WO2019005076A1

WO2019005076A1 - Magnetic tunneling junction devices with a carbon-doped magnet layer

Info

Publication number: WO2019005076A1
Application number: PCT/US2017/040044
Authority: WO
Inventors: Charles Kuo; Anurag Chaudhry; Kaan OGUZ
Original assignee: Intel Corporation
Priority date: 2017-06-29
Filing date: 2017-06-29
Publication date: 2019-01-03

Abstract

MTJ material stacks including a carbon-doped ferromagnetic material, MTJ devices employing such stacks, and computing platforms employing such MTJ devices. A free magnet with one or more ferromagnetic material layer that includes carbon may display improved stability and low damping. A fixed magnet with one or more ferromagnetic material layer may also include carbon.

Description

Magnetic Tunneling Junction Devices

With a Carbon-Doped Magnet Layer

BACKGROUND

Non-volatile monolithic 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 layer 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. 1 illustrates a material stack for a MTJ device, in accordance with some embodiments;

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

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

FIG. 4A is a flow diagram illustrating a method of fabricating the MTJ device illustrated in FIG. 1, in accordance with some embodiments;

FIG. 4B is a flow diagram illustrating a method of fabricating the MTJ device illustrated in FIG. 2, in accordance with some embodiments; FIG. 5 is a schematic of a 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 a MTJ-based memory cell, according to some embodiments of the disclosure.

FIG. 7 is a schematic illustrating a mobile computing platform and a data server machine employing an MTJ memory device, in accordance with embodiments; and

FIG. 8 is a functional block diagram illustrating an electronic computing device, in accordance with some embodiments. 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.

Thermal stability is one of the most important issues facing the scaling of STTM based devices and memory arrays, as instability is manifested within a memory element as shortening of the non-volatile lifetime. Magnetic anisotropy is a function of saturation magnetization Mr and effective anisotropy field Hk,_eff such that thermal stability may be improved through a reduction in r.

MTJ material stacks with a ferromagnetic layer including carbon, MTJ devices employing such material stacks, and computing platforms employing such MTJ devices are described herein. In some embodiments, perpendicular MTJ material stacks include a fixed magnet and a free magnet, each having 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. At least one of the ferromagnetic material layers in the MTJ material stack is an alloy including carbon. In some embodiments, a perpendicular MTJ material stack includes a free magnet with one or more magnetic layers that are doped with carbon for improved stability and low damping.

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 the scaling of MTJ-based devices. 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)). Stability is equal to the product of magnetic anisotropy fc of the free magnetic material and volume of free magnetic material (thickness t multiplied by material stack area A) divided by thermal energy B ):

A= (1)

k_BT >

Generally, a stability value of at least eOkeT is considered suitable for most memory device applications. However, scaling of MTJ stack area reduces stability and the 60keT target becomes harder to achieve. Magnetic anisotropy is also a function of saturation magnetization Mr and effective anisotropy field Hk,_eff such that thermal stability may be improved through an increase in anisotropy field, and/or through a reduction in saturation magnetization Ms. MTJ damping is a metric associated with a magnetic friction that a spin's

magnetization experiences as the spin switches from one state to another. Greater damping means that a larger critical write current Jc is needed to switch the magnetization of a free magnet from one state to another. Critical current J_c is proportional to a damping constant a multiplied by a ratio of stability over spin transfer efficiency (~ TMR). Often then, increases in anisotropy also increase the critical current density linearly, making it difficult to achieve higher stability without a concomitant increase in damping. Reductions in saturation magnetization M_s can therefore be an advantageous means of improving stability with reduced damping.

