Magnetic devices including multiferroic regions and methods of forming the same

Abstract

A magnetic device includes a first electrode, a second electrode, a plurality of magnetic junctions each including a ferromagnetic reference layer and a ferromagnetic free layer located between the first electrode and the second electrode, and a plurality of magnetoelectric multiferroic portions having different structural defect densities located between the first electrode and the second electrode. Each of the plurality of magnetoelectric multiferroic portions is magnetically coupled to the ferromagnetic free layer of a respective one of the plurality of magnetic junctions.

Description

[0001] Related applications

[0002] This application claims the benefit of priority to U.S. non-provisional patent application No. 16 / 781,225, filed February 4, 2020, the entire contents of which are incorporated herein by reference. Technical Field

[0003] This disclosure relates in general to the field of magnetic (e.g., spintronic) devices, and more specifically to magnetoresistive memory devices including magnetoelectric multiferroic regions and methods for forming the same. Background Technology

[0004] Spin-transfer torque (“STT”) refers to the effect of modifying the magnetic layer orientation in a magnetic tunnel junction or spin valve by a spin-polarized current. Generally, the current is unpolarized, where electrons have random spin orientations. A spin-polarized current is a current in which electrons have a non-zero net spin due to a preferential spin orientation distribution. Spin-polarized current can be generated by passing a current through a magnetically polarized layer. When a spin-polarized current flows through the free layer of a magnetic tunnel junction or spin valve, electrons in the spin-polarized current can transfer at least some of their angular momentum to the free layer, thus generating a torque on the magnetization of the free layer. When a sufficient amount of spin-polarized current passes through the free layer, a spin-transfer torque can be employed to reverse the spin orientation in the free layer (e.g., change the magnetization). The resistance difference of the magnetic tunnel junction between different magnetization states of the free layer can be used to store data in magnetoresistive random access memory (MRAM) cells, depending on whether the magnetization of the free layer is parallel or antiparallel to the magnetization of the polarization layer (also known as the reference layer). Summary of the Invention

[0005] According to one aspect of this disclosure, a magnetic device includes a first electrode, a second electrode, a plurality of magnetic junctions located between the first electrode and the second electrode, each comprising a ferromagnetic reference layer and a ferromagnetic free layer, and a plurality of magnetoelectric multiferroic portions with different structural defect densities located between the first electrode and the second electrode. Each of the plurality of magnetoelectric multiferroic portions is magnetically coupled to the ferromagnetic free layer of a corresponding one of the plurality of magnetic junctions.

[0006] According to yet another aspect of the disclosure, a method of forming a magnetic device includes forming a bottom electrode; forming a continuous magnetoelectric multiferroic layer over the bottom electrode; forming a plurality of magnetoelectric multiferroic portions in the continuous magnetoelectric multiferroic layer by structurally damaging different portions of the continuous magnetoelectric multiferroic layer with different structural defect densities; forming a plurality of magnetic junctions over or under the plurality of magnetoelectric multiferroic portions, wherein each of the magnetic junctions includes a respective reference layer and a respective free layer that contact a respective one of the magnetoelectric multiferroic portions; and forming a top electrode over the bottom electrode, the plurality of magnetoelectric multiferroic portions, and the plurality of magnetic junctions. BRIEF DESCRIPTION OF DRAWINGS

[0007] Figure 1 is a schematic diagram of a random access array of magnetic tunnel junction devices according to an embodiment of the disclosure.

[0008] Figure 2A is a vertical cross-sectional view of a first exemplary structure after forming a continuous magnetoelectric multiferroic layer according to a first embodiment of the disclosure.

[0009] Figure 2B is a vertical cross-sectional view of the first exemplary structure after forming a plurality of magnetoelectric multiferroic portions by ion bombardment according to the first embodiment of the disclosure.

[0010] Figure 2C is a vertical cross-sectional view of the first exemplary structure after forming a magnetic tunnel junction according to the first embodiment of the disclosure.

[0011] Figure 2D is a vertical cross-sectional view of the first exemplary structure after dividing the magnetic tunnel junction into a plurality of magnetic tunnel junctions and after forming a top electrode according to the first embodiment of the disclosure.

[0012] Figure 2E and Figure 2F is a vertical cross-sectional view of an alternative configuration of the first exemplary structure according to the first embodiment of the disclosure.

[0013] Figure 3A is a vertical cross-sectional view of a second exemplary structure after forming a continuous magnetoelectric multiferroic layer according to a second embodiment of the disclosure.

[0014] Figure 3B is a vertical cross-sectional view of the second exemplary structure after forming a plurality of magnetoelectric multiferroic portions by ion bombardment according to the second embodiment of the disclosure.

[0015] Figure 3C is a vertical cross-sectional view of the second exemplary structure after forming a magnetic tunnel junction and a top electrode according to the second embodiment of the disclosure.

[0016] Figure 4A is a perspective view of a unit cell of BiFe03having ferroelectric polarization and magnetic moment.

[0017] Figure 4B shows Figure 4A the relative spatial orientation between the ferroelectric polarization and the magnetic moment direction of a unit cell of BiFe03.

[0018] Figure 5 is a plot of the magnetoresistance of a magnetic tunnel junction device of Figure 2D according to embodiments of the disclosure as a function of applied electric field.

[0019] Figure 6 is an interconnected network of magnetic tunnel junction devices of the disclosure connected in a synapse connection configuration according to embodiments of the disclosure. DETAILED DESCRIPTION

[0020] As discussed above, embodiments of the disclosure relate to magnetic devices including multi-state magnetic junctions employing magnetoelectric multiferroic regions and methods of forming the same, various aspects of which are described in detail below. Particular embodiments of the disclosure provide various spintronic devices having three or more magnetoresistance states that are different from one another.

[0021] The drawings are not to scale. Where multiple instances of an element are shown in a single instance of the drawing, multiple instances of the element can be repeated unless explicitly described or otherwise clearly indicated otherwise. Numerical designations such as “first,” “second,” and “third” are merely used to identify like elements and different numerical designations can be employed throughout the specification and claims of the disclosure. The term “at least one” element means all possibilities including the possibility of a single element and the possibility of multiple elements. Like reference numbers indicate like elements or similar elements. Unless otherwise stated, elements having like reference numbers are assumed to have like composition and like function. Unless otherwise indicated, “contact” between elements means direct contact between elements providing an edge or surface shared by the elements. Two or more elements are “separated” from one another if they are not in direct contact with one another. As used herein, a first element positioned “on” a second element can be positioned on an outer side of a surface of the second element or on an inner side 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 an electrically conductive path between the first element and the second element composed of at least one electrically 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 thereof.

