WITH CARBON DOPED FILTER LAYER

BACKGROUND

Non-volatile random access memory device performance and density can be improved by reducing memory cell dimensions while maintaining the ability to retain state. Magnetoresistive random-access memory (MRAM) holds the promise of significantly higher density than other technologies such as flash memory.

Some magnetic memory cell architectures utilize a phenomenon known as the tunneling magnetoresi stance (TMR) effect. For a structure including two ferromagnetic layers separated by a thin insulating barrier layer, it is more likely that electrons will tunnel through the barrier layer when magnetizations of the two magnetic layers are in a parallel orientation than if they are not (non-parallel or antiparallel orientation). As such, a magnetic tunneling junction (MTJ), typically comprising a fixed magnetic layer and a free magnetic layer separated by a barrier layer, can be switched between two states of electrical resistance, one state having a low resistance and one state with a high resistance. The greater the differential in resistance, the higher the TMR ratio: (RAP-R _P )/R _P * 100 % where R _P and RAP are resistances for parallel and antiparallel alignment of the magnetizations, respectively. The higher the TMR ratio, the more readily a bit can be reliably stored in association with the MTJ resistive state. The TMR ratio of a given MTJ is therefore an important performance metric of an MTJ-based device.

In one MRAM technology referred to as spin transfer torque memory (STTM), current-induced magnetization switching may be used to set the bit states. Polarization states of one ferromagnetic layer can be switched relative to a fixed polarization of the second ferromagnetic layer via the spin transfer torque phenomenon, enabling states of the MTJ to be set by application of current. Angular momentum (spin) of the electrons may be polarized through one or more structures and techniques (e.g., direct current, spin-hall effect, etc.). These spin-polarized electrons can transfer their spin angular momentum to the

magnetization of the free layer and cause it to precess. As such, the magnetization of the free magnetic layer can be switched by a pulse of current (e.g., in about 1 -10 nanoseconds) exceeding a certain critical value, while magnetization of the fixed magnetic layer remains unchanged as long as the current pulse is below some higher threshold associated with the fixed magnet architecture.

BRIEF DESCRIPTION OF THE DRAWINGS

The material described herein is illustrated by way of example and not by way of limitation in the accompanying figures. For simplicity and clarity of illustration, elements illustrated in the figures are not necessarily drawn to scale. For example, the dimensions of some elements may be exaggerated relative to other elements for clarity. Further, where considered appropriate, reference labels have been repeated among the figures to indicate corresponding or analogous elements. In the figures: FIG. 1A illustrates a material stack for an MTJ device, in accordance with some embodiments;

FIG. IB illustrates a material stack for an MTJ device, in accordance with some embodiments;

FIG. 2 illustrates a material stack for an MTJ device, in accordance with some embodiments;

FIG. 3 illustrates a material stack for an MTJ device, in accordance with some embodiments;

FIG. 4 is a flow diagram illustrating a method of fabricating MTJ devices, in accordance with some embodiments; FIG. 5 is a schematic of an MTJ-based memory cell, which includes a perpendicular spin transfer torque element, in accordance with some embodiments;

FIG. 6 is a cross-sectional view of an MTJ-based memory cell, according to some embodiments.

FIG. 7 is a schematic illustrating a mobile computing platform and a data server machine employing an MTJ memory device, in accordance with some embodiments of the present disclosure; and FIG. 8 is a functional block diagram illustrating an electronic computing device, in accordance with some embodiments of the present disclosure.

DETAILED DESCRIPTION

One or more embodiments are described with reference to the enclosed figures. While specific configurations and arrangements are depicted and discussed in detail, it should be understood that this is done for illustrative purposes only. Persons skilled in the relevant art will recognize that other configurations and arrangements are possible without departing from the spirit and scope of the description. It will be apparent to those skilled in the relevant art that techniques and/or arrangements described herein may be employed in a variety of other systems and applications other than what is described in detail herein.

Reference is made in the following detailed description to the accompanying drawings, which form a part hereof and illustrate exemplary embodiments. Further, it is to be understood that other embodiments may be utilized and structural and/or logical changes may be made without departing from the scope of claimed subject matter. It should also be noted that directions and references, for example, up, down, top, bottom, and so on, may be used merely to facilitate the description of features in the drawings. Therefore, the following detailed description is not to be taken in a limiting sense and the scope of claimed subject matter is defined solely by the appended claims and their equivalents.

In the following description, numerous details are set forth. However, it will be apparent to one skilled in the art, that embodiments may be practiced without these specific details. In some instances, well-known methods and devices are shown in block diagram form, rather than in detail, to avoid obscuring the embodiments. Reference throughout this specification to "an embodiment" or "one embodiment" or "some embodiments" means that a particular feature, structure, function, or characteristic described in connection with the embodiment is included in at least one embodiment. Thus, the appearances of the phrase "in an embodiment" or "in one embodiment" or "some embodiments" in various places throughout this specification are not necessarily referring to the same embodiment.

Furthermore, the particular features, structures, functions, or characteristics may be combined in any suitable manner in one or more embodiments. For example, a first embodiment may be combined with a second embodiment anywhere the particular features, structures, functions, or characteristics associated with the two embodiments are not mutually exclusive.

As used in the description and the appended claims, the singular forms "a", "an" and "the" are intended to include the plural forms as well, unless the context clearly indicates otherwise. It will also be understood that the term "and/or" as used herein refers to and encompasses any and all possible combinations of one or more of the associated listed items.

The terms "coupled" and "connected," along with their derivatives, may be used herein to describe functional or structural relationships between components. It should be understood that these terms are not intended as synonyms for each other. Rather, in particular embodiments, "connected" may be used to indicate that two or more elements are in direct physical, optical, or electrical contact with each other. "Coupled" may be used to indicated that two or more elements are in either direct or indirect (with other intervening elements between them) physical or electrical contact with each other, and/or that the two or more elements co-operate or interact with each other (e.g., as in a cause an effect relationship).

The terms "over," "under," "between," and "on" as used herein refer to a relative position of one component or material with respect to other components or materials where such physical relationships are noteworthy. For example in the context of materials, one material or material disposed over or under another may be directly in contact or may have one or more intervening materials. Moreover, one material disposed between two materials or materials may be directly in contact with the two layers or may have one or more intervening layers. In contrast, a first material or material "on" a second material or material is in direct contact with that second material/material. Similar distinctions are to be made in the context of component assemblies. As used throughout this description, and in the claims, a list of items joined by the term "at least one of or "one or more of can mean any combination of the listed terms. For example, the phrase "at least one of A, B or C" can mean A; B; C; A and B; A and C; B and C; or A, B and C.

