excitation amplitude versus frequency (ω) when the resonant frequency of the polarizing magnetic layer (ω PL) is not equal to the resonant frequency of the first reference magnetic layer (ω RL). FIG. 3B shows a plot of the excitation amplitude versus frequency (ω) when the resonant frequency of the polarizing magnetic layer (ω PL) is substantially equal to the resonant frequency of the first reference magnetic layer (ω RL). FIG. 4 shows a plot of excitation amplitude versus frequency (ω) for an embodiment in which the magnetic damping properties of the first magnetic reference layer are increased to increase the width of the resonant peak, thus allowing for greater overlap of the two peaks. FIG. 5A is a graph illustrating the magnetization direction M as a function of time ns for a magnetic free layer in a prior art MTJ pillar in which the resonant frequencies of the polarizing magnetic layer and the reference magnetic layers do not match. FIG. 5B is a graph illustrating the magnetization direction M as a function of time ns for a polarizing free layer in a prior art MTJ pillar in which the resonant frequencies of the polarizing magnetic layer and the reference magnetic layers do not match. FIG. 6A shows a graph illustrating the magnetization direction M as a function of time ns for a magnetic free layer in an MTJ column according to the invention, in which the resonant frequencies of the polarizing magnetic layer and the magnetic reference layers substantially match. FIG. 6B shows a graph illustrating the magnetization direction M as a function of time ns for a polarizing free layer in an MTJ column according to the invention, in which the resonant frequencies of the polarizing magnetic layer and the reference magnetic layers substantially match.DETAILED DESCRIPTIONThe present application will now be described in more detail with reference to the following explanations and the drawings attached to the present application. It should be understood that the drawings of the present application are provided for illustrative purposes only and are therefore not drawn to scale. It is further noted that the same and corresponding elements are referred to with the same reference numerals.In the following description, numerous specific details are set forth, for example, specific structures, components, materials, dimensions, processing steps, and techniques, in order to provide an understanding of the various embodiments of the present application. It will be apparent, however, that the various embodiments of the present application may be practiced without these specific details. In other instances, well-known structures or processing steps have not been described in detail in order not to obscure the present application.It will be understood that when an element in the form of a layer, region or substrate is referred to as being disposed "on" or "over" another element, it may be disposed directly on the other element or intervening elements may also be present. On the other hand, when an element is referred to as being "directly on" or "directly over" another element, there are no elements interposed therebetween. It will be further understood that when an element is referred to as being disposed "below" or "below" another element, it may be disposed directly below or below the other element or intervening elements may also be present. If, on the other hand, an element is referred to as being arranged "directly below" or "directly below" another element, then no elements arranged therebetween are present.As already mentioned, the present application comprises a magnetic storage unit such as a magneto-resistive random access memory (MRAM) comprising an MTJ pillar having a stable resonant SAF reference layer structure, wherein the ferromagnetic resonance properties of a polarizing magnetic layer of the SAF reference layer structure are substantially matched to at least a first magnetic reference layer within the SAF reference layer structure. The "first reference magnetic layer" of the SAF reference layer structure is the reference magnetic layer directly connected to the polarizing magnetic layer via a first connection layer. By substantially matching the ferromagnetic resonance properties of the polarizing layer to at least the first reference magnetic layer, an MTJ column is provided in which the dynamic stability of the polarizing magnetic layer can be improved and undesirable write errors associated with the instability of the reference magnetic layer can be reduced. In particular, when the layers of such a stable resonant SAF reference layer structure are resonant, energy can be extracted from the polarising magnetic layer, which in turn reduces writing errors and in some cases can even be avoided.Referring first to FIGS. 1A through 1B, various MTJ columns are shown according to various embodiments of the present invention. The MTJ column shown in FIG. 1A may be referred to as a bottom pinned MTJ column, while the MTJ column shown in FIG. 1B may be referred to as a top pinned MTJ column.Each of the MTJ columns shown in FIGS. 1A to 1B comprises a magnetic free layer 24, a tunnel barrier layer 22, and a stable resonant SAF reference