CN111682106B - Spin orbit torque based memory cell and method of making same - Google Patents
Spin orbit torque based memory cell and method of making same Download PDFInfo
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Abstract
The invention provides a spin-orbit torque-based memory cell and a method of manufacturing the same. The spin-orbit torque-based memory unit includes: a magnetic tunnel junction comprising a free layer, a barrier layer, and a reference layer stacked in sequence; a horizontal spin orbit torque effect layer in contact with a bottom surface of the free layer; the vertical spin orbit torque effect layer covers one side wall of the free layer. The storage unit based on spin orbit torque can realize the deterministic reversal of the magnetization direction of the free layer under the condition of no external magnetic field.
Description
Technical Field
The invention relates to the technical field of magnetic memories, in particular to a storage unit based on spin orbit torque and a manufacturing method thereof.
Background
The Spin-Orbit Torque Magnetic Random Access Memory (SOT-MRAM) is a novel Memory, has the advantages of nanosecond-level read-write speed, low power consumption, nearly unlimited service life, nonvolatility and the like, and has great application potential.
In the current mainstream SOT-MRAM unit structure, the magnetic tunnel junction adopts interface vertical anisotropy, under the common condition, if no external magnetic field exists, the spin orbit torque can only enable the magnetization direction of the free layer of the magnetic tunnel junction to deflect from the direction vertical to the interface to the horizontal plane of the interface, after the current is removed, the spin orbit torque disappears, and the free layer of the magnetic tunnel junction can not generate the turnover certainty. Therefore, to ensure a deterministic reversal of the magnetization direction of the free layer of the magnetic tunnel junction, an external magnetic field must be applied to ensure proper operation of the SOT-MRAM cell. However, increasing the external magnetic field is not favorable for fabricating a high-density large-capacity memory, and performance and power consumption are also affected. Therefore, there is a need for an SOT-MRAM cell structure that can achieve a deterministic reversal of the magnetization direction of the free layer without the need for an external magnetic field.
Disclosure of Invention
To solve the above problems, the present invention provides a spin-orbit torque-based memory cell and a method of manufacturing the same, which can achieve a deterministic switching of the magnetization direction of the free layer without the need for an external magnetic field.
In a first aspect, the present invention provides a spin-orbit-torque-based memory cell, comprising:
a magnetic tunnel junction comprising a free layer, a barrier layer, and a reference layer stacked in sequence;
a horizontal spin orbit torque effect layer in contact with a bottom surface of the free layer;
the vertical spin orbit torque effect layer covers one side wall of the free layer.
In a second aspect, the present invention provides a method for manufacturing a spin-orbit torque based memory cell, comprising:
providing a substrate, forming a first spin orbit torque effect layer on the substrate, forming a magnetic tunnel junction on the first spin orbit torque effect layer, wherein the magnetic tunnel junction comprises a free layer, a barrier layer and a reference layer which are sequentially stacked, the barrier layer and the reference layer are the same in size, the size of the free layer is larger than that of the barrier layer, and dielectric layers are formed around and on the top of the magnetic tunnel junction;
forming a patterned mask layer above the dielectric layer, wherein the edge of the mask layer is aligned with the edge of one side wall of the free layer;
etching the dielectric layer downwards by taking the mask layer as a mask until the surface of the first spin orbit torque effect layer is exposed;
forming a second spin orbit torque effect layer, wherein the second spin orbit torque effect layer covers the exposed surface of the first spin orbit torque effect layer, the surface of the mask layer and the whole side wall;
etching the second spin orbit torque effect layer, and only reserving the second spin orbit torque effect layer with a certain width to cover the side wall of the magnetic tunnel junction free layer after etching;
and removing the mask layer, filling the gap of the dielectric layer and forming a smooth surface.
In a third aspect, the present invention provides a spin orbit torque based differential memory cell, comprising:
a first magnetic tunnel junction comprising a first free layer, a first barrier layer, and a first reference layer stacked in sequence;
a second magnetic tunnel junction comprising a second free layer, a second barrier layer, and a second reference layer stacked in sequence;
a horizontal spin orbit torque effect layer in contact with a bottom surface of the first free layer and a bottom surface of the second free layer;
the first vertical spin orbit torque effect layer covers one side wall of the first free layer;
a second vertical spin orbit torque effect layer covering one sidewall of the second free layer;
the side wall covered by the first vertical spin orbit torque effect layer and the side wall covered by the second vertical spin orbit torque effect layer are two side walls, which are not on the same side, of the first free layer and the second free layer.
In a fourth aspect, the present invention provides a method for manufacturing a spin-orbit torque-based differential memory cell, comprising:
providing a substrate, forming a first spin orbit torque effect layer on the substrate, forming a first magnetic tunnel junction and a second magnetic tunnel junction on the first spin orbit torque effect layer, wherein the first magnetic tunnel junction comprises a first free layer, a first barrier layer and a first reference layer which are sequentially stacked, the first barrier layer and the first reference layer are the same in size, the first free layer is larger than the first barrier layer in size, the second magnetic tunnel junction comprises a second free layer, a second barrier layer and a second reference layer which are sequentially stacked, the second barrier layer and the second reference layer are the same in size, the second free layer is larger than the second barrier layer in size, and a dielectric layer is formed around and on the top of the first magnetic tunnel junction and the second magnetic tunnel junction;
forming a patterned first mask layer above the dielectric layer, wherein the edge of the first mask layer is aligned with the edge of one side wall of the first free layer;
etching the dielectric layer downwards by taking the first mask layer as a mask until the surface of the first spin orbit torque effect layer is exposed;
forming a second spin orbit torque effect layer, wherein the second spin orbit torque effect layer covers the exposed surface of the first spin orbit torque effect layer, the surface of the first mask layer and the whole side wall;
etching the second spin orbit torque effect layer, and only reserving the second spin orbit torque effect layer with a certain width to cover the side wall of the first free layer of the first magnetic tunnel junction after etching;
removing the first mask layer, filling the gap of the dielectric layer and forming a smooth surface;
forming a patterned second mask layer above the dielectric layer, wherein the edge of the second mask layer is aligned with the edge of one side wall of the second free layer, and the one side wall of the second free layer is the side wall which is not on the same side as the first free layer and is covered with the second spin orbit torque effect layer;
etching the dielectric layer downwards by taking the second mask layer as a mask until the surface of the first spin orbit torque effect layer is exposed;
forming a third spin orbit torque effect layer, wherein the third spin orbit torque effect layer covers the exposed surface of the first spin orbit torque effect layer, the surface of the second mask layer and the whole side wall;
etching the third spin orbit torque effect layer, and only reserving the third spin orbit torque effect layer with a certain width to cover the side wall of the second free layer of the second magnetic tunnel junction after etching;
and removing the second mask layer, filling the gap of the dielectric layer and forming a smooth surface.
