Dual-pinned magnetic tunnel junction, magnetic memory chip and manufacturing methods therefor

Abstract

The present invention relates to the field of magnetic memory chips in integrated circuits, and in particular to a dual-pinned magnetic tunnel junction, a magnetic memory chip and manufacturing methods therefor. The present invention provides a dual-pinned magnetic tunnel junction, a magnetic memory chip and manufacturing methods therefor. The dual-pinned magnetic tunnel junction comprises a structure in which a bottom pin layer is formed by three ferromagnetic thin film structure layers by means of anti-parallel coupling. Then, the thickness and material of each ferromagnetic thin film structure layer of the structure are provided from the perspective of a coupling magnetic field from the bottom pin layer to a free layer, and the structure of a top pin layer is further provided on the basis of the bottom pin layer. The present invention provides manufacturing methods for a dual-pinned magnetic tunnel junction and a magnetic memory chip. The present invention greatly reduces the energy consumption for writing information into STT-MTJ-based MRAM chips, greatly increases the durability of the STT-MTJ-based MRAM chips, and achieves the large-scale application of MRAMs as replacements for DRAMs and SRAMs.

Description

Double-fixed-layer magnetic tunnel junction, magnetic memory chip, and its manufacturing method Technical Field

[0001] This invention relates to the field of magnetic storage chips in integrated circuits, specifically to a double fixed-layer magnetic tunnel junction, a magnetic storage chip, and a method for manufacturing the same. Background Technology

[0002] A magnetic tunnel junction (MTJ) consists of two ferromagnetic thin-film structures sandwiching a tunneling layer of insulating oxide (usually MgO). By fixing the spin direction (also called magnetization direction) of one ferromagnetic thin-film structure (fixed layer) of the MTJ and changing the spin direction of the other ferromagnetic thin-film structure (free layer), two different resistance states can be generated. This can be used for storing and reading digital information "0" and "1", thus enabling its application in magnetic random access memory (MRAM).

[0003] MRAMs based on spin transfer moment (STT) MTJs have high write energy, resulting in poor durability, as the high write energy can easily damage the insulator of the tunneling layer. Since STT writes are achieved by the magnetic torque generated by the spin polarization of the current in the fixed layer, which changes the spin direction of the free layer, a greater difference in the number of upward and downward spins generated during spin polarization in the fixed layer will decrease the write current from one state to another (e.g., from parallel to antiparallel) and increase the write current for the opposite process (corresponding to from antiparallel to parallel). Conversely, a smaller difference in the number of upward and downward spins will also decrease the write current. Therefore, a dual-fixed-layer STT-MTJ and its MRAM structure and manufacturing method (Chinese Patent: CN2024106136795) has been proposed. Furthermore, considering the ease of manufacturing the top fixed layer, coercivity, and the coupling magnetic field between the fixed layer and the free layer, a dual-fixed-layer STT-MTJ and its MRAM structure and manufacturing method has been further proposed (Chinese Patent: CN2024110822877).

[0004] The aforementioned proposals did not simultaneously discuss the influence of the top and bottom fixed layers of the dual-fixed-layer structure on the free layer, and in particular, did not specify the structure of the bottom fixed layer. This invention proposes the structure and fabrication method of the top and bottom fixed layers of a dual-fixed-layer magnetic tunnel junction and the MRAM composed thereof, considering the coupling angle between the top fixed layer thin film structure (hereinafter referred to as the top fixed layer, Top, or Top Pin) and the bottom fixed layer thin film structure (hereinafter referred to as the bottom fixed layer, Bottom, or Btm, or Btm Pin), and the magnetization direction of the fabricated dual-fixed-layer magnetic tunnel junction. Designing the bottom fixed layer of an MRAM using conventional methods can lead to several problems, as explained below:

[0005] Figure 7(A) shows the structure of an MTJ fixed layer (left) composed of a single ferromagnetic thin film structure and an MTJ fixed layer (right) composed of two antiparallel coupled ferromagnetic thin film structures. The coupling layers between the ferromagnetic thin film structures and between them and the free layer are omitted. In the case of a single ferromagnetic thin film structure fixed layer, the fixed layer exerts both static magnetic field and exchange coupling forces on the free layer. Therefore, the force exerted by the fixed layer on the free layer is relatively large, which is detrimental to information writing (i.e., spin inversion) into the free layer. In the case of the two antiparallel coupled ferromagnetic thin film structures on the right, the magnetic moment (also called magnetization) of the ferromagnetic material Pin 1, which is closer to the free layer, is usually smaller than that of Pin 2, which is farther from the free layer. Pin 1 exerts both static magnetic field and exchange coupling on the adjacent free layer. When the magnetic moment of Pin 1 is small, both of these effects are relatively small, especially the exchange coupling, which can be almost negligible. Although the magnetic moment far from Pin 2 is relatively large, the static magnetic force and exchange coupling force generated by the adjacent free layer are also relatively small due to the distance from the free layer. Figure 7(B) is a schematic diagram of the hysteresis loop when the fixed layer of the MTJ in Figure 7(A) generates magnetic coupling with the free layer. Although the effect of exchange coupling on the free layer is negligible, the static magnetic force of Pin 1 and Pin 2 will generate a coupling magnetic field (H) on the free layer. biasFor the structure in Figure 7(A), assume the free layer is a CoFeB alloy film with a thickness of x nanometers, where x is typically less than 3 nanometers. The ferromagnetic film structure in the fixed layer is usually a multilayer repeating structure of Co and Pt composite, denoted as (Co / Pt)z. In the MTJ fixed layer of the single ferromagnetic film structure in Figure 7(A), z is L, while in the MTJ fixed layers of the two antiparallel coupled ferromagnetic film structures, z for Pin 1 and Pin 2 are M and N, respectively. Since Pin 1 and Pin 2 are both based on the same main structure (Co / Pt)z, the number of repetitions of the main structure is positively correlated with the magnetic moments of Pin 1 and Pin 2. As mentioned earlier, the magnetic moment of Pin 1 needs to be smaller than that of Pin 2, so M < N. With the same main structure, by adjusting the thickness of the ferromagnetic thin film structure or the number of repetitions z of the main structure (Co / Pt), the main parameters of the magnetic properties (including saturation magnetic moment, coercivity, and coupling of the fixed layer to the free layer) can be affected, thus creating the thickness-related limitations (here, the number of layers) in the claims. Using a commonly used Co with a thickness of less than 0.8 nm and Pt with a thickness of less than 0.5 nm to form a (Co / Pt) structure, Figure 7(C) compares the coupling magnetic fields of the fixed layer to the free layer when z is an integer L less than 9 in the MTJ fixed layer of a single ferromagnetic thin film structure (Pin 1), and z is M (< 4) and N (< 6) in the MTJ fixed layers of Pin 1 and Pin 2 of two antiparallel coupled ferromagnetic thin film structures, respectively, and L = M + N. As shown in Figure 7(C), for MTJ diameters between 10 nm and 80 nm, the coupling magnetic field generated by the MTJ fixed layer of two antiparallel coupled ferromagnetic thin film structures on the free layer is much smaller than that of a fixed layer composed of a single ferromagnetic thin film structure. The smaller the coupling magnetic field (also known as coupling bias), the less energy is required for free layer reversal.