layer structure 10. In some embodiments, the ferromagnetic resonant characteristics of the polarizing magnetic layer of the stable resonant SAF reference layered structure are substantially matched to each of the reference magnetic layers present in the SAF reference layered structure 10. In the present application, the SAF reference layer structure is configured such that the resonance frequency peak of the polarizing magnetic layer substantially overlaps a resonance frequency peak of at least the first reference magnetic layer of the SAF reference layer structure. Resonant frequency peaks can be determined by magnetization, shape, anisotropy fields, and internal magnetic fields. Substantially overlapping resonant frequency peaks are peaks in which a portion of one peak coincides with a portion of another.The stable resonant SAF reference layer structure 10 comprises a polarising magnetic layer 20 which interfaces with the tunnel barrier layer 22. In the MTJ columns shown in Figs. 1A to 1B, information is stored in the magnetic free layer 24 which is referenced to the polarizing magnetic layer 20 via the tunnel barrier layer 22. In order to increase the stability of the polarizing magnetic layer 20, the polarizing magnetic layer 20 is connected to a first reference magnetic layer 16 via a first connection layer 18. The first magnetic reference layer 16 is connected antiferromagnetically interacting with a second magnetic reference layer 12; a second connection layer 14 is arranged between the first magnetic reference layer 16 and the second magnetic reference layer 12. Additional magnetic reference layers and interconnect layers may be present in the MTJ pillars of the present application.In Figs. 1A to 1B, the double arrow in the magnetic free layer 24 means that the orientation of magnetization of these layers can be changed, while the single arrow in the respective polarizing magnetic layer 20, first reference magnetic layer 16 and second reference magnetic layer 12 means that the orientation of magnetization of these layers is fixed. The MTJ pillars shown in FIGS. 1A through 1B are typically located at the back-end-of-the-line (BEOL) end and are disposed between an upper electrode (not shown) and a lower electrode (also not shown). The lower electrode is usually arranged on a surface of an electrically conductive structure (likewise not shown). The electrically conductive structure is embedded in a layer (also not shown) of dielectric interconnect material. Another layer of dielectric interconnect material (also not shown) may embed the MTJ pillars shown in FIGS. 1A and 1B. Another electrically conductive structure (also not shown) may be disposed on the top electrode.The MTJ pillars shown in FIGS. 1A-1B may be formed by first applying a material stack including each of the material layers present in the MTJ pillar, and then subjecting the material stack to a patterning process. Applying the material stack may include chemical vapor deposition (CVD), plasma enhanced chemical vapor deposition (PECVD), physical vapor deposition (PVD), or sputtering (sputtering). In some embodiments of the present application, the same deposition method can be used to form the individual layers of the material stack. In other embodiments, at least two different deposition methods may be used to form the material stack. Patterning the material stack may include photolithography and etching. The etching may include reactive ion etching (RIE) and / or ion beam etching (IBE) and / or plasma etching (plasma etching).The MTJ column being formed may include various shapes, including, for example, cylindrical. The critical dimension (CD) of the MTJ column may vary and is not critical to the present application. In some embodiments, the CD of the MTJ column is equal to a CD of the bottom electrode. In other embodiments, the CD of the MTJ column is larger than a CD of the bottom electrode. In another embodiment of the present application, the CD of the MTJ column is smaller than a CD of the lower electrode.The magnetic free layer 24 is made of at least one magnetic material having a magnetization whose orientation can be changed relative to the orientation of magnetization of the polarizing magnetic layer 20 present in the SAF reference layered structure 10. Exemplary magnetic materials for the magnetic free layer 24 include alloys and / or multi-layers of cobalt (Co), iron (Fe), alloys of cobalt-iron (Co-Fe), nickel (Ni), alloys of nickel-iron (Ni-Fe), and alloys of cobalt-iron-boron (Co-Fe-B). The magnetic free layer 24 that may be used in the present application may have a thickness of 1 nm to 3 nm; however, other thicknesses may also be used for the magnetic free layer 24. The magnetic state of the magnetic free layer 24 can be switched to an up or down state (spin) state by passing a current through the MTJ column. A polarized spin current is generated by the polarizing magnetic layer 20, which applies an alternating torque to the magnetic free layer 24.The tunnel barrier layer 22 is made of an insulating material and is of such a thickness as to provide an appropriate tunnel resistance. Exemplary materials for the tunnel barrier layer 22 include