Multiferroic voltage-controlled magnetic anisotropic memory device and its manufacturing method

Abstract

A magnetic memory device includes a first electrode, a second electrode, and a stack between the first and second electrodes. The stack includes a reference layer, a tunnel barrier layer, a free layer, and a magnetoelectric multiferroic layer comprising at least one grain. The magnetization of the magnetoelectric multiferroic layer can be axial, tilted, or in-plane. For axial or tilted 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

[0001] Related applications

[0002] This application claims priority to U.S. Nonprovisional Patent Application No. 17 / 004,534, filed August 27, 2020, and U.S. Nonprovisional Patent Application No. 17 / 004,690, filed August 27, 2020, the entire contents of which are incorporated herein by reference. Technical Field

[0003] This disclosure generally relates to the field of magnetic (e.g., spin) memory devices, and more specifically to magnetoresistive random access memory (“MRAM”) devices comprising multiple iron layers and methods of manufacturing the same. Background Technology

[0004] Magnetoresistive memory devices can store information about the resistance difference using a first configuration and a second configuration. In the first configuration, the magnetization direction of the ferromagnetic free layer is parallel to the magnetization direction of the ferromagnetic reference layer. In the second configuration, the magnetization direction of the free layer is antiparallel to the magnetization direction of the reference layer. Programming a magnetoresistive memory device requires various external power supplies to flip the magnetization direction of the free layer. These external power supplies can be magnetic in nature or employ a spin-transfer mechanism.

[0005] Voltage-controlled magnetic anisotropy (VCMA) refers to the effect where the vertical magnetic anisotropy of a free layer has a first-order correlation with an externally applied voltage located on the free layer in a magnetic tunnel junction comprising a dielectric tunnel barrier layer between the free layer and a ferromagnetic reference layer. The thickness of the dielectric tunnel barrier layer can be at least 1 nm, which reduces the tunneling current flowing through the dielectric tunnel barrier layer below the critical current required to switch the magnetization direction of the free layer during programming. Therefore, the applied voltage is used to switch the magnetization direction of the free layer. The applied voltage reduces the energy vertical magnetic anisotropy in one bias direction and increases it in another. However, VCMA programming is nondeterministic and requires precise control of the timing of the applied voltage pulses to obtain the desired magnetization direction of the free layer. Summary of the Invention

[0006] According to one aspect of this disclosure, a magnetic memory device is provided, comprising: a first electrode; a second electrode; and a stack located between the first electrode and the second electrode and sequentially comprising from one side to the other: a reference layer, a tunnel barrier layer, a free layer, and a magnetoelectric multiferroic layer containing at least one grain, wherein the at least one grain has an easy magnetization axis along an axial direction or along a first tilt direction having a first tilt angle of less than 90 degrees relative to the axial direction, the axial direction being perpendicular to the interface between the free layer and the tunnel barrier layer.

[0007] According to another aspect of this disclosure, a method of programming a magnetic memory device includes applying a first programming voltage mode and a second programming voltage mode, the first programming voltage mode including a first positive voltage with a magnitude greater than a coercive voltage sufficient to switch the magnetization direction of a magnetoelectric multiferroic layer, the second programming voltage mode including a negative voltage with a magnitude greater than the coercive voltage, followed by a second positive voltage with a magnitude less than the coercive voltage.

[0008] In one embodiment, a first positive voltage definitively 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 reduce the vertical magnetic anisotropy of the free layer, allowing the free layer to switch its magnetization direction to be parallel to the magnetization direction of the reference layer. A negative voltage definitively 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 vertical magnetic anisotropy of the free layer, making it impossible for the free layer to switch its magnetization direction. A 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 reduce the vertical magnetic anisotropy of the free layer, allowing the free layer to definitively switch its magnetization direction to be antiparallel to the magnetization direction of the reference layer.

[0009] According to another aspect of this disclosure, a magnetic memory device includes a first electrode, a second electrode, and a stack of layers located between the first electrode and the second electrode, and sequentially includes a reference layer, a tunnel barrier layer, a free layer, and a voltage-controlled magnetic anisotropy (VCMA) auxiliary structure having an in-plane magnetization direction from one side to the other. Attached Figure Description

[0010] Figure 1 This is a schematic diagram of a random access array of a magnetic tunnel junction device according to an embodiment of the present disclosure.

[0011] Figure 2A This is a vertical cross-sectional view of a first exemplary structure formed according to a first embodiment of the present disclosure.

[0012] Figure 2B This is a vertical cross-sectional view of an alternative embodiment of the first exemplary structure according to the first embodiment of this disclosure.

[0013] Figure 3A It is a perspective view of a BiFeO3 unit cell with ferroelectric polarization and magnetic moment.

[0014] Figure 3B Show Figure 3A The relative spatial orientation between the ferroelectric polarization and magnetic moment direction of the BiFeO3 unit cell.

[0015] Figure 4A This is a vertical cross-sectional view of a first exemplary structure in a first programming state according to a first embodiment of the present disclosure.

[0016] Figure 4B This is a vertical cross-sectional view of a first exemplary structure in a second programming state according to a first embodiment of the present disclosure.

[0017] Figure 5 This is a diagram illustrating the variation of axial ferroelectric polarization in a magnetoelectric multiferroic layer according to a first embodiment of the present disclosure.

[0018] Figure 6A This 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 aspects of this disclosure.

[0019] Figure 6B This is a diagram illustrating a second voltage pulse pattern for programming a magnetic memory cell of a first exemplary structure to a second magnetic state, according to aspects of this disclosure.

[0020] Figure 7A This is a vertical cross-sectional view of a second exemplary structure formed according to the first embodiment of this disclosure.

[0021] Figure 7B This is a vertical cross-sectional view of an alternative embodiment of a second exemplary structure according to a first embodiment of the present disclosure.

[0022] Figure 8 This is a vertical cross-sectional view of another alternative embodiment of the second exemplary structure according to the second embodiment of this disclosure.

[0023] Figure 9A This 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.

[0024] Figure 9B This 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.

[0025] Figure 10A This is a diagram of a sensing voltage pattern for sensing the magnetic state of a magnetic memory device of a second exemplary structure according to a second embodiment of the present disclosure.

[0026] Figure 10B This is a diagram of a programming voltage mode for programming the magnetic state of a magnetic memory device of a second exemplary structure according to a second embodiment of the present disclosure. Detailed Implementation

[0027] Embodiments of this 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 does not depend on the duration of the programming voltage pulse) and / or provides a precisely controlled in-plane auxiliary magnetic field determined by the crystal properties of the magnetoelectric multiferroic layer.

