BACKGROUND

Field

[0001 ] Examples of the present disclosure generally relate to fabricating magnetic tunnel junction structures for magnetic random access memory (MRAM) applications.

Description of the Related Art

[0002] Spin transfer torque magnetic random access memories, or STT-MRAMs, employ magnetic tunnel junction structures in the memory cells thereof, wherein two ferro-magnetic layers are spaced from one another by a thin insulating or“dielectric” layer. One of the magnetic layers has a fixed magnetic polarity, the other has a magnetic polarity which is selectively changeable, i.e. , switched, between two states. The magnetic layers have perpendicular magnetic anisotropy in the depth direction of a stack of film layers including the magnetic tunnel junction“MTJ”. The polarity of the changeable polarity layer can be switched between having the same polarity as the fixed polarity layer or an opposite polarity to that of the fixed polarity layer. The electric resistance across the MTJ is a function of the polarity in the changeable polarity layer with respect to the fixed polarity layer. For example, where the polarities of the two layers are the same in the depth direction of the MTJ, the electric resistance across the MTJ is low, i.e., is assigned a value of 0. In an example where the polarities of the two layers are opposite to one another in the depth direction of the MTJ, the electric resistance across the MTJ is high, i.e., is assigned a value of 1. Thus, the electrical resistance across the memory cell can be used to indicate a value of 1 or 0, and thus used to store binary data values.

[0003] The Internet of Things (loT) includes devices such as cellphones, tablets and other portable devices, as well as wearable devices such as exercise trackers, smart watches, and health monitors. These loT devices capture, process, analyze, and store large amounts of data. Current memory storage approaches include the development of embedded flash (eFIash) memory which is used for storage in cellphones, tablets and other portable devices. This is because eFIash is then associated with the higher cost, lower reliability, and higher write energy consumption of the logic circuits of the same chip. As the eFIash device and logic device are formed at the front end of the chip, additional mask layers must be added to minimize the impact of the eFIash floating gate on the performance of the logic gate. As eFIash is utilized for more advanced nodes (i.e. more advance advanced circuit generations and circuit architectures), the added cost of additional mask layers sharply increase the cost of memory storage.

[0004] Thus, there remains a need for a new memory technology that can be integrated at the back end of the chip at more advanced nodes. Therefore, an improved MTJ stack and methods for fabricating the same are needed in order to improve data retention, while lowering the cost of production.

SUMMARY

[0005] The present disclosure generally relates to magnetic tunnel junction structures (i.e. stacks) suitable for magnetic random access memory (MRAM) applications and methods for fabricating the same. In one example, a magnetic tunnel junction stack includes a structure blocking layer and a magnetic reference layer. The magnetic reference layer is disposed on the structure blocking layer. The magnetic reference layer formed from cobalt (Co) or iron (Fe). A tunnel barrier layer is disposed on the magnetic reference layer. The tunnel barrier layer is formed from magnesium (Mg). A magnetic storage layer is disposed in contact with the tunnel barrier layer. The magnetic storage layer includes a first magnetic layer formed from cobalt (Co), iron (Fe), and boron (B). The magnetic storage layer includes a non magnetic layer formed from one of molybdenum (Mo), tantalum (Ta), tungsten (W). A second magnetic layer is formed from Co, Fe, and B. The non-magnetic layer is disposed in contact with first magnetic layer and the second magnetic layer.

[0006] In a second example, a magnetic tunnel junction stack includes a first pinning layer. A magnetic reference layer is disposed on the first pinning layer. The magnetic reference layer is formed from Co. A tunnel barrier layer is in contact with the magnetic reference layer. A magnetic storage layer is in contact with the tunnel barrier layer. The magnetic storage layer includes a first magnetic layer. The first magnetic layer is in contact with a non-magnetic layer. The first magnetic layer is formed from Co, iron (Fe), and boron (B). A non-magnetic layer is formed from a transition metal. A second magnetic layer is formed from Co, Fe, and B. The non magnetic layer is in contact with the first magnetic layer and the second magnetic layer.

[0007] In another example, a magnetic tunnel junction stack includes a magnetic reference layer and a tunnel barrier layer. The magnetic reference layer is disposed on the tunnel barrier layer. The magnetic reference layer is formed from cobalt (Co). A magnetic storage layer is in contact with the tunnel barrier layer. The magnetic storage layer includes a first magnetic layer that is in contact with a non-magnetic layer. The first magnetic layer is formed from Co, iron (Fe), and boron (B). A non magnetic layer is formed from at least one of molybdenum (Mo), tantalum (Ta), and tungsten (W). A second magnetic layer is formed from Co, Fe, and B. The non magnetic layer separates the first magnetic layer and the second magnetic layer. A capping layer is in contact with the magnetic storage layer. The capping layer includes a first interlayer, a second interlayer, and a third interlayer. The second interlayer and the first magnetic layer are formed from at least one of a same element. The third interlayer and the non-magnetic layer are formed from at least one of Mo, Ta, or W. The first layer is formed from an oxide of an alkaline earth metal or an oxide of a transition metal. The second interlayer separates the first interlayer and the third interlayer.

