Resonant Synthesis of Antimagnetic Body Reference Layer Structure

Abstract

The magnetic memory device includes a magnetic tunnel junction (MTJ) pillar including a stable resonating synthetic antiferromagnet (SAF) reference layer structure, wherein ferromagnetic resonance characteristics of a polarized magnetic layer of the SAF reference layer structure are substantially matched to at least a first magnetic reference layer in the SAF reference layer structure. By substantially matching the ferromagnetic resonance characteristics of the polarized magnetic layer to the at least the first magnetic reference layer, the dynamic stability of the polarized magnetic layer may be improved, and write errors associated with undesired magnetic reference layer instability may be mitigated for the MTJ pillar.

Description

[Technical Field]

[0001] The present invention relates to magnetic memory in general, and more particularly to a magnetic memory device including a magnetic tunnel junction (MTJ) pillar having a stable resonant composite antiferromagnetic (SAF) reference layer structure. [Background technology]

[0002] Magnetic tunnel junction (MTJ) pillars are potential candidates for non-volatile memory applications. Devices containing MTJ pillars store information about the magnetization of the magnetic free layer. By passing an electric current through the MTJ pillar, which includes the magnetic free layer, tunnel barrier layer, and polarization layer, state switching and reading are achieved. The larger the current flowing, the faster the bits switch. However, if the write current is too large, the polarization layer may also switch, causing a "flip-flop" motion between the magnetic free layer and the top of the polarization layer, resulting in a write error.

[0003] To stabilize the polarization magnetic layer, it is exchange-coupled with a stack of highly anisotropic magnetic reference layers to support it. Such a structure is sometimes called a synthetic antiferromagnet (SAF) reference layer structure. In static tests, this structure can enhance stability. However, under dynamic conditions with large spin currents (such as when the MTJ pillar is biased with a high voltage), in conventional SAF reference layer designs, undesirable spin current excitations in the magnetic reference layer often localize to the polarization magnetic layer only. [Overview of the project]

[0004] Embodiments of the present invention provide a magnetic memory device comprising a magnetic tunnel junction (MTJ) pillar including a stable resonant composite antiferromagnet (SAF) reference layer structure in which the ferromagnetic resonance characteristics of the polarizing magnetic layer of the SAF reference layer structure substantially match those of at least a first magnetic reference layer within the SAF reference layer structure. The “first magnetic reference layer” of the SAF reference layer structure is a magnetic reference layer directly coupled to the polarizing magnetic layer via a first coupling layer. By substantially matching the ferromagnetic resonance characteristics of the polarizing magnetic layer to those of at least a first magnetic reference layer, an MTJ pillar is provided in which the dynamic stability of the polarizing magnetic layer may be improved, and write errors associated with undesirable magnetic reference layer instability may be mitigated.

[0005] According to one aspect of the present invention, a magnetic memory device includes an MTJ pillar comprising a tunnel barrier layer sandwiched between a synthetic antiferromagnetic (SAF) reference layer structure and a magnetic free layer. The SAF reference layer structure includes a polarization magnetic layer exchange-coupled to a stack of magnetic reference layers, including a first magnetic reference layer and a second magnetic reference layer. The polarization magnetic layer forms an interface with the tunnel barrier layer and has a resonance frequency peak that substantially overlaps with the resonance frequency peak of at least the first magnetic reference layer. In some embodiments, the resonance frequency peak of the polarization magnetic layer may substantially overlap with the resonance frequency peaks of both the first and second magnetic reference layers.

[0006] In another embodiment, the magnetic memory device includes an MTJ pillar comprising a tunnel barrier layer sandwiched between a synthetic antiferromagnetic (SAF) reference layer structure and a magnetic free layer. The SAF reference layer structure includes a polarizing magnetic layer exchange-coupled to a stack of magnetic reference layers, which includes a first magnetic reference layer and a second magnetic reference layer. According to the present application, both the polarizing magnetic layer and the first magnetic reference layer have spin current excitations present therein. In some embodiments, the polarizing magnetic layer and the first and second magnetic reference layers all have spin current excitations present therein.

[0007] In any embodiment of the present application, the first magnetic reference layer is antiferromagnetically exchanged coupled with the second magnetic reference layer. In the present invention, the first coupling layer separates the polarization magnetic layer from the first magnetic reference layer, and the second coupling layer separates the first magnetic reference layer from the second magnetic reference layer.

