Patent ID: 12249361

EXAMPLES OF EMBODIMENTS

FIG.3shows a side view andFIG.4shows a top view of a magnetoresistive element10according to an embodiment. The magnetoresistive element10comprises a MTJ20comprising a tunnel barrier layer22sandwiched between a first ferromagnetic layer21having a first magnetization210, a second ferromagnetic layer23having a second magnetization230.

In an embodiment, the first and second ferromagnetic layers21,23can comprise a ferromagnetic material including a metal or alloy having a specific perpendicular magnetic anisotropy whereby the first and second magnetizations210,230are oriented substantially perpendicular to the plane of the ferromagnetic layers21,23(out-of-plane, also known as perpendicular magnetic anisotropy (PMA)). Such metal or alloy can comprise FePt, FePd, CoPt, or a rare earth/transition metal alloy, in particular GdCo, TdFeCo, or Co, Fe, CoFe, Ni, CoNi, CoFeB, FeB. Alternatively, the first and second ferromagnetic layers21,23can comprise a metal or alloy with the first and second magnetizations210,230being oriented parallel to the plane of the ferromagnetic layers21,23(in-plane). Such metal or alloy can comprise Co, Fe, CoFe, Ni, NiFe, CoNi, CoFeB, FeB. The thickness of the first and second ferromagnetic layers21,23can be between 0.5 nm and 10 nm and preferably between 1 and 3 nm.

The MTJ20can further comprise a capping layer24. The capping layer24can comprise an antiferromagnetic layer exchange coupling the first ferromagnetic layer21such as to first magnetization210such as to pin the first magnetization210in a particular direction. Alternatively, the capping layer24can comprise a SAF structure including a metallic non-magnetic spacer layer and a ferromagnetic layer.

The tunnel barrier layer22can include a material, such as MgO or Al2O3.

The magnetoresistive element10further comprises a writing current layer30configured for passing a writing current31and an electrically conductive interconnect layer50destined to supply the writing current31to the writing current layer30. The interconnect layer50can include an electrically conductive material such as Cu, W, Au, Ag, Fe, Pt, Al, Co, Ru, Mo, NiSi, carbon nano tubes (CNT), graphene or an alloy of these elements.

The writing current layer30contacts the second ferromagnetic layer23and is configured for passing a writing current31adapted for switching the second magnetization230by a SOT interaction. The writing current layer30comprises a SOT material, where the SOT material can include an electrically conductive material, such as Pt, W, Ir, Ru, Pd, Cu, Au, Bi, Hf, Se, Sb or of an alloy of these elements, or is formed of a stack of a plurality of layers of each of these metals. Alternatively, the current layer30can be made from an antiferromagnetic material. Examples of antiferromagnetic materials include alloys with a base of Mn such as IrMn, FeMn, PtMn, or alloys of these compounds such as PtFeMn. Alternatively, the current layer30can be made from a ferromagnetic material, such as Fe, Co, Ni or of an alloy of these elements. The writing current layer30has a thickness that ranges between 0.5 nm and 200 nm, more particularly between 0.5 nm and 100 nm, or less than 10 nm. Preferably, the writing layer30has thickness lying in the range 0.5 nm to 5 nm.

The writing current layer30has lateral dimension that are substantially the same as the one of the MTJ20. Here, the lateral dimension is in a layer plane PL substantially parallel to the layers21,22,23of the MTJ20(along the directions “x” and “y” inFIGS.3and4). The MTJ20including the writing current layer30forms a pillar40.

The interconnect layer50contacts the writing current layer30and extends on each side of the writing current layer30and MTJ20, such that the lateral dimension along the direction “y” of the interconnect layer50are much larger than the lateral dimension of the writing current layer30and the MTJ20.

In one aspect, the interconnect layer50comprises a gap34underneath the MTJ20. In the example ofFIGS.3and4, the gap34is represented as a slit underneath the MTJ20, such that the interconnect layer50comprises two discontinuous interconnect segments51connecting the writing current layer30in series. The interconnect segments51extend along the layer plane PL.

As shown inFIG.4, the gap34can be configured such that each of the interconnect segments51are in contact with a portion at the periphery of the writing current layer30.

In an embodiment, the gap34can be configured to have a gap width WGbeing a factor of about 0.9 to 0.1 of the lateral dimension D30of the writing current layer30.