[0028] The accompanying drawings are not to scale. Where a single instance of an element is shown, multiple instances of the element may be repeated unless explicitly described or otherwise clearly indicated that no repetition of an element exists. Numbers such as “first,” “second,” and “third” are used only to identify similar elements and may be used differently throughout the specification and claims of this disclosure. The term “at least one” element refers to all possibilities, including the possibility of a single element and the possibility of multiple elements. The same reference numerals denote the same or similar elements. Unless otherwise stated, elements having the same reference numerals are assumed to have the same composition and the same function. Unless otherwise specified, “contact” between elements means direct contact between elements providing a shared edge or surface. If two or more elements are not in direct contact with each other or with each other, the two elements are “separated” from each other or “separated from each other.” As used herein, a first element positioned “on” a second element may be positioned on the outer side of the surface of the second element or on the inner side of the second element. As used herein, if there is physical contact between the surfaces of the first element and the second element, the first element is positioned “directly” on the second element. As used herein, if a conductive path of at least one conductive material exists between a first element and a second element, the first element is “electrically connected” to the second element. As used herein, a “prototype” structure or a “process” structure refers to a transient structure in which the shape or composition of at least one of its components is subsequently modified.

[0029] As used herein, a “layer” refers to a portion of material comprising a region having thickness. A layer may extend over the entirety of a lower or upper overlay structure, or may have a range smaller than that of the lower or upper overlay structure. Additionally, a layer may be a region of uniform or non-uniform continuous structure whose thickness is less than that of the continuous structure. For example, a layer may be positioned between the top and bottom surfaces of a continuous structure or between any pair of horizontal planes at the top and bottom surfaces of a continuous structure. A layer may extend horizontally, vertically, and / or along a tapered surface. A substrate may be a layer, which may include one or more layers, or may have one or more layers on, above, and / or below it. As used herein, a “layer stack” refers to a stack of layers. As used herein, a “line” or “line structure” refers to a layer having a predominant direction of extension, i.e., the direction in which the layer extends the most. As used herein, a “ferroelectric material” refers to any material exhibiting spontaneous ferroelectric polarization (e.g., exhibiting ferroelectricity) that can be reversed by the application of an external electric field. As used herein, a “multiferroic” material refers to a material exhibiting at least two ferroelectric sequences, such as magnetic (ferromagnetic, antiferromagnetic, or ferrimagnetic) and ferroelectric properties. As used in this article, "magnetoelectric multiferroic" refers to materials that exhibit both ferromagnetic order and ferroelectric properties. The change in total magnetization is related to the change in total ferroelectric polarization in the magnetoelectric multiferroic material, and therefore the change in the direction of the magnetic moment of the material can be related to the change in the direction of ferroelectric polarization, and vice versa.

[0030] Figure 1 This is a schematic diagram of the random access memory device 501 of the magnetic tunnel junction device 180 according to an embodiment of the present disclosure. As used herein, "random access memory device" means a memory device that includes memory cells that allow random access, i.e., access to any selected memory cell when a command is given to read the contents of a selected memory cell.

[0031] The random access memory device 501 of the embodiments of this disclosure may include an MRAM device, such as a multi-state STT-type MRAM device containing a multiferroic portion. Device 501 includes a memory array region 550 containing a corresponding array of magnetic devices, such as magnetic tunnel junction devices (e.g., magnetoresistive memory cells) 180 located at the intersection of word lines (which may include the first conductive line 30 as shown or the second conductive line 90 in an alternative configuration) and bit lines (which may include the second conductive line 90 as shown or the first conductive line 30 in an alternative configuration). For example, the first conductive line 30 may be electrically connected to and / or may include the bottom electrode of a corresponding 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 the top electrode of a corresponding column of magnetic tunnel junction devices 180 in the memory array region 550.

[0032] Random access memory device 501 may also include a row decoder 560 connected to word lines, sensing and programming circuitry 570 (which may include a sense amplifier, programming transistor, and control circuitry) connected to bit lines, a column decoder 580 connected to bit lines, and a data buffer 590 connected to the sensing circuitry system. Magnetic tunnel junction devices 180 are provided in an array configuration forming random access memory device 501. In one embodiment, magnetic tunnel junction devices 180 may be provided as a rectangular array. Thus, each magnetic tunnel junction device in magnetic tunnel junction devices 180 may be a two-terminal device including a corresponding first electrode and a corresponding second electrode. It should be noted that the location and interconnection of the components are illustrative, and the components may be arranged in different configurations. Furthermore, magnetic tunnel junction devices 180 may be manufactured as discrete devices, i.e., single isolated devices.

[0033] The random access configuration shown in the random access memory device 501 is merely exemplary, and the magnetic tunnel junction device 180 of the embodiments of this disclosure can be connected in different interconnect configurations.

[0034] refer to Figure 2A and Figure 2B An exemplary configuration of the magnetic tunnel junction device 180 is shown in the first exemplary structure. Figure 2A configuration and Figure 2B The configuration is an alternative configuration that can be derived from each other by reversing the material deposition sequence during the formation of the magnetic tunnel junction device 180, which is a magnetic memory device.

[0035] A first exemplary structure includes an optional insulating layer 110 comprising an insulating material, such as undoped silicate glass, doped silicate glass, organosilicon glass, silicon nitride, dielectric metal oxide, or a combination thereof. In one embodiment, the insulating layer 110 includes an insulating substrate, such as a ceramic or glass substrate. In another embodiment, the insulating layer 110 may be disposed on a semiconductor substrate (not shown) having a semiconductor device (not shown), such as a field-effect transistor. In this case, the insulating layer 110 may include a plurality of interconnect-level dielectric material layers with metal interconnect structures embedded therein. The metal interconnect structures provide electrical connections between semiconductor devices and to first conductive lines 30 and second conductive lines 90 formed above the insulating layer 110. In this case, structural elements formed above the insulating layer 110 may be embedded within a dielectric matrix (not explicitly shown) into which the first conductive lines 30 and second conductive lines are embedded.

[0036] A first conductive line 30 may be formed above an insulating material layer 110. The first conductive line 30 can be formed above 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 a linear structure extending laterally along a first horizontal direction. In one embodiment, the 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 cavity may be formed in the upper portion of the insulating material layer 110, and the first conductive line 30 may be formed by an inlay method, wherein at least one metal material is deposited in the cavity, and excess portions of the at least one metal material are removed above a horizontal plane containing the top surface of the insulating material layer 110. Each portion of the first conductive line 30 contacting the overlying magnetic tunnel junction device 180 includes a first electrode of the magnetic tunnel junction device 180, which is a magnetic memory device.