One challenge with MTJ devices is that as the MTJ material stack becomes more complex, during a thermal anneal, crystallization fronts may be propagated from more than one material layer. These crystallization fronts may compete with each other and induce undesirable crystallization within the fixed magnet and/or free magnet, which may adversely impact TMR. MTJ material stacks including a carbon-doped filter layer, MTJ devices employing such material stacks, and computing platforms employing such MTJ devices are described herein. In some embodiments, MTJ material stacks include a fixed magnet and a free magnet, each of which includes one or more ferromagnetic material layers. As employed herein, the term "ferromagnetic" refers to the magnetic mechanism of the material and such a material need not be an iron alloy, although it may be. In some embodiments, MTJ material stacks include one or more carbon-doped material layer within the fixed magnet structure or adjacent to the fixed magnet structure. Exemplary MTJ material stacks having one or more of the features described herein may be employed in devices, such as, but not limited to, embedded memory, embedded non-volatile memory (eNVM), magnetic random access memory (MRAM), and non-embedded or stand-alone memories.

As noted above, thermal stability A is one of the most important issues facing scaling of MTJ-based devices. For example, greater thermal stability is associated with longer non- volatile memory lifetimes. With the scaling of MTJ device area (e.g., x-y dimensional footprint of an MTJ stack), it becomes more difficult to maintain sufficient stability.

Thermal stability is defined as the energy barrier E between two magnetic states (e.g., (1, 0), (parallel, anti-parallel)). In a fixed magnet, a synthetic antiferromagnetic (SAF) structure may advantageously counter fringing fields associated with one or more ferromagnetic layer(s), thereby improving MTJ device stability. Materials employed within the SAF however may have some crystallinity other than the crystallinity suitable for one or more adjacent ferromagnetic layer(s). As described further below, within an MTJ material stack a filter layer may be introduced on either side of a SAF structure to reduce effects of any crystallinity mismatch between the SAF and an adjacent layer. For example, a filter layer may be placed between a SAF and a ferromagnetic layer for which PMA is desired, or between a SAF and a contact interfacing the MTJ material stack to circuitry interconnects. In accordance with some embodiments where a filter layer is between a SAF structure and a ferromagnetic layer, the filter layer is advantageously ferromagnetic to maintain strong coupling with the SAF structure. The filter layer may also have a crystallization temperature that is advantageously higher than that of the ferromagnetic layer(s) so that a desired crystallinity and texture of the ferromagnetic layer(s) may be achieved regardless of any crystallinity that may develop within the SAF structure. In accordance with some other embodiments where a filter layer is between a contact and a SAF structure, the filter layer need not be ferromagnetic but is advantageously amorphous to allow the SAF structure to develop a desired crystallinity regardless of crystallinity in the contact material (e.g., metal). The filter layer in either of these capacities preferably minimizes additional IR drop across the MTJ material stack. Notably, such "SAF filter" layers may be combined so that an MTJ material stack includes a filter layer on both sides of the SAF structure.

The inventors have found some metal alloys that include carbon (i.e., have carbon doping) may serve as good SAF filter layers. Generally, for embodiments where the SAF filter layer is to be ferromagnetic, the upper bound of carbon concentration within the alloy is limited to below the concentration at which the alloy loses ferromagnetism. For embodiments where the SAF filter layer need not be ferromagnetic, the upper bound of carbon concentration within the alloy may be relatively higher, limited by constraints on the MTJ material stack resistance, for example. With the addition of carbon, the crystallization temperature of the filter alloy may be increased, thereby enabling the filter layer to act as a barrier that decouples crystal growth of material layers on opposite sides of the filter layer.

FIG. 1A illustrates an MTJ material layer stack 101 for an MTJ device 100, in accordance with some embodiments. In the illustrated example, MTJ device 100 has a columnar or pillar architecture with the material stack having layers with thicknesses in a direction (e.g., z-axis) perpendicular to a plane of the device footprint (e.g., x-y axis). MTJ device 100 includes a first contact 107 (e.g., bottom contact) and a second contact 180 (e.g., top contact) with the material layer stack 101 there between. First contact 107 may include one or more metal layers, each layer comprising an elemental or alloyed metal. First contact 107 may have some microstructure (i.e., not completely amorphous). In one exemplary embodiment, contact 107 includes a layer comprising tantalum (Ta) or ruthenium (Ru). Second contact 180 may also include one or more metal layers, each comprising an elemental or alloyed metal. In some exemplary embodiments, contact 180 includes a layer comprising tantalum (Ta), tungsten (W), or ruthenium (Ru). Although vertically oriented in FIG. 1A, material layer stack 101 may also extend horizontally such that the columnar structure illustrated is instead a series of material stripes across the x-y plane. Notably, MTJ device 100 is monolithic and may be built up on any substrate (not depicted) that is known to be suitable for MTJ devices.

MTJ device 100 includes a free magnet and a fixed magnet separated by an intervening barrier layer that is to filter electrons based on their Fermi wavevector.. The term "free magnet" and "fixed magnet" are employed herein to emphasize that each "magnet" may be composite structure that includes a plurality of material layers that together comprise a functional component of MTJ device 100. In FIG. 1A, ellipses are drawn between illustrated material layers to further emphasize that MTJ device 100 may have any number of layers, and only a selected material layers relevant to the present disclosure are specifically illustrated in FIG. 1A.

A fixed magnet may comprise any material or stack of materials suitable for maintaining a fixed magnetization direction while a free magnet is magnetically softer (i.e. magnetization can more easily rotate to parallel and antiparallel state with respect to the fixed magnet). In the illustrated embodiment, a fixed magnet includes at least one fixed magnet layer 120 disposed over contact 107. Fixed magnet layer 120 is ferromagnetic. A free magnet includes at least one free magnet layer 140 separated from fixed magnet layer 120 by at least a barrier layer 130. Free magnet layer 140 is ferromagnetic. In some embodiments, MTJ material layer stack 101 is a perpendicular system. In FIG. 1 A, arrows in fixed magnet layer 120 and free magnet layer 140 shows the magnetic easy axis to be in the z-direction out of the x-y plane of material layers in MTJ material layer stack 101. This perpendicular magnetic anisotropy (PMA) may advantageously reduce the switching current between "high" and "low" resistance states and may improve the scalability of MTJ material layer stack 101. Fixed magnet layer 120 advantageously has crystallinity associated with PMA. In some exemplary embodiments, fixed magnet layer 120 has body-centered cubic (BCC) crystal structure, which is advantageous for promoting perpendicular magnetic anisotropy in certain metal alloys comprising one or more of iron, cobalt, and nickel. Fixed magnet layer 120 may further have (001) out-of-plane texture, where texture refers to the distribution of crystallographic orientations within in fixed magnet layer 120. The inventors have found a number of iron alloys crystallize with BCC, (001) texture. In some exemplary embodiments, fixed magnet layer 120 is a CoFeB alloy. In some specific examples, Fe content within the CoFeB is at least 50 at. %. Exemplary embodiments include 20-30 at. % B with one specific alloy being Co2oFe6oB2o. This iron-rich alloy has been found to promote perpendicular magnetic anisotropy. Other embodiments with equal parts cobalt and iron are also possible (e.g., Co4oFe4oB2o), as are more iron-rich alloys. The fixed magnet may also include other material layers, such as an anti- ferromagnetic layer or a synthetic antiferromagnetic (SAF) structure. SAF structures and/or anti-ferromagnetic layers may be considered part of a multi-layered, or composite, fixed magnet. Anti-ferromagnetic layers or SAF structures may be useful for countering a fringing magnetic field associated with an adjacent ferromagnetic material layer of the fixed magnet. Exemplary anti-ferromagnetic layers include, but are not limited to, iridium manganese (IrMn) or platinum manganese (PtMn). Exemplary SAF structures include, but are not limited to Co/Pt bilayers, Co/Pd bilayers, CoFe/Pt bilayers, or CoFe/Pd bilayers. Such material layers may have crystallinity other than BCC (e.g., FCC or HCP crystallinity) and/or may have other than (001) texture (e.g., (I l l) texture). In FIG. 1 A, MTJ material layer stack 101 includes a SAF structure 110. In some exemplary embodiments, SAF structure 110 includes a first plurality of bilayers forming a superlattice of ferromagnetic material (e.g., Co, CoFe, Ni) and a nonmagnetic material (e.g., Pd, Pt, Ru). SAF structure 110 may include n bi-layers (e.g., n [Co/Pt] bilayers, or n [CoFe/Pd] bilayers, etc.) that are separated from a p bilayers (e.g., /? [Co/Pt]) by an intervening non-magnetic spacer. The spacer may provide antiferromagnetic coupling between the bi-layers. The spacer may be a Ruthenium (Ru) layer less than 1 nm thick, for example. Other layers within SAF structure 110 may having thickness ranging from 0.1-0.4 nm, for example.

