CN114730832A

CN114730832A - Multiferroic assisted voltage controlled magnetic anisotropic memory device and method of manufacturing the same

Info

Publication number: CN114730832A
Application number: CN202180006547.0A
Authority: CN
Inventors: B·普拉萨德; A·卡利佐夫; N·史密斯
Original assignee: Western Digital Technologies Inc
Current assignee: Western Digital Technologies Inc
Priority date: 2020-08-27
Filing date: 2021-06-04
Publication date: 2022-07-08
Also published as: WO2022046237A1

Abstract

A magnetic memory device includes a first electrode, a second electrode, and a stacked stack between the first electrode and the second electrode. The stack of layers includes a reference layer, a tunnel barrier layer, a free layer, and a magnetoelectronics multiferroic layer including at least one grain. The magnetization of the magnetoelectric multiferroic layer may be axial, lateral, or in-plane. For axial or roll magnetization of the magnetoelectric multiferroic layer, deterministic switching of the free layer can be achieved by coupling with the axial component of the magnetization of the magnetoelectric multiferroic layer. Alternatively, in-plane magnetization of the magnetoelectric multiferroic layer can be used to induce precession of the magnetization angle of the free layer.

Description

Multi-iron auxiliary voltage control magnetic anisotropic memory device and manufacturing method thereof

RELATED APPLICATIONS

This application claims benefit of priority to united states non-provisional patent application No. 17/004,534 filed on day 27, 8/2020 and united states non-provisional patent application No. 17/004,690 filed on day 27, 8/2020; the entire contents of these patent applications are incorporated herein by reference.

Technical Field

The present disclosure relates generally to the field of magnetic (e.g., spin) memory devices, and in particular to magnetoresistive random access memory ("MRAM") devices including multiferroic layers and methods of fabricating the same.

Background

Magnetoresistive memory devices may store information for a difference in resistance in a first configuration in which a magnetization direction of a ferromagnetic free layer is parallel to a magnetization of a ferromagnetic reference layer and a second configuration in which the magnetization direction of the free layer is anti-parallel to the magnetization of the reference layer. Programming a magnetoresistive memory device requires switching the magnetization direction of the free layer using various external power sources, which may be magnetic in nature or may employ a self-transfer mechanism.

Voltage Controlled Magnetic Anisotropy (VCMA) refers to an effect in which the perpendicular magnetic anisotropy of the free layer has a first order of dependence on an externally applied voltage on the free layer located in a magnetic tunnel junction that includes a dielectric tunnel barrier layer between the free layer and a ferromagnetic reference layer. The dielectric tunnel barrier layer may be at least 1nm thick, which reduces a tunneling current flowing through the dielectric tunnel barrier layer that is below a critical current required to switch the magnetization direction of the free layer during programming. Thus, the applied voltage is used to switch the magnetization direction of the free layer. The applied voltage reduces the energy perpendicular magnetic anisotropy in one bias direction and increases it in the other bias direction. However, VCMA programming is non-deterministic and requires precise control of the timing of the applied voltage pulses to obtain the desired magnetization direction of the free layer.

Disclosure of Invention

According to an aspect of the present disclosure, there is provided a magnetic memory device, including: a first electrode; a second electrode; and a stack located between the first and second electrodes and comprising, in order from one side to the other: a reference layer, a tunnel barrier layer, a free layer, and a magnetoelectric multiferroic layer including at least one crystal grain having an axis of easy magnetization in an axial direction or in a first tilt direction having a first tilt angle less than 90 degrees with respect to the axial direction, the axial direction being perpendicular to an interface between the free layer and the tunnel barrier layer.

According to another aspect of the present disclosure, a method of programming a magnetic memory device includes applying a first programming voltage pattern including a first positive voltage having a magnitude greater than a coercive voltage sufficient to switch a magnetization direction of a magneto-electric multiferroic layer and applying a second programming voltage pattern including a negative voltage having a magnitude greater than the coercive voltage followed by a second positive voltage having a magnitude less than the coercive voltage.

In one embodiment, the first positive voltage deterministically programs the magnetization direction of the magnetoelectric multiferroic layer to be parallel to the magnetization direction of the reference layer, and the magnitude of the first positive voltage is sufficient to weaken the perpendicular magnetic anisotropy of the free layer, which allows the free layer to switch its magnetization direction to be parallel to the magnetization direction of the reference layer. The negative voltage positively programs the magnetization direction of the magnetoelectric multiferroic layer to be antiparallel to the magnetization direction of the reference layer, and the negative voltage enhances the perpendicular magnetic anisotropy of the free layer so that the free layer cannot switch its magnetization direction. The magnitude of the second positive voltage is insufficient to switch the magnetization direction of the magnetoelectric multiferroic layer, and the magnitude of the second positive voltage is sufficient to weaken the perpendicular magnetic anisotropy of the free layer, which allows the free layer to positively switch its magnetization direction antiparallel to the magnetization direction of the reference layer.

In accordance with yet another aspect of the present disclosure, a magnetic memory device includes a first electrode, a second electrode, and a stacked stack between the first electrode and the second electrode, and includes, in order from one side to the other, a reference layer, a tunnel barrier layer, a free layer, and a Voltage Controlled Magnetic Anisotropy (VCMA) assist structure having an in-plane magnetization direction.

Drawings

FIG. 1 is a schematic diagram of a random access array of magnetic tunnel junction devices according to an embodiment of the present disclosure.

Fig. 2A is a vertical cross-sectional view of a first exemplary structure after formation according to a first embodiment of the present disclosure.

Fig. 2B is a vertical cross-sectional view of an alternative embodiment of the first exemplary structure according to the first embodiment of the present disclosure.

FIG. 3A is BiFeO having ferroelectric polarization and magnetic moment₃Perspective view of the unit cell.

FIG. 3B shows BiFeO of FIG. 3A₃The relative spatial orientation between the ferroelectric polarization and the direction of the magnetic moment of the unit cell.

Figure 4A is a vertical cross-sectional view of a first example structure in a first programmed state, according to a first embodiment of the present disclosure.

Figure 4B is a vertical cross-sectional view of a first example structure in a second programmed state, according to a first embodiment of the present disclosure.

Fig. 5 is a graph illustrating a change in axial ferroelectric polarization of a magnetoelectric multiferroic layer according to a first embodiment of the present disclosure.

FIG. 6A is a diagram illustrating a first voltage pulse pattern for programming a magnetic memory cell of a first exemplary structure to a first magnetic state, according to an aspect of the present disclosure.

FIG. 6B is a diagram illustrating a second voltage pulse pattern for programming the magnetic memory cell of the first exemplary structure to a second magnetic state, according to an aspect of the present disclosure.

Fig. 7A is a vertical cross-sectional view of a second exemplary structure after formation according to the first embodiment of the present disclosure.

Fig. 7B is a vertical cross-sectional view of an alternative embodiment of a second exemplary structure according to the first embodiment of the present disclosure.

Fig. 8 is a vertical cross-sectional view of another alternative embodiment of a second exemplary structure according to a second embodiment of the present disclosure.

Fig. 9A is a vertical cross-sectional view of a second exemplary structure in a first magnetic state according to a second embodiment of the present disclosure.

Fig. 9B is a vertical cross-sectional view of a second exemplary structure in a second magnetic state according to a second embodiment of the present disclosure.

Fig. 10A is a diagram of a sensing voltage pattern for sensing a magnetic state of a magnetic memory device of a second exemplary structure according to a second embodiment of the present disclosure.

Fig. 10B is a diagram of a programming voltage pattern for programming the magnetic state of a magnetic memory device of the second exemplary structure, according to a second embodiment of the present disclosure.