[0006] Based on the above, the influence of the top fixed layer is further considered. Figure 8(A) is a schematic diagram of a double-fixed-layer MTJ structure, where both the top and bottom fixed layers consist of two antiparallel coupled ferromagnetic thin film structures, and the magnetic moment of the ferromagnetic thin film structure near the free layer in the two fixed layers is smaller. The purpose of using a smaller magnetic moment structure in the ferromagnetic thin film structure near the free layer in the fixed layer is to reduce the coupling magnetic field of the fixed layer to the free layer. However, when the structure in Figure 8(A) is excited by a magnetic field of 10 kOe and then removed from the external magnetic field, as shown in Figure 8(B), the spin directions of the ferromagnetic thin film structure near the free layer in the top fixed layer are parallel to those of the ferromagnetic thin film structure near the free layer in the bottom fixed layer. In this case, information cannot be written according to the double-fixed-layer STT-MTJ proposed in the previous proposal (Chinese Patent: CN2024106136795), so it cannot be applied.

[0007] In Figure 9, the MTJ consists of two antiparallel coupled ferromagnetic thin film structures in both the top and bottom fixed layers. The ferromagnetic thin film structure near the free layer in the bottom fixed layer has a larger magnetic moment, while the ferromagnetic thin film structure near the free layer in the top fixed layer has a smaller magnetic moment. In this case, the spin directions of the ferromagnetic thin film structures near the free layer in the top and bottom fixed layers are antiparallel. Therefore, the coupled magnetic fields of the top and bottom fixed layers to the free layer will cancel each other out, resulting in a smaller coupled magnetic field, which is theoretically usable.

[0008] Figure 10(A) is a schematic diagram of the bottom fixed layer and free layer of a double-fixed-layer MTJ, where the bottom fixed layer is composed of two antiparallel coupled ferromagnetic thin film structures, and the ferromagnetic thin film structure closer to the free layer has a larger magnetic moment. As shown in Figure 10(B), with a free layer of 2.3 nm and distances of 0.9 nm between the free layer and Pin 1, and between Pin 1 and Pin 2, different thicknesses of Pin 1 and Pin 2 were set. The coupling magnetic fields of the fixed layer to the free layer under different MTJ diameters are shown in Figure 10(C). For STT-MTJs with diameters below 20 nm, where large-scale application is possible, the coupling magnetic fields under all three conditions are greater than 1000 Oe; for diameters of 40 nm, the coupling magnetic fields under all three conditions are greater than 750 Oe. Considering that the coupling magnetic fields generated by the top and bottom fixed layers can partially cancel each other out, it is believed that a coupling magnetic field generated by either fixed layer of the double-fixed-layer MTJ is less than 750 Oe for large-scale application. When the MTJ is below 40 nanometers, the coupling magnetic field generated by the bottom fixing layer is greater than 750 Oe, so this structure is difficult to produce large-scale applications.

[0009] To address the aforementioned issues, this invention first proposes a dual-fixed-layer magnetic tunnel junction (MTJ), a magnetic storage chip, and its manufacturing method. The MTJ comprises a bottom fixed layer formed by antiparallel coupling of three ferromagnetic thin-film structures. The thickness and materials of each ferromagnetic thin-film structure are then proposed from the perspective of the coupling magnetic field between the bottom fixed layer and the free layer. Furthermore, the structure of the top fixed layer is proposed based on the bottom fixed layer. Simultaneously, the dual-fixed-layer MTJ of the proposed structure and its manufacturing method are also proposed. Summary of the Invention

[0010] Based on the above background and problems, this invention proposes a dual-fixed-layer magnetic tunnel junction, a magnetic storage chip, and a method for manufacturing the same. Specifically:

[0011] A double-fixed-layer magnetic tunnel junction, comprising, from near to far from the substrate, a bottom fixed-layer thin film structure, a bottom tunneling layer oxide thin film structure, a free layer thin film structure, a top tunneling layer oxide thin film structure, and a top fixed-layer thin film structure; the bottom fixed-layer thin film structure, from near to far from the free layer, comprises, from near to far from the free layer, a bottom first ferromagnetic thin film structure with a spin direction opposite to that of the ferromagnetic thin film structure closest to the free layer in the top fixed-layer thin film structure, a bottom first antiparallel coupled thin film structure, a bottom second ferromagnetic thin film structure with a spin direction opposite to that of the bottom first ferromagnetic thin film structure, a bottom second antiparallel coupled thin film structure, and a bottom third ferromagnetic thin film structure with a spin direction opposite to that of the bottom second ferromagnetic thin film structure; the thicknesses D1 of the bottom first ferromagnetic thin film structure, D2 of the bottom second ferromagnetic thin film structure, and D3 of the bottom third ferromagnetic thin film structure satisfying D1 < D2 and D1 < D3 and 0.29 < D2 / (D1+D2+D3) < The relationship is 0.5.

