A multi-state magnetic memory based on double-layer magnetic tunnel junction
By using a multi-state magnetic memory with a double-layer magnetic tunnel junction, the magnetization reversal of the magnetic layer can be independently controlled by the STT and SOT currents, achieving efficient storage of three or four bits. This solves the problem of limited storage density in MRAM and has non-volatility and low power consumption characteristics.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Patents(China)
- Current Assignee / Owner
- NANJING UNIV
- Filing Date
- 2023-02-27
- Publication Date
- 2026-07-21
AI Technical Summary
In existing MRAM memory devices, a single MTJ can only store one bit of data, which limits the storage density. Furthermore, traditional multilayer stacked structures fail to effectively utilize the magnetization reversal of the reference layer for information writing.
A multi-state magnetic memory based on a double-layer magnetic tunnel junction is adopted. Magnetization reversal is achieved in multiple magnetic layers by independently controlling the spin-transfer torque STT and spin-orbit torque SOT current. Data writing and reading are carried out by utilizing the resistance difference. A structure with at least three or four ports is designed to independently control the magnetization state of each layer.
It enables the writing of three or four bits of information into a dual-layer MTJ memory device, significantly improving storage density and reducing process requirements. Data writing and reading are achieved through independent current channels, and it features non-volatility, low power consumption, and high thermal stability.
Smart Images
Figure CN116406221B_ABST
Abstract
Description
Technical Field
[0001] This invention relates to a multi-state magnetic memory based on a double-layer magnetic tunnel junction and its data reading and writing method, belonging to the field of spintronic device technology. Background Technology
[0002] With the rapid development of the information age, the amount of data generated by human society is exploding, making the development of storage devices with higher storage density and lower power consumption one of the challenges facing the integrated circuit industry today. Constructing new non-volatile memories has become an effective way to solve the problems of volatility and high power consumption in current storage systems. Magnetic Random Access Memory (MRAM) has been developed in this context.
[0003] The core unit of a magnetic random access memory (MRM) is a magnetic tunnel junction (MTJ), which offers advantages such as non-volatility, low power consumption, high read / write speeds, and long storage life. Its basic principle lies in the change in the overall resistance state caused by the change in the magnetization orientation of the magnetic layers at both ends of the junction region; the high and low voltage levels correspond to digital signals 1 and 0. The magnetization of the magnetic layers is reversed using spin transfer torque (STT) and spin orbit torque (SOT), corresponding to data writing.
[0004] In traditional MRAM, a single MTJ can only store one bit of data. While developed MRAMs such as MLC and TLC stack MTJs to increase storage density, they are still limited to a single MTJ-single-bit storage format. Therefore, simultaneously utilizing STT and SOT to manipulate the flipping of more magnetic layers can more effectively improve the storage density of MTJs. Summary of the Invention
[0005] This invention addresses the problems existing in the prior art by providing a multi-state magnetic memory based on a double-layer magnetic tunnel junction. Compared with the single MTJ-single bit storage form in the traditional MRAM structure, this technical solution further improves the data storage density.
[0006] To achieve the above objectives, the technical solution of the present invention is as follows: a multi-state magnetic memory based on a double-layer magnetic tunnel junction, the memory comprising a top electrode (10), a first magnetic tunnel junction, a metal intercalation layer (50), a second magnetic tunnel junction, and a bottom electrode (90);
[0007] The first magnetic tunnel junction, from top to bottom, includes a free layer FL1 (20), a tunneling layer (30) of the first magnetic tunnel junction, and a reference layer RL1 (40).
[0008] The second magnetic tunnel junction comprises, from top to bottom, a free layer FL2 (60), a tunneling layer (70) of the second magnetic tunnel junction, and a reference layer RL2 (80);
[0009] The memory is also provided with at least three ports. Port 1 (1) is connected to the top electrode (10), and port 2 (2) and port 3 (3) are provided at the left and right ends of the bottom electrode (90), respectively. The direction of the current flowing through port 2 is opposite to the direction of the current flowing through port 3. The current referred to here refers to charge flow, and the direction of the current refers to the direction of electron movement. Unless otherwise stated, the current in the entire text refers to charge flow.
