CN111370571B - Magnetic memory cell and SOT-MRAM memory - Google Patents
Magnetic memory cell and SOT-MRAM memory Download PDFInfo
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- CN111370571B CN111370571B CN201811602786.9A CN201811602786A CN111370571B CN 111370571 B CN111370571 B CN 111370571B CN 201811602786 A CN201811602786 A CN 201811602786A CN 111370571 B CN111370571 B CN 111370571B
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Abstract
The present invention provides a magnetic memory cell comprising: a bottom electrode for providing spin orbit torque; a magnetic tunnel junction comprising a free layer, a tunneling barrier layer, and a reference layer stacked in sequence, the free layer being adjacent to the bottom electrode; a separation layer on and in contact with a reference layer of the magnetic tunnel junction; a bias layer on and in contact with the separation layer for providing a magnetic moment having an initial direction parallel to a magnetization direction of the magnetic tunnel junction; the piezoelectric layer is positioned on the bias layer and is in contact with the bias layer, and is used for generating stress which enables the magnetic moment of the bias layer to change the direction under the action of control voltage, and the magnetic moment of the bias layer is used for assisting the free layer to turn over after changing the direction; and the top electrode is positioned on the piezoelectric layer and is in contact with the piezoelectric layer, and is used for switching in the control voltage when data is written. The invention can improve the stability of the magnetic storage unit.
Description
Technical Field
The invention relates to the technical field of magnetic memories, in particular to a magnetic storage unit and an SOT-MRAM memory.
Background
It has been found that when a current is passed through a material having a Spin Orbit Torque (SOT) effect, a Spin polarized Spin current is generated at the interface of the material, which can be used to flip the free layer in a nanomagnet, such as a magnetic tunnel junction MTJ. A new magnetic memory device based on spin orbit torque and MTJ (which may be referred to as SOT-MRAM memory) has the advantages of separate read and write, fast write speed, low write current density, etc., and is considered to be a future development trend.
For a magnetic tunnel junction with a perpendicular structure, the spin orbit torque induced by the spin hall effect cannot realize the directional inversion of the free layer. At present, two main means are used, namely spin orbit torque overturning of a perpendicular anisotropic material is realized through an external bias magnetic field and structural asymmetry.
As shown in FIG. 1, which is a schematic structural diagram of a conventional magnetic memory cell, a bias magnetic field providing layer with in-plane magnetization is added above a reference layer of a magnetic tunnel junction, and a horizontal bias magnetic field generated by the bias magnetic field providing layer to a free layer during data writing breaks the symmetry of spin-orbit torque when the free layer spins upwards and downwards, so that data can be effectively written in an auxiliary manner. However, stray fields corresponding to the bias magnetic field from the bias magnetic field providing layer may seriously affect the stability of the magnetic memory cell, and thus affect the storage of data.
Disclosure of Invention
In order to solve the above problems, the present invention provides a magnetic memory cell and an SOT-MRAM memory, which can effectively assist writing when a bias magnetic field is used to write data, and can improve the stability of the magnetic memory cell without affecting the storage of data at other times.
In a first aspect, the present invention provides a magnetic memory cell comprising:
a bottom electrode for providing spin orbit torque;
a magnetic tunnel junction comprising a free layer, a tunneling barrier layer and a reference layer stacked in sequence, the free layer being adjacent to the bottom electrode;
a separation layer on and in contact with a reference layer of the magnetic tunnel junction;
a bias layer on and in contact with the separation layer for providing a magnetic moment having an initial direction parallel to a magnetization direction of the magnetic tunnel junction;
the piezoelectric layer is positioned on the bias layer and is in contact with the bias layer, and is used for generating stress which enables the magnetic moment of the bias layer to change the direction under the action of control voltage, and the magnetic moment of the bias layer is used for assisting the free layer to turn over after changing the direction;
and the top electrode is positioned on the piezoelectric layer and is in contact with the piezoelectric layer, and is used for switching in the control voltage when data is written.
Optionally, the piezoelectric layer is configured to generate a stress under the action of a control voltage, so that the magnetic moment of the bias layer is flipped by 90 degrees.
