WO2021000748A1 - 磁性隧道结 - Google Patents

磁性隧道结 Download PDF

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WO2021000748A1
WO2021000748A1 PCT/CN2020/097105 CN2020097105W WO2021000748A1 WO 2021000748 A1 WO2021000748 A1 WO 2021000748A1 CN 2020097105 W CN2020097105 W CN 2020097105W WO 2021000748 A1 WO2021000748 A1 WO 2021000748A1
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layer
coupling
polarization
tunnel junction
magnetic tunnel
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PCT/CN2020/097105
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French (fr)
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何世坤
杨晓蕾
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浙江驰拓科技有限公司
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    • H—ELECTRICITY
    • H10—SEMICONDUCTOR DEVICES; ELECTRIC SOLID-STATE DEVICES NOT OTHERWISE PROVIDED FOR
    • H10N—ELECTRIC SOLID-STATE DEVICES NOT OTHERWISE PROVIDED FOR
    • H10N50/00—Galvanomagnetic devices
    • H10N50/10—Magnetoresistive devices
    • G—PHYSICS
    • G11—INFORMATION STORAGE
    • G11C—STATIC STORES
    • G11C11/00—Digital stores characterised by the use of particular electric or magnetic storage elements; Storage elements therefor
    • G11C11/02—Digital stores characterised by the use of particular electric or magnetic storage elements; Storage elements therefor using magnetic elements
    • G11C11/16—Digital stores characterised by the use of particular electric or magnetic storage elements; Storage elements therefor using magnetic elements using elements in which the storage effect is based on magnetic spin effect
    • G—PHYSICS
    • G11—INFORMATION STORAGE
    • G11C—STATIC STORES
    • G11C11/00—Digital stores characterised by the use of particular electric or magnetic storage elements; Storage elements therefor
    • G11C11/02—Digital stores characterised by the use of particular electric or magnetic storage elements; Storage elements therefor using magnetic elements
    • G11C11/16—Digital stores characterised by the use of particular electric or magnetic storage elements; Storage elements therefor using magnetic elements using elements in which the storage effect is based on magnetic spin effect
    • G11C11/161—Digital stores characterised by the use of particular electric or magnetic storage elements; Storage elements therefor using magnetic elements using elements in which the storage effect is based on magnetic spin effect details concerning the memory cell structure, e.g. the layers of the ferromagnetic memory cell

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  • the present invention relates to the technical field of magnetic memory, in particular to a magnetic tunnel junction.
  • the core storage device of MRAM Magnetic Random Access Memory
  • MTJ Magnetic Tunnel Junctions
  • TMR magnetic tunnel magnetoresistance
  • the most typical structure includes two layers of magnetic layers and The tunnel layer between two magnetic layers, one of which has a fixed magnetization direction, is called a reference layer, and the other magnetic layer can change its magnetization direction by a magnetic field or current, and is called a free layer.
  • the MTJ presents a high resistance state, which can represent "1”.
  • the free layer magnetization direction is parallel to the reference layer magnetization direction
  • the MTJ presents a low resistance state, which can represent " 0", and vice versa.
  • the write current is applied to the MTJ, and the free layer will be subjected to the polarization current from the reference layer, which is manifested in the free layer feeling the torque from the reference layer .
  • the spin transfer torque STT the magnitude of this torque is related to the angle between the magnetization directions of the free layer and the reference layer, the write current, and the spin polarizability.
  • the larger the angle between the magnetization directions of the free layer and the reference layer the larger the STT.
  • the write current can be appropriately reduced.
  • the angle between the magnetization directions of the free layer and the reference layer is caused by random thermal disturbance, and is a random angle, which is generally 0°-0.5°. It is precisely because of such a random angle that the magnetization direction of the free layer can be reversed during the MTJ write operation.
  • the magnetization reversal time of the free layer is a probability distribution event, and it is also uncertain. In order to ensure the same writing speed, it is necessary to pass a larger writing current.
  • the present invention provides a magnetic tunnel junction, which can reduce the write current of the magnetic tunnel junction.
