WO2020192207A1

WO2020192207A1 - Mram storage array

Info

Publication number: WO2020192207A1
Application number: PCT/CN2019/127813
Authority: WO
Inventors: 杨保林; 熊保玉; 承祎琳; 何世坤
Original assignee: 浙江驰拓科技有限公司
Priority date: 2019-03-25
Filing date: 2019-12-24
Publication date: 2020-10-01
Also published as: CN111739567A; CN111739567B

Abstract

Provided is an MRAM storage array, comprising: a plurality of storage units arranged in the form of a rectangular array, wherein each of the storage units comprises an MTJ unit, and a magnetization direction of the MTJ unit is a growth direction along an MTJ thin film; the tops of the MTJ units in two adjacent storage units in the array are provided with a shared magnetic electrode; and all magnetic electrodes in the array are arranged in the same direction, and the magnetic electrode is used for providing a magnetic moment for the MTJ units in the two adjacent storage units to assist free layers of the MTJ units in realizing turning over. The shape of the cross section of the MTJ units in the storage units is a circular shape, and the shape of the cross section of the magnetic electrode shared by the two adjacent storage units is a geometrical shape having a long axis and a short axis. According to the present invention, the density of a storage array can be improved. According to the present invention, the density of a storage array can be improved.

Description

MRAM storage array

Technical field

The present invention relates to the technical field of MRAM memory, in particular to an MRAM storage array.

Background technique

Spin transfer torque magnetic memory (STT-MRAM) is a kind of magnetic random access memory that uses spin-polarized current to change the MTJ state. In addition to the advantages of simple circuit design, fast reading and writing, and unlimited erasing and writing, the memory is relatively The biggest advantage of traditional memory such as DRAM is non-volatile (data is not lost after power off). In order to reduce the size of the MTJ as much as possible on the basis of meeting the data retention time of the MTJ, the magnetic recording and reference layers in the MTJ need to use perpendicular magnetization materials.

For the vertical structure of the MTJ unit, in order to speed up the free layer flip and achieve the consistency of the free layer flip, another layer of magnetic layer or magnetic electrode whose magnetization direction is fixed in the plane is grown above the free layer to generate a magnetic field at the free layer. There is an initial angle between the free layer and the fixed layer, which can accelerate the turnover speed of the MTJ at room temperature and reduce the writing voltage at the same time. In order to fix the magnetization direction of the magnetic electrode in a specific direction, an anisotropic field brought about by shape anisotropy is needed. The corresponding magnetic electrode is generally elliptical.

However, when forming the memory array, in order to prevent leakage between the metal electrodes, the metal electrodes must maintain a certain distance. The use of elliptical electrodes in the traditional memory array design will affect the density of the memory array. Therefore, how to increase the density of the magnetic memory array has become a problem that must be solved.

Summary of the invention

In order to solve the above problems, the present invention provides an MRAM storage array, which can increase the density of the storage array.

The present invention provides an MRAM storage array, which includes: a plurality of storage cells arranged in a rectangular array, the storage cells include MTJ cells, the magnetization direction of the MTJ cells is along the growth direction of the MTJ film, and two adjacent ones in the array A common magnetic electrode is provided on the top of the MTJ cell in each of the memory cells, all the magnetic electrodes in the array are arranged in the same direction, and the magnetic electrode is used to provide one MTJ cell in two adjacent memory cells. Magnetic moment to assist the free layer of the MTJ unit to achieve flipping;

Wherein, the cross-sectional shape of the MTJ cell in the memory cell is a circular shape, and the cross-sectional shape of the magnetic electrode shared by two adjacent memory cells is a geometric shape with a long axis and a short axis.

Optionally, the magnetic electrode includes a horizontal magnetization layer and an isolation layer, the horizontal magnetization layer is magnetized in the film plane, the magnetization direction is along the long axis direction of the magnetic electrode, and the isolation layer is located between the horizontal magnetization layer and the Between the MTJ units, they are used to isolate the horizontal magnetization layer from the MTJ units.