In some embodiments, the stability of an MTJ, and therefore any device employing such an MTJ, such as an STTM, is enhanced by including one or more carbon-doped ferromagnetic layer. The carbon-doped ferromagnetic layer(s) may also reduce damping. The inventors have found that carbon doping of some alloys that have perpendicular magnetic anisotropy can reduce saturation magnetization Mr. The inventors have further found that saturation magnetization trends down as the concentration of carbon within the ferromagnetic alloy increases. Generally, the upper bound of carbon concentration within a magnetic alloy is where the ferromagnetic property is lost. As described further below, one or more ferromagnetic layers within a free magnet of an MTJ device may include carbon. Although the advantages associated with reduced saturation magnetization noted above may be achieved by including carbon in one or more ferromagnetic layer of the free magnet, similar carbon doping may also be used within one or more layers of a fixed magnet. FIG. 1 illustrates an MTJ material stack 101 for a MTJ device 100, in accordance with some embodiments. In the illustrated example, MTJ device 100 has a columnar or pillar structure with the material stack having layers with a layer thickness 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 stack 101 there between. First contact 107 may include one or more metal layers, each layer comprising an elemental or alloyed metal. In one exemplary embodiment, contact 107 includes a layer comprising tantalum (Ta) or ruthenium (Ru). Contact 180 may also include one or more metal layers, each layer comprising an elemental or alloyed metal. In one exemplary embodiment, contact 180 includes a layer comprises tantalum (Ta), tungsten (W), or ruthenium (Ru). Although vertically oriented, material stack 101 may also extend horizontally such that the columnar structure illustrated is instead a series of material stripes across the x-y plane. MTJ devices 100 may be monolithic with other devices of an integrated circuit, sharing the same substrate (not depicted) that is known to be suitable for integrated circuits. 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 a composite structure including a plurality of material layers that together comprise a functional component of MTJ device 100. In FIG. 1, ellipses are drawn between illustrated material layers to further emphasize that MTJ device 100 may have any number of layers, and only a selected subset of the material layers relevant to the present disclosure are specifically illustrated in FIG. 1. In the illustrated embodiment, a fixed magnet layer 120 is over contact 107. Fixed magnet layer 120 is a ferromagnetic material. A fixed magnet may also include other material layers. A free magnet layer 140 is separated from fixed material layer 120 by at least a barrier layer 130. Free magnet layer 140 is also a ferromagnetic material. A free magnet may further include other material layers. 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 stack 101. Barrier layer 130 may further provide a crystallization template (e.g., BCC with (001) texture) for epitaxy (e.g., 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.

In further reference to FIG. 1, it is noted the material layers within an MTJ material stack may vary considerably without deviating from the scope of the present disclosure. For example, one or more intermediate material layer may be disposed between a free magnet and nearest contact. For example, in FIG. 1, a cap layer 170 is between ferromagnetic material layer 140 and contact 180. In some embodiments, cap layer 170 comprises a metal oxide (e.g., MgO, VO, WO, TaO, HfO, MoO). A cap layer may be absent for some MTJ device implementations, such as a spin-hall effect (SHE) device. As another example, one or more intermediate material layer may be disposed between fixed magnet layer 120 and contact 107. In some embodiments, for example, an anti-ferromagnetic layer or a synthetic antiferromagnetic (SAF) structure 110 is incorporated into MTJ material stack 101, which may be useful for countering a fringing magnetic field associated with fixed magnet layer 120. 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. 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 s bi-layers (e.g., n [Co/Pt] bilayers, or «

[CoFe/Pd] bilayers, etc.) that are separated from a p bilayers (e.g., p [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 have thicknesses ranging from 0.1-0.4 nm, for example. SAF structures and/or anti-ferromagnetic layers may be considered part of a multi-layered fixed magnet. Although not depicted, one or more additional material layers may be located between SAF structure 110 and contact 107.

In some embodiments, MTJ material stack 101 is a perpendicular system. In FIG. 1, arrows in fixed magnet layer 120 and free magnet layer 140 show the magnetic easy axis as in the z-direction out of the x-y plane of material layers in MTJ material stack 101. MTJs with magnetic layers having a magnetic easy axis perpendicular (out of plane of the device footprint) have a potential for realizing higher density memory than in-plane variants.

