Patent Application
20240347089
This application claims priority to and the benefit of Greek Patent Application No. 20230100323, filed on Apr. 12, 2023, the entire content of which is hereby incorporated by reference.
The present disclosure relates to magnetic memory devices and methods of manufacturing the same.
Magnetic random-access memory (MRAM) devices store information utilizing magnetic materials as an information recording medium. One type of MRAM is a spin-transfer-torque magnetic random-access memory (STT-MRAM). STT-MRAM devices include a magnetic tunnel junction (MTJ) having a tunnel barrier layer stacked between a magnetic free layer and a magnetic pinned (or fixed) layer. To write to a STT-MRAM device, current is driven through the MTJ, which causes the magnetic moment of the free layer to be either aligned or anti-aligned with the magnetic moment of the pinned layer using spin transfer torque (STT). To read from the STT-MRAM, a read current passes through the MTJ.
In some related art STT-MRAM devices, the magnetic free layer includes a Heusler compound, which has a large perpendicular magnetic anisotropy (PMA) and a low moment due to ferrimagnetic configuration that are suitable for STT-MRAM applications. These STT-MRAM devices may include a ferromagnetic Heusler compound. The moment of the Heusler compound depends on the constituent elements. Additionally, related art STT-MRAM devices may include a CoAl, IrAl, RuAl, or PtAl chemical templating layer that promotes the ordered growth of the Heusler compound at an ultrathin thickness and at room temperature. The chemical templating layer needs to have a (001) orientation (these chemical templating layers have body-centered cubic (BCC) structure so (001) orientation is equivalent to (100) or (010) orientations), and thus related art STT-MRAM devices may include a seed layer below the chemical templating layer to promote such ordered growth of the chemical templating layer. Accordingly, these seed layers dictate that the magnetic free layer including the Heusler compound is located underneath the tunnel barrier layer. However, locating the magnetic free layer underneath the tunnel barrier layer, and thus locating the magnetic reference (pinned or fixed) layer above the tunnel barrier layer, is a severe limitation because currently developed SAF layers for use on a top reference layer are not as thermally robust as SAF layers below the tunnel barrier layer. For instance, in the related art, the top SAF layer can be annealed up to a maximum temperature of approximately 350° C. whereas bottom SAF layers can withstand temperatures of 400° C. or more. Additionally, the magnetic coercivity (Hc) of top SAF layers is only approximately 4 to 5 kOe, whereas the magnetic coercivity of bottom SAF layers is approximately 8 to 10 kOe.
The present disclosure relates to various embodiments of a magnetic random-access memory (MRAM) device. In one embodiment, the MRAM device includes a substrate, a bottom magnetic reference layer above the substrate, a tunnel barrier layer above the bottom magnetic reference layer, and a top magnetic free layer above the tunnel barrier layer. The top magnetic free layer includes a chemical templating layer on the tunnel barrier layer and a magnetic layer on the chemical templating layer. The chemical templating layer includes a binary alloy of FeyX having a BiF3 prototype structure, and the magnetic layer includes a Heusler compound having perpendicular magnetic anisotropy.
The present disclosure also relates to various methods of manufacturing a magnetic random-access memory (MRAM) device. In one embodiment, the method includes forming a reference magnetic layer on a substrate, forming a tunnel barrier layer on the reference magnetic layer, and forming a free magnetic layer above the tunnel barrier layer. Forming the top magnetic free layer includes forming a chemical templating layer on the tunnel barrier layer and growing a magnetic layer on the chemical templating layer. The chemical templating layer includes a binary alloy of FeyX having a BiF3 prototype structure, and the chemical templating layer causes the magnetic layer to include a Heusler compound having perpendicular magnetic anisotropy.
This summary is provided to introduce a selection of features and concepts of embodiments of the present disclosure that are further described below in the detailed description. This summary is not intended to identify key or essential features of the claimed subject matter, nor is it intended to be used in limiting the scope of the claimed subject matter. One or more of the described features may be combined with one or more other described features to provide a workable device.