[0012] The following supplementary explanation is provided: The top fixed-layer thin-film structure in this proposal is also composed of multiple ferromagnetic thin-film structures. However, the spin directions of the ferromagnetic thin-film structure closest to the free layer in the top fixed-layer thin-film structure must be opposite to those of the ferromagnetic thin-film structure closest to the free layer in the bottom fixed-layer thin-film structure. This is the basis for enabling the dual fixed-layer MTJ of this invention to perform STT information writing. All thin-film structures in this specification refer to structures composed of one or more thin films. Specifically, a fixed-layer thin-film structure refers to a one- or multi-layer thin-film structure with ferromagnetism as its primary property, serving as the fixed layer of the magnetic tunnel junction. A bottom tunneling layer oxide thin-film structure refers to a one- or multi-layer thin-film structure primarily composed of oxides, serving as the tunneling layer of the magnetic tunnel junction. A free-layer thin-film structure refers to a one- or multi-layer thin-film structure primarily composed of ferromagnetic thin films, serving as the free layer of the magnetic tunnel junction. In other words, a certain thin-film structure refers to a one- or multi-layer thin-film structure primarily composed of a certain (main characteristic or main material). The aforementioned fixed-layer thin-film structure can also be called a fixed layer; similarly, free-layer thin-film structures can also be simply referred to as free layers. Since the main components of the bottom first ferromagnetic thin film structure, the bottom second ferromagnetic thin film structure, and the bottom third ferromagnetic thin film structure are the same in this proposal, this proposal adjusts the main parameters of magnetic properties (including saturation magnetic moment, coercivity, and coupling of the fixed layer to the free layer) by adjusting the thickness of the ferromagnetic thin film structure, thereby generating the above-mentioned thickness-related limitations, as detailed in the embodiments.

[0013] According to the double-fixed-layer magnetic tunnel junction provided by the present invention, the bottom first ferromagnetic thin film structure is composed of an integer n repeating structures of two thin films, a cobalt metal thin film and a platinum thin film, arranged from near to far from the substrate, upon which a cobalt metal thin film and a cobalt-iron-boron alloy thin film are deposited sequentially, and the integer n is 0 or 1; the bottom second ferromagnetic thin film structure is composed of an integer m repeating structures of two thin films, a cobalt metal thin film and a platinum thin film, arranged from near to far from the substrate, upon which a cobalt metal thin film is deposited; the bottom third ferromagnetic thin film structure is composed of an integer l repeating structures of two thin films, a cobalt metal thin film and a platinum thin film, arranged from near to far from the substrate, upon which a cobalt metal thin film is deposited.

[0014] To further clarify the above: The integer x repeating structures of a cobalt (Co) thin film and a platinum (Pt) thin film are usually denoted as (Co / Pt)x, representing x (x=n, m, l) repeating structures of the Co-on-Pt structure. This can be extrapolated to other structures. The cobalt-iron-boron alloy of the bottom first ferromagnetic thin film structure is essential for the formation of the subsequent magnesium oxide tunneling layer. Based on some experimental and simulation results, a smaller thickness of the bottom first ferromagnetic thin film structure reduces the coupling magnetic field generated by the bottom fixed layer on the free layer. The relationships between n, m, and l mentioned above are also derived from the aforementioned thickness relationships.

[0015] The double-fixed-layer magnetic tunnel junction provided by the present invention includes the following structure:

[0016] (1.1) The top fixing layer thin film structure is composed of a top first ferromagnetic thin film structure, a top first antiparallel coupling thin film structure, a top second ferromagnetic thin film structure with the opposite spin direction to the top first ferromagnetic thin film structure, a top first oxide coupling thin film structure, and a top third ferromagnetic thin film structure with the same spin direction as the top second ferromagnetic thin film structure, arranged from near to far from the substrate; the top of the top fixing layer thin film structure is composed of a magnesium oxide thin film for improving magnetic vertical anisotropy.

[0017] (1.2) The top fixing layer thin film structure is composed of a top first ferromagnetic thin film structure, a top first antiparallel coupling thin film structure, a top second ferromagnetic thin film structure with the opposite spin direction to the top first ferromagnetic thin film structure, a top first oxide coupling thin film structure, a top third ferromagnetic thin film structure with the same spin direction as the top second ferromagnetic thin film structure, a top second oxide coupling thin film structure, and a top fourth ferromagnetic thin film structure with the same spin direction as the top third ferromagnetic thin film structure, from near to far from the substrate. The top of the top fixing layer thin film structure is composed of a magnesium oxide thin film structure for improving magnetic vertical anisotropy.

[0018] (1.3) The top fixing layer thin film structure is composed of a top first ferromagnetic thin film structure, a top first oxide coupling thin film structure, a top second ferromagnetic thin film structure with the same spin direction as the top first ferromagnetic thin film structure, a top first antiparallel coupling thin film structure, a top third ferromagnetic thin film structure with the opposite spin direction to the top second ferromagnetic thin film structure, a top second oxide coupling thin film structure, and a top fourth ferromagnetic thin film structure with the same spin direction as the top third ferromagnetic thin film structure, from near to far from the substrate. The top of the top fixing layer thin film structure is composed of an antiferromagnetic thin film structure for spin pinning.

[0019] (1.4) The top fixing layer thin film structure is composed of a top first ferromagnetic thin film structure, a top first oxide coupling thin film structure, a top second ferromagnetic thin film structure with the same spin direction as the top first ferromagnetic thin film structure, a top first antiparallel coupling thin film structure, a top third ferromagnetic thin film structure with the opposite spin direction to the top second ferromagnetic thin film structure, a top second oxide coupling thin film structure, a top fourth ferromagnetic thin film structure with the same spin direction as the top third ferromagnetic thin film structure, a top third oxide coupling thin film structure, and a top fifth ferromagnetic thin film structure with the same spin direction as the top fourth ferromagnetic thin film structure, from near to far from the substrate. The top of the top fixing layer thin film structure is composed of a magnesium oxide thin film structure for improving magnetic vertical anisotropy.

[0020] (1.5) The top fixing layer thin film structure is composed of a top first ferromagnetic thin film structure, a top first antiparallel coupling thin film structure, a top second ferromagnetic thin film structure with the opposite spin direction to the top first ferromagnetic thin film structure, a top first oxide coupling thin film structure, a top third ferromagnetic thin film structure with the same spin direction as the top second ferromagnetic thin film structure, a top second antiparallel coupling thin film structure, and a top fourth ferromagnetic thin film structure with the opposite spin direction to the top third ferromagnetic thin film structure, from near to far from the substrate. The top of the top fixing layer thin film structure is composed of an antiferromagnetic thin film structure for spin pinning.

