WO2020135053A1 - 磁存储单元及sot-mram存储器 - Google Patents

磁存储单元及sot-mram存储器 Download PDF

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WO2020135053A1
WO2020135053A1 PCT/CN2019/124566 CN2019124566W WO2020135053A1 WO 2020135053 A1 WO2020135053 A1 WO 2020135053A1 CN 2019124566 W CN2019124566 W CN 2019124566W WO 2020135053 A1 WO2020135053 A1 WO 2020135053A1
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magnetic
layers
layer
storage unit
magnetic field
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PCT/CN2019/124566
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French (fr)
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何世坤
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浙江驰拓科技有限公司
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    • 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
    • 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
    • G11C11/165—Auxiliary circuits
    • G11C11/1675—Writing or programming circuits or methods
    • 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

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  • the invention relates to the technical field of magnetic memory, in particular to a magnetic storage unit and a SOT-MRAM memory.
  • SOT-MRAM memory The new magnetic storage device based on spin orbital moment and MTJ (which can be called SOT-MRAM memory) has the advantages of read and write separation, fast write speed, low write current density, etc., and is considered to be the future development trend.
  • the spin orbital moment material of SOT-MRAM is integrated with the magnetic tunnel junction MTJ, if the magnetic tunnel magnetic resistance TMR of the MTJ is high, the integration of the two is difficult to achieve. At present, the TMR of the MTJ can only be around 100, which will directly Affect the read and write speed of SOT-MRAM.
  • the present invention provides a magnetic storage unit and a SOT-MRAM memory, which can improve the read and write speed of the SOT-MRAM memory.
  • the present invention provides a magnetic memory cell, including: a spin orbit moment supply line and two magnetic tunnel junctions, each of which includes a free layer, a tunnel layer, and a reference layer stacked in sequence, two The magnetic tunnel junctions are located on the same side of the spin orbital moment supply line and the respective free layers are close to the spin orbital moment supply line, and two reference magnetic layers of the two magnetic tunnel junctions are each provided with a layer of bias magnetic field Layer, the bias magnetic field providing layer is separated from the magnetic tunnel junction by a separation layer, the two bias magnetic field providing layers have different geometric dimensions, and the magnetization directions of the two bias magnetic field providing layers are opposite And each is perpendicular to the magnetization direction of the corresponding free layer of the magnetic tunnel junction.
  • two reference layers of the magnetic tunnel junction are vertically magnetized, and the two bias magnetic fields provide the layer with horizontal magnetization and have opposite horizontal magnetization directions.
  • the two bias magnetic field providing layers adopt the same geometry.
  • both of the bias magnetic field providing layers are elliptical, the length of the short axis is the same, and the length of the long axis is different, the ratio of the long and short axes is between 1.2 and 3, and the long axes are parallel to or The line is provided approximately parallel to the spin orbital moment.
  • both of the bias magnetic field providing layers are rectangular, the lengths of the short sides are the same, and the lengths of the long sides are different.
  • the ratio of the long and short sides is between 1.2 and 3, and the long sides are parallel or close to each other.
  • the line is provided parallel to the spin orbital moment.
  • the material of the spin orbital moment providing wire is a material having a spin orbital moment effect, including: heavy metal, BiSe alloy or antiferromagnetic alloy.
  • the spin orbit moment supply line adopts a multi-segment structure, and the portions located at the two magnetic tunnel junction positions are materials with spin orbit moment effects, and the portions located at other positions are low-resistance metal materials.
  • the difference in the inversion field corresponding to the inversion of the magnetization directions of the two bias magnetic field providing layers is greater than 100 Oe.
  • the magnetization directions of the reference layers of the two magnetic tunnel junctions are the same, and correspondingly, the magnetization directions of the free layers of the two magnetic tunnel junctions are opposite.
  • the present invention provides a SOT-MRAM memory including the above-mentioned magnetic storage unit.
  • the magnetic storage unit and the SOT-MRAM memory provided by the present invention are designed with dual MTJ differential characteristics.
  • the spin orbital moment provides a current in the line, which can simultaneously write to two MTJs, which improves reading. Write speed, and does not require external magnetic field.
  • FIG. 1 is a schematic structural diagram of an embodiment of a magnetic storage unit of the present invention.