The features and advantages of embodiments of the present disclosure will become more apparent by reference to the following detailed description when considered in conjunction with the following drawings. In the drawings, like reference numerals are used throughout the figures to reference like features and components. The figures are not necessarily drawn to scale.
The present disclosure relates to various embodiments of a magnetic random-access memory (MRAM) device including a magnetic tunnel junction (MTJ) including a bottom magnetic reference layer and a top magnetic free layer including a Heusler compound. The MRAM device according to various embodiments of the present disclosure also includes a top chemical templating layer configured to enable growth of the Heusler compound. The top chemical templating layer may include a binary compound having the form FeyX, where X is aluminum, germanium, or gallium, y is in a range from 0.9 to 3.3, and the FeyX binary compound may have a BiF3 prototype structure. Utilizing the top chemical templating layer to grow the ordered Heusler compound above the tunnel barrier layer enables the magnetic reference layer and the associated synthetic antiferromagnetic (SAF) layer to be below the tunnel barrier layer. An SAF layer provided below the tunnel barrier layer can be annealed at higher temperatures (e.g., 400° C. or more) and has a higher magnetic coercivity (Hc) and a higher exchange field (Hex) compared to a top SAF layer provided above the tunnel barrier layer.
With reference now to
In the illustrated embodiment, the top magnetic free layer 104 includes a chemical templating layer 105 above the tunnel barrier layer 103 (e.g., directly on an upper surface 106 of the tunnel barrier layer 103), and a magnetic free layer having a Heusler compound 107 above (e.g., directly on) the chemical templating layer 105. In one or more embodiments, the Heusler compound of the magnetic free layer 107 may be Mn3Ge. In one or more embodiments, the Heusler compound of the magnetic free layer 107 may be Mn3Sn, Mn3Sb, Mn2CoSn, Mn2FeSb, Mn2CoAl, Mn2CoGe, Mn2CoSi, Mn2CuSi, Co2CrAl, Co2CrSi, Co2MnSb, or Co2MnSi. The chemical templating layer 105 includes a binary alloy with the composition FeyX, where X is aluminum (Al), germanium (Ge), or gallium (Ga), and wherein y is in a range from 0.9 to 3.3. Additionally, in the illustrated embodiment, the binary alloy of the chemical templating layer 105 may have a BiF3 prototype structure. As used herein, the term “BiF3 prototype structure” refers to a crystal structure having a Strukturbericht designation of D03, a Pearson symbol of cF16, a face-centered cubic (FCC) Bravais Lattice, a space group of Fm
In one or more embodiments, the tunnel barrier layer 103 comprises MgO, MgAlOx, and/or AlN. In one or more embodiments, the tunnel barrier layer 103 comprises MgO, and the lattice constant of MgO is 4.20 Å. As illustrated in Table 1 above, the a/Sqrt(2) of the FeyX compound of the chemical templating layer 105 ranges from 4.07 Å to 4.1 Å (e.g., the a/Sqrt(2) of Fe3Al, Fe3Ge, and Fe3Ga are 4.09 Å, 4.07 Å, and 4.1 Å, respectively). Accordingly, the lattice mismatch between the binary alloy of the chemical templating layer 105 and the MgO of the tunnel barrier layer 103 is in a range from only approximately 2% to approximately 3%. The relatively small lattice mismatch enables the FeyX compound of the chemical templating layer 105 to grow on top of the MgO tunnel barrier layer 103. Additionally, as described in more detail below, the binary alloy with the composition FeyX of the chemical templating layer 105 is configured to promote the growth of the Heusler compound of the magnetic free layer 107 with perpendicular magnetic anisotropy (PMA). In one or more embodiments, the tunnel barrier 103 may be formed from MgAl2O4 where the lattice spacing is tuned (engineered) by controlling the Mg—Al composition to result in better lattice matching with the FeyX compounds (as listed above). For example, and without limitation, the composition of this tunnel barrier 103 can be represented as Mg1−zAl2+(2/3)zO4, where −0.5<z<0.5.
