Fixed layer of magnetic tunnel junction, and magnetic storage chip and manufacturing method therefor

Abstract

The present invention relates to a fixed layer of a magnetic tunnel junction (MTJ), and a magnetic storage chip and a manufacturing method therefor. Specifically, provided are a new MTJ device structure and a manufacturing method therefor. Specifically, fixed layers are prepared on both sides of a free layer of a conventional MTJ, thereby forming a double-fixed-layer structure. A double-fixed-layer MTJ is a high-spin-polarization ferromagnetic material that exhibits certain differences in coercivity strength and has mutually opposite spin directions after being subjected to a specific magnetization treatment. The structure can achieve, for the first time, a reduction in information writing energy required for both the parallel-to-antiparallel and antiparallel-to-parallel spin transitions between a fixed layer and a free layer of an MTJ.

Description

Magnetic tunnel junction fixed layer, magnetic memory chip, and manufacturing method thereof

[0001] This application claims priority to the Chinese patent application No. 2024106136795, filed on May 17, 2024, and entitled “Magnetic tunnel junction fixed layer, magnetic memory chip, and manufacturing method thereof”, the entire content of which is incorporated herein by reference. TECHNICAL FIELD

[0002] The present application relates to the field of memory chips in integrated circuits, in particular to a fixed layer of a magnetic tunnel junction, a magnetic memory chip formed by the magnetic tunnel junction, and a manufacturing method thereof. BACKGROUND

[0003] Random access memories (such as SRAM, DRAM, etc.) based on metal-oxide-semiconductor field-effect transistors (MOSFET) have been continuously reduced in size in order to pursue high speed, low energy consumption, and high integration. When MOSFET is reduced to nanometer size, standby energy consumption (i.e., volatility) of SRAM and DRAM caused by short channel effect, etc. becomes more and more serious. Magnetic random access memory (MRAM) based on magnetic tunnel junction (MTJ) of spintronic device is the most promising memory chip for large-scale application in the new generation of integrated circuits because it does not require standby energy consumption (non-volatility) when storing information.

[0004] The MTJ constituting the MRAM is composed of a layer of ferromagnetic film with fixed spin direction (referred to as fixed layer or pinned layer) and a layer of ferromagnetic film with controllable spin direction (referred to as free layer or reference layer) sandwiching an insulating tunneling layer (usually MgO). The antiparallel and parallel spin directions of the two layers of magnetic film will form high and low resistance states through the MTJ, respectively used to store numerical information 0 and 1 (or 1 and 0), and measuring the two resistances can read the information, while changing the spin direction of the free layer can write the information.

[0005] The most likely large-scale application at present is to use the spin transfer torque (STT) method to write information to the MTJ. The principle is that the spin electrons in the transmission process from the fixed layer through the insulating tunneling layer into the free layer or from the free layer through the insulating tunneling layer into the fixed layer will produce a magnetic moment that changes the spin direction of the free layer. Electrons have upward and downward spins, and since the number of upward and downward spins is different, a magnetic moment that reverses the free layer can be generated. That is, the greater the difference between the number of upward and downward spins, the easier it is to reverse the magnetization direction of the free layer.

[0006] The difference between the upward and downward spins is the electron spin polarization rate η shown by the following equation (1):

[0007] η = (s + -s - ) / (s + + s - ) (1)

[0008] Here, s + is the number of upward spins, and s - is the number of downward spins. When a free electron passes through a metal ferromagnetic layer, it becomes an electron of the conduction band of the ferromagnetic layer. In general, ferromagnetic materials such as Fe, Co, and Ni are often used, and the number difference (s + >s - ) of the conduction band electrons s + and s - is responsible for the generation of ferromagnetic magnetization, and η is not equal to zero and is a positive finite value.

