Free layer of magnetic tunnel junction, magnetic random access memory chip, and manufacturing method for magnetic tunnel junction

Abstract

The present invention relates to the structure of a free layer of a magnetic tunnel junction (MTJ) as a core device of a magnetic random access memory (MRAM) chip, and a manufacturing method for a magnetic tunnel junction. A free layer is composed of one or more ferromagnetic thin film layers and a coupling superposition layer sandwiched between each pair of adjacent ferromagnetic thin film layers. During information writing, ferromagnetic thin films can each undergo spin reversal, thereby reducing the energy required for information writing; and due to the coupling effect of the ferromagnetic thin film layers, the free layer can still maintain high thermal stability. Thus, the contradiction between low information writing energy and high thermal stability in large-scale applications of an MTJ-based MRAM is resolved.

Description

Magnetic tunnel junction free layer, magnetic storage chip, and manufacturing method thereof

[0001] CROSS-REFERENCE TO RELATED APPLICATIONS

[0002] This application claims priority to the Chinese patent application filed with the China Patent Office on March 5, 2024, with application number 2024102453457 and invention name “Magnetic tunnel junction free layer, magnetic storage chip, and manufacturing method thereof”, the entire contents of which are incorporated by reference into this application. Technical Field

[0003] The present invention relates to the field of memory chips in integrated circuits, and in particular to a free layer of a magnetic tunnel junction, an important component of a new generation of non-volatile magnetic memory, a magnetic storage chip formed by a magnetic tunnel junction, and their manufacturing methods. Background Art

[0004] The standby power consumption (or volatility) of random access memories (RAMs, DRAMs, etc.) based on metal-oxide-semiconductor field-effect transistors (MOSFETs) has become increasingly severe as device sizes have become smaller. Magnetic random access memory (MRAM), based on the spintronic magnetic tunnel junction (MTJ), is the most promising memory chip for large-scale application in next-generation integrated circuits because it does not require standby power consumption to store information. The MTJ that makes up MRAM consists of two ferromagnetic films (one with a fixed spin direction, called the pinned layer, and the other with a controllable spin direction for writing information, called the free layer, or reference layer) sandwiched by an insulating tunneling layer (typically MgO). Opposing and parallel spins in the two magnetic films create high and low resistance states, respectively, used to store information 0 and 1.

[0005] Currently, the most promising method for large-scale application is to use spin transfer torque (STT) to write information to MTJs. The principle is that during the transfer of spin electrons from the fixed layer through the insulating tunneling layer into the free layer, or vice versa, a spin transfer torque is generated that changes the spin direction of the free layer. However, the free layer of MTJ-MRAM using STT writing faces the contradiction between low information writing energy consumption and high thermal stability, which limits its large-scale application.

[0006] Summary of the Invention

[0007] In view of the above background and problems, the present invention proposes an MTJ with a free layer composed of multiple coupled ferromagnetic thin film layers. When information is written, the individual ferromagnetic thin film layers that make up the free layer are reversed separately. Compared with a free layer composed of a single ferromagnetic thin film layer, the energy required for information writing can be significantly reduced. In addition, due to the coupling between the ferromagnetic thin film layers, the thermal stability of the free layer is not reduced. Specifically:

[0008] The present invention provides a magnetic tunnel junction for a magnetic storage chip, characterized in that: a free layer is composed of one or more ferromagnetic thin film layers and a coupling stacking layer sandwiched between all adjacent layers of the ferromagnetic thin film layers to couple adjacent ferromagnetic thin film layers; the coupling stacking layer is composed of two oxide coupling layers and a magnetic insertion layer sandwiched between the two oxide coupling layers; the ferromagnetic thin film layers contain at least one element of cobalt and iron; the two oxide coupling layers are composed of either magnesium oxide or magnesium oxide containing at least one element of iron, cobalt, nickel, zinc, and boron; and the magnetic insertion layer contains at least one element of iron, cobalt, and nickel.

[0009] The following supplementary explanations are provided for the above content:

[0010] Here, more than one ferromagnetic film layer generally refers to two or more ferromagnetic film layers. In the case of two ferromagnetic layers, the coupling stacking layer sandwiched between all adjacent layers of the ferromagnetic film layer to couple the adjacent ferromagnetic film layers is one layer; in the case of three ferromagnetic layers, the coupling stacking layer sandwiched between all adjacent layers of the ferromagnetic film layer to couple the adjacent ferromagnetic film layers is two layers; usually, because all adjacent ferromagnetic film layers are sandwiched between the coupling stacking layer, the number of coupling stacking layers must be one less than the number of ferromagnetic film layers to meet the above claims. The most important feature of the present invention is the structure of the two oxide coupling layers and the magnetic insertion layer sandwiched between the two oxide coupling layers possessed by the coupling stacking layer.

