VERTICAL SOT-MRAM STORAGE CELL USING SPIN-SWAPPING INDUCED SPIN CURRENT

Abstract

Device comprising: a magnetic tunnel junction (202) comprising a free layer (212) in a plane, wherein the free layer has a switchable direction of magnetization perpendicular to the plane; a ferromagnetic layer (220);and a spacer layer (214) between the ferromagnetic layer and the free layer, wherein the ferromagnetic layer is configured to generate perpendicularly polarized spin current in response to an electric current (222) through the ferromagnetic layer, wherein the ferromagnetic layer is further configured to inject the perpendicularly polarized spin current into and through the spacer layer and from the spacer layer into the free layer to change the direction of magnetization of the free layer, wherein the ferromagnetic layer is a spin-swapping layer configured to induce perpendicularly polarized spin current by spin-swapping in response to the electric current through the ferromagnetic layer, and wherein the perpendicularly polarized spin current is polarized perpendicular to the plane.

Description

[0001] This application claims priority over preliminary application 62 / 714.001, filed on 2 August 2018, entitled “Vertical SOT-MRAM memory cell using spin-swapping induced spin current”, which is incorporated herein by reference in its entirety. BACKGROUND

[0002] Memory is used in various electronic devices such as mobile phones, digital cameras, personal digital assistants, medical electronics, mobile computing devices, stationary computing devices, and data servers. Memory can be either non-volatile or volatile. Non-volatile memory allows information to be stored and retained even when the device is not connected to a power source (such as a battery).

[0003] An example of non-volatile memory is magnetoresistive random-access memory (MRAM), which uses magnetization to represent stored data, unlike some other memory technologies that use electronic charges for data storage. In general, MRAM comprises a large number of magnetic memory cells formed on a semiconductor substrate, with each memory cell representing one bit of data. A bit of data is written to a memory cell by changing the direction of magnetization of a magnetic element within the memory cell, and a bit is read by measuring the resistance of the memory cell (a low resistance typically represents a "0" bit, and a high resistance typically represents a "1" bit). As used here, the magnetization direction is the direction in which the magnetic moment is oriented.

[0004] Although MRAM is a promising technology, previous MRAM memory cells have been operated inefficiently and / or not switched deterministically. List of characters

[0005] Elements with the same number refer to common components in the different figures. Fig. 1A is a block diagram of an MRAM memory cell. Fig. Figure 1B is a block diagram of an MRAM memory cell. Fig. 1C is a block diagram of an MRAM memory cell. Fig. 1D is a block diagram of an MRAM memory cell. Fig. 1E represents electron scattering by a negative charge. Fig. Figure 2 represents an embodiment of a proposed MRAM memory cell that uses spin swapping. Fig. Figure 3 represents an embodiment of a proposed MRAM memory cell that uses spin swapping. Fig. Figure 4 represents an embodiment of a proposed MRAM memory cell that uses spin swapping. Fig. Figure 5 is a flowchart that describes one embodiment of a process for programming an MRAM memory cell. Fig. Figure 6 is a block diagram of a memory system using the new memory cell proposed herein. DETAILED DESCRIPTION

[0006] Fig. 1A is a schematic perspective view of a previous MRAM memory cell. 10 , which uses field-induced switching. In general, the MRAM cell includes 10 a magnetic tunnel junction (MTJ) 11 , having an upper ferromagnetic layer 12 , a lower ferromagnetic layer 14 and a tunnel barrier (TB) 16, which is an insulating layer between the two ferromagnetic layers. In this example, the upper ferromagnetic layer is 12 A free layer FL and the direction of its magnetization can be switched. The lower ferromagnetic layer 14 is a pinned (or fixed) PL layer and the direction of its magnetization does not change.

[0007] If the magnetization in the free layer FL 12 parallel to the magnetization in the pinned layer PL 14 If the magnetization is in the free layer FL, the resistance across the memory cell is relatively low, at least partially due to the spin-dependent scattering of the minority electrons. 12 antiparallel to the magnetization in the pinned layer PL 14 is the resistance across the memory cell 10relatively high, at least partially due to the spin-dependent scattering of minority and majority electrons. The data ("0" or "1") in memory cell 10 are determined by measuring the resistance of the memory cell 10 read. In this context, electrical conductors 20 / 30 , which are located at the memory cell 10 are attached and used to read the MRAM data.

[0008] The direction of magnetization in the free layer 12 changes in response to the current 34 , which is in a numeric line 32 flows, and in response to the current 22 , who is in a writing department 20 flows, each of which has a magnetic field 36 and 26 generate. Fig. 1A represents the situation in which the current 34 in the digit line 32 flows from the side and the current 22 in the writing department 20The current flows from left to right, resulting in two orthogonal fields, which leads to the magnetization in the free layer. 12 from parallel to antiparallel relative to the magnetization in the solid layer 14 The orientation of a bit changes by reversing the polarity of the current. 22 in the writing department 20 while maintaining a constant polarity of the current 34 in the digit line 32 changed.

[0009] The above for the memory cell of Fig. The field-induced switching technique described in 1A has some practical limitations, particularly when the design requires scaling the memory cell to smaller dimensions. For example, because this technique requires two sets of magnetic field write lines, the array of MRAM cells is susceptible to bit interference (i.e., adjacent cells can be unintentionally changed when the write current is directed to a particular cell). Furthermore, reducing the physical size of the MRAM memory cells results in lower magnetic stability against magnetization changes due to temperature fluctuations. Bit stability can be improved by using a magnetic material for the free layer with high magnetic anisotropy and therefore a large switching field, but then the currents required to generate a magnetic field strong enough to switch the bit are impractical in existing applications.