Optionally, the stress generated by the piezoelectric layer disappears after the control voltage is removed.
Optionally, the material of the piezoelectric layer is cadmium sulfide, lead magnesium niobate-lead titanate, lead zirconate titanate, or barium titanate.
Optionally, the thickness of the piezoelectric layer is 1-3 nanometers.
Optionally, the magnetic tunnel junction is magnetized perpendicular to the film plane or magnetized in the film plane.
Optionally, the bias layer is a single layer film structure or a multilayer film structure.
Optionally, the material of the bottom electrode is a heavy metal, a topological insulator, or an antiferromagnetic alloy.
Optionally, the material of the top electrode is one of tantalum Ta, aluminum Al, or copper Cu.
In a second aspect, the present invention provides an SOT-MRAM memory comprising the above-described magnetic memory cell.
Compared with the prior art, the bias magnetic field is controlled by the external voltage, the bias magnetic field can effectively assist writing in data writing, and the bias magnetic field does not influence data storage at other moments, so that the stability of the magnetic storage unit can be improved.
Drawings
FIG. 1 is a schematic diagram of a conventional stacked structure of a magnetic memory cell;
FIG. 2 is a schematic diagram of a stacked structure of one embodiment of a magnetic memory cell of the present invention;
FIG. 3 is a schematic diagram of a stacked structure of another embodiment of a magnetic memory cell of the present invention;
FIG. 4 is a schematic diagram of a process for writing a data "0" to the magnetic memory cell of FIG. 2;
FIG. 5 is a schematic diagram of a process for writing a data "1" to the magnetic memory cell of FIG. 2;
FIG. 6 is a process diagram of reading data from the magnetic memory cell of FIG. 2.
Detailed Description
In order to make the objects, technical solutions and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the drawings in the embodiments of the present invention, and it is obvious that the described embodiments are only a part of the embodiments of the present invention, and not all of the embodiments. All other embodiments, which can be derived by a person skilled in the art from the embodiments given herein without making any creative effort, shall fall within the protection scope of the present invention.
An embodiment of the present invention provides a magnetic storage unit, as shown in fig. 2, including: a bottom electrode, a free layer, a tunneling barrier layer, a reference layer, a separation layer, a bias layer, a piezoelectric layer, and a top electrode stacked in this order from bottom to top,
the free layer, the tunneling barrier layer and the reference layer form a Magnetic Tunnel Junction (MTJ), the free layer and the reference layer are made of CoFeB, and the tunneling barrier layer is made of MgO; the magnetization direction of the MTJ is perpendicular to the long direction of the bottom electrode (i.e., the direction of the current), or the included angle is greater than 60 degrees;
the free layer of the MTJ is in contact with a bottom electrode that provides spin-orbit torque, and the bottom electrode can be made of a material selected from the group consisting of heavy metals such as Pt, Ta, W, Ir, Hf, Ru, Tl, Bi, Au, Os, topological insulators such as BiSe alloys, BiTe alloys such as Bi2Se3, BiSeTe alloys, TlBiSe, antiferromagnetic alloys such as PtMn, IrMn, etc.;
the separation layer is positioned on and contacted with the reference layer of the Magnetic Tunnel Junction (MTJ) and used for separating the reference layer from the bias layer, the separation layer uses non-magnetic metal, and the material comprises but is not limited to Ta, Ru and the like and is helpful for the specific orientation of the magnetic moment of the bias layer;
the bias layer is positioned on the separation layer and is in contact with the separation layer and used for providing a magnetic moment, and the initial direction of the magnetic moment is parallel to the magnetization direction of the Magnetic Tunnel Junction (MTJ);
the piezoelectric layer is positioned on the bias layer and is in contact with the bias layer, and is used for generating stress which enables the magnetic moment of the bias layer to change the direction under the action of control voltage;
the top electrode is located on the piezoelectric layer and is in contact with the piezoelectric layer and used for being connected with a control voltage when data are written, and the material of the top electrode is one of tantalum Ta, aluminum Al or copper Cu.