[0011] In the magnetic tunnel junction with the above characteristics, it is further defined as follows: the free layer is sandwiched between magnesium oxide thin film layers. The following supplementary explanation is made to the above content:

[0012] The free layer is sandwiched between two magnesium oxide thin films. One layer serves as the insulating tunneling layer for the magnetic tunnel junction, while the other layer enhances the perpendicular anisotropy of the free layer. The position of the magnesium oxide, acting as the insulating tunneling layer, depends on the relative positions of the pinned and free layers relative to the substrate.

[0013] In the magnetic tunnel junction with the above characteristics, its characteristics are further defined as: the magnetic insertion layer contains at least one non-magnetic element such as boron, silicon, aluminum, tungsten, tantalum, hafnium, zirconium, niobium, molybdenum, titanium, vanadium, chromium, palladium, platinum, etc.; the thickness of the magnetic insertion layer is less than 1 nanometer.

[0014] The following supplementary explanations are provided for the above content:

[0015] The magnetic insertion layer, sandwiched between the two oxide coupling layers in the coupling stack, primarily regulates the coupling between the ferromagnetic thin film layers sandwiching the coupling stack. Therefore, in addition to at least one ferromagnetic element selected from the group consisting of iron, cobalt, and nickel, it may also contain at least one non-magnetic element such as boron, silicon, aluminum, tungsten, tantalum, hafnium, zirconium, niobium, molybdenum, titanium, vanadium, chromium, palladium, or platinum. Furthermore, the thickness of the magnetic insertion layer must not exceed 1 nanometer, otherwise the coupling effect between the ferromagnetic thin film layers will not be achieved effectively.

[0016] In the magnetic tunnel junction of the aforementioned characteristics, the characteristics are further defined as follows: the top view of the free layer is any one of a circle with a diameter between 20 nanometers and 50 nanometers and a non-circular shape with an area between 310 square nanometers and 1960 square nanometers; the coupling energy between any adjacent ferromagnetic film layers of the ferromagnetic film layer is not greater than 0.5 mJ / m 2 .

[0017] The following supplementary explanations are provided for the above content:

[0018] The present invention takes into account the spin-electron reversal mode of the free layer when information is written, and considers the top-view size of the device that can meet the spin-electron reversal mode, that is, the diameter of the circular device is between 20 nanometers and 50 nanometers, and the top-view area of ​​the device is between 310 square nanometers and 1960 square nanometers in the case of non-circular devices. Similarly, based on the spin-electron reversal mode of the free layer when information is written, the coupling energy between any adjacent ferromagnetic film layers is no more than 0.5mJ / m 2 .

[0019] In the magnetic tunnel junction of the aforementioned characteristics, it is further characterized as follows: the coupling stacking layer is thicker than the insulating tunneling layer connecting the free layer and the fixed layer of the magnetic tunnel junction.

[0020] The following supplementary explanations are provided for the above content:

[0021] Considering the MTJ resistance, the thickness of the two oxide coupling layers in the coupling stacking layer must be less than or equal to the thickness of the insulating tunneling layer connecting the free layer and the fixed layer. However, after adding a magnetic insertion layer between the two oxide coupling layers, the thickness of the coupling stacking layer (including the two oxide coupling layers and the magnetic insertion layer sandwiched between the two oxide coupling layers) will be greater than the thickness of the insulating tunneling layer connecting the free layer and the fixed layer. Since the magnetic insertion layer is usually less than 1 nanometer, which is equivalent to several atomic layers, the actual film prepared may not show a clear stratification using a transmission electron microscope (TEM), so what is actually observed in the above coupling stacking layer may be the oxide coupling layer doped with a magnetic insertion layer, or the oxide coupling layer has become thicker, hence the above limitations.

[0022] In the magnetic tunnel junction for a magnetic memory chip with all the above-mentioned structural features, its characteristics are further defined as: the material, composition, and thickness of the ferromagnetic thin film layer at different positions are either the same or different; the material, composition, and thickness of the coupling stacking layer at different positions are either the same or different; the material, composition, and thickness of the oxide coupling layer at different positions are either the same or different; the material, composition, and thickness of the magnetic insertion layer at different positions are either the same or different.

[0023] The following supplementary explanations are provided for the above content:

[0024] Because the present invention aims to use multiple mutually coupled ferromagnetic film layers to replace the traditional single ferromagnetic film layer to serve as the free layer of the magnetic tunnel junction, the changes in the materials, composition, and thickness of the above-mentioned ferromagnetic film layers, coupling stacking layers, oxide coupling layers, and magnetic insertion layers are used to adjust the coupling of multiple ferromagnetic film layers, thereby controlling the spin reversal of each film layer to reduce the information writing energy and maintain a certain thermal stability.