  • FIG. 2 is a top view of an embodiment of the magnetic storage unit of the present invention.
  • FIG. 3 is a schematic structural view of another embodiment of the magnetic storage unit of the present invention.
  • Figure 4 is a schematic diagram of the principle of the flipping of the surface magnetization layer
  • FIG. 5 is a schematic diagram of the principle of current flipping written by a magnetic storage device
  • FIG. 6 is a schematic diagram of the state of the magnetic memory device when writing
  • Figure 7-8 shows the two data storage states after the magnetic memory device writes data.
  • the present invention provides a magnetic storage unit, as shown in FIG. 1, which is an embodiment of the magnetic storage unit of the present invention.
  • the magnetic memory cell includes a spin orbit moment supply line 101 and two magnetic tunnel junctions MTJ A and MTJ B.
  • MTJ A and MTJ B have the same stack structure, and they include a free layer, a tunnel layer, and a reference layer stacked in sequence, MTJ A and MTJ. B is located on the same side of the spin orbital moment supply line 101 and the respective free layers are close to the spin orbital moment supply line 101.
  • IPM A The layer that provides the bias magnetic field outside the layer
  • IPM B the layer that provides the bias magnetic field outside the MTJ B reference layer
  • IPM A and IPM B are separated from MTJ A and MTJ B by corresponding separation layers, In this embodiment, IPM A and IPM B have different geometric dimensions, IPM B is larger than IPM A , and the in-plane magnetization directions of IPM A and IPM B are opposite and perpendicular to the magnetization directions of the free layers of MTJ A and MTJ B , respectively.
  • the two bias magnetic fields provide the layers IPM A and IPM B can use the same material or different materials. Considering the realization of the process, the same material is usually used. IPM A and IPM B can adopt the same geometric shape, such as ellipse or rectangle, but they need to have different geometric dimensions. When both IPM A and IPM B are elliptical, as shown in FIG. 2, it is a top view of the magnetic memory unit shown in FIG. 1. In Figure 2, the length of the short axis is the same, and the length of the long axis is different. The ratio of the long axis to the short axis is between 1.2 and 3.
  • the short axis length of IPM A and IPM B are both 80 nm, and the short axis of IPM A
  • the ratio of the long axis to the long axis is about 1:1.5
  • the ratio of the short axis to the long axis of IPM B is about 1:2
  • the long axis of IPM B is longer.
  • the long axes of each of IPM A and IPM B are parallel or nearly parallel to the spin orbital moment supply line 101.
  • IPM A and IPM B are rectangular, the lengths of the short sides are the same and the lengths of the long sides are different.
  • the ratio of the long and short sides is between 1.2 and 3.
  • the long sides of IPM A and IPM B are the same. Both are parallel or nearly parallel to the spin orbital moment providing lines.
  • the material of the spin orbital moment supply line is a material with spin orbital moment effect
  • heavy metals such as Pt, Ta, W, Ir, Hf, Ru, Tl, Bi, Au , Os
  • the spin orbital moment supply line can also adopt a multi-segment structure.
  • the parts located at two MTJ positions and in contact with the two MTJs are materials with spin orbital moment effect, such as BiSe, etc., which can provide a free layer through the spin orbital moment effect A certain spin magnetic moment, but the resistance is large; the parts located at other positions are low-resistance metals, such as Ta, etc.
  • the introduction of low-resistance metals can reduce the resistance of the spin orbital moment supply line, thereby reducing device energy consumption.
  • the free layer of MTJ is CoFeB, preferably, the free layer is CoFeB
  • the reference layer of MTJ is CoFeB
  • the tunnel layer of MTJ is MgO
  • the top separation layer is a non-magnetic material containing Ta or TaN.
  • the bias magnetic field providing layer is composed of a layer of NiFe material and has a thickness of about 10 nm.
  • FIG. 3 it is another embodiment of the magnetic storage unit of the present invention.
  • the reference layer is pinned by a synthetic antiferromagnetic structure
  • the synthetic antiferromagnetic structure includes a Co/Pt multilayer film that is repeated multiple times at the top and bottom, and a non-magnetic layer located between the two layers Ferromagnetic coupling layers such as Ru, Ir, Cr, Mo, etc. form antiferromagnetic coupling.
