An optimization method for the fixed layer in the MTJ structure

Abstract

The present invention provides a method for optimizing the fixed layer in an MTJ structure, comprising the following steps: reducing the thickness of the fixed layer magnetic layer; and adjusting the magnetic moment of each magnetic layer so that the bias field of the fixed layer at the free layer meets a set value. Compared with the prior art, the method for optimizing the fixed layer in an MTJ structure provided by the present invention can reduce the thickness of the fixed layer without affecting the overall stability of the MTJ structure, thereby reducing MTJ etching damage. Experimental results show that the method for optimizing the fixed layer in an MTJ structure provided by the present invention, on the one hand, reduces MTJ etching damage while not affecting the stability of the reference layer; on the other hand, it reduces the thickness of the entire storage unit, which is beneficial for reducing etching time and also provides more options for photolithography (Litho) and hard mask (HM) for expansion to small sizes.

Description

Technical Field

[0001] The present invention relates to the field of memory technology, and more particularly to a method for optimizing a fixed layer in an MTJ structure. Background Art

[0002] The mainstream MRAM fabrication process uses a bottom-pin magnetic tunnel junction (MTJ) structure with a pinned layer. This creates a problem: after etching the barrier layer (usually MgO), the reference layer, antiferromagnetic coupling (SAF) pinning layer, and seed layer must also be etched. However, prolonged exposure of the barrier layer to high-energy etching ions significantly damages MTJ properties such as endurance, breakdown voltage (BDV), tunnel resistance (Rp), and the magnetic properties of the storage layer (such as coercivity Hc). Therefore, mitigating etching damage after the barrier layer is exposed is key to improving MTJ performance.

[0003] Typical tunnel junction stack (MTJ stack) structure is as follows Figure 1 As shown in the figure, there is material >20nm (including seed layer and fixed layer, where the fixed layer is >10nm) under the MgO barrier layer. Therefore, during the MTJ etching process, after completing the MgO etching, it takes a long time to etch from the reference layer (RL) to the seed layer (Seed layers), which has a significant impact on the edges of the MgO and free layer (FL), resulting in the degradation of the MTJ performance of the MRAM storage unit.

[0004] The overall thickness of the fixed layer is too large due to the following two factors:

[0005] On the one hand, the demand for high PMA leads to an increase in the thickness of the fixed layer;

[0006] On the other hand, the total bias field of the fixed layer at the free layer needs to be controlled within a reasonable range, and the thickness of some magnetic layers in the fixed layer increases, resulting in an increase in the thickness of the fixed layer. Summary of the Invention

[0007] In view of this, the object of the present invention is to provide a method for optimizing the fixed layer in the MTJ structure, which can reduce the thickness of the fixed layer without affecting the overall stability of the MTJ structure, thereby alleviating MTJ etching damage.

[0008] The present invention provides a method for optimizing a fixed layer in an MTJ structure, comprising the following steps:

[0009] Reduce the thickness of the fixed layer magnetic layer; adjust the magnetic moment of each magnetic layer so that the bias field of the fixed layer at the free layer meets the set value.

[0010] Preferably, reducing the thickness of the fixed layer magnetic layer; and adjusting the magnetic moment of each magnetic layer comprises:

[0011] a) reducing the thickness of the first pinned layer PL1 and increasing the magnetic moment of the first pinned layer PL1;

[0012] b) reducing the magnetic moment of the second pinned layer PL2 and reducing the thickness of the second pinned layer PL2;

[0013] c) Reducing the thickness of the reference layer RL and lowering the magnetic moment of the reference layer RL.

[0014] Preferably, it also includes:

[0015] Optimize the structure adjustment layer TL.

[0016] Preferably, the process of reducing the thickness of the first pinned layer PL1 in step a) is specifically as follows:

[0017] The thickness of Co and Pt in the (Co / Pt)n multilayer was reduced to each molecular layer.

[0018] Preferably, the thickness of each layer of Co is The thickness of each Pt layer is n is 4 to 8.

[0019] Preferably, the method of increasing the magnetic moment of the first pinned layer PL1 in step a) is to use a Co alloy with high magnetic saturation magnetization Ms; the Co alloy with high magnetic saturation magnetization Ms is selected from Co x Fe 1-x Or CoFeNi, wherein x is 0.1 to 0.4.