[0009] When the spin polarization rate of the ferromagnetic material of the fixed layer of a general MTJ is high, the information writing current required to change the spin of the free layer from the anti-parallel (AP) state to the parallel (P) state can be reduced, but the information writing current from the P state to the AP state can increase. When the information writing current is too large, the voltage can damage the tunnel layer of the MTJ, which is one of the important issues of the STT writing method of the MTJ-MRAM. It is a subject of the present invention to reduce the information writing current from the P state to the AP state and from the AP state to the P state. SUMMARY

[0010] In view of the above background and problems, the present invention provides a new magnetic tunnel junction (MTJ) device for a magnetic memory chip and a method of manufacturing the same, which has a fixed layer on both sides of a free layer, i.e., a double fixed layer structure. The double fixed layer is a high spin polarization rate ferromagnetic material having a certain difference in coercive force strength and opposite spin directions by a certain magnetization process. Specifically, as follows:

[0011] The application provides a magnetic tunnel junction for a magnetic storage chip, which is characterized in that the device is composed of a free layer ferromagnetic film structure whose spin direction can be changed during information storage, a first magnesium oxide film and a second magnesium oxide film existing on both sides of the free layer ferromagnetic film structure, a first fixed layer ferromagnetic film structure whose spin direction does not change during information storage existing on the other side of the first magnesium oxide film, and a second fixed layer ferromagnetic film structure whose spin direction does not change during information storage existing on the other side of the second magnesium oxide film; the spin polarization rate of the first fixed layer ferromagnetic film structure and the second fixed layer ferromagnetic film structure is greater than 0.4; the spins of the first fixed layer ferromagnetic film structure, the second fixed layer ferromagnetic film structure and the free layer ferromagnetic film structure are all perpendicular to the plane where the films are located; the coercive force of the first fixed layer ferromagnetic film structure is greater than that of the second fixed layer ferromagnetic film structure, and the coercive force of the second fixed layer ferromagnetic film structure is greater than that of the free layer ferromagnetic film structure.

[0012] The following is a supplementary description of the above: the film structure generally refers to a structure composed of one or more films. The ferromagnetic film structure refers to a structure in which ferromagnetism is the main or the structure mainly exhibits ferromagnetic properties.

[0013] On the basis of the above structure characteristics of the magnetic tunnel junction device for a magnetic storage chip, the structure characteristics are further limited in that the first fixed layer ferromagnetic film structure and the second fixed layer ferromagnetic film structure are composed of at least one ferromagnetic film of Co, Fe, Fe-Co alloy, Fe-Co-B alloy, Co-Mn-X (X=Si, Al) alloy, Co-Fe-X (X=Al, Si) alloy, Co-Cr-X (X=Al, Si) alloy, Co-Cr-Fe-Al alloy, Co-Mn-Al-Si alloy, Co-Mn-Fe-Si alloy, Co-Fe-Al-Si alloy Co-Cr-V-Al alloy, Co-V-Fe-Al alloy.

[0014] The following is a supplementary description of the above: the at least one ferromagnetic film refers to a possible existence of only one ferromagnetic film, or a possible existence of a multilayer film composed of a ferromagnetic film and other components (including ferromagnetic, antiferromagnetic or non-magnetic).

[0015] On the basis of the above structure characteristics of the magnetic tunnel junction for a magnetic storage chip, the structure characteristics are further limited in that when the spin directions of the first fixed layer ferromagnetic film structure, the second layer fixed ferromagnetic film structure and the free layer ferromagnetic film structure are all parallel, the resistance RA R, when the spin direction of the first fixed layer ferromagnetic thin film structure and the second layer fixed ferromagnetic thin film structure is anti-parallel and the spin direction of the second layer fixed ferromagnetic thin film structure and the free layer ferromagnetic thin film structure is parallel B R, when the spin direction of the first fixed layer ferromagnetic thin film structure and the second layer fixed ferromagnetic thin film structure is anti-parallel and the spin direction of the second layer fixed ferromagnetic thin film structure and the free layer ferromagnetic thin film structure is parallel C R A R B R C R C R B R A R A R B R C When the result calculated from (2R

