A free layer of a magnetic tunnel junction, a magnetic tunnel junction, and a spin-transfer torque magnetic random access memory.

Abstract

This invention belongs to the field of magnetic tunnel junction technology, and particularly relates to a free layer of a magnetic tunnel junction, a magnetic tunnel junction, and a spin-transfer torque magnetic random access memory (STM). The free layer provided by this invention comprises a first ferromagnetic layer, a spacer layer, and a second ferromagnetic layer in sequential contact; the thicknesses of both the first and second ferromagnetic layers are ≤1 nm, and the thickness of the second ferromagnetic layer is less than the thickness of the first ferromagnetic layer; the spacer layer comprises at least two non-magnetic elements. By controlling the thickness of the first and second ferromagnetic layers in the free layer structure to less than 1 nm, this invention effectively improves STT efficiency and reduces write current; simultaneously, the spacer layer in this free layer structure is composed of at least two different non-magnetic elements with strong binding energy, ensuring the stability of the spacer layer structure, suppressing element diffusion caused by the thinning of the magnetic layer, and improving erasure and write resistance.

Description

Technical Field

[0001] This invention belongs to the field of magnetic tunnel junction technology, and particularly relates to a free layer of a magnetic tunnel junction, a magnetic tunnel junction, and a spin-transfer torque magnetic random access memory. Background Technology

[0002] Spin Transfer Torque Magnetic Random Access Memory (STT-MRAM) is a novel type of non-volatile memory whose core storage unit is a magnetic tunnel junction (MTJ) structure. A typical MTJ consists of a pinned layer, a barrier layer, and a free layer. The pinned layer, also known as the reference layer, maintains its magnetization direction while the magnetization direction of the free layer is changed to be either in the same or opposite direction as the pinned layer. MTJ devices rely on quantum tunneling to allow electrons to pass through the barrier layer. The tunneling probability of polarized electrons is related to the relative magnetization directions of the pinned and free layers. When the magnetization directions of the pinned and free layers are the same, the tunneling probability of polarized electrons is high, and the MTJ device exhibits a low-resistance state (Rp). Conversely, when the magnetization directions of the pinned and free layers are opposite, the tunneling probability of polarized electrons is low, and the MTJ device exhibits a high-resistance state (Rap). MRAM utilizes the Rp and Rap states of the MTJ device to represent the logic states "1" and "0," respectively, thereby achieving data storage. The tunneling magnetoresistance value is expressed as: TMR = 100% × (R) ap -R p ) / R p .

[0003] STT-MRAM utilizes the spin-transfer torque (STT) effect of current to perform write operations on MRAM. When a spin-polarized current passes through a magnetic thin film, the polarization current interacts with the local electrons of the magnetic film, exerting a torque on the local magnetic moment of the film, causing it to tend to align with the polarization direction of the spin-polarized current. This phenomenon is called the spin-transfer torque effect (STT effect). Applying a polarization current opposite to the magnetization direction to the magnetic film, when the polarization current intensity exceeds a certain threshold, causes the magnetic moment of the film itself to flip. The spin-transfer torque effect allows the magnetization direction of the free layer in an MTJ device to be parallel or antiparallel to the magnetization direction of the pinned layer, thus enabling the "write" operation.

[0004] Currently, the critical write current required for MRAM is relatively high. A high write current increases chip power consumption and the risk of the insulating barrier layer breaking down, shortening chip lifespan. Furthermore, to further shrink the process node and fabricate high-density memory chips, it is necessary to reduce the write current of STT-MRAM. Summary of the Invention

[0005] In view of this, the purpose of the present invention is to provide a free layer of a magnetic tunnel junction, a magnetic tunnel junction, and a spin-transfer torque magnetic random access memory. The free layer provided by the present invention can reduce the write current of the MRAM and improve the erasure and write resistance of the device.

[0006] The present invention provides a free layer of a magnetic tunnel junction, comprising a first ferromagnetic layer, a spacer layer and a second ferromagnetic layer in sequential contact; the thickness of the first ferromagnetic layer and the second ferromagnetic layer are both ≤1nm, and the thickness of the second ferromagnetic layer is less than the thickness of the first ferromagnetic layer; the spacer layer comprises at least two non-magnetic elements.