Specifically, under the action of an external control voltage, the piezoelectric layer generates a large stress, so that the piezoelectric layer is required to have a large piezoelectric coefficient, and the material of the piezoelectric layer can be cadmium sulfide (CdS), lead magnesium niobate-lead titanate (PMN-PT), lead zirconate titanate (PZT), barium titanate (BaTiO) 3 ) And the like. The stress generated by the piezoelectric layer can cause the magnetic moment of the bias layer to flip 90 degrees in orientation, for example, from vertical to horizontal, thereby changing the direction of the bias field. In addition, the piezoelectric layer has good volatility, namely after the control voltage is removed, the generated stress disappears, so that the magnetic moment of the bias layer returns to the initial state, and the direction of magnetization intensity in the free layer of the MTJ returns to the initial state, so that the stability of the device is improved. The thickness of the piezoelectric layer can be designed according to the piezoelectric coefficient and the resistivity of the piezoelectric material used for the piezoelectric layer, and generally the thickness of the piezoelectric layer varies within the range of 1-3 nm.
The free layer and the reference layer of the magnetic tunnel junction can be single-layer films, and can also be multi-layer film structures, such as synthetic antiferromagnetic structures and the like. Wherein the magnetic material is selected from one or more of iron, cobalt and nickel and is used for storing data.
The bias layer may be a single layer film or a multi-layer film structure, such as an artificially synthesized antiferromagnetic structure. Wherein the material is selected from one of mixed metal materials of cobalt iron CoFe, cobalt iron boron CoFeB or nickel iron NiFe, and the compositions of the elements in the mixed metal materials are different.
As shown in fig. 3, in another embodiment of the magnetic memory cell of the present invention, the bias layer is a multi-layer film structure, which includes a magnetic layer 1/a non-magnetic layer/a magnetic layer 2, the non-magnetic layer is located between two magnetic layers, wherein the magnetic layer 1 contacts the separation layer, and the magnetic layer 2 contacts the piezoelectric layer.
It should be noted that the magnetic tunnel junction MTJ may be of a vertical structure or a horizontal structure. The MTJ is a perpendicular structure with its magnetization direction perpendicular to the film plane; MTJs are horizontal structures that are magnetized in the film plane.
Correspondingly, for the MTJ with a vertical structure, the magnetic moment of the bias layer is perpendicular to the contact surface of the piezoelectric layer and the bias layer in the initial state, when data is written, after the top electrode is connected with a control voltage, the piezoelectric layer generates a stress, under the action of the stress, the magnetic moment of the bias layer is forced to generate 90-degree orientation reversal, and the magnetic moment of the bias layer is parallel to the contact surface of the piezoelectric layer and the bias layer, so that a horizontal bias field is generated for the magnetic moment of the free layer to assist writing. When the writing process is complete, the top electrode removes the control voltage and the magnetic moment of the bias layer returns to its original state, i.e., perpendicular to the interface of the piezoelectric layer and the bias layer.
Similarly, it can be obtained that, for the MTJ with the horizontal structure, the magnetic moment of the bias layer is parallel to the contact surfaces of the piezoelectric layer and the bias layer in the initial state, and when data is written, after the top electrode is connected to a control voltage, the piezoelectric layer generates a stress, and under the action of the stress, the magnetic moment of the bias layer is forced to undergo a 90 ° orientation flip, and at this time, the magnetic moment of the bias layer is perpendicular to the contact surfaces of the piezoelectric layer and the bias layer, so as to generate a vertical bias field for the magnetic moment of the free layer, thereby assisting writing. When the writing process is completed, the top electrode removes the control voltage and the magnetic moment of the bias layer returns to the original state, i.e. parallel to the interface of the piezoelectric layer and the bias layer.
The writing and reading processes of the magnetic memory cell will be described in detail by taking the magnetic memory cell shown in fig. 2 as an example.
When the magnetic memory unit writes data, the top electrode is connected with a control voltage and can be applied through an MOS tube controlled by a peripheral circuit.
