A free layer of MRAM and its preparation method and magnetic tunnel junction of MRAM

Abstract

The present invention belongs to the technical field of magnetoresistive devices, and in particular relates to a free layer of an MRAM, a preparation method thereof, and a magnetic tunnel junction of an MRAM. The free layer provided by the present invention is arranged on a barrier layer, and includes at least two magnetic layers, with a coupling layer arranged between adjacent magnetic layers; each magnetic layer is deposited by magnetron sputtering; the magnetic layer in contact with the barrier layer is deposited under at least two different magnetron sputtering powers, and the magnetron sputtering power on the side near the barrier layer is the smallest. Based on the traditional free layer structure, the present invention can significantly improve the perpendicular magnetic anisotropy field (H) of the free layer while maintaining the thickness of the magnetic layer unchanged by reducing the deposition power of the magnetic layer adjacent to the barrier layer. k ), reducing interface damage and improving the data retention capability of MRAM.

Description

Technical Field

[0001] The present invention belongs to the technical field of magnetoresistive devices, and in particular relates to a free layer of an MRAM and a preparation method thereof, and a magnetic tunnel junction of the MRAM. Background Art

[0002] Spin Transfer Torque Magnetic Random Access Memory (STT-MRAM) offers advantages such as simple circuit design, fast read / write speeds, and non-volatility. Its basic structure is a magnetic tunnel junction (MTJ), consisting of a free layer, a reference layer, and a barrier layer sandwiched between them. The magnetization direction of the reference layer is fixed and does not flip during device operation; the magnetization direction of the free layer is collinear (parallel or antiparallel) with the reference layer. By utilizing the spin torque of electrons, the magnetization direction of the free layer is flipped, causing the magnetization directions of the reference layer and free layer to be parallel (lower resistance) or antiparallel (higher resistance), thereby enabling the writing of a "0" or "1."

[0003] For the free layer, MRAM switches between "0" and "1" by flipping the free layer. Therefore, the easier the free layer flips (the smaller Hc), the smaller the required driving force (current / voltage) and the lower the power consumption. However, if Hc is too small, there is a risk that the read current / thermal disturbance will flip the free layer. Therefore, both SRAM-like MRAM and Flash-like MRAM have certain requirements for the reliable operation of the device at different temperatures, which requires MRAM to have a relatively high Δ. According to the calculation formula of Δ, under the premise that the free layer material / structure does not change much, pSTT-MRAM is mainly related to the perpendicular magnetic anisotropy field (H) of the free layer. k ) is related to volume / thickness (free layer magnetic film thickness) as described in the following formula:

[0004]

[0005] However, simply increasing the thickness of the free layer will lead to H k By increasing the thickness of H k , which will reduce the thickness of the magnetic film. Therefore, an improved process is needed to increase H while keeping the thickness of the magnetic film unchanged. k , to increase data retention. Summary of the Invention

[0006] In view of this, an object of the present invention is to provide an MRAM free layer and a preparation method thereof, and an MRAM magnetic tunnel junction. The MRAM free layer structure provided by the present invention can reduce interface damage and improve the data retention capability of the MRAM by reducing the deposition power of the magnetic layer adjacent to the barrier layer.

[0007] The present invention provides a free layer of an MRAM, which is arranged on a barrier layer and includes at least two magnetic layers, with a coupling layer arranged between adjacent magnetic layers;

[0008] Each magnetic layer is deposited by magnetron sputtering;

[0009] The magnetic layer in contact with the barrier layer is deposited and formed under at least two different magnetron sputtering powers, and the magnetron sputtering power on the side near the barrier layer is the smallest.

[0010] Preferably, the magnetron sputtering power on the side of the near-barrier layer is 10-150W.

[0011] Preferably, the magnetron sputtering power of the magnetic layer in contact with the barrier layer on the side far from the barrier layer is 200-1000W.

[0012] Preferably, the thickness of the magnetic layer in contact with the barrier layer deposited at the minimum magnetron sputtering power is 0.1-0.5 nm.

[0013] Preferably, the total thickness of each magnetic layer is independently selected to be 0.6-2.5 nm.

[0014] Preferably, the material of each magnetic layer is independently selected from Co, Fe, Co-Fe alloy, Fe-B alloy, Co-B alloy, Co-Fe-B alloy or Heusler alloy.

[0015] Preferably, the free layer includes a first magnetic layer, a coupling layer, and a second magnetic layer stacked in sequence;

[0016] The material of the coupling layer is Ir, Ir alloy, Ru, Ru alloy, W, W alloy, Mo, Mo alloy, Ta or Ta alloy.