[0037] A continuous stack may be deposited above the first conductive line 30. The continuous stack may contain, from bottom to top or from 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.

[0038] The optional SAF structure may comprise a superlattice structure containing alternating sequences of ferromagnetic and conductive nonmagnetic material layers. In an illustrative example, the superlattice structure may comprise [X / Q]. n Where X represents a ferromagnetic material layer, such as a Co, CoFe, Fe, or CoFeB layer, Q represents a non-magnetic material layer, such as a Pt or Pd layer, and n represents the total number of repetitions of the double stack of ferromagnetic and non-magnetic material layers. The total number of repetitions n can be in the range of 2 to 20, such as 3 to 8, but more repetitions can also be used.

[0039] The continuous reference layer comprises a ferromagnetic material with perpendicular magnetic anisotropy. The continuous reference layer comprises a ferromagnetic material such as CoFe or CoFeB. The continuous reference layer can be deposited, for example, by physical vapor deposition, and can have a thickness in the range of 1 nm to 3 nm, but smaller and larger thicknesses are also possible.

[0040] The continuous tunneling barrier layer contains a tunneling dielectric material, such as MgO. The continuous tunneling barrier layer can be deposited, for example, by physical vapor deposition. The thickness of the continuous tunneling barrier layer can range from 1 nm to 2 nm, such as 1.5 nm to 2 nm, but smaller and larger thicknesses are also possible.

[0041] The continuous free layer contains a ferromagnetic material with perpendicular magnetic anisotropy. The continuous free layer contains ferromagnetic materials such as CoFe or CoFeB. The continuous free layer can be deposited, for example, by physical vapor deposition, and can have a thickness ranging from 0.6 nm to 2 nm, but smaller and larger thicknesses are also possible.

[0042] Continuous magnetoelectric multiferroic layers include magnetoelectric multiferroic materials. As used herein, "multiferroic" refers to a material exhibiting at least two ferroic sequences (e.g., ferromagnetism and ferroelectricity). As used herein, "magnetoelectric multiferroic" refers to a material exhibiting both ferromagnetic and ferroelectric sequences. Changes in total magnetization are related to changes in total polarization within the magnetoelectric multiferroic layer, and therefore magnetic transitions can be related to changes in ferroelectric polarization and vice versa.

[0043] Continuous magnetoelectric multiferroic layers can comprise any polycrystalline or single-crystal multiferroic material capable of generating non-zero net magnetization during deposition or upon application of an initial magnetic or electric field. In illustrative examples, continuous magnetoelectric multiferroic layers can comprise materials 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, LiCu2O2, and Ni3B7O. 13 The material of I. Continuous magnetoelectric multiferroic layers can be deposited using suitable deposition methods, such as physical vapor deposition. The thickness of continuous magnetoelectric multiferroic layers can be 1 nm or less, such as in the range of 0.3 nm to 1 nm, or 0.5 nm to 0.8 nm, but even smaller and larger thicknesses are also possible.

[0044] In one embodiment, the polarization and magnetization directions of the continuous magnetoelectric multiferroic layer are orthogonal to each other. The continuous magnetoelectric multiferroic layer comprises at least one grain having an easy magnetization axis along an axial direction or along a first tilt (i.e., lateral tilt) direction having a first tilt angle of less than 90 degrees relative 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 magnetoelectric multiferroic layer comprises a plurality of grains having an easy magnetization axis along an axial direction or along a corresponding first tilt direction having a corresponding first tilt angle of less than 90 degrees relative to the axial direction.

[0045] Typically, the magnetization orientation within the grains of a continuous magnetoelectric multiferroic layer can depend on the preferred grain orientation and / or impurity doping within the magnetoelectric multiferroic layer. If the magnetoelectric multiferroic material comprises BiFeO3, a polycrystalline BiFeO3 layer with a preferred grain orientation along the (110) plane can provide the dominant axial magnetization orientation, i.e., more than 50% of all grains can have a corresponding magnetization orientation (e.g., spin orientation) perpendicular to the interface between the continuous tunnel barrier layer and the continuous free layer. A polycrystalline BiFeO3 layer with a preferred grain orientation along the (100) plane can also have a magnetization orientation along the (110) plane. <111> The orientation provides the dominant tilt magnetization orientation, i.e., more than 50% of all grains may have a corresponding magnetization orientation that is neither perpendicular to nor parallel to the interface between the continuous tunnel barrier layer and the continuous free layer (e.g., spin orientation). Conversely, a polycrystalline BiFeO3 layer with a preferred grain orientation along the (100) plane but doped with La at Bi lattice sites can provide the dominant axial magnetization orientation, i.e., more than 50% of all grains may have a corresponding magnetization orientation perpendicular to the interface between the continuous tunnel barrier layer and the continuous free layer (e.g., spin orientation). A polycrystalline BiFeO3 layer with a preferred grain orientation along the (111) plane can provide the dominant in-plane magnetization orientation, i.e., more than 50% of all grains may have a corresponding magnetization orientation parallel to the interface between the continuous tunnel barrier layer and the continuous free layer (e.g., spin orientation).

[0046] Optional continuous nonmagnetic capping layers comprise a nonmagnetic metal that resists oxidation and / or diffusion. In one embodiment, the continuous nonmagnetic capping layer may comprise a metal with a melting point above 1,500 degrees Celsius. For example, the metal in the continuous nonmagnetic capping layer may comprise ruthenium, tantalum, platinum, or gold. The continuous nonmagnetic capping layer can be deposited by physical vapor deposition. The thickness of the continuous nonmagnetic capping layer can range from 0.5 nm to 2 nm, but smaller and larger thicknesses are also possible.

[0047] A two-dimensional array of pillar structures can be patterned from a continuous stack of layers. Patterning can be performed using ion beam polishing and / or photolithography and etching. Each pillar structure may contain a magnetic tunnel junction device 180, which is a magnetic memory device (e.g., an MRAM cell).

[0048] 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 an SAF structure 120. Each patterned portion of the continuous reference layer includes a reference layer 132. If the SAF structure 120 comprises a superlattice, the reference layer 132 may contact the nonmagnetic 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 a magnetoelectric multiferroic layer 140.