[0025] The method for manufacturing a magnetic tunnel junction for a magnetic storage chip according to all the above claims is characterized by comprising the following main steps:

[0026] (1.1) preparing a first magnesium oxide thin film layer;

[0027] (1.2) forming a first ferromagnetic thin film layer on one side of the first magnesium oxide thin film layer, wherein the first ferromagnetic thin film layer has a magnetization direction perpendicular to the film surface;

[0028] (1.3) forming a first oxide coupling layer on an adjacent surface of the first ferromagnetic thin film layer opposite to the first magnesium oxide thin film layer;

[0029] (1.4) forming a first magnetic insertion layer on an adjacent surface of the first oxide coupling layer opposite to the first ferromagnetic thin film layer;

[0030] (1.5) forming a second oxide coupling layer on an adjacent surface of the first magnetic insertion layer opposite to the first oxide coupling layer;

[0031] (1.6) forming a second ferromagnetic thin film layer having a magnetization direction perpendicular to the film surface on an adjacent surface of the second oxide coupling layer opposite to the first magnetic insertion layer;

[0032] (1.7) A second magnesium oxide thin film layer is formed on the adjacent surface of the second ferromagnetic thin film layer opposite to the second oxide coupling layer.

[0033] The following supplementary explanations are provided for the above content:

[0034] The above-mentioned fabrication method is designed to produce the free layer portion of a magnetic tunnel junction. In actual manufacturing, MTJs can be fabricated in the back-end (BEOL) of a CMOS logic circuit or directly on a wafer. Furthermore, the MTJ's free layer can be fabricated either first or last.

[0035] Based on the above manufacturing method, it is further limited and characterized in that: after the above step (1.6), steps (1.3) to (1.6) are repeated to form a structure in which multiple coupled stacked layers and multiple ferromagnetic thin film layers are alternately stacked.

[0036] The following supplementary explanations are provided for the above content:

[0037] Here, steps (1.3) to (1.6) are repeated to form a structure in which multiple coupled stacked layers and multiple ferromagnetic thin film layers are alternately stacked. However, the structures formed multiple times can be the same or different.

[0038] Based on the above manufacturing method, a further limitation is characterized in that: the ferromagnetic thin film layer is formed by any thin film deposition method of co-sputtering with other target materials, alternating sputtering with other target materials, and directly adding cobalt and iron doping to other target materials and then sputtering.

[0039] Based on the above manufacturing method, a further limitation is characterized in that: the oxide coupling layer is formed by any thin film deposition method of co-sputtering with other target materials, alternating sputtering with other target materials, and directly adding cobalt and iron doping to other target materials and then sputtering.

[0040] [Corrected 19.11.2024 according to Rule 91] Based on the above manufacturing method, it is further limited and characterized in that: the magnetic insertion layer is formed by any thin film deposition method of co-sputtering with other target materials, alternating sputtering with other target materials, and sputtering after directly adding cobalt and iron dopants to other targets. [0040.1] [Corrected 19.11.2024 according to Rule 91] The above requirements respectively restrict the manufacturing methods of the ferromagnetic thin film layer, the oxide coupling layer, and the magnetic insertion layer. [0040.2] [Corrected 19.11.2024 according to Rule 91] The present invention has the following effects: the free layer is composed of multiple ferromagnetic thin film layers, and each ferromagnetic layer undergoes sequential magnetization reversal, thereby significantly reducing the device's information writing current. Simultaneously, by adjusting the coupling between the multiple ferromagnetic thin film layers, thermal stability can be improved. The greater the current (voltage), the more easily the MgO insulating tunneling layer is destroyed. Therefore, the present invention can also significantly increase the durability of the MTJ's insulating tunneling layer, thereby improving the durability of the device. BRIEF DESCRIPTION OF THE DRAWINGS

[0041] FIG1 shows one embodiment of the present invention, which shows the basic structure of a free layer composed of two ferromagnetic thin film layers whose magnetic coupling is regulated by a magnetic insertion layer and a coupling stacking layer sandwiched between the two ferromagnetic thin film layers.

[0042] FIG2 is an embodiment of the present invention, which is a basic structure formed by sandwiching the basic structure of FIG1 between two magnesium oxide thin film layers.

[0043] FIG3 shows one embodiment of the present invention, which shows the basic structure of a free layer consisting of three ferromagnetic thin film layers whose magnetic coupling is regulated by a magnetic insertion layer and a coupling stacking layer sandwiched between the ferromagnetic thin film layers.

[0044] FIG4 shows one embodiment of the present invention, which shows the basic structure of a free layer composed of four ferromagnetic thin film layers whose magnetic coupling is regulated by a magnetic insertion layer and a coupling stacking layer sandwiched between the ferromagnetic thin film layers.

[0045] FIG5 is one of the embodiments of the present invention, which shows the basic structure of a free layer consisting of two ferromagnetic thin film layers whose magnetic coupling is regulated by a magnetic insertion layer and a coupling stacking layer sandwiched between the two ferromagnetic thin film layers. The difference from FIG1 is that the magnetic insertion layer and the oxide coupling layer sandwiching the magnetic insertion layer cannot be clearly distinguished due to the thin magnetic field insertion layer, but the coupling stacking layer is obviously thicker than the insulating tunneling layer.

[0046] FIG6 is one of the embodiments of the present invention, which is the same as FIG5 , but the ferromagnetic film layers constituting the free layer are three layers.

