Method and system for providing magnetic junctions including free layers that are cobalt-free

A magnetic junction usable in a magnetic device and a method for providing the magnetic junction are described. The magnetic junction includes a free layer, a nonmagnetic spacer layer, and a reference layer. The free layer includes at least one of Fe and at least one Fe alloy. Furthermore, the free layer excludes Co. The nonmagnetic spacer layer adjoins the free layer. The nonmagnetic spacer layer residing between reference layer and the free layer. The magnetic junction is configured such that the free layer is switchable between a plurality of stable magnetic states when a write current is passed through the magnetic junction.

BACKGROUND OF THE INVENTION

Magnetic memories, particularly magnetic random access memories (MRAMs), have drawn increasing interest due to their potential for high read/write speed, excellent endurance, non-volatility and low power consumption during operation. An MRAM can store information utilizing magnetic materials as an information recording medium. One type of MRAM is a spin transfer torque random access memory (STT-MRAM). STT-MRAM utilizes magnetic junctions written at least in part by a current driven through the magnetic junction. A spin polarized current driven through the magnetic junction exerts a spin torque on the magnetic moments in the magnetic junction. As a result, layer(s) having magnetic moments that are responsive to the spin torque may be switched to a desired state.

For example,FIG. 1depicts a conventional magnetic tunneling junction (MTJ)10as it may be used in a conventional STT-MRAM. The conventional MTJ10typically resides on a substrate12. A bottom contact14and top contact22may be used to drive current through the conventional MTJ10. The conventional MTJ, uses conventional seed layer(s) (not shown), may include capping layers (not shown) and may include a conventional antiferromagnetic (AFM) layer (not shown). The conventional magnetic junction10includes a conventional reference layer16, a conventional tunneling barrier layer18, and a conventional free layer20. Also shown is top contact22. Conventional contacts14and22are used in driving the current in a current-perpendicular-to-plane (CPP) direction, or along the z-axis as shown inFIG. 1. Typically, the conventional reference layer16is closest to the substrate12of the layers16,18and20.

The conventional reference layer16and the conventional free layer20are magnetic. For example, the conventional free layer20typically includes at least a CoFeB layer with the desired stoichiometry. Other magnetic and nonmagnetic layers may be part of the conventional free layer20. The magnetization17of the conventional reference layer16is fixed, or pinned, in a particular direction. Although depicted as a simple (single) layer, the conventional reference layer16may include multiple layers. For example, the conventional reference layer16may be a synthetic antiferromagnetic (SAF) layer including magnetic layers antiferromagnetically coupled through thin conductive layers, such as Ru. In such a SAF, multiple magnetic layers interleaved with a thin layer of Ru may be used. In another embodiment, the coupling across the Ru layers can be ferromagnetic.

The conventional free layer20has a changeable magnetization21. Although depicted as a simple layer, the conventional free layer20may also include multiple layers. For example, the conventional free layer20may be a synthetic layer including magnetic layers antiferromagnetically or ferromagnetically coupled through thin conductive layers, such as Ru. Although shown as perpendicular-to-plane, the magnetization21of the conventional free layer20may be in plane. Thus, the reference layer16and free layer20may have their magnetizations17and21, respectively oriented perpendicular to the plane of the layers.

Because of their potential for use in a variety of applications, research in magnetic memories is ongoing to improve the performance of the STT-RAM. For example, in order to achieve perpendicular magnetic moments17and21, various structures have been proposed. However, such structures may suffer from higher damping (which increases the required switching current), a lower magnetoresistance that decreases the signal and/or other issues. Accordingly, what is needed is a method and system that may improve the performance of the spin transfer torque based memories. The method and system described herein address such a need.

BRIEF SUMMARY OF THE INVENTION

A magnetic junction usable in a magnetic device and a method for providing the magnetic junction are described. The magnetic junction includes a free layer, a nonmagnetic spacer layer, and a reference layer. The free layer includes at least one of Fe and at least one Fe alloy. Furthermore, the free layer excludes Co. The nonmagnetic spacer layer adjoins the free layer. The nonmagnetic spacer layer residing between reference layer and the free layer. The magnetic junction is configured such that the free layer is switchable between a plurality of stable magnetic states when a write current is passed through the magnetic junction.