[0017] Preferably, the free layer includes a first magnetic layer, a first coupling layer, a second magnetic layer, a second coupling layer, a third magnetic layer, a third coupling layer and a fourth magnetic layer stacked in sequence;

[0018] The materials of the first coupling layer and the third coupling layer are independently selected from Ir, Ir alloy, Ru, Ru alloy, W, W alloy, Mo, Mo alloy, Ta or Ta alloy;

[0019] The material of the second coupling layer is MgO.

[0020] The present invention provides a method for preparing the free layer described in the above technical solution, comprising the following steps:

[0021] A plurality of magnetic layers and coupling layers are alternately deposited on the barrier layer using magnetron sputtering technology to form a free layer;

[0022] The magnetic layer in contact with the barrier layer is deposited and formed under at least two different magnetron sputtering powers, and the magnetron sputtering power on the side close to the barrier layer is the smallest.

[0023] The present invention provides a magnetic tunnel junction, comprising a reference layer, a barrier layer, a free layer and a cover layer stacked in sequence, characterized in that the free layer is the free layer described in the above technical solution.

[0024] Compared with the prior art, the present invention provides an MRAM free layer and a preparation method thereof, as well as an MRAM magnetic tunnel junction. The free layer provided by the present invention is arranged on the barrier layer, and includes at least two magnetic layers, with a coupling layer arranged between adjacent magnetic layers; each magnetic layer is deposited by magnetron sputtering; the magnetic layer in contact with the barrier layer is deposited under at least two different magnetron sputtering powers, and the magnetron sputtering power on the side near the barrier layer is the smallest. Based on the traditional free layer structure, the present invention can significantly improve the perpendicular magnetic anisotropy field (H) of the free layer while maintaining the thickness of the magnetic layer unchanged by reducing the deposition power of the magnetic layer adjacent to the barrier layer. k ), reducing interface damage and improving the data retention capability of MRAM. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the following briefly introduces the drawings required for use in the embodiments or the description of the prior art. Obviously, the drawings described below are merely embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on the provided drawings without paying any creative work.

[0026] Figure 1 1 is a schematic structural diagram of a free layer having a dual magnetic layer structure provided by an embodiment of the present invention;

[0027] Figure 2 is a schematic diagram of the free layer structure provided by Example 1 of the present invention;

[0028] Figure 3 This is a schematic diagram of the free layer structure provided in Example 2 of the present invention. DETAILED DESCRIPTION

[0029] The following will clearly and completely describe the technical solutions in the embodiments of the present invention in conjunction with the accompanying drawings. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the 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.

[0030] The present invention provides a free layer of an MRAM, which is arranged on a barrier layer and includes at least two magnetic layers, with a coupling layer arranged between adjacent magnetic layers;

[0031] Each magnetic layer is deposited by magnetron sputtering;

[0032] The magnetic layer in contact with the barrier layer is deposited and formed under at least two different magnetron sputtering powers, and the magnetron sputtering power on the side near the barrier layer is the smallest.

[0033] In the free layer provided by the present invention, the material of each magnetic layer is preferably Co, Fe, Co-Fe alloy, Fe-B alloy, Co-B alloy, Co-Fe-B alloy or Heusler alloy; the total thickness of each magnetic layer is preferably 0.6 to 2.5 nm, specifically 0.6 nm, 0.7 nm, 0.8 nm, 0.9 nm, 1 nm, 1.1 nm, 1.2 nm, 1.3 nm, 1.4 nm, 1.5 nm, 1.6 nm, 1.7 nm, 1.8 nm, 1.9 nm, 2 nm, 2.1 nm, 2.2 nm, 2.3 nm, 2.4 nm or 2.5 nm.

[0034] In the free layer provided by the present invention, each magnetic layer is deposited by magnetron sputtering. The magnetic layer in contact with the barrier layer is deposited at at least two different magnetron sputtering powers, with the magnetron sputtering power being lowest on the side proximal to the barrier layer. Preferably, the magnetic layer in contact with the barrier layer is deposited at two different magnetron sputtering powers, with the magnetron sputtering power being lower on the side proximal to the barrier layer than on the side distal to the barrier layer.