[0021] The following is a supplementary explanation of the above five novel MTJ structures: The above five structures were proposed after the bottom fixed layer structure was determined. Considering how to arrange the spin directions of the ferromagnetic layers of the bottom and top fixed layers in a predetermined manner after the magnetic tunnel junction is formed, and considering factors such as minimizing the coupling magnetic field of the top fixed layer to the free layer, the proposals were made for the top fixed layer.

[0022] According to the double-fixed-layer magnetic tunnel junction provided by the present invention, the material of the antiparallel coupled thin film structure is usually either ruthenium or iridium; the oxide coupled thin film structure is composed of magnesium oxide containing either iron or cobalt plus boron and being thicker than the magnesium oxide tunneling layer, iron oxide, and any one of the following: iron oxide and cobalt oxide.

[0023] According to the double-fixed-layer magnetic tunnel junction provided by the present invention, the antiferromagnetic thin film structure contains at least one antiferromagnetic material selected from manganese-platinum alloy or manganese-iridium alloy.

[0024] To further clarify the above: In this proposal, the spin direction of the multilayer ferromagnetic thin film structure needs to be arranged in an antiparallel manner through antiparallel coupling, while oxide coupling is used to form a parallel spin direction arrangement.

[0025] On the other hand, the present invention also provides a method for manufacturing a dual-fixed-layer magnetic tunnel junction magnetic memory chip based on a dual-fixed-layer magnetic tunnel junction, comprising the following steps:

[0026] (2.1) Fabrication of the peripheral circuitry for the magnetic storage chip on the substrate;

[0027] (2.2) Fabrication of the bottom electrode of the magnetic tunnel junction on the metal interconnect layer of the peripheral circuit;

[0028] (2.3) Prepare the connection layer between the bottom electrode and the bottom fixing layer thin film structure;

[0029] (2.4) Prepare the bottom first ferromagnetic thin film structure, the bottom first antiparallel coupling thin film structure, the bottom second ferromagnetic thin film structure, the bottom second antiparallel coupling thin film structure, and the bottom third ferromagnetic thin film structure containing the bottom fixed layer thin film structure;

[0030] (2.5) Prepare the bottom tunneling layer oxide thin film structure;

[0031] (2.6) Prepare the free layer thin film structure;

[0032] (2.7) Prepare the top tunneling layer oxide thin film structure;

[0033] (2.8) Prepare the top fixing layer thin film structure;

[0034] (2.9) Prepare a top protective layer;

[0035] (2.10) A device for patterning thin films to form magnetic storage chips;

[0036] (2.11) Connect and package the devices to form a chip.

[0037] To further clarify the above, the actual fabrication of MRAM chips is very complex. The steps described above are only the main steps related to the structure of this proposal during the formation and fabrication of MRAM chips. Many details exist between and before / after these steps, which are omitted here due to space limitations, but do not affect the characteristic steps claimed in this invention.

[0038] According to the manufacturing method of the dual fixed-layer magnetic tunnel junction magnetic memory chip provided by the present invention, after any step of preparing the top fixed-layer thin film structure, preparing the top protective layer, patterning the thin film, and forming the magnetic memory chip device, a magnetic field of not less than 1 Tesla is applied to magnetize the chip and then the process is restored to an environment without external field.

[0039] The following supplementary explanation is provided: Annealing and magnetization is a crucial manufacturing step for MRAM chips. For the characteristic structure proposed in this invention, the aforementioned annealing and magnetization process enables the alignment of the spin directions of each ferromagnetic thin film structure.

[0040] Traditional single-fixed-layer STT-MTJs use ferromagnetic thin films with high spin polarization as the fixing layer. While this reduces the write current in one direction, it increases the write current in the other. Using dual-fixed-layer STT-MTJs promises to solve this problem. Specifically, this invention proposes a top-and-bottom dual-fixed-layer structure and its manufacturing method, focusing on the coupling magnetic field between the fixing layer and the free layer, and the spin alignment control of the components of the fixing layer. This is expected to reduce the write current in both directions of the STT-MTJ while obtaining a stable magnetic storage MRAM chip. Attached Figure Description

[0041] Figure 1 is a schematic diagram of the basic structure of a double-fixed-layer magnetic tunnel junction (MTJ) device with a characteristic bottom fixed-layer structure, one of the embodiments of the present invention.

[0042] Figures 2-6 are schematic diagrams of five embodiments of the present invention, namely, five different top fixing layers of the double-fixed-layer MTJ based on the characteristic bottom fixing layer structure of Figure 1.

[0043] Figure 7(A) shows the structure of the MTJ fixed layer of a single ferromagnetic thin film structure and the MTJ fixed layer of two antiparallel coupled ferromagnetic thin film structures. The coupling layers between the ferromagnetic thin film structures and between them and the free layer are omitted. (B) is a schematic diagram of the hysteresis loop when the MTJ fixed layer generates magnetic coupling with the free layer. (C) is a comparison of the coupling fields generated by the two types of MTJ fixed layers in (A) with the free layer at different MTJ device diameters.

[0044] Figure 8(A) is a schematic diagram of a double-fixed-layer MTJ structure in which both the top and bottom fixed layers are composed of two antiparallel coupled ferromagnetic thin film structures, and the magnetic moment of the ferromagnetic thin film structure closer to the free layer in the two fixed layers is smaller; (B) is a schematic diagram of the spin direction arrangement of each ferromagnetic thin film structure in (A) under a magnetic field of 10 kOe and under the condition that the external magnetic field is removed.

[0045] Figure 9 shows a schematic diagram of the double-fixed-layer MTJ structure and the arrangement of the spin directions of each ferromagnetic thin film structure after excitation with 10 kOe and removal of the external magnetic field, where both the top and bottom fixed layers are composed of two antiparallel coupled ferromagnetic thin film structures, and the magnetic moment of the ferromagnetic thin film structure near the free layer in the bottom fixed layer is larger than that of the ferromagnetic thin film structure near the free layer in the top fixed layer.