  • the present invention provides a magnetic tunnel junction, comprising: a reference layer, a tunnel layer, a free layer, a cover layer, a polarization layer, and a first coupling layer that are stacked in sequence, wherein:
  • the reference layer is magnetized in a vertical direction
  • the free layer is magnetized in a vertical direction
  • the first coupling layer is magnetized in a horizontal direction
  • the first coupling layer is directly coupled with the polarization layer, the magnetization direction of the polarization layer deviates from the vertical direction by an angle, and the component in the vertical direction is anti-parallel to the magnetization direction of the reference layer, The component in the direction is parallel to the magnetization direction of the first coupling layer;
  • the reference layer and the polarization layer provide spin-polarized electrons for the free layer at the same time, so as to provide a spin transfer torque of the magnetization reversal of the free layer.
  • the angle at which the magnetization direction of the polarization layer deviates from the vertical direction is between 0° and 30°.
  • the polarization layer includes one of alternately grown Co/Ni multilayer films, alternately grown Co/Pt multilayer films, and alternately grown Co/Pd multilayer films.
  • the reference layer includes one of CoFeB and alternately grown Co/Pt multilayer films.
  • the vertical flipping magnetic field strength of the polarization layer is greater than the vertical flipping magnetic field strength of the reference layer, so that the polarization layer and the vertical component of the reference layer's magnetization direction are arranged anti-parallel when the magnetic field is initialized.
  • the first coupling layer includes NiFe.
  • the covering layer includes one or a combination of MgO, Mg, Mo, Ta, and MgAlO.
  • it further includes: a coupling modulation layer located between the first coupling layer and the polarization layer, and the coupling modulation layer is used to adjust the gap between the first coupling layer and the polarization layer. Coupling effect.
  • the coupling modulation layer includes one of Ru, Cr, Mo, Ir, Hf, and Ta.
  • the free layer includes CoFeB
  • the tunnel layer includes one or a combination of MgO, Mg, Mo, Ta, and MgAlO
  • the reference layer includes one of CoFeB, CoB, and FeB, or A combination of several, or one of Ta, Mo, Ir and Ru single-layer films, or alternately grown Co/Ni multilayer films, alternately grown Co/Pt multilayer films and alternately grown Co/Pd A type of multilayer film.
  • it also includes:
  • the second coupling layer is located on the side of the first coupling layer opposite to the coupling modulation layer, the second coupling layer is magnetized in a horizontal direction, and the magnetization direction is opposite to the magnetization direction of the first coupling layer;
  • the isolation layer is located between the second coupling layer and the first coupling layer.
  • the second coupling layer includes NiFe, and the isolation layer includes Ru.
  • the magnetization direction of the polarization layer deviates from the vertical direction by an angle through the coupling effect of the first coupling layer and the polarization layer.
  • the reference layer and the polarization layer can provide self Rotationally polarized electrons, that is, the polarized layer that deviates from the vertical direction by a certain angle provides the free layer with a second transfer torque, which makes the free layer magnetization direction reversal speed faster, and then can pass in more information while maintaining the current writing speed. Small write current.
  • the polarization layer has a deflection angle, the initial delay of the spin transfer torque can be significantly reduced.
  • FIG. 1 is a schematic structural diagram of a magnetic tunnel junction according to an embodiment of the present invention
  • FIG. 2 is a schematic structural diagram of a magnetic tunnel junction according to another embodiment of the present invention.
  • Figure 3 is a schematic diagram of the MTJ shown in Figure 2 flipping from an anti-parallel state to a parallel state;
  • Figure 4 is a schematic diagram of the MTJ shown in Figure 2 flipping from a parallel state to an anti-parallel state
  • Fig. 5 is a dynamic reversal curve of normalized vertical magnetization obtained by simulation with time
  • Figure 6 is the curve of the change of the turning time with the deflection angle of the polarization layer
  • FIG. 7 is a schematic structural diagram of a magnetic tunnel junction according to another embodiment of the invention.
  • the magnetic tunnel junction 10 includes: a reference layer 101, a tunnel layer 102, a free layer 103, a cover layer 104, a polarization layer 105, and a second layer stacked in sequence.
  • a coupling layer 107 in which,
  • the reference layer 101 is magnetized in a vertical direction
  • the free layer 103 is magnetized in a vertical direction
  • the first coupling layer 107 is magnetized in a horizontal direction
  • the first coupling layer 107 is directly coupled with the polarization layer 105, the magnetization direction of the polarization layer 105 deviates from the vertical direction by an angle, and the component in the vertical direction is opposite to the magnetization direction of the reference layer 101 Parallel, the component in the horizontal direction is parallel to the magnetization direction of the first coupling layer 107;
  • the reference layer 101 and the polarization layer 105 provide spin-polarized electrons to the free layer 103 at the same time, so as to provide the spin transfer torque of the magnetization reversal of the free layer 103.