  • FIG. 3 labeled 321 MTJ B free layer, the tunnel layer 322, a synthetic antiferromagnetic reference layer 323 and the separation layer 324, MTJ A structure of layers in the MTJ B the same, reference MTJ B, not marked.
  • the magnetic storage unit of the embodiment of the present invention has an initialization process before writing data.
  • the initialization is to make the in-plane magnetized bias magnetic field provide the layer IPM A and IPM B have opposite magnetization directions.
  • the two bias magnetic fields provide the layer IPM A and the geometric dimensions of the IPM B are significantly different in order to obtain The opposite direction of horizontal magnetization.
  • the in-plane anisotropic field of IPM A and IPM B is determined by the shape and magnetic properties of the material. By designing the shape of IPM A and IPM B , the anisotropy of shape is used to control the coercive force corresponding to IPM A and IPM B.
  • the coercive force Hc A and Hc B are significantly different. Referring to Figure 4, the theoretical demonstration process of initialization is as follows:
  • the first write current forward
  • the second write current reverse
  • the writing process is specifically described below.
  • MTJ A is subjected to the equivalent magnetic field from IPM A in the positive direction (ie, the positive direction of current I), corresponding to a counterclockwise flip Characteristics
  • MTJ B receives the equivalent magnetic field from IPM B in the negative direction (ie, the negative direction of current I), and the corresponding flip is a clockwise characteristic.
  • MTJ A receives the equivalent magnetic field from IPM A in the positive direction
  • the corresponding flip is a clockwise feature
  • MTJ B receives from The equivalent magnetic field of IPM B reverses in a negative direction
  • the corresponding flip is a counterclockwise characteristic
  • the spin orbit moment supply line when writing data to the device, a certain direction of current is applied to the spin orbit moment supply line, and the free layer magnetization directions corresponding to the two MTJs are in the first and second directions, respectively, and the first direction Antiparallel to the second direction, both along the growth direction of the MTJ film. That is, the magnetization directions of the reference layers of the two MTJs are the same. Since the magnetization directions of the bias magnetic field providing layers are opposite, when the spin orbital moment provides current into the line, the magnetization directions of the free layers of the two MTJs are opposite.
  • the process of writing data can refer to FIG. 6, when the first write current I 1 is passed in the spin-orbit moment supply line, MTJ A is in antiparallel (high resistance) and MTJ B is in parallel state (low resistance) ;
  • the second write current I 2 is passed in the spin orbit moment, MTJ A is in parallel (low resistance) and MTJ B is in anti-parallel state (high resistance);
  • the direction of the first write current I 1 is magnetized with IPM B
  • the direction is the same, and the direction of the second write current I 2 is the same as the magnetization direction of the IPM A.
  • FIGS. 7 and 8 The state of the magnetic memory cell after writing data: as shown in FIGS. 7 and 8, define FIG. 7 as state 1, define FIG. 8 as state 2, ie: when the magnetic memory cell is state 1, MTJ A : parallel, MTJ B : Antiparallel; when the magnetic storage unit is in state 2, MTJ A : antiparallel, MTJ B : parallel.
  • FIGS. 7 and 8 define FIG. 7 as state 1, define FIG. 8 as state 2, ie: when the magnetic memory cell is state 1, MTJ A : parallel, MTJ B : Antiparallel; when the magnetic storage unit is in state 2, MTJ A : antiparallel, MTJ B : parallel.
  • the memory when the first write current is applied to the spin track moment, the memory is in state 2; when the second write current is applied to the spin track moment, the memory is in state 1.
  • the above state can be read out through the resistance state corresponding to MTJ. In practice, current or voltage sensitive amplifiers are used.
  • the spin orbital moment when writing data, the spin orbital moment provides a current in the line, and can write to two MTJs at the same time, and the reading and writing speed is fast, and no external is required. magnetic field.
  • the magnetic storage unit of the embodiment of the present invention has a single write current path, which improves the current utilization rate and facilitates a more concise circuit design.
  • the differential of two MTJs is complementary The storage unit can reduce the read error rate of the device and increase the read speed, and can be used for SRAM replacement.
  • An embodiment of the present invention further provides a SOT-MRAM memory.
  • the SOT-MRAM memory includes the foregoing magnetic storage unit.