[0010] Spin-transfer torque (STT) switching is another technique for programming MRAM memory cells. Fig. Figure 1B is a schematic representation of an STT circuit technique for an MRAM cell 50 , which has a magnetic levitation tunnel junction (MTJ) 51 includes, having an upper ferromagnetic layer 52 , a lower ferromagnetic layer 54 and a tunnel barrier (TB) 56 , which is an insulating layer between the two ferromagnetic layers. In this example, the lower ferromagnetic layer is 54 The free layer FL and the direction of its magnetization can be switched. The upper ferromagnetic layer 52 The pinned (or fixed) layer is PL and the direction of its magnetization cannot be easily changed. If the magnetization is in the free layer 54 parallel to the magnetization in the pinned layer PL 52The resistance across the memory cell is as follows: 50 relatively low. If the magnetization in the free layer FL 54 antiparallel to the magnetization in the pinned layer PL 52 is the resistance across the memory cell 50 relatively high. The data ("0" or "1") in memory cell 50 are determined by measuring the resistance of the memory cell 50 read. In this context, electrical conductors 60 / 70 , which are located at the memory cell 50 The pins are fixed and used to read the MRAM data. By default, both the parallel and antiparallel configurations remain stable in idle mode and / or during a read operation (with a sufficiently low read current).

[0011] In the rest of the text and the characters, the direction of the writing current is defined as the direction of the electron flow. Therefore, the term "writing current" refers to an electron flow.

[0012] To “set” the bit value of the MRAM cell (i.e., to choose the direction of magnetization of the free layer), an electrical write current is used. 62 from the leader 60 on ladder 70 applied. The electrons in the writing current are generated as they pass through the pinned layer. 52 spin-polarized, since the pinned layer 52is a ferromagnetic metal. While conduction electrons in a ferromagnetic metal have a spin orientation that is collinear with the direction of magnetization, a substantial majority of them have a certain orientation that is parallel to the direction of magnetization, resulting in a net polarized spin current. (Electron spin refers to angular momenta that are directly proportional to, but antiparallel to, the direction of the electron's magnetic moment, but this directional distinction will not be used in the future for the sake of simplicity.) When the spin-polarized electrons pass through the tunnel barrier 56 Moving, the conservation of angular momentum can lead to the fact that both on the free layer 54 as well as on the pinned layer 52A torque is transmitted, but this torque is (intentionally) insufficient to influence the magnetization direction of the pinned layer. In contrast, this torque is (intentionally) sufficient to influence the magnetization orientation in the free layer. 54 to modify it so that it runs parallel to that of the pinned layer 52 proceeds when the initial magnetization orientation of the free layer 54 antiparallel to the pinned layer 52 was. The parallel magnetizations then remain stable before and after the write current is switched off. In contrast, if the magnetization of the free layer 54 and the pinned layer 52 Initially parallel, the magnetization of the free layer is switched to STT to be antiparallel to the pinned layer. 52to become, by applying a writing current opposite to the case described above. Thus, the direction of magnetization of the free layer can be determined using the same STT physics. 54 by deliberately choosing the direction of the writing current (polarity), it can be deterministically set to one of two stable orientations.

[0013] The MRAM memory cell in Fig. 1B uses materials where the magnetization of both the pinned and free layers lies in the plane. In contrast, Fig. 1C a schematic representation of an STT-switching MRAM memory cell 75 This represents the magnetization of both the pinned and the free layer in a perpendicular direction. The memory cell 75 includes a magnetic tunnel junction (MTJ) 76 , having an upper ferromagnetic layer 78 , a lower ferromagnetic layer 80and a tunnel barrier (TB) 82 , which is an insulating layer between the two ferromagnetic layers. In this example, the lower ferromagnetic layer is 80 The free layer FL and the direction of its magnetization can be switched. The upper ferromagnetic layer 78 The pinned (or fixed) layer is PL and the direction of its magnetization cannot be easily changed. If the magnetization is in the free layer 80 parallel to the magnetization in the pinned layer PL 78 The resistance across the memory cell is as follows: 75 relatively low. If the magnetization in the free layer FL 80 antiparallel to the magnetization in the pinned layer PL 78 is the resistance across the memory cell 50 relatively high. The data ("0" or "1") in memory cell 75 are determined by measuring the resistance of the memory cell 75read. In this context, electrical conductors 84 / 88 , which are located at the memory cell 75 The pins are fixed and used to read the MRAM data. By default, both the parallel and antiparallel configurations remain stable at rest and / or during a read operation (with a sufficiently low read current). To "set" the bit value of the MRAM cell (i.e., to choose the direction of magnetization of the free layer), an electrical write current is applied. 86 from the leader 84 on ladder 88 installed and the memory cell works as above in relation to Fig. 1B described.

[0014] Compared to the earliest MRAM cells, which used magnetic fields from current-carrying conductors near the MRAM cell, STT switching requires relatively little power, virtually eliminates the problem of adjacent bit interference, and offers more favorable scaling for higher cell densities (reduced MRAM cell size). This latter advantage also benefits STT-MRAM, where the magnetizations of the free and pinned layers are oriented perpendicular to the film plane rather than in the plane. In practice, however, STT switching requires the full write current to flow through the tunnel barrier, which negatively impacts the long-term reliability of the STT-MRAM cell, as the necessary stress from moderate to high write voltages is applied across the tunnel barrier.

[0015] Fig. 1D represents an alternative MRAM memory cell 100This technique utilizes the spin-orbit torque (SOT) to switch the free layer via spin current. The electron spin is an intrinsic angular momentum that is separate from the angular momentum due to its orbital motion. In a solid, the spins of many electrons can interact to influence the magnetic and electronic properties of a material, for example, by imparting a permanent magnetic moment, as in a ferromagnet. In many materials, electron spins are equally present in both the up- and down directions, and no transport properties are spin-dependent. However, various techniques can be used to generate a spin-polarized electron population, resulting in an excess of spin-up or spin-down electrons, to modify the properties of a material.This spin-polarized population of electrons moving in a common direction through a common material is called a spin current. As described herein, a spin current can be used to power an MRAM memory cell.

[0016] In general, the spin Hall effect (SHE) can be used to generate a transverse (perpendicular to the plane) spin current when a longitudinal (in-plane) charging current is applied. The spin polarization direction of such an SHE-generated spin current lies orthogonal to the charging current flow in the plane. The memory cell 100 includes three connections A, B and C; a magnetic tunnel junction (MTJ) 101 ; and a SHE material 120 In one implementation, MTJ could 101 They feature a free layer, a tunnel barrier, and a pinned layer. In another implementation, MTJ features 101the pinned layer (PL) 102 on, the intermediate layer for coupling (ILC) 104 , the reference layer (RL) 106 , the tunnel barrier (TB) 108 and the free shift (FL) 110 The ILC layer 104 promotes a strong antiferromagnetic (i.e., antiparallel) coupling between PL ( 102 ) and RL ( 106 ), so that their net magnetic moment is largely canceled out, thereby greatly reducing unwanted stray field on the free layer. The SHE layer 120 It contains a heavy metal, such as platinum, tantalum, or tungsten, which has a strong SHE. The magnetization direction of the free layer 110 The direction alternates between upwards and downwards.