Optionally, the material of the horizontal magnetization layer is iron (Fe), cobalt (Co), nickel (Ni), CoFe alloy, CoFeB alloy or NiFe alloy.

Optionally, the material of the isolation layer is tantalum (Ta), ruthenium (Ru), molybdenum (Mo), iridium (Ir), platinum (Pt), palladium (Pd) or tungsten (W).

Optionally, the cross-sectional shape of the magnetic electrode is a rectangle with a long axis and a short axis, an ellipse, or a rectangle with rounded corners.

Optionally, the storage cell is an STT-MRAM storage cell, the STT-MRAM storage cell includes an MTJ cell and a transistor, the fixed layer of the MTJ cell is connected to the drain of the transistor, and the transistor The gate is connected to the word line, the source of the transistor is connected to the source line, and the isolation layer of the magnetic electrode is above the free layer of the MTJ cell.

Optionally, the memory cell is a SOT-MRAM memory cell, the SOT-MRAM memory cell includes an MTJ cell, a spin orbital moment supply line and a transistor, and the free layer of the MTJ cell is close to the spin Orbital moment supply line, the spin orbital moment supply line is connected to the drain of the transistor, the gate of the transistor is connected to the word line, the source of the transistor is connected to the source line, and the MTJ unit is fixed Above the layer is the isolation layer of the magnetic electrode.

In the MRAM storage array provided by the present invention, the tops of the MTJ cells of two adjacent storage cells in the array share a magnetic electrode, and all the magnetic electrodes in the array are arranged in the same direction. This design can increase the density of the storage array. In addition, the horizontal magnetization layer is introduced into the magnetic electrode, and the magnetization direction of the horizontal magnetization layer is arranged in the plane, which can accelerate the flip speed and consistency of the free layer magnetic moment of the MTJ unit. Further, the magnetic electrode is prepared into a specific shape with a long axis and a short axis, and the anisotropy is induced by the shape, so that the magnetic moment of the MTJ free layer deviates from the vertical by a small angle, thereby accelerating the flipping speed of the MTJ at room temperature. Lower the write voltage.

Description of the drawings

FIG. 1 is a top view of an MRAM storage array according to an embodiment of the present invention;

2 is a structural side view of two adjacent memory cells sharing a magnetic electrode in an MRAM memory array according to an embodiment of the present invention;

3 is a structural side view of two adjacent memory cells sharing a magnetic electrode in an MRAM memory array according to another embodiment of the present invention;

FIG. 4 is a schematic diagram of the optimization effect comparison of the storage array structure shown in FIG. 1 compared with the traditional array structure.

detailed description

In order to make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be described clearly and completely in conjunction with the accompanying drawings in the embodiments of the present invention. Obviously, the described embodiments It is only a part of the embodiments of the present invention, not all the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative work shall fall within the protection scope of the present invention.

The embodiment of the present invention provides an MRAM memory array, which includes: a plurality of memory cells arranged in a rectangular array, each memory cell includes an MTJ cell, the magnetization direction of the MTJ cell is along the growth direction of the MTJ film, and two adjacent ones in the array A common magnetic electrode is provided on the top of the MTJ cell in each memory cell. All the magnetic electrodes in the array are arranged in the same direction. The common magnetic electrode is used to provide a magnetic moment for the MTJ cell in two adjacent memory cells to assist The free layer of the MTJ unit is flipped;

Wherein, the cross-sectional shape of the MTJ cell in each memory cell is a circular shape, and the cross-sectional shape of the magnetic electrode shared by two adjacent memory cells is a geometric shape with a long axis and a short axis.

For example, the cross-sectional shape of the magnetic electrode may be a rectangle with a long axis and a short axis, an ellipse, or a rectangle with rounded corners that has both characteristics. In the embodiment of the present invention, it is defined that the length of the magnetic electrode along a certain direction is the longest, which is the long axis direction of the magnetic electrode.