Additionally, the binary alloy with the composition FeyX of the chemical templating layer 105 functions as a polarization enhancement layer (PEL) due to its high spin polarization. Thus, the binary alloy having the FeyX composition functions as both a chemical templating layer and a polarization enhancing layer. The relatively high spin polarization of the chemical templating layer 105 provides high tunneling magnetoresistance (TMR), which enables the chemical templating layer 105 to be part of the MTJ. Accordingly, unlike related art chemical templating layers that do not provide TMR and thus can only be utilized when the chemical templating layer is not adjacent to the tunnel barrier layer and the Heusler compound layer is below the tunnel barrier layer, the chemical templating layer 105 provides TMR and is adjacent to the tunnel barrier layer 103, and the chemical templating layer 105 and the magnetic free layer including the Heusler compound 107 are above the tunnel barrier layer 103.
In the illustrated embodiment, the MRAM device 100 also includes an oxide layer 108 (e.g., MgO or other suitable oxide) on an upper surface of the magnetic free layer 107. The oxide layer 108 above the magnetic free layer 107 is configured to minimize (or at least reduce) spin pumping and thereby lower the switching current and thus reduce the power consumption of the MRAM device 100.
In the illustrated embodiment, the MRAM device 100 also includes a synthetic antiferromagnetic (SAF) layer 109 above (e.g., indirectly or directly on an upper surface of) the substrate 101, and a metallic dusting layer 110 above (e.g., indirectly or directly on an upper surface of) the SAF layer 109. In one or more embodiments, an optional seed layer may be between the SAF layer 109 and the substrate 101. In one or more embodiments, the metallic dusting layer 110 may include tantalum (Ta), iridium (Ir), molybdenum (Mo), tungsten (W), cobalt/iron (Co/Fe) doped W, or Co/Fe-doped Mo. Both the SAF layer 109 and the metallic dusting layer 110 are below the tunnel barrier layer 103. In the illustrated embodiment, the bottom magnetic reference layer 102 (e.g., an alloy of Co, Fe, and B where the composition may be of the form (CoFe)1-xBx where x is in a range from approximately 0.15 to approximately 0.35 (0.15≤x≤0.35), or an alloy of Co, Fe, and B where the composition may be of the form (Co1-xFex)1-yBy where x is in a range from approximately 0.3 to approximately 0.7 (0.3<x<0.7) and y is in a range from approximately 0.15 to approximately 0.5 (0.15<y<0.5)) is in direct contact with a lower surface of the tunnel barrier layer 103 and an upper surface of the metallic dusting layer 110. Providing the SAF layer 109 below enables the SAF layer 109 to be annealed at higher temperatures and to have a higher exchange field (Hex) compared to a top SAF layer provided above the tunnel barrier layer. For instance, in one or more embodiments, the SAF layer 109 below the tunnel barrier layer 103 may be annealed up to approximately 400° C. or more, whereas related art SAF layers above the tunnel barrier layer can be annealed up to only approximately 350° C. (i.e., the SAF layer 109 below the tunnel barrier layer 103 is more thermally robust than related art SAF layers above the tunnel barrier layer). Additionally, in one or more embodiments, the SAF layer 109 has an exchange field (Hex) in a range from approximately 8 kOe to approximately 10 kOe, whereas related art SAF layers above the tunnel barrier layer have an exchange field of only approximately 4 kOe to approximately 5 kOe. Furthermore, in one or more embodiments, the SAF layer 109 below the tunnel barrier layer 103 has a higher magnetic coercivity (Hc) and compared to a top SAF layer provided above the tunnel barrier layer.
With reference now to
In one or more embodiments, the top magnetic free layer 204 may be the same as the top magnetic free layer 104 described above with reference to the embodiment of the MRAM device 100 illustrated in
Additionally, in the illustrated embodiment, the bottom magnetic reference layer 202 includes a magnetic reference layer comprising a Heusler compound 208. In one or more embodiments, the Heusler compound of the magnetic reference layer 208 may be Mn3Ge. In one or more embodiments, the Heusler compound of the magnetic reference layer 208 may be Mn3Sn, Mn3Sb, Mn2CoSn, Mn2FeSb, Mn2CoAl, Mn2CoGe, Mn2CoSi, Mn2CuSi, Co2CrAl, Co2CrSi, Co2MnSb, or Co2MnSi. In one or more embodiments, the magnetic reference layer comprising the Heusler compound 208 has a thickness t such that the coercivity (Hc) of the magnetic reference layer 208 is greater than approximately 10 kOe (e.g., the magnetic reference layer 208 has an anisotropy field of at least approximately 10 kOe).