[0017] One advantage of the SOT switching concept, which uses the SHE, is that the write current 122 exclusively through the SHE layer 120 flows and not through the tunnel barrier 108This eliminates the previously mentioned long-term deterioration of the tunnel barrier due to the switching current in the previous STT switching design for MRAM cells. A disadvantage of the SOT switching concept of Fig. However, 1D is the fact that the one from SHE 120 into the off-duty shift 110 The flowing SHE-generated spin current includes a spin polarization in the plane (i.e., orthogonal to the magnetization of the free layer) and not perpendicular to the plane (i.e., collinear with the magnetization of the free layer), as was the case with the STT switching concept ( Fig. 1B). The negative consequences of this orthogonality are twofold. First, the critical write current density in the SHE layer can be increased. 120The current required to initiate the switching process is many times greater than in the STT circuit, because the physics of the switching process makes the orthogonal SOT circuit less intrinsically efficient (e.g., requiring more current) than the STT circuit. Secondly, the SHE-induced orthogonally polarized spin current that enters the free layer 110 This occurs in both orientations of the free layer, causing destabilization, and cannot in itself be used to deterministically determine a preferred direction of the free layer. However, this problem can be mitigated by applying an external bias field collinear with the charging current flow in the SHE layer in one direction. 120 If such a system is implemented, it would be a major technical difficulty to find the means to provide the necessary strength of the magnetic field at the cell level in a practical MRAM memory.

[0018] Another approach to solving the “orthogonality problem” inherent in the SOT circuit, as in Fig. Represented in 1D, the solution involves using in-plane magnetized free layers and pinned layers instead, so that the magnetization is again collinear with the spin polarization direction of the injected SHE-induced spin current. However, this option has the same disadvantages in scaling the MRAM cell size that previously led to the technological preference for the perpendicular MRAM cell design. What is needed is an efficient MRAM memory cell concept where the write current does not flow through the tunnel barrier and which allows deterministic switching of a perpendicular free layer simply by choosing the write current polarity. It would also be preferable to retain the TMR-based readback scheme, which enables fast readback and makes the entire system suitable for memory applications.

[0019] To address the shortcomings of previous MRAM memory cells described above, a novel SOT-MRAM memory cell is proposed that utilizes spin-swapping-induced spin currents to reverse the magnetization direction of the free layer. Spin-swapping is a mechanism in which a primary spin current induces a transverse spin current with reversed spin and current directions. In ferromagnets, the resulting spin accumulation exhibits a complex spatial profile where the spin-swapping effect is enhanced by spin polarization and spin precision, leading to additional contributions to the anomalous charge and spin currents. These effects can be exploited to generate spin-orbit-mediated torques and reversibly control the magnetization in centrosymmetric structures.

[0020] Before describing the structure of the proposed new memory cell, the background for the spin-swapping effect is provided. The spin current is described by a tensor q. ij described, where the first index indicates the flow direction and the second indicates which spin component is flowing. The phenomenological equations describing the coupling between spin and charge currents, q, are listed below. ij and q i , describe (more precisely, q is the electron flux density, relative to the electric current density j by q= j / e, where e is the elementary charge). q i = q i ( 0 ) + ϒ ε i j k q j k ( 0 ) q i j = q i j ( 0 ) + ϒ ε i j k q j k ( 0 ) where q i ( 0 ) und q i j ( 0 ) the primary currents that can exist in the absence of a spin-orbit interaction, ε ijk the antisymmetric tensor of unity and γ is a dimensionless parameter proportional to the strength of the spin-orbit interaction.

[0021] Pure symmetry considerations allow additional terms in equation (2) proportional to q i j ( 0 ) und δ i j q k k ( 0 ) , describe the transformations of spin currents. In the presence of the electric field E and the spin polarization P, this would lead to additional contributions to q. ij proportional to E j P i and δ ij (E·P) lead to these contributions. These contributions are due to the existing spin-swapping; therefore, equation (2) should be modified to: q i j = q i j ( 0 ) + ϒ ε i j k q k ( 0 ) + X ( q j i ( 0 ) ) − δ i j q k k ( 0 ) ) with a new dimensionless parameter X. The resulting exchange of spin currents arises from the correlation between scattering direction and spin rotation during collisions. This effect is more robust than spin-charge coupling: The exchange constant X already exists in the Born approximation, while Y only appears beyond this approximation.

[0022] Fig. 1E represents electron scattering, including spin-dependent scattering, by a negative charge. The electron spin sees a magnetic field B ~ v XE perpendicular to the trajectory plane. 180 It should be noted that the magnetic field (and thus the direction of spin rotation) points to the left (electron path). 182 ) and to the right (electron track) 184 ) scattered electrons in opposite directions.

[0023] Fig. Figure 1E shows the magnetic field B that is present in the electron's frame of motion and is seen through the electron spin. This field is perpendicular to the plane. 180 and to the electron orbit and has the opposite sign for electrons moving to the right (electron orbit). 184 ) and left (electron track) 182 ) of the charged center. The Zeeman energy of the electron spin in this field is the spin-orbit interaction.

[0024] Three spin-dependent effects are in Fig. 1E to see. If there is a metallic material with charge impurities, an electron moving in the material senses the electric field from the impurities. Spin-orbit coupling involves the moving electron with velocity v experiencing an electric field that is converted into an effective magnetic field. (1) The electrons sensing the magnetic field will process around the magnetic field, changing the electron's spin. This precession of the electron spin around B during the collision is called Elliott-Yafet spin relaxation. (2) The spin asymmetry in the scattering (Mott effect or skewed scattering) results from the additional force proportional to the gradient of the electron Zeeman energy. That is, the spin Hall effect involves a force acting on the electrons based on their spin direction.Some are deflected in one direction, while others are deflected in the opposite direction. This creates a spin current based on SHE. This phenomenon is stronger for heavy metals that are not ferromagnetic. (3) The third effect attributable to spin is the spin-swapping effect, which is based on a correlation between the directions of electron spin precession and scattering. While the spin on the left trajectory... 182 When the spin is rotated clockwise, the spin on the right-hand trajectory is rotated counterclockwise. This correlation leads to a transformation of the spin currents. In ferromagnetic materials, spin swapping is stronger and SHE weaker, while in heavy metals, spin swapping is weaker and SHE is stronger.