As further illustrated in FIG. 1 A, a filter layer 115 is between SAF structure 110 and fixed magnet layer 120. Filter layer 115 may be in direct contact with at least one of SAF structure 110 or fixed magnet layer 120, and in some embodiments it is in direct contact with both SAF structure 110 and fixed magnet layer 120. In other embodiments, however, one or more intervening layers may be present between filter layer 115 and SAF structure 110 and/or between filter layer 115 and fixed magnet layer 120. Filter layer 115 is advantageously ferromagnetic to maintain strong coupling between SAF structure 110 and fixed magnet layer 120. Filter layer 115 advantageously has a crystallization temperature that is higher than that of fixed magnet layer 120 so that fixed magnet layer 120 may achieve the desired crystallinity (e.g., BCC) and texture (e.g., (001) texture) regardless of any crystallinity and texture (e.g., FCC with (111) texture) that may be present within SAF structure 110. During a thermal anneal (e.g., of 350 °C, or more) fixed magnet layer 120 may develop BCC (001) crystallization, for example with a crystallization front advancing from an interface with an adjacent layer, such as barrier layer 130, and toward filter layer 115. Crystallization within SAF structure 110 may also proceed at this anneal temperature, for example with a crystallization front advancing from an interface with an adjacent layer, such as a seed layer (not depicted). The higher carbon content within filter layer 115 retards crystallization at the anneal temperature and filter layer 115 may remain completely amorphous unless the thermal anneal temperature is significantly higher (e.g., over 400 °C). Even if filter layer 115 becomes partially crystallized, ferromagnetic material layer 120 and SAF structure 110 should have already crystallized earlier in time without interacting with each other. For example, even where filter layer 115 becomes partially crystallized with (001) texture at the interface proximal to ferromagnetic material layer 120, and partially crystallized with (111) texture at the interface proximal to SAF structure 110, the benefit of the higher crystallization temperature may still impact crystallization within ferromagnetic material layer(s) of the fixed magnet. Accordingly, MTJ device 100 can be expected to display higher TMR, and better quality BCC (001) crystallinity in at least fixed magnet layer 120.

In some embodiments, filter layer 115 includes carbon. The amount of carbon content (doping) within filter layer 115 may vary to the extent that ferromagnetism is maintained. Carbon may be alloyed with a range of ferromagnetic materials, and in some advantageous embodiments carbon is alloyed with one or more of Fe, Co, or Ni. For either of these metal alloys, boron (B) may be added. In some embodiments, filter layer 115 is an iron and carbon alloy (FeC). In some further embodiments, boron may be added (FeBC). In other embodiments, filter layer 115 is a cobalt and carbon alloy (CoC). In some further embodiments, boron may be added (CoBC). In some other embodiments, filter layer 115 is a cobalt, iron and carbon alloy (CoFeC), to which boron may again be added (CoFeBC).

Carbon content within filter layer 115 may be varied depending on the presence of other alloy constituents. In some embodiments, carbon is advantageously less than 50 at. % to ensure ferromagnetism. In one exemplary embodiment, filter layer is (CoFeB)i- _x C _x . The (CoFeB)i-xCx alloy may advantageously have up to approximately 30 at. % C. Alloys of (FeB)i-xC x, (CoFe)i-xC _x , or (CoFeB)i-xCx may also have less carbon, for example no more than 20 at. %, which may better ensure filter layer 115 is ferromagnetic and/or reduce the resistive drop attributable to filter layer 115. In some (CoFeB)i-xCx embodiments, Fe content within the CoFeB fraction is at least 50 at. %, and may be at least 50 at. % within the

(CoFeB)i-xCx alloy, as well. Some exemplary embodiments comprise the addition of carbon to a ferromagnetic alloy having 20-30 at. % B, with one specific alloy being (Co2oFe6oB2o) ι- xCx, where x is between 0.1 and 0.2. Other embodiments with equal parts cobalt and iron are also possible (e.g., Co4oFe4oB2o)i-xC _x , as are more iron-rich alloys with the limit being an FeBC embodiment.

For some embodiments, filter layer 115 comprises the alloy of fixed magnet layer 120, however with additional carbon. Hence, where fixed magnet layer 120 is a CoFeB alloy, filter layer 1 15 may be that same CoFeB alloy further doped with carbon. As one specific example, where fixed magnet layer 120 is Co2oFe6oB2o, filter layer 115 is

(Co2oFe6oB2o)i-xC _x with x between 0.01 and 0.20. Furthermore, where fixed magnet layer 120 is also a carbon-doped alloy (e.g., (CoFeB)i- _y C _y ), the carbon content is higher in filter layer 1 15 than in fixed magnet layer 120. In other exemplary embodiments, boron concentration within filter layer 1 15 is reduced to less than 20 at.% with the limit being the (CoFe)i-xCx embodiment. A (CoFe)i-xCx alloy may also have up to 30 at. % C. In some embodiments, Fe content within the CoFe fraction is between 30 at. % and 60 at. %, and may be less than 50 at. % within the (CoFe)i-xCx alloy. The thickness of filter layer 115 may vary as a function of alloy composition. For

(CoFeB) 1-xCx and (CoFe)i-xCx alloys having carbon content within the exemplary range of 1 - 20 at. %, filter layer 1 15 may have a thickness between approximately 0.5 nm and 2.0 nm.