magnesium oxide, aluminum oxide, and titanium oxide, or materials having higher electrical tunnel conductivity, for example, low band gap semiconductors or insulators. In one embodiment, magnesium oxide is used as the material that provides the tunnel barrier layer 22. The thickness of the tunnel barrier layer 22 may be between 0.5 nm and 1.5 nm; however, other thicknesses may be used for the tunnel barrier layer 22 as long as the selected thickness provides a desired tunnel barrier resistance. The tunnel barrier layer 22 forms a first interface with the magnetic free layer 24 and a second interface opposite the first interface with the polarizing magnetic layer 20 of the stable resonant SAF reference layer structure 10.Polarizing magnetic layer 20 is made of a magnetic material that enhances the polarization of the spin torque current by enhancing coherent tunneling through its interface with tunnel barrier layer 22. Exemplary magnetic materials that may be used as the polarizing magnetic layer 20 include, but are not limited to, an alloy of cobalt-iron-boron (Co-Fe-B), an alloy of cobalt-iron (Co-Fe), iron (Fe), cobalt (Co), or any multilayer stack thereof. The perpendicular anisotropy of the polarizing magnetic layer 20 is determined by its interface with the tunnel barrier layer 22 and the strength of the polarizing magnetic layer 20. The polarizing magnetic layer 20 generally has a perpendicular anisotropy, H k, of -0.1 T to 1 T. The polarizing magnetic layer 20 may have a thickness of 0.5 nm to 3 nm; however, other thicknesses may be used for the polarizing magnetic layer 20.Each of the first bonding layer 18 and the second bonding layer 14 may be made of a non-magnetic metal-containing material, for example, tantalum (Ta), tungsten (W), ruthenium (Ru), iridium (Ir), or an alloy of tantalum-iron (Ta-Fe). According to the present invention, the first bonding layer 18 is disposed between the polarizing magnetic layer 20 and the first reference magnetic layer 16, while the second bonding layer 14 is disposed between the first reference magnetic layer 16 and the second reference magnetic layer 12. Both the first bonding layer 18 and the second bonding layer 14 may have a thickness of 0.4 nm to 1 nm; however, other thicknesses may be used for both the first bonding layer 18 and the second bonding layer 14.Both the first magnetic reference layer 16 and the second magnetic reference layer 12 have a fixed magnetization. Each of the first magnetic reference layer 16 and the second magnetic reference layer 12 may be made of cobalt / nickel (Co / Ni), cobalt / platinum (Co / Pt), cobalt / palladium (Co / Pd), cobalt (Co), nickel (Ni), platinum (Pt), palladium (Pd), or any multilayer stack thereof. In some embodiments, the first magnetic reference layer 16 and the second magnetic reference layer 12 are made of a magnetic material having the same composition. In other embodiments, the first magnetic reference layer 16 is made of a magnetic material different in composition from that of the second magnetic reference layer 12. The thickness of the first magnetic reference layer 16 and the second magnetic reference layer 12 may be between 0.2 nm and 1 nm.The first magnetic reference layer 16 generally has a perpendicular anisotropy, H k, of 0 T to 1 T. In the present application, the perpendicular anisotropy of the first reference magnetic layer 16 substantially matches (within ±10%) the perpendicular anisotropy of the polarizing magnetic layer 20. By substantially matching the perpendicular anisotropy of the first reference magnetic layer 16 and the polarizing magnetic layer 20, the resonant frequency peaks of these layers substantially match.The second magnetic reference layer 12 generally has a perpendicular anisotropy, H k, of 0 T to 1 T. In some embodiments of the present application, the perpendicular anisotropy of the second reference magnetic layer 12 substantially matches (within ±10%) the perpendicular anisotropy of both the first reference magnetic layer 16 and the polarizing magnetic layer 20. In such an embodiment, the resonant frequency peak of the polarizing magnetic layer 20 substantially overlaps the resonant frequency peak of both the first and second reference magnetic layers.In some embodiments, and to increase the overlap of the resonant frequency peaks of the polarizing magnetic layer 20 and the first reference magnetic layer 16, the first reference magnetic layer 16 may include a rare earth element incorporated therein. Rare earth elements include cerium (Ce), dysprosium (Dy), erbium (Er), europium (Eu), gadolinium (Gd), holmium (Ho), lanthanum (La), lutetium (Lu), neodymium (Nd), praseodymium (Pr), promethium (Pm), samarium (Sm), scandium (Sc), terbium (Tb), thulium (Tm), ytterbium (Yb), and yttrium (Y). In some embodiments, incorporating a rare earth element comprises a discrete layer containing a rare earth element and disposed within the first magnetic reference layer 16. In other embodiments, incorporating a rare earth element includes doping the first reference magnetic layer 16 with a rare earth element. In some embodiments, when a rare earth element is present in the first reference magnetic layer 16, the first