[0008] In some embodiments, the MTJ pillar is an upper-mounted MTJ pillar having a magnetic free layer located above the SAF reference layer structure, and in other embodiments, the MTJ pillar is an lower-mounted MTJ pillar having a magnetic free layer located below the SAF reference layer structure.

[0009] In some embodiments of the present application, the polarization magnetic layer consists of a cobalt-iron-boron (Co-Fe-B) alloy, a cobalt-iron (Co-Fe) alloy, iron (Fe), cobalt (Co), or a multilayer stack thereof, and has a thickness of 0.5 nm to 3 nm. In some embodiments, the polarization magnetic layer has perpendicular anisotropy H of -1 kOe to 10 kOe. K It holds.

[0010] In some embodiments of the present application, the first and second magnetic reference layers consist of cobalt / nickel (Co / Ni), cobalt / platinum (Co / Pt), cobalt / palladium (Co / Pd), cobalt (Co), nickel (Ni), platinum (Pt), palladium (Pd), or a multilayer stack thereof, and have a thickness of 0.2 nm to 1 nm. In some embodiments, the first magnetic reference layer has a perpendicular anisotropy of 0 kOe to 10 kOe. K The first magnetic reference layer has a perpendicular anisotropy that substantially coincides with the perpendicular anisotropy of the polarizing magnetic layer.

[0011] In some embodiments, and to increase the overlap of the resonant frequency peaks between the polarization magnetic layer and the first magnetic reference layer, the first magnetic reference layer includes an inserted rare earth element therein. In such embodiments, the first magnetic reference layer including the inserted rare earth element has an attenuation value of 0.0001 to 1. [Brief explanation of the drawing]

[0012] [Figure 1A] This is a cross-sectional view of an MTJ pillar according to one embodiment of the present application. [Figure 1B] This is a cross-sectional view of an MTJ pillar according to another embodiment of the present application. [Figure 2A] This figure shows the magnetic moment vector processing around the stationary axis when the resonant frequency (ωPL) of the polarization magnetic layer is not equal to the resonant frequency (ωRL) of the first magnetic reference layer. [Figure 2B] This figure shows the magnetic moment vector processing around the stationary axis when the resonant frequency (ωPL) of the polarization magnetic layer is substantially equal to the resonant frequency (ωRL) of the first magnetic reference layer. [Figure 3A] This is a graph of excitation amplitude versus frequency (ω) when the resonant frequency (ωPL) of the polarization magnetic layer is not equal to the resonant frequency (ωRL) of the first magnetic reference layer. [Figure 3B] This is a graph of excitation amplitude versus frequency (ω) when the resonant frequency (ωPL) of the polarization magnetic layer is substantially equal to the resonant frequency (ωRL) of the first magnetic reference layer. [Figure 4] This is a graph of excitation amplitude versus frequency (ω) in one embodiment in which the magnetic damping characteristics of the first magnetic reference layer are enhanced to widen the resonance peak and increase the overlap between the two peaks. [Figure 5A] This plot shows the magnetization direction M of the magnetic free layer as a function of time ns in a prior art MTJ pillar where the resonant frequencies of the polarized magnetic layer and the magnetic reference layer do not coincide. [Figure 5B] This plot shows the magnetization direction M of the free polarization layer as a function of time ns in a prior art MTJ pillar where the resonant frequencies of the polarized magnetic layer and the magnetic reference layer do not coincide. [Figure 6A] This plot shows the magnetization direction M of the magnetic free layer as a function of time ns in the MTJ pillar of the present invention, where the resonant frequencies of the polarizing magnetic layer and the magnetic reference layer substantially coincide. [Figure 6B] This plot shows the magnetization direction M of the polarization free layer as a function of time ns in the MTJ pillar of the present invention, where the resonance frequencies of the polarization magnetic layer and the magnetic reference layer substantially coincide.

Best Mode for Carrying Out the Invention

[0013] Next, the present application will be described in more detail by referring to the following discussion and the drawings attached to the present application. Note that the drawings of the present application are provided for the purpose of illustration only, and thus, it should be noted that the drawings are not drawn to scale. Also, note that similar elements and corresponding elements are referred to by similar reference numerals.