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  • Computer Hardware Design (AREA)
  • Mram Or Spin Memory Techniques (AREA)
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Abstract

本发明提供一种磁存储单元及SOT-MRAM存储器，所述磁存储单元包括：自旋轨道矩提供线和两个磁性隧道结，每个所述磁性隧道结包括依次堆叠的自由层、隧道层和参考层，两个所述磁性隧道结位于所述自旋轨道矩提供线的同一侧且各自的自由层靠近所述自旋轨道矩提供线，两个所述磁性隧道结的参考层外侧分别有一层偏置磁场提供层，所述偏置磁场提供层通过分离层与所述磁性隧道结隔开，两个所述偏置磁场提供层具有不同的几何尺寸，同时两个所述偏置磁场提供层的磁化方向相反且分别垂直于各自对应的磁性隧道结的自由层的磁化方向。本发明能够提高SOT-MRAM存储器的读写速度。

Description

磁存储单元及SOT-MRAM存储器 技术领域
本发明涉及磁存储器技术领域，尤其涉及一种磁存储单元及SOT-MRAM存储器。
背景技术
研究发现，在具有自旋轨道矩效应(Spin Orbit Torque，SOT)的材料中通入电流时，会在材料的界面处产生自旋极化的自旋电流，该自旋电流可以用于翻转纳米磁铁，例如磁性隧道结MTJ中的自由层。基于自旋轨道矩和MTJ的新型磁存储器件(可以称为SOT-MRAM存储器)具有读写分离、写入速度快、写电流密度低等优点，被认为是未来的发展趋势。
但是，SOT-MRAM的自旋轨道矩材料与磁性隧道结MTJ集成时，如果MTJ的磁性隧道磁阻TMR较高，二者的集成难以实现，目前MTJ的TMR只能在100左右，这会直接影响SOT-MRAM的读写速度。
发明内容
为解决上述问题，本发明提供一种磁存储单元及SOT-MRAM存储器，能够提高SOT-MRAM存储器的读写速度。
第一方面，本发明提供一种磁存储单元，包括：自旋轨道矩提供线和两个磁性隧道结，每个所述磁性隧道结包括依次堆叠的自由层、隧道层和参考层，两个所述磁性隧道结位于所述自旋轨道矩提供线的同一侧且各自的自由层靠近所述自旋轨道矩提供线，两个所述磁性隧道结的参考层外侧分别有一层偏置磁场提供层，所述偏置磁场提供层通过分离层与所述磁性隧道结隔开，两个所述偏置磁场提供层具有不同的几何尺寸，同时两个所述偏置磁场提供层的磁化方向相反且分别垂直于各自对应的磁性隧道结的自由层的磁化方向。
可选地，两个所述磁性隧道结的参考层垂直磁化，两个所述偏置磁场提供层水平磁化且具有相反的水平磁化方向。
可选地，两个所述偏置磁场提供层采用相同的几何形状。
可选地，两个所述偏置磁场提供层均为椭圆形，短轴长度相同，长轴长度不同，各自的长短轴比例均介于1.2～3之间，各自的长轴均平行于或者接近平行于所述自旋轨道矩提供线。
可选地，两个所述偏置磁场提供层均为矩形，短边长度相同，长边长度不同，各自的长短边比例均介于1.2～3之间，各自的长边均平行于或者接近平行于所述自旋轨道矩提供线。
可选地，所述自旋轨道矩提供线的材料为具有自旋轨道矩效应的材料，包括：重金属、BiSe合金或者反铁磁合金。
可选地，所述自旋轨道矩提供线采用多段结构，位于两个所述磁性隧道结位置的部分为具有自旋轨道矩效应的材料，位于其他位置的部分为低电阻金属材料。
可选地，两个所述偏置磁场提供层的磁化方向翻转所对应的翻转场差别大于100Oe。
可选地，两个所述磁性隧道结的参考层的磁化方向相同，对应地，两个所述磁性隧道结的自由层的磁化方向相反。
第二方面，本发明提供一种SOT-MRAM存储器，所述SOT-MRAM存储器包括上述磁存储单元。
本发明提供的磁存储单元及SOT-MRAM存储器，采用双MTJ差分特性设计，在写入数据时，自旋轨道矩提供线中通一次电流，可以同时对两个MTJ进行写操作，提高了读写速度，而且不需要外界磁场。