According to the spin orbit torque-based storage unit provided by the invention, the vertical spin orbit torque effect layer covering the side wall of the free layer is utilized, the deterministic inversion of the magnetization direction of the free layer can be realized under the condition of no need of an external magnetic field, the storage density is improved, the performance decline is reduced, and the power consumption is reduced. And provides a differential memory cell based on the above, which can reduce the error rate.
Drawings
FIG. 1 is a schematic diagram of a spin-orbit torque based memory cell according to an embodiment of the present invention;
FIG. 2 is a schematic diagram of the magnetization direction flipping of the free layer of the spin-orbit torque based memory unit shown in FIG. 1;
FIG. 3 is a schematic diagram of the magnetization reversal of the free layer of the spin-orbit torque based memory cell of FIG. 1;
FIG. 4 is a schematic structural diagram of a spin-orbit torque based memory cell according to an embodiment of the present invention;
FIG. 5 is a schematic diagram of the magnetization reversal of the free layer of the spin-orbit torque based memory unit shown in FIG. 4;
FIG. 6 is a schematic diagram of the magnetization reversal of the free layer of the spin-orbit torque based memory unit shown in FIG. 4;
FIGS. 7-12 are schematic process flow diagrams of a method for fabricating a spin-orbit torque-based memory cell according to an embodiment of the invention;
FIG. 13 is a schematic structural diagram of a spin-orbit torque based differential memory cell according to an embodiment of the present invention;
FIG. 14 is a schematic diagram of the magnetization reversal of the free layer of the differential memory cell of FIG. 13;
FIG. 15 is a schematic diagram of the magnetization reversal of the free layer of the differential memory cell of FIG. 13;
FIG. 16 is a schematic structural diagram of a spin-orbit torque based differential memory cell according to an embodiment of the present invention;
FIG. 17 is a schematic diagram of the magnetization reversal of the free layer of the differential memory cell of FIG. 16;
FIG. 18 is a schematic diagram of the magnetization reversal of the free layer of the differential memory cell of FIG. 16;
FIG. 19 is a schematic structural diagram of a spin-orbit torque based differential memory cell according to an embodiment of the present invention;
20-30 are process flow diagrams of a method for manufacturing a spin-orbit torque based differential memory cell according to an embodiment of the invention.
Detailed Description
In order to make the objects, technical solutions and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the drawings in the embodiments of the present invention, and it is obvious that the described embodiments are only a part of the embodiments of the present invention, and not all the embodiments. All other embodiments, which can be derived by a person skilled in the art from the embodiments given herein without making any creative effort, shall fall within the protection scope of the present invention.
Hereinafter, embodiments of the present disclosure will be described with reference to the accompanying drawings. It should be understood that the description is illustrative only and is not intended to limit the scope of the present disclosure. Moreover, in the following description, descriptions of well-known structures and techniques are omitted so as to not unnecessarily obscure the concepts of the present disclosure.
Various structural schematics according to embodiments of the present disclosure are shown in the figures. The figures are not drawn to scale, wherein certain details are exaggerated and possibly omitted for clarity of presentation. The shapes of various regions, layers, and relative sizes and positional relationships therebetween shown in the drawings are merely exemplary, and deviations may occur in practice due to manufacturing tolerances or technical limitations, and a person skilled in the art may additionally design regions/layers having different shapes, sizes, relative positions, as actually required.
In the context of the present disclosure, when a layer/element is referred to as being "on" another layer/element, it can be directly on the other layer/element or intervening layers/elements may be present. In addition, if a layer/element is "on" another layer/element in one orientation, then that layer/element may be "under" the other layer/element when the orientation is reversed.
The embodiment of the invention provides a storage unit based on spin orbit torque, which comprises: the magnetic tunnel junction comprises a free layer, a barrier layer and a reference layer which are sequentially stacked, wherein the free layer is arranged at the lowermost layer, a horizontal spin orbit torque effect layer is arranged below the free layer and is in contact with the bottom surface of the free layer, when current passes through the horizontal spin orbit torque effect layer, a magnetic field in the horizontal direction can be generated by utilizing the spin orbit torque effect, one side wall of the free layer can be a left side wall or a right side wall, a vertical spin orbit torque effect layer covers the side wall, and when current passes through the vertical spin orbit torque effect layer, a magnetic field in the vertical direction can be generated by utilizing the spin orbit torque effect.
FIG. 1 shows the case where the left side wall of the free layer is covered with the vertical spin orbit torque effect layer. As shown in fig. 1, the spin orbit torque based memory cell includes a magnetic tunnel junction 103, the magnetic tunnel junction 103 includes a free layer 1031, a barrier layer 1032 and a reference layer 1033 which are sequentially stacked, a horizontal spin orbit torque effect layer 101 is in contact with a bottom surface of the free layer 1031, and a vertical spin orbit torque effect layer 102 is overlaid on a left side wall of the free layer 1031. In this embodiment, the vertical spin orbit torque effect layer 102 and the horizontal spin orbit torque effect layer 101 are connected, and the same current is applied. In order to prevent the free layer 1031 from being short-circuited with the reference layer 1033, the free layer 1031 may be sized slightly larger than the barrier layer 1032 and the reference layer 1033, and the dimensions of the barrier layer 1032 and the reference layer 1033 may be the same. This is done in order that a layer of dielectric will be attached to the sidewalls of the reference layer when the device is manufactured. In this case, the height of the vertical spin orbit torque effect layer 102 is not particularly limited, and may be higher or lower than the surface height of the free layer.