DETAILED DESCRIPTION OF THE INVENTION

The exemplary embodiments relate to magnetic junctions usable in magnetic devices, such as magnetic memories, and the devices using such magnetic junctions. The magnetic memories may include spin transfer torque magnetic random access memories (STT-MRAMs) and may be used in electronic devices employing nonvolatile memory. Such electronic devices include but are not limited to cellular phones, smart phones, tables, laptops and other portable and non-portable computing devices. The following description is presented to enable one of ordinary skill in the art to make and use the invention and is provided in the context of a patent application and its requirements. Various modifications to the exemplary embodiments and the generic principles and features described herein will be readily apparent. The exemplary embodiments are mainly described in terms of particular methods and systems provided in particular implementations. However, the methods and systems will operate effectively in other implementations. Phrases such as “exemplary embodiment”, “one embodiment” and “another embodiment” may refer to the same or different embodiments as well as to multiple embodiments. The embodiments will be described with respect to systems and/or devices having certain components. However, the systems and/or devices may include more or less components than those shown, and variations in the arrangement and type of the components may be made without departing from the scope of the invention. The exemplary embodiments will also be described in the context of particular methods having certain steps. However, the method and system operate effectively for other methods having different and/or additional steps and steps in different orders that are not inconsistent with the exemplary embodiments. Thus, the present invention is not intended to be limited to the embodiments shown, but is to be accorded the widest scope consistent with the principles and features described herein.

The exemplary embodiments are described in the context of particular methods, magnetic junctions and magnetic memories having certain components. One of ordinary skill in the art will readily recognize that the present invention is consistent with the use of magnetic junctions and magnetic memories having other and/or additional components and/or other features not inconsistent with the present invention. The method and system are also described in the context of current understanding of the spin transfer phenomenon, of magnetic anisotropy, and other physical phenomenon. Consequently, one of ordinary skill in the art will readily recognize that theoretical explanations of the behavior of the method and system are made based upon this current understanding of spin transfer, magnetic anisotropy and other physical phenomena. However, the method and system described herein are not dependent upon a particular physical explanation. The method and system are described in the context of a structure having a particular relationship to the substrate. However, one of ordinary skill in the art will readily recognize that the method and system are consistent with other structures. In addition, the method and system are described in the context of certain layers being synthetic and/or simple. However, one of ordinary skill in the art will readily recognize that the layers could have another structure. Furthermore, the method and system are described in the context of magnetic junctions and/or substructures having particular layers. However, one of ordinary skill in the art will readily recognize that magnetic junctions and/or substructures having additional and/or different layers not inconsistent with the method and system could also be used. Moreover, certain components are described as being magnetic, ferromagnetic, and ferrimagnetic. As used herein, the term magnetic could include ferromagnetic, ferrimagnetic or like structures. Thus, as used herein, the term “magnetic” or “ferromagnetic” includes, but is not limited to ferromagnets and ferrimagnets. As used herein, “in-plane” is substantially within or parallel to the plane of one or more of the layers of a magnetic junction. Conversely, “perpendicular” and “perpendicular-to-plane” corresponds to a direction that is substantially perpendicular to one or more of the layers of the magnetic junction.

A magnetic junction usable in a magnetic device and a method for providing the magnetic junction are described. The magnetic junction includes a free layer, a nonmagnetic spacer layer, and a reference layer. The free layer includes at least one of Fe and at least one Fe alloy. Furthermore, the free layer excludes Co. The nonmagnetic spacer layer adjoins the free layer. The nonmagnetic spacer layer residing between reference layer and the free layer. The magnetic junction is configured such that the free layer is switchable between a plurality of stable magnetic states when a write current is passed through the magnetic junction.

FIG. 2depicts an exemplary embodiment of a free layer100that is Co-free. For clarity,FIG. 2is not to scale. Also shown are layers102and104. The layer102may be seed layer(s) if the free layer100resides at the bottom of the magnetic junction in which it is used. Stated differently, the layer102may be a seed layer, such as MgO, if the free layer100is closer to the substrate than the reference layer. In such an embodiment, the layer104is a nonmagnetic spacer layer for a magnetic junction. The layer104may, for example, be a crystalline MgO nonmagnetic spacer layer. If the free layer100is at the top of the magnetic junction in which it is used, then the layer104may be a capping layer. Stated differently, the layer104may be a capping layer, such as MgO, if the free layer100is further from the substrate than the reference layer. In such an embodiment, the layer102is a nonmagnetic spacer layer for the magnetic junction. For example, the layer102may be a crystalline MgO nonmagnetic spacer layer. If the free layer100is in the center of a dual magnetic junction, then the layers102and104may be nonmagnetic spacer layers. In such embodiments, the layers102and104may be MgO tunneling barrier layers.