[0022] As used herein, a“layer” refers to a portion of material that includes a region having a thickness. A layer can extend over the entirety of an underlying or overlying structure, or can have a scope less than the scope of an underlying or overlying structure. Additionally, a layer can be a region of uniform or non-uniform thickness less than the thickness of a continuous structure. For example, a layer can be positioned between or between any pair of horizontal planes between a top surface and a bottom surface of a continuous structure. A layer can extend horizontally, vertically, and / or along a tapered surface. A substrate can be a layer, can include one or more layers therein, or can have one or more layers thereon, thereabove, and / or therebelow. As used herein, a“stack of layers” 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., having a direction in which the layer extends the most. As used herein, a“ferroelectric material” refers to any material that exhibits a spontaneous ferroelectric polarization that can be reversed by the application of an external electric field (e.g., exhibits ferroelectricity). As used herein, a“multiferroic” material refers to a material that exhibits at least two of ferromagnetic-type order (such as ferromagnetism, antiferromagnetism, or ferrimagnetism), ferroelectricity, and ferroelasticity. As used herein,“magnetoelectric multiferroicity” refers to a material that exhibits ferromagnetic-type order and ferroelectricity. Changes in total magnetization couple to changes in total ferroelectric polarization in a magnetoelectric multiferroic material, and thus, changes in the direction of the magnetic moment of the material can couple to changes in the direction of the ferroelectric polarization, and vice versa.

[0023] Figure 1 is a schematic of a random access memory device 501 of a magnetic tunnel junction device 180 according to embodiments of the present disclosure. As used herein, a“random access memory device” refers to a memory device that includes memory cells that allow random access, i.e., any selected memory cell is accessed upon a command to read the contents of the selected memory cell.

[0024] A random access memory device 501 of embodiments of the present disclosure can include an MRAM device, such as a multi-state STT-type MRAM device containing a multiferroic portion. The device 501 includes a memory array region 550 containing an array of respective magnetic devices (such as magnetic tunnel junction devices (e.g., magnetoresistive memory cells) 180) at the intersections of word lines (which can include first conductive lines 30 as shown or second conductive lines 90 in an alternative configuration) and bit lines (which can include second conductive lines 90 as shown or first conductive lines 30 in an alternative configuration). For example, the first conductive lines 30 can be electrically connected to and / or can include bottom electrodes of respective rows of the magnetic tunnel junction devices 180 in the memory array region 550, while the second conductive lines 90 can be electrically connected to and / or can include top electrodes of respective columns of the magnetic tunnel junction devices 180 in the memory array region 550.

[0025] The random access memory device 501 can also include a row decoder 560 connected to the word lines, sensing circuitry 570 (e.g., sense amplifiers and other bit line control circuitry) connected to the bit lines, a column decoder 580 connected to the bit lines, and a data buffer 590 connected to the sensing circuitry. The magnetic tunnel junction devices 180 are arranged in an array configuration forming the random access memory device 501. In one embodiment, the magnetic tunnel junction devices 180 can be arranged in a rectangular array. Thus, each of the magnetic tunnel junction devices 180 can be a two-terminal device including a respective first electrode and a respective second electrode. It should be noted that the positions and interconnections of the elements are illustrative, and the elements can be arranged in different configurations. Moreover, the magnetic tunnel junction devices 180 can be fabricated as discrete devices, i.e., individual isolated devices.

[0026] Embodiments of the present disclosure provide non-volatile memory elements based on the property that each of the magnetic tunnel junction devices 180 can be programmed to a target magnetoresistive state of at least three possible magnetoresistive states. Thus, each of the magnetic tunnel junction devices 180 can be used to store a ternary bit, a quaternary bit, a quinary bit, or a bit having six or more possible values. Moreover, the random access configuration shown in the random access memory device 501 is merely exemplary, and the magnetic tunnel junction devices 180 of embodiments of the present disclosure can be connected in different interconnection configurations.

[0027] Referring to Figure 2A A first exemplary structure for forming the magnetic tunnel junction devices 180 is shown. The first exemplary structure includes an optional insulating material layer 101 including an insulating material such as undoped silicate glass, doped silicate glass, organosilicate glass, silicon nitride, a dielectric metal oxide, or combinations thereof. In one embodiment, the insulating material layer 101 includes an insulating substrate such as a ceramic or glass substrate. In another embodiment, the insulating material layer 101 can be disposed over a semiconductor substrate (not shown) with semiconductor devices (not shown) such as field effect transistors thereon. In this case, the insulating material layer 101 can include a plurality of interconnect level dielectric material layers in which metal interconnect structures are embedded. The metal interconnect structures can provide electrical connections between the semiconductor devices and the first and second conductive lines 30, 90 formed over the insulating material layer 101. In this case, the structural elements formed over the insulating material layer 101 can be embedded within a dielectric matrix (not explicitly shown) that embeds the first and second conductive lines 30, 90.

[0028] A bottom electrode 170 can be formed in each region in which a magnetic tunnel junction device 180 is to be subsequently formed. The bottom electrode 170 can be formed as part of the first conductive line 30, or can be formed as a discrete structure on top of the first conductive line 30. The bottom electrode 170 can include at least one electrically conductive metallic material, such as an electrically conductive metallic nitride material, an elemental metal, or an intermetallic alloy. In one embodiment, the at least one electrically conductive metallic material can include a non-magnetic and non-ferroelectric metallic material, such as TiN, TaN, WN, Ti, Ta, W, Cu, or combinations thereof. The thickness of the bottom electrode 170 can be in a range from 5 nm to 100 nm, although lesser and greater thicknesses can also be employed.