When writing in the '0', namely writing in a parallel state, firstly introducing forward current to the bottom electrode, then adding control voltage between the top electrode and the bottom electrode, and regulating and controlling a bias field of a bias layer through the piezoelectric layer so as to realize the writing in of data '0'. The process of writing "0" is shown in FIG. 4, where (a) shows the magnetic memory cell without control voltage applied, and the magnetic moment of the bias layer is perpendicular to the contact surface of the piezoelectric layer and the bias layer, (b) shows the magnetic memory cell with control voltage applied, and the magnetic moment of the bias layer is parallel to the contact surface of the piezoelectric layer and the bias layer, and (c) shows the magnetic memory cell after the control voltage is removed after the writing process is completed, and the magnetic moment of the bias layer is restored to the original state and is perpendicular to the contact surface of the piezoelectric layer and the bias layer.
When writing '1', namely writing an anti-parallel state, firstly introducing negative current to the bottom electrode, then adding control voltage between the top electrode and the bottom electrode, and regulating and controlling the bias field of the bias layer through the piezoelectric layer, thereby realizing the writing of data '1'. The process of writing "1" is shown in fig. 5, where (a) represents a magnetic memory cell to which no control voltage is applied, and the magnetic moment of the bias layer is perpendicular to the contact surface of the piezoelectric layer and the bias layer, (b) represents a magnetic memory cell to which a control voltage is applied, and the magnetic moment of the bias layer is parallel to the contact surface of the piezoelectric layer and the bias layer, and (c) represents a magnetic memory cell to which a control voltage is removed after the writing process is completed, and the magnetic moment of the bias layer is restored to the original state, perpendicular to the contact surface of the piezoelectric layer and the bias layer.
When reading data from the magnetic memory cell, the reading process is as shown in fig. 6, and similar to the conventional STT-MRAM, it should be noted that the reading voltage is smaller than the threshold voltage of the bias layer. The magnitude of the external reading voltage is closely related to the thickness of the piezoelectric layer, the thicker the piezoelectric layer is, the smaller the piezoelectric coefficient is, and the larger the required external reading voltage is generally, whereas the thinner the piezoelectric layer is, the larger the piezoelectric coefficient is, the smaller the required external reading voltage is. Therefore, in the design process, only the piezoelectric layer with proper thickness and piezoelectric coefficient needs to be selected, so that the reading voltage is smaller than the threshold voltage of the bias layer, and the misreading is avoided.
In summary, in the magnetic memory cell provided in the embodiments of the present invention, when data is written, the top electrode applies a control voltage, the piezoelectric layer generates a stress, and the stress causes the magnetic moment of the bias layer to realize 90-degree directional flipping in the horizontal and vertical directions, so as to control the direction of the bias magnetic field and assist in writing data; after the writing process is finished, the control voltage is removed, the magnetic moment of the bias layer can be restored to the initial state, the bias magnetic field does not influence the storage of data, and the influence of the bias magnetic field on the stability of the device is greatly reduced. Therefore, the invention can improve the stability of the magnetic storage unit. In addition, when the current generated by control voltage passes through the MTJ structure during data writing, the generated spin transfer torque also helps to flip the magnetic moment of the free layer, thereby greatly reducing the writing current and reducing the power consumption.
The embodiment of the invention also provides an SOT-MRAM memory, which comprises the magnetic storage unit.
The above description is only for the specific embodiment of the present invention, but the scope of the present invention is not limited thereto, and any changes or substitutions that can be easily conceived by those skilled in the art within the technical scope of the present invention are included in the scope of the present invention. Therefore, the protection scope of the present invention shall be subject to the protection scope of the claims.
Claims (10)
1. A magnetic memory cell, comprising:
a bottom electrode for providing spin orbit torque;
a magnetic tunnel junction comprising a free layer, a tunneling barrier layer, and a reference layer stacked in sequence, the free layer being adjacent to the bottom electrode;
a separation layer on and in contact with a reference layer of the magnetic tunnel junction;
a bias layer on and in contact with the separation layer for providing a magnetic moment having an initial direction parallel to a magnetization direction of the magnetic tunnel junction;
a piezoelectric layer on and in contact with the bias layer;
the top electrode is located on the piezoelectric layer and is in contact with the piezoelectric layer, the top electrode is used for accessing control voltage when data are written, the piezoelectric layer is used for generating stress for changing the direction of the magnetic moment of the bias layer under the action of the control voltage, and the magnetic moment of the bias layer is used for assisting the free layer to turn over when data are written after the direction is changed.