[0010] As an improvement of the present invention, when the free layer of the magnetic tunnel junction is parallel or antiparallel to the magnetization direction of the reference layer, its overall resistance state exhibits a low-resistance state R. P or high impedance state R AP The resistance difference is ΔR. Specifically, the resistance difference of the first magnetic tunnel junction is ΔR1, and the resistance difference of the second magnetic tunnel junction is ΔR2, where ΔR1 is not equal to ΔR2. The corresponding spin transfer torque (STT) critical reversing current I... S1 with I S2 They are not equal;
[0011] The magnetic moment direction of the reference layer RL (40) of the first magnetic tunnel junction remains constant, and its free layer FL1 (20) is connected to the top electrode (10). The reference layer RL2 (80) of the second magnetic tunnel junction is connected to the bottom electrode (90). The magnetic tunnel junctions are separated by metal intercalation layers (50) and form a series connection in the circuit. Ports 2 and 3 are used to write the spin orbit torque (SOT) current flowing through the bottom electrode of the heavy metal layer. In response to the energizing direction of the port, the magnetization direction of the reference layer RL2 (80) changes from state 1 to state 2. The magnetization directions of the reference layer RL2 (80) in state 1 and state 2 are opposite. The electrical signal input at port 2 is defined as I. + The electrical signal at port three input is I. - I + with I - Opposite direction, I + Corresponding to the magnetization direction state of the reference layer RL2(80), I -Corresponding to the second magnetization direction of the reference layer RL2(80), either port one, port two, or port three is used to write a spin-transfer torque (STT) current into the tunnel junction to flip the free layer magnetic moment of the tunnel junction. The STT current input from port one is defined as negative, and the STT current input from port two or port three is defined as positive. The corresponding STT currents for the first and second magnetic tunnel junctions are I... S1 + I S1 - I S2 + I S2 - Correspondingly, the magnetization direction of the free layer FL1 (20) changes to be in the same direction or opposite to the magnetization direction of the reference layer RL1 (40), while the magnetization direction of the free layer FL2 (60) remains in the same direction or opposite to the magnetization direction of the reference layer RL2 (80). Corresponding to the magnetic moment reversal of the free layer, the resistance of the first magnetic tunnel junction changes in R... 1P With R 1AP The transition between the two, the resistance of the second magnetic tunnel junction in R 2P With R 2AP Convert between them.
[0012] As an improvement of the present invention, the SOT switching current supplied to the bottom electrode (90) only acts on the reference layer RL2 (80), and the STT switching current only acts on the free layers FL1 (20) and FL2 (60). The data writing channels are independent and do not affect each other. The SOT switching current input is port two or port three, corresponding to I + with I - The STT flip current input is either port one or port two or port three, corresponding to I according to the function of the tunnel junction and the current direction. S1 + I S1 - I S2 + I S2 - .
[0013] As an improvement of the present invention, the top electrode is composed of at least one of the following materials, including but not limited to: platinum, gold, titanium, copper, chromium, tantalum, and tungsten; the free layer and reference layer include materials including but not limited to magnetic materials with magnetic anisotropy such as CoFeB, CoPt, NiFe, and CoFeAl, including but not limited to in-plane magnetic anisotropy and perpendicular magnetic anisotropy; the tunneling layer includes but is not limited to oxide insulators such as MgO and Al2O3, and semiconductors. The bottom electrode includes but is not limited to strong spin-orbit coupling materials such as platinum, tantalum, and tungsten that can provide spin-orbit moments.
[0014] A multi-state magnetic memory based on a double-layer magnetic tunnel junction, the memory comprising a top electrode (10), a first magnetic tunnel junction, a metal intercalation layer (50), a second magnetic tunnel junction, and a bottom electrode (90); wherein the first magnetic tunnel junction is stacked in reverse, thereby deriving a structure in which all four magnetic layers can be flipped, i.e., the reference layer RL1 (40) is connected to the top electrode (10), and the top electrode (10) leads out port one (1) and port four (4), and the bottom electrode leads out port two (2) and port three (3). In the input SOT flip current, the directions of port one (1) and port four (4) are opposite, and the directions of port two (2) and port three (3) are opposite. The resistance difference of the first magnetic tunnel junction is ΔR1, the resistance difference of the second magnetic tunnel junction is ΔR2, and ΔR1 is not equal to ΔR2, and its corresponding spin-transfer torque STT critical flip current I S1 with I S2 Not equal. In response to the SOT current signal of the top and bottom electrodes, the magnetization direction of the reference layers RL1 (40) and RL2 (80) changes from state one to state two, and the magnetization direction of the reference layers in state one is opposite to that in state two. The STT flip current is input from port one or port four and port two or port three. In response to the STT current of different directions and magnitudes, the magnetization direction of the free layers FL1 (20) and FL2 (60) changes from state one to state two, and the magnetization direction of the free layers in state one is opposite to that in state two. Correspondingly, the resistance of the tunnel junction changes from resistance state one to resistance state two.