In the illustrated embodiment, the bottom magnetic reference layer 202 also includes an optional polarization enhancement layer (PEL) 209 may comprise FeyX, where X is aluminum (Al), germanium (Ge), or gallium (Ga) and y is in a range from 0.9 to 3.3 (e.g., the bottom magnetic reference layer 202 includes a stack of the magnetic reference layer 208 and the PEL 209). In the illustrated embodiment, the PEL 209 is above (e.g., directly on an upper surface of) the magnetic reference layer 208, and the PEL 209 is between the magnetic reference layer 208 and the tunnel barrier layer 203. In one or more embodiments, the PEL 209 comprising FeyX may have relatively high spin polarization. In the illustrated embodiment in which the MRAM device 200 includes FeyX layers symmetrically above and below the tunnel barrier layer 203 (e.g., the PEL layer 209 comprising FeyX below the tunnel barrier layer 203 and the chemical templating layer 205 comprising FeyX above the tunnel barrier layer 203), the MRAM device 200 may have symmetric (or substantially symmetric) spin filtering and thus enhanced tunneling magnetoresistance (TMR) compared to an otherwise MRAM device without symmetric spin filtering. In one or more embodiments, the bottom magnetic reference layer 202 may not include the PEL 209.
In the illustrated embodiment, the MRAM device 200 also includes a chemical templating layer 210 below the magnetic reference layer 208 (e.g., the magnetic reference layer 208 is directly on the chemical templating layer 210). The chemical templating layer 210 is configured to promote the growth of the Heusler compound of the magnetic reference layer 208 with substantially perpendicular magnetic anisotropy (PMA) (e.g., from approximately 80 degrees to approximately 90 degrees). In one or more embodiments, the chemical templating layer 210 may include CoAl or a bilayer of IrAl and CoAl.
In the illustrated embodiment, the MRAM device 200 also includes a seed layer 211 below the chemical templating layer 210 (e.g., the chemical templating layer 210 is directly on the seed layer 211). The seed layer 211 is configured to promote the growth of the chemical templating layer 210. In one or more embodiments, the seed layer 211 may include ScxN, where x is in a range from 0.8 to 1.2. Additionally, in one or more embodiments, the seed layer 211 may include ScxN and chromium (Cr).
Additionally, in the illustrated embodiment, the MRAM device 200 includes a metallic dusting layer 212 comprising tantalum (Ta), molybdenum (Mo), tungsten (W), cobalt/iron (Co/Fe) doped W, Co/Fe-doped Mo, and/or CoFeB above the substrate 201. In the illustrated embodiment, the metallic dusting layer 212 is between the substrate 201 and the seed layer 211. In one or more embodiments, the metallic dusting layer 212 may be directly on an upper surface of the substrate 201.
In the illustrated embodiment, the MRAM device 200 also includes an oxide layer 213 (e.g., MgO or other suitable oxide) on an upper surface of the magnetic free layer 207. The oxide layer 213 above the magnetic free layer 207 is configured to minimize (or at least reduce) spin pumping and thereby lower the switching current and thus reduce the power consumption of the MRAM device 200.
In the illustrated embodiment, the method 300 includes a task 305 of forming (e.g., depositing) a synthetic antiferromagnetic (SAF) layer on a substrate, and forming (e.g., depositing) a metallic dusting layer (e.g., tantalum (Ta), iridium (Ir), molybdenum (Mo), tungsten (W), cobalt/iron (Co/Fe) doped W, or Co/Fe-doped Mo) on the SAF layer. In one or more embodiments, the task may include annealing the SAF layer. In one or more embodiments, the SAF layer may be annealed at a temperature greater than approximately 350° C., such as approximately 400° C. or more. The SAF layer, which is below a tunnel barrier layer formed in a subsequent task, is more thermally robust than related art SAF layers above the tunnel barrier layer. For instance, in one or more embodiments, the SAF layer formed in task 305 below the tunnel barrier layer may be annealed up to approximately 400° C. or more, whereas related art SAF layers above the tunnel barrier layer can be annealed up to only approximately 350° C. Additionally, in one or more embodiments, the SAF layer formed in task 305 below the tunnel barrier layer has an exchange field (Hex) in a range from approximately 8 kOe to approximately 10 kOe, whereas related art SAF layers above the tunnel barrier layer have an exchange field of only approximately 4 kOe to approximately 5 kOe.