reference magnetic layer 16 including the rare earth element may have an attenuation value, α, of 0.0001 to 1.In some embodiments, the second magnetic reference layer 12 may include incorporating rare earth elements. In some embodiments, both the first magnetic reference layer 16 and the second magnetic reference layer 12 include the rare earth incorporation. In some embodiments, when a rare earth element is present in the second reference magnetic layer 12, the second reference magnetic layer 12 including the rare earth element may have an attenuation value, α, of 0.0001 to 1.The stable resonant SAF reference layer structure 10 can be integrated into the bipolar magnetic tunnel junction design by adjusting the material properties of the first magnetic reference layer 16. In order to improve stability, the resonant frequency of the first magnetic reference layer 16 must be substantially matched to the polarizing magnetic layer 20. If the resonant frequency of the polarizing magnetic layer (ωPL) and the resonant frequency of the first reference magnetic layer (ωRL) are not approximately equal, the spin current excitations are confined to the polarizing magnetic layer 20. A sufficiently large spin current excitation results in a reversal of this polarizing magnetic layer 20. The total energy supplied to the polarizing magnetic layer 20 is reduced, resulting in less spin current excitation of the polarizing magnetic layer 20.The resonant frequency of the polarizing magnetic layer 20 and the first reference magnetic layer 16 is linearly dependent on the energy of the perpendicular anisotropy. The perpendicular anisotropy of the first magnetic reference layer 16 is generated at the material interfaces. The total anisotropy energy generated at the interface is then distributed to the entire polarizing magnetic layer 20, which means that the total energy and the resonant frequency can be adjusted by changing the thickness of the first reference magnetic layer 16 within the above-mentioned thickness range. By optimizing the thicknesses of these layers, matching of the resonant frequencies of the polarizing magnetic layer 20 and the first reference magnetic layer 16 can be achieved.There is some degree of resonant frequency mismatch between the polarizing magnetic layer 20 and the first reference magnetic layer 16, whereby the desired effect can be observed.The excitation frequency of a precessional magnetic moment is not a single discrete value. Rather, it comprises a frequency range whose extent is determined by the magnetic damping in the material. Below, the excitation amplitude is shown as a function of frequency. When the two resonant frequencies are separated, there is no overlap of the two peaks; see, for example, FIG. 3A. When the resonant frequencies are close to each other, the peaks overlap; see, for example, FIG. 3B. In this case, there may be resonance between the polarizing magnetic layer 20 and the first reference magnetic layer 16.For the present application to work, the resonant line of the polarizing magnetic layer must overlap significantly the remainder of the linewidth of the first reference magnetic layer. In addition to adjusting the resonant center frequency, the first magnetic reference layer 16 may also be configured to increase the magnetic attenuation characteristics. In one embodiment, as mentioned above, increased magnetic attenuation of the first magnetic reference layer 16 may be achieved by incorporating rare earth elements into the first magnetic reference layer 16. In the simple collinear geometry, the line width of the ferromagnetic resonance is directly proportional to the magnetic attenuation constant of the material used. As shown in FIG. 4, as the attenuation α is increased, the width of the resonance peak increases, thereby enabling a larger overlap area.The effectiveness of this embodiment is illustrated by numerical simulations using the macrospin model. The model is based on the Landau-Lifshitz-Gilbert equation: where n m1 is the direction vector of the magnetic free layer and n m2 is the direction vector of the polarising magnetic layer. J s represents the spin current, H k the perpendicular anisotropy field, α the attenuation, t the layer thickness, and M s the saturation magnetization. E ex represents the interactive bonding energy between the layers. Additional equations for the first and second magnetic reference layers are included, but not shown here.First, a structure (according to the prior art) in which the reference magnetic layer and the polarizing magnetic layer have different resonant frequencies (different H k) with the following parameters was simulated as shown in Table 1: Table 1:Magnetic free layer0,40,0056001,5Polarizing magnetic layer0,10,01210001First Magnetic Reference Layer0,50,0310002,5Second Magnetic Reference Layer0,50,0310003Reference is now made to Figures 5A-5B, which are diagrams showing the magnetization direction, M, as a function of time, ns, for the magnetic free layer (Figure 5A) and the polarizing magnetic layer (Figure 5B) in a prior art MTJ column in which the resonant frequencies of the polarizing magnetic layer and the reference magnetic layers do not