Perpendicular magnetic anisotropy (PMA) can be achieved in the free magnetic layer, for example through interfacial perpendicular anisotropy established by an adjacent layer. PMA may advantageously reduce the switching current between "high" and "low" resistance states and may improve the scalability of MTJ material stack 101. The fixed magnet may comprise any material or stack of materials suitable for maintaining a fixed magnetization direction while the free magnet is magnetically softer (i.e. magnetization can more easily rotate to parallel and antiparallel state with respect to the fixed magnet). As noted above, at least one of magnet layers 120 and 140 is an alloy including carbon. In some embodiments, at least free magnet layer 140 includes carbon. The amount of carbon content (doping) within free magnet layer 140 may vary to the extent that ferromagnetism is maintained. Carbon may be alloyed with a range of ferromagnetic materials and Heusler alloys. In some advantageous embodiments with perpendicular magnetic anisotropy, carbon may be alloyed with one or more of Fe and Co. For either of these alloys, boron may be added. In some embodiments, free magnet layer 140 is an iron and carbon alloy (FeC). In some further embodiments, boron may be added (FeBC). In other embodiments, free magnet layer 140 is a cobalt and carbon alloy (CoC). In some further embodiments, boron may be added (CoBC). In some other embodiments, free magnet layer 140 is a cobalt, iron and carbon alloy (CoFeC), to which boron may again be added

(CoFeBC).

In some advantageous embodiments, free magnet layer 140 has body-centered cubic (BCC) crystal structure, which is advantageous for promoting perpendicular magnetic anisotropy in one or more of the above alloys. Free magnet layer 140 may further have (001 ) out-of-plane texture, where texture refers to the distribution of crystallographic orientations within in free magnet layer 140. Of the alloys above, the inventors have found those with iron to most readily crystallize with BCC, (001) texture.

Carbon content within free magnet layer 140 may vary depending on what the other alloy constituents are, but can be expected to be less than 50 at. % to ensure ferromagnetism. In one exemplary embodiment where free magnet layer 140 is (CoFeB)i-_xC_x, the (CoFeB)i- xCx alloy may advantageously have up to approximately 20 at. % C. An alloy of (CoFeB)i- xCx may have more iron than cobalt for increased magnetic perpendicularity. In some embodiments, Fe content within the CoFeB is at least 50 at. %, and may be at least 50 at. % within the (CoFeB)i-xCx alloy, as well. Exemplary embodiments include 20-30 at. % B within the CoFeB fraction with one specific alloy being (Co2oFe6oB2o) i-xC_x, where x is between 0. 1 and 0.2. For such an alloy, carbon content of about 10- 15 at. %, will render the alloy iron-rich to promote perpendicular magnetic anisotropy while still providing a significant reduction in saturation magnetization. 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 the FeBC embodiment.

In other exemplary embodiments, the boron concentration is reduced to less than 20 at. % with the limit being a (CoFe)i-xCx embodiment. For CoFe alloys, perpendicular magnetic anisotropy may be difficult to achieve but for the presence of the carbon, which may introduce tetragonal strain within the CoFe lattice. This strain may impart perpendicular magnetic anisotropy to free magnet layer 140 that would otherwise be absent from a CoFe alloy. Hence, for such an alloy, the inclusion of carbon may serve the further purpose of improving PMA of a ferromagnetic layer composition that is very lean in boron (or boron- free). An alloy of (CoFe)i-xCx may advantageously have up to 10 at. % C. In some embodiments, Fe content within the CoFe alloy is between 30 at. % and 60 at. %, and may be less than 50 at. % within the (CoFe)i-xCx alloy. The thickness of free magnet layer 140 may vary as a function of alloy composition, including the carbon content. For an alloy of (CoFeB)i-_XC_X with carbon content within the exemplary range of 1 -20 at. %, free magnet layer 140 may have a thickness between approximately 1 .0 nm and 2.0 nm with greater thicknesses suitable for alloys with higher carbon content. For one specific example where an alloy of (Co2oFe6oB2o) I-XCX has 15 at. % C, free magnet layer 140 may have a thickness between approximately 1.4 nm and 1.6 nm. For an alloy of (CoFe)i-xCxwith a carbon content within the exemplary range of 1 - 10 at. %, free magnet layer 140 may again have a thickness between approximately 1 .0 nm and 2.0 nm.