[0029] At least one optional cap layer 150 can be formed over the bottom electrode 170. The at least one optional cap layer 150 is optional, and thus can or can not be employed. If employed, the at least one optional cap layer 150 can include a non-magnetic conductive cap layer and / or a dielectric cap layer. The non-magnetic conductive cap layer can include at least one non-magnetic conductive material, such as tantalum, ruthenium, tantalum nitride, copper, and / or copper nitride. For example, the non-magnetic conductive cap layer can include a single layer, or a layer stack including a first ruthenium layer, a tantalum layer, and a second ruthenium layer from one side to the other. For example, the first ruthenium layer can have a thickness in a range from 5 angstroms to 15 angstroms, the tantalum layer can have a thickness in a range from 10 angstroms to 30 angstroms, and the second ruthenium layer can have a thickness in a range from 5 angstroms to 15 angstroms. For example, the dielectric cap layer can include a magnesium oxide cap layer having a thickness in a range from 4 angstroms to 10 angstroms, although lesser and greater thicknesses can also be employed. Thus, the magnesium oxide cap layer has a negligible or much smaller resistance-area product than the tunnel barrier layer to be subsequently formed. In this case, the magnetic tunnel junction device 180 can be formed as a single tunnel junction device including only one magnetic tunnel junction. If both a non-magnetic conductive cap layer and a dielectric cap layer are employed, the dielectric cap layer can be on top of or below the non-magnetic conductive cap layer. The thickness of the at least one optional cap layer 150 can be in a range from 1 nm to 30 nm, although lesser and greater thicknesses can also be employed.

[0030] A continuous magnetoelectric multiferroic layer 148L can be formed over at least one optional cap layer 150 and / or a bottom electrode 170. The continuous magnetoelectric multiferroic layer 148L can have a uniform initial structural defect density. As discussed above, the magnetoelectric multiferroic layer exhibits both ferromagnetic-type order and ferroelectricity, and a change in total magnetization is coupled to a change in total ferroelectric polarization in the magnetoelectric multiferroic material, and thus, a change in the magnetization / magnetic moment direction of the material can be coupled to a change in the ferroelectric polarization direction, and vice versa. Accordingly, the magnetization direction of the multiferroic material can be deterministically switched (i.e., programmed) by applying a programming voltage across the material without applying an external magnetic field or a tunneling current through a magnetic tunnel junction formed over the multiferroic layer 148L. Thus, the magnetic tunnel junction device 180 can be programmed by tunable electric field control (EFCEC) coupled with exchange coupling to the magnetoelectric multiferroic material.

[0031] In one embodiment, the continuous magnetoelectric multiferroic layer 148L can be formed as a single-crystalline material or a polycrystalline material having a plurality of crystalline grains. In one embodiment, a single-crystalline material of the continuous magnetoelectric multiferroic layer 148L can have a magnetization / magnetic moment direction and a ferroelectric polarization direction. The same relative spatial orientation between the magnetization / magnetic moment direction and the ferroelectric polarization direction can be the same throughout the continuous magnetoelectric multiferroic layer 148L. In another embodiment, each grain of the continuous magnetoelectric multiferroic layer 148L can have a respective magnetization / magnetic moment direction and a respective ferroelectric polarization direction, and the relative spatial orientation between the respective magnetization / magnetic moment and the respective ferroelectric polarization direction within each grain of the continuous magnetoelectric multiferroic layer 148L is the same.

[0032] The continuous magnetoelectric multiferroic layer 148L can be deposited by chemical vapor deposition, atomic layer deposition, pulsed laser deposition, or physical vapor deposition. The thickness of the continuous magnetoelectric multiferroic layer 148L can be in a range from 1 nm to 10 nm, such as 1.5 nm to 5 nm, although lesser and greater thicknesses can also be employed. The continuous magnetoelectric multiferroic layer 148L can be formed as a continuous layer of material having the same material composition and the same thickness throughout.

[0033] In one embodiment, the continuous magnetoelectric multiferroic layer 148L includes and / or consists essentially of a multiferroic 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 13I. Preferably, the multiferroic material comprises an electrically insulating multiferroic material (such as BiFe03) having an antiferromagnetic spin arrangement and a direction of magnetic moment from spin canting.

[0034] With reference to Figure 2B , at least three multiferroic portions 148A, 148B, and 148C of the continuous magnetoelectric multiferroic layer 148L can be structurally damaged to form different structural defect densities therein. For example, an area of the continuous magnetoelectric multiferroic layer 148L corresponding to an area of the magnetic tunnel junction device 180 can be divided into multiple zones, such as a first magnetic tunnel junction zone 100A in which a first magnetic tunnel junction is subsequently formed over a first portion 148A of the layer 148L, a second magnetic tunnel junction zone 100B in which a second magnetic tunnel junction is subsequently formed over a second portion 148B of the layer 148L, and a third magnetic tunnel junction zone 100C in which a third magnetic tunnel junction is subsequently formed over a third portion 148C of the layer 148L. More than three magnetic tunnel junction zones can be formed covering more than three corresponding multiferroic portions of the layer 148L.

[0035] A local ion bombardment process, such as a scanning focused ion beam (FIB) process, can be subsequently performed to introduce different structural defect densities in the magnetoelectric multiferroic portions (148A, 148B, 148C) located in different corresponding magnetic tunnel junction zones (100A, 100B, 100C).

[0036] In one embodiment, a focused ion beam (FIB) device can be used to scan a first focused ion beam 149 over one of the portions (e.g., zones) of the multiferroic layer 148L, such as the first portion 148, along a first direction (e.g., in and / or out Figure 2B of the plane) having a first diameter at an impact point on the multiferroic layer 148L that is small enough so that only the first portion 148A is irradiated with the ion beam. For example, the diameter at the impact point can be 10 nm to 20 nm wide, and the first portion 148A can have a width in a second horizontal direction (e.g., left to right in Figure 2B ) of 10 nm to 20 nm. The width of the first portion 148A is substantially the same as the diameter of the focused ion beam at the impact point. As used herein, substantially the same width includes a width that is exactly the same as or within 10% of the diameter of the focused ion beam at the impact point.

[0037] A focused ion beam has a first ion dose, a first beam energy, and a first beam dwell time. The dwell time includes the time the beam contacts a given cell region. The beam can be scanned once or multiple times along a first horizontal direction in a first section. Therefore, the dwell time is a function of at least the beam scanning speed and the number of traversals (i.e., scans) in the section. The energy of the focused ion beam can be in the range of 1 keV to 300 keV, such as 5 keV to 50 keV, but smaller and larger ion beam energies can also be used. The dose of the focused ion beam can be 1.0 × 10⁻⁶. 12 atoms / cm 2 Up to 1.0×10 15 atoms / cm 2 Within the range, but smaller and larger doses can also be used. The atomic species of the ion beam can be any element that can be used in a focused ion beam. For example, the atomic species of ions in a focused ion beam can include helium or gallium and / or can be composed essentially of helium or gallium.