[0015] The data read / write method based on a multi-state magnetic memory with a double-layer magnetic tunnel junction is characterized in that the magnetic storage device unit has at least three input ports.
[0016] The reading method is as follows: a reading current I is applied to the device unit. R To obtain the total resistance of the current tunnel junction, given the total resistance of the junction region R... 1P +R 2P R 1P +R 2AP R 1AP +R 2P R 1AP +R 2APThe reading result must be one of the four different resistance states, thus obtaining the relative state of the free layer and the reference layer in the first tunnel junction and the second tunnel junction, i.e., parallel or antiparallel. If the magnetization direction of the reference layer RL1(40) in the first tunnel junction remains unchanged, then the magnetization direction of the free layer FL1(20) is either parallel or antiparallel. The data bit content stored in the free layer FL1(20) is obtained. The SOT flip current input from port two is used to initialize the reference layer RL2(80) of the second tunnel junction so that its magnetization direction becomes state one. Then, the reading current is applied again to obtain the current resistance value. If it remains unchanged, then the initial magnetization direction of the reference layer RL2(80) is state one, and the data bit content stored in the reference layer RL2(80) is obtained. If the resistance value changes, then the initial magnetization direction of the reference layer RL2(80) is state two, and the data bit stored therein is obtained. The first reading of the tunnel junction resistance value is known to the relative state of the free layer FL2(60) and the reference layer RL2(80) of the second tunnel junction. The magnetization direction of the free layer FL2(60) is known, and the data bit content stored in the free layer FL2(60) is obtained.
[0017] The writing method is as follows: if the STT switching current of the first tunnel junction is less than the STT switching current of the second tunnel junction, the STT switching current is input from port two or port three, the magnetization direction of the reference layer RL2 (80) changes to state one or state two, and the data bit stored in the reference layer is "0" or "1"; the STT switching current of the second tunnel junction is input from port one or port two (three), the magnetization direction of the free layer FL2 (60) changes to be antiparallel or parallel to the reference layer RL2 (80), and the data stored in the free layer is "1" or "0"; the writing method is as follows: if the STT switching current of the first tunnel junction is less than the STT switching current of the second tunnel junction, the STT switching current ... two or port three, the magnetization direction of the free layer FL2 (60) changes to be antiparallel or parallel to the reference layer RL2 (80), and the data stored in the free layer is "1" or "0"; the writing method is as follows: if the STT switching current of the first tunnel junction is less than the STT switching current of the second tunnel junction, the STT switching current is input from port one or port two (three), the STT switching current of the second tunnel junction is input from port two or port three, the STT switching current of the second tunnel junction is input from port two or port three, the STT switching current of the second tunnel junction is input from port two or port three, the STT switching current of the second tunnel junction is input from port two or port three, the STT switching current of the second tunnel junction is input from port two or port three, the STT switching current of the second tunnel junction If the STT reversal current of the first tunnel junction is input at port one or port two (three), the magnetization direction of the free layer FL1 (20) changes to be antiparallel or parallel to the reference layer RL1 (40). The data stored in the free layer is "0" or "1". If the STT reversal current of the first tunnel junction is greater than that of the second tunnel junction, the STT reversal current of the first tunnel junction is input first to write the information into the free layer FL1 (20). Subsequently, the SOT reversal current and the STT reversal current of the second tunnel junction are input sequentially to write the data into the reference layer RL2 (80) and the free layer FL2 (60).
[0018] As an improvement of the present invention, the ΔR1 of the first tunnel junction is not equal to the ΔR2 of the second tunnel junction, and the corresponding STT critical switching currents are not equal. The magnetic tunnel junction thin film can be grown by sputtering deposition or other methods.
[0019] Compared with the prior art, the present invention has the following advantages:
[0020] 1. This technical solution provides a method to write three or four bits of information into a memory device cell composed of a dual-layer MTJ and read it. By controlling the resistance difference of the MTJ and the STT critical switching current density, the direction and magnitude of the writing current can be controlled to achieve data writing to different magnetic layers.
[0021] 2. This invention achieves the storage of three or four bits of information in a dual-layer MTJ by controlling the flipping of multiple magnetic layers. Compared to traditional MLC MRAM cells, which can only store two bits of information, this significantly increases the storage density. Compared to traditional TLC or MRAM cells with multiple stacked MTJs, storing the same amount of data reduces the number of MTJs and lowers the corresponding process requirements. Unlike traditional MTJs where the magnetization direction of the reference layer remains constant, the innovative design of this invention involves applying magnetization flipping to the reference layer to write information to it. Simultaneously, the resistive logic of the device unit is used to determine the state of each magnetic layer and read its corresponding data bits.