Detailed Description

Embodiments of the present disclosure relate to a voltage controlled magnetic anisotropic memory device containing a magnetoelectric multiferroic layer and a method of operating the same, various aspects of which are described in detail below. The magnetoelectric multiferroic layer provides a deterministic VCMA programming mechanism (e.g., where the magnetization direction of the free layer is not dependent on the duration of the programming voltage pulse) and/or provides a precisely controlled in-plane auxiliary magnetic field determined by the crystalline properties of the magnetoelectric multiferroic layer.

The figures are not drawn to scale. Where a single instance of an element is illustrated, multiple instances of the element may be repeated unless explicitly described or otherwise clearly indicated to be absent repetition of the element. Ordinal numbers such as "first," "second," and "third" are used merely to identify similar elements, and different ordinal numbers may be employed throughout the specification and claims of the present disclosure. The term "at least one" element is intended to mean all possibilities including single element possibilities and multiple element possibilities. The same reference numbers indicate the same or similar elements. Elements having the same reference numerals are assumed to have the same composition and the same function unless otherwise specified. Unless otherwise specified, "contact" between elements refers to direct contact between elements providing an edge or surface shared by the elements. Two or more elements are "separated" or "separated" from each other if the elements are not in direct contact with each other or with each other. As used herein, a first element that is positioned "on" a second element may be positioned on the outside of the surface of the second element or on the inside of the second element. As used herein, a first element is "directly" positioned on a second element if there is physical contact between a surface of the first element and a surface of the second element. As used herein, a first element is "electrically connected" to a second element if there is a conductive path between the first element and the second element that is comprised of at least one conductive material. As used herein, a "prototype" structure or "in-process" structure refers to a transient structure that is subsequently modified in the shape or composition of at least one component therein.

As used herein, "layer" refers to a portion of a material that includes a region having a thickness. A layer may extend over the entirety of an underlying or overlying structure, or may have a range that is less than the range of an underlying or overlying structure. In addition, a layer may be a region of uniform or non-uniform continuous structure having a thickness less than the thickness of the continuous structure. For example, a layer may be positioned between the top and bottom surfaces of the continuous structure or between any pair of horizontal planes at the top and bottom surfaces of the continuous structure. The layers may extend horizontally, vertically, and/or along a tapered surface. The substrate may be a layer, may include one or more layers therein, or may have one or more layers thereon, above, and/or below. As used herein, "stack of layers" refers to a stack of layers. As used herein, "line" or "line structure" refers to a layer having a predominant direction of extension, i.e., having the direction in which the layer extends the most. As used herein, "ferroelectric material" refers to any material that exhibits spontaneous ferroelectric polarization (e.g., exhibits ferroelectricity) that can be reversed by application of an external electric field. As used herein, a "multiferroic" material refers to a material that exhibits at least two ferrimagnetic sequences, such as magnetic (ferromagnetic, antiferromagnetic, or ferrimagnetic) and ferroelectric. As used herein, "magnetoelectric multiferroics" refers to materials that exhibit a ferromagnetic order and ferroelectricity. The change in total magnetization is related to a change in the total ferroelectric polarization in the magnetoelectric multiferroic material, and thus a change in the direction of the magnetic moment of the material can be related to a change in the direction of the ferroelectric polarization, and vice versa.

FIG. 1 is a schematic diagram of a random access memory device 501 of a magnetic tunnel junction device 180 according to an embodiment of the present disclosure. As used herein, "random access memory device" refers to a memory device that includes memory cells that allow random access, i.e., access to any selected memory cell upon a command to read the contents of the selected memory cell.

The random access memory device 501 of embodiments of the present disclosure may include an MRAM device, such as a multi-state STT-type MRAM device that contains a multiferroic portion. The device 501 includes a memory array region 550 containing a respective array of magnetic devices, such as magnetic tunnel junction devices (e.g., magnetoresistive memory cells) 180 located at intersections of word lines (which may include the first conductive lines 30 as shown or the second conductive lines 90 in an alternative configuration) and bit lines (which may include the second conductive lines 90 as shown or the first conductive lines 30 in an alternative configuration). For example, the first conductive lines 30 may be electrically connected to and/or may include bottom electrodes of a respective row of magnetic tunnel junction devices 180 in the memory array region 550, while the second conductive lines 90 may be electrically connected to and/or may include top electrodes of a respective column of magnetic tunnel junction devices 180 in the memory array region 550.

The random access memory device 501 may also contain a row decoder 560 connected to word lines, sense and program circuitry 570 (which may include sense amplifiers, programming transistors, and control circuitry) connected to bit lines, a column decoder 580 connected to bit lines, and a data buffer 590 connected to the sense circuitry. The magnetic tunnel junction devices 180 are provided in an array configuration forming a random access memory device 501. In one embodiment, the magnetic tunnel junction devices 180 may be provided as a rectangular array. Thus, each of the magnetic tunnel junction devices 180 may be a two-terminal device including a respective first electrode and a respective second electrode. It should be noted that the location and interconnection of elements is schematic and that elements may be arranged in different configurations. Furthermore, the magnetic tunnel junction device 180 may be fabricated as a discrete device, i.e., a single isolation device.

The random access configuration shown in random access memory device 501 is merely exemplary, and magnetic tunnel junction devices 180 of embodiments of the present disclosure may be connected in different interconnect configurations.

Referring to fig. 2A and 2B, an exemplary configuration of a magnetic tunnel junction device 180 is shown in a first exemplary structure. The configuration of fig. 2A and the configuration of fig. 2B are alternative configurations that may be derived from each other by reversing the material deposition sequence during formation of the magnetic tunnel junction device 180, which is a magnetic memory device.

The first exemplary structure comprises an optional insulating material layer 110 comprising an insulating material, such as undoped silicate glass, doped silicate glass, organosilicate glass, silicon nitride, dielectric metal oxide, or combinations thereof. In one embodiment, the insulating material layer 110 comprises an insulating substrate, such as a ceramic or glass substrate. In another embodiment, the layer of insulating material 110 may be disposed on a semiconductor substrate (not shown) having semiconductor devices (not shown) such as field effect transistors thereon. In this case, the insulating material layer 110 may comprise a plurality of interconnect-level dielectric material layers in which metal interconnect structures are embedded. The metal interconnect structure may provide electrical connections between semiconductor devices and to the first and second

conductive lines

30, 90 formed over the layer of insulating material 110. In this case, the structural elements formed over the insulating material layer 110 may be embedded within a dielectric matrix (not explicitly shown) that embeds the first and second

conductive lines

30, 30.

The first conductive line 30 may be formed over an insulating material layer 110. The first conductive lines 30 may be formed over the top surface of the insulating material layer 110 by depositing and patterning at least one metal layer and patterning the at least one metal layer into line-shaped structures extending laterally along a first horizontal direction. In one embodiment, at least one metal layer may comprise a stack of metal barrier layers comprising a conductive metal nitride and a highly conductive metal layer, such as a copper layer or a tungsten layer. Alternatively, a line cavity may be formed in an upper portion of the insulating material layer 110, and the first conductive line 30 may be formed by a damascene method, wherein at least one metal material is deposited in the line cavity, and an excess portion of the at least one metal material is removed from above a horizontal plane including a top surface of the insulating material layer 110. Each portion of the first conductive line 30 that contacts an overlying magnetic tunnel junction device 180 includes a first electrode of the magnetic tunnel junction device 180, which is a magnetic memory device.

A continuous layer stack may be deposited over first conductive line 30. The continuous stack comprises, in order from bottom to top or top to bottom, an optional continuous Synthetic Antiferromagnetic (SAF) structure, a continuous ferromagnetic reference layer, a continuous tunnel barrier layer, a continuous ferromagnetic free layer, a continuous magnetoelectric multiferroic layer, and an optional continuous nonmagnetic capping layer.