[0049] A dielectric matrix layer 190 may be deposited above and around the array of magnetic tunnel junction devices 180 (i.e., around the pillar structure). The dielectric matrix layer 190 comprises a dielectric material such as silicon nitride, silicon oxide, silicate glass, and / or dielectric metal oxide. In one embodiment, the dielectric matrix layer 190 may comprise a dielectric diffusion pad (such as a silicon nitride pad) and a dielectric filler material (such as 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 devices 180. For example, chemical mechanical planarization (CMP) may be used to planarize the top surface of the dielectric matrix layer 190.

[0050] A cavity extending laterally along a second horizontal direction may be formed in the upper portion of the dielectric matrix layer 190. The second horizontal direction differs from and may be perpendicular to the first horizontal direction. At least one conductive material may be deposited in the cavity, and excess portions of the at least one conductive material may be removed above a horizontal plane containing the top surface of the dielectric matrix layer 190. Each remaining portion of the at least one conductive material filling the cavity includes a second conductive line 90. Each second conductive line 90 may include at least one second electrode of a two-dimensional array of magnetic tunnel junction devices 180. Alternatively, the second conductive lines 90 may be formed on each pillar structure in the pillar structure, followed by the formation of the dielectric matrix layer 190 above the second conductive lines 90.

[0051] In one embodiment, each first conductive line 30 may contact a corresponding row of magnetic tunnel junction devices 180, and each second conductive line 90 may contact a corresponding 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.

[0052] In one embodiment, the volume-dominant grain group (i.e., a group of grains occupying more than 50% of the total volume of each magnetoelectric multiferroic layer 140) inherent in the magnetoelectric multiferroic layer 140 may be along an axial direction or along a first tilt direction having a first tilt angle of less than 90 degrees relative to the axial direction (e.g., ...). <111> The axial direction has an easy magnetization axis. 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 corresponding easy ferroelectric polarization axis along the axial direction or along a second tilt direction having a second tilt angle of less than 90 degrees relative to the axial direction. The second direction of each grain may or may not be parallel to or antiparallel to the first direction of the corresponding grain. Each magnetoelectric multiferroic layer 140 may be monocrystalline or polycrystalline, i.e., it may contain multiple grains adjacent to grain boundaries where the crystal structure of the magnetoelectric multiferroic material is discontinuous.

[0053] According to embodiments of this disclosure, net axial magnetization can be induced within each magnetoelectric multiferroic layer 140 in an array of magnetic tunnel junction devices 180 by applying an axial initial magnetic field or electric field. The electric field can switch ferroelectric polarization and corresponding magnetization due to magnetoelectric coupling. The axial initial magnetic field or electric field can be applied along a vertical direction perpendicular to the interface between each free layer 136 and the tunnel barrier layer 134. The axial initial magnetic field or electric field can align the vertical component of the magnetization of each grain in each magnetoelectric multiferroic layer 140 along the direction of the axial initial magnetic field or electric field. Therefore, each magnetoelectric multiferroic layer 140 can have a net non-zero axial magnetization. In this case, each magnetoelectric multiferroic layer 140 can have a net non-zero ferroelectric polarization associated with the net non-zero axial magnetization.

[0054] According to another embodiment of this disclosure, net axial ferroelectric polarization can be induced within each magnetoelectric multiferroic layer 140 in the array of the magnetic tunnel junction device 180 by applying an axial initial electric field. The axial initial electric field can 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 can be aligned with the vertical component of the ferroelectric polarization of each grain in each magnetoelectric multiferroic layer 140 along the direction of the axial initial electric field. Therefore, each magnetoelectric multiferroic layer 140 can have net non-zero axial ferroelectric polarization. In this case, each magnetoelectric multiferroic layer 140 can have net non-zero magnetization associated with the net non-zero axial ferroelectric polarization.

[0055] According to an aspect of this disclosure, a magnetic memory device is provided, comprising: a first electrode (including a portion of a first conductive line 30); a second electrode (including a portion of a second conductive line 90); and a stack (120, 132, 134, 136, 140, 170) located between the first electrode and the second electrode and sequentially comprising, from one side to the other, a reference layer 132, a tunnel barrier layer 134, a free layer 136, and a magnetoelectric multiferroic layer 140 comprising at least one grain, wherein the at least one grain has an easy magnetization axis along an axial direction or along a first tilt direction having a first tilt angle of less than 90 degrees relative to the axial direction, the axial direction being perpendicular to the interface between the free layer 136 and the tunnel barrier layer 134.

[0056] In one embodiment, the 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, the magnetoelectric multiferroic layer 140 comprises at least one material selected from and / or substantially composed of the following: 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, LiCu2O2, or Ni3B7O 13 I.

[0057] In one implementation, it can be provided Figure 2A or Figure 2B A two-dimensional array of instances of magnetic memory devices. The magnetic memory array may include: first conductive lines 30, which are parallel to each other and extend along a first direction; and second conductive lines 90, which are parallel to each other and extend along a second direction perpendicular to the first direction. Each of the first conductive lines 30 includes a first electrode of an instance of a corresponding 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 corresponding column of magnetic memory devices in the magnetic memory array.

[0058] In one embodiment, the magnetoelectric multiferroic layer 140 may have a net non-zero axial magnetization. The net in-plane ferromagnetic moment of the magnetoelectric multiferroic layer 140 may be zero (for axial multiferroic materials) or non-zero (for tilted multiferroic materials). Therefore, the net in-plane magnetization of the magnetoelectric multiferroic layer 140 may be zero (for axial multiferroic materials) or non-zero (for tilted multiferroic materials).

[0059] Figure 3A It shows a plane with in (111) <111> BiFeO3 stereocells with ferroelectric polarization direction P, either the group direction (e.g.,

[111] direction) or the tilt magnetic moment direction Mc. Figure 3B The in-plane (100) and out-of-plane (001) components of the magnetic moment direction Mc in the (111) plane are shown. For each magnetoelectric multiferroic unit cell, the relative spatial orientation (e.g., 90-degree angle) between the magnetic moment direction Mc and the polarization direction P is the same. The out-of-plane (001) component of the tilt magnetic moment direction Mc of each multiferroic portion is magnetically coupled to the magnetization direction of the corresponding free layer via exchange bias or coupling (e.g., ferromagnetic or antiferromagnetic coupling) at its interface.

[0060] In one embodiment, the easy magnetization axis of the polycrystalline grains of the magnetoelectric multiferroic layer 140 may be along an axial direction. In another embodiment, the easy magnetization axis of the polycrystalline grains of the magnetoelectric multiferroic layer 140 may be along a corresponding first tilt (i.e., lateral tilt) direction, such as... <111> One of the directions.