[0016] The following is a supplement to the above: the first fixed layer is the fixed layer of the lower part (or bottom, Bottom, Btm) of the free layer, and the second fixed layer is the fixed layer of the upper part (or top, Top) of the free layer. When the spin of the first fixed layer and the free layer is parallel, the resistance of this part is larger than that when the spin of the second fixed layer and the free layer is parallel, and the resistance difference when the spin of the first fixed layer and the free layer is parallel and anti-parallel is larger than that when the spin of the second fixed layer and the free layer is parallel and anti-parallel. Since there are two fixed layers, each fixed layer and the free layer itself has two resistance states, so the whole device has four resistance states. The storage of information is realized by using the resistance difference before and after changing the spin direction of the free layer when the spin of the first fixed layer and the second fixed layer is opposite. The resistance difference before and after changing the spin direction of the free layer is defined as the magnetic resistance ratio of the whole double fixed layer storage device, that is, MR. The description of the above requirements is actually to calculate the MR value. The value of MR greater than 80% can clearly read the high and low resistance signals of the device.

[0017] For the storage device and its magnetic storage chip with all the above structural characteristics, the manufacturing method contains the following characteristic steps:

[0018] (1.1) First, the substrate preparation for the memory device is performed on the substrate, and then the first fixed layer ferromagnetic film structure, the first magnesium oxide film, the free layer ferromagnetic film structure, the second magnesium oxide film, and the second fixed layer ferromagnetic film structure are sequentially prepared from bottom to top, and then the cover layer preparation for the memory device is performed;

[0019] (1.2) Forming a device with a predetermined pattern;

[0020] (1.3) After the device is completed, a magnetic field perpendicular to the film surface of the device is applied, which is greater than the coercive force H c_Btm of the first fixed layer ferromagnetic film structure, and then the magnetic field is gradually reduced to zero, and then the magnetic field is increased in the opposite direction to be greater than the coercive force H c_Top of the second fixed layer ferromagnetic film structure but less than the coercive force H c_Btm of the first fixed layer ferromagnetic film structure, and then the external magnetic field is removed after staying for 1 minute.

[0021] The above content is supplemented as follows:

[0022] When the device preparation of the actual MRAM chip is performed, the preparation of the CMOS peripheral circuit (including reading, writing, address selection, power supply control, etc.) on the silicon wafer is performed first, and then the preparation of the magnetic storage device film is performed on a certain metal layer of the Back End of Line (BEOL) of the above-mentioned circuit. (1.1) describes the preparation sequence of the related film of the storage device with the structural characteristics of the present application. (1.2) requires two processes of photolithography and etching, each of which contains a large number of steps in the actual process, but they can be designed from the general semiconductor process or by referring to the general MTJ preparation process. (1.3) is an important feature step in the preparation process of the present application, that is, the above-mentioned magnetization process needs to be added in the related steps in the preparation process, so as to form the storage device and chip with the characteristic structure proposed in the present application.

[0023] [Corrected according to Rule 91 on 19.11.2024] The effect of the present application is that through the structure, the information writing current can be reduced when the MTJ is in the P to AP state and the AP to P state. Because the greater the current (voltage), the easier the MgO insulating tunnel layer is damaged. Therefore, the present application can also significantly increase the durability of the insulating tunnel layer of the MTJ, thereby improving the durability of the device. BRIEF DESCRIPTION OF DRAWINGS

[0024] Figure 1 is one of the embodiments of the present application, which is the basic structure of the double fixed layer magnetic tunnel junction MTJ device of the present application with opposite spin electron directions.

[0025] Figure 2 is a schematic diagram of the spin direction of the free layer of a double pinned magnetic tunnel junction (MTJ) device of an embodiment of the present application, showing the spin direction transitioning from up to down (a) and from down to up (b) for opposite spin directions.

[0026] Figure 3 is a schematic diagram of the basic structure of a single pinned magnetic tunnel junction (MTJ) device (a, c) and the information write current (I w ) and the pulse time t sw required for its reversal (b, d) for different spin polarization (η) materials for an embodiment of the present application. (a, b) is from AP to P state, (c, d) is from P to AP state.