附图说明
图1为本发明的磁存储单元的一个实施例的结构示意图；
图2为本发明的磁存储单元的一个实施例的俯视图；
图3为本发明的磁存储单元的另一个实施例的结构示意图；
图4为面层磁化层翻转原理示意图；
图5为磁存储器件写入的电流翻转原理示意图；
图6为磁存储器件写入时的状态示意图；
图7-8为磁存储器件写入数据后的两种数据存储状态。
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。
本发明提供一种磁存储单元，如图1所示，为本发明的磁存储单元的一个实施例。磁存储单元包括自旋轨道矩提供线101和两个磁性隧道结MTJ A和MTJ B，MTJ A和MTJ B层叠结构相同，都包括依次堆叠的自由层、隧道层和参考层，MTJ A和MTJ B位于自旋轨道矩提供线101的同一侧且各自的自由层靠近自旋轨道矩提供线101，MTJ A和MTJ B的参考层外侧分别有一层面内磁化的偏置磁场提供层，MTJ A参考层外侧的偏置磁场提供层记为IPM A，MTJ B参考层外侧的偏置磁场提供层记为IPM B，IPM A和IPM B分别通过相对应的分离层与MTJ A和MTJ B隔开，本实施例中，IPM A，IPM B具有不同的几何尺寸，IPM B大于IPM A，同时IPM A，IPM B的面内磁化方向相反且分别垂直于MTJ A， MTJ B的自由层的磁化方向。图1中，只标记出了MTJ B的自由层221、隧道层222、参考层223和分离层224，MTJ A的各层结构与MTJ B相同，可参考MTJ B，未作标记。MTJ A和MTJ B的参考层垂直磁化，磁化方向相同，IPM A和IPM B水平磁化且具有相反的水平磁化方向。
进一步的，两个偏置磁场提供层IPM A，IPM B可以使用相同的材料，也可以使用不同的材料，考虑到工艺的实现性，通常采用同一材料。IPM A，IPM B可以采用相同的几何形状，如都采用椭圆形或者矩形，但需要具有不同的几何尺寸。当IPM A，IPM B都为椭圆形时，如图2所示，为图1所示的磁存储单元的俯视图。图2中，二者短轴长度相同，长轴长度不同，各自的长短轴比例均介于1.2～3之间，例如，IPM A，IPM B的短轴长度均为80nm，IPM A的短轴和长轴比例约为1:1.5，IPM B的短轴和长轴比例约为1:2，IPM B的长轴长度更长。另外，IPM A，IPM B各自的长轴均平行于或者接近平行于自旋轨道矩提供线101。
同理地，当IPM A，IPM B都为矩形时，二者短边长度相同，长边长度不同，各自的长短边比例均介于1.2～3之间，IPM A，IPM B各自的长边均平行于或者接近平行于自旋轨道矩提供线。
另外说明的是，上述实施例中，自旋轨道矩提供线的材料为具有自旋轨道矩效应的材料，可以采用重金属，如Pt，Ta，W，Ir，Hf，Ru，Tl，Bi，Au，Os，也可以采用拓扑绝缘体，如BiSe合金，BiTe合金，如Bi2Se3，BiSeTe合金，TlBiSe，还可以采用反铁磁合金，如PtMn，IrMn等，厚度2～20nm。自旋轨道矩提供线还可以采用多段结构，位于两个MTJ位置、与两个MTJ接触的部分为具有自旋轨道矩效应的材料，如BiSe等，其能通过自旋轨道矩效应提供自由层一定的自旋磁矩，但电阻较大；位于其他位置的部分为低电阻金 属，如Ta等，低电阻金属的引入可以降低自旋轨道矩提供线的电阻，从而降低器件能耗。
两个MTJ的材料如下：MTJ的自由层为CoFeB，优选地，自由层为CoFeB|NM|CoFeB结构，其中NM为非磁性金属如Mo,Ir,Ru,Ta,W,Hf,Au等，厚度为0.2-0.8纳米之间。MTJ的参考层为CoFeB，MTJ的隧道层为MgO，顶部分离层为包含Ta或者TaN等非磁性材料。偏置磁场提供层为包含一层NiFe材料，厚度为10nm左右。