The free layer100has a magnetic moment103and includes Fe in the form of pure Fe layer(s) and/or one or more Fe alloy layer(s). However, the free layer100is free of Co. Co based alloys such as CoFeB as well as pure Co layers are not present in the free layer100. Thus, in some embodiments, the only magnetic element in the free layer100is Fe. Further, in some embodiments, the free layer100has no nonmagnetic insertion layers. In such embodiments, the free layer100consists of Fe layer(s) and/or Fe alloy layer(s). The free layer100may include only Fe layer(s) and/or Fe1-xBxlayer(s), where x is at least 0.2 and not more than 0.5. Further, x may vary between different alloy layers in the free layer100. For example, the free layer100might include an FeB layer that is nominally twenty atomic percent B and another FeB layer that is nominally forty atomic percent B. As used herein, FeB denotes an alloy of Fe and B having a stoichiometry in the ranges described above. In some such embodiments, the free layer100has a thickness that is at least ten Angstroms and not more than twenty-five Angstroms. In some such embodiments, the free layer is at least twelve Angstroms and not more than eighteen Angstroms thick. In some such embodiments, the free layer100has a thickness of at least fifteen Angstroms and not more than twenty Angstroms. In addition, the perpendicular magnetic anisotropy energy of the free layer100exceeds its out-of-plane demagnetization energy. Thus, the magnetic moment of the free layer100may be perpendicular to plane. The free layer100may have a maximum thickness on the order of twenty-five Angstroms or less to ensure that the free layer magnetic moment103is perpendicular to plane. The magnetic junction in which the free layer100is also configured such that the free layer100is switchable between stable magnetic states when a write current is passed through the magnetic junction.

The free layer100may allow the magnetic junction in which it is used to have improved performance. For the free layer100, Fe based material(s) are used. In addition, as discussed above, the free layer100may be without insertion layers, such as W or Ta, and without Co. As a result, the free layer100may have a lower damping constant. In some embodiments, the damping constant may be as low as 0.005 or less. In some such embodiments, the damping constant for the free layer100may be on the order of 0.002. Because of the lower damping constant, the switching current for spin transfer torque (STT) switching may be reduced. Because the free layer100is Fe based as discussed above, the free layer100may have a high saturation magnetization (Ms). A high Msmay also aid in reducing the switching current for STT switching. In addition, the free layer100has a high perpendicular magnetic anisotropy. For example, the magnetic anisotropy may correspond to a magnetic field on the order of at least five hundred Oe and not more than eight thousand Oe. However, other anisotropies are possible. The perpendicular magnetic anisotropy of the free layer100exceeds the out-of-plane demagnetization energy. Thus, the magnetic moment of the free layer100may be stable perpendicular to the plane of the free layer100. In addition, a magnetic junction using the free layer100and layer(s)102and/or104as tunneling barrier layer(s) may have a high tunneling magnetoresistance (TMR). Thus, performance of a magnetic junction may be improved, particularly for STT switching.

FIG. 3depicts an exemplary embodiment of a free layer110that is Co-free. For clarity,FIG. 3is not to scale. The free layer110may be used as the free layer100depicted inFIG. 2. Thus, layers analogous to layers102and104may be present but are not shown for simplicity. The free layer110may be viewed as a particular embodiment of the free layer100.

The free layer110includes an Fe1-xBxlayer112and a pure Fe layer114. The layer112adjoins, or shares an interface with, the layer114. For the Fe1-xBxlayer112, x is at least 0.2 and not more than 0.5. In some embodiments, x is nominally 0.4. In some such embodiments, the Fe1-xBxlayer112has a thickness, t1, that is at least ten Angstroms and not more than twenty-five Angstroms. In some such embodiments, the Fe1-xBxlayer112is at least twelve Angstroms and not more than eighteen Angstroms thick. In some such embodiments, the Fe1-xBxlayer112has a thickness of at least fifteen Angstroms and not more than twenty Angstroms.

The Fe layer114may be significantly thinner than the Fe1-xBxlayer112. For example, the Fe layer114may have a thickness, t2, that does not exceed five Angstroms. In some embodiments, the Fe layer114may be not more than three Angstroms thick and greater than zero Angstroms thick. For example, the Fe layer114may be at least two Angstroms thick and not more than three Angstroms thick. Thus, the Fe layer114may be viewed as a dusting of Fe residing on the Fe1-xBxlayer112. The total thickness of the free layer110, t, is thus very similar to that of the Fe1-xBxlayer114. In addition, the perpendicular magnetic anisotropy energy of the free layer110exceeds its out-of-plane demagnetization energy. Thus, the magnetic moment of the free layer110may be perpendicular to plane. In addition, the free layer110may have a maximum thickness on the order of twenty-five Angstroms or less to ensure that the free layer magnetic moment is perpendicular to plane. The magnetic junction in which the free layer110is also configured such that the free layer110is switchable between stable magnetic states when a write current is passed through the magnetic junction. Thus, the free layer110consists of Fe1-xBxlayer112and Fe layer114. No nonmagnetic insertion layers, no Co layers and no Co based alloys are used.