[0038] Ions impacting portion 148A of the multiferroic layer 148L cause structural damage therein. Specifically, the focused ion beam irradiation process results in at least one of the following: a first density of broken bonds in the multiferroic portion, a first density of displaced atoms in the lattice of the multiferroic portion, and / or a first density of gallium or helium atoms implanted in the multiferroic portion (i.e., implanted ion concentration).

[0039] To avoid being bound by a specific theory, it is believed that fractured joints impede the domain walls in the scanned multiferroic portion, requiring a higher applied voltage (i.e., programming voltage) to switch the polarization state of the portion. Therefore, an even higher applied voltage is needed to also switch the magnetization / magnetic moment direction of the multiferroic portion. The percentage shift in the applied voltage (e.g., coercive field) depends on the degree of structural damage in the multiferroic material of the damaged portion (i.e., the density of fractured joints).

[0040] Displaced atoms shift from their equilibrium positions to metastable positions within the lattice, effectively delaying changes in the electric dipole moment within the multiferroic material. In other words, the multiferroic layer 148L portion with displaced atoms does not lose its multiferroic properties, but the displacement of one or more atoms from their normal positions within the unit lattice structure delays the switching of the electric dipole moment's direction by requiring more energy accumulation to do so. Therefore, by increasing the magnitude of the applied voltage (e.g., a coercive field) required to switch the polarization direction of the portion (and thus the magnetization / magnetic moment direction), the hysteresis curve of the undamaged portion is modified from that of the multiferroic portion. The percentage shift in the applied voltage (e.g., the coercive field) depends on the degree of structural damage in the multiferroic material of the damaged portion (i.e., the density of displaced atoms).

[0041] Similarly, implanting helium or gallium atoms with a focused ion beam into a multiferroic portion results in the disruption of the lattice of the portion containing the helium or gallium atoms. This disruption leads to an increase in the applied voltage (e.g., a coercive field) required to switch the polarization direction (and therefore the magnetization / magnetic moment direction) of the implanted portion. The percentage shift in the applied voltage (e.g., the coercive field) depends at least in part on the concentration of implanted helium or gallium ions (i.e., the density of implanted atoms) in the multiferroic material of the damaged portion.

[0042] A second focused ion beam (not shown for clarity) is scanned over the second portion 148B of the multiferroic layer 148L. The second focused ion beam has a second beam diameter, a second ion dose, a second beam energy, and a second beam dwell time at the impact point on layer 148L.

[0043] In one embodiment, the diameter of the second focused ion beam at the impact point on layer 148L is substantially the same as the width of the second portion 148B, and it is scanned only above the second portion 148B. In this embodiment, at least one of the second ion dose, the second beam energy, and / or the second beam dwell time is less than the corresponding first ion dose, the first beam energy, and / or the first beam dwell time.

[0044] In another embodiment, the diameter of the second focused ion beam at the impact point on layer 148L is the same as that in the second horizontal direction (e.g., in the...). Figure 2B The combined width of the first portion 148A and the second portion 148B (from left to right) is substantially the same. In this embodiment, a second focused ion beam is scanned simultaneously above the first portion 148A and the second portion 148B. In this embodiment, the second ion dose, the second beam energy, and / or the second beam dwell time may be the same as the corresponding first ion dose, the second beam energy, and / or the first beam dwell time. The first portion 148A is scanned twice (i.e., by both the first and second ion beams), while the second portion 148B is scanned once (i.e., by only the second ion beam).

[0045] Of these two embodiments, the first part 148A has a higher structural defect density compared to the second part 148B. In other words, compared to the second part 148B, the first part 148A has a higher density of fracture bonds in the multiferroic layer, a higher density of displaced atoms in the lattice of the multiferroic layer, and / or a higher density of gallium or helium atoms.

[0046] The third portion of 148C remains unscanned by any focused ion beam. Therefore, the third portion of 148C has the lowest structural defect density of any portion. In other words, the third portion of 148C has a lower structural defect density than the first or second portion. Therefore, switching the polarization and magnetization directions of the third portion of 148C requires a minimum applied voltage (i.e., a programming voltage).

[0047] Although three sections (148A, 148B, 148C) and two ion beams have been described above, any number of two or more sections with different structural defect densities can be used. Furthermore, any suitable number of focused ion beams can be used to form different structural defect densities in the respective sections. Finally, while focused ion beams have been described above, any other suitable method for forming structural defects in a section can be used alternatively.

[0048] Implanted gallium or helium ions can penetrate the multiferroic layer 148L, remain within the multiferroic layer 148L, and / or be volatile (e.g., in the case of implanted helium atoms). If the various portions (148A, 148B, 148C) of the multiferroic layer 148L have the same helium or gallium concentration, they can have the same material composition; or if they have different helium or gallium concentrations, they can have different compositions. In one embodiment, the structural defect density (e.g., the density of fractured bonds, displaced atoms, and / or implanted atoms) in the various portions (148A, 148B, 148C) of the multiferroic layer 148L can be 5.0 × 10⁻⁶. 16 / cm 3 Up to 5.0×10 21 / cm 3 Within the range, such as 1.0 × 10 18 / cm 3 Up to 2.5×10 21 / cm 3 However, smaller and larger defect densities can also be used. The average displacement distance of the shifted atoms (which provide structural defects) can range from 0.01 nm to 0.1 nm, but smaller and larger average displacement distances can also be used. Due to the individual focused ion beam scanning, a distinct boundary 146 can exist between adjacent magnetoelectric multiferroic regions (148A, 148B, 148C).