[0025] Assume that the incoming electrons move in the y-direction and are polarized along y (spin current towards q y y ( 0 ) The electrons scattered on the left receive a small positive spin projection on the x-axis. The electrons scattered on the right receive a small positive negative spin projection on the x-axis. This means that the initial q y y ( 0 ) Spin stream partially in -q xx is converted. In the case that incoming electrons (along y) are polarized along x, a similar argument shows that the initial spin current q y x ( 0 ) . . to q xy This leads to the following: In the latter case, the direction of rotation and the direction of flow are reversed. Further details on spin-swapping can be found in "Swapping Spin Current: Interchange Spin and Flow Directions," Maria B. Lifshits and Michel I. Dyakonov, Physical Review Letters, Vol. 103, October 20, 2009, p. 18660, which are incorporated herein by reference in their entirety.

[0026] The spin current reversal described above, the so-called spin-swapping effect, can be used in an MRAM memory cell to change the magnetization direction of the free layer. Specifically, an MRAM memory cell with perpendicular spin-orbit torque is proposed, featuring deterministic switching without an external field. This switching is provided by a perpendicularly polarized spin current in the z-direction, generated by the spin-swapping effect. An exemplary embodiment includes a magnetic tunnel junction comprising a free layer in a plane, a ferromagnetic layer, and a spacer layer between the ferromagnetic layer and the free layer. The free layer has a switchable magnetization direction perpendicular to the plane.The ferromagnetic layer is configured to generate a perpendicularly polarized spin current in response to an electric current passing through it. This perpendicularly polarized spin current is then injected through the spacer layer into the free layer, thus changing the magnetization direction of the free layer. The ferromagnetic layer is also referred to as a spin-swapping layer because it induces the perpendicularly polarized spin current through spin-swapping in response to the electric current passing through it.

[0027] Fig. Figure 2 is a schematic perspective view of an embodiment of the proposed MRAM memory cell with perpendicular spin-orbit torque, which includes deterministic switching (without an external field) provided by a perpendicularly polarized spin current in the z-direction generated by the spin-swapping effect. For the purposes of this document, a memory cell is a storage unit in a memory system. The memory cell 200 includes the three connections A, B and C; the magnetic tunnel junction (MTJ) 202 ; the spacer 214 ; and the spin-swapping layer 220 (also known as a ferromagnetic layer).

[0028] In general, a magnetic tunnel junction (MTJ) is a device comprising two ferromagnets separated by a thin insulator. Thus, one embodiment of the MTJ stack includes 202A pinned layer, a free layer, and a tunnel barrier (insulation layer) between the pinned layer and the free layer. MTJ 202 It can also have more than three layers. As in Fig. As shown in 2, MTJ indicates 202 for example the pinned layer (PL) 204 on, the intermediate layer for coupling (ILC) 206 , the reference layer (RL) 208 , the tunnel barrier (TB) 210 and the free shift (FL) 212 The pinned layer 204 and the reference layer 208 They have fixed magnetization directions, so their magnetization direction does not change. The pinned layer 204 It can consist of many different types of materials, including (but not limited to) multiple layers of cobalt and / or an alloy of cobalt and iron. The reference layer 208It can consist of many different types of materials, including (but not limited to) multiple layers of cobalt and an alloy of cobalt, iron, and boron. In one example, the ILC layer consists of 206 made of ruthenium; however, other materials can also be used. The pinned layer 204 exhibits a magnetization direction that points towards the reference layer 208 is the opposite. For example, it shows Fig. 2 the direction of magnetization of the pinned layer 204 downwards and the direction of magnetization of the reference layer 208 Upwards. The magnetization direction for the pinned layer. 204 and the reference layer 208 lies perpendicular to the direction in the plane. The magnetization of the reference layer 208 removes the magnetization of the pinned layer 204largely (or vice versa) to create a combined layer with a net magnetization close to zero. The ILC layer 206 promotes this antiparallel (i.e., antiferromagnetic) coupling between the pinned layer 204 and the reference layer 208 The pinned layer 204 is connected to terminal A (the first terminal).

[0029] In one embodiment, the tunnel barrier consists of 210 Made of magnesium oxide (MgO); however, other materials can also be used. The tunnel barrier 210 is located between the free layer 212 and the one or more layers of solid magnetization; therefore, the tunnel barrier 210 in one embodiment between the free layer 212 and the reference layer 208 arranged. The free layer 212Iron is a ferromagnetic metal that has the ability to change / switch its magnetization direction. Multilayers based on transition metals such as cobalt, iron, and their alloys can form the free layer. 212 can be used. In one embodiment, the free layer has 212 an alloy of cobalt, iron, and boron. In one embodiment, the free layer has 212 It exhibits a magnetization direction that can be switched between upward and downward. Thus, the magnetization direction of the free layer is 212 perpendicular to the direction in the plane.

[0030] If the magnetization direction of the free layer 212 parallel to the magnetization direction of the reference layer 208 is, has the memory cell 200 a lower resistance. If the magnetization direction of the free layer 212 antiparallel to the magnetization direction of the reference layer208 If so, then the memory cell 200 a higher resistance. In some embodiments, the low resistance represents a "0" bit and the high resistance a "1" bit, or vice versa. The memory cell 100 Stored data (“0” or “1”) is determined by measuring the resistance of the memory cell. 200 The reading is achieved by passing an electric current between terminal A and either terminal B or terminal C to determine the resistance of the memory cell. 200 to record.