[0046] Figure 10(A) is a schematic diagram of the bottom fixed layer and free layer of the double-fixed MTJ in Figure 9, where the bottom fixed layer is composed of two antiparallel coupled ferromagnetic thin film structures and the ferromagnetic thin film structure of the bottom fixed layer has a larger magnetic moment than the one of the free layer. (B) shows three different thickness combinations of the two ferromagnetic thin film structures constituting the bottom fixed layer in (A). (C) shows the result of the coupling magnetic field of the bottom fixed layer to the free layer with the diameter of the MTJ device when there are three different thickness combinations in (B).

[0047] Figure 11 is a schematic diagram of the arrangement of the spin directions of the double-fixed-layer MTJ structure and each ferromagnetic thin film structure after 10 kOe excitation and removal of the external magnetic field, in one embodiment of the present invention. The top fixed layer of the structure is composed of two antiparallel coupled ferromagnetic thin film structures, the bottom fixed layer is composed of three antiparallel coupled ferromagnetic thin film structures, and the magnetic moments of the ferromagnetic thin film structures near the free layer of the bottom and top fixed layers are relatively small.

[0048] Figure 12 shows one embodiment of the present invention. (A) is a schematic diagram of the bottom fixed layer and free layer of the double fixed layer MTJ in Figure 11, where the bottom fixed layer is composed of three antiparallel coupled ferromagnetic thin film structures and the magnetic moment of the ferromagnetic thin film structure close to the free layer is small. (B) shows eight different thickness combinations of the three ferromagnetic thin film structures constituting the bottom fixed layer in (A). (C) shows the result of the coupling magnetic field of the bottom fixed layer to the free layer with the diameter of the MTJ device when there are eight different thickness combinations in (B).

[0049] Figure 13 shows the change in the coupling magnetic field of the bottom fixed layer to the free layer when the thicknesses of the three ferromagnetic thin film structures constituting the fixed layer from near to far from the free layer are D1, D2, and D3, respectively, and the ratio of D2 / (D1+D2+D3) changes when the MTJ device has a diameter of 20 nanometers.

[0050] Figure 14 shows one embodiment of the present invention. (A) is a schematic diagram of the bottom fixed layer and free layer of the double fixed layer MTJ in Figure 11, where the bottom fixed layer is composed of three antiparallel coupled ferromagnetic thin film structures and the magnetic moment of the ferromagnetic thin film structure close to the free layer is small. (B) shows six different thickness combinations of the three ferromagnetic thin film structures constituting the bottom fixed layer in (A). (C) shows the result of the coupling magnetic field of the bottom fixed layer to the free layer with the diameter of the MTJ device when there are six different thickness combinations in (B).

[0051] Figure 15 compares the magnetic coupling field generated by the top fixed layer of the double fixed-layer MTJ in the five embodiments shown in Figures 2-6 on the free layer at different device diameters. Detailed Implementation

[0052] The present invention will now be described with reference to the accompanying drawings and examples of embodiments.

[0053] Example 1:

[0054] Figure 11 illustrates one embodiment of the present invention, showing the characteristic structure of the double-fixed-layer MTJ. The top fixed layer consists of two antiparallel coupled ferromagnetic thin-film structures (top first and second ferromagnetic thin-film structures), and the bottom fixed layer consists of three antiparallel coupled ferromagnetic thin-film structures (bottom first, second, and third ferromagnetic thin-film structures, with magnetic moments m1, m2, and m3, respectively), where m2 < m1 + m3. When a downward magnetic field of 10 kOe is applied, the spin directions of all ferromagnetic thin-film structures (magnetic moments m1, m2, m3, m4, and m5, respectively) in Figure 11 are aligned downwards. When the external magnetic field is removed, m5 is larger than m4, so m5 remains downwards, and m4 and m5 form an antiparallel relationship. Since m1 and m2, and m2 and m3 are antiparallel, and due to the aforementioned relationship of m2 < m1 + m3, m1 and m3 maintain a downward spin, while m2, being antiparallel to them, has an upward spin. In this way, the bottom first ferromagnetic thin film structure m1 and the top first ferromagnetic thin film structure m4 can form an antiparallel relationship, thereby enabling information writing of the dual-fixed-layer STT-MTJ as mentioned above.

[0055] Figure 12(A) shows a specific embodiment of the bottom structure in Figure 11. The thickness d5 of the free layer FL, and the distances between each pair of the free layer FL, the first bottom ferromagnetic thin film structure (Pin 1), the second bottom ferromagnetic thin film structure (Pin 2), and the third bottom ferromagnetic thin film structure (Pin 3) are d6, d7, and d8, respectively, in nanometers. The composition of each part from bottom to top is as follows:

[0056] Pin1: [Co(d1) / Pt(d2)] xn / Co(d3) / CoFeB(d4)

[0057] Pin2: [Co(d1) / Pt(d2)] xm / Co(d3)

[0058] Pin3: [Co(d1) / Pt(d2)] xl / Co(d3)

[0059] The units for d1, d2, d3, and d4 in parentheses are nanometers. n, m, and l are integers representing the number of repetitions of [Co(d1) / Pt(d2)]. The film thickness can be adjusted by changing the values ​​of these integers. When d1 < 0.8, d2 < 0.5, d3 < 0.85, d4 < 2, d5 < 3, d6 < 1.2, d7 < 1.2, and d7 < 1.2 (all units from d1 to d8 are nanometers), and keeping the magnetic moment Ms of FL < 1.5 Tesla and the magnetic moment Ms of the bottom fixed layer < 1.4 Tesla, the coupling magnetic field of the bottom fixed layer to the free layer was compared in Figure 12(C) according to the eight different thickness combinations listed in Figure 12(B). It can be observed that when n is 0 and m is greater than 2 (Case # s-3 to Case # s-8), within the compared diameter range of 10 nm to 80 nm, the coupling magnetic field of the bottom fixed layer to the free layer is less than 750 Oe. Therefore, the application conditions of the double fixed-layer MTJ are met. However, when n is 0 and m equals 2, i.e., Case # s-2, within the compared diameter range of 10 nm to 80 nm, the coupling magnetic field of the bottom fixed layer to the free layer is greater than 750 Oe. In particular, for Ref. where n equals 7, the coupling magnetic field is greater than 1500 Oe, and based on the aforementioned analysis, it cannot be applied.