In the free magnet, free magnet layer 140 advantageously has PMA and the corresponding crystallinity. In some exemplary embodiments, free magnet layer 140 has body-centered cubic (BCC) crystal structure, which is advantageous for promoting perpendicular magnetic anisotropy in certain metal alloys comprising one or more of iron, cobalt, and nickel. Free magnet layer 140 may further have (001) out-of-plane texture. Free magnet layer 140 may have the same alloy composition as fixed magent layer 120, or a distinct composition. In some exemplary embodiments, free magnet layer 140 is a CoFeB alloy. In some specific examples, Fe content within the CoFeB is at least 50 at %.

Exemplary embodiments include 20-30 at. % B. Other embodiments with equal parts cobalt and iron are also possible (e.g., Co4oFe4oB2o), as are more iron-rich alloys. Free magnet layer 140 may be one of a stack of material layers (not depicted) making up the free magnet structure. The stack may include multiple ferromagnetic material layers with a coupling layer separating adjacent ferromagnetic layers. The alloy compositions for any of these layers may be any of those described above for free magnet layer 140, for example. The coupling layer may comprise one or more of W, Mo, Ta, Nb, V, Hf and Cr, for example. Barrier layer 130 may be any material or stack of materials for which current of a first (e.g., majority) spin passes more readily than does current of a second (e.g., minority) spin. Barrier layer 130 is therefore a quantum mechanical barrier, a spin filter, or spin- dependent barrier, through which electrons may tunnel according to probability that is dependent on their spin. The extent by which current of one spin is favored over the other impacts the tunneling magneto-resistance associated with MTJ material layer stack 101. Barrier layer 130 may further provide a crystallization template (e.g., BCC with (001) texture) for solid phase epitaxy of the free and/or fixed magnets within MTJ material layer stack 101. In some embodiments, barrier layer 130 comprises one or more metal and oxygen (i.e., a metal oxide). In some exemplary embodiments, barrier layer 130 is magnesium oxide (MgO). In some other embodiments, barrier layer 130 comprises predominantly metal or graphene, and may even be substantially oxygen-free in some embodiments.

Notably, the material layers within an MTJ material stack may vary considerably without deviating from the scope of the present disclosure. For example, in FIG. 1 A a cap layer 170 is between free magnet layer 140 and contact 180. In some embodiments, cap layer 170 comprises a metal oxide (e.g., MgO, VO, WO, TaO, HfO, MoO). Such a cap layer may be absent for some MTJ device implementations, such as a spin-hall effect (SHE) device. As another example, although not depicted, one or more material layers may be located between SAF structure 110 and contact 107. Notably, the ordering of the material layers 107-180 may be inverted, or deposited so the layers extend laterally away from a topographic feature sidewall, in alternative embodiments. FIG. IB illustrates a material stack 103 for an MTJ device 102, in accordance with some alternative embodiments. A material layer of MTJ material layer stack 103 that shares the same properties of a material layer of MTJ material layer stack 101 is labeled in FIG. IB with the same reference number employed for that material layer in FIG. 1A. As can be seen in FIG. IB, MTJ material layer stack 103 is nearly an inversion of material layer stack 101. In this embodiment, the fixed magnet is over the free magnet with cap layer 170 more proximal to the fixed magnet than the free magnet. In MTJ device 102, filter layer 115 is again located between SAF structure 110 and fixed magnet layer 120, allowing SAF structure 110 and fixed magnet layer 120 to crystallize independently at a temperature lower than that at which filter layer 115 crystallizes. As shown, fixed magnet layer 120 and free magnet layer 140 are again separated by at least barrier layer 130. In this embodiment, free magnet layer 140 is between barrier layer 130 and contact 107. Such an embodiment may benefit from the introduction of one or more layers between free magnet layer 140 and first contact 107. As one example, a seed layer 109 is between free magnet layer 140 and contact 107. Seed layer 109 may be of a material having any composition and microstructure suitable for promoting advantageous crystallinity in free magnet layer 140. In some embodiments, the seed layer comprises Pt and may be a substantially pure Pt (i.e. not intentionally alloyed). A Pt seed layer may have a thickness of at least 2 nm (e.g., 2-5 nm), for example. A Pt seed layer may have FCC structure unless strongly templated by an underlay er. As described further below, one or more additional layers between seed layer 109 and contact 107 may be present to prevent seed layer from developing a crystal structure based on microstructure of contact 107.

In some embodiments, to decouple a seed layer crystallinity from that of an underlay er in a manner that promotes the desired crystallinity (e.g., FCC or HCP) in the seed layer, an MTJ material stack includes a filter layer located between a free (or fixed) magnet seed layer and an underlying contact. The underlying contact may be a metal layer have any arbitrary crystallinity, and the filter layer in this context is an amorphous interface material that permits the seed layer to develop a desired crystallinity. FIG. 2 illustrates a material layer stack 201 for an MTJ device 200, in accordance with some embodiments. Material layers of MTJ material layer stack 201 that have the same properties of material layers in MTJ material layers stack 101 retain the reference numbers employed in FIG. 1 A.

As can be seen in FIG. 2, MTJ material layer stack 201 has a layer sequence that is similar to that of MTJ material layer stack 101 in FIG. 1A (e.g., fixed magnet below the free magnet). As further shown in FIG. 2, a filter layer 108 is between contact 107 and seed layer 109. For such embodiments, filter layer 108 is advantageously amorphous at least at the time when seed layer 109 is deposited, decoupling crystallinity in the seed layer from that of contact 107. In some embodiments, where filter layer 108 is of a material with an advantageously high crystallization temperature, at least a portion of filter layer 108 remains amorphous upon completion of MTJ device 200 (e.g., after all thermal anneals have been completed).

In some exemplary embodiments, filter layer 108 is an alloy that includes carbon. The filter layer alloy may further include one or more metals. Exemplary metals include one or more ferromagnetic metals, such as, but not limited to, Ni, Co or Fe. One or more of these metals may be alloyed with carbon, for example to form any of the alloys described above for filter layer 115 (e.g., FIG. 1A). In some embodiments, filter layer 108 is an iron and carbon alloy (FeC). In other embodiments, filter layer 115 is a cobalt and carbon alloy (CoC). In other embodiments, filter layer 115 is a cobalt, iron and carbon alloy (CoFeC).