[0031] Below MTJ 202 The spin-swapping layer is located there. 220 The spacer 214 is located between the free layer 212 and the spin-swapping layer 220 (and thus between MTJ) 202 and the spin-swapping layer 220 In one embodiment, an upper surface of the spacer borders 214 to the free shift 212on and touches them, and a lower surface of the spacer 214 borders the spin-swapping layer 220 and touches them. In an example implementation, the spacer 214 the same shape as the MTJ 202 , so that the spacer 214 among the MTJ 202 fits.

[0032] For the purposes of this document, a spin-swapping layer is a layer of material that generates a resultant spin current in response to a writing current through the spin-swapping layer. This resultant spin current is primarily generated by a spin-swapping effect involving electrons from the writing current undergoing a spin-orbit torque interaction. This interaction exhibits a first spin current in the spin-swapping layer, which induces a transverse spin current with reversed spin and flux directions. The spin-swapping layer 220This can be a ferromagnet or a semimetal with a high degree of spin polarization at the Fermi surface, which allows for a more efficient conversion of the charging current into the spin current of the desired perpendicular polarization. In one set of embodiments, it is desirable to have a high degree of spin polarization and a long spin diffusion length in the area designated for the spin-swapping layer. 220 to have the material used. In one embodiment, the spin-swapping layer 220 A ferromagnetic material whose magnetic moment is aligned in the plane. Heusler alloys can also be used for spin-swapping of the layer. 220 can be used. Other examples of materials for the spin-swapping layer include cobalt-manganese-germanium and cobalt-manganese-silicon. In one embodiment, the spin diffusion length of the spin-swapping layer is 220 greater than half the thickness of the spin-swapping layer 220In another embodiment, the spin diffusion length of the spin-swapping layer 220 greater than the total thickness of the spin-swapping layer 220 .

[0033] In one set of embodiments, it is desirable that the spin-swapping layer 220 the free shift 212 not touched, as both the spin-swapping layer 220 as well as the free shift 212 They are made of ferromagnetic material that tries to align itself when they touch. Therefore, the spacer 214 (e.g. 1-10 nanometers thick) between the spin-swapping layer 220 and the free shift 212 positioned so that the spin-swapping layer 220 and the free shift 212 are magnetically decoupled. In one embodiment, the spacer 214a material that can efficiently transfer spin current and has a long spin diffusion length and high specific resistance to carry the writing current 222 not to shunt. The spacer can be an alloy of form A. x B 1-x be, where A can be selected from the following set (without limitation): Au, Ag, Cu, Pd; and B can be selected from the following set (without limitation): Sn, Zn, Pt, Ni. The spacer can be a material with lower conductivity and high spin diffusion. A topological insulator or Rashba 2D material can also be used. In a set of embodiments, the spacer 214 Made from copper, silver, or a silver-tin alloy.

[0034] The in Fig. Figure 2, a graphic representation, shows the magnetization direction of the pinned layer. 204downwards, the magnetization direction of the reference layer 208 upwards and the magnetization direction of the free layer 212 upwards and downwards, all perpendicular to the plane (e.g., the plane of the free layer). 212 ) stand.

[0035] The data is stored in the memory cell of Fig. 2 written by passing an electric current through a spin-swapping layer 220 is created. That is, for a write operation in which the magnetization direction of the free layer 212 To switch between terminals, a current is applied between terminal B and terminal C. For example, this shows... Fig. 2 an electric writing current 222 through spin-swapping layer 220 from port B to port C, with the data going into the memory cell of Fig. 2 can be written by indicating the direction of magnetization of the free layer 212is changed in a first direction. A write current through a spin-swapping layer. 220 The connection from port C to port B is used to transfer data into the memory cell of Fig. 2 to write by the direction of magnetization of the free layer 212 is changed in a second direction that is antiparallel to the first direction.

[0036] The electrons of the writing current 222 experience a spin-orbit torque interaction, which includes the spin-swapping effect described above, so that in response to the electrical writing current 222 a vertically polarized spin current through the spin-swapping layer 220 is generated as a spin-orbit interaction, which creates an initial spin stream in the spin-swapping layer 220 exhibits a transverse spin current with reversed spin and flux directions. In the spin-swapping layer 220In a device with a magnetization direction M in the x-direction, an electric current flows in the x-direction. Electrons that are in the plane of the spin-swapping layer 220 Moving above / below the scattering center, they experience an effective magnetic field B that lies in the + / - y-direction. This magnetic field induces the spin current J. s in the z-direction, where the spin stream J s exhibits a polarization direction that is perpendicular to the plane of the spin-swapping layer 220 lies (which means that the polarization direction of the spin stream J s in the z-direction - parallel or antiparallel to the magnetization direction of the free layer 212 Thus, the spin current J flows s due to the spin-swapping effect upwards towards the spacer 214 , through the spacer 214 and into the off-duty shift 212 This spin current is directed parallel or antiparallel to the magnetization direction of the free layer.212 polarized, resulting in a more efficient torque on the free layer 212 is exerted. This torque also enables the deterministic switching of the free layer 212.

[0037] The spin direction of the spin stream emanating from the spin-swapping layer 220 into the off-duty shift 212 The injected polarization direction is the same as the magnetization direction of the free layer. 212 The current in the spin-swapping layer 220 is in the plane. The magnetic moment is aligned in the plane. The spins are oriented in the same direction. A spin current is introduced into the spin-swapping layer. 220 in the z-direction (e.g. upwards - see Fig. 2) induced, which is collinear with the magnetization direction of the free layer 212 is. Thus, the spin-swapping layer is 220 in the plane and parallel to a flow direction of the electric writing current 222magnetized.

[0038] To perform the reading, a read stream is passed from terminal A through MTJ. 202 through to port B or port C. The read current (not shown) is typically a lower current that overcomes the tunnel barrier. 210 not damaged. By measuring the voltage drop across terminals A and B, the resistance of MTJ can be determined. 202 can be determined. If the magnetization is in the free layer 212 parallel to the magnetization in the reference layer 208 (or the combination of pinned layer 204 and reference layer 208 ) is the resistance across the memory cell 200 relatively low. If the magnetization is in the free layer 212 antiparallel to the magnetization in the reference layer 208 (or the combination of pinned layer 204 and reference layer 208) is, is the resistance across the memory cell 200 relatively high. Thus, MTJ shows 202 (i.e. the free shift) 212 ) a programmable resistor that can be detected in response to a read bias voltage.