[0020] Preferably, the step a) further comprises:

[0021] The thickness of the Co layer or the Co alloy layer in contact with the antiferromagnetic coupling layer AFC is increased.

[0022] Preferably, in step b), the method of reducing the magnetic moment of the second pinned layer PL2 is to use a magnetic layer with a low saturation magnetization Ms.

[0023] Preferably, the process of reducing the thickness of the second pinned layer PL2 in step b) is specifically as follows:

[0024] The thickness of Co and Pt in the (Co / Pt)n multilayer was reduced to each molecular layer.

[0025] Preferably, the thickness of each layer of Co is The thickness of each Pt layer is n is 2 to 5.

[0026] Preferably, the step b) further comprises:

[0027] The thickness of the Co layer in contact with the antiferromagnetic coupling layer AFC is made thicker than the thickness of other Co layers in the (Co / Pt)n multilayer.

[0028] Preferably, the method of optimizing the structure adjustment layer TL in step c) includes one or more of using a heavy metal material with strong B absorption, using a non-magnetic material, and reducing the thickness of the structure adjustment layer TL.

[0029] Preferably, the thickness of the reference layer RL is reduced to ≤1 nm in step d).

[0030] Preferably, in step d), the method of reducing the magnetic moment of the reference layer RL is to use a ferromagnetic material with low saturation magnetization Ms and high damping factor.

[0031] The present invention also provides an MTJ structure, comprising a fixed layer formed by the optimization method described in the above technical solution.

[0032] The present invention provides a method for optimizing the fixed layer in an MTJ structure, comprising the following steps: reducing the thickness of the fixed layer magnetic layer; and adjusting the magnetic moment of each magnetic layer so that the bias field of the fixed layer at the free layer meets a set value. Compared with the prior art, the method for optimizing the fixed layer in an MTJ structure provided by the present invention can reduce the thickness of the fixed layer without affecting the overall stability of the MTJ structure, thereby reducing MTJ etching damage. Experimental results show that the method for optimizing the fixed layer in an MTJ structure provided by the present invention, on the one hand, reduces MTJ etching damage while not affecting the stability of the reference layer; on the other hand, it reduces the thickness of the entire storage unit, which is beneficial for reducing etching time and also provides more options for photolithography (Litho) and hard mask (HM) for expansion to small sizes. BRIEF DESCRIPTION OF THE DRAWINGS

[0033] Figure 1 Schematic diagram of a typical tunnel junction stack (MTJ stack) structure. DETAILED DESCRIPTION

[0034] The following will clearly and completely describe the technical solutions of the present invention in conjunction with the embodiments of the present invention. Obviously, the embodiments described are only some embodiments of the present invention, not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative efforts are within the scope of protection of the present invention.

[0035] The present invention provides a method for optimizing a fixed layer in an MTJ structure, comprising the following steps:

[0036] Reduce the thickness of the fixed layer magnetic layer; adjust the magnetic moment of each magnetic layer so that the bias field of the fixed layer at the free layer meets the set value.

[0037] In the present invention, reducing the thickness of the fixed layer magnetic layer and adjusting the magnetic moment of each magnetic layer preferably includes:

[0038] a) reducing the thickness of the first pinned layer PL1 and increasing the magnetic moment of the first pinned layer PL1;

[0039] b) reducing the magnetic moment of the second pinned layer PL2 and reducing the thickness of the second pinned layer PL2;

[0040] c) Reducing the thickness of the reference layer RL and lowering the magnetic moment of the reference layer RL.

[0041] Based on the structure of the existing magnetic tunnel junction MTJ, the present invention proposes a method of reducing the thickness of the reference layer and the pinning layer to reduce the etching damage without affecting the stability of the reference layer in order to reduce the etching damage after MgO exposure.

[0042] See also Figure 1 As shown, Figure 1 Shown is a typical MRAM memory cell structure, including:

[0043] (1) The first pinning layer PL1 is composed of a (Co / Pt)n multilayer film with a thickness of > n is typically between 5 and 10;

[0044] (2) an antiferromagnetic coupling layer AFC, which forms a strong antiferromagnetic coupling between the first pinned layer PL1 and the second pinned layer PL2. Typical materials are Ru, Ir, and Cr. The thickness is between 0.3 nm and 1.0 nm, preferably around 0.45 nm.