[0007] Preferably, the materials of the first ferromagnetic layer and the second ferromagnetic layer are independently selected from Co, Fe, Ni, cobalt boride, iron boride, nickel boride, Co-Fe alloy, Ni-Fe alloy, Co-Ni alloy, Co-Fe-Ni alloy, Co-Fe-B alloy, Ni-Fe-B alloy, Co-Ni-B alloy, Co-Fe-Ni-B alloy, Fe-Pt alloy, Fe-Pd alloy, Co-Pt alloy, Co-Pd alloy, Co-Fe-Pt alloy, Co-Fe-Pd alloy, Fe-Pt-Pd alloy, Co-Pt-Pd alloy, or Co-Fe-Pt-Pd alloy.

[0008] Preferably, the thickness difference between the first ferromagnetic layer and the second ferromagnetic layer is 0.05 to 0.5 nm.

[0009] Preferably, the spacer layer is composed of at least one heavy metal non-magnetic element and at least one non-magnetic element with an atomic number less than 20.

[0010] Preferably, the heavy metal nonmagnetic element includes one or more of Ta, Mo, W, Ti, Hf, Zr, Nb, Ta, Ti, Nb, Ta, and Ti;

[0011] The nonmagnetic elements with atomic numbers less than 20 include one or more of B, C, O, Mg, Al, and Si.

[0012] Preferably, the proportion of non-magnetic heavy metal elements in the spacer layer is less than 50 wt%.

[0013] Preferably, the free layer further includes a covering layer disposed on the surface of the second ferromagnetic layer.

[0014] Preferably, the material of the covering layer includes one or more of Ta, Mo, W, Ti, Hf, Zr, Nb, Ru, Mg, TaN, TiN, NbN, tantalum boride, titanium boride, molybdenum boride, hafnium boride, zirconium boride, tungsten boride, magnesium oxide, aluminum oxide, magnesium-aluminum composite oxide, titanium oxide, tantalum oxide, gallium oxide, and iron oxide.

[0015] The present invention provides a magnetic tunnel junction, including the free layer described in the above technical solution.

[0016] This invention provides a spin-transfer torque magnetic random access memory, including the magnetic tunnel junction described in the above technical solution.

[0017] Compared with existing technologies, this invention provides a free layer of a magnetic tunnel junction, a magnetic tunnel junction, and a spin-transfer torque magnetic random access memory (STM). The free layer provided by this invention comprises a first ferromagnetic layer, a spacer layer, and a second ferromagnetic layer in sequential contact; the thicknesses of both the first and second ferromagnetic layers are ≤1 nm, and the thickness of the second ferromagnetic layer is less than that of the first ferromagnetic layer; the spacer layer comprises at least two non-magnetic elements. By controlling the thickness of the first and second ferromagnetic layers in the free layer structure to less than 1 nm, this invention effectively improves STT efficiency and reduces write current. Simultaneously, the spacer layer in this free layer structure is composed of at least two different non-magnetic elements with strong binding energies, ensuring the stability of the spacer layer structure, suppressing element diffusion caused by the thinning of the magnetic layer, and improving erasure and write resistance. Experimental results show that the free layer structure provided by this invention can significantly reduce the write current of STT-MRAM devices while maintaining high data retention stability, thus improving STT efficiency. Attached Figure Description

[0018] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on the provided drawings without creative effort.

[0019] Figure 1 This is a schematic diagram of the structure of a free layer formed on a barrier layer according to an embodiment of the present invention;

[0020] Figure 2 This is a schematic diagram of the structure of STT-MTJ provided in an embodiment of the present invention. Detailed Implementation