BRIEF DESCRIPTION OF THE DRAWING

[0008] So that the manner in which the above recited features of the present disclosure can be understood in detail, a more particular description of the disclosure, briefly summarized above, may be had by reference to examples, some of which are illustrated in the appended drawings. It is to be noted, however, that the appended drawings illustrate only exemplary examples and are therefore not to be considered limiting of its scope, may admit to other equally effective examples.

[0009] FIG. 1 is a schematic illustration of an MTJ stack according to examples of the present disclosure.

[0010] FIG. 2A is an enlargement of a buffer layer of the MTJ stack of FIG. 1.

[001 1 ] FIG. 2B is an enlargement of a first pinning layer of the MTJ stack of FIG.

1. [0012] FIG. 2C is an enlargement of a second pinning layer of the MTJ stack of FIG. 1.

[0013] FIG. 2D is an enlargement of an exemplary magnetic storage layer of the MTJ stack of FIG. 1.

[0014] FIG. 2E is an enlargement of an exemplary capping layer of the MTJ stack of FIG. 1.

[0015] FIG. 3 illustrates the magnetic coercivity for a magnetic storage layer of the MTJ stack of FIG. 1.

[0016] FIG. 4 is an enlargement of an exemplary first magnetic layer of the magnetic storage layer of FIG. 2D.

[0017] To facilitate understanding, identical reference numerals have been used, where possible, to designate identical elements that are common to the figures. It is contemplated that elements and features of one example may be beneficially incorporated in other examples without further recitation.

DETAILED DESCRIPTION

[0018] Examples of the present disclosure generally relate to magnetic tunnel junction stacks for magnetic random access memory (MRAM) applications. More specifically, the examples described herein relate to magnetic tunnel junction (MTJ) stacks and Spin-transfer Torque Magnetoresistive Random-Access Memory (STT MRAM). The MTJ stacks are incorporated in a film stack including upper and lower electrodes (not shown) of a logic circuit. The MTJ stack is sandwiched between the upper and lower electrodes, and can be used to form a plurality of memory cells used in magneto-resistive random-access memory (MRAM). In each MTJ stack of an MRAM, there are two magnetic layers. One magnetic layer has a fixed polarity and the second magnetic layer has a polarity that can be switched by imposing a voltage across the second magnetic layer or applying a current to the second magnetic layer. The electrical resistance across the MRAM changes based on the relative polarity between the first and second magnetic layers. The first layer, i.e. , the fixed polarity layer, is referred to herein as a magnetic reference layer. The second magnetic, i.e., the switching polarity layer, is referred to herein as the magnetic storage layer. The memory cells formed from the MTJ stacks operate when there is a voltage imposed across, or a current passed through, the memory cell to switch the polarity of the second magnetic layer. In response to the application of voltage of sufficient strength, the polarity of the switchable magnetic layer is changed for writing, or storing, a value to the memory cell. Additionally, the resistivity of the memory cell can be determined by measuring the current vs voltage relationship across the memory cell at a relatively low voltage below the threshold required to switch the magnetic polarity of the magnetic storage layer. Determining the resistivity of the memory cell with the low voltage allows for the memory cell to be read without writing or changing a value of the memory cell.

[0019] The MTJ stack disclosed herein increases the amount of time the magnetic storage layer can retain data by increasing the magnetic coercivity in the magnetic storage layer. Magnetic coercivity is a measure of the ability of a ferromagnetic material to withstand an external magnetic field without becoming demagnetized. MRAM operates to store information by measuring the difference of polarity in each of the magnetic memory cells. The memory cells are formed from two ferromagnetic plates, each of which can hold a magnetization, i.e. , magnetic polarization, separated by an insulating layer. One of the two plates is set to a particular fixed polarity. Data is stored by changing the magnetization of the second ferromagnetic plate to match the magnetization of an external field. The MTJ stack of the instant disclosure is capable of storing data within the magnetic storage layer for 10 years at temperatures exceeding 125° Celsius.

[0020] The MTJ stack discussed herein is formed using a plurality of deposition chambers to deposit thin film layers on a substrate, and ultimately pattern and etch those deposited film layers. The deposition chambers used to form the MTJ stack discussed herein includes physical vapor deposition (PVD) chambers among other processing chambers. Here PVD chambers are particularly suited for forming the plurality of thin film layers of the MTJ stack. However, it should be appreciated that other processing chambers may be equally suited to form the thin film layers of the MTJ stack.