[0039] Some earlier MRAM devices were two interconnected memory cells that shared read and write paths through the magnetic tunnel junction. These shared read and write paths caused endurance and reliability issues. For writing, the tunnel barrier layer in the magnetic tunnel junction needed to be sufficiently thin (and with relatively low resistance) to allow the current necessary for switching to flow. However, a thin barrier layer is more susceptible to dielectric breakdown due to repeated write operations. The new proposed design by Fig. 2 does not require a write current that passes through the tunnel barrier. 210flows. While the spin stream flows into the free layer 212 can diffuse the writing current 222 through the spin-swapping layer 220 and not through MTJ 202 directed. That is, the generated perpendicular spin polarization, which was discussed above, diffuses into the free layer. 212 and exerts a torque on the free layer 212 to determine the magnetization direction of the free layer 212 to change it without a high electric current passing through the tunnel barrier 210 (the insulation layer) flows.

[0040] Although it is mentioned above that some embodiments of the structure of Fig. 2. Data is written by the perpendicular spin polarization exerting a torque on the free layer without an electric current flowing through the magnetic tunnel junction stack. Other embodiments write data by having the perpendicular spin polarization exert a torque on the free layer while a small electric current flows through the magnetic tunnel junction stack. For example, in one embodiment, the generated perpendicular spin polarization exerts a torque on the free layer to change the direction of the free layer's magnetization without an electric current through the insulating layer greater than 1 MA / cm². 2 is.

[0041] Fig. Figure 3 is a perspective view of another embodiment of the proposed MRAM memory cell with perpendicular spin-orbit torque, which features deterministic switching (without an external field) provided by a perpendicularly polarized spin current in the z-direction generated by the spin-swapping effect. The memory cell 300 from Fig. 3 includes the same MTJ 202 , the spacer 214 and the spin-swapping layer (also called ferromagnetic layer) 220 like the memory cell 200 from Fig. 2. Additionally, the memory cell contains 300 an antiferromagnetic layer 302 adjacent to and below the spin-swapping layer 220 The antiferromagnetic layer and the spin-swapping layer are arranged such that the exchange bias of the antiferromagnetic layer 302 a magnetization direction of the spin-swapping layer 220pinned. In this way, the magnetization direction of the spin-swapping layer is determined. 220 fixed and held in the direction that maximizes the generation of the perpendicularly polarized spin current density by the spin-swapping effect.

[0042] In materials exhibiting antiferromagnetism, the magnetic moments of atoms or molecules (relative to the spin electrons) align in a regular pattern with neighboring spins (on different sublattices) pointing in opposite directions to achieve zero net magnetization. That is, magnetic moments align in opposite or antiparallel arrangements throughout the material, resulting in almost no overall external magnetism. When an antiferromagnetic material comes into contact with a ferromagnetic material, the ferromagnetic material couples to the antiferromagnetic material at the interface, creating a strong interaction between the magnetic moments at the interface between the antiferromagnetic and ferromagnetic materials. This interaction aligns the magnetic moments and thus establishes a preferred magnetization direction for the ferromagnet.This phenomenon is called "exchange bias." Due to the coupling between the antiferromagnetic and ferromagnetic materials, it is significantly more difficult to change the magnetization direction of the ferromagnetic material. Examples of suitable materials for the antiferromagnetic layer. 302 The materials used are IrMn, FeMn, PtMn, and NiMn. Other materials can also be used.

[0043] Fig. Figure 4 is a perspective view of another embodiment of the proposed MRAM memory cell with perpendicular spin-orbit torque, which features deterministic switching (without an external field) provided by a perpendicularly polarized spin current in the z-direction generated by the spin-swapping effect. The memory cell 400 from Fig. 4 includes the same MTJ 202 like the memory cell 200 from Fig. 2. The memory cell 300This also includes the spin-swapping layer. 402 (also referred to as ferromagnetic layer), which is analogous to the spin-swapping layer 220 in Fig. 2 is. Between the spin-swapping layer 402 and the free shift 212 The SHE spacer is located 404 .

[0044] The SHE spacer 404 It serves for the magnetic decoupling of the spin-swapping layer. 402 and the free shift 212 Additionally, the SHE spacer offers 404 a second source for the spin current, based on spin-orbit interaction. Thus, the memory cell includes 400 the generation of two different spin currents in response to the electrical writing current 406 between terminal B and terminal C. The first spin current is a perpendicular spin current that occurs in the spin-swapping layer. 402due to the spin-swapping effect in response to the electrical writing current 406 is generated. The second spin stream is the spin stream generated in the plane, which is generated in the SHE spacer. 404 due to the spin Hall effect in response to the electrical writing current 406 is generated. The amount of spin current in the plane can be determined by the thickness of the SHE spacer. 404 and controlled by the conductivity ratio. The SHE spacer 404 It can be fabricated from a non-ferromagnetic conventional SOT layer, such as Pt or beta W. Both spin currents are introduced into the free layer. 212 injected to impart a spin-orbit torque to the free layer 212 to apply in order to determine the direction of magnetization of the free layer 212 to change (e.g., either downwards or upwards). In this embodiment, the memory cell has 400both polarizations (in the plane and perpendicular) of the free layer 212 injected spin currents that generate a supported switching mechanism. In one embodiment, the perpendicular spin current is the primary spin current for switching, and the in-plane spin current is located in the free layer. 212 The injected polarized spin current supports the change in the magnetization direction of the free layer. 212 However, the roles of the primary spin stream and the supporting spin stream can be modified and / or designed. The thickness and resistance of the SHE spacer layer 404 as well as the thickness and resistance of the spin-swapping layer 402 They can be adjusted to adapt the respective amount of spin current. Greater thickness and lower resistance result in a greater spin current for the respective layer.

[0045] In the case where the spin current is dominated by the spin polarization in the plane (e.g., a thicker and lower-resistance SHE spacer layer with a thinner and higher-resistance spin-swapping layer), the switching is determined by the spin Hall effect-based spin current. However, the supporting spin current from the spin-swapping layer generates an effective magnetic field in the plane, providing deterministic switching. This eliminates the need for an external magnetic field on the chip. Thus, the spin-swapping layer offers 402 in one embodiment an effective magnetic field in the plane to break the symmetry, and the inversion of the free layer 212 This is achieved via the SHE mechanism.