[0035] In the free layer provided by the present invention, the magnetron sputtering power of the magnetic layer in contact with the barrier layer on the side near the barrier layer is preferably 10 to 150 W, specifically 10 W, 15 W, 20 W, 25 W, 30 W, 35 W, 40 W, 45 W, 50 W, 55 W, 60 W, 65 W, 70 W, 75 W, 80 W, 85 W, 90 W, 95 W, 100 W, 105 W, 110 W, 115 W, 120 W, 125 W, 130 W, 135 W, 140 W, 145 W or 150 W; the thickness of the magnetic layer in contact with the barrier layer deposited at the minimum magnetron sputtering power is preferably 0.1 to 0.5 nm, specifically 0.1 nm, 0.2 nm, 0.3 nm, 0.4 nm or 0.5 nm.

[0036] In the free layer provided by the present invention, the magnetron sputtering power of the magnetic layer in contact with the barrier layer on the side far from the barrier layer is preferably 200-1000 W, specifically 200 W, 250 W, 300 W, 350 W, 400 W, 450 W, 500 W, 550 W, 600 W, 650 W, 700 W, 750 W, 800 W, 850 W, 900 W, 950 W or 1000 W.

[0037] In the free layer provided by the present invention, there is no particular limitation on the magnetron sputtering power when depositing the magnetic layer not in contact with the barrier layer. The magnetic layer can be deposited under the same magnetron sputtering power or under different magnetron sputtering powers.

[0038] In the free layer provided by the present invention, the thickness of the coupling layer is preferably 0.1-1 nm, specifically 0.1 nm, 0.2 nm, 0.3 nm, 0.4 nm, 0.5 nm, 0.6 nm, 0.7 nm, 0.8 nm, 0.9 nm or 1 nm.

[0039] In one embodiment of the present invention, the free layer includes a first magnetic layer, a coupling layer, and a second magnetic layer stacked in sequence. Figure 1 The material selection, formation method, and thickness of the first and second magnetic layers have been described above in the introduction to the magnetic layer and will not be repeated here. The material of the coupling layer is preferably Ir, Ir alloy, Ru, Ru alloy, W, W alloy, Mo, Mo alloy, Ta, or Ta alloy. The thickness of the coupling layer has been described above in the introduction to the coupling layer and will not be repeated here.

[0040] In another embodiment provided by the present invention, the free layer includes a first magnetic layer, a first coupling layer, a second magnetic layer, a second coupling layer, a third magnetic layer, a third coupling layer, and a fourth magnetic layer stacked in sequence. The material selection, formation method, and thickness of the first, second, third, and fourth magnetic layers have been described above in the introduction to the magnetic layer and are not repeated here. The materials of the first and third coupling layers are preferably independently Ir, Ir alloy, Ru, Ru alloy, W, W alloy, Mo, Mo alloy, Ta, or Ta alloy. The material of the second coupling layer is preferably MgO. The thicknesses of the first, second, and third coupling layers have been described above in the introduction to the coupling layer and are not repeated here.

[0041] The present invention also provides a method for preparing the free layer described in the above technical solution, comprising the following steps:

[0042] A plurality of magnetic layers and coupling layers are alternately deposited on the barrier layer using magnetron sputtering technology to form a free layer;

[0043] The magnetic layer in contact with the barrier layer is deposited and formed under at least two different magnetron sputtering powers, and the magnetron sputtering power on the side close to the barrier layer is the smallest.

[0044] In the preparation method provided herein, a free layer structure is prepared by layer-by-layer deposition on a barrier layer. The deposition method is magnetron sputtering, and the magnetic layer in contact with the barrier layer is deposited at at least two different magnetron sputtering powers, with the magnetron sputtering power being lowest near the barrier layer. The magnetron sputtering power, deposition thickness, and deposited materials have been described above and will not be further elaborated here.

[0045] The present invention also provides a magnetic tunnel junction (MTJ), comprising a reference layer, a barrier layer, a free layer, and a capping layer stacked in sequence. The free layer is the free layer described in the above technical solution; the barrier layer is preferably made of MgO; the thickness of the barrier layer is preferably 0.5 to 3 nm, specifically 0.5 nm, 1 nm, 1.5 nm, 2 nm, 2.5 nm, or 3 nm; the capping layer is preferably made of MgO; the thickness of the capping layer is preferably 0.2 to 2 nm, specifically 0.2 nm, 0.3 nm, 0.4 nm, 0.5 nm, 0.7 nm, 1 nm, 1.2 nm, 1.5 nm, 1.7 nm, or 2 nm.

[0046] The technical solution provided by the present invention can significantly increase the perpendicular magnetic anisotropy field (H) of the free layer while keeping the thickness of the magnetic layer unchanged by reducing the deposition power of the magnetic layer adjacent to the barrier layer on the basis of the traditional free layer structure. k), reducing interface damage and improving the data retention capability of MRAM.