2. The magnetic memory cell of claim 1 wherein the piezoelectric layer is configured to generate a stress under the control voltage to flip the magnetic moment of the bias layer by a 90 degree orientation.
3. A magnetic memory cell according to claim 1, characterized in that the stress generated by the piezoelectric layer disappears after the control voltage is removed.
4. The magnetic memory cell of claim 1, wherein the material of the piezoelectric layer is cadmium sulfide, lead magnesium niobate-lead titanate, lead zirconate titanate, or barium titanate.
5. The magnetic memory cell of claim 1, wherein the piezoelectric layer has a thickness of 1 to 3 nanometers.
6. The magnetic memory cell of claim 1, wherein the magnetic tunnel junction is perpendicular to film plane magnetization or in-film plane magnetization.
7. The magnetic memory cell of claim 1, wherein the bias layer is a single layer film structure or a multi-layer film structure.
8. The magnetic memory cell of claim 1, wherein the material of the bottom electrode is a heavy metal, a topological insulator, or an antiferromagnetic alloy.
9. The magnetic memory cell of claim 1, wherein the material of the top electrode is one of Ta, Al, or Cu.
10. An SOT-MRAM memory, characterized in that the SOT-MRAM memory comprises magnetic memory cells according to any of the claims 1-9.
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| US10720570B2 (en) * | 2017-06-12 | 2020-07-21 | Western Digital Technologies, Inc. | Magnetic sensor using spin hall effect |
| CN112186094B (en) * | 2020-09-30 | 2023-02-28 | 北京航空航天大学 | Magnetic random access memory |
| CN114551716A (en) * | 2020-11-26 | 2022-05-27 | 浙江驰拓科技有限公司 | Magnetic tunnel junction free layer and magnetic tunnel junction structure with same |
| CN113013324A (en) * | 2021-03-02 | 2021-06-22 | 浙江驰拓科技有限公司 | Magnetic storage unit and memory |
| CN113178518B (en) * | 2021-04-26 | 2022-08-02 | 中国科学院微电子研究所 | SOT-MRAM based on bottom electrode parallel voltage control and manufacturing method |
| CN113223562B (en) * | 2021-05-27 | 2022-08-23 | 王旭 | Magneto-optical memory structure |
| CN117321975A (en) * | 2021-08-22 | 2023-12-29 | 华为技术有限公司 | Magnetic random access memory and electronic equipment |
| CN116784022A (en) * | 2022-01-13 | 2023-09-19 | 华为技术有限公司 | Magnetic memory cell and method of manufacturing the same |
| CN115542207B (en) * | 2022-09-22 | 2023-10-31 | 江苏多维科技有限公司 | Magnetoresistive structure and uniaxial measuring magnetic sensor |
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| US6829157B2 (en) * | 2001-12-05 | 2004-12-07 | Korea Institute Of Science And Technology | Method of controlling magnetization easy axis in ferromagnetic films using voltage, ultrahigh-density, low power, nonvolatile magnetic memory using the control method, and method of writing information on the magnetic memory |
| KR100754930B1 (en) * | 2004-12-22 | 2007-09-03 | 한국과학기술원 | Information storage and interpretation method of magnetic random access memory using voltage-control magnetization reversal as the writing type |
| US8310861B2 (en) * | 2008-09-30 | 2012-11-13 | Micron Technology, Inc. | STT-MRAM cell structure incorporating piezoelectric stress material |
| US8102703B2 (en) * | 2009-07-14 | 2012-01-24 | Crocus Technology | Magnetic element with a fast spin transfer torque writing procedure |
| US9721631B2 (en) * | 2013-03-14 | 2017-08-01 | New York University | Precessional magnetization reversal in a magnetic tunnel junction with a perpendicular polarizer |
| US9647032B2 (en) * | 2014-08-27 | 2017-05-09 | Avalanche Technology, Inc. | Spin-orbitronics device and applications thereof |
| US20170082697A1 (en) * | 2015-09-18 | 2017-03-23 | Regents Of The University Of Minnesota | Spin hall effect magnetic structures |
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