[0021 ] FIG. 1 is a schematic illustration of an MTJ stack 100 according to an example of the present disclosure. An x direction 150 is orthogonal to a stacking direction of the MTJ stack 100. A y direction 170 is parallel or in line with the stacking direction of to the MTJ stack 100. The MTJ stack 100 includes a substrate 102, a buffer layer 104, a seed layer 106, a first pinning layer 108, a coupling layer 1 10, a second pinning layer 112, a structure blocking layer 114, a magnetic reference layer 1 16, a tunnel barrier layer 1 18, a magnetic storage layer 120, a capping layer 122, and a hard mask layer 124. The stacking direction is perpendicular to a plane of the substrate 102. In the illustrated example, the buffer layer 104 is formed via sputtering, or other suitable technique, on a conductive portion of, or a conductive film formed on a substrate 102. The substrate 102 can include tungsten (W), tantalum nitride (TaN), titanium nitride (Tin), or other metal layers. The buffer layer 104 improves the adhesion of a seed layer 106 to the substrate 102, which aids in the formation and performance of subsequently- deposited layers of the MTJ stack 100. The buffer layer 104 includes CoxFe _y Bz, Ta, and/or TaN, and is formed in one or more deposition operations in a processing chamber. In one example, the buffer layer 104 is formed in a PVD chamber using Ar plasma and a sputtering target that is a CoxFeyBz alloy, or by using individual sputtering targets of Co, Fe, or B, or by a combination of an alloy sputtering target and a single-element sputtering target, e.g., a CoFe target and a B target. In one example, x is an integer such that the molecular weight percentage of Cox is about 10% to about 40% of the molecular weight of Co _x Fe _y B _z (i.e. the compound), y is an integer such that the molecular weight percentage of Fe _y is about 20% to about 60% of the molecular weight of the compound, and z is an integer such that the molecular weight percentage of B _z is equal to or less than 70% of the molecular weight of the compound. In another example, where a Ta layer is included in the buffer layer 104, the Ta layer can be formed in a PVD chamber using a Ta target and Ar plasma.

[0022] In one example, the buffer layer 104 includes TaN and the buffer layer 104 is formed on the substrate 102 in the processing chamber. The processing chamber may use a Ta target in the presence of both Ar plasma and N2 The N2 reacts with the Ta material to form the TaN layer. In another example, a TaN sputtering target is used in the PVD chamber with Ar plasma to form the buffer layer 104. In one example, the buffer layer 104 is formed directly on and in contact with a conductive layer on the substrate 102. In other examples, there is a conductive transitional layer in between the conductive layer on the substrate 102 and the buffer layer 104 that does not affect performance of the MTJ stack 100. The buffer layer 104 is optionally employed in the illustrated example and may, in some circumstances, not be used in other examples discussed herein.

[0023] When present, the optional buffer layer 104 has an overall thickness of the buffer layer 104 is from about 0 A to about 60 A. In one example, the buffer layer 104 is a single layer of Ta, TaN, or Co _x Fe _y B _z formed directly on, and in contact with, a conductive layer on the substrate 102 to a thickness of up to about 20 A. In another example, the buffer layer 104 is a combination of layers. Each layer of the buffer layer 104 is at least one of Ta, TaN, or Co _x Fe _y B _z . The buffer layer 104 forms a thickness between about 1 A to about 60 A. In an example where TaN is employed for the buffer layer 104 instead of Ta or Co _x Fe _y B _z , a thickness can be about 20 A. In one example where Co _x Fe _y B _z is used alone to form the buffer layer 104, the thickness of the buffer layer 104 may be about 10 A. In another example of the buffer layer 104, Ta or TaN is employed in conjunction with Co _x Fe _y B _z , and the thickness of the buffer layer 104 is about 20 A. Within the buffer layer 104, the Ta and/or TaN layers may have a thickness between about 0 A to about 40 A. In one example, the TaN layer has a thickness of about 20 A.

[0024] The seed layer 106 is deposited on the buffer layer 104. The seed layer 106 includes at least one of Cr, NiCr, NiCrFe, RuCr, IrCr, CoCr. Herein, Co is cobalt, Cr is chromium, Ir is iridium, Fe is iron, and Ru is ruthenium. The seed layer 106 may be formed as one or more layers of Cr, NiCr, NiCrFe, RuCr, IrCr, or CoCr, which can include combinations of those elements or combinations of alloys in a single layer. In one example, the seed layer 106 is about 100 A or less in thickness. For example, the thickness of the seed layer 106 is from about 30 A to about 60 A thick.

[0025] The seed layer 106 is formed directly on and in contact with the buffer layer 104. Alternatively, a transitional layer may be present between the seed layer 106 and the buffer layer 104. The transition layer is selected to have a de minimis affect performance of the MTJ stack 100.

[0026] In one example of the disclosed MTJ stack 100, the seed layer 106 is fabricated from NiCr, the first pinning layer 108 is fabricated from a Co/Pt bilayer stack, and the second pinning layer 1 12 is fabricated from Co. In a second example, the first pinning layer 108 can be fabricated from a Co/Ni bilayer stack and the second pinning layer 1 12 is fabricated from Co. In this example, the MTJ stack 100 exhibits a tunnel-magnetoresistance (TMR) of 175% after being.

[0027] The first pinning layer 108 is formed on the seed layer 106. The first pinning layer 108 may be formed using a physical vapor deposition process. In one example, the first pinning layer 108 is fabricated as a single layer of Co having a thickness of about 1 A to about 18 A. In another example, the first pinning layer 108 is fabricated from one or more bilayers of various materials, wherein each bilayer can include two or more interlayers. The first pinning layer 108 can include one or more bilayers alone or in combination with a Co layer. In an example where one or more bilayers are included in the first pinning layer 108, each bilayer contains a first interlayer of Co and a second interlayer of a compound that includes at least one element other than Co. The first pinning layer 108 may be formed by sputtering a Co target using Ar plasma and, subsequently, sputtering a second target of Pt, Ir, Ni, or Pd. In an example where Pt is used with Co to form the bilayer, Xe plasma may be used instead of or in addition to Ar plasma. In an example where one or more bilayers are used to form the first pinning layer, repeated deposition cycles in the processing chamber can be performed by forming a first interlayer of a bilayer. In one example, the first interlayer includes Co and is formed by shielding targets in a PVD chamber that do not include Co, and the Co target and other targets are shielded to expose a second target that includes a second element used for the second interlayer of the bilayer. Deposition of the first and second interlayer may be repeated in an iterative fashion to form one or more bilayers of the first pinning layer 108. Optionally, the first interlayer may be formed in an ALD, CVD or other deposition chamber such as a PECVD chamber. In one example, the first pinning layer 108 is formed directly on and in contact with the seed layer 106. In other examples, there is an optional transitional layer formed between the seed layer 106 and the first pinning layer 108.