  • the magnetic tunnel junction 10 further includes a coupling modulation layer 106 located between the first coupling layer 107 and the polarization layer 105, and the coupling modulation layer 106 is used for To adjust the coupling between the first coupling layer 107 and the polarization layer 105.
  • the magnetic tunnel junction shown in FIG. 1 and FIG. 2 can reduce the writing current that passes during writing. Use the magnetic tunnel junction shown in Figure 2 to analyze the writing process. The specific analysis is as follows:
  • the reference layer 101 provides the free layer 103 with transmission spin-polarized electron injection; the polarization layer 105 provides the free layer 103 Reflected spin-polarized electron injection; wherein the polarization direction of the transmitted spin-polarized electron provided by the reference layer 101 is the same as the magnetization direction of the reference layer; the polarization direction of the reflected spin-polarized electron provided by the polarization layer 105 is the same as the polarization direction
  • the magnetization direction of the layer is opposite, that is, the polarization direction of the transmitted spin-polarized electrons provided by the reference layer 101 is deflected by a certain angle. Under the combined action of the two parts of the spin-polarized electrons, the spin transfer torque is provided to realize the free layer magnetization. The direction is reversed. Compared with the existing MTJ, the turning speed is accelerated.
  • the polarization layer 105 provides the free layer 103 with transmission spin-polarized electron injection; the reference layer 101 provides the free layer 103 with Reflected spin-polarized electron injection; wherein the polarization direction of the reflected spin-polarized electrons provided by the reference layer 101 is opposite to the magnetization direction of the reference layer; the polarization direction of the transmitted spin-polarized electrons provided by the polarization layer 105 is The magnetization direction of the layer is the same, that is, the polarization direction of the reflected spin-polarized electron provided by the reference layer 101 is deflected by a certain angle. Under the combined action of the two parts of the spin-polarized electron, the spin transfer torque is provided to realize the free layer magnetization. The direction is reversed. Compared with the existing MTJ, the turning speed is accelerated.
  • both the reference layer and the polarization layer can provide spin-polarized electrons, that is, the polarization layer that deviates from the vertical direction by a certain angle is the free layer.
  • the second transfer torque is provided, so that the reversal speed of the magnetization direction of the free layer is accelerated, so that a smaller writing current can be passed while keeping the current writing speed unchanged.
  • the polarization layer has a deflection angle, the initial delay of the spin transfer torque can be significantly reduced.
  • the model is as follows:
  • ⁇ is the damping coefficient
  • ⁇ is the gyromagnetic ratio
  • Is the normalized magnetization of the free layer
  • Is the normalized magnetization of the reference layer Is the effective field
  • P is the polarization rate
  • I is the current through the MTJ
  • Is the reduced Planck constant A is the area
  • t is the thickness of the free layer
  • Ms is the saturation magnetization of the free layer.
  • the model is revised, and the revised model is as follows:
  • the deflection angle of the polarized layer magnetization direction 0° ⁇ 30°, the reversal time is reduced, and 25° is the best; the polarization layer magnetization direction is deflected by 25°, and the reversal time is improved by 10% compared with vertical polarization and 17% compared with horizontal polarization.
  • both the polarized layer 105 and the reference layer 101 choose materials with larger coercivity Hc.
  • the polarized layer 105 can adopt alternately grown Co/Ni multilayer films and alternately grown Co /Pt multilayer film and alternately grown Co/Pd multilayer film.
  • the reference layer 101 can be one or a combination of CoFeB, CoB and FeB, one of Ta, Mo, Ir and Ru single-layer films, or alternatively grown Co/Ni multilayer films, One of alternately grown Co/Pt multilayer films and alternately grown Co/Pd multilayer films.
  • the free layer 103 may be CoFeB, and the tunnel layer 102 includes one or a combination of MgO, Mg, Mo, Ta, and MgAlO.
  • the cover layer 104 and the tunnel layer 102 located between the polarization layer 105 and the free layer 103 can use the same material, including one or a combination of MgO, Mg, Mo, Ta, and MgAlO, but the thickness of the two is different ,
  • the cover layer 104 can not only enhance the perpendicular magnetic anisotropy at the interface, but also play a role of spin filtering.