Notably, filter layer 108 need not be ferromagnetic, and indeed, it may be advantageous for filter layer 108 to be non- magnetic. Constraints on the composition of filter layer 108 may therefore be relaxed relative to those filter layer 115. For example, the amount of carbon content (doping) within filter layer 108 may vary to a greater extent as higher carbon content is acceptable. Other constituents, such as, but not limited to boron, may be added to any of these exemplary alloy compositions. For example, boron may be added to any of the alloys listed above with the filter layer 108 then comprising an alloy of (FeB)i- _x Cx, (CoB)i-xCx, or (CoFeB)i-xCx. Boron content may be varied in concert with the carbon content to ensure filter layer 115 is deposited in an amorphous state and remains amorphous at least until the crystallinity of seed layer 109 is established. In some exemplary embodiments, filter layer 108 is a metal alloy where carbon and boron sum to at least 20 at. %. For an alloy without boron, carbon content is then at least 20 at. %. Generally, the upper bound on the carbon content is limited by the resistive drop is tolerable for filter layer 108, and carbon content of up to 60 at. % may be acceptable in this respect. The sum of carbon and boron may therefore be as high as 80 at. % with the balance being Fe, Co or CoFe, for example.

In one exemplary embodiment, filter layer 108 is (CoFeB)i-xCx with up to approximately 60 at. % C. In some (CoFeB)i-xCx embodiments, Fe content within the CoFeB fraction is at least 50 at. %, and may be less than 50 at. % within the (CoFeB)i-xCx alloy. Exemplary embodiments include 20-30 at. % B within the CoFeB fraction with one specific alloy being (Co2oFe6oB2o) I-XCX, where x is between 0.1 and 0.6. Other embodiments with equal parts cobalt and iron are also possible, as are very iron-rich alloys with the limit being an (FeB)i- _x C _x embodiment.

For some embodiments, filter layer 108 comprises the alloy of fixed magnet layer 120, however with additional carbon. Hence, where fixed magnet layer 120 is a CoFeB alloy, filter layer 108 may be that same CoFeB alloy further doped with carbon. As one specific example, where fixed magnet layer 120 is Co2oFe6oB2o, filter layer 108 is (Co2oFe6oB2o)i-xC _x with x between 0.1 and 0.6. Furthermore, where fixed magnet layer 120 is also a carbon-doped alloy (e.g., (CoFeB)i- _y C _y ), the carbon content is higher in filter layer 108 than in fixed magnet layer 120. In other exemplary embodiments, boron concentration within filter layer 108 is reduced to less than 20 at.% with the limit being the (CoFe)i-xCx embodiment having at least 20 at. % C. In some embodiments, Fe content within the CoFe fraction is between 30 at. % and 60 at. %, and may be less than 50 at. % within the (CoFe)i- xCx alloy.

The thickness of filter layer 108 may vary as a function of alloy composition, and MTJ material layer stack resistance considerations. For (CoFeB)i- _x C _x and (CoFe)i-xCx alloys with carbon and boron content summing to at least 20 at. %, filter layer 108 may have a thickness anywhere between approximately 0.5 nm and 2.0 nm.

MTJ material layer stack 201 further includes a free magnet having at least one free magnet layer 140 that is separated from fixed magnet layer 120 by at least barrier layer 130. Ferromagnetic free magnet layers may have any of the properties described above in the context of MTJ device 100. Free magnet layer 140 advantageously has PMA. In some exemplary embodiments, free magnet layer 140 has body-centered cubic (BCC) crystal structure, which is advantageous for promoting perpendicular magnetic anisotropy in certain metal alloys comprising one or more of iron, cobalt, and nickel. Free magnet layer 140 may further have (001) out-of-plane texture. Magnet layers 120 and 140 may have the same alloy composition, or a distinct compositions. In some exemplary embodiments, magnet layers 120 and 140 are both CoFeB alloys. In some specific examples, Fe content within the CoFeB alloys is at least 50 at %. Exemplary embodiments include 20-30% B. Other embodiments with equal parts cobalt and iron are also possible (e.g., Co4oFe4oB2o), as are more iron-rich alloys. Free magnet layer 140 may be one of a stack of material layers (not depicted) making up the free magnet. The stack may include multiple ferromagnetic material layers with a coupling layer separating the ferromagnetic layers. Any, or all, of these layers may be CoFeB alloys, for example. The coupling layer may comprise one or more of W, Mo, Ta, Nb, V, Hf and Cr, for example.

For MTJ device 200, barrier layer 130 may again be any material or stack of materials suitable for allowing current of a majority spin to pass through the layer, while impeding current of a minority spin (i.e., a spin filter), impacting the tunneling magneto- resistance associated with MTJ material layer stack 101. Barrier layer 130 may further provide a crystallization template (e.g., BCC with (001) texture) for solid phase epitaxy of the free and/or fixed magnets within MTJ material layer stack 101. In some embodiments, barrier layer 130 is a tunneling dielectric material comprising one or more metal and oxygen (i.e., a metal oxide). In some exemplary embodiments, barrier layer 130 is magnesium oxide (MgO).

Between free magnet layer 140, and contact 180 is a cap layer 170. In some embodiments, cap layer 170 comprises a metal oxide (e.g., MgO, VO, WO, TaO, HfO, MoO). In further reference to FIG. 2, it is noted the material layers within an MTJ material stack may vary considerably without deviating from the scope of the embodiments of the present disclosure. For example, the material layers 107-180 may extend laterally away from a topographic feature sidewalk Also, for an MTJ material stack inverted in the manner illustrated in FIG. IB, if a seed layer is employed within the fixed magnet, a similar filter layer may be inserted between the fixed magnet seed layer and an underlay er, such as contact 107. In some further embodiments, an MTJ device includes both a carbon-doped filter layer between a SAF structure and a ferromagnetic layer of a fixed magnet, and a carbon- doped filter layer between a seed layer and a contact metal. FIG. 3 illustrates an MTJ material layer stack 301 for an MTJ device 300, in accordance with some embodiments including a plurality of carbon-doped filter layers. As shown, MTJ material layer stack 301 includes both filter layer 108 and filter layer 115. Hence, within stack 301 there is a carbon- doped filter layer on both sides of SAF structure 110. In the context of MTJ material layer stack 301, filter layer 115 may have any of the attributes described above in the context of MTJ material layer stack 101. Likewise, in the context of MTJ material layer stack 301, filter layer 108 may have any of the attributes described above in the context of MTJ material layer stack 201. Layers of MTJ material layer stack 301 that share the same properties as layers of MTJ material layer stacks 101 and 201 are again labeled in FIG. 3 with the same reference number employed FIG. 1 A and FIG. 2.

MTJ material stacks in accordance with the device architectures above may be fabricated by a variety of methods applying a variety of techniques and processing chamber configurations. FIG. 4 is a flow diagram illustrating methods 401 for fabricating the MTJ material stacks 101, 201, or 301, in accordance with some exemplary embodiments.

Methods 401 begin with receiving a substrate at operation 410. Any substrate known to be suitable for microelectronic fabrication may be received, such as, but not limited to crystalline silicon substrates. Transistors and/or one or more levels of interconnect metallization may be present on the substrate as received at operation 410.