In some exemplary embodiments where free magnet layer 140 includes carbon, fixed magnet layer 120 has significantly less carbon, and may have no intentional carbon doping (e.g., trace impurity levels of less than 1 .0 at. %). However, in other embodiments one or more layers of the fixed magnet is also deliberately carbon-doped. For example, fixed magnet layer 120 may also include carbon to the extent that ferromagnetism is maintained. Carbon content within fixed magnet layer 120 may be the same or different than the carbon content of free magnet layer 140. Carbon may again be alloyed with a range of ferromagnetic materials or Heusler alloys. In some advantageous embodiments with perpendicular magnetic anisotropy, carbon is alloyed with one or more of Fe and Co. For either of these alloys, boron may be added. For embodiments where both magnet layers 140 and 120 are carbon alloys, the two carbon alloys may include the same constituents, or not. In some embodiments where the carbon-doped ferromagnetic alloys have the same constituents, the carbon content of fixed magnet layer 120 is lower than that of free magnet layer 140.

In some embodiments, fixed magnet layer 120 is an iron and carbon alloy (FeC). In some further embodiments, boron may be added (FeBC). In other embodiments, fixed magnet layer 120 is a cobalt and carbon alloy (CoC). In some further embodiments, boron may be added (CoBC). In some other embodiments, fixed magnet layer 120 is a cobalt, iron and carbon alloy (CoFeC), to which boron may again be added (CoFeBC).

In some advantageous embodiments, fixed magnet layer 120 also has body-centered cubic (BCC) crystal structure, which is advantageous for promoting perpendicular magnetic anisotropy in one or more of the above alloys. Fixed magnet layer 120 may also have (001 ) out-of-plane texture. In one exemplary embodiment, where free magnet layer 140 is

(CoFeB)i-xCx fixed magnet layer 120 is an alloy of either CoFeB or (CoFeB)i-xCx. In some embodiments, Fe content within the CoFeB fraction of fixed magnet layer 120 is again at least 50 at. %, and may be at least 50 at. % within an alloy of (CoFeB)i-xCx, as well. Exemplary embodiments include 20-30 at. % B in the CoFeB fraction with one specific alloy being Co2oFe6oB2o with no carbon doping. Other embodiments with equal parts cobalt and iron are also possible (e.g., Co4oFe4oB2o).

FIG. 2 illustrates a MTJ device 200 that includes an MTJ material layer stack 201, in accordance with some embodiments. Material layers of MTJ material layer stack 201 that shares the same properties layers of MTJ material stack 101 are labeled in FIG. 2 with the same reference number employed in FIG. 1. For MTJ device 200, free magnet layer 140 may have any of the properties described above in the context of MTJ device 100. Free magnet layer 120 may likewise have any of the properties described above in the context of MTJ device 100.

As can be seen from FIG. 2, MTJ material layer stack 201 is nearly an inversion of material 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. 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 embodiments may benefit from the inclusion of one or more layers between free magnet layer 140 and contact 107. In FIG. 2, placeholders for various intervening material layers are again represented by ellipses. As one example, a seed layer (not depicted) may be between free magnet layer 140 and contact 107. The seed layer may be of a material having any composition and microstructure suitable to promote 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. One or more additional layers may be present to prevent seed layer from developing an undesirable crystal structure through interactions with contact 107.

In some embodiments, a free magnetic includes multiple ferromagnetic material layers, and at least the ferromagnetic material layer nearest to the fixed magnet includes carbon. FIG. 3 illustrates a material layer stack 340 of a free magnet, in accordance with some exemplary multi-layered embodiments. Stack 340 may replace free magnet layer 140 in either MTJ device 100 or MTJ device 200, for example. As shown, stack 340 includes a first ferromagnetic material layer 140A and a second ferromagnetic material layer 140C with at least a coupling layer 140B separating them. Coupling layer 140B may comprise one or more of W, Mo, Ta, Nb, V, Hf and Cr, for example, and may have a thickness less than lnm (e.g., 0.3-0.5 nm).