[0022] 3. This invention utilizes both STT and SOT switching mechanisms, ensuring independent input current channels and preventing interference between write and read signals. The magnetization switching of the reference layer increases the data write space while providing logical judgment for reading data bits.
[0023] 4. This invention utilizes magnetic tunnel junctions (MTJs) for data writing and reading, exhibiting non-volatility while also possessing the high write / read lifetime, high thermal stability, and low power consumption of MTJs, thus meeting the cell design requirements of MRAM. Attached Figure Description
[0024] Figure 1 This is a schematic diagram of the three-port magnetic storage unit structure of the present invention;
[0025] Figure 2a This is a schematic diagram of the resistance-STT current reversal of the first magnetic tunnel junction of the present invention;
[0026] Figure 2b This is a schematic diagram of the resistance-STT current reversal of the second magnetic tunnel junction of the present invention;
[0027] Figure 2c This is a schematic diagram of the resistance-STT current reversal of the double-layer magnetic tunnel junction of the present invention;
[0028] Figure 3a This is a schematic diagram of a magnetic storage data writing method according to the present invention;
[0029] Figure 3b This is a schematic diagram of a magnetic storage data writing method according to the present invention;
[0030] Figure 3cThis is a schematic diagram of a magnetic storage data reading method according to the present invention;
[0031] Figure 4 This is a schematic diagram of a four-port magnetic storage unit structure according to the present invention;
[0032] Figure 5 This is a schematic diagram of a four-port magnetic storage reading method according to the present invention.
[0033] Figure 1 In the diagram: 10 is the top electrode, 20 is the free layer of the first magnetic tunnel junction (FL1), 30 is the tunneling layer of the first magnetic tunnel junction, 40 is the reference layer of the first magnetic tunnel junction (RL1), 50 is the metal intercalation layer, 60 is the free layer of the second magnetic tunnel junction (FL2), 70 is the tunneling layer of the second magnetic tunnel junction, 80 is the reference layer of the second magnetic tunnel junction (RL2), and 90 is the bottom electrode; 1 is port one, 2 is port two, and 3 is port three. Detailed Implementation
[0034] To enhance understanding of the present invention, the embodiments will be described in detail below with reference to the accompanying drawings.
[0035] Example 1: See Figure 1 Those skilled in the art will understand that the terms "first", "second", "state one", "state two" and other terms used in this application are only used to distinguish different devices, parameters or physical states, and do not represent any specific meaning or limit their order or logic.
[0036] Figure 1This is a schematic diagram of the three-port magnetic memory cell structure proposed in this invention. From top to bottom, it includes a top electrode (10), a first magnetic tunnel junction including a free layer FL1 (20), a tunneling layer (30) of the first magnetic tunnel junction, a reference layer RL1 (40), a metal intercalation layer (50), a second magnetic tunnel junction including a free layer FL2 (60), a tunneling layer (70) of the second magnetic tunnel junction, a reference layer RL2 (80), and a bottom electrode (90). The top electrode is composed of at least one of the following materials, including but not limited to: platinum, gold, titanium, copper, chromium, tantalum, tungsten, etc. The free layer and the reference layer include the following materials, including but not limited to magnetic materials with magnetic anisotropy such as CoFeB, CoPt, NiFe, CoFeAl, etc., including but not limited to in-plane magnetic anisotropy and perpendicular magnetic anisotropy. The tunneling layer includes but is not limited to oxide insulators such as MgO and Al2O3, and semiconductors. The bottom electrode is made of strong spin-orbit coupling materials, including but not limited to platinum, tantalum, and tungsten, which can provide spin-orbit moments.