[0049] Typically, multiple magnetoelectric multiferroic portions (148A, 148B, 148C) are formed in a continuous magnetoelectric multiferroic layer 148L by structurally damaging different portions of the continuous magnetoelectric multiferroic layer 148L with varying structural defect densities through ion bombardment. The magnetoelectric multiferroic portions (148A, 148B, 148C) are formed above the bottom electrode 170 and have different structural defect densities. The plurality of magnetoelectric multiferroic portions (148A, 148B, 148C) may include a minimum structural defect density magnetoelectric multiferroic portion (such as a third magnetoelectric multiferroic portion 148C) among all structural defect densities of the plurality of magnetoelectric multiferroic portions (148A, 148B, 148C), and a maximum structural defect density magnetoelectric multiferroic portion (such as a first magnetoelectric multiferroic portion 148A) among all structural defect densities of the plurality of magnetoelectric multiferroic portions (148A, 148B, 148C). In one embodiment, the maximum structural defect density may be at least five times the minimum structural defect density. For example, the minimum structural defect density may be 1.0 × 10⁻⁶. 12 / cm 3 Up to 1.0×10 18 / cm 3 Within this range, and the maximum structural defect density can reach 5.0 × 10⁻⁶. 15 / cm 3 Up to 5.0×10 21 / cm 3 Within the range. In one embodiment, the structural defect density of the magnetoelectric multiferroic portions (such as the magnetoelectric multiferroic portion within the highest defect density) of the multiple magnetoelectric multiferroic portions (148A, 148B, 148C) can be 5.0 × 10⁻⁶. 19 / cm 3 Up to 5.0×10 21 / cm 3 Within the range.

[0050] In one embodiment, multiple magnetoelectric multiferroic portions (148A, 148B, 148C) have different electrical coercivity, and for each pair of magnetoelectric multiferroic portions 148B and additional magnetoelectric multiferroic portions 148A with a higher structural defect density, the additional magnetoelectric multiferroic portion 148A has a higher electrical coercivity than the magnetoelectric multiferroic portion 148B.

[0051] refer to Figure 2C Magnetic tunnel junctions (136L, 134L, 132L) can be formed over multiple magnetoelectric multiferroic portions (148A, 148B, 148C) by sequentially depositing a free layer 136L, a tunnel blocking layer 134L, and a reference layer 132L.

[0052] The free layer 136L can be formed as a single ferromagnetic material layer or as multiple ferromagnetic material layers magnetically coupled to each other to provide the same magnetization direction overall. The thickness of the free layer 136L is less than 2 nm, and preferably less than 1.5 nm, such as 0.8 nm to 1.5 nm. For example, the free layer 136L may comprise a CoFeB layer and / or a CoFe layer.

[0053] The tunnel barrier layer 134L may include a tunnel barrier dielectric material (such as magnesium oxide). The tunnel barrier layer 134L may have a thickness in the range of 0.6 nm to 3 nm (such as 0.8 nm to 2 nm).

[0054] The reference layer 132L can be formed as a single ferromagnetic material layer or as multiple ferromagnetic material layers magnetically coupled to each other to provide the same magnetization direction overall. The reference layer 132L may comprise a Co / Ni multilayer structure or a Co / Pt multilayer structure. In one embodiment, the reference layer 132L may further comprise a thin nonmagnetic layer of tantalum or tungsten with a thickness of 0.2 nm to 0.5 nm, and a thin CoFeB layer (having a thickness in the range of 0.5 nm to 3 nm). The thickness of the reference layer 132L may be in the range of 2 nm to 5 nm.

[0055] In one embodiment, the reference layer 132L and the free layer 136L have corresponding positive uniaxial magnetic anisotropy. Positive uniaxial magnetic anisotropy is also called perpendicular magnetic anisotropy (PMA), where the minimum energy preference for static magnetization is along an axis perpendicular to the plane of the magnetic film.

[0056] The configuration of the reference layer 132L and the free layer 136L, with their respective vertical magnetic anisotropies, provides a bistable magnetization state for the free layer 136L. The bistable magnetization states include a parallel state where the free layer 136L has a fixed vertical magnetization (e.g., magnetization direction) parallel to the reference layer 132L, and an antiparallel state where the free layer 136L has a fixed vertical magnetization (e.g., magnetization direction) antiparallel to the reference layer 132L. The fractional resistance change between the parallel (P) and antiparallel (AP) alignments (i.e., orientations) of the magnetization directions of each pair of vertically adjacent portions of the free layer 136L and the reference layer 132L is called the tunnel magnetoresistance (TMR), i.e., TMR = (R... AP -R P ) / R P .

[0057] refer to Figure 2DThe stack of free layer 136L, tunnel barrier layer 134L, and reference layer 132L can be patterned, for example, by applying a photoresist layer (not shown) over reference layer 132L, by patterning the photoresist layer to form gaps between each adjacent pair of magnetic tunnel junction regions (100A, 100B, 100C), and by transferring the pattern in the photoresist layer through the stack of free layer 136L, tunnel barrier layer 134L, and reference layer 132L using an anisotropic etching process. In each region of magnetic tunnel junction device 180, the stack of free layer 136L, tunnel barrier layer 134L, and reference layer 132L is divided into multiple portions. Therefore, in each region of magnetic tunnel junction device 180, the magnetic tunnel junction formed by free layer 136L, tunnel barrier layer 134L, and reference layer 132L is divided into multiple magnetic tunnel junctions 140. For example, a plurality of magnetic tunnel junctions 140 include: a first magnetic tunnel junction 140A, which includes a first free layer 136A, a first tunnel blocking layer 134A, and a first reference layer 132a; a second magnetic tunnel junction 140B, which includes a second free layer 136B, a second tunnel blocking layer 134B, and a second reference layer 132B; and a third magnetic tunnel junction 140C, which includes a third free layer 136C, a third tunnel blocking layer 134C, and a third reference layer 132C. In this case, the plurality of magnetic tunnel junctions 140 include discrete magnetic tunnel junctions 140 that are not in direct contact with each other. A dielectric material (such as silicon oxide or aluminum oxide) may be deposited in the gaps between the plurality of magnetic tunnel junctions 140 to form a dielectric isolation wall 122 between adjacent magnetic tunnel junctions 140. The dielectric isolation wall 122 has a region overlapping with the boundary 146 between the multiferroic regions. A common top electrode 110 is formed over the magnetic tunnel junctions 140.

[0058] In an alternative embodiment, since the focused ion beam typically does not cause significant damage to the magnetic tunnel junction 140 and / or the common top electrode 110, it is possible to... Figure 2D The device shown is patterned before focused ion beam irradiation is performed. In other words, Figure 2B The focused ion beam 149 shown can reach the magnetoelectric multiferroic portion (148A, 148B, 148C) by irradiating through the magnetic tunnel junction 140 and / or through the common top electrode 110.