At least one of ferromagnetic material layers 140A and 140C include carbon, and in some embodiments both ferromagnetic material layers 140A and 140C include carbon. For embodiments where only one of ferromagnetic material layers 140A and 140C is doped with carbon, it is the ferromagnetic material layer nearest to the fixed magnet carbon-doped.

Hence, where stack 340 is inserted into MTJ device 100, at least ferromagnetic material layer 140 A, being closer to the fixed magnet, includes carbon. Likewise, where stack 340 is inserted into MTJ device 200, at least ferromagnetic material layer 140C, being closer to the fixed magnet, includes carbon.

The alloy compositions for ferromagnetic material layers 140A and 140C may be any of those described above for fixed magnet layer 140. In some embodiments where both ferromagnetic material layer 140A and 140C include carbon, the alloy compositions for these two layers is the same, and may be any of those alloys described above for free magnet layer 140 (e.g., CoFeBC). The thickness of ferromagnetic layer closest to the fixed magnet (e.g., 140 A) may range from 0.6 to 1.6 nm, for example, while the thickness of the other ferromagnetic layer may be less than 1.0 nm, for example.

MTJ material stacks in accordance with the architectures above may be fabricated by a variety of methods applying a variety of techniques and processing chamber configurations. FIG. 4A is a flow diagram illustrating methods 401 for fabricating the MTJ device illustrated in FIG. 1, in accordance with some 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 and fixed magnet base layers, such as a SAF structure, are deposited. At operation 430, one or more ferromagnetic layers of the fixed magnet are deposited. At operation 440, a barrier layer material is deposited over the fixed magnet. At operation 451 one or more ferromagnetic material layers including carbon, such as CoFeBC, are deposited over the barrier layer material. At operation 460, a cap layer, such as a metal oxide (e.g., MgO), is deposited over the free magnet. Deposition of 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 470, a top contact metal is deposited over the cap layer.

In exemplary embodiments, operations 420, 430, 440, 451, 460 and 470 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 ferromagnetic material layer deposited at operation 451, for example. If desired, co-sputtering may also be practiced at operation 430 to incorporate carbon into one or more ferromagnetic material layer of the fixed magnet. For PVD embodiments, one or more of the material layers, such as but not limited to the ferromagnetic layers of the fixed and free magnets, are deposited in amorphous form that may also be discontinuous over a substrate area (e.g., forming islands that do not coalesce). Alternate deposition techniques, such as atomic layer deposition (ALD) may be performed for those materials of an MTJ stack known to have suitable precursors. 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 490, a vacuum thermal anneal of at least 350 °C is performed to allow magnetic materials develop 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. Notably, because many processes in MOS transistor integrated circuitry (IC) fabrication are performed at 400 °C, the inventors have found that the addition of carbon to at least the free magnet improves the stability of the MTJ material stack to the extent that a higher temperature anneal (e.g., 400 °C) may be performed at operation 490 in accordance with some advantageous embodiments.

Methods 401 are completed with any remaining MTJ device or MOS transistor IC processing. 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.

FIG. 4B is a flow diagram illustrating methods 402 for fabricating the MTJ device illustrated in FIG. 2, in accordance with some embodiments. Operations substantially the same as those introduced in the context of methods 401 have the same reference numbers as provided in FIG. 4A. Methods 402 begin with receiving a substrate at operation 410. At operation 421, a bottom contact metal and one or more bottom layers, such as a seed layer, are deposited. At operation 431 one or more ferromagnetic layers including carbon, such as CoFeBC, are deposited. Any other layers of the free magnet may further be deposited prior to, or subsequent to, operation 431. At operation 440, a barrier layer material is deposited over the free magnet. At operation 450 one or more ferromagnetic material layers of the fixed magnet are deposited over the barrier layer. At operation 455 any additional fixed magnet layers, such as a SAF structure, are deposited. At operation 460, a cap layer is deposited over the fixed magnet. At operation 470, the top contact metal is deposited over the cap layer. In exemplary embodiments, operations 421, 431, 440, 450, 455, 460 and 470 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 ferromagnetic material layer deposited at operation 431, for example. If desired, co-sputtering may also be practiced at operation 450 to incorporate carbon into one or more ferromagnetic material layer of the fixed magnet.