[0037] The magnetic storage device unit includes three ports: port one (1) connected to the top electrode, and ports two (2) and three (3) connected to the left and right ends of the bottom electrode, respectively. The direction of the current flowing through port two is opposite to the direction of the current flowing through port three. When the free layer of the first and second magnetic tunnel junctions is parallel or antiparallel to the magnetization direction of the reference layer, their overall resistance state exhibits a low-resistance state R. P With high-resistivity state R AP The resistance difference is ΔR. Specifically, the resistance difference of the first magnetic tunnel junction is ΔR1, and the resistance difference of the second magnetic tunnel junction is ΔR2. In this device, ΔR1 is not equal to ΔR2, and their corresponding spin-transfer torque STT critical switching current I... S1 with I S2 They are not equal. The magnetic moment direction of the reference layer of the first magnetic tunnel junction remains constant, and its free layer FL1 (20) is connected to the top electrode (10). The reference layer RL2 (80) of the second magnetic tunnel junction is connected to the bottom electrode (90). The magnetic tunnel junctions are separated by metal intercalation layers (50) and form a series connection in the circuit. For ease of explanation, the example here is ΔR1>ΔR2, I S1 S2 The relationship between the resistance of the first and second tunnel junctions and the STT switching current is as follows: Figure 2a and Figure 2b As shown, the relationship between the total resistance of the two-layer MTJ device cell and the STT switching current is as follows: Figure 2c As shown, in this example, all magnetic layers of the magnetic tunnel junction are perpendicular magnetic anisotropy (PMA), and the magnetic moment direction of the reference layer of the first magnetic tunnel junction is fixed to be perpendicular to the bottom electrode and upward. In this example, a magnetic layer magnetization direction perpendicular to the bottom electrode and upward is represented as data 0, and a direction perpendicular to the bottom electrode and downward is represented as data 1. The following explanations of the principles will be based on this example.
[0038] Ports 2 and 3 are used to write the spin-orbit moment (SOT) current flowing through the bottom electrode. For ease of explanation, the example specifies that the electrical signal input to port 2 is I. + The electrical signal at port three input is I. - I + with I - In the opposite direction, when the SOT current is input to the bottom electrode, the magnetic moment of the reference layer RL2(80) is reversed due to the spin orbital moment effect, as shown in Example I. + The magnetization direction of the reference layer RL2(80) is flipped upwards, I - The magnetization direction of the reference layer RL2(80) is flipped downwards.
[0039] Port 1, port 2, or port 3 is used to write a spin-transfer torque (STT) current into the tunnel junction, generating a spin-transfer torque effect that flips the free-layer magnetic moment of the tunnel junction. The STT current input from port 1 is defined as negative, and the STT current input from port 2 or port 3 is defined as positive. The corresponding STT currents for the first and second magnetic tunnel junctions are I. S1 + I S1 - I S2 + I S2 - Correspondingly, the magnetization direction of the free layer FL1 (20) changes to be in the same direction or opposite to the magnetization direction of the reference layer RL1 (40), and the magnetization direction of the free layer FL2 (60) changes to be in the same direction or opposite to the magnetization direction of the reference layer RL2 (80). Corresponding to the magnetic moment reversal of the free layer, the resistance of the first magnetic tunnel junction in R 1P With R 1AP The transition between the two, the resistance of the second magnetic tunnel junction in R 2P With R 2AP Convert between them.
[0040] This invention provides a data read / write method. Based on the above example, the read / write method is described as follows:
[0041] like Figure 3a As shown, the writing method is as follows: First, an initialization operation is performed, and the SOT switching current I is input from port two. +The magnetization direction of the reference layer RL2 (80) changes to upward, and the data bits stored in the reference layer are "0"; the STT switching current I of the second tunnel junction is input from port three. S2 + The magnetization direction of the free layer FL2 (60) changes to be parallel to the reference layer RL2 (80), and the data stored in the free layer FL2 (60) is "0"; the STT switching current I of the first tunnel junction is input from port two or port three. S1 + The magnetization direction of the free layer FL1(20) is changed to be parallel to the reference layer RL1(40), and the data stored in the free layer is "0". The data is arranged from top to bottom, and the data bits are initialized to 000 at this time; Write 1: Enter I from port tee - Current, the magnetization direction of reference layer RL2(80) is reversed to downward, at which time the data written is 001; I is introduced from port one S1 - Current, the magnetization direction of the free layer FL1(20) is flipped downwards, and the data bit is 101. Writing 2: Input I through port 1 S2 - Current, because I S2 >I S1 Both free layers FL1 (20) and FL2 (60) are flipped downwards, at which point the data bits are 110; I is input from the port tee. - Current, reference layer RF2(80) flips down, at this time the data bit is 111, if I is passed in from port two or port three S1 + Current, free layer FL1(20) flips upward, at this time the data bit is 010, then if I is entered from port 3 - Current, reference layer RF2(80) flips downwards, at this time the data bit is 011. Write 3: Input I through port 1 S1 - The current is applied, and the free layer FL1(20) flips downwards, at which point the data bit is 100. The above writing method implements all three-bit data writing. It should be noted that the writing of any three-bit information in this example is not the only writing method. Modification of a single bit is often based on the previous storage state. For example, writing 101 from 100 only requires inputting I through port 3. - This can be achieved using electric current; theoretically, writing any three bits of information requires at most three steps. If the example is I... S1 >I S2 The writing method is as follows: Figure 3b As shown, the writing principle and process are similar, and will not be repeated here.