[0014] In the following description, numerous specific details, such as specific structures, components, materials, dimensions, processing steps, and techniques, are set forth in order to provide an understanding of the various embodiments of the present application. However, it will be understood by those skilled in the art 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.

[0015] When an element as a layer, region, or substrate is referred to as being "on" or "over" another element, it will be understood that it can be directly on the other element or intervening elements may be present. In contrast, when an element is referred to as being "directly on" or "directly over" another element, no intervening elements are present. Also, when an element is referred to as being "beneath" or "under" another element, it will be understood that it can be directly beneath or directly under the other element or intervening elements may be present. In contrast, when an element is referred to as being "directly beneath" or "directly under" another element, no intervening elements are present.

[0016] As described above, the present application provides, for example, a magnetic memory device such as a magnetic random access memory (MRAM), and the magnetic memory device includes a MTJ pillar including a stable resonant SAF reference layer structure in which the ferromagnetic resonance characteristics of the polarized magnetic layer of the SAF reference layer structure substantially coincide with at least a first magnetic reference layer in the SAF reference layer structure. The "first magnetic reference layer" of the SAF reference layer structure is a magnetic reference layer directly coupled to the polarized magnetic layer via a first coupling layer. By substantially matching the ferromagnetic resonance characteristics of the polarized layer to at least the first magnetic reference layer, the dynamic stability of the polarized magnetic layer can be improved, and a MTJ pillar that can mitigate write errors associated with the instability of the undesirable magnetic reference layer is provided. It should be noted that when the layers of such a stable resonant SAF reference layer structure resonate, energy can be pulled away from the polarized magnetic layer, and as a result, write errors can be reduced and, in some cases, even eliminated.

[0017] First, refer to FIGS. 1A-1B showing various MTJ pillars according to different embodiments of the present invention. The MTJ pillar shown in FIG. 1A can be referred to as a bottom-fixed MTJ pillar, and the MTJ pillar shown in FIG. 1B can be referred to as a top-fixed MTJ pillar.

[0018] Each MTJ pillar shown in Figures 1A-1B includes a magnetic free layer 24, a tunnel barrier layer 22, and a stable resonant SAF reference layer structure 10. The term "stable resonant SAF reference layer structure" means that the SAF reference layer structure is designed such that the ferromagnetic resonance characteristics of the polarized magnetic layer of the stable resonant SAF reference layer structure substantially match those of at least one first magnetic reference layer within the stable resonant SAF reference layer structure 10. In some embodiments, the ferromagnetic resonance characteristics of the polarized magnetic layer of the stable resonant SAF reference layer structure substantially match those of each of the magnetic reference layers present within the SAF reference layer structure 10. In this application, the SAF reference layer structure is designed such that the resonant frequency peak of the polarized magnetic layer substantially overlaps with the resonant frequency peak of at least one first magnetic reference layer within the SAF reference layer structure. The resonant frequency peak can be determined by magnetization, shape, anisotropic magnetic field, and internal magnetic field. A substantially overlapping resonant frequency peak is one in which a portion of one peak coincides with a portion of another peak.

[0019] The stable resonant SAF reference layer structure 10 includes a polarizing magnetic layer 20 that forms an interface with the tunnel barrier layer 22. In the MTJ pillar shown in Figures 1A-1B, information is stored on the magnetic free layer 24 and referenced to the polarizing magnetic layer 20 across the tunnel barrier layer 22. To enhance the stability of the polarizing magnetic layer 20, it is coupled to a first magnetic reference layer 16 via a first coupling layer 18. The first magnetic reference layer 16 is antiferromagnetic exchange coupled to a second magnetic reference layer 12, and the second coupling layer 14 is positioned between the first magnetic reference layer 16 and the second magnetic reference layer 12. Additional magnetic reference layers and coupling layers may be present in the MTJ pillar of this application.

[0020] In Figures 1A and 1B, the double-headed arrows on the magnetic free layer 24 indicate that the magnetization direction of that layer can be switched, while the single-headed arrows on the polarizing magnetic layer 20, the first magnetic reference layer 16, and the second magnetic reference layer 12 indicate that the magnetization direction of those layers is fixed. The MTJ pillars shown in Figures 1A and 1B are typically located in the back end (BEOL) and are sandwiched between an upper electrode (not shown) and a lower electrode (also not shown). The lower electrode is typically located on the surface of a conductive structure (also not shown). The conductive structure is embedded in an interconnect dielectric material layer (also not shown). Another interconnect dielectric material layer (also not shown) can embed the MTJ pillars shown in Figures 1A and 1B. Another conductive structure (also not shown) can be located on the upper electrode.