The optional SAF structure may comprise a superlattice structure comprising an alternating sequence of ferromagnetic material layers and electrically conductive nonmagnetic material layers. In illustrative examples, the superlattice structure may comprise [ X/Q ]]_nWhere X represents a ferromagnetic material layer such as a Co, CoFe, Fe, or CoFeB layer, Q represents a nonmagnetic material layer such as a Pt or Pd layer, and n represents the total number of repetitions of the bilayer stack of the ferromagnetic material layer and the nonmagnetic material layer. The total number of repetitions n may be in the range of 2 to 20, such as 3 to 8, but more may be used.

The continuous reference layer comprises a ferromagnetic material having perpendicular magnetic anisotropy. The continuous reference layer includes a ferromagnetic material, such as CoFe or CoFeB. The continuous reference layer may be deposited, for example, by physical vapor deposition, and may have a thickness in the range of 1nm to 3nm, although lesser and greater thicknesses may also be employed.

The continuous tunnel barrier layer comprises a tunneling dielectric material, such as MgO. The continuous tunnel barrier layer may be deposited, for example, by physical vapor deposition. The thickness of the continuous tunnel barrier layer may be in the range of 1nm to 2nm, such as 1.5nm to 2nm, although lesser and greater thicknesses may also be employed.

The continuous free layer comprises a ferromagnetic material having perpendicular magnetic anisotropy. The continuous free layer comprises a ferromagnetic material such as CoFe or CoFeB. The continuous free layer may be deposited, for example, by physical vapor deposition, and may have a thickness in the range of 0.6nm to 2nm, although lesser and greater thicknesses may also be employed.

The continuous magnetoelectric multiferroic layer comprises a magnetoelectric multiferroic material. As used herein, "multiferroic" refers to a material that exhibits at least two ferroic sequences (e.g., ferromagnetism and ferroelectricity). As used herein, "magnetoelectric multiferroics" refers to materials that exhibit a ferromagnetic order and ferroelectricity. The change in total magnetization is related to a change in total electrical polarization in the magnetoelectric multiferroics, and thus the magnetic transition may be related to a change in ferroelectric polarization and vice versa.

The continuous magnetoelectric multiferroic layer may comprise any polycrystalline multiferroic material or single crystal multiferroic material that can produce a non-zero net magnetization upon deposition or upon application of an initial magnetic field or an initial electric field. In an illustrative example, the continuous magnetoelectric multiferroic layer may include a material selected from BiFeO₃、h-YMnO₃、BaNiF₄、PbVO₃、BiMnO₃、LuFe₂O₄、HoMn₂O₅、h-HoMnO₃、h-ScMnO₃、h-ErMnO₃、h-TmMnO₃、h-YbMnO₃、h-LuMnO₃、K₂SeO₄、Cs₂CdI₄、TbMnO₃、Ni₃V₂O₈、MnWO₄、CuO、ZnCr₂Se₄、LiCu₂O₂And Ni₃B₇O₁₃And (I) a material. The continuous magnetoelectric multiferroic layer may be deposited by a suitable deposition method, such as physical vapor deposition. The thickness of the continuous magnetoelectric multiferroic layer may be 1nm or less, such as in the range of 0.3nm to 1nm, such as 0.5nm to 0.8nm, although lesser and greater thicknesses may also be employed.

In one embodiment, the polarization and magnetization directions of the continuous magnetoelectric multiferroic layer are orthogonal to each other. The continuous magnetoelectric multiferroic layer contains at least one kind of crystal grains having a magnetization easy axis in an axial direction or in a first oblique (i.e., rolling) direction having a first oblique angle of less than 90 degrees with respect to the axial direction. The axial direction is perpendicular to the interface between the continuous free layer and the continuous tunnel barrier layer. In one embodiment, the continuous magnetoelectronics multiferroic layer includes a plurality of grains having an easy axis of magnetization along an axial direction or along a respective first oblique direction having a respective first oblique angle less than 90 degrees with respect to the axial direction.

In general, the direction of magnetization in the grains of the continuous magnetoelectric multiferroic layer may depend on the preferred grain orientation and/or impurity doping within the magnetoelectric multiferroic layer. If the magnetoelectric multiferroic material comprises BiFeO₃Polycrystalline BiFeO having a preferred grain orientation along the (110) plane₃The layer may provide a predominant axial magnetization direction, i.e., more than 50% of all grains may have a respective magnetization direction (e.g., spin orientation) perpendicular to the interface between the continuous tunnel barrier layer and the continuous free layer. Polycrystalline BiFeO having preferred grain orientation along (100) plane₃The layer can be along<111>The directions provide a predominant roll magnetization direction, i.e., more than 50% of all grains may have respective magnetization directions (e.g., spin orientations) that are not perpendicular and parallel to the interface between the continuous tunnel barrier layer and the continuous free layer. In contrast, polycrystalline BiFeO having a preferred grain orientation along the (100) plane but which is doped with La at the Bi lattice sites₃The layer may provide a predominant axial magnetization direction, i.e., more than 50% of all grains may have a respective magnetization direction (e.g., spin orientation) perpendicular to the interface between the continuous tunnel barrier layer and the continuous free layer. Polycrystalline BiFeO having a preferred grain orientation along the (111) plane₃The layer may provide a predominantly in-plane magnetization direction, i.e., more than 50% of all grains may have a respective magnetization direction (e.g., spin orientation) parallel to the interface between the continuous tunnel barrier layer and the continuous free layer.

The optional continuous non-magnetic capping layer comprises a non-magnetic metal that is resistant to oxidation and/or diffusion. In one implementation, the continuous non-magnetic capping layer may comprise a metal having a melting point above 1,500 degrees celsius. For example, the metal of the continuous non-magnetic capping layer may comprise ruthenium, tantalum, platinum, or gold. The continuous non-magnetic capping layer may be deposited by physical vapor deposition. The thickness of the continuous nonmagnetic capping layer may range from 0.5nm to 2nm, although lesser and greater thicknesses may also be employed.

The successive stacked stacks may be patterned into a two-dimensional array of pillar structures. Patterning may be performed using ion beam milling and/or photolithography and etching. Each of the pillar structures may include a magnetic tunnel junction device 180, which is a magnetic memory device (e.g., an MRAM cell).

In each pillar structure (e.g., in each magnetic tunnel junction device 180 including MRAM cells), each patterned portion of the continuous SAF structure includes the SAF structure 120. Each patterned portion of the continuous reference layer includes a reference layer 132. If the SAF structure 120 includes a superlattice, the reference layer 132 may contact a non-magnetic layer of the SAF structure superlattice. Each patterned portion of the continuous tunnel barrier layer includes a tunnel barrier layer (i.e., a tunneling dielectric layer) 134. Each patterned portion of the continuous free layer includes a free layer 136. Each patterned portion of the continuous magnetoelectric multiferroic layer includes magnetoelectric multiferroic layer 140.

A dielectric matrix layer 190 may be deposited over and around the array of magnetic tunnel junction devices 180 (i.e., around the pillar structures). The dielectric matrix layer 190 comprises a dielectric material, such as silicon nitride, silicon oxide, organosilicate glass, and/or a dielectric metal oxide. In one embodiment, dielectric matrix layer 190 may comprise a dielectric diffusion liner (e.g., a silicon nitride liner) and a dielectric fill material (e.g., silicon oxide). The dielectric matrix layer 190 may be planarized to provide a horizontal top surface above a horizontal plane containing the top surface of the magnetic tunnel junction device 180. For example, Chemical Mechanical Planarization (CMP) may be employed to planarize the top surface of dielectric matrix layer 190.