[0060] Figure 13 shows the ratio of the thickness of Pin 2 (Pin 2) to the sum of the thicknesses of Pin 1 (Pin 1), Pin 2, and Pin 3 (Pin 3) at 20 nm for various double-fixed-layer MTJ structures in Figure 12(B), denoted as Pin2 / (Pin1 + Pin2 + Pin3). Using this ratio as the x-axis and the coupling magnetic field value of the bottom fixed layer to the free layer as the y-axis, it is found that Pin2 / (Pin1 + Pin2 + Pin3) has a linear relationship with the coupling magnetic field. It is found that for the coupling magnetic field to be less than 750 Oe, Pin2 / (Pin1 + Pin2 + Pin3) needs to be greater than 0.35. When Pin2 / (Pin1 + Pin2 + Pin3) is 0.5, the coupling magnetic field is 0, which is the ideal situation. However, because the spin orientation arrangement in the previous example (Figure 11) requires m2 < m1 + m3, that is, Pin2 / (Pin1 + Pin2 + Pin3) needs to be less than 0.5. Considering the 20 nm comparison here, and the previous results (Figures 7(C), 10(C), and 12(C)) showing that the smaller the diameter, the larger the coupling magnetic field, this invention proposes to ensure that the coupling magnetic field is less than 1000 Oe. Therefore, the following condition needs to be met: 0.29 < Pin2 / (Pin1 + Pin2 + Pin3) < 0.50. It should be noted that since Figure 13 mainly uses a Co / Pt alloy, the thickness or the number of repetitions of the two thin films in the main structure (Co / Pt) is positively correlated with magnetic properties such as magnetic moment (m).

[0061] Figure 14(A) is based on the same feature structure as Figure 12, but the thicknesses of the bottom first ferromagnetic thin film structure (Pin 1), the bottom second ferromagnetic thin film structure (Pin 2), and the bottom third ferromagnetic thin film structure (Pin 3) are adjusted. The value of n in [Co(d1) / Pt(d2)]n of the bottom first ferromagnetic thin film structure is adjusted to 1 and 2, and the specific thickness can be found in Figure 14(B). When n is 1 and 2, the coupling magnetic fields of the fixed layer to the free layer obtained under MTJ conditions with different diameters are shown in Figure 14(C) and Figure 14(D), respectively. When n = 1, the coupling magnetic field of the fixed layer to the free layer is less than 750 Oe when the diameter is above 30 nm. However, when n = 2, the coupling magnetic field of the fixed layer to the free layer is less than 750 Oe when the diameter is above 60 nm. Because when STT-MTJ based MRAM replaces SRAM and DRAM applications, device size (high integration density) is an important metric. Considering practical applications, MRAM typically needs to be below 40 nanometers to be most likely to replace DRAM and SRAM on a large scale. That is, when n = 1, this structure is expected to be widely used, while when n = 2, it is difficult to use on a large scale. Referring to Figure 12(C), in the structure proposed in this invention, n < 2 is required, preferably n = 0. In the embodiments of this proposal, n < 2, which corresponds to the thickness of the bottom first ferromagnetic thin film structure (Pin 1 or m1) being less than 2.8 nanometers.

[0062] Example 2:

[0063] Figure 1 is a schematic diagram of the basic structure of a double-fixed-layer magnetic tunnel junction (MTJ) device with a characteristic bottom fixed-layer structure, one embodiment of the present invention. 7 is the free layer, and 1 and 2 are the bottom tunneling layer oxide thin film structure and the top tunneling layer oxide thin film structure, respectively. 81, 82, and 83 are the first, second, and third bottom ferromagnetic thin film structures, respectively, and 31 and 32 are the first and second bottom antiparallel coupled thin film structures, respectively. 81 and 82 are antiparallel coupled through 31, and 82 and 83 are antiparallel coupled through 32. 81, 82, 83, 31, and 32 constitute the characteristic structure of the bottom fixed-layer thin film structure of the double-fixed-layer structure proposed in this invention. 9 is the top fixed-layer thin film structure.

[0064] After excitation, this structure enables the spin direction of the first ferromagnetic thin film structure in the top fixed layer thin film structure to be opposite to the spin direction of the first ferromagnetic thin film structure in the bottom layer, and the spin direction of the first ferromagnetic thin film structure in the bottom layer is opposite to the spin direction of the second ferromagnetic thin film structure, and the spin direction of the second ferromagnetic thin film structure is opposite to the spin direction of the third ferromagnetic thin film structure. In Figure 1, the spin direction of the first ferromagnetic thin film structure in the bottom layer is downward, while the tops of the second and third ferromagnetic thin film structures in the bottom layer are upward, downward, and upward, respectively. Conversely, if the spin direction of the first ferromagnetic thin film structure in the bottom layer is upward, the directions of the other ferromagnetic thin film structures will also change. As mentioned earlier, the top fixed layer thin film structure in this invention is also composed of multiple ferromagnetic thin film structures. Figure 1 does not specify the detailed definition of the top fixed layer, so although the spin direction of the first ferromagnetic thin film structure in the top fixed layer thin film structure is opposite to the spin direction of the first ferromagnetic thin film structure in the bottom layer, Figure 1 treats the top fixed layer thin film structure as a whole and cannot specify its spin direction.

[0065] Example 3:

[0066] Figures 2-6 are schematic diagrams of five embodiments of the present invention, namely, five different top fixing layers of the double-fixed-layer MTJ based on the characteristic bottom fixing layer structure of Figure 1.

[0067] In Figure 2, 91 and 92 are the top first and second ferromagnetic thin film structures antiparallel coupled through the top first antiparallel coupling thin film structure 33. 101 is the top third ferromagnetic thin film structure, which is parallel coupled to the top second ferromagnetic thin film structure 92 through the top first oxide coupling thin film structure 41. 5 is a magnesium oxide thin film structure used to improve magnetic vertical anisotropy. The above-mentioned 91, 33, 92, 41, and 101 constitute the top fixed layer thin film structure of Figure 2. After excitation and removal of the external magnetic field, when the spin direction of the bottom first ferromagnetic thin film structure is downward, the spin directions of the top first, second, and third ferromagnetic thin film structures are upward, downward, and downward, respectively. Conversely, when the spin direction of the bottom first ferromagnetic thin film structure is upward, the spin directions of the top first, second, and third ferromagnetic thin film structures are downward, upward, and upward, respectively.