For PVD embodiments, one or more of the material layers, such as but not limited to the ferromagnetic layers of the fixed and free magnets, are deposited in amorphous form that may also be discontinuous over a substrate area (e.g., forming islands that do not coalesce). Alternate deposition techniques, such as atomic layer deposition (ALD) may be performed for those materials of the MTJ stack having precursors 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 490, a vacuum thermal anneal of at least 350 °C is performed to allow magnetic materials develop a desirable crystallinity and texture from their as-deposited states, which may be substantially amorphous. A higher temperature anneal (e.g., 400 °C) may also be performed at operation 490 in accordance with some advantageous embodiments.

Methods 402 are completed with the performance of any remaining MTJ device or MOS transistor IC processing.

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 MTJ memory bit cell 501, which includes a spin transfer torque element 510, in accordance with some embodiments. The spin transfer torque element 510 includes at least one free magnet layer 140. Element 510 further includes first contact 107 proximate to a fixed magnet layer 120. At least one of magnet layers 120 and 140 include carbon, for example 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 example, 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 alternative embodiments, a cross-point architecture is employed and the selector may be a two terminal device, such as a 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 100 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 device 100 is formed in the Metal 3 (M3) region. In some embodiments, the perpendicular fixed magnet of MTJ device 100 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 100 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 ferromagnetic layer including carbon, 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 a packaged device 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 ferromagnetic layer including carbon. SOC 760 may further include memory circuitry and/or a processor circuitry 751 (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 ferromagnetic 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 815, 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 an MTJ material layer stack there between. The stack includes a fixed magnet comprising a first layer, a free magnet comprising one or more second layers, wherein at least the second layer nearest to the fixed magnet comprises carbon, and a barrier layer between the fixed magnet and the free magnet.

In one or more second examples, for any of the first examples the second layer nearest to the fixed magnet has BCC crystal structure with (001) texture.

In one or more third examples, for any of the first through second examples the second layer nearest to the fixed magnet comprises no more than 20 at. % carbon.

In one or more fourth examples, for any of the first through third examples the second layer nearest to the fixed magnet comprises at least one of Co or Fe. In one or more fifth examples, for any of the first through fourth examples the second layer nearest to the fixed magnet comprises CoFeBC, FeBC, or CoFeC.

In one or more sixth examples, for any of the first through fifth examples the second layer nearest to the fixed magnet comprises (CoFeB)i-_xC_x, x is between 0.01 and 0.20, and has a thickness of 1.0-2.0 nm. In one of more seventh examples, for any of the sixth examples x is no more than 0.15 and the thickness is no more than 1.6 nm.

In one or more eighth examples, for any of the fifth examples the second layer nearest to the fixed magnet comprises (CoFe)i-xCx, x is between 0.01 and 0.10, and has a thickness of 1.0-2.0 nm. In one or more ninth examples, for any of the first through eighth examples the free magnet comprises two of the second layers separated by a spacer layer comprising a non- ferromagnetic material, and wherein the two second layers both comprise carbon.

In one or more tenth examples, for any of the first through ninth examples the first and second layers comprise CoFeB with at least 50 % Fe, the barrier layer comprises MgO, VO, TaO, HfO, ZrO, WO, or TiO, the stack further comprises a cap layer comprising oxygen, wherein either the free magnet or the fixed magnet is between the cap layer and the barrier layer, the second layer is between the barrier layer and a synthetic antiferromagnet (SAF) structure. In one or more eleventh examples a system, comprises a processor, and a memory coupled to the processor, the memory comprising the MTJ device in any of the first through the tenth examples.

In one or more twelfth examples, for any of the eleventh examples the memory further comprises a selector with a first terminal electrically coupled to one of the contacts, and a second terminal electrically coupled to a source line of the memory.