It should be noted that, if the free layer and the reference layer are manufactured to have the same size, in order to prevent the free layer and the reference layer from short circuit, the height of the vertical spin orbit torque effect layer 102 should not exceed the surface height of the barrier layer 1032, and is generally slightly lower than the surface height of the free layer 1031, a dielectric layer 104 is deposited on the surface of the device, and the dielectric layer 104 is located above the horizontal spin orbit torque effect layer 101, and surrounds the magnetic tunnel junction 103 and the vertical spin orbit torque effect layer 102.
For the spin-orbit torque based memory cell shown in fig. 1, the magnetization direction of the free layer can be switched deterministically when a current is applied, as follows:
as shown in FIG. 2, assuming that the magnetization direction of the reference layer is downward, when the direction of the current flowing through the horizontal spin orbit torque effect layer 101 and the vertical spin orbit torque effect layer 102 is in the direction of the sheet (to
And indicated by the dotted arrow in the figure), the equivalent magnetic field generated by the horizontal spin orbit torque effect layer 101 is oriented rightward (indicated by the dotted arrow in the figure), the magnetization direction of the free layer is confined in the horizontal plane by the horizontal magnetic field, and the equivalent magnetic field generated by the vertical spin orbit torque effect layer 102 is oriented downward (indicated by the dotted arrow in the figure), and the magnetization direction of the free layer is inclined downward by the vertical magnetic field. When the current is removed, the magnetization direction of the free layer is reversed to a direction which is relatively easy to reverse, namely, downwards reversed according to the characteristics of the free layer, so that the downwards reversing of the magnetization direction of the free layer is realized in a deterministic way.
As shown in FIG. 3, assuming that the magnetization direction of the reference layer is downward, when the current flowing into the horizontal spin orbit torque effect layer 101 and the vertical spin orbit torque effect layer 102 flows out of the paper (indicated by [) direction, the equivalent magnetic field generated by the horizontal spin orbit torque effect layer 101 is oriented leftward, the magnetization direction of the free layer is limited in the horizontal plane by the horizontal magnetic field, meanwhile, the equivalent magnetic field generated by the vertical spin orbit torque effect layer 102 is oriented upward, and the magnetization direction of the free layer is inclined upward by the vertical magnetic field. When the current is removed, the magnetization direction of the free layer can be inverted to a direction which is relatively easy to be inverted, namely, the free layer is inverted upwards according to the characteristics of the free layer, so that the upward inversion of the determinacy of the magnetization direction of the free layer is realized.
Fig. 4 shows a case where the right side wall of the free layer is covered with the vertical spin orbit torque effect layer. As shown in fig. 4, the spin-orbit torque based memory cell includes a magnetic tunnel junction 203, the magnetic tunnel junction 203 includes a free layer 2031, a barrier layer 2032, and a reference layer 2033 stacked in this order, a horizontal spin-orbit torque effect layer 201 is in contact with the bottom surface of the free layer 2031, and a vertical spin-orbit torque effect layer 202 is covered on the right side wall of the free layer 2031. In this embodiment, the vertical spin orbit torque effect layer 202 and the horizontal spin orbit torque effect layer 201 are connected, and the same current is applied. To prevent the free layer 2031 from shorting to the reference layer 2033, the free layer 2031 may be sized slightly larger than the barrier layer 2032 and the reference layer 2033, and the barrier layer 2032 and the reference layer 2033 may be the same size. This is done in order that a layer of dielectric will be attached to the sidewalls of the reference layer when the device is manufactured. In this case, the height of the vertical spin orbit torque effect layer 202 is not particularly limited, and may be higher or lower than the surface height of the free layer.
However, it should be noted that if the free layer and the reference layer are fabricated to have the same size, then in order to prevent the free layer and the reference layer from short-circuiting, the height of the vertical spin-orbit torque effect layer 202 should not exceed the surface height of the barrier layer 2032, and is generally slightly lower than the surface height of the free layer 2031, a dielectric layer 204 is deposited on the surface of the device, and the dielectric layer 204 is located above the horizontal spin-orbit torque effect layer 201 and surrounds the magnetic tunnel junction 203 and the vertical spin-orbit torque effect layer 202.
For the spin-orbit torque based memory unit shown in FIG. 4, the magnetization direction of the free layer can be switched deterministically when current is applied, as follows:
as shown in FIG. 5, assuming that the magnetization direction of the reference layer is downward, when the direction of the current flowing through the horizontal spin orbit torque effect layer 201 and the vertical spin orbit torque effect layer 202 is in the direction of the paper (to
Indicated by (b) to the right, the magnetization direction of the free layer is limited to the horizontal plane by the horizontal magnetic field generated by the horizontal spin orbit torque effect layer 201Meanwhile, the direction of the equivalent magnetic field generated by the vertical spin orbit torque effect layer 202 is upward, and the magnetization direction of the free layer is inclined upward under the action of the vertical magnetic field. When the current is removed, the magnetization direction of the free layer can be inverted to a direction which is relatively easy to be inverted, namely, the free layer is inverted upwards according to the characteristics of the free layer, so that the upward inversion of the determinacy of the magnetization direction of the free layer is realized.
As shown in FIG. 6, assuming that the magnetization direction of the reference layer is downward, when the current flows into the horizontal spin orbit torque effect layer 201 and the vertical spin orbit torque effect layer 202 in the direction out of the plane (indicated by [) the direction of the magnetic field equivalent generated by the horizontal spin orbit torque effect layer 201 is leftward, the magnetization direction of the free layer is confined in the horizontal plane by the horizontal magnetic field, and the direction of the magnetic field equivalent generated by the vertical spin orbit torque effect layer 202 is downward, the magnetization direction of the free layer is downward inclined by the vertical magnetic field. When the current is removed, the magnetization direction of the free layer is reversed to a direction which is relatively easy to reverse, namely, downwards reversed according to the characteristics of the free layer, so that the downwards reversing of the magnetization direction of the free layer is realized in a deterministic way.