如图3所示，为本发明的磁存储单元的另一个实施例。该实施例和上述实施例的区别在于，参考层被合成反铁磁结构钉扎，所述合成反铁磁结构包含上下两处多次重复的Co/Pt多层膜以及位于两层中间的非铁磁耦合层如Ru，Ir，Cr，Mo等形成反铁磁耦合。图3中只标记了MTJ B的自由层321、隧道层322、合成反铁磁参考层323和分离层324，MTJ A的各层结构与MTJ B相同，可参考MTJ B，未作标记。
上面重点介绍了本发明实施例的磁存储单元的结构特征，下面介绍一下磁存储单元的工作过程。
本发明实施例的磁存储单元，在写数据之前，有一个初始化的过程。初始化是为了使两个面内磁化的偏置磁场提供层IPM A，IPM B具有相反的磁化方向，两个偏置磁场提供层IPM A，IPM B的几何尺寸之所以有显著差别，就是为了得到相反的水平磁化方向。
IPM A，IPM B面内各向异性场由形状和材料磁性质决定，通过设计IPM A，IPM B形状，利用形状各向异性控制IPM A，IPM B对应的矫顽力，使得二者的矫顽力Hc A与Hc B有显著的差别，参考图4，初始化的理论论证过程如下：
偏置磁场提供层长短轴分别标记为a，b，厚度标记为t，NiFe饱和磁化强 度为Ms＝800emu/cc情况下，各向异性场近似为：Hk＝2(1/b-1/a)*t*4π*Ms，将各参数数值带入公式中，IPM A对应的Hk A＝838Oe，IPM B对应的Hk B＝1257Oe，由于NiFe为超软磁材料，其面内矫顽力由各向异性场Hk决定。即Hc A＝Hk A，Hc B＝Hk B。因此在初始化时，可以采用正向施加2000Oe磁场，再负向施加-1000Oe磁场，即可将所有磁存储单元初始化到所需状态。由于IPM A，IPM B稳定地处于相反的磁化方向，MTJ A和MTJ B中感受到的水平方向耦极子耦合磁场沿相反方向。
按下述方法对磁存储单元初始化：
①沿第一方向施加足够大水平磁场，H>|Hc B|，使得IPM A,IPM B具有相同的磁化方向，均沿第一方向排列。
②反方向施加水平磁场，|Hc A|<H<|Hc B|,在此条件下，IPM A磁化方向反向(沿第二方向)，而IPM B磁化方向仍沿第一方向。
③使得IPM A,IPM B形成磁化反平行排列,去掉初始化磁场，初始化结束。
通过上述初始化使得IPM A，IPM B水平磁化方向相反，初始化后的器件状态即为图2所示。
初始化完成之后，可以对磁存储单元写入数据。根据MTJ参考层磁性方向的不同，在自旋轨道矩提供线中通入第一写电流(正向)可以将磁存储单元设置为第1数据状态，通入第二写电流(反向)可以将磁存储单元设置为第2数据状态。下面具体说明写入过程。
写入数据依赖自旋轨道矩效应，对于垂直磁化材料(MTJ自由层)，依据有效水平磁场的方向，磁矩随自旋轨道矩提供线中电流大小和方向而翻转的回线可构成顺时针或逆时针变化特征。
例如，如图5所示，对某种选定的自旋轨道矩提供线材料，MTJ A受到来自于IPM A的等效磁场沿正方向(即电流I的正方向)，对应翻转为逆时针特征，MTJ B受到来自于IPM B的等效磁场沿负反向(即电流I的负方向)，对应的翻转为顺时针特征。需要说明的是，改变自旋轨道矩提供线材料，有可能达到相反的翻转特性，即MTJ A受到来自于IPM A的等效磁场沿正方向，对应翻转为顺时针特征，MTJ B受到来自于IPM B的等效磁场沿负反向，对应的翻转为逆时针特征。
基于该电流翻转原理，在器件进行写入数据时，在自旋轨道矩提供线中施加某一方向电流，2个MTJ对应的自由层磁化方向分别处于第一和第二方向，且第一方向反平行于第二方向，均为沿MTJ薄膜生长方向。即2个MTJ的参考层的磁化方向相同，由于偏置磁场提供层的磁化方向相反，自旋轨道矩提供线中通入电流时，两个MTJ的自由层磁化方向相反。