[0028] A synthetic ferromagnet (SyF) coupling layer 1 10 is formed on the first pinning layer 108, and a second pinning layer 1 12 is formed on the SyF coupling layer 1 10. The SyF coupling layer 1 10 is formed by a PVD process using process gasses or targets containing Ru, Rh, Cr, or Ir. The SyF coupling layer 1 10 has a thickness from about 3 A to about 10 A. In one example, Ru has a thickness from about 4 A to about 5 A. In another example, Ru has a thickness from about 7 A to about 9 A. In another example, the SyF coupling layer 1 10 includes Ir that has a thickness from about 4 A to about 6 A. In another example, the second pinning layer 1 12 is fabricated by sputtering a Co target. In one example, the SyF coupling layer 1 10 is formed directly on and in contact with the first pinning layer 108 and the second pinning layer 1 12. In other examples, there is a transitional layer in between the SyF coupling layer 1 10 and either or both of the first pinning layer 108 or second pinning layer 1 12 that does not affect performance of the MTJ stack 100. [0029] The second pinning layer 1 12 may be formed from one or more bilayers of Co and another element included in the second pinning layer 1 12. In one example, the second pinning layer 1 12 is formed by sputtering a Co target using an Ar plasma and, subsequently, sputtering a second target of Pt, Ir, Ni, or Pd using the Ar plasma. Repeated deposition cycles performed in the processing chamber, for example using various process gasses or a Co target and the second target in the presence of Ar plasma, can be used to form the one or more bilayers of the second pinning layer 1 12. In one example, the second pinning layer 1 12 is formed as a single Co layer having a thickness from about 0 A to about 10 A. In another example, the thickness of the second pinning layer 1 12 is about 5 A. Alternate configurations of the second pinning layer 1 12 are shown in FIG. 2C.

[0030] A structure blocking layer 1 14 is optionally formed on the second pinning layer 1 12. The structure blocking layer 114 prevents the formation of a short circuit between the MTJ stack 100 and metallic contacts that can be coupled to the MTJ stack 100 in the formation of the MRAM memory cells. The structure blocking layer 1 14, depending upon the intended composition of the layer, may include one or more of Ta, Mo, and W. In one example, during formation of the structure blocking layer 1 14, or one or more alloys may include at least one of Ta, Mo, and W in the formation of the structure blocking layer 1 14 in the processing chamber. The structure blocking layer 1 14 is a body-centered-cubic (bcc) structure oriented in the <100 direction, in contrast to the seed layer 106 and the first pinning layer 108 and the second pinning layer 1 12 which can each be oriented in a face-centered-cubic <11 1 > direction. When present, the structure blocking layer 1 14 is from about 0 A to about 8 A thick. In one example, the structure blocking layer 1 14 is formed to a thickness of about 4 A. In another example, the structure blocking layer 1 14 is formed directly on and in contact with the second pinning layer 1 12. In other examples, an optional transitional layer is present between the structure blocking layer 1 14 and the second pinning layer 1 12

[0031 ] A magnetic reference layer 1 16 is formed on the structure blocking layer 1 14. The magnetic reference layer 1 16 can be formed by PVD or other suitable process using a single Co-Fe-B alloy, or by using two or more of a Co, Fe, and B. In another example, the magnetic reference layer 116 can be formed in the PVD chamber in the presence of Ar plasma using an alloy target and an element target, such as a CoFe target and a B target. The magnetic reference layer 1 16 can be formed to a thickness from about 5 A to about 10 A. In one example, the magnetic reference layer 1 16 can be formed to a thickness of about 10 A. The magnetic reference layer 1 16 may include CoxFe _y B _z. In one example, x is an integer that when multiplied by the atomic weight of Co, the molecular weight percentage of Co _x is from about 10% to about 40% of the total molecular weight of the compound (i.e. CoxFeyBz); y is an integer that when multiplied by the atomic weight of Fe, the molecular weight percentage of Fe _y is from about 20% to about 60% of Co _x Fe _y B _z ; and z is an integer that when multiplied by the atomic weight of B, the molecular weight percentage of B _z is equal to or less than 70% of CoxFe _y B _z . The magnetic reference layer 1 16 can also include different metal combinations having different molecular weight percentages. In another example, which can be combined with other examples herein, z is an integer that when multiplied by the atomic weight of B, the molecular weight percentage of B _z is equal to at least 20% of the total compound. In one example, the magnetic reference layer 1 16 is formed directly on and in contact with the structure blocking layer 1 14. In other examples, an optional transitional layer is present between the magnetic reference layer 1 16 and the structure blocking layer 1 14.