[0046] If the spin current is dominated by perpendicular spin polarization (e.g., thicker and lower spin-swapping layer with a thinner and more resistive SHE spacer layer), the switching current in the precessive region (sub-10 ns) is reduced because the spin polarization is in the plane of the SHE layer. 404 The magnetization is moved away from its simple axis and helps to overcome the stagnation point. Thus, the SHE spacer layer 404 In one embodiment, an initiation mechanism is provided to tilt the magnetization of the free layer away from its simple axis, thereby reducing the switching current in the fast range (<10 ns).

[0047] Fig. Figure 5 is a flowchart that describes one embodiment of a process performed to program an MRAM memory cell, such as the memory cell 200 out of Fig. 2, the memory cell 300 out of Fig. 3 and / or the memory cell 400 out of Fig. 4. In step 502 an electric current (e.g., writing current) 222 or write current 406 ) through a ferromagnetic layer (e.g. spin-swapping layer) 220 or 402 ) adjacent to a spacer layer (e.g. spacer) 214 or spacers 404 The spacer layer is located between the ferromagnetic layer and a free layer. The free layer is capable of changing the direction of magnetization, as described above with respect to the free layer. 212 explained in step 504 A perpendicularly polarized spin current is generated in the ferromagnetic layer (e.g., spin-swapping layer). 220 or 402 ) in response to electric current (e.g., writing current) 222 or write current 406 ) by spin-swapping. In step 506The generated vertically polarized spin current is injected through the spacer layer into the free layer to change the direction of the free layer's magnetization. This writes data to the memory cell. Step 508 This process is performed to read the memory cell by passing an electrical read current through the MTJ (also through the free layer). The current state of the free layer is detected by the sampling resistor of the MTJ, based on the detection of the read current by the MTJ. Fig. Step 5 shows a dashed line to step 508 , to indicate that step 508 much later after completion of step 506 can be performed (or immediately after step 506 ).

[0048] Fig. 6 is a block diagram that shows an example of a storage system 600 This represents a system that can implement the technology described here. The storage system 600includes a storage array 602 , which can contain any of the memory cells described above. The array connection lines of the memory array. 602 This includes the various layers of word lines, organized as rows, and the various layers of bit lines, organized as columns. However, other orientations are also possible. The storage system 600 includes a line control circuit 620 , whose exits 608 with the corresponding word lines of the storage array 602 are connected. The line control circuit 620 receives a group of M-line address signals and one or more different control signals from the system control logic. 660 and can typically include circuits such as line decoders 622 , Array connector driver 624 and block selection circuit 626for read and write operations. The storage system 600 also includes a column control circuit 610 , whose inputs / outputs 606 with the corresponding bit lines of the memory array 602 are connected. The column control circuit 606 receives a group of N column address signals and one or more different control signals from the system control logic. 660 and can typically include circuits such as column decoders 612 , Array connector receiver or driver 614, block selection circuit 616 as well as read / write circuits and I / O multiplexers. The system control logic 660 It receives data and commands from a host and provides output data and status to the host. In further embodiments, the system control logic receives... 660Data and commands are received from a separate control circuit, and output data is provided to this control circuit, which then communicates with the host. The system control logic 660 can include one or more state machines, registers, and other control logic to control the operation of the storage system 600 include.

[0049] In one embodiment, all in Fig. The six components shown are arranged on a single integrated circuit. For example, the system control logic is... 660 , the column control circuit 610 and the line control circuit 620 formed on the surface of a substrate, and the storage array 602 is formed on or above the substrate.

[0050] The above discussion provides details of a new proposed MRAM memory cell with perpendicular spin-orbit torque that can deterministically switch the magnetization direction of the free layer by means of a perpendicularly polarized spin current in a z-direction generated via a spin-swapping effect without an external magnetic field.

[0051] One embodiment includes a device comprising a magnetic tunnel junction with a free layer in a plane, a ferromagnetic layer, and a spacer layer between the ferromagnetic layer and the free layer. The free layer has a switchable magnetization direction perpendicular to the plane. The ferromagnetic layer is configured to generate a perpendicularly polarized spin current in response to an electric current passing through it and to inject this perpendicularly polarized spin current through the spacer layer into the free layer to change the magnetization direction of the free layer.

[0052] One embodiment comprises a method comprising passing an electric current through a ferromagnetic layer adjacent to a spacer layer, wherein the spacer layer is located between the ferromagnetic layer and a free layer, the free layer being capable of changing the magnetization direction; generating a perpendicularly polarized spin current in the ferromagnetic layer in response to the electric current; and injecting the perpendicularly polarized spin current through the spacer layer into the free layer to change the direction of magnetization of the free layer. In an exemplary implementation, the ferromagnetic layer is configured to receive the perpendicularly polarized spin current in response to the electric current through the ferromagnetic layer by means of a spin-orbit interaction (i.e.,spin-swapping) to generate a first spin current in the ferromagnetic layer that induces a transverse spin current with reversed spin direction and flux direction (the transverse spin current is the perpendicularly polarized spin current).

[0053] One embodiment includes a perpendicular spin-orbit torque MRAM memory cell comprising a magnetic tunnel junction containing a free layer capable of changing the direction of the free layer's magnetization, and means for deterministically switching the direction of the free layer's magnetization by means of a perpendicularly polarized spin current in a z-direction, generated via a spin-swapping effect without an external magnetic field. One embodiment of the means for deterministically switching the magnetization direction of the free layer includes a ferromagnetic layer and a spacer layer between the ferromagnetic layer and the free layer. Examples of the ferromagnetic layer include the spin-swapping layer. 220 the Fig. 2 and Fig. 3, which the process of Fig. 5, and the spin-swapping layer 402 the Fig. 4, which the process of Fig. 5. Examples of the spacer layer are the spacer layer. 214 the Fig. 2 and Fig. 3 and the spacer layer 404 the Fig. 4.

[0054] For the purposes of this document, reference in the description to “one embodiment”, “some embodiments” or “another embodiment” may be used to describe different embodiments or the same embodiment.