[0047] FIG. 7 is one embodiment of the present invention, which is the same as FIG. 5 , but the number of ferromagnetic thin film layers constituting the free layer is four.

[0048] FIG8 is a schematic diagram illustrating the contradiction between thermal stability, information writing performance, and durability faced by an MRAM having a free layer composed of a single ferromagnetic thin film layer according to one embodiment of the present invention.

[0049] FIG9 is a schematic diagram of a free layer composed of two ferromagnetic thin film layers whose magnetic coupling is regulated by a magnetic insertion layer and a coupling stacking layer sandwiched between the two ferromagnetic thin film layers according to one embodiment of the present invention.

[0050] FIG10 is an embodiment of the present invention, showing how the free layer composed of two ferromagnetic thin film layers in FIG9 generates magnetic reversal under external current when the magnetic coupling between the two ferromagnetic thin film layers is very strong.

[0051] FIG11 is one embodiment of the present invention, showing one way in which the free layer composed of two ferromagnetic thin film layers in FIG9 generates magnetic reversal under external current when the magnetic coupling between the two ferromagnetic thin film layers is relatively weak.

[0052] FIG12 is one embodiment of the present invention, showing one way in which the free layer composed of two ferromagnetic thin film layers in FIG9 generates magnetic reversal under external current when the magnetic coupling between the two ferromagnetic thin film layers is relatively weak.

[0053] FIG13 is one embodiment of the present invention, the device of FIG9 structure, assuming that the ferromagnetic film layer has a thickness of 1.5 nanometers and a diameter of 30 nanometers, at J cpl 0.3mJ / m 2 (two free layers are reversed) and 1.0mJ / m 2 The relationship between the write current and the required inversion time was calculated when both free layers were inverted simultaneously. The results showed that the write current can be significantly reduced when both free layers are inverted separately.

[0054] FIG14 is one embodiment of the present invention, FIG13 J cpl 0.3mJ / m 2 The reversal modes of the magnetization curves on the X-axis and Z-axis at points A, B, and C on the information writing current versus required reversal current time curve (when the two free layers are reversed separately) correspond to Phase 2 and Phase 3 in Figures 11 and 12, respectively.

[0055] FIG15 is one embodiment of the present invention, FIG13 J cpl 1.0mJ / m 2 The reversal modes of the magnetization curves on the X-axis and Z-axis at points D, E, and F on the information writing current versus required reversal current time curve when both free layers are reversed in unison correspond to Phase 4 in FIG. 10 .

[0056] FIG16 is an embodiment of the present invention. In the device of FIG9 structure, it is assumed that the ferromagnetic film layer has a thickness of 1.5 nm, a diameter of 30 nm, and an effective magnetic anisotropy energy of 0.52 mJ / m 2When the relationship between thermal stability Δ and coupling energy is calculated according to the empirical formula, it shows that J cpl At 0.3mJ / m 2 When the thermal stability Δ is greater than 90, it meets the use requirements of MRAM. DETAILED DESCRIPTION

[0057] The present invention will be described below with reference to the accompanying drawings and by way of examples of embodiments.

[0058] Figure 1 shows the basic structure of a free layer (FL) comprising two ferromagnetic thin film layers with magnetic coupling mediated by a magnetic insertion layer, and a coupling stacking layer sandwiched between the two ferromagnetic thin film layers. 2 and 6 are ferromagnetic thin film layers, 3a and 5a are oxide coupling layers, and 4a is a magnetic insertion layer. Oxide coupling layers 3a and 5a and magnetic insertion layer 4a form a coupling stacking layer CPL1. The ferromagnetic thin film layers (2 and 6) both contain at least one of cobalt and iron; the two oxide coupling layers (3a and 5a) are composed of either magnesium oxide or magnesium oxide containing at least one of iron, cobalt, nickel, zinc, and boron; and the magnetic insertion layer 4a contains at least one of iron, cobalt, and nickel.

[0059] [Corrected 19.11.2024 in accordance with Rule 91] Figure 2 illustrates an embodiment of the present invention, comprising the basic structure of the free layer FL of Figure 1 sandwiched between two magnesium oxide thin film layers 1 and 7. The magnesium oxide thin film layer at one end serves as the insulating tunneling layer for the magnetic tunnel junction, while the magnesium oxide thin film layer at the other end serves to enhance the perpendicular anisotropy of the free layer. The position of the magnesium oxide thin film layer, serving as the insulating tunneling layer, depends on the relative positions of the pinned and free layers relative to the substrate.

[0060] Figure 3 illustrates the basic structure of a free layer, one embodiment of the present invention, consisting of three ferromagnetic thin film layers (2, 6a, and 6b) with magnetic coupling mediated by magnetic insertion layers, and coupled stacking layers (CPL1 and CPL2) sandwiched between the ferromagnetic thin film layers. 3a and 5a are oxide coupling layers, which, together with the magnetic insertion layer 4a they sandwich, form coupled stacking layer CPL1. 3b and 5b are oxide coupling layers, which, together with the magnetic insertion layer 4b they sandwich, form coupled stacking layer CPL2.