The free layer110may improve the performance of the magnetic junction in which it is used. For the free layer110, a pure Fe layer114and a CoFeB layer112are used. The free layer110is without insertion layers, such as W or Ta, and without Co. As a result, the free layer110may have a lower damping constant and the switching current for STT switching. The free layer110may also have a high Ms, again reducing the switching current for STT switching. In addition, the free layer110has a high perpendicular magnetic anisotropy, particularly if MgO layers adjoin the free layer110. Further, the magnetic junction using the free layer110may have a high TMR. Thus, performance of a magnetic junction may be improved, particularly for STT switching.

FIG. 4depicts an exemplary embodiment of a free layer110′ that is Co-free. For clarity,FIG. 4is not to scale. The free layer110′ may be used as the free layer100depicted inFIG. 2. Thus, layers analogous to layers102and104may be present but are not shown for simplicity. The free layer110′ may be viewed as a particular embodiment of the free layer100. The free layer110′ is also analogous to the free layer110. The free layer110′ thus includes layers112and114having thicknesses t1and t2, respectively, that are analogous to those of the free layer110and layers112and114, respectively. However, the Fe layer114is closer to the substrate than the FeB layer112in the embodiment shown inFIG. 4.

Thus, the free layer110′ consists of Fe1-xBxlayer112and Fe layer114. The layer112adjoins, or shares an interface with, the layer114. The free layer110′ thus shares the benefits of the free layer(s)100and/or110. A magnetic junction using the free layer110′ may thus have a high perpendicular anisotropy, low damping and high TMR.

FIG. 5depicts an exemplary embodiment of a free layer110″ that is Co-free. For clarity,FIG. 5is not to scale. The free layer110′ may be used as the free layer100depicted inFIG. 2. Thus, layers analogous to layers102and104may be present but are not shown for simplicity. In addition, the free layer110″ may be viewed as a particular embodiment of the free layer100. The free layer110″ is also analogous to the free layers110and110′. The free layer110″ thus includes layers112and114having thicknesses t1and t2, respectively, that are analogous to those of the free layer110and layers112and114, respectively.

In addition, the free layer110′″ includes Fe layer118. The Fe layer118is analogous to the Fe layer114and may thus have a thickness in the same range. The thickness of the Fe layer118can, but need not, be the same as that of the Fe layer114. The layers112and114and the layers112and118adjoin, sharing interfaces. Thus, the free layer110″ consists of Fe1-xBxlayer112sharing interfaces with and sandwiched by Fe layer114and Fe layer118.

The free layer110″ shares the benefits of the free layer(s)100,110and/or110′. The free layer110′ may thus have a high perpendicular anisotropy, low damping resulting in a lower spin transfer switching current and high TMR when used in a magnetic junction.

FIG. 6depicts an exemplary embodiment of a free layer120that is Co-free. For clarity,FIG. 6is not to scale. The free layer120may be used as the free layer100depicted inFIG. 2. Thus, layers analogous to layers102and104may be present but are not shown for simplicity. The free layer120may be viewed as a particular embodiment of the free layer100. The free layer120is also analogous to the free layer110,110′ and110″. Thus, analogous components have similar labels

The free layer120includes an Fe1-xBxlayer122and a pure Fe layer124that are analogous to the layers112and114, respectively, described above. The Fe1-xBxlayer122adjoins, or shares an interface with, the Fe layer124. For the Fe1-xBxlayer122, x is at least 0.2 and not more than 0.5. In some embodiments, x is nominally 0.4. In some such embodiments, the Fe1-xBxlayer122has a thickness, t1, that is at least ten Angstroms and not more than twenty-five Angstroms. In some such embodiments, the Fe1-xBxlayer122is at least twelve Angstroms and not more than eighteen Angstroms thick. In some such embodiments, the Fe1-xBxlayer122has a thickness of at least fifteen Angstroms and not more than twenty Angstroms.

The Fe layer124may be significantly thinner than the Fe1-xBxlayer122. For example, the Fe layer124may have a thickness, t2, that does not exceed five Angstroms. In some embodiments, the Fe layer124may be not more than three Angstroms thick and greater than zero Angstroms thick. For example, the Fe layer124may be at least two Angstroms thick and not more than three Angstroms thick. Thus, the Fe layer124may be viewed as a dusting of Fe residing on the Fe1-xBxlayer122.