[0021] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0022] This invention provides a free layer for a magnetic tunnel junction, comprising a first ferromagnetic layer, a spacer layer, and a second ferromagnetic layer in sequential contact. Preferably, the material of the first ferromagnetic layer is Co, Fe, Ni, cobalt boride, iron boride, nickel boride, Co-Fe alloy, Ni-Fe alloy, Co-Ni alloy, Co-Fe-Ni alloy, Co-Fe-B alloy, Ni-Fe-B alloy, Co-Ni-B alloy, Co-Fe-Ni-B alloy, Fe-Pt alloy, Fe-Pd alloy, Co-Pt alloy, Co-Pd alloy, Co-Fe-Pt alloy, Co-Fe-Pd alloy, or Fe-P The alloy can be t-Pd, Co-Pt-Pd, or Co-Fe-Pt-Pd; the thickness of the first ferromagnetic layer is ≤1nm, specifically 0.1nm, 0.15nm, 0.2nm, 0.25nm, 0.3nm, 0.35nm, 0.4nm, 0.45nm, 0.5nm, 0.55nm, 0.6nm, 0.65nm, 0.7nm, 0.75nm, 0.8nm, 0.85nm, 0.9nm, 0.95nm, or 1nm.

[0023] In the free layer provided by the present invention, the material of the second ferromagnetic layer is preferably Co, Fe, Ni, cobalt boride, iron boride, nickel boride, Co-Fe alloy, Ni-Fe alloy, Co-Ni alloy, Co-Fe-Ni alloy, Co-Fe-B alloy, Ni-Fe-B alloy, Co-Ni-B alloy, Co-Fe-Ni-B alloy, Fe-Pt alloy, Fe-Pd alloy, Co-Pt alloy, Co-Pd alloy, Co-Fe-Pt alloy, Co-Fe-Pd alloy, Fe-Pt-Pd alloy, Co-Pt-Pd alloy, or Co-Fe-Pt-Pd alloy; the thickness of the second ferromagnetic layer is less than that of the first ferromagnetic layer, and the thickness difference is preferably 0.05 to 0.5 nm, specifically 0.05 nm, 0.1 nm, 0.15 nm, 0.2 nm, 0.25 nm, 0.3 nm, 0.35 nm, 0.4 nm, 0.45 nm, or 0.5 nm. In the embodiments provided by the present invention, the thickness of the second ferromagnetic layer may specifically be 0.05, 0.1 nm, 0.15 nm, 0.2 nm, 0.25 nm, 0.3 nm, 0.35 nm, 0.4 nm, 0.45 nm, 0.5 nm, 0.55 nm, 0.6 nm, 0.65 nm, 0.7 nm, 0.75 nm, 0.8 nm, 0.85 nm, 0.9 nm, or 0.95 nm.

[0024] The free layer provided by this invention comprises at least two non-magnetic elements in the spacer layer, preferably consisting of at least one heavy metal non-magnetic element and at least one non-magnetic element with an atomic number less than 20. The heavy metal non-magnetic element preferably includes one or more of Ta, Mo, W, Ti, Hf, Zr, Nb, Ta, Ti, Nb, Ta, and Ti; the non-magnetic element with an atomic number less than 20 preferably includes one or more of B, C, O, Mg, Al, and Si; the proportion of the heavy metal non-magnetic element in the spacer layer is preferably less than 50 wt%, specifically 5 wt%, 10 wt%, 15 wt%, 20 wt%, 25 wt%, 30 wt%, 35 wt%, 40 wt%, or 45 wt%. In this invention, the thickness of the spacer layer is preferably 0.05 to 0.8 nm, specifically 0.05 nm, 0.1 nm, 0.15 nm, 0.2 nm, 0.25 nm, 0.3 nm, 0.35 nm, 0.4 nm, 0.45 nm, 0.5 nm, 0.55 nm, 0.6 nm, 0.65 nm, 0.7 nm, 0.75 nm, or 0.8 nm.

[0025] The free layer provided by the present invention preferably further includes a capping layer, which is disposed on the surface of the second ferromagnetic layer; the material of the capping layer preferably includes one or more of Ta, Mo, W, Ti, Hf, Zr, Nb, Ru, Mg, TaN, TiN, NbN, tantalum boride, titanium boride, molybdenum boride, hafnium boride, zirconium boride, tungsten boride, magnesium oxide, aluminum oxide, magnesium-aluminum composite oxide, titanium oxide, tantalum oxide, gallium oxide, and iron oxide; the thickness of the capping layer is preferably 0.5-3 nm, specifically 0.5 nm, 0.6 nm, 0.7 nm, 0.8 nm, 0.9 nm, 1 nm, 1.2 nm, 1.5 nm, 1.7 nm, 2 nm, 2.3 nm, 2.5 nm, 2.7 nm, or 3 nm.