A line cavity extending laterally along the second horizontal direction may be formed in an upper portion of the dielectric matrix layer 190. The second horizontal direction is different from the first horizontal direction and can be perpendicular to the first horizontal direction. At least one conductive material may be deposited in the line cavity and an excess portion of the at least one conductive material may be removed from above a horizontal plane including the top surface of the dielectric matrix layer 190. Each remaining portion of the at least one conductive material filling the line cavity comprises a second conductive line 90. Each second conductive line 90 may include at least one second electrode of the two-dimensional array of magnetic tunnel junction devices 180. Alternatively, the second conductive line 90 may be formed on each of the pillar structures followed by forming a dielectric matrix layer 190 over the second conductive line 90.

In one implementation, each first conductive line 30 may contact a respective row of magnetic tunnel junction devices 180 and each second conductive line 90 may contact a respective column of magnetic tunnel junction devices 180. In this case, each first conductive line 30 may include a row of first electrodes, and each second conductive line 90 may include a column of second electrodes.

In one embodiment, a volumetrically predominant subset of the grains within magnetoelectronics multiferroic layer 140 (i.e., a set of grains that occupy more than 50% of the entire volume of each magnetoelectronics multiferroic layer 140) may have an easy axis of magnetization along the axial direction or along a first tilt direction having a first tilt angle less than 90 degrees relative to the axial direction (e.g., <111> direction). The axial direction is perpendicular to each interface between the free layer 136 and the tunnel barrier layer 134 within each magnetic tunnel junction device 180. In one embodiment, each magnetoelectric multiferroic layer 140 may have a respective easy ferroelectric polarization axis along the axial direction or along a second tilt direction having a second tilt angle less than 90 degrees with respect to the axial direction. The second direction of each die may or may not be parallel or anti-parallel to the first direction of the respective die. Each magnetoelectronics multiferroic layer 140 may be monocrystalline or polycrystalline, i.e., may contain a plurality of grains that are adjoined at grain boundaries that are discontinuous in the crystalline structure of the magnetoelectronics multiferroic material.

In accordance with embodiments of the present disclosure, a net axial magnetization may be induced within each magnetoelectric multiferroic layer 140 within the array of magnetic tunnel junction devices 180 by applying an axial initial magnetic or electric field. The electric field can switch the ferroelectric polarization and the corresponding magnetization due to the magnetoelectric coupling. An axial initial magnetic or electric field may be applied in a vertical direction perpendicular to the interface between each free layer 136 and the tunnel barrier layer 134. The axial initial magnetic or electric field may align a vertical component of the magnetization of each grain in each magnetoelectric multiferroic layer 140 along a direction of the axial initial magnetic or electric field. Thus, each magnetoelectric multiferroic layer 140 may have a net non-zero axial magnetization. In this case, each magnetoelectric multiferroic layer 140 may have a net non-zero ferroelectric polarization associated with a net non-zero axial magnetization.

According to another embodiment of the present disclosure, a net axial ferroelectric polarization may be induced within each magnetoelectric multiferroic layer 140 within the array of magnetic tunnel junction devices 180 by applying an axial initial electric field. An axial initial electric field may be applied along a vertical direction perpendicular to the interface between each free layer 136 and the tunnel barrier layer 134. The axial initial electric field may align a vertical component of the ferroelectric polarization of each grain in each magnetoelectric multiferroic layer 140 along a direction of the axial initial electric field. Thus, each magnetoelectric multiferroic layer 140 may have a net non-zero axial ferroelecfrode. In this case, each magnetoelectric multiferroic layer 140 may have a net non-zero magnetization associated with a net non-zero axial ferroelectric polarization.

According to an aspect of the present disclosure, there is provided a magnetic memory device, including: a first electrode (including a portion of the first conductive line 30); a second electrode (including a portion of second conductive line 90); and a layer stack (120, 132, 134, 136, 140, 170) between the first and second electrodes and comprising, in order from side to side, a reference layer 132, a tunnel barrier layer 134, a free layer 136, and a magnetoelectric multiferroic layer 140 comprising at least one crystal grain having an easy axis of magnetization in an axial direction or in a first oblique direction having a first oblique angle less than 90 degrees with respect to the axial direction, the axial direction being perpendicular to an interface between the free layer 136 and the tunnel barrier layer 134.

In one embodiment, the layer stack (120, 132, 134, 136, 140, 170) further includes a nonmagnetic capping layer 170 comprising a nonmagnetic metal and contacting the magnetoelectric multiferroic layer 140 and one of the first and second electrodes. In one embodiment, magnetoelectric multiferroic layer 140 includes and/or consists essentially of at least one material selected from the group consisting of: BiFeO₃、h-YMnO₃、BaNiF₄、PbVO₃、BiMnO₃、LuFe₂O₄、HoMn₂O₅、h-HoMnO₃、h-ScMnO₃、h-ErMnO₃、h-TmMnO₃、h-YbMnO₃、h-LuMnO₃、K2SeO₄、Cs₂CdI₄、TbMnO₃、Ni₃V₂O₈、MnWO₄、CuO、ZnCr₂Se₄、LiCu₂O₂Or Ni₃B₇O₁₃I。

In one implementation, a two-dimensional array of examples of the magnetic memory device of FIG. 2A or FIG. 2B can be provided. The magnetic memory array may include: first conductive lines 30 parallel to each other and extending in a first direction; and second conductive lines 90 parallel to each other and extending in a second direction perpendicular to the first direction. Each of the first conductive lines 30 includes a first electrode of an instance of a respective row of magnetic memory devices in the magnetic memory array. Each of the second conductive lines 90 includes a second electrode of an instance of a respective column of magnetic memory devices in the magnetic memory array.

In one embodiment, magnetoelectric multiferroic layer 140 may have a net non-zero axial magnetization. The net in-plane iron magnetic moment of magnetoelectric multiferroic layer 140 may be zero (for axial multiferroic materials) or non-zero (for roll multiferroic materials). Thus, the net in-plane magnetization of magnetoelectric multiferroic layer 140 may be zero (for axial multiferroic materials) or non-zero (for roll multiferroic materials).

FIG. 3A shows a cross-section having a plane along (111)<111>Family orientation (e.g., [111 ]]Direction) and roll moment direction Mc), and BiFeO of ferroelectric polarization direction P of one of the directions₃A stereo unit cell. Fig. 3B shows in-plane (100) and out-of-plane (001) components of the in-plane magnetic moment direction Mc of (111). The relative spatial orientation (e.g., 90 degree angle) between the magnetic moment direction Mc and the polarization direction P is the same for each magnetoelectric multiferroic unit cell. The out-of-plane (001) component of the roll moment direction Mc of each multiferroic portion is magnetically coupled to the magnetization direction of the corresponding free layer via exchange biasing or coupling (e.g., ferromagnetic or antiferromagnetic coupling) at its interface.

In one embodiment, the easy axis of magnetization of the polycrystalline grains of magnetoelectric multiferroic layer 140 may be along the axial direction. In another embodiment, the easy axis of magnetization of the polycrystalline grains of magnetoelectric multiferroic layer 140 may be along a respective first tilt (i.e., roll) direction, such as one of the <111> directions.