  • the tunnel layer 102 can not only enhance the perpendicular magnetic anisotropy at the interface, but also play a role of spin filtering, and also forms a barrier layer for tunneling current.
  • the first coupling layer 107 needs to have interlayer coupling with the polarization layer 105, and the material of the first coupling layer 107 includes NiFe.
  • the coupling modulation layer 106 located between the first coupling layer 107 and the polarization layer 105 includes one of Ru, Cr, Mo, Ir, Hf, and Ta. It has been verified that NiFe is used for the first coupling layer 107, and Co/Pd multilayer films grown alternately for the polarization layer 105, which can achieve a controllable tilt of the magnetization direction of the polarization layer 105.
  • the vertical switching magnetic field (Hc) corresponding to the polarization layer 105 and the reference layer 101 are both a large value, but the two are not equal, for example, the Hc corresponding to the polarization layer 105 is 5000 Oe , The Hc corresponding to the reference layer 101 is 3000 Oe.
  • the second vertical magnetic field can only reverse the magnetization direction of one of the polarization layer and the reference layer, so that the magnetization direction of the polarization layer 105 and the magnetization direction of the reference layer 101 are in an antiparallel state.
  • the magnetization direction of the polarization layer and the reference layer are opposite through the magnetic field initialization, which can eliminate the stray field felt by the free layer.
  • the magnetization direction of the polarization layer 105 deviates from the vertical direction by a small angle, which can be deviated to the left or right, depending on the first coupling layer 107.
  • a small angle such as ⁇ in Fig. 1, between 0° and 30°. Through this included angle, the initial delay of the spin transfer torque can be significantly reduced.
  • the magnetization direction of the polarized layer is roughly antiparallel to the magnetization direction of the reference layer.