[0026] In one embodiment of the present invention, the free layer is formed on the barrier layer by layer deposition, and its structure is as follows: Figure 1 As shown, Figure 1 This is a schematic diagram of the structure of a free layer formed on a barrier layer according to an embodiment of the present invention.

[0027] The present invention also provides a magnetic tunnel junction (MTJ), comprising a pinned layer (also called a reference layer), a barrier layer, and a free layer as described above, which are sequentially contacted. A first ferromagnetic layer in the free layer is in contact with the barrier layer. The reference layer is composed of a magnetic material, and the barrier layer is composed of a non-magnetic material.

[0028] This invention also provides a spin-transfer torque magnetic random access memory (STT-MRAM), wherein the spin-transfer torque magnetic tunnel junction (STT-MTJ) in the STT-MRAM comprises an artificial antiferromagnetic layer, a structural transition layer, and the magnetic tunnel junction described above, which are sequentially contacted. A reference layer in the magnetic tunnel junction is in contact with the structural transition layer. Preferably, the artificial antiferromagnetic layer comprises a first magnetic composite layer, an antiferromagnetic coupling layer, and a second magnetic composite layer, wherein the first and second magnetic composite layers are antiferromagnetically coupled through the antiferromagnetic coupling layer, and their magnetization directions are opposite and perpendicular to the film surface. In one embodiment of this invention, the STT-MTJ is fabricated using a layer-by-layer deposition method, and its structure is as follows: Figure 2 As shown, Figure 2 This is a schematic diagram of the structure of STT-MTJ provided in an embodiment of the present invention.

[0029] The technical solution provided by this invention effectively improves STT efficiency and reduces write current by controlling the thickness of the first and second ferromagnetic layers in the free-layer structure to less than 1 nm. Simultaneously, the spacer layer in this free-layer structure is composed of at least two different non-magnetic elements with strong binding energies, ensuring the stability of the spacer layer structure, suppressing element diffusion caused by the thinning of the magnetic layer, and improving erasure and write resistance. Experimental results show that the technical solution provided by this invention can significantly reduce the write current of STT-MRAM devices while maintaining high data retention stability, thus improving STT efficiency.

[0030] For clarity, the following examples will be used to provide a detailed description.

[0031] Example 1

[0032] The free layer provided in this embodiment includes a first ferromagnetic layer, a spacer layer, a second ferromagnetic layer, and a capping layer deposited sequentially. The first ferromagnetic layer is made of a Co-Fe-B alloy (30 wt% Co and 50 wt% Fe) and has a thickness of 0.9 nm; the second ferromagnetic layer is made of a Co-Fe alloy (30 wt% Co) and has a thickness of 0.7 nm; the spacer layer is composed of W and Mg (40 wt% W) and has a thickness of 0.3 nm; the capping layer is made of Ru and has a thickness of 3 nm.

[0033] Example 2

[0034] The free layer provided in this embodiment includes a first ferromagnetic layer, a spacer layer, a second ferromagnetic layer, and a capping layer deposited sequentially. The first ferromagnetic layer is made of a Co-Fe-B alloy (30 wt% Co and 50 wt% Fe) and has a thickness of 0.8 nm; the second ferromagnetic layer is made of a Ni-Fe alloy (40 wt% Ni) and has a thickness of 0.6 nm; the spacer layer is composed of Ta and Al (30 wt% Ta) and has a thickness of 0.6 nm; and the capping layer is made of MgO and has a thickness of 2.5 nm.

[0035] Example 3

[0036] The free layer provided in this embodiment includes a first ferromagnetic layer, a spacer layer, a second ferromagnetic layer, and a capping layer deposited sequentially. The first ferromagnetic layer is made of a Co-Fe-Ni alloy (20 wt% Co and 60 wt% Fe) and has a thickness of 0.6 nm; the second ferromagnetic layer is made of a Ni-Fe alloy (40 wt% Ni) and has a thickness of 0.5 nm; the spacer layer is composed of W and Si (30 wt% W) and has a thickness of 0.3 nm; and the capping layer is made of MgO and has a thickness of 1.5 nm.