[0061] refer to Figure 4A and Figure 4B The magnetic state (corresponding to the magnetoresistive state) of the magnetic tunnel junction device 180 in the first exemplary structure is shown. Figure 4A The first magnetic state of the magnetic tunnel junction device 180 is shown, and Figure 4B The second magnetic state of the magnetic tunnel junction device 180 is shown. The magnetization direction Mm of the magnetoelectric multiferroic layer 140 is magnetically coupled to the magnetization direction Mf of the free layer 136. Therefore, in each of the first and second magnetic states of the magnetic tunnel junction device 180, the magnetization direction Mm of the magnetoelectric multiferroic layer 140 can be aligned with the magnetization direction Mf of the free layer 136. Figure 4A In this configuration, the magnetization direction Mf of the free layer 136 is parallel to the magnetization direction Mr of the reference layer 132. Therefore, the magnetic tunnel junction device 180 (e.g., an MRAM cell) is in a low-resistance state. Figure 4B In this configuration, the magnetization direction Mf of the free layer 136 is antiparallel to the magnetization direction Mr of the reference layer 132. Therefore, the magnetic tunnel junction device 180 (e.g., an MRAM cell) is in a high-resistance state.

[0062] refer to Figure 5 Schematic illustration Figure 4A and Figure 4B The programming mechanism of the magnetic memory device shown. Figure 5 The diagram shows the hysteresis curve of the axial polarization of the magnetoelectric multiferroic layer 140 as a function of external voltages applied to the second and first electrodes, i.e., the external voltage applied to the second electrode relative to the first electrode. The magnetization direction Mm of the magnetoelectric multiferroic layer 140 can be switched when a voltage is applied across the magnetoelectric multiferroic layer 140, exceeding the magnitude of the coercivity voltage (which, depending on polarity, can be Vc+ or Vc-) of the magnetoelectric multiferroic material of the magnetoelectric multiferroic layer 140. The positive coercivity voltage Vc and the negative coercivity voltage Vc- can have equal values ​​and can have different polarities.

[0063] Figure 6A The first programming voltage mode P1 is shown, which can be used to program the magnetic tunnel junction device 180 as... Figure 4A The lower resistance state in the configuration shown. Figure 6B A second programming voltage mode P2 is shown, which can be used to program the magnetic tunnel junction device 180 as... Figure 4B The higher resistance state is shown.

[0064] refer to Figure 5 and Figure 6A The first programming voltage mode P1 includes a first polarity voltage with a magnitude greater than the coercive voltage applied to the magnetic tunnel junction device 180 between the first and second electrodes. Figure 5 and Figure 6A In one embodiment, the first polarity voltage is a positive voltage VP1, the magnitude of which is greater 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 an alternative embodiment, the first polarity voltage can be a negative voltage with a magnitude greater than the coercive voltage. The positive voltage definitively programs the magnetization direction Mm of the magnetoelectric multiferroic layer 140 to be parallel to the magnetization direction Mr of the reference layer 132. Furthermore, the magnitude of the positive voltage is sufficient to reduce the vertical magnetic anisotropy (“PMA”) and magnetic anisotropy barrier height at the interface between the tunnel barrier layer 134 and the free layer 136, allowing the free layer 136 to definitively switch its magnetization direction Mf. Since the magnetization direction Mf of the free layer 136 is coupled to the magnetization direction Mm of the magnetoelectric multiferroic layer 140, the magnetization direction Mf of the free layer 136 is aligned with the magnetization direction Mm of the magnetoelectric multiferroic layer 140. Therefore, the magnetization direction Mf of the free layer 136 is definitively programmed to be parallel to the magnetization direction Mr of the reference layer 132, as follows: Figure 4A As shown. Therefore, the magnetic tunnel junction device 180 is specifically programmed to a lower resistance state.

[0065] refer to Figure 5 and Figure 6B The second programming voltage mode P2 includes a second polarity voltage opposite to the first polarity voltage, the magnitude of which is greater than the coercive voltage applied to the magnetic tunnel junction device 180 between the first and second electrodes. Figure 5 and Figure 6B In one embodiment, the second polarity voltage is a negative voltage VP2, the magnitude of which is greater 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 an alternative embodiment, the second polarity voltage can be a positive voltage greater than the coercive voltage. The negative voltage definitively programs the magnetization direction Mm of the magnetoelectric multiferroic layer 140 to an antiparallel magnetization direction Mr to the reference layer 132. However, the negative voltage increases the vertical magnetic anisotropy (“PMA”) and magnetic anisotropy barrier height at the interface between the tunnel barrier layer 134 and the free layer 136, making it impossible for the free layer 136 to switch its magnetization direction Mf.

[0066] Therefore, the second programming voltage mode P2 also includes a first polarity voltage with a magnitude smaller than the coercive voltage applied to the magnetic tunnel junction device 180 between the first and second electrodes. Figure 5 and Figure 6BIn one embodiment, the first polarity voltage is a positive voltage VP3, the magnitude of which is less 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 an alternative embodiment, the first polarity voltage may be a negative voltage with a magnitude less than the coercive voltage.

[0067] The magnitude of the positive voltage VP3 is insufficient to switch the magnetization direction Mm of the magnetoelectric multiferroic layer 140. However, the magnitude of the positive voltage VP3 is also insufficient to reduce the vertical magnetic anisotropy (“PMA”) and 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 deterministically switch its magnetization direction Mf. Since the magnetization direction Mf of the free layer 136 is coupled to the magnetization direction Mm of the magnetoelectric multiferroic layer 140, the magnetization direction Mf of the free layer 136 is aligned with the magnetization direction Mm of the magnetoelectric multiferroic layer 140. Therefore, the magnetization direction Mf of the free layer 136 is deterministically programmed to be antiparallel to the magnetization direction Mr of the reference layer 132, as... Figure 4B As shown. Therefore, when a negative voltage pulse VP2 is followed by a smaller positive voltage pulse VP3, the magnetic tunnel junction device 180 is definitively programmed into a higher resistance state.

[0068] refer to Figure 5 , Figure 6A and Figure 6B The magnitude of the positive voltage pulse VP1 can be between 0.5V and 2V, the magnitude of the negative voltage pulse VP2 can be between -0.5V and -2V, and the magnitude of the third positive voltage pulse VP3 can be between 0.3V and 1V, and the absolute value of the third positive voltage pulse is less than the absolute value of the negative voltage pulse VP2.

[0069] Typically, the magnetic memory device of this disclosure embodiment may include programming circuitry, such as... Figure 1 The components of the sensing and programming circuitry 570 of the random access memory device 501, which is subject to applied voltage avoidance. Alternatively, each magnetic tunnel junction device 180 may be individually connected to a corresponding programming circuit configured to program a single magnetic tunnel junction device 180.