[0061] [Corrected 19 / 11 / 2024 in accordance with Rule 91] Figure 4 illustrates the basic structure of a free layer, according to one embodiment of the present invention, comprising four ferromagnetic thin film layers (2, 6a, 6b, 6c) magnetically coupled via magnetic insertion layers, and coupled stacking layers (CPL1, CPL2, CPL3) sandwiched between the ferromagnetic thin film layers. Compared to Figure 3, 3c and 5c are added as oxide coupling layers, which, together with the magnetic insertion layer 4c they sandwich, form coupled stacking layer CPL3.

[0062] Figure 5 shows the basic structure of a free layer consisting of two ferromagnetic thin film layers with magnetic coupling mediated by a magnetic insertion layer, and a coupling stacking layer sandwiched between the two ferromagnetic thin film layers. Unlike Figure 2 , the magnetic insertion layer and the oxide coupling layer sandwiching the magnetic insertion layer cannot be clearly distinguished due to the thin magnetic insertion layer. However, the coupling stacking layer (CPL1) is significantly thicker than the insulating tunneling layer (1 or 7). Figures 6 and 7 are similar to Figure 5 and show the basic structure of a free layer consisting of a coupling stacking layer sandwiched between three and four ferromagnetic thin film layers, respectively.

[0063] Figure 8 is a schematic diagram of the contradiction between thermal stability, information writing energy, and durability faced by an MRAM with a single ferromagnetic thin film layer as a free layer, one of the embodiments of the present invention. For an MRAM with a single ferromagnetic thin film layer as a free layer, the higher the thermal stability, the greater the required information writing energy consumption, that is, the greater the write current. The information writing current also has a greater voltage on the insulating tunnel layer, making it easier to break down the insulating tunnel layer and reducing durability. The following is a diagram of thermal stability and data storage retention performance (Retention)

[0064] As a memory, MRAM is usually required to retain data for 10 years in the temperature range of -25 degrees Celsius to 125 degrees Celsius, that is, the data storage retention performance is 10 years. If the free layer is a single ferromagnetic material, the thermal stability constant Δ is expressed as follows: Δ = E b / (k B T)=K eff V / (k B T); V = (π / 4) D 2 tk (1)

[0065] [Corrected 19.11.2024 according to Rule 91] In formula (1), E b is the energy barrier between the “0” state and the “1” state of the free layer, k B is the Boltzmann constant, T is the absolute temperature, K eff is the effective perpendicular magnetic anisotropy energy per unit volume, D is the diameter of the free layer, tk is the thickness of the free layer, K eff V is the effective magnetic anisotropy energy of the free layer.

[0066] In formula (1), the thermal stability constant Δ and K eff V is proportional to the effective magnetic anisotropy of the free layer. Since magnetic anisotropy decreases with increasing temperature, the thermal stability constant Δ is lowest at high temperatures. Therefore, ensuring thermal stability at high temperatures is sufficient. For STT-MTJs, empirically, to maintain data for 10 years, the thermal stability constant Δ at room temperature must be above 90.

[0067] In addition, MRAM chips require that information be written within a temperature range of -25 degrees Celsius to 125 degrees Celsius for 10 16 No degradation, that is, durability (Endurance) is greater than 10 16 The main factor affecting the information writing current is the effective perpendicular magnetic anisotropy of the free layer. According to the literature 1 (JZ Sun "Spin-current interaction with a monodomain magnetic body: A model study", Phys. Rev. B vol. 62, pp570–578 (2000)), the magnitude of the spin current equivalent to the effective magnetic field caused by the magnetization reversal of electron spin can be calculated as follows:

[0068] in, is the Dirac constant, e is the electron charge, η is the spin polarization, J is the current density, K eff tk is the effective magnetic anisotropy of the free layer of the MTJ device. The magnetization reversal caused by the spin current is: θ(τ)=θ0exp(-τ / τ1), 1 / τ1=α+h s (2b)

[0069] In the equation (2b), τ is proportional to the time t(sec) called the Natural time unit. From equation (2b), we know that the free layer magnetization reversal must satisfy 1 / τ1<0, and α+h s <0. That is, h s It is negative (current density J < 0), its absolute value is larger than the magnetic damping constant α, and the larger its absolute value is, the larger -1 / τ1 is, so that high-speed magnetization reversal can be achieved.

[0070] From formula (2a), we can see that h s The magnitude of the free layer's effective magnetic anisotropy energy per unit area, K eff tk is inversely proportional. K eff The larger tk is, the more difficult it is to write information, that is, the larger the current (voltage) is when writing information.

[0071] In summary, the issue that needs to be improved in MTJ is to maintain the thermal stability constant Δ of the free layer above 90 at room temperature while reducing the current (voltage) during information writing.