  • the reason why there is an angle between the magnetization direction of the polarization layer and the vertical direction is due to the direct coupling between the polarization layer and the first coupling layer.
  • the size is related to the thickness of the polarization layer and the first coupling layer.
  • the magnetic tunnel junction 20 further includes: a second coupling layer 109 located in the first coupling On the side of the layer 107 opposite to the coupling modulation layer 106, the second coupling layer 109 is magnetized in a horizontal direction, and the magnetization direction is opposite to the magnetization direction of the first coupling layer 107;
  • the isolation layer 108 is located between the second coupling layer 109 and the first coupling layer 107.
  • the material of the second coupling layer 109 includes NiFe, and the material of the isolation layer 108 includes Ru.
  • the first coupling layer 107, the isolation layer 108, and the second coupling layer 109 form a composite antiferromagnetic structure, which can offset the influence of stray fields on the magnetic properties of other layers, and can basically eliminate the equivalent level felt by the free layer
  • the deflection field (dipole field) prevents the uncontrollable bias field caused by further reduction in size.

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Abstract

本发明提供一种磁性隧道结，包括：依次堆叠设置的参考层、隧道层、自由层、覆盖层、极化层以及第一耦合层，其中，所述参考层沿垂直方向磁化；所述自由层沿垂直方向磁化；所述第一耦合层沿水平方向磁化；所述第一耦合层与所述极化层直接耦合，所述极化层的磁化方向偏离垂直方向一个角度，并且在垂直方向上的分量与所述参考层的磁化方向处于反平行，在水平方向上的分量与所述第一耦合层的磁化方向平行；所述参考层和所述极化层同时为所述自由层提供自旋极化电子，以提供所述自由层磁化翻转的自旋转移矩。本发明能够降低磁性隧道结的写入电流。

Description

磁性隧道结 技术领域
本发明涉及磁性存储器技术领域，尤其涉及一种磁性隧道结。
背景技术
MRAM(Magnetic Random Access Memory，磁性随机存储器)的核心存储器件是MTJ(Magnetic Tunnel Junctions，磁性隧道结)，MTJ基于磁性隧道磁阻(TMR)效应，最典型的结构包括两层磁性层和介于两层磁性层之间的隧道层，其中一个磁性层的磁化方向固定，称为参考层，另一个磁性层的磁化方向可以通过磁场或电流改变，称为自由层。实际应用中，当自由层磁化反平行于参考层磁化时，MTJ呈现高阻态，可以代表“1”，当自由层磁化方向平行于参考层磁化方向时，MTJ呈现低阻态，可以代表“0”，反之亦然。
要改变MTJ的存储状态，需要对MTJ进行写操作：在MTJ中通入写入电流，自由层将受到来自参考层的极化电流作用，该作用表现为自由层感受到来自于参考层的力矩，称为自旋转移矩STT，这个力矩的大小与自由层和参考层的磁化方向之间的夹角、写入电流、自旋极化率等有关。其中，自由层和参考层的磁化方向之间的夹角越大，STT越大，在STT一定的情况下，可以适当降低写入电流。
但是，实际对MTJ进行写操作时，自由层和参考层的磁化方向之间的夹角是由随机热扰动引起的，为一个随机夹角，该随机夹角一般为0°～0.5°。正是因为存在这样一个随机夹角，才使得MTJ写操作时自由层的磁化方向能够翻转。