At operation 420, a bottom contact metal is deposited through any technique known to be suitable for the formation of a first MTJ device contact. At operation 430 layers of a composite fixed magnet, including one or more carbon-doped filter layer, are deposited. In some embodiments, a SAF structure is deposited and one or more ferromagnetic layers, such as, but not limited to, CoFeBC, are deposited over the SAF structure. In some embodiments, a carbon-doped filter layer having one or more of the attributes described elsewhere herein is deposited before deposition of the SAF structure. In some embodiments, a carbon-doped filter layer having one or more of the attributes described elsewhere herein is deposited after deposition of the SAF structure, and before deposition of an overlying ferromagnetic layer. In some embodiments, operation 430 entails the deposition of a carbon-doped filter layer both before and after deposition of the SAF structure. At operation 440, a barrier layer material is deposited over the fixed magnet, and at operation 450 a free magnet is deposited over the barrier layer. Deposition of the free magnet may entail the deposition of one or more ferromagnetic material layers, such as, but not limited to CoFeBC, over the barrier layer material. Operation 450 may also entail depositing a cap layer, such as a metal oxide (e.g., MgO) over the ferromagnetic layer(s). Deposition of such a cap layer is optional, and may be omitted from the fabrication process for a spin-hall effect implementation of an MTJ device, for example. At operation 460, a top contact metal is deposited over the cap layer.

In some exemplary embodiments, operations 420, 430, 440, 450 and 460 all include a physical vapor deposition (sputter deposition) performed at a temperature below 250 °C. One or more of co-sputter and reactive sputtering may be utilized in any capacity known in the art to form the various layer compositions described herein. Co-sputtering may be practiced to incorporate carbon into one or more filter layer deposited at operation 420, for example. For PVD embodiments, one or more of the material layers, including the ferromagnetic layer(s) and carbon-doped filter layers of the fixed magnet, are deposited in amorphous form. These layers may also be discontinuous over a substrate area (e.g., forming islands that do not coalesce during deposition). Alternate deposition techniques, such as atomic layer deposition (ALD) may be performed at operations 420, 430, 440, 450 and 460 for embodiments where precursors for the materials are known to be suitable. Alternatively, epitaxial processes such as, but not limited to, molecular beam epitaxy (MBE) may be practiced to grow one or more of the MTJ material layers. For one or more of these alternative deposition techniques, at least the ferromagnetic material layers of the fixed and free magnets may be deposited with at least some microstructure (e.g., poly crystalline with texture).

At operation 470, a vacuum thermal anneal of at least 350 °C is performed to allow one or more layers of ferromagnetic material reach a desirable crystallinity and texture from their as-deposited states, which may be substantially amorphous. The anneal may be performed under any conditions known in the art to promote solid phase epitaxy of the ferromagnetic layers imparting poly crystalline BCC microstructure and (001) texture, for example. During operation 470 however, one or more of the carbon-doped filter layers deposited at operation 420 remain at last partially amorphous, decoupling the crystallization of adjacent layers from one another. The inventors have found that the inclusion of carbon in the filter layer compositions described herein may advantageously increase the filter layer crystallization temperature to 400 °C, or more. With many processes conventional to MOS transistor integrated circuitry (IC) fabrication being performed at 400 °C, carbon-doped filter layers with high crystallization temperature may enable MTJ devices formed by methods 401 to achieve higher TMR even when subjected to processing at operation 470 at temperatures as high as 400 °C.

Methods 401 are completed with the performance of any remaining MTJ device or MOS transistor IC processing. Any standard microelectronic fabrication processes such as lithography, etch, thin film deposition, planarization (e.g., CMP), and the like may be performed to complete delineation and/or interconnection of an MTJ device employing any of the MTJ material stacks described herein or a subset of the material layers therein.

In some embodiments, the MTJ devices having one or more of the features or attributes described above function essentially as a resistor, where the resistance of an electrical path through the MTJ may exist in two resistive states, either "high" or "low," depending on the direction or orientation of magnetization in the free magnetic layer(s) and in the fixed magnetic layer(s). In the case that the spin direction is down (minority) in the free magnetic layer(s), a high resistive state exists and the directions of magnetization in the coupled free magnet and the fixed magnet are substantially opposed or anti-parallel with one another. In the case that the spin direction is up (majority) in a ferromagnetic material layer of the coupled free magnet, a low resistive state exists, and the directions of magnetization in the ferromagnetic layers of the coupled free magnet and the fixed magnet are substantially aligned or parallel with one another. The terms "low" and "high" with regard to the resistive state of the MTJ device and are relative to one another. In other words, the high resistive state is merely a detectibly higher resistance than the low resistive state, and vice versa. Thus, with a detectible difference in resistance, the low and high resistive states can represent different bits of information (i.e. a "0" or a "1"). The direction of magnetization in the ferromagnetic layer(s) may be switched through a process called spin transfer torque ("STT") using a spin-polarized current. An electrical current is generally non-polarized (e.g. consisting of about 50% spin-up and about 50% spin-down electrons). A spin-polarized current is one with a greater number of electrons of either spin-up or spin-down. The spin-polarized current may be generated by passing a current through the fixed magnetic layer. The electrons of the spin polarized current from the fixed magnet may tunnel through the barrier layer and transfer spin angular momentum to a ferromagnetic layer of the free magnet, wherein the ferromagnetic layer will orient its magnetic direction from anti-parallel to that of the fixed magnet, or parallel.

The spin-hall effect may also be employed to generate spin-polarized current through a particular electrode material that is in contact with a free magnet. For such embodiments, the ferromagnetic material layer(s) of a free magnet may be oriented without applying current through the fixed magnet and other material layers of the MTJ device. In either implementation, the free magnetic layer may be returned to its original orientation by reversing the current. Thus, an MTJ device may store a single bit of information ("0" or "1") by its state of magnetization. The information stored in the MTJ device is sensed by driving a current through the MTJ material stack. The magnetic layer(s) of the free magnet do not require power to retain their magnetic orientations. As such, the state of the MTJ device may be preserved when power to the device is removed. Therefore, a spin transfer torque memory bit cell including the MTJ material stacks described herein are considered non- volatile.

FIG. 5 is a schematic of a STTM bit cell 501, which includes a spin transfer torque element 510, in accordance with some embodiments. The spin transfer torque element 510 includes a free magnet including at least one free magnet layer 140. Element 510 further includes first contact 107 proximate to a fixed magnet including at least one fixed magnet layer 120. At least one material layer between fixed magnet layer 120 and contact 107 includes carbon, for example one or more carbon-doped filter layers, as described elsewhere herein. Barrier layer 130 is located between the free magnet and the fixed magnet. A second contact 180 is proximate to the free magnet. Second contact 180 is electrically coupled to a first metal interconnect 592 (e.g., bit line). First contact 107 is electrically connected to a second metal interconnect 591 (e.g., source line) through a selector. In the illustrated embodiment, the selector is transistor 515. The transistor 515 is further connected to a third metal interconnect 593 (e.g., word line) in any manner conventional in the art. In SHE implementations second contact 180 may be further coupled to a fourth metal interconnect 594 (e.g., maintained at a reference potential relative to first metal interconnect 592). In an altemative embodiment, a cross-point interconnect architecture is employed and the selector may be a two terminal device (e.g., diode). The spin transfer torque memory bit cell 501 may further include additional read and write circuitry (not shown), a sense amplifier (not shown), a bit line reference (not shown), and the like, as understood by those skilled in the art of solid state non-volatile memory devices. A plurality of the spin transfer torque memory bit cells 501 may be operably connected to one another to form a memory array (not shown), and the memory array can be incorporated into a non-volatile memory device following any known techniques and architectures.