The free layer120also includes an Fe1-yBylayer126that is analogous to the layers112and122, described above. The Fe1-yBylayer126adjoins, or shares an interface with, the Fe layer124and Fe1-xBxlayer122. The thickness and stoichiometry ranges for the Fe1-yBylayer126are analogous to those of the Fe1-xBxlayer122. Although it is possible, the stoichiometries may but need not match for the layers122and126. For example, the Fe1-yBylayer126may be nominally forty percent Co, while the Fe1-xBxlayer122may be nominally twenty atomic percent B. In some embodiments, the higher Fe concentration layer may be closer to the substrate. However, FeB layers122and126with different stoichiometries within the range described above may be present in other embodiments. Similarly, the thickness, t3, of the Fe1-yBylayer126may, but need not be, equal to the thickness of the Fe1-xBxlayer122.

The perpendicular magnetic anisotropy energy of the free layer120exceeds its out-of-plane demagnetization energy. Thus, the magnetic moment of the free layer120may be perpendicular to plane. The free layer120may have a maximum thickness on the order of twenty-five Angstroms or less to ensure that the free layer magnetic moment is perpendicular to plane. The magnetic junction in which the free layer120is also configured such that the free layer120is switchable between stable magnetic states when a write current is passed through the magnetic junction. Thus, the free layer120consists of Fe1-xBxlayer122and Fe layer124and Fe1-yBylayer126. No nonmagnetic insertion layers, no Co layers and no Co based alloys are used.

The free layer120may allow the magnetic junction in which it is used to have improved performance. For the free layer120, a pure Fe layer123and CoFeB layers122and126are used. The free layer120is without insertion layers, such as W or Ta, and without Co. As a result, the free layer120may have a lower damping constant and the switching current for STT switching. The free layer120may also have a high Ms, again reducing the switching current for STT switching. In addition, the free layer120has a high perpendicular magnetic anisotropy, particularly if MgO layers adjoin the free layer120. Further, the magnetic junction using the free layer120may have a high TMR. Thus, performance of a magnetic junction may be improved, particularly for STT switching.

FIG. 7depicts an exemplary embodiment of a free layer120′ that is Co-free. For clarity,FIG. 4is not to scale. The free layer120′ may be used as the free layer100depicted inFIG. 2. Thus, layers analogous to layers102and104may be present but are not shown for simplicity. In addition, the free layer120′ may be viewed as a particular embodiment of the free layer100. The free layer120′ is also analogous to the free layer120. The free layer120′ thus includes layers122,124and126having thicknesses t1, t2and t3, respectively, that are analogous to those of the free layer120and layers122,124and126, respectively. However, the Fe layer124is closer to the substrate than the FeB layers122and126in the embodiment shown inFIG. 7.

Thus, the free layer120′ consists of Fe1-xBxlayer122, Fe1-yBylayer126and Fe layer124. The layer122adjoins, or shares an interface with, the layer124. Similarly, the layer FeB122adjoins the FeB layer126. The free layer120′ thus shares the benefits of the free layer(s)100,110,110′,110″ and/or120. A magnetic junction including the free layer120′ may thus have a high perpendicular anisotropy, low damping, low switching current and high TMR.

FIG. 8depicts an exemplary embodiment of a free layer120″ that is Co-free. For clarity,FIG. 8is not to scale. The free layer120″ may be used as the free layer100depicted inFIG. 2. Thus, layers analogous to layers102and104may be present but are not shown for simplicity. In addition, the free layer120″ may be viewed as a particular embodiment of the free layer100. The free layer120″ is also analogous to the free layers120and120′. The free layer120″ thus includes layers122,124and126having thicknesses t1, t2and t3, respectively, that are analogous to those of the free layer120and layers122,124and126, respectively.

In addition, the free layer120″ includes Fe layer128. The Fe layer128is analogous to the Fe layer124and may thus have a thickness, t4, in the same range. The thickness of the Fe layer128can, but need not, be the same as that of the Fe layer124. The layers122and124, the layers122and126and the layers126and128adjoin, sharing interfaces. Thus, the free layer120″ consists of Fe1-xBxlayer122, Fe1-yBylayer126and Fe layers124and128.

The free layer120″ shares the benefits of the free layer(s)100,120and/or120′. The free layer120′ may thus have a high perpendicular anisotropy, low damping resulting in a lower spin transfer switching current and high TMR when used in a magnetic junction.