[0021] The MTJ pillars shown in Figures 1A-1B can be formed by first depositing a material stack containing each of the material layers present in the MTJ pillar, and then subjecting the material stack to a patterning process. The deposition of the material stack can include chemical vapor deposition (CVD), plasma CVD (PECVD), or sputtering physical vapor deposition (PVD). In some embodiments of this application, the same deposition process can be used to form each layer of the material stack. In other embodiments, at least two different deposition processes can be used to form the material stack. Patterning of the material stack can include photolithography and etching. Etching can include at least one of reactive ion etching (RIE), ion beam etching (IBE), or plasma etching.

[0022] The formed MTJ pillar can have various shapes, including, for example, a cylindrical shape. The critical dimension (CD) of the MTJ pillar is variable and not important to the present application. In some embodiments, the CD of the MTJ pillar is equal to the CD of the lower electrode. In other embodiments, the CD of the MTJ pillar is greater than the CD of the lower electrode. In yet another embodiment of the present application, the CD of the MTJ pillar is less than the CD of the lower electrode.

[0023] The magnetic free layer 24 is composed of at least one magnetic material having a magnetization that can change its orientation relative to the magnetization orientation of the polarization magnetic layer 20 present in the SAF reference layer structure 10. Exemplary magnetic materials for the magnetic free layer 24 include alloys, multilayer films, or both of the following: cobalt (Co), iron (Fe), cobalt-iron (Co-Fe) alloys, nickel (Ni), nickel-iron (Ni-Fe) alloys, and cobalt-iron-boron (Co-Fe-B) alloys. The magnetic free layer 24 that can be used in this application may have a thickness of 1 nm to 3 nm, but other thicknesses of the magnetic free layer 24 can also be used. By passing an electric current through the MTJ pillar, the magnetic state of the magnetic free layer 24 can be switched to either an up state or a down state. The polarization magnetic layer 20 generates a polarization spin current, which acts a switching torque on the magnetic free layer 24.

[0024] The tunnel barrier layer 22 is composed of an insulating material and is formed to a thickness that provides appropriate tunnel resistance. Exemplary materials for the tunnel barrier layer 22 include magnesium oxide, aluminum oxide, and titanium oxide, or materials with higher electrical tunnel conductance, such as semiconductors or low bandgap insulators. In one embodiment, magnesium oxide is used as the material providing the tunnel barrier layer 22. The thickness of the tunnel barrier layer 22 can be 0.5 nm to 1.5 nm, but other thicknesses of the tunnel barrier layer 22 can be used as long as the selected thickness provides the desired tunnel barrier resistance. The tunnel barrier layer 22 forms a first interface with the magnetic free layer 24 and a second interface with the polarizing magnetic layer 20 of the stable resonant SAF reference layer structure 10, which is on the opposite side of the first interface.

[0025] The polarization magnetic layer 20 is composed of a magnetic material that enhances the polarization of the spin torque current by enhancing the coherent tunnel through the interface with the tunnel barrier layer 22. Exemplary magnetic materials that can be used as the polarization magnetic layer 20 include, but are not limited to, cobalt-iron-boron (Co-Fe-B) alloys, cobalt-iron (Co-Fe) alloys, iron (Fe), cobalt (Co), or any multilayer stacks thereof. The perpendicular anisotropy of the polarization magnetic layer 20 is determined by the interface with the tunnel barrier layer 22 and the thickness of the polarization magnetic layer 20 itself. The polarization magnetic layer 20 typically has a perpendicular anisotropy of -1kOe to 10kOe. K The polarization magnetic layer 20 can have a thickness of 0.5 nm to 3 nm, but other thicknesses of the polarization magnetic layer 20 can also be used.

[0026] The first bonding layer 18 and the second bonding layer 14 can both be composed of a non-magnetic metal-containing material, such as tantalum (Ta), tungsten (W), ruthenium (Ru), iridium (Ir), or a tantalum-iron (Ta-Fe) alloy. According to the present invention, the first bonding layer 18 is sandwiched between the polarization magnetic layer 20 and the first magnetic reference layer 16, and the second bonding layer 14 is sandwiched between the first magnetic reference layer 16 and the second magnetic reference layer 12. Both the first bonding layer 18 and the second bonding layer 14 can have a thickness of 0.4 nm to 1 nm, but other thicknesses can also be used for both the first bonding layer 18 and the second bonding layer 14.