It can be seen from the above two embodiments that the spin orbit torque-based storage unit provided in the embodiment of the present invention utilizes the vertical spin orbit torque effect layer covering the sidewall of the free layer to realize the deterministic flipping of the magnetization direction of the free layer without an external magnetic field, thereby improving the storage density, reducing the performance degradation, and reducing the power consumption.
For the storage unit based on spin-orbit torque disclosed by the above embodiment, the embodiment of the invention discloses a manufacturing method of the storage unit based on spin-orbit torque. For a detailed description of the fabrication of the free layer with its left sidewall covered with the vertical spin-orbit torque effect layer, the schematic diagrams of the fabrication flow can be referred to fig. 7-12.
First, as shown in fig. 7, a substrate (not shown) is provided, which has completed the previous process flow, and a first spin orbit torque effect layer 301 is formed on the substrate, the first spin orbit torque effect layer 301 generates spin orbit torque effect when passing current, and the first spin orbit torque effect layer 301 is usually a heavy metal material, such as Pt, Ta, W, Ir, Hf, Ru, Tl, Bi, Au, Os, and the like. A magnetic tunnel junction 302 is formed on the first spin orbit torque effect layer 301, and here, only a free layer 3021, a barrier layer 3022, and a reference layer 3023 of the magnetic tunnel junction 302 are illustrated, but the laminated structure of the magnetic tunnel junction 302 is not limited thereto. A dielectric layer 303 is formed around and on top of the magnetic tunnel junction 302 to achieve a protective function. In this embodiment, in order to facilitate the subsequent process flow, prevent the short-circuit defect between the free layer and the reference layer, and improve the yield, in the magnetic tunnel junction structure, the barrier layer and the reference layer have the same size, and the size of the free layer is larger than that of the barrier layer, so that a layer of medium is reserved on the side walls of the barrier layer and the reference layer for protection. If the magnetic tunnel junction is made cylindrical, the diameter of the free layer may be slightly larger relative to the diameter of the barrier layer, the reference layer.
Then, as shown in FIG. 8, a patterned mask layer 304 is formed over the dielectric layer 303, and since a vertical spin-orbit-moment effect layer is formed on the left sidewall of the free layer 3021, in this embodiment, the left edge of the mask layer 304 should extend beyond the edges of the barrier layer 3022 and the reference layer 3023 to be aligned with the edge of the left sidewall of the free layer 3021.
Next, as shown in fig. 9, the mask layer 304 is used as a mask, the part of the dielectric layer 303 not covered by the mask layer 304 is removed by etching or the like, the etching is stopped on the surface of the first spin orbit torque effect layer 301, and after the etching, the left sidewall of the free layer 3021 has no dielectric adhesion.
Then, as shown in fig. 10, a second spin orbit torque effect layer 305 is formed by a deposition process, the material of the second spin orbit torque effect layer 305 is the same as that of the first spin orbit torque effect layer 301, such as a heavy metal, and the second spin orbit torque effect layer 305 covers the exposed surface of the first spin orbit torque effect layer 301, the surface of the mask layer 304, and the entire side wall. Typically, the sidewall deposition will be less thick than the planar deposition.
Next, as shown in fig. 11, the second spin orbit torque effect layer 305 is etched, in order to form a vertical spin orbit torque effect layer on the left side wall of the free layer 3021, an anisotropic etching method may be adopted, mainly using a downward etching method, to remove a portion of the second spin orbit torque effect layer 305 on the surface of the first spin orbit torque effect layer 301 and a portion of the second spin orbit torque effect layer 305 on the surface of the mask layer 304, and after the etching, only the second spin orbit torque effect layer 305 with a certain width is remained to cover the left side wall of the magnetic tunnel junction free layer 3021.
Finally, as shown in fig. 12, the mask layer 304 is removed, and a dielectric is deposited in the left gap position of the dielectric layer 303 to protect the device, and then a smooth surface is formed by CMP or the like.
For another situation, namely the situation that the right side wall of the free layer covers the vertical spin orbit torque effect layer, the pattern of the mask is only required to be adjusted to enable the mask layer to be aligned with the edge of the right side wall of the free layer, other processes are similar, and description is not provided.
Because the error rate of a single storage unit based on spin orbit torque is high, the embodiment of the invention provides a differential storage unit based on spin orbit torque, the differential storage unit stores two opposite data, and the error rate can be reduced.
Specifically, the differential memory cell includes: the two magnetic tunnel junctions are marked as a first magnetic tunnel junction and a second magnetic tunnel junction, the first magnetic tunnel junction comprises a first free layer, a first barrier layer and a first reference layer which are sequentially stacked from bottom to top, and the second magnetic tunnel junction comprises a second free layer, a second barrier layer and a second reference layer which are sequentially stacked from bottom to top. And a horizontal spin orbit torque effect layer is arranged below the two magnetic tunnel junctions, is in contact with the bottom surface of the first free layer and the bottom surface of the second free layer, and can generate a horizontal magnetic field when current is introduced into the horizontal spin orbit torque effect layer. A first vertical spin orbit torque effect layer covers the side wall of the first free layer of the first magnetic tunnel junction, and a second vertical spin orbit torque effect layer covers the side wall of the second free layer of the second magnetic tunnel junction. It is to be noted here that the sidewall of the first free layer covered by the first vertical spin orbit torque effect layer and the sidewall of the second free layer covered by the second vertical spin orbit torque effect layer are two sidewalls of the first free layer and the second free layer which are not on the same side. That is, if the first vertical spin orbit torque effect layer covers the left sidewall of the first free layer, the second vertical spin orbit torque effect layer covers the right sidewall of the second free layer. If the first vertical spin orbit torque effect layer covers the right side wall of the first free layer, the second vertical spin orbit torque effect layer covers the left side wall of the second free layer.