The gap34can comprise a gap material that is preferably an electrically insulating material. In other words, the gap34has an electrical conductivity being at least ten times smaller than that of the interconnect segments51, such that substantially no current flows in the gap34but rather flows only in the interconnect segments51and the writing current layer30.

The interconnect layer50can have any arbitrary shape as long as the above mentioned dimensional constrains are respected. InFIG.4, the discontinuous interconnect segments51forming the interconnect layer50have a trapezoidal shape but could have a rectangular shape. The discontinuous interconnect segments51do not need to be aligned symmetrically with each other and a shift along the “y” axis can be tolerated as long as the interconnect segments51are in contact with a portion at the periphery of the writing current layer30. Wide interconnect segments51(large size along the “y” axis) allows for decreasing the resistance of the interconnect layer50.

In an embodiment, the interconnect layer50has an interconnect width D50(along the “y” axis inFIG.4) that is larger than the gap width WG. For example, the interconnect width D50can be at least 1.5 times the gap width WGor twice the gap width WG.

In the configuration of the magnetoresistive element10, all the writing current31flowing in the writing current layer30generated a spin current exerting a torque on the second magnetization23in order to switch it. The rest of the writing current31flows in the interconnect layer50that has a lower electrical resistance than the one of the writing current layer30so that less heating occurs during the write/read operations of the magnetoresistive element10.

The pillar40can have a geometrically isotropic shape, for example a shape having substantially identical dimensions in the “x” and “y” directions, such a circular shape (as shown inFIG.4) or a square shape. Alternatively, the pillar40can have a geometrically anisotropic shape, for example a shape having a larger dimension the “x-y” plane PL (called “long axis” afterwards). Examples of geometrically anisotropic shapes can include an ellipsoidal, a rectangular, a trapezoidal or a diamond shape.

FIG.5shows a top view of the magnetoresistive element10, wherein the pillar40has an ellipsoid shape. In one aspect, the long axis41of the ellipsoidal MTJ20can be parallel to the gap width WG. Alternatively, the long axis41of the pillar40can be perpendicular to the gap width WGor can be oriented with any angle θ between 0° (parallel) and 90° (perpendicular) relative to the gap width WG. For example, the long axis of the MTJ20can be oriented with any angle θ between 10° and 80° relative to the gap width WG. When the ellipsoidal pillar40is oriented perpendicular or with an angle greater that 0°, the gap width WGcan be larger, relaxing the fabrication constraint along the gap width WG(along the x axis). In the case where the first and second magnetizations210,230are in-plane, the ellipsoidal pillar40oriented perpendicular or with an angle greater that 0° allows for breaking the symmetry. The orientation of the long axis as discussed in the example ofFIG.5can be applied to any other geometrically anisotropic shapes.

In an embodiment illustrated inFIG.6, the gap material comprises a magnetic material having a bias magnetization60configured for breaking the symmetry, i.e., to provide a magnetic bias field61adapted to interact with the second magnetization230such as to provide deterministically switching of the second magnetization230when the writing current31is passed. In the case the first and second magnetizations210,230are out-of-plane, the bias magnetization60should be oriented in-plane (along the “x” axis).

The magnetic material can have a coercivity between a few hundred to few thousand Oe.

In one aspect, the gap magnetic material can comprise a ferromagnet material such as: Co, Fe, CoFe, Ni, NiFe, CoNi, CoPt, CoCrPt, CoCrTa, CoSm. In the case the gap magnetic material is electrically conductive, the interconnect layer50can comprise an electrically insulating spacer52between the gap34, the interconnect segments51and the writing current layer30.

The gap magnetic material can be electrically insulating and no electrically insulating spacer between the gap34, the interconnect segments51and the writing current layer30is needed.

In another embodiment illustrated inFIG.7, the interconnect layer50(the interconnect segments51) comprises a ferromagnetic material (ferromagnet) having a bias magnetization60configured to provide a magnetic bias field61adapted to interact with the second magnetization230such as to provide deterministically switching of the second magnetization230when the writing current31is passed. In the case the first and second magnetizations210,230are out-of-plane, the bias magnetization60should be oriented in-plane (along the “x” axis).

According to an embodiment (not illustrated), a method for fabricating the magnetoresistive element10comprises successively depositing the interconnect layer50, forming the gap34in the interconnect layer50, depositing a gap layer comprising the gap material on top of the interconnect layer50such as to fill the gap34, planarizing the gap layer such as to free the upper surface of the interconnect layer50, successively depositing the writing current layer30, second ferromagnetic layer23, tunnel barrier layer22, first ferromagnetic layer21and capping layer24. The gap34can be formed by using lithographic and etching steps. Planarizing the gap layer can be performed by using a chemical mechanical polishing process or lithographic and etching steps.