Referring to fig. 4A and 4B, the magnetic state (which corresponds to the magnetoresistive state) of the magnetic tunnel junction device 180 in a first exemplary structure is shown. Fig. 4A illustrates a first magnetic state of the magnetic tunnel junction device 180, and fig. 4B illustrates a second magnetic state of the magnetic tunnel junction device 180. The magnetization direction Mm of magnetoelectric multiferroic layer 140 is magnetically coupled to the magnetization direction Mf of free layer 136. Thus, in each of the first and second magnetic states of magnetic tunnel junction device 180, magnetization direction Mm of magnetoelectric multiferroic layer 140 may be aligned with magnetization direction Mf of free layer 136. In FIG. 4A, the magnetization direction Mf of the free layer 136 is parallel to the magnetization direction Mr of the reference layer 132. Thus, the magnetic tunnel junction device 180 (e.g., an MRAM cell) is in a lower resistance state. In FIG. 4B, the magnetization direction Mf of the free layer 136 is antiparallel to the magnetization direction Mr of the reference layer 132. Thus, the magnetic tunnel junction device 180 (e.g., an MRAM cell) is in a higher resistance state.

Referring to fig. 5, a programming mechanism of the magnetic memory device shown in fig. 4A and 4B is schematically illustrated. Fig. 5 shows a hysteresis curve of the axial electric polarization of magnetoelectric multiferroic layer 140 as a function of the external voltage applied to the second electrode and the first electrode, i.e., relative to the external voltage applied to the second electrode by the first electrode. The magnetization direction Mm of magnetoelectric multiferroic layer 140 may be switched when a voltage is applied across magnetoelectric multiferroic layer 140 that exceeds the magnitude of the coercive voltage (which may be Vc + or Vc-, depending on the polarity) of the magnetoelectric multiferroic material of magnetoelectric multiferroic layer 140. The positive coercive voltage Vc and the negative coercive voltage Vc-may have equal magnitudes and may differ in polarity from each other.

FIG. 6A illustrates a first programming voltage pattern P1 that may be used to program the magnetic tunnel junction device 180 to a lower resistance state in the configuration illustrated in FIG. 4A. FIG. 6B illustrates a second programming voltage pattern P2 that may be used to program the magnetic tunnel junction device 180 to the higher resistance state shown in FIG. 4B.

Referring to fig. 5 and 6A, the first programming voltage pattern P1 includes a first polarity voltage having a magnitude greater than the coercive voltage applied to the magnetic tunnel junction device 180 between the first and second electrodes. In the embodiment of fig. 5 and 6A, the first polarity voltage is a positive voltage VP1, which is greater in magnitude than the coercive voltage (Vc +) applied to the magnetic tunnel junction device 180 between the first and second electrodes. However, it should be understood that in alternative embodiments, the first polarity voltage may be a negative voltage having a magnitude greater than the coercive voltage. The positive voltage positively programs the magnetization direction Mm of magnetoelectric multiferroic layer 140 to be parallel to the magnetization direction Mr of reference layer 132. Further, the magnitude of the positive voltage is sufficient to reduce the perpendicular magnetic anisotropy ("PMA") and the magnetic anisotropy barrier height at the interface between the tunnel barrier layer 134 and the free layer 136 to allow the free layer 136 to positively switch its magnetization direction Mf. Because magnetization direction Mf of free layer 136 is coupled to magnetization direction Mm of magnetoelectric multiferroic layer 140, magnetization direction Mf of free layer 136 is aligned with magnetization direction Mm of magnetoelectric multiferroic layer 140. Thus, the magnetization direction Mf of the free layer 136 is certainly programmed to be parallel to the magnetization direction Mr of the reference layer 132, as shown in FIG. 4A. Thus, the magnetic tunnel junction device 180 is positively programmed to a lower resistance state.

Referring to fig. 5 and 6B, the second programming voltage pattern P2 includes a second polarity voltage opposite the first polarity voltage having a magnitude greater than a coercive voltage applied to the magnetic tunnel junction device 180 between the first and second electrodes. In the embodiment of fig. 5 and 6B, the second polarity voltage is a negative voltage VP2, which is greater in magnitude than the coercive voltage (Vc-) applied to the magnetic tunnel junction device 180 between the first and second electrodes. However, it should be understood that in alternative embodiments, the second polarity voltage may be a positive voltage having a magnitude greater than the coercive voltage. The negative voltage positively programs the magnetization direction Mm of magnetoelectric multiferroic layer 140 to be antiparallel to the magnetization direction Mr of reference layer 132. However, a negative voltage increases the perpendicular magnetic anisotropy ("PMA") and the magnetic anisotropy barrier height at the interface between the tunnel barrier layer 134 and the free layer 136, such that the free layer 136 cannot switch its magnetization direction Mf.

Thus, the second programming voltage pattern P2 also includes a first polarity voltage having a magnitude less than the coercive voltage applied to the magnetic tunnel junction device 180 between the first and second electrodes. In the embodiment of fig. 5 and 6B, the first polarity voltage is a positive voltage VP3 that is less in magnitude than the coercive voltage (Vc +) applied to the magnetic tunnel junction device 180 between the first and second electrodes. However, it should be understood that in alternative embodiments, the first polarity voltage may be a negative voltage having a magnitude less than the coercive voltage.

The magnitude of positive voltage VP3 is insufficient to switch the magnetization direction Mm of magnetoelectric multiferroic layer 140. However, the magnitude of the positive voltage VP3 is insufficient to reduce the perpendicular magnetic anisotropy ("PMA") and the magnetic anisotropy barrier height at the interface between the tunnel barrier layer 134 and the free layer 136 to allow the free layer 136 to positively switch its magnetization direction Mf. Because magnetization direction Mf of free layer 136 is coupled to magnetization direction Mm of magnetoelectric multiferroic layer 140, magnetization direction Mf of free layer 136 is aligned with magnetization direction Mm of magnetoelectric multiferroic layer 140. Thus, the magnetization direction Mf of the free layer 136 is programmed deterministically antiparallel to the magnetization direction Mr of the reference layer 132, as shown in FIG. 4B. Thus, when the negative voltage pulse VP2 is followed by a smaller positive voltage pulse VP3, the magnetic tunnel junction device 180 is positively programmed to a higher resistance state.

Referring to fig. 5, 6A and 6B, the magnitude of the positive voltage pulse VP1 may be between 0.5V and 2V, the magnitude of the negative voltage pulse VP2 may be between-0.5V and-2V, and the magnitude of the third positive voltage pulse VP3 may be between 0.3V and 1V, and the absolute value of the third positive voltage pulse is smaller than the absolute value of the negative voltage pulse VP 2.

In general, the magnetic memory device of embodiments of the present disclosure may include programming circuitry, such as components of the sensing and programming circuitry 570 of the random access memory device 501 of fig. 1 that applies the avoidance voltage. Alternatively, each magnetic tunnel junction device 180 may be individually connected to a respective programming circuit configured to program a single magnetic tunnel junction device 180.

Referring to fig. 7A and 7B, configurations of a second exemplary structure according to a second embodiment of the present disclosure are shown. The second exemplary embodiment replaces the magnetoelectric multiferroic layer 140 with a VCMA auxiliary structure 200 having an in-plane magnetization directionThe configuration of the structure may be derived from the configuration of the first exemplary structure shown in fig. 2A and 2B. In the configuration of fig. 7A and 7B, VCMA auxiliary structure 200 includes magnetoelectric multiferroic layer 140' having in-plane magnetization direction Mm. In-plane magnetization provides an in-plane magnetic dipole magnetic field for the precessional switching of VCMA. Layer 140' can include polycrystalline BiFeO having a preferred grain orientation along the (111) plane that can provide a predominant in-plane magnetization direction₃The layer, i.e., more than 50% of all grains, may have respective magnetization directions (e.g., spin orientations) parallel to the interface between the tunnel barrier layer 134 and the free layer 136.