In some embodiments, transistors are formed in the front end of the line (FEOL) while an MTJ device is formed within the back end of the line (BEOL). Fig. 6 illustrates a cross-section 600 of a die layout including MTJ device 101 located in metal 3 and metal 2 layer regions, according to some embodiments of the disclosure. Elements in FIG. 6 having the same reference numbers (or names) as the elements of any other figures or description provided herein can comprise materials, operate, or function, substantially as described elsewhere herein.

Cross-section 600 illustrates an active region having a transistor MN comprising diffusion region 601, a gate terminal 602, drain terminal 604, and source terminal 603. The source terminal 603 is coupled to SL (source line) via polysilicon or a metal via, where the SL is formed on Metal 0 (M0). In some embodiments, the drain terminal 604 is coupled to MOa (also metal 0) through via 605. The drain terminal 604 is coupled to contact 107 through via 0-1 (e.g., via connecting metal 0 to metal 1 layers), metal 1 (Ml), via 1-2 (e.g., via connecting metal 1 to metal 2 layers), and metal 2 (M2). In some embodiments, MTJ 101 is formed in the metal 3 (M3) region. In some embodiments, the perpendicular fixed magnet of MTJ 101 couples to contact 107 and the perpendicular free magnet couples to the bit-line (BL) through Via 3-4 (e.g., via connecting metal 4 region to metal 4 (M4)). In this example, bit-line is formed on M4. In other embodiments, MTJ device 101 is formed in the metal 2 region and/or Via 1 -2 region. In still other embodiments, MTJ device 100 is inverted with the perpendicular free magnet of MTJ device 100 coupling to contact 107 and the perpendicular fixed magnet coupling to Via 3-4 (e.g., via connecting metal 4 region to metal 4 (M4)).

FIG. 7 illustrates a system 700 in which a mobile computing platform 705 and/or a data server machine 706 employs an MTJ device with an MTJ material stack including at least one carbon-doped filter layer, for example as described elsewhere herein. Server machine 706 may be any commercial server, for example including any number of high- performance computing platforms disposed within a rack and networked together for electronic data processing, which in the exemplary embodiment includes data processor circutry 750. The mobile computing platform 705 may be any portable device configured for each of electronic data display, electronic data processing, wireless electronic data transmission, or the like. For example, the mobile computing platform 705 may be any of a tablet, a smart phone, laptop computer, etc., and may include a display screen (e.g., a capacitive, inductive, resistive, or optical touchscreen), a chip-level or package-level integrated system 710, and a battery 715.

Whether disposed within the integrated system 710 illustrated in the expanded view 720, or as a stand-alone packaged device within the server machine 706, SOC 760 includes at least an MTJ device with an MTJ material stack that has one or more carbon-doped filter layer, for example as described elsewhere herein. SOC 760 may further include memory circuitry and/or a processor circuitry 750 (e.g., STTM, MRAM, a microprocessor, a multi- core microprocessor, graphics processor, etc.). Any of controller 735, PMIC 730, or RF (radio frequency) integrated circuitry (RFIC) 725 may also be communicatively coupled to an MTJ device, such as an embedded STTM employing MTJ material stacks including one or more carbon-doped filter layers. As further illustrated, in the exemplary embodiment, RFIC 725 has an output coupled to an antenna (not shown) to implement any of a number of wireless standards or protocols, including but not limited to Wi-Fi (IEEE 802.11 family), WiMAX (IEEE 802.16 family), IEEE 802.20, long term evolution (LTE), Ev-DO, HSPA+, HSDPA+, HSUPA+, EDGE, GSM, GPRS, CDMA, TDMA, DECT, Bluetooth, derivatives thereof, as well as any other wireless protocols that are designated as 3G, 4G, 5G, and beyond. In alternative implementations, each of these SoC modules may be integrated onto separate ICs coupled to a package substrate, interposer, or board.

FIG. 8 is a functional block diagram of a computing device 800, arranged in accordance with at least some implementations of the present disclosure. Computing device 800 may be found inside platform 705 or server machine 706, for example. Device 800 further includes a motherboard 802 hosting a number of components, such as, but not limited to, a processor 804 (e.g., an applications processor), which may further incorporate embedded magnetic memory 830 based on MTJ material stacks including one or more carbon-doped ferromagnetic layers, in accordance with embodiments of the present disclosure. Processor 804 may be physically and/or electrically coupled to motherboard 802. In some examples, processor 804 includes an integrated circuit die packaged within the processor 804. In general, the term "processor" or "microprocessor" may refer to any device or portion of a device that processes electronic data from registers and/or memory to transform that electronic data into other electronic data that may be further stored in registers and/or memory.

In various examples, one or more communication chips 806 may also be physically and/or electrically coupled to the motherboard 802. In further implementations,

communication chips 806 may be part of processor 804. Depending on its applications, computing device 800 may include other components that may or may not be physically and electrically coupled to motherboard 802. These other components include, but are not limited to, volatile memory (e.g., DRAM 832), other non-volatile memory 835 (e.g., flash memory), a graphics processor 822, a digital signal processor, a crypto processor, a chipset 812, an antenna 825, touchscreen display 815, touchscreen controller 875, battery 810, audio codec, video codec, power amplifier 821, global positioning system (GPS) device 840, compass 845, accelerometer, gyroscope, speaker 820, camera 841. Computing device 800 may also include a mass storage device (not depicted), such as a hard disk drive, solid-state drive (SSD), compact disk (CD), digital versatile disk (DVD), or the like.

Communication chips 806 may enable wireless communications for the transfer of data to and from the computing device 800. The term "wireless" and its derivatives may be used to describe circuits, devices, systems, methods, techniques, communications channels, etc., that may communicate data through the use of modulated electromagnetic radiation through a non-solid medium. The term does not imply that the associated devices do not contain any wires, although in some embodiments they might not. Communication chips 806 may implement any of a number of wireless standards or protocols, including but not limited to those described elsewhere herein. As discussed, computing device 800 may include a plurality of communication chips 806. For example, a first communication chip may be dedicated to shorter-range wireless communications, such as Wi-Fi and Bluetooth, and a second communication chip may be dedicated to longer-range wireless communications such as GPS, EDGE, GPRS, CDMA, WiMAX, LTE, Ev-DO, and others. While certain features set forth herein have been described with reference to various implementations, this description is not intended to be construed in a limiting sense. Hence, various modifications of the implementations described herein, as well as other

implementations, which are apparent to persons skilled in the art to which the present disclosure pertains are deemed to lie within the spirit and scope of the present disclosure. It will be recognized that the disclosure is not limited to the embodiments so described, but can be practiced with modification and alteration without departing from the scope of the appended claims. For example the above embodiments may include specific combinations of features as further provided below.