[0027] Both the first magnetic reference layer 16 and the second magnetic reference layer 12 have fixed magnetization. Both the first magnetic reference layer 16 and the second magnetic reference layer 12 can be composed 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 composed of the same magnetic material. In other embodiments, the first magnetic reference layer 16 is composed of a different magnetic material from the second magnetic reference layer 12. The thickness of both the first magnetic reference layer 16 and the second magnetic reference layer 12 can be 0.2 nm to 1 nm.

[0028] The first magnetic reference layer 16 typically has a perpendicular anisotropy H of 0kOe to 10kOe. K In this application, the perpendicular anisotropy of the first magnetic reference layer 16 substantially matches (within ±10%) the perpendicular anisotropy of the polarization magnetic layer 20. By substantially matching the perpendicular anisotropy of the first magnetic reference layer 16 and the polarization magnetic layer 20, the resonant frequency peaks of these layers substantially coincide with each other.

[0029] The second magnetic reference layer 12 typically has a perpendicular anisotropy H of 0kOe to 10kOe. K In some embodiments of the present application, the perpendicular anisotropy of the second magnetic reference layer 12 substantially matches (within ±10%) the perpendicular anisotropy of both the first magnetic reference layer 16 and the polarization magnetic layer 20. In one such embodiment, the resonant frequency peak of the polarization magnetic layer 20 substantially overlaps with the resonant frequency peaks of both the first and second magnetic reference layers.

[0030] In some embodiments, the first magnetic reference layer 16 may also contain inserted rare earth elements in order to increase the overlap of the resonant frequency peaks of the polarizing magnetic layer 20 and the first magnetic reference layer 16. Examples of 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, the insertion of rare earth elements includes discrete rare earth element-containing layers located within the first magnetic reference layer 16. In other embodiments, the insertion of rare earth elements includes doping the first magnetic reference layer 16 with rare earth elements. In some embodiments, and when rare earth elements are present in the first magnetic reference layer 16, the first magnetic reference layer 16 containing the rare earth elements may have a decay value α of 0.0001 to 1.

[0031] In some embodiments, the second magnetic reference layer 12 may include insertions of rare earth elements. In some embodiments, both the first magnetic reference layer 16 and the second magnetic reference layer 12 include insertions of rare earth elements. In some embodiments, and when rare earth elements are present in the second magnetic reference layer 12, the second magnetic reference layer 12 containing the rare earth elements may have a decay value α of 0.0001 to 1.

[0032] A stable resonant SAF reference layer structure 10 can be implemented in the fabrication of a two-terminal magnetic tunnel junction by adjusting the material properties of the first magnetic reference layer 16. To improve stability, the resonant frequency of the first magnetic reference layer 16 needs to substantially match that of the polarization magnetic layer 20. If the resonant frequency (ωPL) of the polarization magnetic layer and the resonant frequency (ωRL) of the first magnetic reference layer are not equal, spin current excitations are confined to the polarization magnetic layer 20. This conceptually illustrates the magnetic moment vector processing around the stationary axis in Figure 2A. Sufficiently large spin current excitations result in the inversion of this polarization magnetic layer 20. If the resonant frequencies are equal, the spin current excitations spread to the first magnetic reference layer 16, which is conceptually illustrated in Figure 2B. The total energy deposited in the polarization magnetic layer 20 decreases, and as a result, the spin current excitations in the polarization magnetic layer 20 become lower.

[0033] The resonance frequencies of the polarization magnetic layer 20 and the first magnetic reference layer 16 depend linearly on the perpendicular anisotropy energy. The perpendicular anisotropy of the first magnetic reference layer 16 is generated at the material interface. The total anisotropy energy generated at the interface is distributed to the bulk of the polarization magnetic layer 20, meaning that the total energy and resonance frequency can be adjusted by changing the thickness of the first magnetic reference layer 16 within the specified thickness range. By optimizing the thickness of these layers, the condition for matching the resonance frequencies of the polarization magnetic layer 20 and the first magnetic reference layer 16 can be achieved.