The net in-plane magnetization of magnetoelectric multiferroic layer 140' can be induced by application of an in-plane magnetic field or by application of an out-of-plane external electric field. Thus, a substantial portion (i.e., greater than 50% by volume) of the grains of magnetoelectronics multiferroic layer 140' can have a net non-zero in-plane magnetization. In this case, each magnetoelectric multiferroic layer 140' can have a net non-zero ferroelectric polarization associated with a net non-zero in-plane magnetization. In other words, a net in-plane magnetization of each magnetoelectronics multiferroic layer 140' may be induced by applying an external magnetic field in an in-plane direction parallel to the interface between the free layer 136 and the tunnel barrier layer 134. The net in-plane ferroelectric polarization of magnetoelectric multiferroic layer 140 'and the net in-plane magnetization of magnetoelectric multiferroic layer 140' may be simultaneously induced by an external magnetic field.

In accordance with another embodiment of the present disclosure, a net in-plane ferroelectric polarization may be induced within each magnetoelectric multiferroic layer 140' within the array of magnetic tunnel junction devices 180 by applying an in-plane or out-of-plane initial electric field. An in-plane initial electric field may be applied in a horizontal direction parallel to the interface between each free layer 136 and the tunnel barrier layer 134. The in-plane initial electric field may align an in-plane component of the ferroelectric polarization of each grain in each magnetoelectric multiferroic layer 140' along a direction of the in-plane initial electric field. Thus, each magnetoelectric multiferroic layer 140' may have a net non-zero in-plane electrical polarization. In this case, each magnetoelectric multiferroic layer 140' may have a net non-zero in-plane magnetization associated with a net non-zero in-plane ferroelectric polarization. In other words, a net in-plane magnetization of each magnetoelectric multiferroic layer 140' can be induced by applying an external electric field in an in-plane direction parallel to the interface between free layer 136 and tunnel barrier layer 134. The net in-plane ferroelectric polarization of each magnetoelectric multiferroic layer 140 'and the net in-plane magnetization of each magnetoelectric multiferroic layer 140' can be simultaneously induced by an external electric field.

In general, the magnitude of the net in-plane magnetization of each magnetoelectronics multiferroic layer 140 'may be at least an order of magnitude greater, i.e., 10 times greater, such as 30 or 100 times greater, than the magnitude of any net axial magnetization of the corresponding magnetoelectronics multiferroic layer 140'.

Referring to fig. 8, an alternative configuration of the second exemplary structure is shown that can be derived from the configuration of the second exemplary structure shown in fig. 7A and 7B by using a VCMA assist structure 200 that includes a ferromagnetic or ferrimagnetic layer 240 having an in-plane magnetization direction and a conductive nonmagnetic spacer layer 138 between the free layer 136 and the ferromagnetic or ferrimagnetic layer 240. The ferromagnetic or ferrimagnetic layer 240 may comprise a CoFe or CoFeB ferromagnetic layer or Fe₃O₄A ferrimagnetic layer. The conductive nonmagnetic spacer layer 138 may comprise any suitable nonmagnetic metal layer, such as Pt, Ta, Ru, W, or the like. The thickness of each of layers 238 and 240 may be between 1nm and 2nm, although lesser and greater thicknesses may also be employed.

Referring collectively to fig. 7A, 7B and 8, there is provided a magnetic memory device comprising: a first electrode (including a portion of the first conductive line 30); a second electrode (including a portion of the second electrically conductive line 90); and a layer stack (optionally 120, 132, 134, 136, 200, optionally 170) between the first and second electrodes and comprising, in order from side to side, a reference layer 132 having a fixed axial magnetization direction, a tunnel barrier layer 134, a free layer 136 having an easy axis parallel or anti-parallel to the fixed axial magnetization direction, and a VCMA assist structure 200 having an in-plane magnetization direction.

In one embodiment, the VCMA assist structure includes a magnetoelectric multiferroic layer 140 'including at least one grain having an easy axis of magnetization parallel to an interface between the free layer 136 and the tunnel barrier layer 134, and a net in-plane magnetization of the magnetoelectric multiferroic layer 140' is non-zero.

In one implementation, magnetoelectric multiferroic layer 140' has a net ferroelectric polarization parallel to the interface between free layer 136 and tunnel barrier layer 134. In one embodiment, magnetoelectronics multiferroic layer 140 ' may be polycrystalline, and a subset of the volumetrically predominant grains within magnetoelectronics multiferroic layer 140 ' (i.e., a group of grains that occupy more than 50% of the entire volume of each magnetoelectronics multiferroic layer 140) may have a respective magnetization direction that is aligned with or at an angle of less than 145 degrees to the net in-plane magnetization direction of magnetoelectronics layer 140 '. In one embodiment, the net in-plane magnetization of magnetoelectric multiferroic layer 140 'may be parallel or anti-parallel to the net in-plane magnetization direction of magnetoelectric multiferroic layer 140'.

In one embodiment, the magnetoelectric multiferroic layer 140' includes a material selected from BiFeO₃、h-YMnO₃、BaNiF₄、PbVO₃、BiMnO₃、LuFe₂O₄、HoMn₂O₅、h-HoMnO₃、h-ScMnO₃、h-ErMnO₃、h-TmMnO₃、h-YbMnO₃、h-LuMnO₃、K2SeO₄、Cs₂CdI₄、TbMnO₃、Ni₃V₂O₈、MnWO₄、CuO、ZnCr₂Se₄、LiCu₂O₂And Ni₃B₇O₁₃And (I) a material. For example, the magnetoelectronics multiferroic layer 140' includes BiFeO having a (111) preferred grain orientation and a thickness of 1nm or less₃A layer.

In one embodiment, the stack further includes a SAF structure 120. In one embodiment, the layer stack (optional 120, 132, 134, 136, 200, optional 170) includes a nonmagnetic capping layer 170 comprising a nonmagnetic metal in contact with the magnetoelectric multiferroic layer 140' and one of the electrode and the second electrode.

In another embodiment shown in fig. 8, the VCMA assist structure 200 includes a ferromagnetic or ferrimagnetic layer 240 having an in-plane magnetization direction and an electrically conductive nonmagnetic spacer layer 138 located between the free layer 136 and the ferromagnetic or ferrimagnetic layer 240.

Referring to fig. 9A and 9B, the first and second programmed states of the second exemplary structure are shown. Fig. 9A shows the first programmed state, and fig. 9B shows the second programmed state. The first programmed state (e.g., the lower resistance state) has a parallel alignment between the magnetization Mf of the free layer 136 and the magnetization Mr of the reference layer 132. The second programmed state (e.g., the higher resistance state) has an antiparallel alignment between the magnetization Mf of the free layer 136 and the magnetization Mr of the reference layer 132. The first programmed state of fig. 9A and the second programmed state of fig. 9B have different tunneling magnetoresistance values. Thus, the magnetic state of the magnetic tunnel junction device 180 in the second exemplary structure may be determined by applying a low voltage sensing bias voltage across the second electrode and the first electrode and measuring the magnitude of the tunneling current through the magnetic tunnel junction device 180.

Referring to fig. 10A, a second exemplary structure may include a sensing circuit (which may be a component of the sensing and programming circuit 570 shown in fig. 1, or may be a separate sensing circuit) configured to determine the tunneling magnetoresistance of the stack (optional 120, 132, 134, 136, 200, optional 170) between the first electrode and the second electrode. The sensing circuit can be configured to determine whether the memory state of the magnetic memory device (i.e., the magnetic tunnel junction device 180) is in a target state by comparing the measured value of the tunneling magnetoresistance of the layer stack to a target value, which can be a target value for the parallel state shown in fig. 9A or a target value for the anti-parallel state shown in fig. 9B.