FIG. 9depicts an exemplary embodiment of a magnetic junction200and which is usable in a magnetic memory programmable utilizing spin transfer and which includes a free layer100,110,110′,110″,120,120′ and/or120″. For clarity,FIG. 9is not to scale. The magnetic junction200may be used in a magnetic device such as a STT-RAM and, therefore, in a variety of electronic devices. The magnetic junction200includes a free layer210having magnetic moment211, a nonmagnetic spacer layer220, and a reference layer230having magnetic moment231. Also shown is an underlying substrate201in which devices including but not limited to a transistor may be formed. Bottom contact202, top contact208, optional seed layer(s)204and optional capping layer(s)206are also shown.

As can be seen inFIG. 9, the reference layer230is closer to the top (furthest from a substrate201) of the magnetic junction200. However, in other embodiments, the reference layer230may be closer to the substrate201than the free layer210. An optional pinning layer (not shown) may be used to fix the magnetization (not shown) of the reference layer230. In some embodiments, the optional pinning layer may be an AFM layer or multilayer that pins the magnetization (not shown) of the reference layer230by an exchange-bias interaction. However, in other embodiments, the optional pinning layer may be omitted or another structure may be used.

The magnetic junction200is also configured to allow the free layer210to be switched between stable magnetic states when a write current is passed through the magnetic junction200. Thus, the free layer210is switchable utilizing spin transfer torque. In some embodiments, the switching is accomplished using only STT. However, in other embodiments, other mechanisms including but not limited to spin orbit torque and/or an applied field may also contribute to the switching.

In addition to contacts202and206and substrate201, seed layer(s)204and capping layer(s)206are shown. The free layer210is closer to the substrate201than the reference layer230and grown on the seed layer204. Thus, the seed layer204may be crystalline MgO in order to improve the perpendicular anisotropy of the free layer210. Thus, the seed layer204may be analogous to the layer102described above.

The nonmagnetic spacer layer220may be an MgO tunneling barrier layer. The MgO layer may have a 200 orientation for enhanced tunneling magnetoresistance (TMR). However, in other embodiments, the nonmagnetic spacer layer220may be a conductor, such as Cu, or another insulating tunneling barrier layer. Other configurations, such as conductive channels in an insulating matrix, are also possible.

The reference layer230and the free layer210are magnetic. In the embodiment shown, the perpendicular magnetic anisotropy of the free layer210exceeds its out-of-plane demagnetization energy. Similarly, the perpendicular magnetic anisotropy of the reference layer230exceeds its out-of-plane demagnetization energy. Thus, the easy axis211of the free layer210and the magnetic moment231of the reference layer230are shown as perpendicular-to-plane (in the z-direction). In other embodiments, one or both of the layers210and230might be in-plane.

The reference layer230may be a multilayer. For example, the reference layer230may be a SAF including multiple ferromagnetic layers interleaved with nonmagnetic layer(s). In such embodiments, the magnetic moments of the ferromagnetic layers maybe coupled antiparallel. Each ferromagnetic layer may also include sublayers including but not limited to multiple ferromagnetic layers. In other embodiments, the reference layer230may be another multilayer. Further, a polarization enhancement layer (PEL)222having a high spin polarization and/or other layer(s) is provided between the reference layer230and the nonmagnetic spacer layer220. In some embodiments, a PEL (not shown) may be between the free layer210and the nonmagnetic spacer layer220. For example, the PEL222may include a CoFeB layer. However, in the embodiment shown, the free layer210shares an interface with the nonmagnetic spacer layer220.

The free layer210is a free layer100,110,110′,110″,120,120′ and/or120″. Thus, the free layer210may consist of Fe layer(s) and Fe alloy layer(s). Nonmagnetic insertion layers and Co-containing layers may be omitted. As a result, the magnetic junction200may enjoy the benefits of free layer(s)100,110,110′,110″,120,120′ and/or120′″. The magnetic junction200including the free layer210may have a high perpendicular anisotropy, low damping resulting in a lower spin transfer switching current and high TMR. Thus, a magnetic junction200having the desired magnetic orientation, signal and moderate switching current for STT switching may be achieved.

FIG. 10depicts an exemplary embodiment of a magnetic junction200′ which is usable in a magnetic memory programmable utilizing spin transfer and that uses the free layer100,110,110′,110″,120,120′ and/or120″. For clarity,FIG. 10is not to scale. The magnetic junction200′ may be used in a magnetic device such as a STT-RAM and, therefore, in a variety of electronic devices. The magnetic junction200′ is analogous to the magnetic junction200. As a result, similar components have similar labels. The magnetic junction200′ includes a free layer210having magnetic moment211, a nonmagnetic spacer layer220, and a reference layer230having magnetic moment231that are analogous to the free layer210having magnetic moment211, the nonmagnetic spacer layer220, and the reference layer230having magnetic moment231, respectively, depicted inFIG. 9. Also shown are an underlying substrate201, bottom contact202, top contact208, optional seed layer(s)204, optional capping layer(s)206and optional PEL222that are analogous to the substrate201, bottom contact202, top contact208, optional seed layer(s)204, optional capping layer206and optional PEL222shown inFIG. 9.