In the illustrated embodiment, the method 300 includes a task 310 of forming (e.g., depositing) a bottom magnetic reference layer (i.e., a pinned or fixed magnetic layer) on the SAF layer and the Ta layer formed in task 305. In one embodiment, the task 310 of forming the bottom magnetic reference layer includes depositing CoFeB (e.g., an alloy of Co, Fe, and B where the composition may be of the form (CoFe)1-xBx where x is in a range from approximately 0.15 to approximately 0.35 (0.15≤x≤0.35), or an alloy of Co, Fe, and B where the composition may be of the form (Co1-xFex)1-yBy where x is in a range from approximately 0.3 to approximately 0.7 (0.3<x<0.7) and y is in a range from approximately 0.15 to approximately 0.5 (0.15<y<0.5)). In one or more embodiments, the task 310 of forming the bottom magnetic reference layer comprises depositing a Mn3Ge layer and then optionally depositing a FeyX polarization enhancement layer (PEL) (where X is aluminum (Al), germanium (Ge), or gallium (Ga) and y is in a range from 0.9 to 3.3) on the Mn3Ge layer. In one or more embodiments, the Mn3Ge layer deposited in task 310 may have a thickness of at least approximately 25 Å such that the coercivity (Hc) of the bottom magnetic reference layer is greater than approximately 8 kOe, as illustrated in
In the illustrated embodiment, the method 300 also includes a task 315 of forming (e.g., depositing) a tunnel barrier layer above the bottom magnetic reference layer formed in task 310. In one or more embodiments, the tunnel barrier layer formed in task 315 may include MgO or MgAl2O4.
In the illustrated embodiment, the method 300 also includes a task 320 of forming (e.g., depositing) a top magnetic free layer above the tunnel barrier layer formed in task 315. In the illustrated embodiment, the task 320 of forming the top magnetic free layer includes a sub-task 320-1 of forming (e.g., growing) a chemical templating layer on (e.g., directly on) an upper surface of the tunnel barrier layer. In one or more embodiments, the chemical templating layer formed in sub-task 320-1 includes a binary alloy with the composition FeyX, where X is aluminum (Al), germanium (Ge), or gallium (Ga) and y is in a range from 0.9 to 3.3, and the binary alloy of the chemical templating layer may have a BiF3 prototype structure, as illustrated in
In the illustrated embodiment, the task 320 of forming the top magnetic free layer also includes a sub-task 320-2 of forming (e.g., growing) a magnetic layer comprising a Heusler compound on the chemical templating layer formed in sub-task 320-1. The chemical templating layer formed in sub-task 320-1 is configured to promote the growth of the Heusler compound of the magnetic free layer formed in sub-task 320-2 with substantially perpendicular magnetic anisotropy (PMA).
In the illustrated embodiment, the method 300 also includes a task 325 of forming (e.g., depositing) an oxide layer on the top magnetic free layer formed in task 320 to complete the MRAM device. In one or more embodiments, the oxide layer formed in task 325 may include MgO or other suitable oxide. The oxide layer formed above the magnetic free layer is configured to minimize (or at least reduce) spin pumping and thereby lower the switching current and thus reduce the power consumption of the MRAM device formed according to the method 300.
In the illustrated embodiment, the method 400 includes a task 405 of forming (e.g., depositing) a metallic dusting layer including, for example, tantalum (Ta), molybdenum (Mo), tungsten (W), cobalt/iron (Co/Fe) doped W, Co/Fe-doped Mo and/or CoFeB on a substrate.