In one or more first examples, a magnetic tunneling junction (MTJ) device, comprises a pair of contacts, each comprising one or more metals, and a material layer stack between the contacts. The material layer stack comprises a barrier layer between a fixed magnet layer and a free magnet layer, and a filter layer between the fixed magnet layer and one of the contacts, on a side of the fixed magnet layer opposite the barrier layer, wherein the filter layer comprises carbon. In one or more second examples, for any of the first examples the layer stack comprises an anti-ferromagnetic layer or a synthetic antiferromagnetic (SAF) structure and the filter layer is between the fixed magnet layer and the anti-ferromagnetic layer, or the SAF structure.

In one or more third examples, for any of the first through second examples the filter layer comprises a ferromagnetic alloy with less than 30 at. % carbon. In one or more fourth examples, for any of the first through the third examples the filter layer comprises at least one of Co or Fe.

In one or more fifth examples, for any of the first through the fourth examples the filter layer comprises CoFeBC, FeBC, or CoFeC with no more than 20 at. % carbon.

In one or more sixth examples, for any of the first through the fifth examples the fixed magnet layer comprises CoFeB and the filter layer comprises (CoFeB)i- _x C _x .

In one or more seventh examples, for any of the first through the sixth examples the filter layer has a thickness between 0.5 nm and 2 nm.

In one ore more eighth examples, for any of the second through the seventh examples one or more layers of the SAF have a first crystallinity and the fixed magnet layer has a second crystallinity different than the first crystallinity.

In one or more ninth examples, for any of the eighth examples the first crystallinity is FCC with (111) texture and the second crystallinity is BCC with (001) texture.

In one or more tenth examples, for any of the first through the ninth examples the material layer stack comprises a synthetic antiferromagnetic (SAF) structure and the filter layer is between the SAF and one of the contacts, on a side of the SAF structure opposite the fixed magnet layer.

In one or more eleventh examples, for any of the first through the tenth examples the material layer stack further comprises a seed layer between the filter layer and the SAF structure, the seed layer having FCC or HCP crystallinity. In one or more twelfth examples, for any of the eleventh examples the seed layer comprises at least one of Pt or Ru. In one or more thirteenth examples for any of the first through the twelfth examples the filter layer comprises at least one of Co or Fe.

In one or more fourteenth examples, for any of the thirteenth examples the filter layer further comprises boron with the boron and the carbon summing to at least 20 at. %. In one or more fifteenth examples, for any of the fourteenth examples the filter layer comprises CoFeBC with between 1.0 at. % and 60 at. % carbon.

In one or more sixteenth examples, for any of the thirteenth examples the filter layer comprises CoFeC with between 20 at. % and 80 at. % carbon.

In one or more seventeenth examples, a system, comprises a processor, and a memory coupled to the processor, the memory comprising a magnetic tunneling junction (MTJ) device, further comprising a pair of contacts, each comprising one or more metals, and a material layer stack between the contacts. The material layer stack comprises a barrier layer between a fixed magnet layer and a free magnet layer, at least one of which has perpendicular magnetic anisotropy, and a filter layer between the fixed magnet layer and one of the contacts, on a side of the fixed magnet layer opposite the barrier layer, wherein the filter layer comprises carbon.

In one or more eighteenth examples, for any of the seventeenth examples the filter layer comprises at least one of Co and Fe with no more than 20 at. % C.

In one or more nineteenth examples, A method of forming a magnetic tunneling junction (MTJ) device, the method comprising forming a pair of contacts, each comprising one or more metals, and forming a material stack between the pair of contacts. Forming the stack further comprises forming a first of a fixed magnet layer and a free magnet layer, forming a barrier layer over the first of the fixed magnet layer and the free magnet layer, forming a second of the fixed magnet layer and the free magnet layer over the barrier layer, and forming a filter layer between the fixed magnet layer and one of the contacts, on a side of the fixed magnet layer opposite the barrier layer, wherein the filter layer comprises carbon.

In one or more twentieth examples, for any of the nineteenth examples forming the stack further comprises depositing a first of the contacts, depositing a synthetic antiferromagnetic structure (SAF) over the first of the contacts, and depositing the filter layer comprising an alloy of (CoFeB)i- _x C _x or (CoFe)i-xCx Over the SAF, and depositing a fixed magnet layer comprising CoFeB over the filter layer.

In one or more twenty-first examples, for any of the twentieth examples the method further comprises annealing the MTJ stack at a temperature of at least 350 °C to allow the SAF material layers to develop crystallinity with (111) texture and allow the fixed magnet layer to develop crystallinity with (001) texture.

In one or more twenty-second examples, for any of the nineteenth through the twenty-first examples depositing the filter layer further comprises sputter depositing a layer of (CoFeB)i-xCx to a thickness no more than 2.0 nm, and wherein x is between 0.01 and 0.30 at. %.

In one or more twenty -third examples, for any of the nineteenth through the twenty- second examples forming the stack further comprises depositing a first of the contacts, depositing a filter layer comprising an alloy of (CoFeB)i-xCx or (CoFe)i-yCy over the first of the contacts, depositing a synthetic antiferromagnetic (SAF) structure over the filter layer, and depositing a fixed magnetic layer comprising CoFeB over the SAF structure.

In one or more twenty -fourth examples, for any of the nineteenth through twenty- third examples the method further comprises depositing a seed layer comprising Pt or Ru over the filter layer.

In one or more twenty-fifth examples, for any of the nineteenth through twenty- fourth examples depositing the filter layer further comprises sputter depositing a layer of (CoFeB)i-xCx to a thickness no more than 2.0 nm, and wherein x is at least 1.0 at. %.

In one or more twenty-sixth examples, for any of the twenty -third through twenty fifth examples depositing the filter layer further comprises sputter depositing a layer of (CoFe)i-yCy to a thickness no more than 2.0 nm, and wherein y is at least 20 at. %.

In one or more twenty-seventh examples a system, comprises a processor, and a memory coupled to the processor, the memory comprising the MTJ device recited in any one of the first through the sixteenth examples. In one or more twenty-eighth examples a system comprises a processing means, and a memory means coupled to the processing means, wherein the memory means comprises the MTJ device recited in any of the first through the sixteenth examples.

However, the above embodiments are not limited in this regard and, in various implementations, the above embodiments may include the undertaking only a subset of such features, undertaking a different order of such features, undertaking a different combination of such features, and/or undertaking additional features than those features explicitly listed. The scope of the disclosure should, therefore, be determined with reference to the appended claims, along with the full scope of equivalents to which such claims are entitled.