[0032] A tunnel barrier layer 1 18 is formed on the magnetic reference layer 1 16. The tunnel barrier layer 1 18 includes a metal-oxide, such as magnesium oxide (MgO), hafnium oxide (HfCte), titanium oxide (T1O2), tantalum oxide (TaOx), aluminum oxide (AI2O3), or other materials. In one example, the tunnel barrier layer 1 18 can be formed in a PVD chamber in the presence of Ar using a sputtering target of a metal- oxide. Alternately, the tunnel barrier layer 1 18 can be formed using a PVD process in the presence of Ar and O2 and a metal of the desired metal-oxide. The metal-oxide layer may be formed using a PVD process in the presence of O2. The tunnel barrier layer 1 18 has a thickness from about 1 A to about 15 A. An exemplary tunnel barrier layer 118 may have a thickness that corresponds to the resistance-area (RA) requirements of the MTJ stack 100. The resistance-area product (RA) is between about 1 Qpm ² and about 20 Qpm ² , such as about 10 Dprn ² . In one example, the tunnel barrier layer 1 18 is formed directly on and in contact with the magnetic reference layer 1 16. In other examples, there is a transitional layer between the tunnel barrier layer 1 18 and the magnetic reference layer 1 16 that does not affect performance of the MTJ stack 100. [0033] The MTJ stack 100 additionally includes a magnetic storage layer 120 formed on the tunnel barrier layer 1 18. The magnetic storage layer 120 can include one or more layers of Co Fe _y B _z. In some examples, the magnetic storage layer 120 can alternatively or additionally include one or more layers of Ta, Mo, W, and Hf. As such, the deposition of the magnetic storage layer 120 can be performed using a PVD process using Ar plasma, and one or more targets fabricated from a CoxFeyBz alloy, individually Co, Fe, or B, or a combination of the alloy and the elements such as CoFe and B.

[0034] A thickness of the magnetic storage layer 120 can depend upon a material or materials used to form the magnetic storage layer 120. In one example, the magnetic storage layer 120 is fabricated from Co _x Fe _y B _z where x is an integer such that the molecular weight percentage of Co _x is from about 10% to about 40% of Co _x Fe _y B _z , y is an integer such that the molecular weight percentage of Fe _y is from about 20% to about 60% of Co _x Fe _y B _z , and z is an integer such that the molecular weight percentage of B _z is equal to or less than about 70% of Co _x Fe _y B _z . The thickness of the magnetic storage layer 120 may be from about 5 A to about 20 A, and in some examples, the magnetic storage layer 120 thickness is about 20 A. In one example, the magnetic storage layer 120 is formed directly on and in contact with the tunnel barrier layer 118. In other examples, an optional transitional layer is disposed between the magnetic storage layer 120 and the tunnel barrier layer 1 18. The magnetic storage layer is further described and shown in FIG. 2D below.

[0035] In an example of the MTJ stack 100, a capping layer 122 is formed on the magnetic storage layer 120. The capping layer 122 includes a plurality of interlayers. One or more of the interlayers may include an oxide that contains Fe. One or more interlayers of the capping layer 122 may be formed from a dielectric material. Additionally, in some examples, a hard mask layer 124 is formed directly on and in contact with the capping layer 122.

[0036] In another example, the hard mask layer 124 is formed on the capping layer 122 with a transitional layer disposed between the capping layer 122 and the hard mask layer 124. The hard mask layer 124 may be formed of a metal-oxide, amorphous carbon, ceramics, metallic materials, or combinations thereof. In one example, the magnetic storage layer 120 is formed directly on and in contact with the capping layer 122. In other examples, an optional transitional layer is disposed between the magnetic storage layer 120 and the capping layer. The capping layer 122 is shown in FIG. 2E below.

[0037] FIG. 2A is an enlargement of the buffer layer 104 of the MTJ stack 100 of FIG. 1. The buffer layer 104 includes tantalum (Ta) or TaN, or a layered stack of Ta and TaN. In some examples, the buffer layer 104 includes CoxFe _y B _z, alone or in combination with Ta, TaN, or a Ta/TaN layered stack. In an example of the buffer layer 104, the buffer layer 104 includes a bilayer 204D. The bilayer 204D includes a first buffer interlayer 204A and a second buffer interlayer 204B. Each bilayer 204D can include one or more groupings of the first buffer interlayer 204A and second buffer interlayer 204B. In this example, the first buffer interlayer 204A includes Ta and the second buffer interlayer 204B includes TaN. The first buffer interlayer 204A is in contact with the substrate 102. In another example the first buffer interlayer 204A includes TaN and the second buffer interlayer 204B includes Ta.

[0038] In other examples, the buffer layer 104 is made from Co _x Fe _y Bz. Therefore, the CoxFe _y Bz material made from the buffer layer 104 is in direct contact with the substrate 202. In another example, as shown in FIG. 2A, a third buffer interlayer 204C is formed over the at least one bilayer 204D. In this example, the third buffer interlayer 204C is fabricated from Co _x Fe _y B _z and formed to a thickness of 10 A. Thus, depending upon the configuration of the buffer layer 104, a thickness of the buffer layer 104 ranges from 0 A thick to about 60 A thick. In an example where the third buffer interlayer 204C Co _x Fe _y B _z is employed, x is an integer such that the molecular weight percentage of Co _x is from about 10% to about 40% of Co _x Fe _y B _z (i.e. the molecular weight of the compound), y is an integer such that the molecular weight percentage of Fe _y is from about 20% to about 60% of the molecular weight of the compound, and z is an integer such that the molecular weight percentage of B _z is equal to or less than or equal to about 70% of the molecular weight of the compound.