[0059] Typically, multiple magnetic tunnel junctions 140 can be formed above multiple magnetoelectric multiferroic portions (148A, 148B, 148C). Each magnetic tunnel junction (140A, 140B, 140C) can be formed on a corresponding one of the magnetoelectric multiferroic portions (148A, 148B, 148C) in a corresponding magnetic tunnel junction region (100A, 100B, 100C). For example, a first magnetic tunnel junction 140A can be formed on a first magnetoelectric multiferroic portion 148A in region 100A, a second magnetic tunnel junction 140B can be formed on a second multiferroic portion 148B in region 100B, and a third magnetic tunnel junction 140C can be formed on a third multiferroic portion 148C in region 100C. Each of the magnetic tunnel junctions 140 includes a corresponding reference layer (132A, 132B, or 132C), a corresponding tunnel blocking layer (134A, 134B, or 134C), and a corresponding free layer (136A, 136B, 136C), which contacts a corresponding one of the magnetoelectric multiferroic portions (148A, 148B, 148C).

[0060] In one embodiment, reference layers (132A, 132B, 132C) may be configured as components within a co-synthesized antiferromagnetic structure (SAF structure) 120. In this case, an antiferromagnetic coupling layer 114 and a fixed (or “hard”) ferromagnetic layer 112 may be formed over the reference layers (132A, 132B, 132C). The SAF structure 120 may include the ferromagnetic layer 112, the antiferromagnetic coupling layer 114, and the reference layers (132A, 132B, 132C). The antiferromagnetic coupling layer 114 has a thickness that induces strong antiferromagnetic coupling between the reference layers (132A, 132B, 132C) and the commonly fixed ferromagnetic layer 112, such that the antiferromagnetic coupling layer 114 can "lock" the antiparallel alignment of magnetization between the ferromagnetic layer 112 and the reference layers (132A, 132B, 132C), which in turn "locks" a specific (fixed) vertical direction of magnetization of the reference layers (132A, 132B, 132C). In this case, each of the reference layers (132A, 132B, 132C) can have the same magnetization direction, which can be upward or downward.

[0061] exist Figure 2EIn the alternative embodiment shown, the common SAF structure 120 can be omitted, and the reference layers (132A, 132B, 132C) can be configured as non-fixed reference layers. In this alternative embodiment, the antiferromagnetic coupling layer 114 and the ferromagnetic layer 112 are omitted (i.e., the SAF 120 is omitted). In this alternative embodiment, a common top electrode 110 is formed on the top surface of the reference layers (132A, 132B, 132C). The ferromagnetic reference layers (132A, 132B, 132C) can remain non-fixed, while the ferromagnetic free layers (136A, 136B, 136C) are fixed by magnetoelectric multiferroic portions (148A, 148B, 148C) oriented parallel or antiparallel to the ferromagnetic reference layers (132A, 132B, 132C). In other words, the application of the programming voltage fixes the magnetization direction of the ferromagnetic free layers (136A, 136B, 136C) in a parallel or antiparallel configuration relative to the magnetization direction of the ferromagnetic reference layers (132A, 132B, 132C) to achieve a low-resistance state or a high-resistance state for each pair of reference layers and free layers (e.g., 132A and 136A, 132B and 136B and / or 132C and 136C).

[0062] As described above, the common top electrode 110 can be formed on the top surface of the fixed ferromagnetic layer 112 or on top of the reference layers (132A, 132B, 132C) (if the antiferromagnetic coupling layer 114 and the ferromagnetic layer 112 of SAF 120 are omitted, such as...). Figure 2E (As shown). Typically, the common top electrode 110 may be electrically connected (e.g., electrically shorted) to each reference layer (132A, 132B, 132C) of the plurality of magnetic tunnel junctions 140. The top electrode 110 may be formed as part of a second conductive line 90, or may be formed as a discrete structure on which the second conductive line 90 is subsequently formed. The top electrode 110 may comprise at least one conductive metallic material, such as a conductive metal nitride material, an elemental metal, or an intermetallic alloy. In one embodiment, the at least one conductive metallic material may comprise a nonmagnetic and nonferroelectric metallic material, such as TiN, TaN, WN, Ti, Ta, W, Cu, or combinations thereof. The thickness of the top electrode 110 may range from 5 nm to 100 nm, but smaller and larger thicknesses are also possible. Thus, at least three individual magnetic tunnel junctions 140 of the same magnetic tunnel junction device 180 have a common top electrode and a bottom electrode.

[0063] While embodiments for forming a magnetic tunnel junction device 180 in which a magnetic tunnel junction 140 covers a magnetoelectric multiferroic portion (148A, 148B, 148C) are described herein, embodiments in which the magnetoelectric multiferroic portion (148A, 148B, 148C) covers the magnetic tunnel junction 140 are explicitly contemplated herein. In this alternative embodiment, a stack of layers is formed in reverse order from at least one optional cap layer 150 to a fixed ferromagnetic layer 112 (or, if layers 112 and 114 are omitted, reference layers 132A, 132B, and 132C) to provide a magnetic tunnel junction device 180, wherein the magnetoelectric multiferroic portion (148A, 148B, 148C) covers a free layer (136A, 136B, 136C) of the magnetic tunnel junction 140.

[0064] refer to Figure 2F Another alternative implementation of the first exemplary structure can be found from Figure 2C The first exemplary structure is derived without dividing the stack of the free layer 136L, tunnel blocking layer 134L, and reference layer 132L within the region of the magnetic tunnel junction device 180. Instead, the magnetic tunnel junction device 180 includes a monopillar structure comprising at least one optional cap layer 150, magnetoelectric multiferroic portions (148A, 148B, 148C), free layer 136L, tunnel blocking layer 134L, reference layer 132L, optional antiferromagnetic coupling layer 114, and optional fixed ferromagnetic layer 112.

[0065] The stack of the free layer 136L, tunnel barrier layer 134L, and reference layer 132L includes multiple magnetic tunnel junctions (e.g., junction regions) 140, including a first magnetic tunnel junction 140A covering a first magnetoelectric multiferroic portion 148A, a second magnetic tunnel junction 140B covering a second magnetoelectric multiferroic portion 148B, and a third magnetic tunnel junction 140C covering a third magnetoelectric multiferroic portion 148C. The multiple magnetic tunnel junctions 140 are in physical contact with each other within the same magnetic tunnel junction device 180.

[0066] refer to Figure 3A This illustrates a second exemplary structure for forming a magnetic tunnel junction device, which can be used with... Figure 2A The first exemplary structure shown is the same.