[0034] There is a mismatch in resonant frequencies between the polarization magnetic layer 20 and the first magnetic reference layer 16 to the extent that the desired effect is observed.

[0035] The excitation frequency of the processed magnetic moment is not a single, independent value. Rather, it spans a frequency range with a width determined by the magnetic decay of the material. Below, the excitation frequency is expressed as a function of frequency. When the two resonance frequencies are separated, there is no overlap of the two peaks (see, for example, Figure 3A). When the resonance frequencies are close together, the peaks overlap (see, for example, Figure 3B). In this situation, resonance can occur between the polarization magnetic layer 20 and the first magnetic reference layer 16.

[0036] The requirement for the present application to operate is that the resonance line of the polarized magnetic layer largely overlaps with the remaining linewidth of the first magnetic reference layer. In addition to adjusting the resonance center frequency, the first magnetic reference layer 16 can also be designed to increase the magnetic damping characteristics. In one embodiment, and as described above, the increased magnetic damping of the first magnetic reference layer 16 can be obtained by inserting rare earth elements into the first magnetic reference layer 16. In a simple collinear geometry, the linewidth of ferromagnetic resonance is directly proportional to the magnetic damping constant of the material used. As shown in FIG. 4, increasing the damping α increases the width of the resonance peak, allowing for a wider range of overlap.

[0037] To demonstrate the effectiveness of this design, numerical simulations are performed using the macrospin model. This model is based on the Landau-Lifshitz-Gilbert equation. TIFF2023548888000002.tif56150Here, n m1 is the magnetic free layer direction vector, n m2 is the polarized magnetic layer direction vector. J s is the spin current, H k is the perpendicular anisotropy magnetic field, α is the damping, t is the layer thickness, M s represents the saturation magnetization. E ex represents the interlayer exchange coupling energy. Additional equations for the first and second magnetic reference layers are included but not shown here.

[0038] First, a structure (according to the prior art) in which the magnetic reference layer and the polarized magnetic layer have different resonance frequencies (H k is different) was simulated with the following parameters as shown in Table 1.

[0039]

Table 1

[0040] Here, Figures 5A and 5B are referenced, which are plots showing the magnetization direction M as a function of time ns for the magnetic free layer (Figure 5A) and the polarized magnetic layer (Figure 5B) in a prior art MTJ pillar where the resonant frequencies of the polarized magnetic layer and the magnetic reference layer do not match. Figures 5A and 5B are based on the parameters shown in Table 1 above. Magnetization M z The z component determines the state of the device. In this simulation, the magnetic free layer switches after a few nanoseconds. Immediately afterward, excitation begins in the polarizing magnetic layer, followed by inversion and a write error.

[0041] Next, the resonant frequency (H) at which the magnetic reference layer and the polarization magnetic layer substantially coincide. k Another structure (according to the present application) having different properties was simulated with the following parameters as shown in Table 2.

[0042] [Table 2]

[0043] Next, Figures 6A and 6B are referenced, which are plots showing the magnetization direction M as a function of time ns for the magnetic free layer (Figure 6A) and the polarized magnetic layer (Figure 6B) in an MTJ pillar where the resonant frequencies of the polarized magnetic layer and the magnetic reference layer substantially coincide. Figures 6A and 6B are based on the parameters shown in Table 2 above. In this simulation, switching of the magnetic free layer (Figure 6A) occurred without error. When the resonant frequencies of the polarized magnetic layer (Figure 6B) and at least the first magnetic reference layer coincide (in this simulation, the resonant frequencies of the polarized magnetic layer and the first and second magnetic references all substantially coincide), current-driven excitation of the polarized magnetic layer decreases. Excitation also begins to occur in the coupled magnetic reference layer, but the amplitude of the polarized magnetic layer decreases. In this way, energy is distributed throughout the entire structure, improving overall stability. The structure can be further stabilized by further tuning material parameters such as damping.

[0044] While this application has been shown and described in particular with respect to its preferred embodiments, it will be understood by those skilled in the art that the aforementioned and other modifications in form and detail can be made without departing from the scope of this application. Accordingly, this application is not intended to be limited to the exact form and detail described and illustrated, but rather to fall within the scope of the appended claims.