[0027] Figure 4 is a schematic diagram illustrating the principle of information write in spin transfer torque mode for a single pinned MTJ for an embodiment of the present application. (a) is from AP to P state, (b) is from P to AP state.

[0028] Figure 5 is a schematic diagram of the information write current (I w ) and the pulse time t sw required for its reversal for different spin polarization (η) materials for the double pinned MTJ of the present application when the spin of the free layer is changing. (a) is the process of the spin of the free layer transitioning from up to down, (b) is the process of the spin of the free layer transitioning from down to up.

[0029] Figure 6 is a schematic diagram of the reversal mechanism of the spin of the free layer for the double pinned MTJ of the present application. (a) is the process of the spin of the free layer transitioning from up to down, (b) is the process of the spin of the free layer transitioning from down to up.

[0030] Figure 7 is a schematic diagram of the magnetization hysteresis loops of the first pinned layer, the free layer, and the second pinned layer of the double pinned MTJ of the present application, from top to bottom.

[0031] Figure 8 is a schematic diagram of the magnetization hysteresis loops of the first pinned layer, the free layer, and the second pinned layer of the double pinned MTJ of the present application, from top to bottom.

[0032] Figure 9 is one of the embodiments of the present application, Figure 9(a) is the variation of the magnetic resistance of the proposed double pinned magnetic tunnel junction of the present application under a large range of magnetic field scan (Major Loop) and under a magnetic field scan smaller than the coercivity of the second pinned layer (Top Pin), i.e. Minor Loop; Figure 9(b) is the magnetization direction of the first pinned layer, free layer, and second pinned layer in each region of (a). DETAILED DESCRIPTION

[0033] The present application will be described with respect to the figures and embodiments. Embodiment 1

[0034] [Corrected according to Rule 91 on 19.11.2024] Figure 1 is one of the embodiments of the present application, it is the basic structure of the double pinned magnetic tunnel junction (MTJ) device of the present application with opposite spin directions. Wherein 1 is the first pinned layer thin film structure, also called the first pinned layer, Pin 1 layer, bottom pinned layer, Bottom Pin, Btm Pin, etc., usually referred to as Btm or Pin 1 in the specification and drawings. 2 is the first magnesium oxide (MgO) thin film. 3 is the free layer thin film structure, also called the free layer, FL layer. 4 is the second magnesium oxide thin film. 5 is the second pinned layer thin film structure, also called the second pinned layer, Pin 2 layer, top pinned layer, Top Pin, etc., usually referred to as Top or Pin2 in the specification and drawings. The magnesium oxide thin films of 2 and 4, in actual processes, can be thin film structures with magnesium oxide as the main component, serving as a tunneling function. Figure 2 is a schematic diagram of the spin direction of the free layer of the double pinned magnetic tunnel junction (MTJ) device with opposite spin directions (a) changing from upward to downward (b) changing from downward to upward. Wherein Up and Down are the upward and downward spin directions of the free layer (FL), respectively. Embodiment 2

[0035] [Corrected according to Rule 91 on 19.11.2024] Figure 3 is one of the embodiments of the present application, it is the basic structure of the commonly used single pinned magnetic tunnel junction (MTJ) device. The pinned layer is usually at the bottom, i.e. between the free layer and the substrate. In Figures 3(a) and (c), 1 is the pinned layer, 2 is the MgO tunneling layer, 3 is the free layer, and 4 is the MgO layer for increasing thermal stability. The right side is a schematic diagram of the spin direction change. In Figure 3(a), the spin directions of the free layer and the pinned layer are anti-parallel (AP), and the right side is a schematic diagram of the spin direction of the free layer and the pinned layer changing from anti-parallel (AP) to parallel (P). Figure 3(b) corresponds to the information writing current (I w ) and the pulse time t swThe experimental simulation results show that as η increases from 0.4 to 0.9, the required information writing current decreases. In Figure 3(c), the spin directions of the free layer and the fixed layer are parallel (P), and the diagram on the right shows the transition from parallel (P) to antiparallel (AP) spin directions of the free layer and the fixed layer. Figure 3(d) corresponds to the information writing current (I) when the MTJ diameter is 30 nm and different spin polarizabilities (η) materials are used during the above P to AP process. w The pulse time t required for its reversal sw The experimental simulation results show that as η increases from 0.4 to 0.9, the required write current increases. Specifically, when the resolution changes from η: 0.4 → 0.9, (a) the write current from AP to P state halves, but (b) the write current from P to AP increases fivefold. This is a major problem with commonly used single-layer fixed-layer MTJs. In typical MTJ devices, increasing the spin polarization of the ferromagnetic layer can reduce the write current in one direction, but simultaneously increases the write current in the other direction. The large write current makes the MgO tunneling layer prone to damage, reducing the performance of the MTJ and its memory chip.