[0042] like Figure 3cAs shown, the reading method is as follows: a reading current I is applied to the device unit. R To obtain the total resistance of the current tunnel junction, we have R. 1P +R 2P R 1P +R 2AP R 1AP +R 2P R 1AP +R 2AP The reading result must be one of the four different resistance states, thus obtaining the relative state of the free layer and the reference layer in the first and second tunnel junctions, i.e., parallel or antiparallel. Since the magnetization direction of the reference layer RL1(40) in the first tunnel junction is fixed upwards, it can be known that the magnetization direction of the free layer FL1(20) is upwards or downwards, and the data bit content stored in the free layer FL1(20) is 0 or 1. The SOT switching current I is input from port two. + The reference layer RL2(80) of the second tunnel junction is initialized so that its magnetization direction is upward. Then, a read current is applied again to obtain the current resistance value. If it remains unchanged, the initial magnetization direction of the reference layer RL2(80) is upward, and the data bit content stored in the reference layer RL2(80) is 0. If the resistance value changes, the initial magnetization direction of the reference layer RL2(80) is downward, and the data bit content stored in the reference layer RL2(80) is 1. The first read of the tunnel junction resistance value is known to be the relative state of the free layer FL2(60) of the second tunnel junction and the reference layer RL2(80). It can be known that the magnetization direction of the free layer FL2(60) is upward or downward, and the data bit content stored in the free layer FL2(60) is 0 or 1. The reading method for any bit information is fixed. The first step I R The information of the free layer FL1(20) and the resistance state of the second tunnel junction can be determined by reading the data. The second step I + After flipping, the information of the reference layer RL2(80) can be determined, and then the information of the free layer FL2(60) can be determined.
[0043] Furthermore, based on the aforementioned three-port double-layer magnetic tunnel junction storage device, the first magnetic tunnel junction can be stacked in reverse, i.e., the reference layer RL1 (40) is connected to the top electrode 10, and the top electrode 10 leads out to port one and port four, while the bottom electrode leads out to port two and port three, as shown below. Figure 4 As shown, a four-port device is derived. In the input SOT switching current, the input directions of port one and port four are opposite, and the input directions of port two and port three are opposite. The resistance difference of the first magnetic tunnel junction is ΔR1, and the resistance difference of the second magnetic tunnel junction is ΔR2, where ΔR1 is not equal to ΔR2. The corresponding spin-transfer torque STT critical switching current I... S1 with I S2They are not equal. In response to the SOT current signals of the top and bottom electrodes, the magnetization directions of reference layers RL1 (40) and RL2 (80) change from state one to state two, where the magnetization directions of the reference layers in state one are opposite to those in state two. STT switching currents are input from port one or port four and port two or port three. In response to STT currents of different directions and magnitudes, the magnetization directions of free layers FL1 (20) and FL2 (60) change from state one to state two. The magnetization directions of the free layers in state one are opposite to those in state two. Correspondingly, the resistance of the tunnel junction changes from resistance state one to resistance state two. This enables data writing to four magnetic layers, storing four bits of data. For ease of explanation, the example here uses an SOT current of I1 input to port one and port two. + With I2 + The magnetization directions of the corresponding reference layers RL1 (40) and RL2 (80) are reversed to upwards and downwards, respectively. Therefore, the resistance state of the device unit is R. 1P +R 2P R 1P +R 2AP R 1AP +R 2P R 1AP +R 2AP Four types. For example... Figure 5 As shown, one reading method is to input I... R By reading the unit resistance, and based on its inherent four resistance states, the resistance states of the first and second magnetic tunnel junctions can be obtained. It can be seen that the magnetic layers of the first and second tunnel junctions are either parallel or antiparallel. Then, I2 is applied. + Attempt to flip the reference layer RF2(80). If the resistance remains unchanged, the data stored in the reference layer RL2(80) is 0; otherwise, it is 1. Simultaneously, based on the known resistance state, the data of the free layer FL2(60) is obtained. Then, I1 is introduced. + Attempting to flip the reference layer RL1(40), if the resistance remains unchanged, the data stored in the reference layer RL1(40) is 0; otherwise, it is 1. Simultaneously, the data in the free layer FL1(20) is obtained based on the known resistance state. Thus, a complete four-bit data bit can be read. Thanks to the symmetrical stacking of the tunnel junction, both the top and bottom electrodes can be supplied with SOT current to individually write two bits of data stored in the two reference layers. Simultaneously, by utilizing different sizes of STT flip current, the corresponding adjustable free layer can be used for information writing. Thus, a complete four-bit data bit can be written.