In the illustrated embodiment, the method 400 includes a task 410 of forming (e.g., depositing) a seed layer on the metallic dusting layer formed in task 405. In one or more embodiments, the seed layer formed in task 410 may include ScxN, where x is in a range from 0.8 to 1.2. Additionally, in one or more embodiments, the seed layer formed in task 410 may include ScxN and chromium (Cr).
In the illustrated embodiment, the method 400 also includes a task 415 of forming (e.g., depositing or growing) a chemical templating layer on the seed layer formed in task 410. The seed layer formed in task 410 is configured to promote the growth of the chemical templating layer in task 415. In one or more embodiments, the chemical templating layer formed in task 415 may include CoAl or a bilayer of IrAl and CoAl.
In the illustrated embodiment, the method 400 includes a task 420 of forming (e.g., depositing) a bottom magnetic reference layer (i.e., a pinned or fixed magnetic layer) on the chemical templating layer formed in task 415. In one or more embodiments, the task 420 of forming the bottom magnetic reference layer includes a first sub-task of growing a Mn3Ge layer on the chemical templating layer, and then a second sub-task of depositing a FeyX polarization enhancement layer (PEL) (where X is aluminum (Al), germanium (Ge), or gallium (Ga)) on the Mn3Ge layer. In one or more embodiments, the Mn3Ge layer formed in task 420 may have a thickness of at least approximately 25 Å such that the coercivity (Hc) of the bottom magnetic reference layer is greater than approximately 8 kOe, as illustrated in
In the illustrated embodiment, the method 400 also includes a task 425 of forming (e.g., depositing) a tunnel barrier layer above the bottom magnetic reference layer formed in task 420. In one or more embodiments, the tunnel barrier layer formed in task 425 may include MgO or MgAl2O4.
In the illustrated embodiment, the method 400 also includes a task 430 of forming (e.g., depositing) a top magnetic free layer above the tunnel barrier layer formed in task 425. In the illustrated embodiment, the task 430 of forming the top magnetic free layer includes a sub-task 430-1 of forming (e.g., growing) a chemical templating layer on (e.g., directly on) an upper surface of the tunnel barrier layer. In one or more embodiments, the chemical templating layer formed in sub-task 430-1 includes a binary alloy with the composition FeyX, where X is aluminum (Al), germanium (Ge), or gallium (Ga), and the binary alloy of the chemical templating layer may have a BiF3 prototype structure, as illustrated in
In the illustrated embodiment, the task 430 of forming the top magnetic free layer also includes a sub-task 430-2 of forming (e.g., growing) a magnetic layer comprising a Heusler compound (e.g., Mn3Ge) on the chemical templating layer formed in sub-task 430-1. The chemical templating layer formed in sub-task 430-1 is configured to promote the growth of the Heusler compound of the magnetic free layer formed in sub-task 430-2 with substantially perpendicular magnetic anisotropy (PMA).
In one or more embodiments in which the method 400 includes forming (e.g., depositing or growing) FeyX layers symmetrically above and below the tunnel barrier layer, the MRAM device formed according to method 400 may have symmetric (or substantially symmetric) spin filtering and thus enhanced tunneling magnetoresistance (TMR) compared to an otherwise MRAM device without symmetric spin filtering.
In the illustrated embodiment, the method 400 also includes a task 435 of forming (e.g., depositing) an oxide layer on the top magnetic free layer formed in task 430 to complete the MRAM device. In one or more embodiments, the oxide layer formed in task 435 may include MgO or other suitable oxide. The oxide layer formed above the magnetic free layer is configured to minimize (or at least reduce) spin pumping and thereby lower the switching current and thus reduce the power consumption of the MRAM device formed according to the method 400.
While this invention has been described in detail with particular references to exemplary embodiments thereof, the exemplary embodiments described herein are not intended to be exhaustive or to limit the scope of the invention to the exact forms disclosed. Persons skilled in the art and technology to which this invention pertains will appreciate that alterations and changes in the described structures and methods of assembly and operation can be practiced without meaningfully departing from the principles, spirit, and scope of this invention, as set forth in the following claims.
| Number | Date | Country | Kind |
|---|---|---|---|
| 20230100323 | Apr 2023 | GR | national |