[0047] For the purpose of greater clarity, the present invention is described in detail with reference to the following examples.

[0048] Example 1

[0049] Using magnetron sputtering technology, Co-Fe-B alloy layer 1, Co-Fe-B alloy layer 2, coupling layer, Co-Fe-B alloy layer 3, Co-Fe-B alloy layer 4 and cover layer are deposited in sequence on the barrier layer.

[0050] Among them, the material of the barrier layer is MgO and the thickness is 2nm, the deposition power of Co-Fe-B alloy layer 1 is 30W and the deposition thickness is 0.3nm, the deposition power of Co-Fe-B alloy layer 2 is 300W and the deposition thickness is 1.2nm, the material of the coupling layer is Ta and the thickness is 0.4nm, the deposition power of Co-Fe-B alloy layer 3 is 500W and the deposition thickness is 0.8nm, the deposition power of Co-Fe-B alloy layer 4 is 500W and the deposition thickness is 0.2nm, and the material of the cover layer is MgO and the thickness is 1.0nm. The final free layer structure is as follows Figure 2 As shown, Figure 2 It is a schematic diagram of the free layer structure provided in Example 1 of the present invention.

[0051] According to the calculation formula of Δ, under the premise that the free layer material / structure does not change much, pSTT-MRAM is mainly related to the perpendicular magnetic anisotropy field (H k ) is related to volume / thickness (free layer magnetic film thickness) as described in the following formula:

[0052]

[0053] However, simply increasing the thickness of the free layer will lead to H k By increasing the thickness of H k , which will reduce the thickness of the magnetic film. Therefore, this embodiment reduces the deposition power of the Co-Fe-B alloy layer above the barrier layer MgO, reducing the physical bombardment damage to MgO during the Co-Fe-B alloy deposition process, thereby improving the film quality and interface flatness of the barrier layer MgO, while maintaining the thickness of the magnetic film unchanged, and improving the H k , to increase data retention.

[0054] Comparative Example 1

[0055] Referring to the free layer structure provided in Example 1, the only difference is that the deposition power of the Co—Fe—B alloy layer 1 is 300 W, thereby obtaining a free layer structure.

[0056] Performance evaluation (Example 1, Comparative Example 1)

[0057] The free layer structure of Comparative Example 1 was used as a reference to determine the test conditions for its coercivity (Hc), magnetoresistance (TMR), and anisotropy field (Hk) when it was 1.00 au. The free layer structure of Example 1 was then tested under the same test conditions to obtain the coercivity (Hc), magnetoresistance (TMR), and anisotropy field (Hk) test results of the free layer structure of Example 1, as shown in the following table:

[0058] Free layer process Coercive force (Hc) / au Magnetoresistance (TMR) / au Anisotropy field (Hk) / au Comparative Example 1 1.00 1.00 1.00 Example 1 1.24 1.04 1.14

[0059] From the Hc / Hk data in the table above, it can be seen that the perpendicular magnetic anisotropy (PMA) of the free layer has been significantly improved, indicating that the interface quality of the barrier layer / free layer has been significantly improved. At the same time, the spin filtering effect of MgO and the polarizability of the free layer have been enhanced, and the TMR has also been improved to a certain extent, thereby improving Δ.

[0060] Example 2

[0061] Using magnetron sputtering technology, Co-Fe-B alloy layer 1, Co-Fe-B alloy layer 2, coupling layer 1, Co-Fe-B alloy layer 3, Co-Fe-B alloy layer 4, coupling layer 2, Co-Fe-B alloy layer 5, Co-Fe-B alloy layer 6, coupling layer 3, Co-Fe-B alloy layer 7, Co-Fe-B alloy layer 8 and a covering layer are deposited in sequence on the barrier layer.

[0062] Among them, the material of the barrier layer is MgO and the thickness is 2.0nm. The deposition power of the Co-Fe-B alloy layer 1 is 30W and the deposition thickness is 0.3nm. The deposition power of the Co-Fe-B alloy layer 2 is 300W and the deposition thickness is 1.2nm. The material of the coupling layer 1 is Ta and the thickness is 0.3nm. The deposition power of the Co-Fe-B alloy layer 3 is 500W and the deposition thickness is 0.8nm. The deposition power of the Co-Fe-B alloy layer 4 is 50W and the deposition thickness is 0.2nm. The material of the coupling layer 2 is M The deposition power of the Co-Fe-B alloy layer 5 is 30W, the deposition thickness is 0.3nm, the deposition power of the Co-Fe-B alloy layer 6 is 300W, the deposition thickness is 1.2nm, the material of the coupling layer 3 is Ta, the thickness is 0.3nm, the deposition power of the Co-Fe-B alloy layer 7 is 500W, the deposition thickness is 0.8nm, the deposition power of the Co-Fe-B alloy layer 8 is 50W, the deposition thickness is 0.2nm, and the material of the cover layer is MgO, the thickness is 0.5nm. The free layer structure finally formed is as follows Figure 3 As shown, Figure 3This is a schematic diagram of the free layer structure provided in Example 2 of the present invention.