[0072] [Corrected 19.11.2024 according to Rule 91] FIG9 is a schematic diagram of a free layer composed of two ferromagnetic thin film layers (FL1 and FL2) with magnetic coupling mediated by a magnetic insertion layer and a coupling stack layer sandwiched between the two ferromagnetic thin film layers (FL1 and FL2) according to one embodiment of the present invention. In FIG9, the two ferromagnetic thin film layers FL1 and FL2 have a diameter D and a thickness tk0 and have a common magnetization M s and the effective perpendicular magnetic anisotropy energy per unit volume K eff 1 and K eff 2. The magnetic coupling energy per unit area between FL1 and FL2 is J cpl . Then they can all be defined using magnetic properties as follows: [0072.1] [Corrected 19.11.2024 according to Rule 91] H cpl =J cpl / (M s tk0);H keff 1=2K eff 1 / M s ;H keff 2=2K eff 2 / M s .

[0073] The following Figures 10, 11, and 12 are magnetic reversal modes calculated based on the model of Figure 9 with reference to Reference 2 (K. Nishioka el.al., “Effect of Magnetic Coupling between two CoFeB layers on Thermal Stability in Perpendicular Magnetic Tunnel Junctions with MgO / CoFeB / Insertion Layer / CoFeB / MgO”, IEEE Transactions on Magnetics 58(2), 1-6, 2021.).

[0074] FIG10 is an embodiment of the present invention, in which the free layer composed of two ferromagnetic thin film layers in FIG9 is subjected to magnetic reversal by external current when the magnetic coupling between the two ferromagnetic thin film layers is strong. Region A is where the current density J is less than the critical current density J. crt , FL1 and FL2 cannot undergo magnetization reversal (Phase 0). crt In Region B, FL1 and FL2 are integrated and magnetized (Phase 4). The reversal speed can be calculated using Equation (5). The greater the current density J, the greater the magnetization reversal speed. The conditions in Figure 10 are: H cpl >Hkeff 1 and H cpl >H keff 2. The magnetization between FL1 and FL2 is always parallel. Due to the existence of strong magnetic coupling, the two ferromagnets become one. The magnetization reversal caused by the current can be expressed as follows:

[0075] Among them, τ is the time called natural time unit, h s is the effective magnetic field of the spin current, and α is the magnetic damping coefficient of the two ferromagnets. α is usually 0.013. τ is expressed by the following three equations (Equation 4).

[0076] τ=Ω k (t) / (1+α 2 );Ω k =γH keff ;H keff =(H keff 1+H keff 2) / 2. (4)

[0077] Where γ is the magnetic rotation ratio, Ω k is the ferromagnetic resonance frequency. H keff is the effective perpendicular magnetic anisotropy field.

[0078] The effective magnetic field h generated by the spin current s As shown in formula (6), it is proportional to the current density J and the effective perpendicular magnetic anisotropy magnetic field H keff Inversely proportional.

[0079] in, is the Dirac constant, e is the electron charge, η is the magnetic polarizability of the electron spin at the current density J, and is usually taken as 0.5. From formula (5), we know that in order to reverse the magnetization, 1 / τ1 must be negative, and the larger the absolute value of the negative value, the faster the reversal. Therefore, h is needed s <-α.

[0080] Therefore, the critical current density J for determining whether there is magnetization reversal is crt , available h s =-α to define, then:

[0081] Figures 11 and 12 are two embodiments of the present invention, respectively, showing how the free layer composed of two ferromagnetic thin film layers in Figure 9 generates magnetic reversal when the magnetic coupling between the two ferromagnetic thin film layers is relatively weak. cpl <H keff 1, Hkeff 2-H cpl <H keff 1+H cpl Figure 12 Magnetization reversal needs to satisfy: H cpl <H keff 1, H keff 1+H cpl <H keff 2-H cpl The specific instructions are as follows:

[0082] Magnetic coupling magnetic field H cpl Specific anisotropy magnetic field H keff 1 small (H cpl <H keff 1), the magnetization reversal process is more complicated. The effective magnetic field of FL1 and FL2 during spin current reversal is as follows:

[0083] The normalized magnetic coupling of FL1 and FL2 is defined by h1 and h2 respectively. When the magnetizations of FL1 and FL2 are parallel, they are positively coupled and can be expressed as follows: h1 = H cpl / H keff 1; h2 = H cpl / H keff 2 (9)

[0084] When the magnetizations of FL1 and FL2 are antiparallel, they are negatively magnetically coupled and can be expressed as follows: h1 = -H cpl / H keff 1; h2 = -H cpl / H keff 2 (10)

[0085] The premise of magnetization reversal in the Figure 11 method is that both |h1| and |h2| are smaller than 1, and the directions of the magnetic momentum of FL1 and FL2 are and Use the following formula to determine:

[0086] Among them, τ1 and τ2 are the natural time units of FL1 and FL2 respectively, h s 1 and h s 2 is the effective magnetic field generated by the spin currents of FL1 and FL2 in equation (8). τ1 and τ2 can be expressed as: τ1 = Ω k 1t / (1+α 2 ),τ2=Ω k 2t / (1+α 2 );Ω k 1=γH keff 1,Ω k 2=γH keff2. (12)

[0087] The solution to the above equation is:

[0088] The magnetization reversal of FL1 and FL2, (-τ1 / τ 1_ 1)(-τ2 / τ 1_ 2) It needs to be a positive value. Therefore, when FL1 and FL2 are reversed, (α+h1)+h s 1 and (α+h2)+h s 2 needs to be negative. That is, h s 1<-α(1+h1),h s 2<-α(1+h2).