具体地，写入数据的过程可以参考图6，在自旋轨道矩提供线中通入第一写电流I 1时，MTJ A处于反平行(高电阻)，MTJ B处于平行态(低电阻)；在自旋轨道矩中通入第二写电流I 2时，MTJ A处于平行(低电阻)，MTJ B处于反平行态(高电阻)；其中第一写电流I 1的方向与IPM B磁化方向相同，第二写电流I 2的方向与IPM A的磁化方向相同。
写入数据后的磁存储单元状态：如图7和图8所示，定义图7为状态1，定义图8为状态2，即：磁存储单元为状态1时，MTJ A：平行，MTJ B：反平行；磁存储单元为状态2时，MTJ A：反平行，MTJ B：平行。具体可以参考下表。
磁存储单元状态 MTJ状态
状态1 MTJ A：平行；MTJ B：反平行
状态2 MTJ A：反平行；MTJ B：平行
因此，在自旋轨道矩中通入第一写电流时，存储器处于状态2；在自旋轨道矩中通入第二写电流时，存储器处于状态1。根据MTJ的特性，上述状态可以通过MTJ对应的电阻状态读出。实际中使用电流或电压型灵敏放大器。
综上所述，本发明实施例的磁存储单元，在写入数据时，自旋轨道矩提供线中通一次电流，可以同时对两个MTJ进行写操作，读写速度快，而且不需要外界磁场。另外，本发明实施例的磁存储单元具有单一的写电流通路，提高了电流利用率和有利于更简洁的电路设计，同时相比具有固定参考电阻的传统存储单元，两个MTJ组成的差分互补存储单元，能降低器件的读错误率，提升读取速度，可以用于SRAM替代。
本发明实施例还提供一种SOT-MRAM存储器，所述SOT-MRAM存储器包括上述磁存储单元。
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 (10)

  1. 一种磁存储单元，其特征在于，包括：自旋轨道矩提供线和两个磁性隧道结，每个所述磁性隧道结包括依次堆叠的自由层、隧道层和参考层，两个所述磁性隧道结位于所述自旋轨道矩提供线的同一侧且各自的自由层靠近所述自旋轨道矩提供线，两个所述磁性隧道结的参考层外侧分别有一层偏置磁场提供层，所述偏置磁场提供层通过分离层与所述磁性隧道结隔开，两个所述偏置磁场提供层具有不同的几何尺寸，同时两个所述偏置磁场提供层的磁化方向相反且分别垂直于各自对应的磁性隧道结的自由层的磁化方向。
  2. 根据权利要求1所述的磁存储单元，其特征在于，两个所述磁性隧道结的参考层垂直磁化，两个所述偏置磁场提供层水平磁化且具有相反的水平磁化方向。
  3. 根据权利要求1所述的磁存储单元，其特征在于，两个所述偏置磁场提供层采用相同的几何形状。
  4. 根据权利要求3所述的磁存储单元，其特征在于，两个所述偏置磁场提供层均为椭圆形，短轴长度相同，长轴长度不同，各自的长短轴比例均介于1.2～3之间，各自的长轴均平行于或者接近平行于所述自旋轨道矩提供线。
  5. 根据权利要求3所述的磁存储单元，其特征在于，两个所述偏置磁场提供层均为矩形，短边长度相同，长边长度不同，各自的长短边比例均介于1.2～3之间，各自的长边均平行于或者接近平行于所述自旋轨道矩提供线。
  6. 根据权利要求1所述的磁存储单元，其特征在于，所述自旋轨道矩提供线的材料为具有自旋轨道矩效应的材料，包括：重金属、BiSe合金或者反铁磁合金。
  7. 根据权利要求1所述的磁存储单元，其特征在于，所述自旋轨道矩提供线采用多段结构，位于两个所述磁性隧道结位置的部分为具有自旋轨道矩效应的材料，位于其他位置的部分为低电阻金属材料。
  8. 根据权利要求1所述的磁存储单元，其特征在于，两个所述偏置磁场提供层的磁化方向翻转所对应的翻转场差别大于100Oe。
  9. 根据权利要求1所述的磁存储单元，其特征在于，两个所述磁性隧道结的参考层的磁化方向相同，对应地，两个所述磁性隧道结的自由层的磁化方向相反。
  10. 一种SOT-MRAM存储器，其特征在于，所述SOT-MRAM存储器包括如权利要求1-9中任一项所述的磁存储单元。
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