[0045] (3) The second pinning layer PL2 is composed of a (Co / Pt)n multilayer film, where n is usually smaller than that of the first pinning layer PL1, generally between 2 and 5. Its main function is to form a strong antiferromagnetic coupling with the first pinning layer PL1 through AFC, and to form a strong ferromagnetic coupling with the reference layer RL through the structure adjustment layer TL (transition layer), thereby providing a pinning effect for the magnetic stability of the reference layer RL.

[0046] (4) Structure adjustment layer TL. The structure adjustment layer TL is generally an amorphous structure. It is not only used for structural transition, but also needs to have the function of absorbing B, absorbing the B in the reference layer RL to prevent it from accumulating on the interface between MgO and the reference layer RL and affecting the perpendicular anisotropy of the reference layer RL. The structure adjustment layer TL also needs to be thin enough to form a strong ferromagnetic coupling between the reference layer RL and the second pinning layer PL2. Typical materials are heavy metals such as Mo, Ta, W, and Hf.

[0047] (5) Reference layer RL: It is composed of CoFeB and is an important component of the magnetic tunnel junction of the storage unit. It is the key to determining the read and write characteristics (tunnel magnetoresistance change rate TMR, write voltage Vc (flip voltage) etc.); it needs to form a lattice match with MgO and have perpendicular magnetic anisotropy to maintain high stability during the read and write process.

[0048] The present invention has no special limitation on the preparation methods of the above-mentioned layers, and the technical solutions for the preparation methods for forming the above-mentioned layer structures well known to those skilled in the art can be adopted.

[0049] The present invention provides a method for optimizing a fixed layer in an MTJ structure, comprising the following steps:

[0050] a) reducing the thickness of the first pinned layer PL1 and increasing the magnetic moment of the first pinned layer PL1;

[0051] b) reducing the magnetic moment of the second pinned layer PL2 and reducing the thickness of the second pinned layer PL2;

[0052] c) Reducing the thickness of the reference layer RL and lowering the magnetic moment of the reference layer RL.

[0053] In the present invention, preferably also includes:

[0054] Optimize the structure adjustment layer TL.

[0055] The present invention first reduces the thickness of the first pinned layer PL1 and increases the magnetic moment of the first pinned layer PL1. In the present invention, the process of reducing the thickness of the first pinned layer PL1 is preferably as follows:

[0056] Reduce the thickness of Co and Pt in the (Co / Pt)n multilayer to each molecular layer, where the thickness of each Co layer is Preferably The thickness of each Pt layer is Preferably The same thickness results in more Co / Pt interfaces, which improves the perpendicular anisotropy PMA; n is preferably 4 to 8. The present invention adopts the above process to reduce the thickness of the first pinned layer PL1 without reducing the perpendicular anisotropy PMA.

[0057] In the present invention, the method of increasing the magnetic moment of the first pinned layer PL1 is preferably to use a Co alloy with high magnetic saturation magnetization Ms (magnetic moment); the Co alloy with high magnetic saturation magnetization Ms is selected from Co x Fe 1-x Or CoFeNi, wherein x is 0.1 to 0.4. The present invention uses the above-mentioned specific type of Co alloy with high magnetic saturation magnetization Ms, which has both high Ms and can form strong perpendicular magnetic anisotropy with Pt.

[0058] In the present invention, the step a) preferably further comprises:

[0059] The thickness of the Co layer or Co alloy layer in contact with the antiferromagnetic coupling layer AFC is increased, preferably from about 0.2 nm in the prior art to about 0.5 nm. This not only improves the coupling of the antiferromagnetic coupling layer AFC, but also helps reduce the magnetic bias field offset at the same thickness of the first pinned layer PL1 because its magnetic moment is close to the free layer. In the above preferred technical solution of the present invention, a Co alloy with a high magnetic saturation magnetization Ms (magnetic moment) is used. On this basis, the structure in contact with the antiferromagnetic coupling layer AFC is a Co alloy layer. In fact, the Co alloy layer is used in the first pinned layer PL1 to reduce the thickness of the first pinned layer PL1, thereby achieving the subsequent effects of reducing the bias field at the same thickness or reducing the thickness at the same bias field. The purpose of increasing the thickness of the Co layer or Co alloy layer in contact with the antiferromagnetic coupling layer AFC is the same.