The sensing circuit may be configured to apply a sensing pulse Vs of a first polarity. The first polarity may be selected such that the sense pulse Vs enhances the perpendicular magnetic anisotropy of the free layer 136. In other words, the magnetization of the free layer 136 is less likely to transition between the parallel and anti-parallel states. Thus, the sensing operation does not disturb the magnetic state of the magnetic tunnel junction device 180 of the second exemplary structure. For example, the sensing pulse may comprise a negative voltage pulse. In one embodiment, the absolute magnitude of the voltage of the sense pulse Vs may be in the range of 0.05V to 0.5V, such as 0.1V to 0.2V, although smaller and larger voltages may also be employed.

If the sensing operation determines that the measured magnetic state of the magnetic tunnel junction device 180 is the same as the target magnetic state of the magnetic tunnel junction device 180, no further action is required.

Referring to fig. 10B, if the sensing operation determines that the measured magnetic state of the magnetic tunnel junction device 180 is opposite the target magnetic state of the magnetic tunnel junction device 180, the magnetic tunnel junction device 180 may be programmed to the target magnetic state using the programming circuit. The programming circuitry may be a component of the sensing and programming circuitry 570 shown in FIG. 1, or may be discrete circuitry configured to program a single magnetic tunnel junction device 180. The programming circuitry may be configured to apply the VCMA programming voltage pulse Vp without the magnetic memory device being in the target state, and may be configured to apply no programming voltage pulse with the magnetic memory device being in the target state that induces precession of an angle between a magnetization direction of the free layer 136 and an axial direction perpendicular to an interface between the free layer 136 and the tunnel barrier layer 134.

The VCMA programming voltage pulse Vp nondeterministically programs the magnetic memory device without applying an external magnetic field. The VCMA programming voltage pulse Vp may have a second polarity opposite the first polarity. The programming voltage pulse Vp attenuates the perpendicular magnetic anisotropy of the free layer 136. Thus, the programming voltage pulse Vp enables the magnetization direction of the free layer 136 to move. For example, the programming voltage Vp may be a positive voltage pulse of 0.3V to 1V having an absolute magnitude greater than the sense pulse Vs.

Various embodiments of the present disclosure may be used to provide a Voltage Controlled Magnetic Anisotropy (VCMA) Tunneling Magnetoresistive (TMR) memory device. The VCMA TMR device may have a deterministic switching mechanism as in the case of the first exemplary architecture, or may have a pulse duration controlled switching mechanism as in the case of the second exemplary architecture. Due to the deterministic nature of the programming mechanism, the programming results are independent of variations in pulse amplitude or pulse duration in the case of the first exemplary structure. The VCMA assist structure of the second exemplary structure provides a predictable and well controlled stray magnetic field (residual magnetic field) that determines the precessional frequency of the angle between the magnetization of the free layer 136 and the vertical axis, thereby improving the accuracy and reliability of VCMA programming of switched magnetic states. Furthermore, when the VCMA auxiliary structure includes an in-plane multiferroic layer 140', such multiferroic layer can provide additional PMA to the free layer due to the hybridization of the oxygen orbital and the metal 3d orbital.

In addition, e.g. BiFeO₃The resistivity of the multiferroic layer of (a) is less than that of typical tunnel barrier materials (e.g., MgO). Because the multiferroic layer has a similar thickness as the tunnel barrier layer, the multiferroic layer does not significantly increase the resistance of the memory device (i.e., does not increase the parasitic resistance significantly). Thus, a relatively small sensing voltage can be used to read the memory device without disturbing the written magnetic state similar to conventional VCMA MRAM lacking a multiferroic layer.

While the foregoing refers to certain preferred embodiments, it is to be understood that the disclosure is not so limited. Various modifications to the disclosed embodiments will be apparent to those skilled in the art, and such modifications are intended to be within the scope of the present disclosure. Embodiments employing specific structures and/or configurations are shown in the present disclosure, it being understood that the present disclosure may be practiced in any other compatible structures and/or configurations that are functionally equivalent, provided that such substitutions are not explicitly prohibited or otherwise considered to be impossible by one of ordinary skill in the art. All publications, patent applications, and patents cited herein are incorporated by reference in their entirety.

Claims

1. A magnetic memory device, the magnetic memory device comprising:

a first electrode;

a second electrode; and

a layer stack between the first and second electrodes and comprising, in order from side to side: a reference layer, a tunnel barrier layer, a free layer, and a magnetoelectric multiferroic layer comprising at least one grain having an easy axis of magnetization along an axial direction or along a first tilt direction having a first tilt angle less than 90 degrees relative to the axial direction, the axial direction being perpendicular to an interface between the free layer and the tunnel barrier layer.

2. The magnetic memory apparatus of claim 1, wherein the at least one grain of the magnetoelectric multiferroic layer has an axis of easy ferroelectric polarization along the axial direction or along a second tilt direction having a second tilt angle less than 90 degrees relative to the axial direction.

3. The magnetic memory device of claim 1, further comprising a programming circuit configured to apply a programming voltage pattern between the first electrode and the second electrode, wherein the programming voltage pattern comprises:

a first programming voltage pattern comprising a first voltage having a first polarity and a magnitude greater than a coercive voltage sufficient to switch a magnetization direction of the magnetoelectric multiferroic layer; and

a second programming voltage pattern comprising a second voltage having a second polarity opposite the first polarity and greater in magnitude than the coercive voltage, followed by a third voltage having the first polarity and less in magnitude than the coercive voltage.

4. The magnetic memory device of claim 3, wherein:

the first voltage comprises a first positive voltage that deterministically programs the magnetization direction of the magnetoelectric multiferroic layer to be parallel to a magnetization direction of the reference layer; and is

The magnitude of the first positive voltage is sufficient to reduce the perpendicular magnetic anisotropy of the free layer, which allows the free layer to positively switch its magnetization direction parallel to the magnetization direction of the reference layer.

5. The magnetic memory device of claim 4, wherein:

the second voltage comprises a negative voltage that deterministically programs the magnetization direction of the magnetoelectric multiferroic layer to be antiparallel to the magnetization direction of the reference layer; and is

The negative voltage enhances the perpendicular magnetic anisotropy of the free layer such that the free layer cannot switch its magnetization direction.

6. The magnetic memory device of claim 5, wherein:

the third voltage comprises a second positive voltage having a magnitude insufficient to switch the magnetization direction of the magnetoelectric multiferroic layer; and is

The magnitude of the second positive voltage is sufficient to reduce the perpendicular magnetic anisotropy at the interface between the tunnel barrier layer and the free layer to allow the free layer to positively switch its magnetization direction antiparallel to that of the reference layer.

7. The magnetic memory device of claim 6, wherein:

the magnitude of the first positive voltage pulse is between 0.5V and 2V;

the magnitude of the negative voltage pulse is between-0.5V and-2V; and is

The magnitude of the second positive voltage pulse is between 0.3V and 1V, and its absolute value is smaller than that of the negative voltage pulse.

8. The magnetic memory apparatus of claim 6, wherein the magnetization direction of the free layer is coupled to the magnetization direction of the magnetoelectric multiferroic layer.

9. The magnetic memory device of claim 6, wherein:

the magnetic memory device is programmed to a lower resistance state by the first programming voltage mode; and is

The magnetic memory device is programmed to a higher resistance state by the second programming voltage mode.

10. The magnetic memory apparatus of claim 1, wherein the easy axis of the at least one grain of the magnetoelectric multiferroic layer is along the axial direction.

11. The magnetic memory apparatus of claim 1, wherein the easy axis of the at least one grain of the magnetoelectric multiferroic layer is along the first tilt direction.

12. The magnetic memory apparatus of claim 1, wherein the layer stack further comprises an SAF structure positioned adjacent to the reference layer.