[0036] Figure 4 is one embodiment of the present invention, illustrating the principle of information writing in a single fixed-layer MTJ using the spin transfer moment method. Figure 4(a) shows the principle of magnetization reversal from AP to P between the spin direction of the free layer and the fixed layer. Assuming 10 electrons (with seemingly random spins) flow from the fixed layer to the free layer, these electrons will spin polarize in the fixed layer. Since the spin polarization rate is 0.6, they are roughly divided into 8 downward and 2 upward spins. After these spins reach the free layer, electrons with the same spin as the free layer will be transported outward through the free layer, while electrons with the opposite spin will accumulate in the free layer. After accumulating a certain number, a magnetic moment (i.e., STT) will be generated that reverses the spin in the free layer. Figure 4(b) illustrates the principle of magnetization reversal from P to AP in the free and fixed layers. Assuming 10 electrons (with seemingly random spins) flow from the free layer to the fixed layer, these electrons will spin-polarize in the free layer. Since the spin polarizability is 0.6, according to the definition of spin polarizability, this results in approximately 8 spins down and 2 spins up. Upon reaching the fixed layer, electrons with the same spin as the fixed layer will be transported outward through the fixed layer, while electrons with the opposite spin will return to the free layer and accumulate. After accumulating a certain number, a magnetic moment will be generated that reverses the spin in the free layer. It can be seen that using the same write current, the magnetic moment generated from AP to P is 4 times larger than that from P to AP, which is close to the experimental simulation results in Figures 3(b) and 3(d). Example 3:

[0037] Figure 5 is one of the embodiments of the present application, Figure 5(a) is the simulation result of the information write current (I w ) and the pulse time t sw required for the spin reversal of the free layer of the double fixed layer MTJ of the present application when using different spin polarization rate (η) materials. The MTJ diameter is 30 nm. It can be seen that the information write current required is halved when η increases from 0.4 to 0.9. Figure 5(b) is the simulation result of the information write current (I w ) and the pulse time t sw required for the spin reversal of the free layer of the double fixed layer MTJ of the present application when using different spin polarization rate (η) materials. The MTJ diameter is 30 nm. It can be seen that the information write current required is halved when η increases from 0.4 to 0.9.

[0038] [Corrected according to Rule 91 on 19.11.2024] Figure 6 is one of the embodiments of the present application, which is the spin reversal mechanism of the double fixed layer MTJ of the present application. Figure 6(a) describes that when the spin of the free layer MTJ of the double fixed layer MTJ is up, 10 disordered electrons are passed through the first fixed layer (Pin 1). After the spin polarization of the fixed layer, because the spin polarization rate is 0.6, according to the definition of the spin polarization rate, approximately 8 spins downward and 2 spins upward can be formed. When these spins pass through the free layer, the spins in the same upward direction as the free layer can pass through the free layer, and then flow out through the second fixed layer (Pin 2) whose spin is also upward. The spins in the opposite direction of the free layer (i.e. downward spins) will accumulate in the free layer to form a magnetic moment (i.e. STT), and after a certain accumulation, the magnetization direction of the free layer will change. Figure 6(b) describes that when the spin of the free layer MTJ of the double fixed layer MTJ is down, 10 disordered electrons are passed through the second fixed layer (Pin 2). After the spin polarization of the fixed layer, because the spin polarization rate is 0.6, according to the definition of the spin polarization rate, approximately 8 spins upward and 2 spins downward can be formed. When these spins pass through the free layer, the spins in the same downward direction as the free layer can pass through the free layer, and then flow out through the first fixed layer (Pin 1) whose spin is also downward. The spins in the opposite direction of the free layer (i.e. upward spins) will accumulate in the free layer to form a magnetic moment (i.e. STT), and after a certain accumulation, the magnetization direction of the free layer will change.