[0039] FIG. 2B is an enlargement of the first pinning layer 108 of the MTJ stack 100 of FIG. 1. In an example, the first pinning layer 108 is fabricated from at least one bilayer 230, and when two or more bilayers are employed, the bilayers form a bilayer stack 234. Each bi layer 230 is fabricated from a first interlayer 208A and a second interlayer 208B. The bilayers 230 of the first pinning layer 108 are expressed as (X/Y)n, (208A/208B) _n , where each bilayer is a combination of X and Y materials, and n is a number of bilayers in the first pinning layer 108. In an example, X is Co and Y is one of Pt, Ir, Ni, or Pd. While n=4 in the example illustrated in FIG. 2B, in an alternate example, n is from 3 to 10.

[0040] In an example where the first interlayer 208A includes Co and the second interlayer 208B includes Pt, the first interlayer 208A may have a thickness from about 1 A to about 7 A, such as from about 1 A to about 3 A. In other examples, second interlayer 208B may have a thickness from about 1 A to about 8 A, such as about 1 A to about 3 A. In the example illustrated in FIG. 2B, the first interlayer 208A has a thickness of about 2.4 A and the second interlayer 208B has a thickness of about 2.4 A. In another example, the first interlayer 208A may have a thickness of about 5 A, and the second interlayer 208B has a thickness of about 3 A. The first interlayer 208A may have a thickness of or greater than about 0 A (i.e. no layer is present) to about 10 A. In one example, the thickness of the first interlayer 208A is about 5 A.

[0041 ] In an example where the first interlayer 208A includes Co and the second interlayer 208B includes Ni, the Co may have a thickness from about 1 A to about 8 A. In this example, the second interlayer 208B may have a thickness from about 1 A to about 8 A. The first interlayer 208A may have a thickness of about 5 A. The bilayers 203 are also expressed as (X/Y)n, (208A/208B)n, where n is 1 to 10 X/Y layer pairs.

[0042] Further in another example, the bilayer 230 is formed directly on and in contact with the seed layer 206 in addition to an optional overlayer 208C of Co formed on top of the at least one bilayer 230. In the examples where the first interlayer 208A includes Co and Pt, or Co and Ni, the optional overlayer 208C may be about 0 A to about 10 A thick. Depending upon the example, an overall thickness of the first pinning layer 108, which may include one or more layers including the bilayer 230, is from about 0.3 nm to about 18 nm. In other examples, one or more optional transitional layers may be formed between the first pinning layer 108 and the seed layer 106.

[0043] FIG. 2C is an enlargement of the second pinning layer 1 12 of the MTJ stack 100 of FIG. 1 . In an example, the second pinning layer 1 12 is fabricated from a single cobalt layer. In alternate examples, the second pinning layer 112 is fabricated from at least one bilayer 232. A bilayer 232 includes a first interlayer 212A formed from Co and a second interlayer 212B formed from one or more of Pt, Ir, Ni, and Pd. When two or more bilayers such as the bilayer 232 are employed in the second pinning layer 1 12, a plurality of bilayers is referred to as a bilayer stack 236.

[0044] In one example, the first interlayer 212A is a Co layer from about 1 A to about 7 A thick and the second interlayer 212B is from about 1 A to about 8 A thick. An overlayer 212C of Co can be disposed on and in contact with at least one bilayer 232. In one example, the bilayer 232 is formed directly on and in contact with the coupling layer 210 formed from SyF.

[0045] The bilayer 232 of the second pinning layer 112 can be expressed as (X/Y)n, (212A/212B)n, where n is a number of bilayers. While n=4 in the example in FIG. 2C, in alternate examples, the bilayer 232 is optional and n can be from 0 to 5. The bilayer 232 of the second pinning layer 112 can include a Co/Pt stack when the first pinning layer 108 also includes the Co/Pt bilayer 230. In one example of the first interlayer 212A, X is Co and Y is Pt. However, Y may also be Ir, Ni, or Pd. While n=4 in the example in FIG. 2C, in an alternate example, n is from 0 to 5. Where the first interlayer 212A includes Co and the second interlayer 212B includes Pt, the first interlayer 212A may have a thickness from about 1 A to about 3 A, or the first interlayer 212A may have a thickness from about 3 A to 7 A. In other examples, the second interlayer 212B may have a thickness from about 1 A to about 3 A, or the second interlayer 212B may have a thickness from about 3 A to about 8 A. In the example illustrated in FIG. 2C, the first interlayer 212A has a thickness of about 2.4 A and the second interlayer 212B has a thickness of about 2.4 A. In another example, the first interlayer 212A may have a thickness of about 3 A and the second interlayer 212B has a thickness of about 3 A.