The fabrication process further comprises forming the pillar40by performing a single etch step until the interconnect layer50, acting as a stop layer, is reached. The etching step can be facilitated since a multi angle etch can be done to clean any redeposited metal on the sidewall of the pillar40. For example, the etching step can start with a 35° etch then a lower angle etch.

In one aspect, the pillar40can have sidewalls substantially vertical or tapered. Here, vertical refers to a direction “z” that is perpendicular to a layer plane PL substantially parallel to the layers21,22,23of the MTJ20.

During the fabrication process of the magnetoresistive element10, the MTJ20can be positioned relative to the interconnect layer50with great precision in only one direction. In the example ofFIG.4, due to the large size of the interconnect width D50of the interconnect layer50(or the interconnect segments51), the MTJ20needs to be precisely positioned along the “x” direction while the dimensional constraint along the “y” axis is low such that the MTJ20needs not be precisely positioned along the “y” axis.

In one embodiment, a magnetic memory100comprises a plurality of the magnetoresistive element10, wherein each magnetoresistive element10is connected to another one via an interconnect segment51.

FIG.8shows a side view of an exemplary magnetic memory100wherein the magnetoresistive element10connected along the interconnect layer50are connected alternatively above the layer plane PL and below the layer plane PL, such that two adjacent magnetoresistive elements10are above and below the layer plane PL.FIG.9shows a top view of the magnetic memory100ofFIG.8. This configuration allows for switching the second magnetization230of two adjacent magnetoresistive elements10in opposed orientation, such that the second magnetization230is parallel to the first magnetization210for one magnetoresistive element10and the second magnetization230is antiparallel to the first magnetization210for the adjacent magnetoresistive element10, when the writing current31is passed in a direction in the interconnect layer50. This configuration corresponds to a differential structure wherein two magnetoresistive elements10are written with the same current but with different magnetization configurations. The magnetoresistive elements10can be read separately and the magnetic state of the two magnetoresistive elements10can be compared. The first magnetization210is pinned in the same direction for the magnetoresistive elements10.

In the configuration ofFIGS.8and9, the first magnetization210can be pinned in the same direction by using a single annealing step. More particularly, the MTJs20can be heated at a high temperature threshold at which the first magnetization210can be freely oriented. A programming magnetic field (not shown) is applied such as to orient the first magnetization210of the MTJs20in accordance to the programming magnetic field. The MTJs20are then cooled such as to pin the first magnetization210in the same programmed direction.

FIG.10shows a side view andFIG.11shows a top view of another arrangement of the magnetic memory100, wherein the magnetoresistive element10are connected along the interconnect layer50having a U shape configuration. The magnetoresistive elements10are connected above of the layer plane PL (the magnetoresistive elements10can also be connected below of the layer plane PL). In the arrangement shown inFIGS.10and11, the interconnect layer50extends along a row in the layer plane PL, such that the writing current31flows in the writing current layer30of two adjacent magnetoresistive elements10in the row with opposed polarity. InFIGS.10and11, the interconnect segment connecting the two adjacent magnetoresistive elements10is indicated by the numeral51′. The magnetic memory configuration ofFIGS.10and11also corresponds to a differential structure wherein two magnetoresistive elements10are written with the same current but with different magnetization configurations.

FIG.12shows a side view of yet another differential arrangement of the magnetic memory100, wherein the interconnect layer50has a U shape configuration extending along a column in a perpendicular plane PP substantially perpendicular to the layer plane PL. The writing current31flows in the writing current layer30of two adjacent magnetoresistive elements10in the column with opposed polarity such that the second magnetization230of adjacent magnetoresistive elements10is oriented in opposite directions. InFIG.12, the magnetoresistive elements10are connected above of the layer plane PL, but can also be connected below the layer plane PL.

REFERENCE NUMBERS AND SYMBOLS

10magnetoresistive element100magnetic memory20MTJ element21first ferromagnetic layer210first magnetization22tunnel barrier layer23second ferromagnetic layer230second magnetization24capping layer30writing current layer31writing current34gap40pillar41long axis50interconnect layer51,51′ interconnect segment52spacer60bias magnetization61magnetic bias fieldθ angleD30lateral dimension of the writing current layerD50interconnect widthPL layer planePP perpendicular planeWGwidth of the gap