[0067] refer to Figure 3BThe multiferroic layer 148L is irradiated by a gradient-focused ion beam having at least one of a gradient ion dose, a gradient beam energy, and / or a gradient beam dwell time. In other words, focused ion beam irradiation is performed such that the ion dose, beam energy, and / or beam dwell time vary gradually or stepwise between different regions of the multiferroic layer 148L. In one embodiment, the ion dose, beam energy, and / or beam dwell time may vary monotonically from one side of the region of the magnetic tunnel junction device to the other side of the region of the magnetic tunnel junction device. As used herein, a function value increases "monotonically" with respect to a variable if, for any pair of a first value of a variable and a second value of a variable greater than the first value, the function value for the second value of the variable is always not less than the function value for the first value of the variable.

[0068] By structurally damaging different portions of the continuous magnetoelectric multiferroic layer 148L with different ion beam doses, beam energies, and / or beam dwell times, magnetoelectric multiferroic portions with different structural defect densities are formed in the continuous magnetoelectric multiferroic layer 148L. In one embodiment, focused ion beam irradiation can generate a gradient structural defect density that changes laterally from one side to the other (e.g., monotonically changing laterally) within the continuous magnetoelectric multiferroic layer 148L to form a magnetoelectric multiferroic layer 248 with a gradient defect density.

[0069] Typically, multiple magnetoelectric multiferroic portions with different structural defect densities can be formed in a continuous magnetoelectric multiferroic layer 148L by structurally damaging different portions of the layer using focused ion beam irradiation to create different structural defect densities. The multiple magnetoelectric multiferroic portions may include a minimum defect density magnetoelectric multiferroic portion and a maximum defect density magnetoelectric multiferroic portion. In one embodiment, the maximum structural defect density may be at least five times the minimum structural defect density, such as five to twenty times. The defect density may gradually (e.g., monotonically) increase from a minimum to a maximum across the multiferroic layer 248. For example, the minimum structural defect density may be 1.0 × 10⁻⁶. 12 / cm 3 Up to 1.0×10 18 / cm 3 Within this range, and the maximum structural defect density can reach 5.0 × 10⁻⁶. 19 / cm 3 Up to 5.0×10 21 / cm 3Within the range. In one embodiment, the plurality of magnetoelectric multiferroic portions may be portions within a single continuous magnetoelectric multiferroic layer (i.e., a graded defect density magnetoelectric multiferroic layer 248) having a graded structural defect density that changes laterally (e.g., monotonically) from one side to the other. In this embodiment, there are no distinct boundaries between adjacent multiferroic regions 248_i in the graded defect density magnetoelectric multiferroic layer 248.

[0070] refer to Figure 3C The free layer 136L, tunnel barrier layer 134L, and reference layer 132L may be sequentially deposited over the graded defect density magnetoelectric multiferroic layer 248. The free layer 136L is formed as a polycrystalline ferromagnetic film having grain boundaries between adjacent grain pairs. In an exemplary example, the region of the magnetic tunnel junction device may include a free layer 136L having N grains. The diameter of each grain may be from 3 nm to 10 nm, such as 5 nm to 7 nm. The grain boundaries may act as domain walls, and each grain (136_i, 1≤i≤N) within the free layer 136L acts as an independent unit of magnetization and ferroelectric polarization, and functions independently of adjacent grains of the free layer 136L. In other words, the magnetization of each grain (136_i, 1≤i≤N) may be flipped independently of the magnetization of other grains (136_i, 1≤i≤N) within the free layer 136L. Therefore, each combination of the grains of the free layer 136L (136_i, 1≤i≤N), the corresponding overlying portion of the tunnel blocking layer 134L, and the corresponding overlying portion of the reference layer 132L constitutes a magnetic tunnel junction (140_i, 1≤i≤N). Multiple magnetic tunnel junctions (140_i, 1≤i≤N) can be formed, each comprising a corresponding grain (136_i, 1≤i≤N) within the free layer 136L. For example, if a portion of the free layer 136L within a region of the magnetic tunnel junction device 180 comprises N grains, then N magnetic tunnel junctions (140_i, 1≤i≤N) can be formed. The number N can be, for example, in the range of 3 to 1,000.

[0071] Each region of the graded defect density magnetoelectric multiferroic layer 248, having regions overlapping with the overlying grains (136_i, 1≤i≤N) of the free layer 136L, is magnetically coupled to the magnetization of the overlying grains (136_i, 1≤i≤N). Therefore, each region of the graded defect density magnetoelectric multiferroic layer 248 may include N magnetoelectric multiferroic portions (248_i, 1≤i≤N). Thus, multiple stacks of magnetoelectric multiferroic portions (248_i, 1≤i≤N) and magnetic tunnel junctions (140_i, 1≤i≤N) can be formed. For example, if N grains exist within the free layer 136L in a region of the magnetic tunnel junction device 180, then N stacks of magnetoelectric multiferroic portions (248_i, 1≤i≤N) and magnetic tunnel junctions (140_i, 1≤i≤N) can be formed in the magnetic tunnel junction device 180.

[0072] Typically, multiple magnetic tunnel junctions 140 can be formed over multiple magnetoelectric multiferroic portions (248_i, 1≤i≤N). Each magnetic tunnel junction (140_i, 1≤i≤N), including a corresponding grain (136_i, 1≤i≤N) of the free layer 136L, can be formed on a corresponding one of the magnetoelectric multiferroic portions (248_i, 1≤i≤N). Each of the magnetic tunnel junctions (140_i, 1≤i≤N) includes a corresponding grain (136_i, 1≤i≤N) of the free layer 136L, an overlying portion of the tunnel blocking layer 134L, and a corresponding overlying portion of the reference layer 132L.

[0073] In a second embodiment, the reference layer 132L may be configured as a component within the synthetic antiferromagnetic (SAF) structure 120. In this case, an antiferromagnetic coupling layer 114 and a fixed (or "hard") ferromagnetic layer 112 may be formed above the reference layer 132L. In another aspect of the second embodiment, the SAF structure 120 including the antiferromagnetic coupling layer 114 and the fixed ferromagnetic layer 112 is omitted.