[0089] The magnetization reversal modes of the two ferromagnetic thin film layers in Figures 11 and 12 are as follows: When the external current is very low, neither FL1 nor FL2 reverses, which is called Phase 0. When the external current increases, the magnetic coupling state can be divided into the following three states: Phase 1, Phase 2, and Phase 3:

[0090] Phase 1: FL1 magnetization reverses while FL2 does not reverse

[0091] From equations (9) and (10), we can see that when FL1 reverses, the values ​​of h1 and h2 change from positive to negative. cpl / H keff 1→-H cpl / H keff 1;h2:H cpl / H keff 2→-H cpl / H keff 2. (14)

[0092] FL1 reverses but FL2 does not reverse when the following conditions are met:

[0093] FL1 reversal conditions:

[0094] FL2 non-reversal conditions:

[0095] Therefore, the conditions that need to be met for Phase 1 to occur are: J crt 1 <J<J crt 2 (16)

[0096] Among them, J crt 1,Jcrt 2,J crt 3 is defined using the following formula.

[0097] Phase 2: FL1 reverses first, then FL2 reverses

[0098] When FL1 reverses, FL2 does not reverse, but after FL1 reverses, FL2 reverses, which is called Phase 2.

[0099] FL1 reversal conditions:

[0100] FL2 non-reversal conditions:

[0101] The conditions for FL2 magnetization reversal after FL1 magnetization reversal are as follows:

[0102] Therefore, the conditions that need to be met for Phase 2 to occur are:

[0103] J crt 1,J crt 2 <J<J crt 3 (19)

[0104] Phase 3: FL1 and FL2 start reversing at the same time, but do not complete reversing at the same time

[0105] The magnetic coupling between FL1 and FL2 is not as strong as the integrated reversal. Since FL1 and FL2 are not integrated reversal, they maintain their interaction and reverse separately, and the reversal ends at different times. The following relationship must be met:

[0106] FL1 reversal conditions:

[0107] FL2 reversal conditions:

[0108] That is, the conditions that need to be met for Phase 3 to occur are: J crt 3 <J.

[0109] (20)

[0110] FIG13 is one embodiment of the present invention, the device of FIG9 structure, assuming that the ferromagnetic film layer has a thickness of 1.5 nanometers and a diameter of 30 nanometers, at J cpl 0.3mJ / m 2 (two free layers are reversed) and 1.0mJ / m2 The calculated information writing current (I w ) and reversal time (t sw The results show that the write current can be significantly reduced when the two are reversed.

[0111] FIG14 is one embodiment of the present invention, FIG13 J cpl 0.3mJ / m 2 The plot of the relationship between write current and required reversal time shows the reversal of the magnetization curves at points A, B, and C on the X and Z axes when the information is written (both free layers are reversed separately). A corresponds to Phase 2, while B and C correspond to Phase 3. The results show that at a write current of 98.2 μA, FL1 and FL2 in Phase 3 begin reversing simultaneously, completing the reversal within 10 nanoseconds. Reducing the current, in accordance with Phase 2, results in FL1 reversing first and FL2 later, but the required reversal time increases.

[0112] [Corrected 19.11.2024 according to Rule 91] FIG15 is one embodiment of the present invention. cpl 1.0mJ / m 2 The reversal of the magnetization curves at points D, E, and F on the X-axis and Z-axis on the relationship curve between the information writing current and the required reversal time when the two free layers are reversed as a whole corresponds to Phase 4 in Figure 10, that is, the integrated reversal of FL1 and FL2. At this time, a write current of 184.3 microamperes is required to complete the reversal within 10 nanoseconds. This write current is the J in Figure 14. cpl 0.3mJ / m 2 The current required for the two free layers to reverse simultaneously in Phase 3 is almost twice the current (98.2 microamperes). Therefore, the magnetic tunnel junction structure of the present invention, in which the free layer is composed of multiple ferromagnetic film layers, adjusts the magnetic coupling between the ferromagnetic layers, and causes each ferromagnetic film to reverse independently, significantly reduces the information writing current compared to the conventional method of using a large ferromagnetic film layer as the free layer, thereby significantly improving the durability of the magnetic tunnel junction (MTJ).

[0113] FIG16 is an embodiment of the present invention. In the device of FIG9 structure, it is assumed that the ferromagnetic film layer has a thickness of 1.5 nm, a diameter of 30 nm, and an effective magnetic anisotropy energy of 0.52 mJ / m 2 When the relationship between thermal stability Δ and coupling energy is calculated according to the empirical formula, it shows that J cpl At 0.3mJ / m 2When the thermal stability Δ is greater than 90, it meets the use requirements of MRAM. This further confirms the effect of the present invention: while maintaining high thermal stability, it reduces the information writing current and improves the durability of the magnetic tunnel junction MTJ.