[0060] The present invention secondly reduces the magnetic moment of the second pinned layer PL2 and reduces the thickness of the second pinned layer PL2. In the present invention, the method for reducing the magnetic moment of the second pinned layer PL2 is preferably to replace the Co layer and / or the Pt layer with a magnetic layer having a low magnetic saturation magnetization Ms. In the present invention, the principle of replacing the Co layer and / or the Pt layer with a magnetic layer having a low magnetic saturation magnetization Ms is the same as the principle of replacing Co with a Co alloy having a high magnetic saturation magnetization Ms (magnetic moment) in the first pinned layer PL1 described above, with the difference that the second pinned layer PL2 is located above the first pinned layer PL1, and therefore the adjustment direction of the magnetic moment is opposite to that of the first pinned layer PL1.

[0061] In the present invention, the process of reducing the thickness of the second pinned layer PL2 is preferably specifically as follows:

[0062] Reduce the thickness of Co and Pt in the (Co / Pt)n multilayer to each molecular layer, where the thickness of each Co layer is Preferably The thickness of each Pt layer is Preferably At the same time, the number of repetitions of the (Co / Pt)n multilayer is reduced, and the repetition number n is preferably 2-5.

[0063] In the present invention, the step b) preferably further comprises:

[0064] The thickness of the Co layer in contact with the antiferromagnetic coupling layer AFC is made thicker than the thickness of the other Co layers in the (Co / Pt)n multilayer. The present invention utilizes the aforementioned optimization method for the (Co / Pt)n multilayer to enhance the coupling of the antiferromagnetic coupling layer AFC. In fact, from the perspective of the (Co / Pt)n multilayer as a whole, except for the increased thickness of the Co layer in contact with the antiferromagnetic coupling layer AFC (maintaining the thickness of the Co layer corresponding to the prior art), the thickness of each other layer is reduced. Therefore, compared to the second pinned layer PL2 of the prior art, the overall thickness of the second pinned layer PL2 of the present invention is reduced. In the aforementioned preferred technical solution of the present invention, a magnetic layer with low saturation magnetization Ms is used in place of the Co layer. On this basis, the Co layer in contact with the antiferromagnetic coupling layer AFC is optimized to be the aforementioned magnetic layer Co alloy layer with low saturation magnetization Ms.

[0065] Finally, the present invention reduces the thickness of the reference layer RL and lowers the magnetic moment of the reference layer RL. In the present invention, the thickness of the reference layer RL is preferably reduced to ≤1 nm.

[0066] In the present invention, the method of reducing the magnetic moment of the reference layer RL is preferably to use a ferromagnetic material with low magnetic saturation magnetization Ms and high damping factor; the ferromagnetic material with low magnetic saturation magnetization Ms and high damping factor is preferably (Co x Fe 1-x ) y B 1-y , where x = 0.1 to 0.2 or higher than 0.5.

[0067] In the present invention, it is preferred to further include:

[0068] Optimize the structure adjustment layer TL.

[0069] The present invention optimizes the structure adjustment layer TL (transition layer). In the present invention, the method of optimizing the structure adjustment layer TL preferably includes one or more of using a heavy metal material with strong B absorption, using a non-magnetic material, and reducing the thickness of the structure adjustment layer TL; wherein the heavy metal material with strong B absorption is preferably Hf, Ta, Mo, or W; using a non-magnetic material is beneficial to reducing the total magnetic moment M2 of the layers above the antiferromagnetic coupling layer AFC (PL2, TL, and RL); reducing the thickness of the structure adjustment layer TL is beneficial to forming a strong magnetic coupling between the reference layer RL and PL2, and reducing the thickness of the structure adjustment layer TL is preferably The present invention adopts the above-mentioned optimization method to optimize the material and thickness of the structure adjustment layer TL.

[0070] The present invention also provides an MTJ structure, including a fixed layer formed by the optimization method described in the above technical solution. The present invention adopts the optimization method of the fixed layer in the above MTJ structure to further obtain a magnetic tunnel junction MTJ structure, including

[0071] a first pinned layer, a second pinned layer, an antiferromagnetic coupling layer between the first pinned layer and the second pinned layer, a transition layer, a reference layer, a barrier layer, and a free layer;