In one or more thirteenth examples, a method of forming a magnetic tunneling junction (MTJ) device comprises forming a pair of contacts, each contact comprising one or more metals, and forming an MTJ material stack between the pair of contacts. Forming the stack further comprises forming a first of a fixed magnet and a free magnet, wherein the fixed magnet comprises a first layer, and the free magnet comprises one or more second layers, the second layer nearest to the fixed magnet including carbon. The method further comprises forming a barrier layer over the first of the fixed magnet and the free magnet, and forming a second of the fixed magnet and the free magnet over the barrier layer.

In one or more fourteenth examples, for any of the thirteenth examples forming the stack further comprises depositing a first layer of an alloy comprising CoFeB, depositing the barrier layer over the first layer, depositing a second layer of an alloy comprising CoFeBC, FeBC, CoFeC, FeC, CoBC, or CoC over the barrier layer, and annealing the MTJ stack at a temperature of at least 375 °C to render the first and second layers poly crystalline with (001) out-of-plane texture.

In one or more fifteenth examples, for any of the thirteenth through fourteenth examples depositing the second layer further comprises co-sputtering a carbon source with another source comprising at least one of Fe, B, or Co.

In one or more sixteenth examples, for any of the fifteenth examples depositing the second layer further comprises sputter depositing a layer of (CoFe)i-xCx to a thickness no more than 2.0 nm, and wherein x is no more than 10 at. %.

In one or more seventeenth examples, for any of the fifteenth examples depositing the second layer further comprises sputter depositing a layer of (CoFeB)i-_xC_x to a thickness no more than 2.0 nm, and wherein x is between 1.0 and 20 at. %. In one or more eighteenth examples, for any of the thirteenth examples forming the stack further comprises depositing a first layer of an alloy comprising CoFeBC, FeBC, CoFeC, FeC, CoBC, or CoC, depositing the barrier layer over the first layer, depositing a second layer of an alloy comprising CoFeB over the barrier layer, and annealing the MTJ stack at a temperature of at least 375 °C to render the first and second layers poly crystalline with (001) out-of-plane texture.

In one or more nineteenth examples, for any of the eighteenth examples depositing the first layer further comprises co-sputtering a carbon source with another source comprising at least one of Fe, B, or Co.

In one or more twentieth examples, for any of the eighteenth examples depositing the first layer further comprises sputter depositing a layer comprising (CoFeB)i-_xC_x to a thickness no more than 2.0 nm, and wherein x is between 1.0 and 20 at. %.

In one or more twenty-first examples, for any of the eighteenth examples depositing the second layer further comprises sputter depositing a layer comprising (CoFe)i-xCx to a thickness no more than 2.0 nm, and wherein x is no more than 10 at. %.

In one or more twenty-second examples, for any of the thirteenth examples forming the free magnet comprises depositing a first of the second layers comprising carbon, depositing a spacer layer comprising a non-ferromagnetic material over the first of the second layers, and depositing a second of the second layers comprising carbon.

In one or more twenty -third examples, for any of the thirteenth examples the method further comprises exposing the MTJ stack at a temperature of at least 400 °C during subsequent material processing.

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

Claims

CLAIMS What is claimed is:

1. A magnetic tunneling junction (MTJ) device, comprising:

a pair of contacts, each comprising one or more metals; and

a material layer stack there between, wherein the stack includes:

a fixed magnet comprising a first layer;

a free magnet comprising one or more second layers, wherein at least the second layer nearest to the fixed magnet comprises carbon; and

a barrier layer between the fixed magnet and the free magnet.

2. The MTJ device of claim 1, wherein the second layer nearest to the fixed magnet has BCC crystal structure with (001) texture.

3. The MTJ device of claim 1, wherein the second layer nearest to the fixed magnet

comprises no more than 20 at. % carbon.

4. The MTJ device of claim 1, wherein the second layer nearest to the fixed magnet

comprises at least one of Co and Fe.

5. The MTJ device of claim4, wherein the second layer nearest to the fixed magnet comprises

CoFeBC, FeBC, CoFeC, FeC, CoBC, or CoC.

6. The MTJ device of claim 5, wherein the second layer nearest to the fixed magnet

comprises (CoFeB)i-_xC_x, x is between 0.01 and 0.20, and has a thickness of 1.0-2.0 nm.