[0070] refer to Figure 7A and Figure 7B The illustration shows a configuration of a second exemplary structure according to a second embodiment of the present disclosure. The configuration of the second exemplary structure can be derived from replacing the magnetoelectric multiferroic layer 140 with a VCMA auxiliary structure 200 having an in-plane magnetization direction. Figure 2A and Figure 2B The configuration of the first exemplary structure shown. Figure 7A and Figure 7BIn the configuration, the VCMA auxiliary structure 200 includes a magnetoelectric multiferroic layer 140′ having an in-plane magnetization direction Mm. The in-plane magnetization provides an in-plane magnetic dipole magnetic field for VCMA precession switching. Layer 140′ may include a polycrystalline BiFeO3 layer with a preferred grain orientation along the (111) plane that can provide a predominant in-plane magnetization direction, i.e., more than 50% of all grains may have a corresponding magnetization direction (e.g., spin orientation) parallel to the interface between the tunnel barrier layer 134 and the free layer 136.

[0071] The net in-plane magnetization of the magnetoelectric multiferroic layer 140′ can be induced by applying an in-plane magnetic field or by applying an out-of-plane external electric field. Therefore, the predominant portion (i.e., volume greater than 50%) of the grains of the magnetoelectric 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 the net non-zero in-plane magnetization. In other words, the net in-plane magnetization of each magnetoelectric multiferroic layer 140′ can 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 and the net in-plane magnetization of the magnetoelectric multiferroic layer 140′ can be simultaneously induced by an external magnetic field.

[0072] According to another embodiment of this disclosure, net in-plane ferroelectric polarization can be induced in each magnetoelectric multiferroic layer 140′ within the array of the magnetic tunnel junction device 180 by applying an in-plane or out-of-plane initial electric field. The in-plane initial electric field can be applied along a horizontal direction parallel to the interface between each free layer 136 and the tunnel barrier layer 134. The in-plane initial electric field can align the in-plane component of the ferroelectric polarization of each grain in each magnetoelectric multiferroic layer 140′ along the direction of the in-plane initial electric field. Therefore, each magnetoelectric multiferroic layer 140′ can have net non-zero in-plane polarization. In this case, each magnetoelectric multiferroic layer 140′ can have net non-zero in-plane magnetization associated with the net non-zero in-plane ferroelectric polarization. In other words, the net in-plane magnetization of each magnetoelectric multiferroic layer 140′ can be induced by applying an external electric field along an in-plane direction parallel to the interface between the free layer 136 and the tunnel barrier layer 134. The in-plane ferropolarization and in-plane magnetization of each magnetoelectric multiferroic layer 140′ can be simultaneously induced by an external electric field.

[0073] Typically, the amount of magnetization in the net plane of each magnetoelectric multiferroic layer 140′ can be at least an order of magnitude larger than the amount of magnetization in any net axial direction of the corresponding magnetoelectric multiferroic layer 140′, i.e., 10 times larger, such as 30 or 100 times larger.

[0074] refer to Figure 8An alternative configuration of the second exemplary structure is shown, which can be derived from a VCMA auxiliary structure 200 comprising a ferromagnetic or ferrimagnetic layer 240 having an in-plane magnetization direction and a conductive nonmagnetic spacer layer 138 located between the free layer 136 and the ferromagnetic or ferrimagnetic layer 240. Figure 7A and Figure 7B The configuration of the second exemplary structure shown is illustrated. The ferromagnetic or ferrimagnetic layer 240 may comprise a CoFe or CoFeB ferromagnetic layer or a Fe3O4 ferrimagnetic layer. The conductive nonmagnetic spacer layer 138 may comprise any suitable nonmagnetic metal layer, such as Pt, Ta, Ru, W, etc. The thickness of each layer in layers 238 and 240 may be between 1 nm and 2 nm, but smaller and larger thicknesses are also possible.

[0075] Common Reference Figure 7A , Figure 7B and Figure 8 A magnetic memory device is provided, comprising: a first electrode (including a portion of a first conductive line 30); a second electrode (including a portion of a second conductive line 90); and a stack (optionally 120, 132, 134, 136, 200, optional 170) located between the first electrode and the second electrode and, from one side to the other, sequentially including a reference layer 132 having a fixed axial magnetization direction, a tunnel barrier layer 134, a free layer 136 having an easy magnetization axis parallel to or antiparallel to the fixed axial magnetization direction, and a VCMA auxiliary structure 200 having an in-plane magnetization direction.

[0076] In one embodiment, the VCMA auxiliary structure includes a magnetoelectric multiferroic layer 140′ containing at least one grain having an easy magnetization axis parallel to the interface between the free layer 136 and the tunnel barrier layer 134, and the magnetization of the magnetoelectric multiferroic layer 140′ in the net plane is not zero.

[0077] In one embodiment, the magnetoelectric multiferroic layer 140' has a net ferroelectric polarization parallel to the interface between the free layer 136 and the tunnel barrier layer 134. In one embodiment, the magnetoelectric multiferroic layer 140' may be polycrystalline, and the volume-dominant grain group within the magnetoelectric multiferroic layer 140' (i.e., a group of grains occupying more than 50% of the total volume of each magnetoelectric multiferroic layer 140) may have a corresponding magnetization direction aligned with or at an angle of less than 145 degrees to the in-plane magnetization direction of the magnetoelectric multiferroic layer 140'. In one embodiment, the in-plane magnetization of the magnetoelectric multiferroic layer 140' may be parallel to or antiparallel to the in-plane magnetization direction of the magnetoelectric multiferroic layer 140'.

[0078] In one embodiment, the magnetoelectric multiferroic layer 140′ 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, LiCu2O2, and Ni3B7O. 13 The material of I. For example, the magnetoelectric multiferroic layer 140′ includes a BiFeO3 layer with a preferred (111) grain orientation and a thickness of 1 nm or less.

[0079] In one embodiment, the stack further includes a SAF structure 120. In one embodiment, the stack (optional 120, 132, 134, 136, 200, optional 170) includes a nonmagnetic capping layer 170 that includes a nonmagnetic metal that contacts a magnetoelectric multiferroic layer 140' and one of an electrode and a second electrode.

[0080] exist Figure 8 In another embodiment shown, the VCMA auxiliary structure 200 includes a ferromagnetic or ferrimagnetic layer 240 having an in-plane magnetization direction and a conductive nonmagnetic spacer layer 138 located between the free layer 136 and the ferromagnetic or ferrimagnetic layer 240.