13. The magnetic memory device according to claim 1, wherein the layer stack further comprises a nonmagnetic conductive capping layer that contacts the magnetoelectric multiferroic layer and one of the electrode and the second electrode.

14. The magnetic memory device of claim 1, wherein:

the tunnel barrier layer comprises a dielectric layer having a thickness of 1nm to 2 nm; and is

The magnetoelectric multiferroic layer comprises BiFeO₃、h-YMnO₃、BaNiF₄、PbVO₃、BiMnO₃、LuFe₂O₄、HoMn₂O₅、h-HoMnO₃、h-ScMnO₃、h-ErMnO₃、h-TmMnO₃、h-YbMnO₃、h-LuMnO₃、K2SeO₄、Cs₂CdI₄、TbMnO₃、Ni₃V₂O₈、MnWO₄、CuO、ZnCr₂Se₄、LiCu₂O₂Or Ni₃B₇O₁₃And (I) a material.

15. The magnetic memory device of claim 14, wherein the magnetoelectric multiferroic layer comprises BiFeO having a thickness of 1nm or less₃And (3) a layer.

16. A method of programming the magnetic memory apparatus of claim 1, comprising:

applying a first programming voltage pattern comprising a first voltage having a first polarity and a magnitude greater than a coercive voltage sufficient to switch a magnetization direction of the magnetoelectric multiferroic layer; and

applying a second programming voltage pattern comprising a second voltage having a second polarity opposite the first polarity and greater in magnitude than the coercive voltage, followed by a third voltage having the first polarity and less in magnitude than the coercive voltage.

17. The method of claim 16, wherein:

The magnitude of the first positive voltage is sufficient to reduce perpendicular magnetic anisotropy at an interface between the tunnel barrier layer and the free layer to allow the free layer to positively switch its magnetization direction parallel to the magnetization direction of the reference layer.

18. The method of claim 17, wherein:

the second voltage comprises a negative voltage that deterministically programs the magnetization direction of the magnetoelectric multiferroic layer to be antiparallel to the magnetization direction of the reference layer;

the negative voltage enhances the perpendicular magnetic anisotropy of the free layer such that the free layer cannot switch its magnetization direction;

19. The method of claim 18, wherein:

the magnitude of the first positive voltage pulse is between 0.5V and 2V;

the magnitude of the negative voltage pulse is between-0.5V and-2V; and is

20. The method of claim 18, wherein:

the magnetization direction of the free layer is coupled to the magnetization direction of the magnetoelectric multiferroic layer;

the magnetic memory device is positively programmed to a lower resistance state by the first programming voltage pattern; and is

The magnetic memory device is positively programmed to a higher resistance state by the second programming voltage pattern.

21. A magnetic memory device, the magnetic memory device comprising:

a first electrode;

a second electrode; (ii) a And

a layer stack between the first and second electrodes and comprising, in order from side to side, a reference layer, a tunnel barrier layer, a free layer, and a Voltage Controlled Magnetic Anisotropy (VCMA) assist structure having an in-plane magnetization direction.

22. The magnetic memory device of claim 21, wherein the VCMA assist structure comprises

A magnetoelectric multiferroic layer comprising at least one grain having an easy axis of magnetization parallel to an interface between the free layer and the tunnel barrier layer, and a net in-plane magnetization of the magnetoelectric multiferroic layer is not zero.

23. The magnetic memory apparatus of claim 22, wherein the magnetoelectric multiferroic layer has a net ferroelectric polarization parallel to the interface between the free layer and the tunnel barrier layer.

24. The magnetic memory device of claim 22, wherein the magnetoelectric multiferroic layer is polycrystalline, wherein respective magnetization directions of volumetrically predominant subsets of grains within the magnetoelectric multiferroic layer are aligned with or at an angle of less than 145 degrees to a direction of in-plane magnetization of the net plane of the magnetoelectric multiferroic layer.

25. The magnetic memory apparatus of claim 24, wherein the net in-plane magnetization of the magnetoelectric multiferroic layer is parallel or anti-parallel to the direction of the net in-plane magnetization of the magnetoelectric multiferroic layer.

26. The magnetic memory device of claim 21 wherein the magnetoelectric multiferroic layer comprises a material selected from BiFeO₃、h-YMnO₃、BaNiF₄、PbVO₃、BiMnO₃、LuFe₂O₄、HoMn₂O₅、h-HoMnO₃、h-ScMnO₃、h-ErMnO₃、h-TmMnO₃、h-YbMnO₃、h-LuMnO₃、K2SeO₄、Cs₂CdI₄、TbMnO₃、Ni₃V₂O₈、MnWO₄、CuO、ZnCr₂Se₄、LiCu₂O₂And Ni₃B₇O₁₃And (I) a material.

27. The magnetic memory device of claim 26, wherein the magnetoelectric multiferroic layer comprises BiFeO having a (111) preferred grain orientation and a thickness of 1nm or less₃And (3) a layer.

28. The magnetic memory device of claim 21, wherein the VCMA assist structure includes a ferromagnetic layer having an in-plane magnetization direction and a conductive nonmagnetic spacer layer between the free layer and the ferromagnetic layer.

29. The magnetic memory device of claim 21, wherein the VCMA assist structure includes a ferrimagnetic layer having an in-plane magnetization direction and a conductive nonmagnetic spacer layer between the free layer and the ferrimagnetic layer.

30. The magnetic memory apparatus of claim 21, wherein the layer stack further comprises a nonmagnetic capping layer including a nonmagnetic metal contacting the magnetoelectric multiferroic layer and one of the electrode and the second electrode.

31. The magnetic memory apparatus of claim 21, wherein the layer stack further comprises an SAF structure contacting the reference layer.

32. The magnetic memory device of claim 21, wherein the tunnel barrier layer comprises a dielectric layer having a thickness of 1nm to 2 nm.

33. The magnetic memory device of claim 21, further comprising

A sensing circuit is included that is configured to determine a tunneling magnetoresistance of the layer stack between the first electrode and the second electrode.

34. The magnetic memory device of claim 33, further comprising a programming circuit connected to the first and second electrodes and configured to non-deterministically program the magnetic memory device using non-deterministic VCMA programming.

35. The magnetic memory device of claim 34, wherein the programming circuitry is configured to:

determining whether a memory state of the magnetic memory device is in a target state by comparing a measured value of the tunneling magnetoresistance of the layer stack to a target value; and

applying a programming voltage pulse without the magnetic memory device in the target state and without applying any programming voltage pulse with the magnetic memory device in the target state, the programming voltage pulse inducing precession of an angle between a magnetization direction of the free layer and an axial direction perpendicular to the interface between the free layer and the tunnel barrier layer.

36. The magnetic memory device of claim 35, wherein the in-plane magnetization of the VCMA assist structure induces precession of the angle between the magnetization direction and the axial direction of the free layer between 0 and 180 degrees when the programming voltage pulse is applied without application of an external magnetic field.

37. A method of operating the magnetic memory device of claim 21, comprising determining a tunneling magnetoresistance of the layer stack.

38. The method of claim 37, further comprising nondeterministically programming the magnetic memory device without applying an external magnetic field by applying a VCMA programming voltage pulse between the first and second electrodes.

39. The method of claim 38, the method further comprising:

applying the VCMA programming voltage pulse without the magnetic memory device being in the target state and without applying any programming voltage pulse with the magnetic memory device being in the target state, the VCMA programming voltage pulse inducing precession of an angle between a magnetization direction of the free layer and an axial direction perpendicular to an interface between the free layer and the tunnel barrier layer.

40. The method of claim 39, wherein a duration of the programming voltage pulse is selected such that the angle between the magnetization direction and the axial direction changes by more than 135 degrees at an end of the programming voltage pulse.