[0072] The first pinning layer and the second pinning layer are composed of multiple magnetic metal films repeatedly overlapped, and the thickness of each metal film is less than or equal to The material of the magnetic metal film includes but is not limited to metal elements such as Co, Fe, Ni, Pt and their alloys such as Co / Fe alloy, Fe / Ni alloy, etc., and is preferably used to maintain or enhance the overall magnetic moment or perpendicular anisotropy of the material while reducing the thickness of the material stack; the repetition number n of the multilayer film of the first pinned layer is 4 to 8; the repetition number n of the multilayer film of the second pinned layer is 2 to 5;

[0073] The upper and lower surfaces of the antiferromagnetic coupling layer are respectively in contact with the two pinned layers, and the thickness of the Co film in contact is greater than the thickness of the Co film inside each of the two pinned layers;

[0074] The material of the transition layer is a heavy metal material with strong B absorption, including but not limited to Hf, Ta, Mo, W, etc., preferably a non-magnetic material, used to reduce the total magnetic moment above the antiferromagnetic coupling layer; the material thickness is less than or equal to

[0075] The reference layer is made of ultra-thin low magnetic moment ferromagnetic material, preferably a material with high damping factor, such as (Co x Fe 1-x ) y B 1-y , wherein x=0.1 to 0.2 or higher than 0.5; the material thickness is less than or equal to 1 nm.

[0076] In the present invention, the structure of the magnetic tunnel junction MTJ is obtained as follows:

[0077] forming a first pinning layer, wherein the first pinning layer is a plurality of repetitions of a plurality of magnetic metal films;

[0078] forming an antiferromagnetic coupling layer on the first pinned layer;

[0079] forming a second pinning layer on the antiferromagnetic coupling layer, wherein the second pinning layer is a plurality of repeated magnetic metal films;

[0080] forming a transition layer on the second pinning layer;

[0081] forming a reference layer on the transition layer, wherein the thickness of the reference layer is preferably less than or equal to 1 nm;

[0082] A barrier layer and a free layer are sequentially formed on the reference layer.

[0083] The present invention provides a method for optimizing the fixed layer in an MTJ structure, comprising the following steps: reducing the thickness of the fixed layer magnetic layer; and adjusting the magnetic moment of each magnetic layer so that the bias field of the fixed layer at the free layer meets a set value. Compared with the prior art, the method for optimizing the fixed layer in an MTJ structure provided by the present invention can reduce the thickness of the fixed layer without affecting the overall stability of the MTJ structure, thereby reducing MTJ etching damage. Experimental results show that the method for optimizing the fixed layer in an MTJ structure provided by the present invention, on the one hand, reduces MTJ etching damage while not affecting the stability of the reference layer; on the other hand, it reduces the thickness of the entire storage unit, which is beneficial for reducing etching time and also provides more options for photolithography (Litho) and hard mask (HM) for expansion to small sizes.

[0084] In order to further illustrate the present invention, the following examples are given below to provide a detailed description.

[0085] Example 1

[0086] See also Figure 1 As shown, the following structures are formed in sequence to optimize the fixed layer in the MTJ structure; the characteristics of each layer structure are:

[0087] (1) Small thickness of the first pinned layer PL1: reduce the thickness of Co and Pt in the (Co / Pt)n multilayer to each molecular layer, that is, the thickness of each layer of Co and Pt is about n is controlled in the range of 4 to 8; PL1 uses a high Ms Co alloy, such as Co x Fe 1-x (x is between 0.1 and 0.4), CoFeNi, etc., which are materials with high Ms and can form strong perpendicular magnetic anisotropy with Pt; at the same time, increase the thickness of the Co layer in contact with AFC.

[0088] (2) Antiferromagnetic coupling layer AFC: It forms a strong antiferromagnetic coupling between PL1 and PL2. Typical materials are Ru, Ir, and Cr. The thickness is between 0.3 and 1.0 nm, preferably around 0.45 nm.

[0089] (3) The second pinned layer PL2 with small thickness and low magnetic moment: reduce the thickness of Co and Pt in the (Co / Pt)n multilayer to each molecular layer, that is, the thickness of each layer of Co and Pt is between about At the same time, the thickness of the Co layer in contact with the AFC is slightly larger than the thickness of Co in the (Co / Pt) multilayer.

[0090] (4) Small thickness transition layer TL: Use heavy metal materials with strong B absorption, such as Hf, Ta, Mo, W, preferably non-magnetic materials, to reduce the total magnetic moment M2 of the layer above AFC; the preferred thickness is

[0091] (5) Reference layer RL with small thickness and low magnetic moment: Use ferromagnetic materials with low Ms, preferably materials with high damping factor, such as (Co x Fe 1-x ) y B 1-y , where x=0.1 to 0.2 or higher than 0.5; the reference layer thickness is preferably less than 1 nm.