[0037] Comparative Example

[0038] The free layer provided in the comparative example comprises a first ferromagnetic layer, a spacer layer, a second ferromagnetic layer, and a capping layer deposited sequentially. The first ferromagnetic layer is made of a Co-Fe-B alloy (30 wt% Co and 50 wt% Fe) and has a thickness of 1.2 nm; the second ferromagnetic layer is also made of a Co-Fe-B alloy (30 wt% Co and 50 wt% Fe) and has a thickness of 1 nm; the spacer layer is made of W and has a thickness of 0.4 nm; and the capping layer is made of MgO and has a thickness of 1.5 nm.

[0039] Performance testing

[0040] The free-layer structures prepared in the above embodiments and comparative examples were processed and assembled into CD50nm STT-MRAM devices using photolithography, etching, and other processes. The read / write performance of the devices was tested using a wafer tester. Writing was performed using a current with a pulse width of 20ns to evaluate the write current density. An accelerated model was used to test the device's write endurance under high voltage (i.e., how many write cycles under high voltage will cause the device to fail) and data retention at high temperature (i.e., how long at high temperature will the device fail). The write endurance under normal write voltage and the data retention at room temperature were then extrapolated. The results are shown in the table below.

[0041]

[0042] As can be seen from the table above, the free layer structure provided by this invention can significantly reduce the write current of the device while maintaining high data retention stability, and the device's write resistance is significantly improved.

[0043] The above description is only a preferred embodiment of the present invention. It should be noted that for those skilled in the art, several improvements and modifications can be made without departing from the principle of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. A magnetic tunnel junction, comprising: The free layer comprises a first ferromagnetic layer, a spacer layer and a second ferromagnetic layer in contact with each other in sequence; the thickness of the first ferromagnetic layer and the second ferromagnetic layer is less than or equal to 1 nm, and the thickness of the second ferromagnetic layer is less than the thickness of the first ferromagnetic layer; the spacer layer is composed of at least one heavy metal non-magnetic element and at least one non-magnetic element with an atomic number less than 20; the heavy metal non-magnetic element comprises one or more of Ta, Mo, W, Ti, Hf, Zr, Nb, Ta, Ti, Nb, Ta and Ti; the non-magnetic element with an atomic number less than 20 comprises one or more of Mg, Al and Si; the proportion of the heavy metal non-magnetic element in the spacer layer is 10-45wt%.

2. The magnetic tunnel junction of claim 1, wherein, The material of the first ferromagnetic layer and the second ferromagnetic layer is independently selected from Co, Fe, Ni, cobalt boride, iron boride, nickel boride, Co-Fe alloy, Ni-Fe alloy, Co-Ni alloy, Co-Fe-Ni alloy, Co-Fe-B alloy, Ni-Fe-B alloy, Co-Ni-B alloy, Co-Fe-Ni-B alloy, Fe-Pt alloy, Fe-Pd alloy, Co-Pt alloy, Co-Pd alloy, Co-Fe-Pt alloy, Co-Fe-Pd alloy, Fe-Pt-Pd alloy, Co-Pt-Pd alloy or Co-Fe-Pt-Pd alloy.

3. The magnetic tunnel junction of claim 1, wherein, The thickness difference between the first ferromagnetic layer and the second ferromagnetic layer is 0.05-0.5nm.

4. The magnetic tunnel junction of claim 1, wherein, A capping layer is further arranged on the surface of the second ferromagnetic layer not in contact with the spacer layer.

5. The magnetic tunnel junction of claim 4, wherein, The material of the capping layer comprises one or more of Ta, Mo, W, Ti, Hf, Zr, Nb, Ru, Mg, TaN, TiN, NbN, tantalum boride, titanium boride, molybdenum boride, hafnium boride, zirconium boride, tungsten boride, magnesium oxide, aluminum oxide, magnesium-aluminum composite oxide, titanium oxide, tantalum oxide, gallium oxide and iron oxide.

6. A spin transfer torque magnetic random access memory, comprising: The magnetic tunnel junction comprises the magnetic tunnel junction of any one of claims 1-5.

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