Claims

1. a MTJ pillar including a tunnel barrier layer sandwiched between a synthetic antiferromagnet (SAF) reference layer structure and a magnetic free layer, the SAF reference layer structure including a polarized magnetic layer exchange-coupled to a stack of magnetic reference layers including a first magnetic reference layer and a second magnetic reference layer, the polarized magnetic layer forming an interface with the tunnel barrier layer and having a resonant frequency peak that substantially overlaps with at least a resonant frequency peak of the first magnetic reference layer; Magnetic memory device.

2. The magnetic memory device of claim 1 , wherein the resonant frequency peak of the polarized magnetic layer substantially overlaps with the resonant frequency peaks of both the first and second magnetic reference layers.

3. 3. The magnetic memory device according to claim 1, wherein the first magnetic reference layer is antiferromagnetically exchange-coupled with the second magnetic reference layer.

4. The magnetic memory device of claim 3 , wherein a first coupling layer separates the polarizing magnetic layer from a first magnetic reference layer, and a second coupling layer separates the first magnetic reference layer from the second magnetic reference layer.

5. 5. The magnetic memory device according to claim 1, wherein the MTJ pillar is a top-pin MTJ pillar having the magnetic free layer located under the SAF reference layer structure.

6. 5. The magnetic memory device according to claim 1, wherein the MTJ pillar is a bottom-pinned MTJ pillar having the magnetic free layer located above the SAF reference layer structure.

7. 7. The magnetic memory device according to claim 1, wherein 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 a multi-layer stack thereof and has a thickness of 0.5 nm to 3 nm.

8. 2. The magnetic memory device of claim 1, wherein 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 a multi-layer stack thereof and have a thickness of 0.2 nm to 1 nm.

9. 8. The magnetic memory device of claim 7, wherein the first magnetic reference layer includes a rare earth element intercalated therein and has a damping value between 0.0001 and 1.

10. The polarizing magnetic layer has a perpendicular anisotropy H of −1 kOe to 10 kOe. Ｋ The first magnetic reference layer has a perpendicular anisotropy H of 0 kOe to 10 kOe. Ｋ 2. The magnetic memory device of claim 1, wherein the perpendicular anisotropy of the polarizing magnetic layer substantially matches the perpendicular anisotropy of the first magnetic reference layer.

11. and an MTJ pillar including a tunnel barrier layer sandwiched between a synthetic antiferromagnet (SAF) reference layer structure and a magnetic free layer, the SAF reference layer structure including a polarized magnetic layer exchange-coupled to a stack of magnetic reference layers including a first magnetic reference layer and a second magnetic reference layer, both of the polarized magnetic layer and the first magnetic reference layer having spin current excitations present therein. Magnetic memory device.

12. The magnetic memory device of claim 11 , wherein the polarized magnetic layer and the first and second magnetic reference layers each have a spin current excitation present therein.

13. 13. The magnetic memory device according to claim 11, wherein the first magnetic reference layer is antiferromagnetically exchange-coupled with the second magnetic reference layer.

14. The magnetic memory device of claim 13 , wherein a first coupling layer separates the polarizing magnetic layer from a first magnetic reference layer, and a second coupling layer separates the first magnetic reference layer from the second magnetic reference layer.

15. 15. The magnetic memory device according to claim 11, wherein the MTJ pillar is a top-pin MTJ pillar having the magnetic free layer located under the SAF reference layer structure.

16. 15. The magnetic memory device according to claim 11, wherein the MTJ pillar is a bottom-pinned MTJ pillar having the magnetic free layer located above the SAF reference layer structure.

17. 12. The magnetic memory device of claim 11, wherein 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 a multi-layer stack thereof and has a thickness of 0.5 nm to 3 nm.

18. 12. The magnetic memory device of claim 11, wherein 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 a multi-layer stack thereof and have a thickness of 0.2 nm to 1 nm.

19. 20. The magnetic memory device of claim 18, wherein the first magnetic reference layer includes a rare earth element intercalated therein and has a damping value between 0.0001 and 1.

20. The polarizing magnetic layer has a perpendicular anisotropy H of −1 kOe to 10 kOe. Ｋ The first magnetic reference layer has a perpendicular anisotropy H of 0 kOe to 10 kOe. Ｋ 12. The magnetic memory device of claim 11, wherein the perpendicular anisotropy of the polarizing magnetic layer substantially matches the perpendicular anisotropy of the first magnetic reference layer.

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