FIG. 1 is a top view of an embodiment of the MRAM memory array of the present invention. As shown in Figure 1, the figure takes a rectangular array with 3 rows and 6 columns as an example. The X direction is defined as the first direction of the array, and the Y direction is the second direction of the array. The X and Y directions are perpendicular to each other. The closed shape enclosed by two semi-circular arcs and two parallel straight lines represents the magnetic electrode. The two circular shapes in the magnetic electrode represent the MTJ cell of the memory cell. The MTJ cells in the two adjacent memory cells in the array share one magnetism. For the electrode, the arrow direction represents the magnetization direction of the horizontal magnetization layer in the magnetic electrode, and the magnetization direction is along the long axis direction of the magnetic electrode. The arrow direction shown in the figure is only an indication. It can be seen from Figure 1 that the cross-sectional shape of the MTJ cell in two adjacent memory cells is a circular shape with the same radius, and the cross-sectional shape of the magnetic electrode is a closed shape surrounded by two semicircular arcs and two parallel straight lines. The center positions of the semi-circular arcs coincide with the center positions of the two MTJ units respectively. The radii of the two semi-circular arcs are larger than the radii of the two MTJ units, and the two parallel lines are parallel to the line connecting the centers of the two MTJ units. All the magnetic electrodes in the array are arranged in the same direction, and the two parallel lines of the magnetic electrodes are parallel to the X direction.

Specifically, there are two types of MRAM memory cells, namely spin-transfer torque magnetic memory (STT-MRAM, Spin-Transfer Torque Magnetic Random Access Memory) and spin-orbit torque magnetic memory (SOT-MRAM, Spin-Orbit Torque Magnetic Random Access Memory), for both types of storage units, the above-mentioned MRAM storage array can be constructed.

Two adjacent memory cells sharing one magnetic electrode are analyzed separately. As shown in Figure 2, the memory cell is an STT-MRAM memory cell. Two adjacent STT-MRAM memory cells share a magnetic electrode 10. The magnetic electrode 10 includes a horizontal magnetization layer 101 and an isolation layer 102. The horizontal magnetization layer 101 is on the film plane. Internal magnetization, the magnetization direction of the horizontal magnetization layer 101 determines the magnetization direction of the magnetic electrode 10. One of the STT-MRAM memory cells includes MTJ cell MTJ11 and transistor M11, and the other STT-MRAM memory cell includes MTJ cell MTJ12 and transistors M12, MTJ11. The fixed layer is connected to the drain of M11, the gate of M11 is connected to word line WL11, the source of M11 is connected to source line SL, the fixed layer of MTJ12 is connected to the drain of M12, and the gate of M12 is connected to word line WL12, The source of M12 is connected to the source line SL, MTJ11 and MTJ12 share the magnetic electrode 10, the magnetic electrode 10 is connected to the bit line BL, the horizontal magnetization layer 101 is close to the free layers of MTJ11 and MTJ12, and the isolation layer 102 is located on the horizontal magnetization layer 101 and the MTJ cell Between the free layers, play a role of isolation.

Further, each STT-MRAM memory cell further includes a non-magnetic bottom electrode, the bottom electrode is located at the bottom of the MTJ cell, close to the fixed layer of the MTJ cell, and the two bottom electrodes are separated, so that the two MTJ cells are separated for reading and writing.

As shown in Figure 3, the memory cell is a SOT-MRAM memory cell. Two adjacent SOT-MRAM memory cells share a magnetic electrode 20. The magnetic electrode 20 includes a horizontal magnetization layer 201 and an isolation layer 202. The horizontal magnetization layer 201 is on the film plane. Internal magnetization, the magnetization direction of the horizontal magnetization layer 201 determines the magnetization direction of the magnetic electrode 20. One SOT-MRAM memory cell includes an MTJ cell MTJ21, a spin orbit moment supply line 21 and a transistor M21, and the other SOT-MRAM memory cell includes an MTJ cell. Cell MTJ22, spin orbit moment supply line 22 and transistor M22, the free layer of MTJ21 is close to spin orbit moment supply line 21, spin orbit moment supply line 21 is connected to the drain of M21, and the gate of M21 is connected to word line WL21 , The source of M21 is connected to the source line SL, the free layer of MTJ22 is close to the spin orbit moment supply line 22, the spin orbit moment supply line 22 is connected to the drain of M22, and the gate of M22 is connected to the word line WL22, The source is connected to the source line SL, MTJ21 and MTJ22 share the magnetic electrode 20, and the magnetic electrode 20 is connected to the bit line BL. The horizontal magnetization layer 201 is close to the fixed layers of MTJ21 and MTJ22, and the isolation layer 202 is located on the horizontal magnetization layer 201 and the fixed MTJ unit. Between the layers, play a role of isolation. For SOT-MRAM memory cells, the spin-orbit moment supply line also serves as the bottom electrode of the memory cell.