在实现本发明的过程中，发明人发现现有技术中至少存在如下技术问题：
由于随机夹角的大小和方向的不确定性，自由层的磁化翻转时间是一个概 率分布事件，也具有不确定性，为了保证同样的写入速度，必然需要通入更大的写入电流。
发明内容
为解决上述问题，本发明提供一种磁性隧道结，能够降低磁性隧道结的写入电流。
本发明提供一种磁性隧道结，包括：依次堆叠设置的参考层、隧道层、自由层、覆盖层、极化层以及第一耦合层，其中，
所述参考层沿垂直方向磁化；
所述自由层沿垂直方向磁化；
所述第一耦合层沿水平方向磁化；
所述第一耦合层与所述极化层直接耦合，所述极化层的磁化方向偏离垂直方向一个角度，并且在垂直方向上的分量与所述参考层的磁化方向处于反平行，在水平方向上的分量与所述第一耦合层的磁化方向平行；
所述参考层和所述极化层同时为所述自由层提供自旋极化电子，以提供所述自由层磁化翻转的自旋转移矩。
可选地，所述极化层的磁化方向偏离垂直方向的角度介于0°～30°之间。
可选地，所述极化层包括交替生长的Co/Ni多层薄膜、交替生长的Co/Pt多层薄膜和交替生长的Co/Pd多层薄膜中的一种。
可选地，所述参考层包括CoFeB和交替生长的Co/Pt多层薄膜中的一种。
可选地，所述极化层的垂直翻转磁场强度大于所述参考层的垂直翻转磁场强度，以实现在磁场初始化时所述极化层和所述参考层磁化方向垂直分量反平行排列。
可选地，所述第一耦合层包括NiFe。
可选地，所述覆盖层包括MgO、Mg、Mo、Ta和MgAlO中的一种或者几种的组合。
可选地，还包括：耦合调制层，位于所述第一耦合层和所述极化层之间，所述耦合调制层用于调节所述第一耦合层和所述极化层之间的耦合作用。
可选地，所述耦合调制层包括Ru、Cr、Mo、Ir、Hf和Ta中的一种。
可选地，所述自由层包括CoFeB，所述隧道层包括MgO、Mg、Mo、Ta和MgAlO中的一种或者几种的组合，所述参考层包括CoFeB、CoB和FeB中的一种或者几种的组合，或者包括Ta、Mo、Ir和Ru单层薄膜中的一种，或者包括交替生长的Co/Ni多层薄膜、交替生长的Co/Pt多层薄膜和交替生长的Co/Pd多层薄膜中的一种。
可选地，还包括：
第二耦合层，位于所述第一耦合层的与所述耦合调制层相对的一侧，所述第二耦合层沿水平方向磁化，且磁化方向与所述第一耦合层的磁化方向相反；
隔离层，位于所述第二耦合层和所述第一耦合层之间。
可选地，所述第二耦合层包括NiFe，所述隔离层包括Ru。
本发明提供的磁性隧道结，通过第一耦合层和极化层的耦合作用，使极化层磁化方向偏离垂直方向一个角度，在写入过程中，由于参考层和极化层都能够提供自旋极化电子，即偏离垂直方向一定角度的极化层为自由层提供第二转移力矩，使得自由层磁化方向翻转速度加快，进而在保持当前写入速度不变的情况下，可以通入更小的写入电流。同时，由于极化层存在一个偏转角度，能够显著降低自旋转移力矩的初始延时。
附图说明
图1为本发明一实施例的磁性隧道结的结构示意图；
图2为本发明另一实施例的磁性隧道结的结构示意图；
图3为图2所示MTJ从反平行态翻转到平行态的示意图；
图4为图2所示MTJ从平行态翻转到反平行态的示意图；
图5为仿真得到的归一化的垂直方向磁化强度随时间的动态翻转变化曲线；
图6为翻转时间随极化层偏转角的变化曲线；
图7为本发明另一实施例的磁性隧道结的结构示意图。
具体实施方式
为使本发明实施例的目的、技术方案和优点更加清楚，下面将结合本发明实施例中的附图，对本发明实施例中的技术方案进行清楚、完整地描述，显然，所描述的实施例仅仅是本发明一部分实施例，而不是全部的实施例。基于本发明中的实施例，本领域普通技术人员在没有做出创造性劳动前提下所获得的所有其他实施例，都属于本发明保护的范围。
本发明实施例提供一种磁性隧道结，如图1所示，该磁性隧道结10包括：依次堆叠设置的参考层101、隧道层102、自由层103、覆盖层104、极化层105以及第一耦合层107，其中，
所述参考层101沿垂直方向磁化；
所述自由层103沿垂直方向磁化；
所述第一耦合层107沿水平方向磁化；
所述第一耦合层107与所述极化层105直接耦合，所述极化层105的磁化方向偏离垂直方向一个角度，并且在垂直方向上的分量与所述参考层101的磁化方向处于反平行，在水平方向上的分量与所述第一耦合层107的磁化方向平行；
所述参考层101和所述极化层105同时为所述自由层103提供自旋极化电子，以提供所述自由层103磁化翻转的自旋转移矩。
可选地，如图2所示，所述磁性隧道结10还包括：耦合调制层106，位于位于所述第一耦合层107和所述极化层105之间，所述耦合调制层106用于调节所述第一耦合层107和所述极化层105之间的耦合作用。
图1和图2所示的磁性隧道结在写入时，能够降低通入的写入电流。以图2所示的磁性隧道结来分析写入过程，具体分析如下：