[0044] It should be noted that the above embodiments are not intended to limit the scope of protection of the present invention. Equivalent transformations or substitutions made based on the above technical solutions all fall within the scope of protection of the claims of the present invention.
Claims
1. A multi-state magnetic memory based on a double-layer magnetic tunnel junction, characterized in that, The memory includes a top electrode (10), a first magnetic tunnel junction, a metal intercalation layer (50), a second magnetic tunnel junction, and a bottom electrode (90). The first magnetic tunnel junction, from top to bottom, includes a free layer FL1 (20), a tunneling layer (30) of the first magnetic tunnel junction, and a reference layer RL1 (40). The second magnetic tunnel junction, from top to bottom, includes the free layer FL2 (60), the tunneling layer (70) of the second magnetic tunnel junction, and the reference layer RL2 (80); The memory is also provided with at least three ports. Port 1 (1) is connected to the top electrode (10), and port 2 (2) and port 3 (3) are provided at the left and right ends of the bottom electrode (90), respectively. The direction of the current flowing into port 2 is opposite to the direction of the current flowing into port 3. When the free layer of a magnetic tunnel junction is parallel or antiparallel to the magnetization direction of the reference layer, its overall resistance state exhibits a low resistance state R. P or high impedance state R AP The resistance difference is ΔR, where the resistance difference of the first magnetic tunnel junction is ΔR1, and the resistance difference of the second magnetic tunnel junction is ΔR2, and ΔR1 is not equal to ΔR2. The corresponding spin transfer torque (STT) critical reversing current I... S1 with I S2 They are not equal; The magnetic moment direction of the reference layer RL1 (40) of the first magnetic tunnel junction remains constant, and its free layer FL1 (20) is connected to the top electrode (10). The reference layer RL2 (80) of the second magnetic tunnel junction is connected to the bottom electrode (90). The magnetic tunnel junctions are separated by metal intercalation layers (50) and form a series connection in the circuit. Ports 2 and 3 are used to write the spin orbit torque (SOT) current flowing through the bottom electrode of the heavy metal layer. In response to the energizing direction of the port, the magnetization direction of the reference layer RL2 (80) changes from state 1 to state 2. The magnetization directions of the reference layer RL2 (80) in state 1 and state 2 are opposite. The electrical signal input at port 2 is defined as I. + The electrical signal input at port three is I. - I + with I - Opposite direction, I + Corresponding to the magnetization direction state of the reference layer RL2(80), I - Corresponding to the second magnetization direction of the reference layer RL2(80), either port one, port two, or port three is used to write a spin-transfer torque (STT) current into the tunnel junction to flip the free layer magnetic moment of the tunnel junction. The STT current input from port one is defined as negative, and the STT current input from port two or port three is defined as positive. The corresponding STT currents for the first and second magnetic tunnel junctions are I... S1 + I S1 - I S2 + I S2 - Correspondingly, the magnetization direction of the free layer FL1 (20) changes to be in the same direction or opposite to the magnetization direction of the reference layer RL1 (40), and the magnetization direction of the free layer FL2 (60) remains in the same direction or opposite to the magnetization direction of the reference layer RL2 (80). Corresponding to the magnetic moment reversal of the free layer, the resistance of the first magnetic tunnel junction is in R 1P With R 1AP The transition between the two, the resistance of the second magnetic tunnel junction in R 2P With R 2AP Convert between them.
2. The multi-state magnetic memory based on a double-layer magnetic tunnel junction according to claim 1, characterized in that, The SOT switching current supplied to the bottom electrode (90) only applies to the reference layer RL2 (80), and the STT switching current only applies to the free layers FL1 (20) and FL2 (60). The data writing channels are independent and do not affect each other. The SOT switching current input is port two or port three, corresponding to I. + with I - The STT flip current input is either port one or port two or port three, corresponding to I according to the function of the tunnel junction and the current direction. S1 + I S1 - I S2 + I S2 - .
3. The multi-state magnetic memory based on a double-layer magnetic tunnel junction according to claim 2, characterized in that, The top electrode is made of one or more of the following materials: platinum, gold, titanium, copper, chromium, tantalum, and tungsten; the free layer and reference layer are made of one of the following magnetic materials: CoFeB, CoPt, NiFe, and CoFeAl; the tunneling layer is made of one of the following oxide insulators: MgO, Al2O3, and semiconductor materials; and the bottom electrode is made of one or more of the following strong spin-orbit coupling materials: platinum, tantalum, and tungsten, which can provide spin-orbit moments.