[0039] As shown in FIG. 1 and FIG. 2, when two fixed layers are provided on both sides of the free layer, the magnetization directions of the two fixed layers must be opposite. To make the magnetization directions of the two fixed layers opposite, the magnetic anisotropy of the three ferromagnetic materials of the two fixed layers and the free layer must be different. The effective magnetic anisotropy energy constant of the unit volume of the second fixed layer (Btm Pin, Pin 2), the free layer (FL), and the first fixed layer (Top Pin, Pin 1) from top to bottom is defined as K eff_Top , K eff_FL , and K eff_Btm , respectively. When the device is a column with a diameter D of 30 nanometers, the magnetic anisotropy energy constants of the above three layers must satisfy the relationship of equation (2), that is:

[0040] K eff_FL <K eff_Top <K eff_Btm (2)

[0041] When the diameter is 30 nanometers, it can be seen that when the domain structure is, the following relationship (collectively referred to as equation (3)) is obtained:

[0042] K eff_FL =(1 / 2)M _FL H c_FL ,

[0043] K eff_Top =(1 / 2)M Top H c_Top ,

[0044] K eff_Btm =(1 / 2)M Btm H c_Btm

[0045] (3)

[0046] Based on the relationship of equation (2), the coercivity of the diameter 30 nanometer column of the above second fixed layer, free layer, and first fixed layer satisfies the following equation (equation (4)):

[0047] H c_FL <H c _Top <H c _Btm (4)

[0048] Figure 7 is a schematic diagram of the hysteresis loop of a 30 nm diameter cylindrical MTJ stack (Btm Pin / MgO1 / FL / MgO2 / Top Pin) prepared based on the above three-layer structure. When the external magnetic field changes from negative to positive, H = H c_FL at which the magnetization of the free layer is first seen to reverse; then H = H c _Top at which the magnetization of the top second pinned layer reverses; and H = H c_Btm at which the magnetization of the bottom first pinned layer reverses. The hysteresis loop when the magnetic field changes from the minimum magnetic field (-H max ) to the maximum magnetic field (+ H max ) has the following regions:

[0049] Region A: -H max <H<H c_FL

[0050] Region B: H c_FL <H<H c_Top

[0051] Region C: H c _Top <H<H c _Btm

[0052] Region D: H c _Btm <H<H max

[0053] The state of the magnetization direction of the above-mentioned stack of the 30 nm diameter MTJ is shown in Figure 8(a) from regions A to D. In region A, the magnetization direction of the three ferromagnetic layers (second pinned layer, free layer, first pinned layer) is all downward. In region B, the magnetization of the free layer is upward, and the magnetization of the two pinned layers is downward. In region C, the magnetization direction of the top second pinned layer also reverses to upward. In region D, the magnetization direction of the three ferromagnetic layers (second pinned layer, free layer, first pinned layer) is all upward. To make the magnetization direction of the two pinned layers opposite, the magnetization process is as follows: first, the external magnetic field H is changed to - H max , then the external magnetic field H is slowly increased to region C (H c _Top <H<H c _Btm ), and the external magnetic field H is kept at 0 for a period of time. In the above-mentioned magnetization process, the magnetization state of each ferromagnetic layer in each region is shown in Figure 8(b). The magnetization of the top second pinned layer and the free layer is upward, and the magnetization of the bottom first pinned layer is downward. In this state, the partial hysteresis loop measured when the external magnetic field is applied when the free layer changes in the upward and downward directions when the device of the present application is used is shown in Figure 8(c), and the coercivity is H c_FL .