MTJ从反平行态(AP)翻转到平行态(P)时，如图3所示，对MTJ施加写电压，正端连接到第一耦合层107，负端连接到参考层101，电流通过MTJ，电子运动方向为从参考层101流经自由层103到极化层105，在这个过程中，参考层101为自由层103提供透射自旋极化电子注入；极化层105为自由层103提供反射自旋极化电子注入；其中，参考层101提供的透射自旋极化电子的极化方向与参考层磁化方向相同；极化层105提供的反射自旋极化电子的极化方向与极化层磁化方向相反，即相对于参考层101提供的透射自旋极化电子的极化方向偏转一定角度，在两部分自旋极化电子的共同作用下，提供自旋转移矩实现自由层磁化方向发生翻转。相对于现有的MTJ，翻转速度加快。
MTJ从平行态(P)翻转到反平行态(AP)时，如图4所示，对MTJ施加写电压，正端连接到参考层101，负端连接到第一耦合层107，电流通过MTJ，电子运动方向为从极化层105流经自由层103到参考层101，在这个过程中，极化层105为自由层103提供透射自旋极化电子注入；参考层101为自由层103提供反射自旋极化电子注入；其中，参考层101提供的反射自旋极化电子的极化方向与参考层磁化方向相反；极化层105提供的透射自旋极化电子的极化方向与极化层磁化方向相同，即相对于参考层101提供的反射自旋极化 电子的极化方向偏转一定角度，在两部分自旋极化电子的共同作用下，提供自旋转移矩实现自由层磁化方向发生翻转。相对于现有的MTJ，翻转速度加快。
通过上面的分析可知，本发明实施例的磁性隧道结，在写入过程中，由于参考层和极化层都能够提供自旋极化电子，即偏离垂直方向一定角度的极化层为自由层提供第二转移力矩，使得自由层磁化方向翻转速度加快，进而在保持当前写入速度不变的情况下，可以通入更小的写入电流。同时，由于极化层存在一个偏转角度，能够显著降低自旋转移力矩的初始延时。
为了找到翻转速度最快时的偏转角度，发明人还进行了物理仿真论证。利用基于LLG方程的理论模型进行仿真：
模型如下：
Figure PCTCN2020097105-appb-000001
上式中，α为阻尼系数，γ为旋磁比，
Figure PCTCN2020097105-appb-000002
为自由层的归一化磁化强度，
Figure PCTCN2020097105-appb-000003
为参考层的归一化磁化强度，
Figure PCTCN2020097105-appb-000004
为有效场，P为极化率，I为通过MTJ的电流，
Figure PCTCN2020097105-appb-000005
为约化普朗克常数，A为面积，t为自由层厚度，Ms为自由层饱和磁化强度。
应用到本发明实施例，对模型进行修正，修正后的模型如下：
Figure PCTCN2020097105-appb-000006
上式中，考虑随机热扰动场，H_thermal均值为0，标准差sigma为
Figure PCTCN2020097105-appb-000007
STT项进行修正，加入参考层和极化层分别引入的STT项。
改变极化层磁化方向偏转角度0°～90°，其中0°代表垂直磁化方向极化层，90°代表水平磁化方向极化层；通过翻转特性仿真，得到仿真结果如图5所示，图5表示极化层105磁化方向的偏转角为0°，15°，30°，90°的情况下，归一化的垂直方向磁化强度随时间的动态翻转变化曲线，通过该动态翻转曲线可以提取翻转时间，得到的翻转时间随极化层偏转角的变化曲线如图6所示，分析图6可得到，相比于磁化方向完全垂直或者完全水平的极化层，极化层磁化方向偏转角度0°～30°，翻转时间均得到降低，其中25°为最佳；极化层磁化方向偏转25°，其翻转时间相比垂直极化改善10％，相比水平极化改善17％。
上述磁性隧道结在物理实现时，极化层105和参考层101都选择矫顽力Hc较大的材料，例如，极化层105可以采用交替生长的Co/Ni多层薄膜、交替生长的Co/Pt多层薄膜和交替生长的Co/Pd多层薄膜中的一种。参考层101可以采用CoFeB、CoB和FeB中的一种或者几种的组合，还可以采用Ta、Mo、Ir和Ru单层薄膜中的一种，或者采用交替生长的Co/Ni多层薄膜、交替生长的Co/Pt多层薄膜和交替生长的Co/Pd多层薄膜中的一种。而自由层103可以采用CoFeB，隧道层102包括MgO、Mg、Mo、Ta和MgAlO中的一种或者几 种的组合。位于极化层105和自由层103之间的覆盖层104和隧道层102可以使用相同的材料，包括MgO、Mg、Mo、Ta和MgAlO中的一种或者几种的组合，但二者厚度不同，覆盖层104不仅能增强界面处的垂直磁各向异性，还起到自旋过滤的作用。隧道层102不仅能增强界面处的垂直磁各向异性，还起到自旋过滤的作用，也是形成隧穿电流的势垒层。
而第一耦合层107要和极化层105发生层间耦合作用，第一耦合层107的材料包括NiFe。位于第一耦合层107和极化层105之间的耦合调制层106包括Ru、Cr、Mo、Ir、Hf和Ta中的一种。经验证，第一耦合层107采用NiFe，极化层105采用交替生长的Co/Pd多层薄膜，能够实现极化层105的磁化方向发生可控倾斜。