7. The MTJ device of claim 6, wherein x is no more than 0.15 and the thickness is no more than 1.6 nm.

8. The MTJ device of claim 5, wherein the second layer nearest to the fixed magnet

comprises (CoFe)i-xCx, x is between 0.01 and 0.10, and has a thickness of 1.0-2.0 nm.

9. The MTJ device of claim 1 , wherein the free magnet comprises two of the second layers separated by a spacer layer comprising a non-ferromagnetic material, and wherein the two second layers both include carbon.

10. The MTJ device of claim 1, wherein:

the first and second layers comprise CoFeB with at least 50 % Fe;

the barrier layer comprises MgO, VO, TaO, HfO, ZrO, WO, or TiO;

the stack further comprises a cap layer comprising oxygen, wherein either the free magnet or the fixed magnet is between the cap layer and the barrier layer; and

the second layer is between the barrier layer and a synthetic antiferromagnet (SAF) structure.

11. A system, comprising:

a processor; and

a memory coupled to the processor, the memory comprising the MTJ device recited in any one of claims 1-10.

12. The system of claim 1 1, wherein the memory further comprises a selector with a first terminal electrically coupled to one of the contacts, a second terminal electrically coupled to a source line of the memory.

13. A method of forming a magnetic tunneling junction (MTJ) device, comprising:

forming a pair of contacts, each contact comprising one or more metals; and

forming a material stack between the pair of contacts, wherein forming the material stack further comprises:

forming a first of a fixed magnet and a free magnet, wherein the fixed magnet

comprises a first layer, wherein the free magnet comprises one or more second layers, and wherein the second layer nearest to the fixed magnet comprises carbon;

forming a barrier layer over the first of the fixed magnet and the free magnet; and forming a second of the fixed magnet and the free magnet over the barrier layer.

14. The method of claim 13, wherein forming the stack further comprises:

depositing a first layer of an alloy comprising CoFeB;

depositing the barrier layer over the first layer; depositing a second layer of an alloy comprising CoFeBC, FeBC, CoFeC, FeC, CoBC, or

CoC over the barrier layer; and

annealing the MTJ stack at a temperature of at least 375 °C to render the first and second layers poly crystalline with (001) out-of-plane texture.

15. The method of claim 14, wherein depositing the second layer further comprises co- sputtering a carbon source with another source comprising at least one of Fe, B, or Co.

16. The method of claim 15, wherein depositing the second layer further comprises sputter depositing a layer comprising (CoFe)i-xCx to a thickness no more than 2.0 nm, and wherein x is no more than 10 at. %.

17. The method of claim 15, wherein depositing the second layer further comprises sputter depositing a layer comprising (CoFeB)i-_xC_x to a thickness no more than 2.0 nm, and wherein x is between 1.0 and 20 at. %.

18. The method of claim 13, wherein:

wherein forming the stack further comprises:

depositing a first layer of an alloy comprising CoFeBC, FeBC, CoFeC, FeC, CoBC, or CoC; depositing the barrier layer over the first layer;

depositing a second layer of an alloy comprising CoFeB over the barrier layer; and annealing the MTJ stack at a temperature of at least 375 °C to render the first and second layers poly crystalline with (001) out-of-plane texture.

19. The method of claim 18, wherein depositing the first layer further comprises co- sputtering a carbon source with another source comprising at least one of Fe, B, or Co

20. The method of claim 18, wherein depositing the first layer further comprises sputter depositing a layer comprising (CoFeB)i-xCx to a thickness no more than 2.0 nm, and wherein x is between 1.0 and 20 at. %.

21. The method of claim 18, wherein depositing the second layer further comprises sputter depositing a layer comprising (CoFe)i-xCx to a thickness no more than 2.0 nm, and wherein x is no more than 10 at. %.

22. The method of claim 13, wherein forming the free magnet comprises:

depositing a first of the second layers comprising carbon;

depositing a spacer layer comprising a non-ferromagnetic material over the first of the second layers; and

depositing a second of the second layers comprising carbon.

23. The method of claim 13, further comprising exposing the MTJ stack at a temperature of at least 400 °C during subsequent material processing.