[0054] Figure 9(a) is a schematic diagram of the structure of the double fixed layer MTJ of the present application, in which the top fixed layer (second fixed layer) and the free layer can be considered as a Top magnetic tunnel junction, and the bottom fixed layer (first fixed layer) and the free layer can be considered as a Bottom magnetic tunnel junction. Their low resistance states of magnetoresistance are R2 (second fixed layer) and Rl (first fixed layer), respectively, and the difference between the low resistance and high resistance states are ΔRl and ΔR2, respectively. The magnetoresistance of the bottom and top tunnel junctions are defined as MRl and MR2, respectively. The ratio of R2 to Rl is defined as α, then we have:

[0055] MRl = ΔRl / Rl, MR2 = ΔR2 / R2

[0056] α = R2 / Rl

[0057] (5)

[0058] Figure 9(b) is a graph of the magnetoresistance value change of the double fixed layer magnetic tunnel junction of the present application under a large range of magnetic field scanning (Major Loop) and the magnetization curve under an external magnetic field scanning smaller than the second fixed layer (Top Pin) coercivity, i.e. Minor Loop. The graph below the two magnetization curves is a schematic diagram of the magnetization direction (also called spin direction) of the first fixed layer, free layer, and second fixed layer under the magnetic field region. In the large range of external magnetic field scanning, the regions A and D of the wide area hysteresis loop (left side of Figure 9(b)) have the lowest resistance R A , the resistance of region B is R B , and the resistance of region C is R C . Then we have the following relationships:

[0059] R A = Rl + R2,

[0060] R B = R0 + ΔRl + ΔR2

[0061] R C = Rl + R2 + ΔRl

[0062] (6)

[0063] In the above large range of external magnetic field scanning, the external magnetic field is changed to 0 in region C, and then the partial hysteresis loop is measured under an external field smaller than H c_Top . The graph of the partial hysteresis loop is shown on the right side of Figure 9(b). When the external field is +H c_FL and -H c_FLThe hysteresis loop will generate a single loop. Using the hysteresis loop, 0 and 1 can be stored.

[0064] The minimum resistance of the local hysteresis loop is set to R min , and the maximum resistance is R max , then R min and R max have the following relationship:

[0065] R max = R C = R1 + R2 + ΔR1

[0066] R min = R A + ΔR2 = R1 + R2 + ΔR2

[0067] (7)

[0068] Further, the magnetic resistance ratio MR of the double fixed layer MTJ device can be calculated as follows:

[0069] MR = (ΔR1-ΔR2) / (R1+R2+ΔR2)

[0070] (8)

[0071] Here, assuming that the magnetic resistance ratio of the tunnel junction at the bottom and top of formula (5) is 150% (ΔR1 / R1 = ΔR2 / R2 = 1.5), the MR of the entire stacked MTJ thin film structure device is:

[0072] MR = 1.5(1-α) / (1+2.5α)

[0073] (9)

[0074] When the ratio α of R2 to R1 is 1 / 5, the MR value is 0.8 (MR ratio 80%), when α is 1 / 10, MR is 1.08 (MR ratio 108%), and when α is 1 / 20, MR is 1.33 (MR ratio 133%). From the perspective of signal reading, it is desirable for the MR ratio to be greater than 80%, and the minimum resistance R2 of the top tunnel junction to be lower than 1 / 5 of the minimum resistance of the bottom tunnel junction. A more ideal condition is for the MR ratio to be greater than 100%, and the minimum resistance R2 of the top tunnel junction to be lower than 1 / 10 of the minimum resistance of the bottom tunnel junction.

[0075] After the device according to the present application grows the thin film according to the structure of Fig. 1 and forms the MTJ device according to the general semiconductor process, a magnetic field larger than the coercive force H c_Btm of the first fixed layer ferromagnetic thin film structure is first applied perpendicularly to the film surface of the device, then the magnetic field is gradually reduced to zero, and then the magnetic field is increased in the opposite direction to be larger than the coercive force H c_Top of the second fixed layer ferromagnetic thin film structure but smaller than the coercive force H c_Btm of the first fixed layer ferromagnetic thin film structure, and then the external magnetic field is removed after staying for 1 minute. At this time, the spin directions of the two fixed layers are guaranteed to be opposite, and then the spin direction of the free layer is changed in the range of the current or magnetic field that does not change the spin direction of the second fixed layer, and the reading, writing and storage of information are performed. That is, the preparation of the double fixed layer MTJ device according to the present application is completed.