[0068] Figure 3 shows a fourth ferromagnetic thin film structure formed above the third ferromagnetic thin film structure 101 in Figure 2, parallel to its spin direction, through a second oxide coupling thin film structure 42. A magnesium oxide thin film structure 5 is then formed to improve magnetic perpendicular anisotropy. The structures 91, 33, 92, 41, 101, 42, and 102 constitute the top fixed layer thin film structure in Figure 3. After excitation and removal of the external magnetic field, when the spin direction of the first ferromagnetic thin film structure at the bottom is downward, the spin directions of the first, second, third, and fourth ferromagnetic thin film structures at the top are upward, downward, downward, and downward, respectively; conversely, the corresponding relationships are also satisfied.

[0069] In Figure 4, the top first ferromagnetic thin film structure 101 and the top second ferromagnetic thin film structure 91 are parallel coupled through the top first oxide coupling thin film structure 41. 91 is then antiparallel coupled to the top third ferromagnetic thin film structure 92 through the top first antiparallel coupling thin film structure 33. 92 is then parallel coupled to the top fourth ferromagnetic thin film structure 102 through the top second oxide coupling thin film structure 42. An antiferromagnetic thin film structure 6 for spin pinning is formed on top of 102. The structures 101, 41, 91, 33, 92, 42, and 102 constitute the top fixed layer thin film structure of Figure 4. After excitation and removal of the external magnetic field, when the spin direction of the bottom first ferromagnetic thin film structure is downward, the spin directions of the top first, second, third, and fourth ferromagnetic thin film structures are upward, upward, downward, and downward, respectively; conversely, the corresponding relationships are also satisfied.

[0070] Figure 5 shows a third oxide coupling thin film structure 43 formed on top of 102 in Figure 4, which is parallelly coupled to the fifth ferromagnetic thin film structure 103. A magnesium oxide thin film structure 5, used to improve magnetic vertical anisotropy, is formed on top of 103. The structures 101, 41, 91, 33, 92, 42, 102, 43, and 103 constitute the top fixed layer thin film structure of Figure 5. After excitation and removal of the external magnetic field, when the spin direction of the first ferromagnetic thin film structure at the bottom is downward, the spin directions of the first, second, third, fourth, and fifth ferromagnetic thin film structures at the top are upward, upward, downward, downward, and downward, respectively; conversely, the corresponding relationships are also satisfied.

[0071] In Figure 6, 91 and 92 are the first and second ferromagnetic thin film structures at the top, antiparallel coupled through the first antiparallel coupling thin film structure 33. 93 is the third ferromagnetic thin film structure at the top, parallel coupled to the second ferromagnetic thin film structure 92 through the first oxide coupling thin film structure 41. The fourth ferromagnetic thin film structure 94 at the top is antiparallel coupled to the third ferromagnetic thin film structure 93 through the second antiparallel coupling thin film structure 34. An antiferromagnetic thin film structure 6 for spin pinning is then formed on top of 94. The aforementioned 91, 33, 92, 41, 93, 34, and 94 constitute the top fixed layer thin film structure of Figure 6. After excitation and removal of the external magnetic field, when the spin direction of the first ferromagnetic thin film structure at the bottom is downward, the spin directions of the first, second, third, and fourth ferromagnetic thin film structures at the top are upward, downward, downward, and upward, respectively; conversely, the corresponding relationships are also satisfied.

[0072] Figure 15 compares the coupling magnetic fields generated by the top fixed layer of the dual-fixed-layer MTJ in the five embodiments shown in Figures 2-6 on the free layer at different device diameters. (d), (e), (f), (g), and (h) correspond to Figures 2, 3, 4, 5, and 6, respectively. It can be seen that all five structures can satisfy the requirement that the coupling magnetic field of the top fixed layer on the free layer is less than 750 Oe when the diameter is greater than 20 nanometers. Since actual MTJs are composed of multiple nanoscale thin films, the film preparation conditions will affect the relevant performance to some extent. Therefore, this proposal only specifies the coupling magnetic fields of the top and bottom fixed layers on the free layer.

[0073] This proposal is expected to significantly reduce the energy consumption of information writing for STT-MTJ-based MRAM chips and greatly increase their durability, enabling the large-scale application of MRAM to replace DRAM and SRAM.

[0074] All the above embodiments merely illustrate certain implementations of the present invention and are described in detail, but they should not be construed as limiting the scope of the invention patent. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of the present invention, and these all fall within the protection scope of the present invention. Therefore, the protection scope of this invention patent should be determined by the appended claims.

Claims

1. A double-fixed-layer magnetic tunnel junction, characterized in that, The magnetic tunnel junction, from near to far from the substrate, consists of a bottom fixed layer thin film structure, a bottom tunneling layer oxide thin film structure, a free layer thin film structure, a top tunneling layer oxide thin film structure, and a top fixed layer thin film structure. The bottom fixed layer thin film structure, from near to far from the free layer, consists of a bottom first ferromagnetic thin film structure (with a spin direction opposite to that of the ferromagnetic thin film structure closest to the free layer in the top fixed layer thin film structure), a bottom first antiparallel coupled thin film structure, a bottom second ferromagnetic thin film structure (with a spin direction opposite to that of the bottom first ferromagnetic thin film structure), a bottom second antiparallel coupled thin film structure, and a bottom third ferromagnetic thin film structure (with a spin direction opposite to that of the bottom second ferromagnetic thin film structure). The thicknesses D1 of the bottom first ferromagnetic thin film structure, D2 of the bottom second ferromagnetic thin film structure, and D3 of the bottom third ferromagnetic thin film structure satisfy the relationship D1 < D2 and D1 < D3 and 0.29 < D2 / (D1+D2+D3) < 0.

5.