[0063] Comparative Example 2

[0064] Referring to the free layer structure provided in Example 2, the only difference is that the deposition power of the Co—Fe—B alloy layer 1 is 300 W, and the deposition power of the Co—Fe—B alloy layer 5 is 300 W, thereby obtaining a free layer structure.

[0065] Performance evaluation (Example 2, Comparative Example 2)

[0066] The free layer structure of Comparative Example 2 was used as a reference to determine the test conditions for its coercivity (Hc), magnetoresistance (TMR), and anisotropy field (Hk) when it was 1.00 au. The free layer structure of Example 2 was then tested under the same test conditions to obtain the coercivity (Hc), magnetoresistance (TMR), and anisotropy field (Hk) test results of the free layer structure of Example 2, as shown in the following table:

[0067] Free layer process Coercive force (Hc) / au Magnetoresistance (TMR) / au Anisotropy field (Hk) / au Comparative Example 2 1.00 1.00 1.00 Example 2 1.14 1.10 1.23

[0068] From the Hc / Hk data in the table above, it can be seen that even for complex structures, the PMA of the free layer can be significantly improved, indicating that the interface quality of the barrier layer / free layer has been significantly improved. At the same time, the spin filtering effect of MgO and the polarization rate of the free layer have been enhanced, and the TMR has also been improved to a certain extent, thereby improving Δ.

[0069] The above is only a preferred embodiment of the present invention. It should be pointed out that for ordinary technicians in this technical field, several improvements and modifications can be made without departing from the principles of the present invention. These improvements and modifications should also be regarded as within the scope of protection of the present invention.

Claims

1. A free layer of an MRAM, disposed on a barrier layer, characterized in that: It comprises at least two magnetic layers, with a coupling layer provided between adjacent magnetic layers; Each magnetic layer is deposited by magnetron sputtering; The magnetic layer in contact with the barrier layer is deposited under at least two different magnetron sputtering powers, and the magnetron sputtering power on the side near the barrier layer is the smallest; The magnetron sputtering power of the magnetic layer in contact with the barrier layer on the side near the barrier layer is 10-150W; the thickness of the magnetic layer in contact with the barrier layer deposited under the minimum magnetron sputtering power is 0.1-0.5nm.

2. The free layer according to claim 1, wherein: The magnetron sputtering power of the magnetic layer in contact with the barrier layer on the side far from the barrier layer is 200-1000W.

3. The free layer according to claim 1, wherein: The total thickness of each magnetic layer is independently selected to be 0.6 to 2.5 nm.

4. The free layer according to claim 1, wherein: The material of each magnetic layer is independently selected from Co, Fe, Co-Fe alloy, Fe-B alloy, Co-B alloy, Co-Fe-B alloy or Heusler alloy.

5. The free layer according to claim 1, wherein: The free layer includes a first magnetic layer, a coupling layer and a second magnetic layer stacked in sequence; The material of the coupling layer is Ir, Ir alloy, Ru, Ru alloy, W, W alloy, Mo, Mo alloy, Ta or Ta alloy.

6. The free layer according to claim 1, wherein: The free layer includes a first magnetic layer, a first coupling layer, a second magnetic layer, a second coupling layer, a third magnetic layer, a third coupling layer and a fourth magnetic layer stacked in sequence; The materials of the first coupling layer and the third coupling layer are independently selected from Ir, Ir alloy, Ru, Ru alloy, W, W alloy, Mo, Mo alloy, Ta or Ta alloy; The material of the second coupling layer is MgO.

7. A method for preparing the free layer according to any one of claims 1 to 6, comprising the following steps: A plurality of magnetic layers and coupling layers are alternately deposited on the barrier layer using magnetron sputtering technology to form a free layer; The magnetic layer in contact with the barrier layer is deposited and formed under at least two different magnetron sputtering powers, and the magnetron sputtering power on the side close to the barrier layer is the smallest.

8. A magnetic tunnel junction comprising a reference layer, a barrier layer, a free layer and a cap layer stacked in sequence, characterized in that: The free layer is the free layer according to any one of claims 1 to 6.

Images