[0076] The above embodiments only express certain embodiments of the present application, are described in more detail, but should not be understood as limiting the scope of the patent. It should be pointed out that for those skilled in the art, several modifications and improvements can be made without departing from the concept of the present application, and these all belong to the protection scope of the present application. Therefore, the protection scope of the patent of the present application should be subject to the appended claims.

Claims

1. A magnetic tunnel junction for a magnetic memory chip, the magnetic tunnel junction characterized by: The device is composed of a free layer ferromagnetic film structure whose spin direction can be changed during information storage, a first magnesium oxide film and a second magnesium oxide film existing on both sides of the free layer ferromagnetic film structure, a first fixed layer ferromagnetic film structure whose spin direction does not change during information storage existing on the other side of the first magnesium oxide film, and a second fixed layer ferromagnetic film structure whose spin direction does not change during information storage existing on the other side of the second magnesium oxide film; the spin polarization rate of the first fixed layer ferromagnetic film structure and the second fixed layer ferromagnetic film structure is greater than 0.4; the spins of the first fixed layer ferromagnetic film structure, the second fixed layer ferromagnetic film structure and the free layer ferromagnetic film structure are all perpendicular to the plane where the films are located; the coercive force of the first fixed layer ferromagnetic film structure is greater than that of the second fixed layer ferromagnetic film structure, and the coercive force of the second fixed layer ferromagnetic film structure is greater than that of the free layer ferromagnetic film structure.

2. The magnetic tunnel junction for a magnetic memory chip according to claim 1, characterized in that the first fixed layer ferromagnetic film structure and the second fixed layer ferromagnetic film structure are composed of at least one ferromagnetic film of Co, Fe, Fe-Co alloy, Fe-Co-B alloy, Co-Mn-X (X=Si, Al) alloy, Co-Fe-X (X=Al, Si) alloy, Co-Cr-X (X=Al, Si) alloy, Co-Cr-Fe-Al alloy, Co-Mn-Al-Si alloy, Co-Mn-Fe-Si alloy, Co-Fe-Al-Si alloy Co-Cr-V-Al alloy, Co-V-Fe-Al alloy.

3. The magnetic tunnel junction for magnetic memory chip of claim 2, wherein the resistance R A , the resistance R B , the resistance R C , the resistance R A , the resistance R B , the resistance R C , when the spin direction of the first fixed layer ferromagnetic thin film structure, the second layer fixed ferromagnetic thin film structure and the free layer ferromagnetic thin film structure are all parallel, antiparallel and parallel respectively, and the value of MR is greater than 80% when MR is defined as the result calculated by (2R C -R B -R A ) / (R A +R B -R C ).

4. The manufacturing method of the magnetic tunnel junction for a magnetic memory chip according to any one of claims 1 to 3, comprising the following steps: (1) first performing substrate preparation necessary for the memory device on the substrate, then successively preparing the first fixed layer ferromagnetic film structure, the first magnesium oxide film, the free layer ferromagnetic film structure, the second magnesium oxide film and the second fixed layer ferromagnetic film structure from bottom to top, and then performing cover layer preparation of the memory device; (2) forming the device with a predetermined pattern. (3) After the device is completed, a magnetic field greater than the coercivity H c_Btm of the first fixed layer ferromagnetic thin film structure is first applied perpendicular to the film surface of the device, then gradually reduced to zero magnetic field, and then increased in the opposite direction to greater than the coercivity H c_Top of the second fixed layer ferromagnetic thin film structure but less than the coercivity H c_Btm of the first fixed layer ferromagnetic thin film structure, and then removed after staying for 1 minute.

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