Fig. 13 shows a cross-sectional structure of a differential memory cell of the present embodiment. As shown in fig. 13, the differential memory cell includes a first magnetic tunnel junction 404 and a second magnetic tunnel junction 405, the first magnetic tunnel junction 404 includes a first free layer 4041, a first barrier layer 4042, and a first reference layer 4043 stacked in this order from bottom to top, and the second magnetic tunnel junction 405 includes a second free layer 4051, a second barrier layer 4052, and a second reference layer 4053 stacked in this order from bottom to top. A horizontal spin orbit torque effect layer 401 is arranged below the two magnetic tunnel junctions, the horizontal spin orbit torque effect layer 401 is in contact with the bottom surface of the first free layer 4041 and the bottom surface of the second free layer 4051, and when current is introduced into the horizontal spin orbit torque effect layer 401, a horizontal magnetic field can be generated. The first vertical spin orbit torque effect layer 402 is coated on the left sidewall of the first free layer 4041 of the first magnetic tunnel junction, and the second vertical spin orbit torque effect layer 403 is coated on the right sidewall of the second free layer 4051 of the second magnetic tunnel junction. In this embodiment, the first vertical spin orbit torque effect layer 402 and the second vertical spin orbit torque effect layer 403 are respectively communicated with the horizontal spin orbit torque effect layer 401, and the same current is applied thereto. To prevent the free layer from shorting to the reference layer, the first free layer 4041 may be sized slightly larger than the first barrier layer 4042 and the second reference layer 4043, and the first barrier layer 4042 and the first reference layer 4043 may be the same size. The second free layer 4051 is sized slightly larger than the second barrier layer 4052 and the second reference layer 4053, and the second barrier layer 4052 and the second reference layer 4053 may be the same size. In one embodiment, the height of the first vertical spin orbit torque effect layer 402 is not more than the surface height of the first barrier layer 4042, and is generally slightly lower than the surface height of the first free layer 4041, and the height of the second vertical spin orbit torque effect layer 403 is not more than the surface height of the second barrier layer 4052, and is generally slightly lower than the surface height of the second free layer 4051. A dielectric layer 406 is deposited on the surface of the device, the dielectric layer 406 is located above the horizontal spin orbit torque effect layer 401, surrounds the first magnetic tunnel junction 404 and the first vertical spin orbit torque effect layer 402 on the sidewall thereof, and surrounds the second magnetic tunnel junction 405 and the second vertical spin orbit torque effect layer 403 on the sidewall thereof.
For the differential memory cell shown in FIG. 13, the magnetization directions of the free layers of the two magnetic tunnel junctions are deterministically switched when current is applied, and the switching directions are opposite. The method comprises the following specific steps:
as shown in FIG. 14, assuming that the magnetization directions of the first reference layer 4043 and the second reference layer 4053 are downward, when the direction of the current flowing through the horizontal spin orbit torque effect layer 401, the first vertical spin orbit torque effect layer 402, and the second vertical spin orbit torque effect layer 403 is in the direction of the sheet (to make the current flow in
Indicated by the dotted arrow in the figure), the equivalent magnetic field generated by the horizontal spin orbit torque effect layer 401 is oriented to the right (indicated by the dotted arrow in the figure), the magnetization direction of the free layer is limited in the horizontal plane by the horizontal magnetic field, and the equivalent magnetic field generated by the first vertical spin orbit torque effect layer 402 is oriented downward, and the magnetization direction of the first free layer 4041 is inclined downward by the vertical magnetic field. When the current is removed, the magnetization direction of the first free layer 4041 flips to a relatively easy direction, i.e., downward, depending on the characteristics of the free layer. The direction of the equivalent magnetic field generated by the second vertical spin orbit torque effect layer 403 is upward, and the magnetization direction of the second free layer 4051 is inclined upward by the vertical magnetic field. When the current is removed, the magnetization direction of the second free layer 4051 flips to a relatively easy direction, i.e., up-flip, depending on the characteristics of the free layer. Freedom of two magnetic tunnel junctionsThe magnetization directions of the layers are opposite, so that the two magnetic tunnel junctions store data in an opposite manner, and a differential structure is realized.
As shown in FIG. 15, assuming that the magnetization directions of the first and second reference layers 4043 and 4053 are downward, when the current flows in the direction out of the paper (indicated by [ ] in the figure), the direction of the magnetic field generated by the horizontal spin orbit torque effect layer 401 is leftward (indicated by the dotted arrow in the figure), the magnetization direction of the free layer is confined in the horizontal plane by the horizontal magnetic field, and the direction of the magnetic field generated by the first vertical spin orbit torque effect layer 402 is upward, and the magnetization direction of the first free layer 4041 is tilted upward by the vertical magnetic field. When the current is removed, the magnetization direction of the first free layer 4041 flips to a relatively easy direction, i.e., up-flip, depending on the characteristics of the free layer. The equivalent magnetic field generated by the second vertical spin orbit torque effect layer 403 is directed downward, and the magnetization direction of the second free layer 4051 is inclined downward by the vertical magnetic field. When the current is removed, the magnetization direction of the second free layer 4051 flips to a relatively easy direction, i.e., downward, depending on the characteristics of the free layer. The magnetization directions of the free layers of the two magnetic tunnel junctions are opposite, so that the two magnetic tunnel junctions store data oppositely, and a differential structure is realized.