The magnetic junction200′ is also configured to allow the free layer210to be switched between stable magnetic states when a write current is passed through the magnetic junction200′. Thus, the free layer210is switchable utilizing spin transfer torque. In some embodiments, the switching is accomplished using only STT. However, in other embodiments, other mechanisms including but not limited to spin orbit torque and/or an applied field may also contribute to the switching.

As can be seen inFIG. 10, the reference layer230is now closer to the substrate201than the free layer210. The nonmagnetic spacer layer220is thus provided on the reference layer210. The reference layer230and the free layer210are magnetic and analogous to those in the magnetic junction200. In the embodiment shown, the perpendicular magnetic anisotropy of the reference layer230exceeds its out-of-plane demagnetization energy. Similarly, the perpendicular magnetic anisotropy of the free layer210exceeds its out-of-plane demagnetization energy. Thus, the easy axis211of the free layer210and the magnetic moment231of the reference layer230are shown as perpendicular-to-plane (in the z-direction). In other embodiments, one or both of the layers210and230might be in-plane. The free layer210is the free layer100,110,110′,110″,120,120′ and/or120″. In the embodiment shown, the capping layer206′ may be an MgO capping layer analogous to the layer104depicted inFIG. 2. Such an MgO capping layer may improve the performance of the free layer210, for example, by enhancing the perpendicular magnetic anisotropy of the free layer210.

The magnetic junction200′ may enjoy the benefits of the free layers100,110,110′,110″,120,120′ and/or120″ as well as the magnetic junction200. Thus, a magnetic junction200′ having the desired magnetic orientation, PMA configuration, magnetoresistance and moderate switching current for STT switching may be achieved.

FIG. 11depicts an exemplary embodiment of a magnetic junction200″ which is usable in a magnetic memory programmable utilizing spin transfer and which includes the free layer100,110,110′,110″,120,120′ and/or120″. For clarity,FIG. 11is not to scale. For simplicity, the substrate is also not shown. The magnetic junction200″ may be used in a magnetic device such as a STT-RAM and, therefore, in a variety of electronic devices. The magnetic junction200″ is analogous to the magnetic junction200and/or200′. As a result, similar components have similar labels. The magnetic junction200″ includes a free layer210having magnetic moment211, a nonmagnetic spacer layer220, and a reference layer230′ that are analogous to the free layer210having magnetic moment211, the nonmagnetic spacer layer220, and the reference layer230having magnetic moment231, respectively, depicted inFIGS. 9-10. Also shown are an underlying substrate201, bottom contact202, top contact208, optional seed layer(s)204, optional capping layer(s)206and optional PEL222that are analogous to the substrate201, bottom contact202, top contact208, optional seed layer(s)204, optional capping layer206and PEL shown inFIGS. 9-10.

The magnetic junction200″ is also configured to allow the free layer210to be switched between stable magnetic states when a write current is passed through the magnetic junction200″. Thus, the free layer210is switchable utilizing spin transfer torque. In some embodiments, the switching is accomplished using only STT. However, in other embodiments, other mechanisms including but not limited to spin orbit torque and/or an applied field may also contribute to the switching.

As can be seen inFIG. 11, magnetic junction200′″ is a dual magnetic junction. Thus, the magnetic junction200′″ also includes an additional nonmagnetic spacer layer240and an additional reference layer250that are analogous to the layers220and230/230′, respectively. In the embodiment shown, the magnetic moments231and251of the reference layers230and250are aligned antiparallel (in a dual state). However, in other embodiments or another configuration, the magnetic moments231and251may be in the anti-dual state (parallel). The nonmagnetic spacer layer240may be a conductor, an insulating tunneling barrier layer such as crystalline MgO or may have another structure. In some embodiments, the spacer layers220and240are crystalline MgO. Such spacer layers220and240may allow not only for increased TMR but also enhanced perpendicular magnetic anisotropy of the free layer210. The perpendicular magnetic anisotropy of the reference layers230and250exceed their out-of-plane demagnetization energy. Thus, the magnetic moments of the reference layers230and250are perpendicular-to-plane. In other embodiments, the magnetic moment of the reference layer230and/or250might be in-plane. The reference layer250may also be a SAF. Although not shown, an optional PEL might be included between the spacer layer240and the reference layer250.