[0046] In another example, the bilayer 232 of the second pinning layer 112 can include a Co/Pt stack, when the first pinning layer 108 includes the Co/Ni bilayer 230. In this example, the first interlayer 212A includes Co and the second interlayer 212B includes Pt. The first interlayer 212A may have a thickness from about 0.5 A to about 8 A. The second interlayer 212B may have a thickness from about 0.5 A to about 7 A. The number of layers‘n’ in the bilayer 232 may be between 0 and 5.

[0047] The overlayer 212C of Co is disposed on top of and in contact with the at least one bilayer 232. In some examples, an optional transitional layer may be employed between the bilayer 232 and the second pinning layer 1 12, and/or between the bilayer 232 and the SyF coupling layer 110, or both. [0048] The overlayer 212C, in both the Co/Pt and the Co/Ni examples discussed above, may have a thickness up to about 10 A. In one example, where the overlayer 212C includes Co, the thickness is about 5 A. The overall thickness of the second pinning layer 1 12, which may include one or more layers including the bilayer 232 as discussed herein, is from about 0.3 nm to about 18 nm.

[0049] In one example, the first pinning layer 108 and second pinning layer 112 may each have substantially the same composition and/or the same thickness. In an alternate example, the first pinning layer 108 and second pinning layer 1 12 may each have different compositions and/or thicknesses. In one example, the first pinning layer 108 is Co and the second pinning layer 1 12 is formed from the bilayer 232. Each bilayer of the second pinning layer 112 can include a first interlayer 212A formed from Co and the second interlayer 212B formed from Pt. In this manner, one or more Co/Pt bilayers are formed. In another example, the first pinning layer 108 is formed from Co and the second pinning layer 1 12 is formed from one or more Co/Ni bilayers. In yet another example, the first pinning layer 108 includes one or more bilayers, each bilayer containing a first interlayer of Co and a second interlayer of Ni, and the second pinning layer 1 12 includes one or more bilayers, each bilayer containing the first interlayer of Co and a second interlayer of Pt. In yet another example, the first pinning layer 108 includes one or more bilayers, each bilayer containing the first interlayer of Co and a second interlayer of Pt, and the second pinning layer 1 12 includes one or more bilayers, each bilayer containing the first interlayer of Co and a second interlayer of Ni.

[0050] FIG. 2D is an enlargement of the exemplary magnetic storage layer 120 of the MTJ stack 100 of FIG. 1. The magnetic storage layer 120 is fabricated from three layers, a first magnetic layer 220A and a second magnetic layer 220B, and an insertion layer 220C disposed between the first magnetic layer 220A and the second magnetic layer 220B. The first magnetic layer 220A of the magnetic storage layer 120 and the second magnetic layer 220B of the magnetic storage layer 120 are each fabricated from Co _x Fe _y Bz. In one example, x is an integer such that the molecular weight percentage of Cox is from about 10% to about 40% of Co _x Fe _y B _z (i.e. the molecular weight of the compound), y is an integer such that the molecular weight percentage of Fe _y is from about 20% to about 60% of the molecular weight of the compound, and z is an integer such that the molecular weight percentage of B _z is less than or equal to about 70% of the molecular weight of the compound. The insertion layer 220C is fabricated from at least one of Ta, Mo, W, and Hf, or one or more combinations thereof. The insertion layer 220C may contain dopants such as boron, oxygen, or other dopants. The insertion layer 220C strengthens a pinning moment perpendicular to the substrate plane (e.g., the plane in the y direction 170 in line with the stacking direction of to the MTJ stack 100 and perpendicular to the substrate 102), which promotes magnetic anisotropy, i.e. , a directional dependence of the structure’s magnetic properties. The first magnetic layer 220A may have a thickness between about 5 A and about 20 A. The second magnetic layer 220B has a thickness between about 5 A and about 20 A. Accordingly, and insertion layer 220C may have a thickness between about 0 A and about 8 A. In another example, the first magnetic layer 220A has a thickness between about 8 A and about 10 A. The second magnetic layer 220B has a thickness between about 6 A to about 12 A, and the insertion layer 220C has a thickness of between about 1 A and about 2 A.

[0051 ] FIG. 2E is an enlargement of the exemplary capping layer 122 of the MTJ stack 100 of FIG. 1. A total thickness of the capping layer 122 is between about 2 A and about 1 10 A. In one example, the total thickness for the capping layer, including all interlayers, is about 60 A. It should be appreciated that the capping layer 122 may include a plurality of interlayers. For example, the capping layer 122 may have a first capping interlayer 222A, a second capping interlayer 222B, a third capping interlayer 222C a fourth capping interlayer 222D, or even more capping interlayers. The first capping interlayer 222A is fabricated from MgO or another iron-containing oxide formed directly on the magnetic storage layer 120 to a thickness from about 2 A to about 10 A. On top of the first capping interlayer 222A, the second capping interlayer 222B of at least one of Co, Fe, and B, or one or more combinations thereof, is formed to a thickness of between about 0 A to about 20 A. In one example, the 222B has a thickness between 6 A to 8 A. The third capping interlayer 222C is optionally formed of at least one of Mo, Ta, and W, or one or more combination thereof, and is formed on the second capping interlayer 222B to a thickness of between about 0 A to about 30 A. The third capping interlayer 222C may have a thickness between about 8 A to about 12 A. When molybdenum is included in the third capping interlayer 222C, a larger lattice is produced. The larger lattice in the third capping interlayer 222C, increases tensile stress on the MgO in the first capping interlayer 222A. The increase in tensile stress in the dielectric elements of the capping layer 122 improves the perpendicular magnetic anisotropy of the metal elements in the capping layer 122. It should be appreciated that some examples of the capping layer 122 do not contain the third capping interlayer 222C. In one or more examples, the fourth capping interlayer 222D is optionally formed on the third capping interlayer 222C. The fourth capping interlayer 222D is formed of at least one or more of Ru, Ir, and a combination thereof to a thickness between about 0 A to about 50 A. In one example, the fourth capping interlayer 222D has a thickness between about 20 A and about 30 A. It should be appreciated that the capping layer 122 includes the first capping interlayer 222A and may include one or more of the second capping interlayer 222B, the third capping interlayer 222C, the fourth capping interlayer 222D or other capping interlayers. An optional transitional layers may be disposed between some or all of the first capping interlayer 222A, the second capping interlayer 222B, the third capping interlayer 222C, fourth capping interlayer 222D, or between other capping interlayers. Additionally, the optional transitional layers may be disposed between the capping layer 122 and the magnetic storage layer 120.