Fig. 16 shows a cross-sectional structure of a differential memory cell of the present embodiment. As shown in fig. 16, the differential memory cell includes a first magnetic tunnel junction 504 and a second magnetic tunnel junction 505, the first magnetic tunnel junction 504 includes a first free layer 5041, a first barrier layer 5042, and a first reference layer 5043 stacked in this order from bottom to top, and the second magnetic tunnel junction 505 includes a second free layer 5051, a second barrier layer 5052, and a second reference layer 5053 stacked in this order from bottom to top. A horizontal spin orbit torque effect layer 501 is provided below the two magnetic tunnel junctions, the horizontal spin orbit torque effect layer 501 is in contact with the bottom surface of the first free layer 5041 and the bottom surface of the second free layer 5051, and a horizontal magnetic field can be generated when a current is applied to the horizontal spin orbit torque effect layer 501. The first vertical spin orbit torque effect layer 502 is overlaid on the right sidewall of the first free layer 5041 of the first magnetic tunnel junction, and the second vertical spin orbit torque effect layer 503 is overlaid on the left sidewall of the second free layer 5051 of the second magnetic tunnel junction. In this embodiment, the first vertical spin orbit torque effect layer 502 and the second vertical spin orbit torque effect layer 503 are respectively communicated with the horizontal spin orbit torque effect layer 501, and the same current is applied. To prevent the free layer from shorting to the reference layer, the first free layer 5041 may be sized slightly larger than the first barrier layer 5042 and the second reference layer 5043, and the first barrier layer 5042 and the first reference layer 5043 may be the same size. The dimensions of the second free layer 5051 are designed to be slightly larger than the dimensions of the second barrier layer 5052 and the second reference layer 5053, which may be the same size as the second barrier layer 5052 and the second reference layer 5053. In one embodiment, the height of the first vertical spin orbit torque effect layer 502 is no more than the surface height of the first barrier layer 5042, typically slightly less than the surface height of the first free layer 5041, and the height of the second vertical spin orbit torque effect layer 503 is no more than the surface height of the second barrier layer 5052, typically slightly less than the surface height of the second free layer 5051. A dielectric layer 506 is deposited on the surface of the device, the dielectric layer 506 is located above the horizontal spin orbit torque effect layer 501, surrounds the first magnetic tunnel junction 504 and the first vertical spin orbit torque effect layer 502 on the side wall of the first magnetic tunnel junction 504, and surrounds the second magnetic tunnel junction 505 and the second vertical spin orbit torque effect layer 503 on the side wall of the second magnetic tunnel junction 505.
For the differential memory cell shown in FIG. 16, the magnetization directions of the free layers of the two magnetic tunnel junctions are deterministically switched when current is applied, and the switching directions are opposite. The method comprises the following specific steps:
as shown in FIG. 17, assuming that the magnetization directions of the first reference layer 5043 and the second reference layer 5053 are downward, when the direction of the current flowing through the horizontal spin orbit torque effect layer 501, the first vertical spin orbit torque effect layer 502, and the second vertical spin orbit torque effect layer 503 is in the direction of the sheet (to make the current flow in
Indicated by the dotted arrow in the figure), the equivalent magnetic field generated by the horizontal spin orbit torque effect layer 501 is oriented to the right (indicated by the dotted arrow in the figure), the magnetization direction of the free layer is limited in the horizontal plane by the horizontal magnetic field, and the equivalent magnetic field generated by the first vertical spin orbit torque effect layer 502 is oriented to the upper side, and the magnetization direction of the first free layer 5041 is inclined to the upper side by the vertical magnetic field. When the current is removed, the magnetization direction of the first free layer 5041 flips to a relatively easy-to-flip direction, i.e., up, depending on the properties of the free layer. The equivalent magnetic field generated by the second vertical spin orbit torque effect layer 503 is directed downward, and the magnetization direction of the second free layer 5051 is tilted downward by the vertical magnetic field. When the current is removed, the magnetization direction of the second free layer 5051 flips to a relatively easy direction, i.e., downward, depending on the characteristics of the free layer. The magnetization directions of the free layers of the two magnetic tunnel junctions are opposite, so that the two magnetic tunnel junctions store data oppositely, and a differential structure is realized.
As shown in FIG. 18, assuming that the magnetization directions of the first reference layer 5043 and the second reference layer 5053 are downward, when the direction of current flowing through the horizontal spin orbit torque effect layer 501 and the first vertical spin orbit torque effect layer 502 and the second vertical spin orbit torque effect layer 503 is the direction of current flowing out of the paper (to⊙To indicate) the direction of the equivalent magnetic field generated by the horizontal spin orbit torque effect layer 501 is to the left (indicated by the arrow of the dotted line in the figure), the magnetization direction of the free layer is limited in the horizontal plane by the horizontal magnetic field, and the magnetization direction of the first free layer 5041 is inclined downward by the vertical magnetic field, while the magnetization direction of the free layer is limited downward by the first vertical spin orbit torque effect layer 502. When the current is removed, the magnetization direction of the first free layer 5041 flips to a relatively easy direction, i.e., downward, depending on the properties of the free layer. The direction of the equivalent magnetic field generated by the second vertical spin orbit torque effect layer 503 is upward, and the magnetization direction of the second free layer 5051 is tilted upward by the vertical magnetic field. When the current is removed, the magnetization direction of the second free layer 5051 flips to a relatively easy-to-flip direction, i.e., depending on the characteristics of the free layerAnd turning upwards. The magnetization directions of the free layers of the two magnetic tunnel junctions are opposite, so that the two magnetic tunnel junctions store data oppositely, and a differential structure is realized.
In particular, for the differential memory cell shown in fig. 16, the first vertical spin orbit torque effect layer 502 and the second vertical spin orbit torque effect layer 503 can be integrated at the time of manufacturing to form the structure shown in fig. 19. In this structure, the magnetization direction flipping process of the free layers of the two magnetic tunnel junctions can refer to fig. 17 to 18, which are not described herein again.
For the spin-orbit torque based differential memory cell disclosed in the above embodiments, a specific fabrication method is disclosed in the embodiments of the present invention. The detailed description will be made in a case where a left sidewall of a first free layer of a first magnetic tunnel junction is formed to cover a first vertical spin orbit torque effect layer, and a right sidewall of a second free layer of a second magnetic tunnel junction is formed to cover a second vertical spin orbit torque effect layer. A schematic of the manufacturing flow can be seen in fig. 20-30.
First, as shown in fig. 20, a substrate (not shown) is provided, which has completed the previous process flow, and a first spin orbit torque effect layer 601 is formed on the substrate, the first spin orbit torque effect layer 601 generates spin orbit torque effect when passing current, and the first spin orbit torque effect layer 601 is typically a heavy metal material, such as Pt, Ta, W, Ir, Hf, Ru, Tl, Bi, Au, Os, and the like. A first magnetic tunnel junction 602 and a second magnetic tunnel junction 603 are formed on the first spin orbit torque effect layer 601, and only the first free layer 6021, the first barrier layer 6022, and the first reference layer 6023 of the first magnetic tunnel junction 602, and the second free layer 6031, the second barrier layer 6032, and the second reference layer 6033 of the second magnetic tunnel junction 603 are illustrated here, but the stacked structure of the two magnetic tunnel junctions is not limited thereto. A dielectric layer 604 is formed around and on top of the first magnetic tunnel junction 602 and the second magnetic tunnel junction 603 to implement a protection function. In this embodiment, in order to facilitate the subsequent process flow, prevent the short-circuit defect between the free layer and the reference layer, and improve the yield, in the two magnetic tunnel junction structures, the barrier layer and the reference layer have the same size, and the size of the free layer is larger than that of the barrier layer, so that a layer of medium is reserved on the side walls of the barrier layer and the reference layer for protection. If the magnetic tunnel junction is made cylindrical, the diameter of the free layer may be slightly larger relative to the diameter of the barrier layer, the reference layer.