2. The double-fixed-layer magnetic tunnel junction according to claim 1, characterized in that, The first ferromagnetic film structure at the bottom is formed by depositing a cobalt metal film and a cobalt-iron-boron alloy film sequentially on an integer n repeating structure of two thin films, a cobalt metal film and a platinum film, from near to far from the substrate, where the integer n is 0 or 1; the second ferromagnetic film structure at the bottom is formed by depositing a cobalt metal film on an integer m repeating structure of two thin films, a cobalt metal film and a platinum film, from near to far from the substrate; the third ferromagnetic film structure at the bottom is formed by depositing a cobalt metal film on an integer l repeating structure of two thin films, a cobalt metal film and a platinum film, from near to far from the substrate.

3. The double-fixed-layer magnetic tunnel junction according to claim 2, characterized in that, The top fixing layer thin film structure is composed of a top first ferromagnetic thin film structure, a top first antiparallel coupling thin film structure, a top second ferromagnetic thin film structure with the opposite spin direction to the top first ferromagnetic thin film structure, a top first oxide coupling thin film structure, and a top third ferromagnetic thin film structure with the same spin direction as the top second ferromagnetic thin film structure, arranged from near to far from the substrate. The top of the top fixing layer thin film structure is composed of a magnesium oxide thin film for improving magnetic vertical anisotropy.

4. The double-fixed-layer magnetic tunnel junction according to claim 2, characterized in that, The top fixing layer thin film structure is composed of, from near to far from the substrate, a top first ferromagnetic thin film structure, a top first antiparallel coupled thin film structure, a top second ferromagnetic thin film structure with the opposite spin direction to the top first ferromagnetic thin film structure, a top first oxide coupled thin film structure, a top third ferromagnetic thin film structure with the same spin direction as the top second ferromagnetic thin film structure, a top second oxide coupled thin film structure, and a top fourth ferromagnetic thin film structure with the same spin direction as the top third ferromagnetic thin film structure; the top of the top fixing layer thin film structure is composed of a magnesium oxide thin film structure for improving magnetic vertical anisotropy.

5. The double-fixed-layer magnetic tunnel junction according to claim 2, characterized in that, The top fixing layer thin film structure is composed of, from near to far from the substrate, a top first ferromagnetic thin film structure, a top first oxide coupling thin film structure, a top second ferromagnetic thin film structure with the same spin direction as the top first ferromagnetic thin film structure, a top first antiparallel coupling thin film structure, a top third ferromagnetic thin film structure with the opposite spin direction to the top second ferromagnetic thin film structure, a top second oxide coupling thin film structure, and a top fourth ferromagnetic thin film structure with the same spin direction as the top third ferromagnetic thin film structure; the top of the top fixing layer thin film structure is composed of an antiferromagnetic thin film structure for spin pinning.

6. The double-fixed-layer magnetic tunnel junction according to claim 2, characterized in that, The top fixing layer thin film structure is composed of, from near to far from the substrate, a top first ferromagnetic thin film structure, a top first oxide coupling thin film structure, a top second ferromagnetic thin film structure with the same spin direction as the top first ferromagnetic thin film structure, a top first antiparallel coupling thin film structure, a top third ferromagnetic thin film structure with the opposite spin direction to the top second ferromagnetic thin film structure, a top second oxide coupling thin film structure, a top fourth ferromagnetic thin film structure with the same spin direction as the top third ferromagnetic thin film structure, a top third oxide coupling thin film structure, and a top fifth ferromagnetic thin film structure with the same spin direction as the top fourth ferromagnetic thin film structure; the top of the top fixing layer thin film structure is composed of a magnesium oxide thin film structure for improving magnetic vertical anisotropy.

7. The double-fixed-layer magnetic tunnel junction according to claim 2, characterized in that, The top fixing layer thin film structure comprises, from near to far from the substrate, a top first ferromagnetic thin film structure, a top first antiparallel coupled thin film structure, a top second ferromagnetic thin film structure with the opposite spin direction to the top first ferromagnetic thin film structure, a top first oxide coupled thin film structure, a top third ferromagnetic thin film structure with the same spin direction as the top second ferromagnetic thin film structure, a top second antiparallel coupled thin film structure, and a top fourth ferromagnetic thin film structure with the opposite spin direction to the top third ferromagnetic thin film structure; the top of the top fixing layer thin film structure contains an antiferromagnetic thin film structure for spin pinning.

8. The double-fixed-layer magnetic tunnel junction according to any one of claims 1 to 7, characterized in that, The antiparallel coupling thin film structure is made of either ruthenium or iridium; the oxide coupling thin film structure is composed of either magnesium oxide containing either iron or cobalt plus boron and having a thickness greater than that of the tunneling layer magnesium oxide, iron oxide, or an oxide containing both iron and cobalt.

9. The double-fixed-layer magnetic tunnel junction according to claim 5 or 7, characterized in that, The antiferromagnetic thin film structure contains at least one type of antiferromagnetic material, either a manganese-platinum alloy or a manganese-iridium alloy.

10. A method for manufacturing a double-fixed-layer magnetic tunnel junction magnetic memory chip based on the double-fixed-layer magnetic tunnel junction according to any one of claims 1 to 7, comprising the following steps: Fabrication of the peripheral circuitry for the magnetic storage chip on a substrate; The bottom electrode of the magnetic tunnel junction is fabricated on the metal interconnect layer of the peripheral circuit; Prepare a connection layer between the bottom electrode and the bottom fixing layer thin film structure; Prepare a bottom first ferromagnetic thin film structure, a bottom first antiparallel coupling thin film structure, a bottom second ferromagnetic thin film structure, a bottom second antiparallel coupling thin film structure, and a bottom third ferromagnetic thin film structure containing the bottom fixed layer thin film structure; Prepare the bottom tunneling layer oxide thin film structure; Prepare the free layer thin film structure; Prepare the top tunneling layer oxide thin film structure; Prepare the top fixing layer thin film structure; Prepare a top protective layer; A device that patterns thin films to form magnetic storage chips; The components are connected and packaged to form a chip.

11. The method for manufacturing a dual-fixed-layer magnetic tunnel junction magnetic memory chip according to claim 10, characterized in that, The step of applying a magnetic field of not less than 1 Tesla to magnetize the device after any of the steps of preparing the top fixed layer thin film structure, preparing the top cover protective layer, patterning the thin film to form a magnetic storage chip, and then returning to an environment without external field.

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