In actual manufacturing, a magnetic film (such as permalloy) with a thickness of about 20 nm is grown on the bottom of the magnetic electrode as the horizontal magnetization layer, and the shape of the horizontal magnetization layer is a specific shape with shape anisotropy. Specifically, the permalloy film has low coercivity, high saturation magnetization, and the magnetic moment is aligned in the plane. By preparing both ends of the electrode with a specific morphology, the permalloy film is single in the plane by using shape anisotropy. Domain distribution, and induce the MTJ free layer magnetic moment to deviate from a small tilt angle in the vertical direction to accelerate the flip speed of the MTJ at room temperature, thereby increasing the writing speed of the MRAM memory device and reducing the writing voltage.

The horizontal magnetization layer includes at least one layer of ferromagnetic material film, and the selectable materials include iron (Fe), cobalt (Co), nickel (Ni) or other alloys such as CoFe, CoFeB, NiFe, etc. The magnetic moment of the horizontal magnetization layer is arranged in a single domain plane. The generated magnetic field is about 100Oe, which is much smaller than the perpendicular anisotropy field (2000Oe), which ensures that the magnetic moment of the free layer of the MTJ flips consistently without affecting the thermal stability and device life. The material of the isolation layer is a non-magnetic metal, such as tantalum (Ta), ruthenium (Ru), molybdenum (Mo), iridium (Ir), platinum (Pt), palladium (Pd) or tungsten (W).

In the above embodiment, the tops of the MTJ cells of two adjacent memory cells of the memory array share one magnetic electrode, and all the magnetic electrodes in the array are arranged in the same direction. This design can increase the density of the memory array. Moreover, the size of the magnetic electrode is increased, which optimizes the minimum size requirements and errors caused by the processing process to the greatest extent, and reduces the process difficulty. In addition, the horizontal magnetization layer is introduced into the magnetic electrode, and the magnetization direction of the horizontal magnetization layer is arranged in the plane, which can accelerate the flip speed and consistency of the free layer magnetic moment of the MTJ unit. Further, the magnetic electrode is prepared into a specific shape with a long axis and a short axis, and the anisotropy is induced by the shape, so that the magnetic moment of the MTJ free layer deviates from the vertical by a small angle, thereby accelerating the flipping speed of the MTJ at room temperature. Lower the write voltage.

The following takes the storage array structure shown in Figure 1 as an example to specifically analyze how the density of the storage array is increased.

In order to prevent leakage between metals (electrodes), the minimum distance between magnetic electrodes must be greater than a certain value g. The minimum size of the upper and lower electrodes needs to be larger than the size of the MTJ and the upper and lower connection holes (VIA) to compensate for the engraving error between the upper and lower layers. This difference is set as d _CD . At the same time, MTJ etching process requirements: the minimum distance between MTJs should not be less than a specific value D. In addition, the size of the bottom MOS tube also limits the array design. Based on the above points, take the MTJ size CD=60nm, the magnetic electrode spacing g=60nm, d _CD =50nm, and the MTJ minimum spacing D=200nm as an example for description. The corresponding magnetic electrode size in Figure 1 is 110*310nm.

The traditional array structure and the array structure shown in FIG. 1 are compared and analyzed. Referring to FIG. 4, the minimum array unit area of the traditional array design under the above conditions is A=280nm*200nm; the array design of the embodiment of the present invention is under the above conditions The smallest array unit area of B=200nm*200nm, which greatly increases the density of the MTJ array.