[0081] refer to Figure 9A and Figure 9B The first and second programming states of the second exemplary structure are shown. Figure 9A The first programming state is shown, and Figure 9B The second programming state is shown. The first programming state (e.g., a 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 programming state (e.g., a 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. Figure 9A First programming state and Figure 9B The second programming state has a different tunneling magnetoresistance value. Therefore, the magnetic state of the magnetic tunnel junction device 180 in the second exemplary structure can be determined by applying a low voltage sensing bias voltage to the second electrode and the first electrode and measuring the magnitude of the tunneling current through the magnetic tunnel junction device 180.

[0082] refer to Figure 10A The second exemplary structure may include a sensing circuit (which may be...) Figure 1The sensing and programming circuit 570 shown is a component of, or may be a separate sensing circuit, configured to determine the tunneling magnetoresistance of the stack (optionally 120, 132, 134, 136, 200, optional 170) between the first and second electrodes. The sensing circuit may 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 a measured value of the tunneling magnetoresistance of the stack with a target value, which may be... Figure 9A The target value of the parallel state shown or Figure 9B The target value for the antiparallel state is shown.

[0083] The sensing circuit can be configured to apply a sensing pulse Vs of a first polarity. The first polarity can be selected such that the sensing pulse Vs enhances the vertical magnetic anisotropy of the free layer 136. In other words, the magnetization of the free layer 136 is less likely to transition between a parallel and antiparallel state. Therefore, the sensing operation does not interfere with the magnetic state of the magnetic tunnel junction device 180 of the second exemplary structure. For example, the sensing pulse may include a negative voltage pulse. In one embodiment, the absolute value of the voltage of the sensing pulse Vs may be in the range of 0.05V to 0.5V, such as 0.1V to 0.2V, but smaller and larger voltages may also be used.

[0084] 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.

[0085] refer to Figure 10B If the sensing operation determines that the measured magnetic state of the magnetic tunnel junction device 180 is opposite to the target magnetic state of the magnetic tunnel junction device 180, a programming circuit can be used to program the magnetic tunnel junction device 180 to the target magnetic state. The programming circuit can be... Figure 1 The components of the sensing and programming circuit 570 shown may also be discrete circuitry configured to program a single magnetic tunnel junction device 180. The programming circuitry may be configured to apply a VCMA programming voltage pulse Vp when the magnetic memory device is not in a target state, and may be configured not to apply any programming voltage pulse when the magnetic memory device is in a target state. This VCMA programming voltage pulse induces a precession of the angle between the magnetization direction of the free layer 136 and the axial direction perpendicular to the interface between the free layer 136 and the tunnel barrier layer 134.

[0086] 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 to the first polarity. The programming voltage pulse Vp reduces the vertical magnetic anisotropy of the free layer 136. Therefore, the programming voltage pulse Vp allows the magnetization direction of the free layer 136 to shift. For example, the programming voltage Vp may be a positive voltage pulse with an absolute value 0.3V to 1V greater than the sensing pulse Vs.

[0087] Various embodiments of this disclosure can be used to provide voltage-controlled magnetic anisotropy (VCMA) tunneling magnetoresistive (TMR) memory devices. VCMA TMR devices may have a deterministic switching mechanism as in the first exemplary structure, or a pulse duration-controlled switching mechanism as in the second exemplary structure. Due to the deterministic nature of the programming mechanism, the programming result is independent of variations in pulse amplitude or pulse duration as in the first exemplary structure. The VCMA auxiliary structure of the second exemplary structure provides a predictable and well-controlled stray magnetic field (residual magnetic field) that determines the precession 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 for switching magnetic states. Furthermore, when the VCMA auxiliary structure includes an in-plane multiferroic layer 140′, such a multiferroic layer can provide additional PMA to the free layer due to the hybridization of oxygen orbitals and metallic 3d orbitals.

[0088] Furthermore, the resistivity of multiferroic layers, such as BiFeO3, is lower than that of typical tunnel barrier materials (e.g., MgO). Since multiferroic layers have a similar thickness to tunnel barrier layers, they do not significantly increase the resistance of the memory device (i.e., they do not increase significant parasitic resistance). Therefore, a relatively small sense voltage can be used to read the memory device without interfering with the write magnetic state, which is similar to that of conventional VCMA MRAM lacking a multiferroic layer.

[0089] While specific preferred embodiments have been mentioned above, it will be understood that this disclosure is not limited thereto. Those skilled in the art will appreciate that various modifications can be made to the disclosed embodiments, and such modifications are intended to fall within the scope of this disclosure. While embodiments employing specific structures and / or configurations are shown in this disclosure, it should be understood that this disclosure can be practiced with any other functionally equivalent compatible structures and / or configurations, provided that such substitutions are not expressly prohibited or otherwise considered impossible by those skilled in the art. All publications, patent applications, and patents cited herein are incorporated herein by reference in their entirety.

Claims

1. A magnetic memory device, comprising: a first electrode; a second electrode; and a layer stack located between the first electrode and the second electrode 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 containing at least one crystalline grain having an easy magnetization axis along an axial direction or along a first tilted direction having a first tilt angle of 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; and wherein the magnetic memory device further comprises 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 a magnitude greater than the coercive voltage, followed by a third voltage having the first polarity and a magnitude less than the coercive voltage.

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

3. The magnetic memory device of claim 1, 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 a magnitude of the first positive voltage is sufficient to reduce a perpendicular magnetic anisotropy of the free layer, which allows the free layer to deterministically switch its magnetization direction to be parallel to the magnetization direction of the reference layer.

4. The magnetic memory device of claim 3, 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 the negative voltage enhances the perpendicular magnetic anisotropy of the free layer such that the free layer is unable to switch its magnetization direction.

5. The magnetic memory device of claim 4, wherein: the third voltage comprises a second positive voltage having a magnitude insufficient to switch the magnetization direction of the magnetoelectric multiferroic layer; and a 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 deterministically switch its magnetization direction to be antiparallel to the magnetization direction of the reference layer.

6. The magnetic memory device of claim 5, wherein: a magnitude of the first positive voltage pulse is between 0.5 V and 2 V; a magnitude of the negative voltage pulse is between -0.5 V and -2 V; and a magnitude of the second positive voltage pulse is between 0.5 V and 2 V. The second positive voltage pulse has a magnitude between 0.3 V and 1 V, and an absolute value less than an absolute value of the negative voltage pulse.

7. The magnetic memory device of claim 5, wherein the magnetization direction of the free layer is coupled to the magnetization direction of the magnetoelectric multiferroic layer.