The free layer210is the free layer100,110,110′,110″,120,120′ and/or120″. The magnetic junction200″ may enjoy the benefits of the free layers100,110,110′,110″,120,120′ and/or120″ as well as the magnetic junction200. Thus, a magnetic junction200″ having the desired magnetic orientation, PMA configuration, magnetoresistance and moderate switching current for STT switching may be achieved.

Various configurations of the free layer100,110,110′,110″,120,120′ and/or120″ as well as the magnetic junction(s)200,200′ and/or200″ are highlighted. One of ordinary skill in the art will recognize that various features of the free layers100,110,110′,110″,120,120′ and/or120″ and particular features of the magnetic junction(s)200,200′ and/or200″ may be combined. For example, the free layer210might include multiple repeats of the bilayer112/114depicted inFIGS. 3-4and/or multiple repeats of the trilayer122/124/126depicted inFIGS. 6-7. However, in such embodiments, the thicknesses of the layers112,114,122,124and/or126may be adjusted such that the total thickness of the free layer210remains sufficiently small for the perpendicular magnetic anisotropy of the free layer to remain high.

FIG. 12depicts an exemplary embodiment of a memory300that may use one or more of the magnetic junctions200,200′ and/or200″ as well as the free layer(s)100,110,110′,110″,120,120′ and/or120″. The magnetic memory300includes reading/writing column select drivers302and306as well as word line select driver304. Note that other and/or different components may be provided. The storage region of the memory300includes magnetic storage cells310. Each magnetic storage cell includes at least one magnetic junction312and at least one selection device314. In some embodiments, the selection device314is a transistor. The magnetic junctions312may be one of the magnetic junctions200,200′ and/or200″ disclosed herein. Although one magnetic junction312is shown per cell310, in other embodiments, another number of magnetic junctions312may be provided per cell. As such, the magnetic memory300may enjoy the benefits described above.

FIG. 15depicts an exemplary embodiment of a method400for fabricating a magnetic junction including free layers that are Co-free and usable in a magnetic device such as a spin transfer torque random access memory (STT-RAM) and, therefore, in a variety of electronic devices. For simplicity, some steps may be omitted, performed in another or combined. Further, the method400may start after other steps in forming a magnetic memory have been performed. For simplicity, the method400is described in the context of the magnetic junctions200,200′ and200″. However, other magnetic junctions may be formed.

A reference layer230/230′/330is provided on the substrate, via step402. In some embodiments, step402includes depositing the material(s) for the reference layer230. Step402may also include providing a multilayer including but not limited to a SAF. The edges of the reference layer230may be defined at a later time, for example after deposition of the remaining layers of the magnetic junction.

A nonmagnetic spacer layer220is provided, via step404. Step404may include depositing MgO, which forms a tunneling barrier layer. In some embodiments, step404may include depositing MgO using, for example, radio frequency (RF) sputtering. In other embodiments, metallic Mg may be deposited, then oxidized in step404. As discussed above with respect to step402, the edges of the nonmagnetic spacer layer220may be defined at a later time, for example after deposition of the remaining layers of the magnetic junction. In addition, the anneal step discussed above may be performed after deposition of the nonmagnetic spacer layer220in step404.

A free layer210is provided, via step406. In some embodiments, step406includes providing the free layer100,110,110′,110″,120,120′ and/or120″. Thus, the nonmagnetic spacer layer220is between the reference layer230and the free layer210. As discussed above with respect to step402, the edges of the reference layer may be defined at a later time, for example after deposition of the remaining layers of the magnetic junction.

If a dual magnetic junction200″ is to be provided, the additional nonmagnetic spacer layer240is provided, via step408. Step408is analogous to step404. In addition, annealing, or otherwise providing adequate energy for crystallization, may be performed for an MgO spacer layer240.

If the dual magnetic junction200″″ is being fabricated, then the reference layer250is provided, via step410. Step410may include providing a multilayer including but not limited to a SAF. Fabrication of the magnetic junction may be completed. For example, capping layers may be deposited and the edges of the magnetic junction defined.

Using the method400, the magnetic junction200,200′ and/or200″ may be formed. Thus, the benefits of the magnetic junction(s)200,200′ and/or200″ and the free layer(s)100,110,110′,110″,120,120′ and/or120″ may be achieved.

A method and system for providing a magnetic junction and a memory fabricated using the magnetic junction has been described. The method and system have been described in accordance with the exemplary embodiments shown, and one of ordinary skill in the art will readily recognize that there could be variations to the embodiments, and any variations would be within the spirit and scope of the method and system. Accordingly, many modifications may be made by one of ordinary skill in the art without departing from the spirit and scope of the appended claims.