The specific derivation principle of the minimum array unit area is as follows:

As shown in (a) in Figure 4, four array units form a primitive cell, and each unit in the primitive cell is shared by the four upper, lower, left, and right primitive cells. Therefore, the primitive cell composed of the four array units is the smallest in the array. Repeating unit, the cell area is the smallest cell area of the array, as shown in the box (b) in Figure 4, the cell area is the area of the quadrilateral connected to the center of each magnetic unit. Therefore, it can be calculated by traditional The area of the smallest array unit of the array structure is: (2CD+2d _CD +g)*D; the area of the smallest array unit of the array structure of the embodiment of the present invention is: D*D.

Substituting the data, it is obtained: the minimum array unit area of the traditional array design is 280nm*200nm, the minimum array unit area of the array design of the embodiment of the present invention is 200nm*200nm, and the memory cell density is increased by 28.57%. At the same time, the high symmetry of the MTJ array is ensured, and better MTJ size and electrical uniformity can be obtained in the key MTJ etching process.

The above are only specific embodiments of the present invention, but the protection scope of the present invention is not limited thereto. Any person skilled in the art can easily think of changes or substitutions within the technical scope disclosed in the present invention. All should be covered within the protection scope of the present invention. Therefore, the protection scope of the present invention should be subject to the protection scope of the claims.

Claims

An MRAM memory array, which is characterized by comprising: a plurality of memory cells arranged in a rectangular array, the memory cells including MTJ cells, the magnetization direction of the MTJ cells is along the growth direction of the MTJ film, adjacent in the array The tops of the MTJ cells in the two memory cells are provided with a common magnetic electrode, all the magnetic electrodes in the array are arranged in the same direction, and the magnetic electrodes are used to provide the MTJ cells in the two adjacent memory cells. A magnetic moment to assist the free layer of the MTJ unit to achieve flipping;

Wherein, the cross-sectional shape of the MTJ cell in the memory cell is a circular shape, and the cross-sectional shape of the magnetic electrode shared by two adjacent memory cells is a geometric shape with a long axis and a short axis.
The MRAM memory array of claim 1, wherein the magnetic electrode comprises a horizontal magnetization layer and an isolation layer, the horizontal magnetization layer is magnetized in the film plane, and the magnetization direction is along the long axis direction of the magnetic electrode, The isolation layer is located between the horizontal magnetization layer and the MTJ unit, and is used to isolate the horizontal magnetization layer and the MTJ unit.
The MRAM memory array according to claim 2, wherein the material of the horizontal magnetization layer is iron (Fe), cobalt (Co), nickel (Ni), CoFe alloy, CoFeB alloy or NiFe alloy.
The MRAM memory array according to claim 2, wherein the material of the isolation layer is tantalum (Ta), ruthenium (Ru), molybdenum (Mo), iridium (Ir), platinum (Pt), palladium (Pd) ) Or tungsten (W).
The MRAM memory array according to claim 1, wherein the cross-sectional shape of the magnetic electrode is a rectangle with a long axis and a short axis, an ellipse, or a rectangle with rounded corners.
The MRAM memory array of claim 1, wherein the memory cell is an STT-MRAM memory cell, the STT-MRAM memory cell includes an MTJ cell and a transistor, and the fixed layer of the MTJ cell is connected to the The drain of the transistor is connected, the gate of the transistor is connected to the word line, the source of the transistor is connected to the source line, and the free layer of the MTJ cell is above the isolation layer of the magnetic electrode.
The MRAM memory array according to claim 1, wherein the memory cell is a SOT-MRAM memory cell, and the SOT-MRAM memory cell includes an MTJ cell, a spin orbit moment supply line and a transistor, so The free layer of the MTJ cell is close to the spin orbital moment supply line, which is connected to the drain of the transistor, the gate of the transistor is connected to the word line, and the source of the transistor Connected to the source line, above the fixed layer of the MTJ unit is an isolation layer of the magnetic electrode.