Then, as shown in fig. 21, a patterned first mask layer 605 is formed over the dielectric layer 604, and since a first vertical spin orbit torque effect layer is to be formed on the left sidewall of the first free layer 6021, in the present embodiment, the left edge of the first mask layer 605 should be aligned with the edge of the left sidewall of the first free layer 6021 beyond the edges of the first barrier layer 6022 and the first reference layer 6023.
Next, as shown in fig. 22, the dielectric layer 604 not covered by the first mask layer 605 is partially removed by etching or the like using the first mask layer 605 as a mask, the etching is stopped on the surface of the first spin orbit torque effect layer 601, and after the etching, the left sidewall of the first free layer 6021 has no dielectric adhesion.
Next, as shown in fig. 23, a second spin orbit torque effect layer 606 is formed by a deposition process, the material of the second spin orbit torque effect layer 606 is the same as that of the first spin orbit torque effect layer 601, for example, heavy metal, and the second spin orbit torque effect layer 606 covers the exposed surface of the first spin orbit torque effect layer 601, the surface of the first mask layer 605, and the entire left side wall. Typically, the sidewall deposition will be less thick than the planar deposition.
Next, as shown in fig. 24, the second spin orbit torque effect layer 606 is etched, in order to form the first vertical spin orbit torque effect layer on the left sidewall of the first free layer 6021, an anisotropic etching method may be adopted, in which a downward etching is mainly used to remove a portion of the second spin orbit torque effect layer on the surface of the first spin orbit torque effect layer 601 and a portion of the second spin orbit torque effect layer on the surface of the first mask layer 605, and after the etching, only the second spin orbit torque effect layer 606 with a certain width is left to cover the left sidewall of the first free layer 6021 of the first magnetic tunnel junction. The remaining second spin orbit torque effect layer 606 is the first vertical spin orbit torque effect layer.
Next, as shown in fig. 25, the first mask layer 605 is removed, a dielectric is deposited in the left gap of the dielectric layer 604 to protect the device, and a smooth surface is formed by CMP or the like.
Next, as shown in fig. 26, a patterned second mask layer 607 is formed over the surface-smoothed dielectric layer 604, an edge of the second mask layer 607 is aligned with an edge of one sidewall of the second free layer 6031, and the one sidewall of the second free layer 6031 is a sidewall of the first free layer 6021 that is not on the same side as the second spin orbit torque effect layer 606. In this embodiment, since the left side wall of the first free layer 6021 is covered with the second spin orbit torque effect layer 606, a second vertical spin orbit torque effect layer is formed on the right side wall of the second free layer 6031. The right edge of the second mask layer 607 should be beyond the edges of the second barrier layer 6032 and the second reference layer 6033 to be aligned with the edge of the right sidewall of the second free layer 6031.
Next, as shown in fig. 27, the second mask layer 607 is used as a mask, and the dielectric layer 604 not covered by the second mask layer 607 is partially removed by etching or the like, the etching is stopped on the surface of the first spin orbit torque effect layer 601, and after the etching, the right sidewall of the second free layer 6031 has no dielectric adhesion.
Next, as shown in fig. 28, a third spin orbit torque effect layer 608 is formed by a deposition process, the material of the third spin orbit torque effect layer 608 is the same as that of the first spin orbit torque effect layer 601, such as a heavy metal, and the third spin orbit torque effect layer 608 covers the exposed surface of the first spin orbit torque effect layer 601, the surface of the second mask layer 607, and the entire right side wall. Typically, the sidewall deposition will be less thick than the planar deposition.
Next, as shown in fig. 29, the third spin orbit torque effect layer 608 is etched, in order to form a second vertical spin orbit torque effect layer on the right side wall of the second free layer 6031, an anisotropic etching method may be adopted, in which a downward etching is mainly used to remove a portion of the second spin orbit torque effect layer on the surface of the first spin orbit torque effect layer 601 and a portion of the second spin orbit torque effect layer on the surface of the second mask layer 607, and after the etching, only the third spin orbit torque effect layer 608 with a certain width is left to cover the right side wall of the second free layer 6031 of the second magnetic tunnel junction. The remaining third spin orbit torque effect layer 608 is the second vertical spin orbit torque effect layer.
Finally, as shown in fig. 30, the second mask layer 607 is removed, a dielectric is deposited in the right gap of the dielectric layer 604 to protect the device, and then a smooth surface is formed by CMP or the like.
For another implementation of the differential memory cell, a similar process flow may be adopted, but the mask pattern is different and will not be described.
In the above description, the technical details of patterning, etching, and the like of each layer are not described in detail. It will be appreciated by those skilled in the art that layers, regions, etc. of the desired shape may be formed by various technical means. In addition, in order to form the same structure, those skilled in the art can also design a method which is not exactly the same as the method described above. In addition, although the embodiments are described separately above, this does not mean that the measures in the embodiments cannot be used in advantageous combination.
The above description is only for the specific embodiment of the present invention, but the scope of the present invention is not limited thereto, and any changes or substitutions that can be easily conceived by those skilled in the art within the technical scope of the present invention are included in the scope of the present invention. Therefore, the protection scope of the present invention shall be subject to the protection scope of the claims.