上述的磁性隧道结在磁化前，由于极化层105和参考层101对应的垂直翻转磁场(Hc)都为一个较大的值，但二者不相等，如极化层105对应的Hc为5000Oe，参考层101对应的Hc为3000Oe。通过磁场初始化时，首先施加第一垂直磁场，使得极化层105和参考层101都沿垂直方向磁化，且磁化方向平行；然后施加第二垂直磁场，磁场方向与第一垂直磁场的方向相反，该第二垂直磁场只能使极化层和参考层中的其中一层的磁化方向发生翻转，使得极化层105的磁化方向和参考层101的磁化方向处于反平行状态。通过磁场初始化使得极化层和参考层磁化方向相反，能够消除自由层感受到的杂散场(stray field)。
进一步地，在第一耦合层107产生的水平磁场的作用下，使得极化层105的磁化方向偏离垂直方向一个小角度，可以向左偏，也可以向右偏，取决于第一耦合层107的水平磁化方向，图1中，由于第一耦合层107水平磁化方向为左，因此极化层磁化方向左偏离垂直方向一个小角度，如图1中的θ，介于0° ～30°。通过该夹角，能够显著降低自旋转移力矩的初始延时。但在垂直方向极化层磁化方向大致上还是和参考层的磁化方向处于反平行。
另外补充说明的是，所述极化层的磁化方向之所以和垂直方向之间存在一个夹角，是由于极化层和第一耦合层之间存在层间的直接耦合作用，该夹角的大小与极化层以及第一耦合层的厚度有关，通过改变极化层以及第一耦合层的厚度，可以改变极化层的磁化方向偏离垂直方向的夹角。
本发明另一实施例提供一种磁性隧道结，如图7所示，在图2所示磁性隧道结的基础上，磁性隧道结20还包括：第二耦合层109，位于所述第一耦合层107的与所述耦合调制层106相对的一侧，所述第二耦合层109沿水平方向磁化，且磁化方向与所述第一耦合层107的磁化方向相反；
隔离层108，位于所述第二耦合层109和所述第一耦合层107之间。
其中，第二耦合层109的材料包括NiFe，隔离层108的材料包括Ru。
第一耦合层107、隔离层108、第二耦合层109形成一合成反铁磁结构，能够抵消杂散场(stray field)对其它层磁性的影响，还能够基本消除自由层感受到的等效水平偏转场(dipole field)，防止尺寸进一步微缩后导致的偏置场不可控。
以上所述，仅为本发明的具体实施方式，但本发明的保护范围并不局限于此，任何熟悉本技术领域的技术人员在本发明揭露的技术范围内，可轻易想到的变化或替换，都应涵盖在本发明的保护范围之内。因此，本发明的保护范围应该以权利要求的保护范围为准。

Claims (11)

  1. 一种磁性隧道结，其特征在于，包括：依次堆叠设置的参考层、隧道层、自由层、覆盖层、极化层以及第一耦合层，其中，
    所述参考层沿垂直方向磁化；
    所述自由层沿垂直方向磁化；
    所述第一耦合层沿水平方向磁化；
    所述第一耦合层与所述极化层直接耦合，所述极化层的磁化方向偏离垂直方向一个角度，并且在垂直方向上的分量与所述参考层的磁化方向处于反平行，在水平方向上的分量与所述第一耦合层的磁化方向平行；
    所述参考层和所述极化层同时为所述自由层提供自旋极化电子，以提供所述自由层磁化翻转的自旋转移矩。
  2. 根据权利要求1所述的磁性隧道结，其特征在于，所述极化层的磁化方向偏离垂直方向的角度介于0°～30°之间。
  3. 根据权利要求1所述的磁性隧道结，其特征在于，所述极化层包括交替生长的Co/Ni多层薄膜、交替生长的Co/Pt多层薄膜和交替生长的Co/Pd多层薄膜中的一种。
  4. 根据权利要求1所述的磁性隧道结，其特征在于，所述极化层的垂直翻转磁场强度大于所述参考层的垂直翻转磁场强度，以实现在磁场初始化时所述极化层和所述参考层磁化方向垂直分量反平行排列。
  5. 根据权利要求1所述的磁性隧道结，其特征在于，所述第一耦合层包括NiFe。
  6. 根据权利要求1所述的磁性隧道结，其特征在于，所述覆盖层包括 MgO、Mg、Mo、Ta和MgAlO中的一种或者几种的组合。
  7. 根据权利要求1所述的磁性隧道结，其特征在于，还包括：耦合调制层，位于所述第一耦合层和所述极化层之间，所述耦合调制层用于调节所述第一耦合层和所述极化层之间的耦合作用。
  8. 根据权利要求7所述的磁性隧道结，其特征在于，所述耦合调制层包括Ru、Cr、Mo、Ir、Hf和Ta中的一种。
  9. 根据权利要求1或7所述的磁性隧道结，其特征在于，所述自由层包括CoFeB，所述隧道层包括MgO、Mg、Mo、Ta和MgAlO中的一种或者几种的组合，所述参考层包括CoFeB、CoB和FeB中的一种或者几种的组合，或者包括Ta、Mo、Ir和Ru单层薄膜中的一种，或者包括交替生长的Co/Ni多层薄膜、交替生长的Co/Pt多层薄膜和交替生长的Co/Pd多层薄膜中的一种。
  10. 根据权利要求1或7所述的磁性隧道结，其特征在于，还包括：
    第二耦合层，位于所述第一耦合层的与所述耦合调制层相对的一侧，所述第二耦合层沿水平方向磁化，且磁化方向与所述第一耦合层的磁化方向相反；
    隔离层，位于所述第二耦合层和所述第一耦合层之间。
  11. 根据权利要求10所述的磁性隧道结，其特征在于，所述第二耦合层包括NiFe，所述隔离层包括Ru。
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