[0114] All of the above embodiments merely represent certain implementations of the present invention, and the descriptions are relatively specific, but they should not be construed as limiting the scope of the patent. It should be noted that a person of ordinary skill in the art may make various modifications and improvements without departing from the spirit of the present invention, and these modifications and improvements fall within the scope of protection of the present invention. Therefore, the scope of protection of the patent for this invention shall be based on the appended claims.

Claims

1. A magnetic tunnel junction for a magnetic storage chip, characterized in that: The free layer is composed of one or more ferromagnetic film layers and a coupling stacking layer sandwiched between all adjacent layers of the ferromagnetic film layers to couple adjacent ferromagnetic film layers; the coupling stacking layer is composed of two oxide coupling layers and a magnetic insertion layer sandwiched between the two oxide coupling layers; the ferromagnetic film layers contain at least one element of cobalt and iron; the two oxide coupling layers are composed of magnesium oxide and magnesium oxide containing at least one element of iron, cobalt, nickel, zinc, and boron; and the magnetic insertion layer contains at least one element of iron, cobalt, and nickel.

2. The magnetic tunnel junction according to claim 1, wherein: The free layer is sandwiched between magnesium oxide thin film layers.

3. The magnetic tunnel junction according to claim 2, wherein: The magnetic insertion layer contains at least one non-magnetic element such as boron, silicon, aluminum, tungsten, tantalum, hafnium, zirconium, niobium, molybdenum, titanium, vanadium, chromium, palladium, platinum, etc.; the thickness of the magnetic insertion layer is less than 1 nanometer.

4. The magnetic tunnel junction according to claim 2, wherein: The top view of the free layer is any one of a circle with a diameter between 20 nanometers and 50 nanometers and a non-circular shape with an area between 310 square nanometers and 1960 square nanometers; the coupling energy between any adjacent ferromagnetic film layers of the ferromagnetic film layer is not greater than 0.5 mJ / m 2 .

5. The magnetic tunnel junction according to claim 2, wherein: The coupling stacking layer is thicker than the insulating tunneling layer connecting the free layer and the fixed layer of the magnetic tunnel junction.

6. The magnetic tunnel junction for a magnetic storage chip according to any one of claims 1 to 5, wherein: The material, composition, and thickness of the ferromagnetic thin film layer at different positions are either the same or different; the material, composition, and thickness of the coupling stacking layer at different positions are either the same or different; the material, composition, and thickness of the oxide coupling layer at different positions are either the same or different; the material, composition, and thickness of the magnetic insertion layer at different positions are either the same or different.

7. A method for manufacturing a magnetic tunnel junction for a magnetic storage chip as claimed in claim 2, characterized in that The main steps include: (1.1) preparing a first magnesium oxide thin film layer; (1.2) forming a first ferromagnetic thin film layer on one side of the first magnesium oxide thin film layer, wherein the first ferromagnetic thin film layer has a magnetization direction perpendicular to the film surface; (1.3) forming a first oxide coupling layer on an adjacent surface of the first ferromagnetic thin film layer opposite to the first magnesium oxide thin film layer; (1.4) forming a first magnetic insertion layer on an adjacent surface of the first oxide coupling layer opposite to the first ferromagnetic thin film layer; (1.5) forming a second oxide coupling layer on an adjacent surface of the first magnetic insertion layer opposite to the first oxide coupling layer; (1.6) forming a second ferromagnetic thin film layer having a magnetization direction perpendicular to the film surface on an adjacent surface of the second oxide coupling layer opposite to the first magnetic insertion layer; (1.7) A second magnesium oxide thin film layer is formed on the adjacent surface of the second ferromagnetic thin film layer opposite to the second oxide coupling layer.

8. The method for manufacturing a magnetic tunnel junction according to claim 7, wherein: After step (1.6), steps (1.3) to (1.6) are repeated to form a structure in which multiple coupled stacked layers and multiple ferromagnetic thin film layers are alternately stacked.

9. The method for manufacturing a magnetic tunnel junction according to claim 7 or 8, wherein: The ferromagnetic thin film layer is formed by co-sputtering with other target materials, alternately sputtering with other target materials, or directly adding cobalt and iron doping into other target materials and then sputtering.

10. The method for manufacturing a magnetic tunnel junction according to claim 7 or 8, wherein: The oxide coupling layer is formed by using any thin film deposition method, including co-sputtering with other target materials, alternate sputtering with other target materials, and sputtering after directly adding cobalt and iron doping into other target materials.

11. The method for manufacturing a magnetic tunnel junction according to claim 7 or 8, wherein: The magnetic insertion layer is formed by using any thin film deposition method, including co-sputtering with other target materials, alternate sputtering with other target materials, and sputtering after directly adding cobalt and iron doping into other target materials.

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