Claims (8)
1. A spin-orbit-torque-based memory cell, comprising:
a magnetic tunnel junction comprising a free layer, a barrier layer, and a reference layer stacked in sequence;
a horizontal spin orbit torque effect layer in contact with a bottom surface of the free layer;
the vertical spin orbit torque effect layer covers one side wall of the free layer;
the vertical spin orbit torque effect layer is communicated with the horizontal spin orbit torque effect layer, when the same current is introduced, the horizontal spin orbit torque effect layer generates a magnetic field in the horizontal direction, and the vertical spin orbit torque effect layer generates a magnetic field in the vertical direction.
2. The spin-orbit torque-based memory unit of claim 1, wherein the barrier layer and the reference layer are the same size, and the free layer is larger in size than the barrier layer.
3. The spin-orbit torque-based memory unit of claim 1, further comprising:
and the dielectric layer is positioned above the horizontal spin orbit torque effect layer and surrounds the magnetic tunnel junction and the vertical spin orbit torque effect layer.
4. A method of fabricating a spin-orbit-torque-based memory cell, comprising:
providing a substrate, forming a first spin orbit torque effect layer on the substrate, forming a magnetic tunnel junction on the first spin orbit torque effect layer, wherein the magnetic tunnel junction comprises a free layer, a barrier layer and a reference layer which are sequentially stacked, the barrier layer and the reference layer are the same in size, the size of the free layer is larger than that of the barrier layer, and dielectric layers are formed around and on the top of the magnetic tunnel junction;
forming a patterned mask layer above the dielectric layer, wherein the edge of the mask layer is aligned with the edge of one side wall of the free layer;
etching the dielectric layer downwards by taking the mask layer as a mask until the surface of the first spin orbit torque effect layer is exposed;
forming a second spin orbit torque effect layer, wherein the second spin orbit torque effect layer covers the exposed surface of the first spin orbit torque effect layer, the surface of the mask layer and the whole side wall;
etching the second spin orbit torque effect layer, and only keeping the second spin orbit torque effect layer with a certain width to cover the side wall of the magnetic tunnel junction free layer and be communicated with the first spin orbit torque effect layer after etching;
and removing the mask layer, filling the gap of the dielectric layer and forming a smooth surface.
5. A spin-orbit torque-based differential memory cell, comprising:
a first magnetic tunnel junction comprising a first free layer, a first barrier layer, and a first reference layer stacked in sequence;
a second magnetic tunnel junction comprising a second free layer, a second barrier layer, and a second reference layer stacked in sequence;
a horizontal spin orbit torque effect layer in contact with a bottom surface of the first free layer and a bottom surface of the second free layer;
the first vertical spin orbit torque effect layer covers one side wall of the first free layer;
a second vertical spin orbit torque effect layer covering one sidewall of the second free layer;
the side wall covered by the first vertical spin orbit torque effect layer and the side wall covered by the second vertical spin orbit torque effect layer are two side walls, which are not on the same side, of the first free layer and the second free layer, the first vertical spin orbit torque effect layer and the second vertical spin orbit torque effect layer are respectively communicated with the horizontal spin orbit torque effect layer, when the same current is introduced, the horizontal spin orbit torque effect layer generates a magnetic field in the horizontal direction, and the first vertical spin orbit torque effect layer and the second vertical spin orbit torque effect layer respectively generate magnetic fields in the vertical directions with opposite directions.
6. The differential memory cell of claim 5, wherein the first barrier layer and the first reference layer are the same size, and the first free layer is larger in size than the first barrier layer; the second barrier layer and the second reference layer are the same size, and the size of the second free layer is larger than the size of the second barrier layer.
7. The differential memory cell of claim 5, further comprising:
the dielectric layer is positioned above the horizontal spin orbit torque effect layer, surrounds the first vertical spin orbit torque effect layer covered by the first magnetic tunnel junction and the side wall of the first free layer, and surrounds the second vertical spin orbit torque effect layer covered by the second magnetic tunnel junction and the side wall of the second free layer.
8. A method of manufacturing a spin-orbit torque-based differential memory cell, comprising:
providing a substrate, forming a first spin orbit torque effect layer on the substrate, forming a first magnetic tunnel junction and a second magnetic tunnel junction on the first spin orbit torque effect layer, wherein the first magnetic tunnel junction comprises a first free layer, a first barrier layer and a first reference layer which are sequentially stacked, the first barrier layer and the first reference layer are the same in size, the first free layer is larger than the first barrier layer in size, the second magnetic tunnel junction comprises a second free layer, a second barrier layer and a second reference layer which are sequentially stacked, the second barrier layer and the second reference layer are the same in size, the second free layer is larger than the second barrier layer in size, and a dielectric layer is formed around and on the top of the first magnetic tunnel junction and the second magnetic tunnel junction;
forming a patterned first mask layer above the dielectric layer, wherein the edge of the first mask layer is aligned with the edge of one side wall of the first free layer;
etching the dielectric layer downwards by taking the first mask layer as a mask until the surface of the first spin orbit torque effect layer is exposed;
forming a second spin orbit torque effect layer, wherein the second spin orbit torque effect layer covers the exposed surface of the first spin orbit torque effect layer, the surface of the first mask layer and the whole side wall;
etching the second spin orbit torque effect layer, and only keeping the second spin orbit torque effect layer with a certain width to cover the side wall of the first free layer of the first magnetic tunnel junction and be communicated with the first spin orbit torque effect layer after etching;
removing the first mask layer, filling the gap of the dielectric layer and forming a smooth surface;
forming a patterned second mask layer above the dielectric layer, wherein the edge of the second mask layer is aligned with the edge of one side wall of the second free layer, and the one side wall of the second free layer is the side wall which is not on the same side as the first free layer and is covered with the second spin orbit torque effect layer;
etching the dielectric layer downwards by taking the second mask layer as a mask until the surface of the first spin orbit torque effect layer is exposed;
forming a third spin orbit torque effect layer, wherein the third spin orbit torque effect layer covers the exposed surface of the first spin orbit torque effect layer, the surface of the second mask layer and the whole side wall;
etching the third spin orbit torque effect layer, and only keeping the third spin orbit torque effect layer with a certain width to cover the side wall of the second free layer of the second magnetic tunnel junction and be communicated with the first spin orbit torque effect layer after etching;
and removing the second mask layer, filling the gap of the dielectric layer and forming a smooth surface.
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