4. A multi-state magnetic memory based on a double-layer magnetic tunnel junction, characterized in that, The memory includes a top electrode (10), a first magnetic tunnel junction, a metal intercalation layer (50), a second magnetic tunnel junction, and a bottom electrode (90). The first magnetic tunnel junction is stacked in reverse, resulting in a structure where all four magnetic layers can be flipped. The reference layer RL1 (40) is connected to the top electrode (10), and the top electrode (10) leads out to port 1 (1) and port 4 (4), while the bottom electrode leads out to port 2 (2) and port 3 (3). In the input SOT flip current, the directions of port 1 (1) and port 4 (4) are opposite, and the directions of port 2 (2) and port 3 (3) are opposite. The resistance difference of the first magnetic tunnel junction is ΔR1, and the resistance difference of the second magnetic tunnel junction is ΔR2. ΔR1 is not equal to ΔR2, and its corresponding spin-transfer torque STT critical flip current I S1 with I S2 The magnetization directions of reference layers RL1 (40) and RL2 (80) change from state one to state two in response to the SOT current signals of the top and bottom electrodes. The magnetization directions of the reference layers in state one are opposite to those in state two. The STT flip current is input from port one or port four and port two or port three. In response to STT currents of different directions and magnitudes, the magnetization directions of free layers FL1 (20) and FL2 (60) change from state one to state two. The magnetization directions of the free layers in state one are opposite to those in state two. Correspondingly, the resistance of the tunnel junction changes from resistance state one to resistance state two.
5. A data read / write method for a multi-state magnetic memory based on a double-layer magnetic tunnel junction, characterized in that, The multi-state magnetic memory based on a double-layer magnetic tunnel junction as described in any one of claims 1-3 is used. Magnetic storage device cells have at least three input ports. The reading method is as follows: a reading current I is applied to the device unit. R To obtain the total resistance of the current tunnel junction, given the total resistance of the junction region R... 1P +R 2P R 1P +R 2AP R 1AP +R 2P R 1AP +R 2AP Four different resistance states, the reading result must be one of the four resistance states, so as to obtain the relative state of the free layer and the reference layer in the first tunnel junction and the second tunnel junction, that is, parallel or antiparallel. The magnetization direction of the reference layer RL1 (40) in the first tunnel junction remains unchanged, so it can be known that the magnetization direction of the free layer FL1 (20) is parallel or antiparallel. The data bit content stored in the free layer FL1 (20) is obtained. The SOT flip current input from port two is used to initialize the reference layer RL2 (80) of the second tunnel junction so that its magnetization direction becomes state one. Then the reading current is applied again to obtain the current resistance value. If it remains unchanged, the initial magnetization direction of the reference layer RL2 (80) is state one. The data bit content stored in the reference layer RL2 (80) is obtained. If the resistance changes, the initial magnetization direction of the reference layer RL2(80) is state two, and the stored data bits are obtained. The first reading of the tunnel junction resistance value gives the relative state of the free layer FL2(60) of the second tunnel junction with the reference layer RL2(80), from which the magnetization direction of the free layer FL2(60) can be determined, and the data bit content stored in the free layer FL2(60) can be obtained. The writing method is as follows: if the STT critical switching current of the first tunnel junction is less than the STT critical switching current of the second tunnel junction, the STT switching current is input from port two or port three, the magnetization direction of the reference layer RL2 (80) changes to state one or state two, and the data bit stored in the reference layer is "0" or "1"; the STT switching current of the second tunnel junction is input from port one, port two or port three, the magnetization direction of the free layer FL2 (60) changes to be antiparallel or parallel to the reference layer RL2 (80), and the data stored in the free layer is "1" or "0"; The STT switching current of the first tunnel junction is input from port one, port two, or port three. The magnetization direction of the free layer FL1 (20) changes to be antiparallel or parallel to the reference layer RL1 (40). The data stored in the free layer is "0" or "1". If the STT switching current of the first tunnel junction is greater than that of the second tunnel junction, the STT switching current of the first tunnel junction is input first to write the information into the free layer FL1 (20). Subsequently, the SOT switching current and the STT switching current of the second tunnel junction are input sequentially to write the data into the reference layer RL2 (80) and the free layer FL2 (60).
6. The data read / write method for a magnetic memory based on a double-layer magnetic tunnel junction according to claim 5, characterized in that, The ΔR1 of the first tunnel junction is not equal to the ΔR2 of the second tunnel junction, and the corresponding STT critical switching currents are not equal.