[0055] For the purposes of this document, a connection can be direct or indirect (e.g., via one or more other parts). In some cases, when an element is described as connected or coupled to another element, the element may be directly connected to the other element or indirectly connected to the other element via intermediate elements. When an element is described as directly connected to another element, there are no intermediate elements between the element and the other element. Two devices are "in communication" when they are connected to each other, directly or indirectly, in such a way that they can transmit electronic signals to each other.

[0056] For the purposes of this document, the term “based on” may be read as “at least partially based on”.

[0057] For the purposes of this document, without additional context, the use of numerical expressions such as a "first" object, a "second" object, and a "third" object may not imply a sorting of objects, but may instead be used for identification purposes to distinguish between different objects.

[0058] For the purposes of this document, the term “set” of objects can refer to a “set” of one or more of the objects.

[0059] The preceding detailed description has been provided for illustrative and descriptive purposes. It is not intended to be exhaustive or to limit the exact form disclosed. Many modifications and variations are possible, taking into account the teaching stated above. The described embodiments have been chosen to best explain the principles of the proposed technology and its practical application, and thus to enable other skilled persons to best utilize it in various embodiments and with various modifications suitable for their respective intended uses. It is intended that the scope is defined by the claims included herein.

Claims

[1] Device comprising: a magnetic tunnel junction comprising a free layer in a plane, wherein the free layer has a switchable direction of magnetization perpendicular to the plane; a ferromagnetic layer; and a spacer layer between the ferromagnetic layer and the free layer, wherein the ferromagnetic layer is configured to generate perpendicularly polarized spin current in response to an electric current through the ferromagnetic layer and to inject the perpendicularly polarized spin current through the spacer layer into the free layer to change the direction of magnetization of the free layer. [2] Device according to claim 1, wherein: The ferromagnetic layer is a spin-swapping layer that is set up to induce perpendicularly polarized spin current by spin-swapping in response to the electric current through the ferromagnetic layer. [3] Device according to claim 1, wherein: the ferromagnetic layer is set up to generate the perpendicularly polarized spin current in response to the electric current through the ferromagnetic layer by means of a spin-orbit interaction which has a first spin current in the ferromagnetic layer which induces a transverse spin current with reversed spin direction and flux direction, wherein the transverse spin current has the perpendicularly polarized spin current. [4] Device according to claim 1, wherein: The ferromagnetic layer is magnetized in the plane. [5] Device according to claim 1, wherein: The ferromagnetic layer is magnetized parallel to the direction of flow of the electric current. [6] Device according to claim 1, wherein: The ferromagnetic layer is a metal with a high degree of spin polarization. [7] Device according to claim 1, wherein: the ferromagnetic layer has a spin diffusion length that is greater than half the thickness of the ferromagnetic layer. [8] Device according to claim 1, wherein: the ferromagnetic layer has a spin diffusion length that is greater than the thickness of the ferromagnetic layer. [9] Device according to claim 1, wherein: The magnetic tunnel junction, the ferromagnetic layer and the spacer exhibit a spin-orbit torque MRAM memory cell. [10] Device according to claim 1, wherein: The ferromagnetic layer is a Heusler alloy. [11] Device according to claim 1, wherein: The spacer layer is set up to magnetically decouple the ferromagnetic layer and the free layer. [12] Device according to claim 1, wherein: The spacer layer is a spin Hall effect (SHE) layer. [13] Device according to claim 1, wherein: The spacer layer has a non-ferromagnetic SHE layer that is configured to generate in-plane polarized spin current in response to the electric current through the ferromagnetic layer and to inject the in-plane polarized spin current into the free layer to assist in changing the direction of magnetization of the free layer. [14] Device according to claim 1, further comprising: an antiferromagnetic layer adjacent to the ferromagnetic layer, wherein the antiferromagnetic layer and the ferromagnetic layer are arranged such that an exchange bias from the antiferromagnetic layer fixes a direction of magnetization of the ferromagnetic layer. [15] Methods, comprising: Conducting an electric current through a ferromagnetic layer adjacent to a spacer layer, wherein the spacer layer is located between the ferromagnetic layer and a free layer, the free layer being able to change the magnetization direction; Generating a vertically polarized spin current in the ferromagnetic layer in response to the electric current; and injecting the vertically polarized spin current through the spacer layer into the free layer to change the direction of the magnetization of the free layer. [16] Method according to claim 15, wherein generating a perpendicularly polarized spin current in the ferromagnetic layer comprises: a first spin current in the ferromagnetic layer that induces a transverse spin current with reversed spin direction and flux direction, wherein the transverse spin current is the perpendicularly polarized spin current, wherein the ferromagnetic layer and the free layer have a spin-orbit torque MRAM memory cell. [17] Method according to claim 15, further comprising: Detecting a current state of the free layer by passing an electrical read current through the free layer, wherein the ferromagnetic layer and the free layer comprise a spin-orbit torque MRAM memory cell, wherein detecting the current comprises reading the spin-orbit torque MRAM memory cell, injecting the perpendicularly polarized spin current through the spacer layer into the free layer to change the direction of magnetization of the free layer, and writing to the spin-orbit torque MRAM memory cell. [18] comprising a device: an MRAM memory cell with vertical spin-orbit torque, exhibiting: a magnetic tunnel junction that includes a free layer capable of changing the direction of magnetization; and Means for deterministic switching of the magnetization direction of the free layer by means of a vertically polarized spin current in a z-direction, which is generated via a spin-swapping effect without an external magnetic field. [19] Device according to claim 18, wherein the means for deterministic switching of the magnetization direction of the free layer comprises: a ferromagnetic layer with a first terminal and a second terminal; and a spacer layer between the ferromagnetic layer and the free layer, such that the ferromagnetic layer does not touch the free layer, wherein the ferromagnetic layer is configured to generate the perpendicularly polarized spin current in response to an electric current through the ferromagnetic layer between the first terminal and the second terminal, wherein the ferromagnetic layer is configured to inject the spin current through the spacer layer into the free layer in order to change the direction of magnetization of the free layer. [20] Device according to claim 19, wherein: The ferromagnetic layer is magnetized in the plane and parallel to one direction of the electric current between the first terminal and the second terminal.