[0092] The present invention adopts the optimization method of the fixed layer in the MTJ structure provided in Example 1, which can achieve the following beneficial effects: on the one hand, it reduces the MTJ etching damage without affecting the stability of the reference layer; on the other hand, it reduces the thickness of the overall storage unit, which is conducive to reducing the etching time and also provides more options for lithography (Litho) and hard mask (HM) for expansion to small sizes.

[0093] The above description of the disclosed embodiments will enable one skilled in the art to implement or use the present invention. Various modifications to these embodiments will be readily apparent to one skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of the present invention. Therefore, the present invention is not limited to the embodiments shown herein but is to be construed in the widest manner consistent with the principles and novel features disclosed herein.

Claims

1. A method for optimizing a fixed layer in an MTJ structure, comprising the following steps: Reduce the thickness of the fixed layer magnetic layer; adjust the magnetic moment of each magnetic layer so that the bias field of the fixed layer at the free layer meets the set value; The MTJ structure includes a first pinned layer, a second pinned layer, an antiferromagnetic coupling layer located between the first pinned layer and the second pinned layer, a transition layer, a reference layer, a barrier layer and a free layer; The pinned layer includes a first pinned layer, a second pinned layer, an antiferromagnetic coupling layer located between the first pinned layer and the second pinned layer, a transition layer and a reference layer; The reducing the thickness of the fixed layer magnetic layer and adjusting the magnetic moment of each magnetic layer comprises: a) reducing the thickness of the first pinned layer PL1 and increasing the magnetic moment of the first pinned layer PL1; The process of reducing the thickness of the first pinned layer PL1 in step a) is specifically as follows: reducing the thickness of Co and Pt in the (Co / Pt)n multilayer to each molecular layer; The method of increasing the magnetic moment of the first pinned layer PL1 in step a) is to use a Co alloy with high magnetic saturation magnetization Ms; the Co alloy with high magnetic saturation magnetization Ms is selected from Co x Fe 1-x or CoFeNi, where x is 0.1 to 0.4; b) reducing the magnetic moment of the second pinned layer PL2 and reducing the thickness of the second pinned layer PL2; In step b), the method of reducing the magnetic moment of the second pinned layer PL2 is to use a magnetic layer with a low saturation magnetization Ms; The process of reducing the thickness of the second pinned layer PL2 in step b) is specifically as follows: reducing the thickness of Co and Pt in the (Co / Pt)n multilayer to each molecular layer; c) reducing the thickness of the reference layer RL and lowering the magnetic moment of the reference layer RL; In step c), the thickness of the reference layer RL is reduced to ≤1 nm; The method of reducing the magnetic moment of the reference layer RL in step c) is to use a ferromagnetic material with low saturation magnetization Ms and high damping factor.

2. The optimization method according to claim 1, characterized in that Also includes: The structure adjustment layer TL is optimized, and the structure adjustment layer TL is a transition layer.

3. The optimization method according to claim 1, characterized in that In the first pinning layer PL1 of step a), the thickness of each Co layer is 1.8Å~2.5Å, the thickness of each Pt layer is 1.8Å~2.5Å, and n is 4~8.

4. The optimization method according to claim 1, characterized in that The step a) further comprises: The thickness of the Co layer or the Co alloy layer in contact with the antiferromagnetic coupling layer AFC is increased.

5. The optimization method according to claim 1, characterized in that In the second pinning layer PL1 of step b), the thickness of each Co layer is 1.8Å~2.5Å, the thickness of each Pt layer is 1.8Å~2.5Å, and n is 2~5.

6. The optimization method according to claim 1, characterized in that: The step b) further comprises: The thickness of the Co layer in contact with the antiferromagnetic coupling layer AFC is made thicker than the thickness of other Co layers in the (Co / Pt)n multilayer.

7. The optimization method according to claim 2, characterized in that: The method of optimizing the structure adjustment layer TL includes one or more of using a heavy metal material with strong B absorption, using a non-magnetic material, and reducing the thickness of the structure adjustment layer TL.

8. An MTJ structure, characterized in that: A fixed layer formed by the optimization method according to any one of claims 1 to 7.

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