8. The magnetic memory device of claim 5, wherein: the magnetic memory device is programmed to a lower resistance state by the first programming voltage pattern; and the magnetic memory device is programmed to a higher resistance state by the second programming voltage pattern.

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

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

11. The magnetic memory device of claim 1, wherein the layer stack further comprises a SAF structure positioned adjacent to the reference layer.

12. The magnetic memory device of claim 1, wherein the layer stack further comprises a non-magnetic conductive capping layer contacting the magnetoelectric multiferroic layer and one of the electrode and the second electrode.

13. The magnetic memory device of claim 1, wherein: the tunnel barrier layer comprises a dielectric layer having a thickness of 1 nm to 2 nm; and the magnetoelectric multiferroic layer comprises a material selected from BiFe03, h-YMn03, BaNiF4, PbVO3, BiMn03, LuFe204, HoMn205, h-HoMn03, h-ScMn03, h-ErMn03, h-TmMn03, h-YbMn03, h-LuMn03, K2Se04, Cs2Cdl4, TbMn03, Ni3V208, MnWO4, CuO, ZnCr2Se4, LiCu202, or Ni3B70 13 material of I.

14. The magnetic memory device of claim 13, wherein the magnetoelectric multiferroic layer comprises a BiFe03 layer having a thickness of 1 nm or less.

15. A method of programming the magnetic memory device 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 a magnitude greater than the coercive voltage, followed by a third voltage having the first polarity and a magnitude less than the coercive voltage.

16. The method of claim 15, 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 the first positive voltage has a magnitude sufficient to reduce a perpendicular magnetic anisotropy at an interface between the tunnel barrier layer and the free layer to allow the free layer to deterministically switch its magnetization direction to be parallel to the magnetization direction of the reference layer.

17. The method of claim 16, wherein: the second voltage comprises a negative voltage that deterministically programs the magnetization direction of the magnetoelectric multiferroic layer to be anti-parallel 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 is unable to switch its magnetization direction; the third voltage comprises a second positive voltage, a magnitude of the second positive voltage being insufficient to switch the magnetization direction of the magnetoelectric multiferroic layer; and a 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 deterministically switch its magnetization direction antiparallel to the magnetization direction of the reference layer.

18. The method of claim 17, wherein: a magnitude of the first positive voltage pulse is between 0.5 V and 2 V; a magnitude of the negative voltage pulse is between -0.5 V and -2 V; and a magnitude of the second positive voltage pulse is between 0.3 V and 1 V, and its absolute value is less than that of the negative voltage pulse.

19. The method of claim 17, wherein: the magnetization direction of the free layer is coupled to the magnetization direction of the magnetoelectric multiferroic layer; the magnetic memory device is deterministically programmed to a lower resistance state by the first programming voltage pattern; and the magnetic memory device is deterministically programmed to a higher resistance state by the second programming voltage pattern.

20. A magnetic memory device, the magnetic memory device comprising: a first electrode; a second electrode; and a layer stack between the first electrode and the second electrode and comprising, 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, wherein the VCMA assist structure comprises a magnetoelectric multiferroic layer comprising at least one grain having an easy axis 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 non-zero; and wherein the magnetic memory device further comprises a sensing circuit configured to determine a tunneling magnetoresistance of the layer stack between the first electrode and the second electrode; and wherein the magnetic memory device further comprises a programming circuit connected to the first electrode and the second electrode and configured to non-deterministically program the magnetic memory device using non-deterministic VCMA programming.

21. The magnetic memory device of claim 20, wherein the magnetoelectric multiferroic layer has a net ferroelectric polarization parallel to the interface between the free layer and the tunnel barrier layer.

22. The magnetic memory device of claim 20, wherein the magnetoelectric multiferroic layer is polycrystalline, wherein a respective magnetization direction of a volume-dominant grain subpopulation within the magnetoelectric multiferroic layer is aligned with or at an angle of less than 145 degrees from a direction of the net in-plane magnetization of the magnetoelectric multiferroic layer.

23. The magnetic memory device of claim 22, wherein the net in-plane magnetization of the magnetoelectric multiferroic layer is parallel or antiparallel to the direction of the net in-plane magnetization of the magnetoelectric multiferroic layer.

24. The magnetic memory device of claim 20, wherein the magnetoelectric multiferroic layer comprises a material selected from the group consisting of BiFe03, h-YMn03, BaNiF4, PbVO3, BiMn03, LuFe204, HoMn205, h-HoMn03, h-ScMn03, h-ErMn03, h-TmMn03, h-YbMn03, h-LuMn03, K2Se04, Cs2Cdl4, TbMn03, Ni3V208, MnWO4, CuO, ZnCr2Se4, LiCu202, and Ni3B70 13 I.

25. The magnetic memory device of claim 24, wherein the magnetoelectric multiferroic layer comprises a BiFe03 layer having a (111) preferred grain orientation and a thickness of 1 nm or less.

26. The magnetic memory device of claim 20, wherein the layer stack further comprises a non-magnetic capping layer comprising a non-magnetic metal in contact with the magnetoelectric multiferroic layer and one of the electrode and the second electrode.

27. The magnetic memory device of claim 20, wherein the layer stack further comprises a SAF structure in contact with the reference layer.

28. The magnetic memory device of claim 20, wherein the tunnel barrier layer comprises a dielectric layer having a thickness of 1 nm to 2 nm.

29. The magnetic memory device of claim 20, wherein the programming circuit is configured to: determine 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 apply a programming voltage pulse that induces a 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 in a case where the magnetic memory device is not in the target state, and not apply any programming voltage pulse in a case where the magnetic memory device is in the target state.

30. The magnetic memory device of claim 29, wherein the in-plane magnetization of the VCMA assist structure induces a precession of the angle between the magnetization direction of the free layer and the axial direction between 0 degrees and 180 degrees when the programming voltage pulse is applied without an external magnetic field.

31. A method of operating the magnetic memory device of claim 20, comprising determining a tunneling magnetoresistance of the layer stack.

32. The method of claim 31, further comprising non-deterministically programming the magnetic memory device by applying a VCMA programming voltage pulse between the first electrode and the second electrode without an external magnetic field.

33. The method of claim 32, further comprising: 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 the VCMA programming voltage pulse that induces a 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 in a case where the magnetic memory device is not in the target state, and not applying any programming voltage pulse in a case where the magnetic memory device is in the target state.

34. The method of claim 33, 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 the end of the programming voltage pulse. ​ ​ ​ ​ ​

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