match; Figures 5A-5B are based on the parameters shown in Table 1 above. The z component of magnetization, M z, determines the state in which the device is located. In this simulation, the magnetic free layer changes after a few nanoseconds. Shortly thereafter, excitations are induced in the polarizing magnetic layer, which then reverses and causes a write error.Subsequently, another structure (according to the present application) was simulated in which the reference magnetic layer and the polarizing magnetic layer have substantially matching resonant frequencies (different H k) with the following parameters, as shown in Table 2: Table 2:Magnetic free layer0,40,0056001,5Polarizing magnetic layer0,10,01210001First Magnetic Reference Layer0,110,0310002,5Second Magnetic Reference Layer0,110,0310003Reference is now made to Figures 6A-6B, which are diagrams showing the magnetization direction, M, as a function of time, ns, for the magnetic free layer (Figure 6A) and the polarizing magnetic layer (Figure 6B) in an MTJ column in which the resonant frequencies of the polarizing magnetic layer and the reference magnetic layers substantially match; Figures 6A-6B are based on the parameters shown in Table 2 above. In this simulation, the magnetic free layer was changed (FIG. 6A ) without errors. If the resonant frequencies of the polarizing magnetic layer (FIG. 6B ) and at least the first reference magnetic layer match (in this simulation, the resonant frequencies of the polarizing magnetic layer and the first and second magnetic references substantially match), current-induced excitations of the polarizing magnetic layer are reduced. The connected magnetic reference layers also employ excitations, but of lower amplitude, for the polarising magnetic layer. This distribution of energy over the entire structure improves overall stability. By further tuning the material parameters, for example by damping, the structure can be further stabilized.

Claims

A magnetic storage device comprising: a magnetic tunnel junction pillar comprising a tunnel barrier layer (22) disposed between a synthetic reference antiferromagnetic layer structure (10) and a magnetic free layer (24), the synthetic reference antiferromagnetic layer structure having a polarizing magnetic layer (20) magnetically interactively connected to a stack of reference magnetic layers comprising a first reference magnetic layer (16) and a second reference magnetic layer (12), the polarizing magnetic layer (20) interfacing with the tunnel barrier layer (22) and having a ferromagnetic resonant frequency peak substantially overlapping a ferromagnetic resonant frequency peak of at least the first reference magnetic layer (16).The magnetic storage device of claim 1, wherein the ferromagnetic resonant frequency peak of the polarizing magnetic layer (20) substantially overlaps the resonant frequency peaks of both the first (16) and second reference magnetic layers (12).The magnetic storage unit of claim 1 or claim 2, wherein the first magnetic reference layer (16) is antiferromagnetically interactively connected to the second magnetic reference layer (12).The magnetic storage device of claim 3, wherein a first bonding layer (18) separates the polarizing magnetic layer (20) from the first reference magnetic layer (16) and a second bonding layer (14) separates the first reference magnetic layer (16) from the second reference magnetic layer (12).The magnetic storage unit according to any one of the preceding claims, wherein the magnetic tunnel junction pillar is a top pinned magnetic tunnel junction pillar in which the magnetic free layer (24) is disposed above the synthetic reference antiferromagnetic layer structure (10).The magnetic storage unit according to any one of claims 1 to 4, wherein the magnetic tunnel junction pillar is a bottom pinned magnetic tunnel junction pillar in which the magnetic free layer (24) is disposed below the reference synthetic antiferromagnetic layer structure (10).The magnetic storage unit according to any one of the preceding claims, wherein the polarizing magnetic layer (20) is made of an alloy of cobalt-iron-boron, an alloy of cobalt-iron, iron, cobalt, or multilayer stacks thereof, and has a thickness of 0.5 nm to 3 nm.The magnetic storage unit according to claim 1, wherein the first magnetic reference layer (16) and the second magnetic reference layer (12) are made of cobalt / nickel, cobalt / platinum, cobalt / palladium, cobalt, nickel, platinum, palladium, or multilayer stacks thereof and have a thickness of 0.2 nm to 1 nm.The magnetic storage unit according to claim 7, wherein the first reference magnetic layer (16) comprises a rare earth element incorporated therein and has a magnetic attenuation value of 0.0001 to 1.The magnetic memory device of claim 1, wherein the polarizing magnetic layer (20) has a perpendicular anisotropy, Hk, of -0.1 T to 1 T and the first reference magnetic layer (16) has a perpendicular anisotropy, Hk, of 0 T to 1 T, and the perpendicular anisotropy of the polarizing magnetic layer (20) substantially matches the perpendicular anisotropy of the first reference magnetic layer (16).

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