[0052] FIG. 3 illustrates a hysteresis graph 300 of the magnetic coercivity of the magnetic storage layer 120 illustrated in FIG. 1. A hysteresis graph illustrates the phenomenon in which the value of a physical property lags behind changes in the effect causing the change in the physical property. Here, a magnetic moment lags behind the changing magnetizing force and relates directly to the magnetic coercivity of the magnetic storage layer 120. The magnetic coercivity is a measure of the ability of a ferromagnetic material to withstand an external magnetic field without becoming demagnetized. To determine the magnetic coercivity, the magnetic moment (A-m ² ) is measured against a changing magnetic force, which is applied in kilo oersted (kOe). The absolute value of a magnetic coercivity 304 of the magnetic storage layer of the MTJ stack 100 has been determined to be more than 0.15 kOe. The level of the magnetic coercivity 304 for the MTJ stack 100 can be increased by increasing the coupling between the first magnetic layer 220A and the second magnetic layer 220B. Thinning the insertion layer 220C additionally enables increased coupling between the first and second magnetic layers 220A and 220B and thus, additionally increases the level of the magnetic coercivity 304 for the MTJ stack 100.

[0053] FIG. 4 is an enlargement of the exemplary first magnetic layer 220A of the magnetic storage layer 220 of FIG. 2D. It is to be understood that the following discussion is not limited to the first magnetic layer 220A, but applies to any magnetic layer discussed herein, including the second magnetic layer 220B. By increasing the coupling between the first magnetic layer 220A and the second magnetic layer 220B, a thickness 408 of a magnetic dead layer 400 is reduced. The magnetic dead layer 400 is a sublayer of the first magnetic layer 220A that has magnetic materials but no magnetic moment. The dimensions (150, 170, and a z direction 160) of the first magnetic layer 220A, having the first magnetic layer 220A and the second magnetic layer 220B, can be in the nanoscale or angstrom range. Together, the lateral dimensions (150 and 160) and a thickness 412 of the first magnetic layer 220A define a magnetic volume 404. The magnetic dead layer 400 does not contribute to the magnetic volume 404, thus reducing the magnetization of the first magnetic layer 220A throughout the thickness direction (i.e. a y direction 170) of first magnetic layer 220A. One potential cause for the magnetic dead layer 400 is due to an intermixing between magnetic materials and other non-magnetic materials. Therefore, reducing the intermixing between the magnetic materials (Fe, Co) of the first and second magnetic storage layers 220A and 220B and transition metals (Ta, W, Mo, Hf) of the insertion layer 220C also reduces the thickness and lateral dimensions of the magnetic dead layer 400. The insertion layer 220C is substantially non-metallic. As previously mentioned, the magnetic storage layer 120 of the MTJ stack 100 disclosed herein may retain data for up to 10 years at 125° Celsius.

[0054] In a conventional MTJ Stacked Structure (shown by graph line 998) having a conventional magnetic storage layer, the absolute value of a conventional magnetic coercivity 999of the conventional magnetic storage layer is about 0.05 kOe. The conventional MTJ Stacked Structure (graph line 998) is shown on the same graph, offset by 0.4 to highlight the difference with the hysteresis graph 300. The conventional magnetic storage layer does not have the same structure of the magnetic storage layer 120 as disclosed herein, and accordingly, has a much more conventional magnetic coercivity 999.

[0055] Advantageously, the magnetic coercivity 304 of the magnetic storage layer 120 is more than twice the conventional magnetic coercivity 999 of the conventional MTJ Stacked Structure (i.e., graph line 998). Moreover, the MTJ stack 100 of the instant disclosure exhibits a tunnel-magnetoresistance (TMR) of over 150% at a resistance-area product (RA) of 10 Wmhi ² . The magnetic storage layer 120 also improves the bake error rate. The bake error rate is the rate of error bits (bits flipped) after baking of the various layers that are included in the magnetic storage layer 220, as illustrated in FIG. 3.

[0056] Disclosed herein is an example of an MTJ stack for STT MRAM memory. While the foregoing is directed to examples of the present disclosure, other and further examples of the disclosure may be devised without departing from the basic scope thereof, and the scope thereof is determined by the claims that follow.