[0074] A top electrode 110 may be formed on the top surface of the fixed ferromagnetic layer 112 (if present) or over the reference layer 132L. Typically, the top electrode 110 may be electrically connected (e.g., electrically shorted) to each portion of the reference layer 132L of a plurality of magnetic tunnel junctions 140. The top electrode 110 may be formed as part of a second conductive line 90, or may be formed as a discrete structure on which the second conductive line 90 is subsequently formed. The top electrode 110 may comprise at least one conductive metallic material, such as a conductive metal nitride material, an elemental metal, or an intermetallic alloy. In one embodiment, the at least one conductive metallic material may comprise a nonmagnetic and nonferroelectric metallic material, such as TiN, TaN, WN, Ti, Ta, W, Cu, or combinations thereof. The thickness of the top electrode 110 may range from 5 nm to 100 nm, but smaller and larger thicknesses are also possible. The graded defect density magnetoelectric multiferroic layer 248 remains as a single continuous material layer at and after the processing steps of forming the top electrode 110.

[0075] Typically, multiple magnetic tunnel junctions 140 may be formed over multiple magnetoelectric multiferroic portions (248_i, 1≤i≤N). Each of the magnetic tunnel junctions (140_i, 1≤i≤N) includes: a corresponding reference layer (which is a portion of a reference layer 132L having regional overlap within the corresponding magnetoelectric multiferroic portion (248_i, 1≤i≤N), a corresponding tunnel blocking layer (which is a portion of a tunnel blocking layer 134L having regional overlap within the corresponding magnetoelectric multiferroic portion (248_i, 1≤i≤N), and a corresponding free layer (which is a grain having a free layer 136L overlapping with the corresponding magnetoelectric multiferroic portion (248_i, 1≤i≤N)), which contacts a corresponding one of the magnetoelectric multiferroic portions (248_i, 1≤i≤N).

[0076] While embodiments of a magnetic tunnel junction device 180 in which a magnetic tunnel junction (140_i, 1≤i≤N) covers a magnetoelectric multiferroic portion (248_i, 1≤i≤N) are described herein, embodiments in which the magnetoelectric multiferroic portion (248_i, 1≤i≤N) covers a magnetic tunnel junction (140_i, 1≤i≤N) are explicitly contemplated herein. In this case, a stack of layers from at least one optional capping layer 150 to a fixed ferromagnetic layer 112 (if present) or a reference layer 132L can be formed in reverse order to provide a magnetic tunnel junction device 180 in which the magnetoelectric multiferroic portion covers a magnetic tunnel junction.

[0077] Figure 4A The cubic unit lattice of BiFeO3 is shown, which has a ferroelectric polarization direction P along the

[111] direction and a tilted magnetic moment direction Mc in the (111) plane. Figure 4B The in-plane (100) and out-plane (001) components of the magnetic moment direction Mc in the (111) plane are shown. 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 portion. The out-plane (001) component of the tilted magnetic moment direction Mc of each multiferroic portion is magnetically coupled to the magnetization direction of the corresponding free layer via an exchange bias or coupling at its interface.

[0078] Because the relative spatial orientation between the tilted magnetic moment and the ferroelectric polarization of each magnetoelectric multiferroic portion is fixed, changing the direction of the ferroelectric polarization in any magnetoelectric multiferroic portion also changes the tilted magnetic moment direction Mc. Since the out-of-plane (001) component of the tilted magnetic moment direction Mc of each multiferroic portion is magnetically coupled to the magnetization direction of the corresponding free layer, the change in the tilted magnetic moment direction Mc of each multiferroic portion also changes the magnetization direction of the corresponding free layer (which can be an independent free layer, such as the first free layer 136A, the second free layer 136B, or the third free layer 136C, or a portion 136_i of a continuous free layer 136L) in contact with the corresponding multiferroic portion (148A, 148B, 148C, or 248_i). The change in the magnetization direction of the free layer places the free layer in a configuration parallel or antiparallel to the magnetization direction of the corresponding reference layer in the same magnetic tunnel junction. The parallel or antiparallel configuration of the free layer magnetization direction and the reference layer magnetization direction respectively places the magnetic tunnel junction in a low-resistance state or a high-resistance state.

[0079] A free layer may include a collection of discrete free layers (such as a collection of first free layer 136A, second free layer 136B, and third free layer 136C) or a collection of multiple grains (136_i, 1≤i≤N) of a free layer 136L whose magnetization direction can be independently reversed. Due to the different structural defect densities therein, the magnetization within each magnetoelectric multiferroic portion {(148A, 148B, 148C) or (248_i, 1≤i≤N)} can be independently reversed under different electrocoercivity. Generally, the ferroelectric coercivity of the magnetoelectric multiferroic portion {(148A, 148B, 148C) or (248_i, 1≤i≤N)} with a higher structural defect density is higher than that of the magnetoelectric multiferroic portion {(148A, 148B, 148C) or (248_i, 1≤i≤N)} with a lower structural defect density. Therefore, compared to the magnetoelectric multiferroic portions {(148A, 148B, 148C) or (248_i, 1≤i≤N)} with lower structural defect density, the ferroelectric polarization and corresponding tilting magnetic moment directions of the magnetoelectric multiferroic portions {(148A, 148B, 148C) or (248_i, 1≤i≤N)} with higher structural defect density are flipped (i.e. switched) under a higher applied electric field (which is generated by a higher programming voltage between the top electrode 110 and the bottom electrode 170).

[0080] Such multiple free layers with different magnetization directions result in multiple spin alignment states between the reference layer {(132A, 132B, 132C) or 132L} and the corresponding free layer {(136A, 136B, 136C) or 136_i} in the corresponding magnetic tunnel junction (140A, 140B, 140C or 140_i).

[0081] Therefore, the magnetic reluctance of the magnetic tunnel junction device 180 in various embodiments of this disclosure may have three or more values ​​of magnetic reluctance between the top electrode 110 and the bottom electrode 170. Specifically, the total number of magnetic reluctance states in the magnetic tunnel junction device 180 in various embodiments of this disclosure may be the same as the total number of magnetoelectric multiferroic portions {(148A, 148B, 148C) or (248_i, 1≤i≤N)} with different ferroelectric coercivity plus one.

[0082] Figure 5 It was shown as Figure 2D The tunnel magnetoresistance is a function of the applied electric field (i.e., the programming voltage) across the magnetoelectric multiferroic portions (148A, 148B, 148C) in an exemplary magnetic tunnel junction device. Figure 5 The curve in the figure shows the maximum electric field E that can be applied between the top electrode 110 and the bottom electrode 170. max The values ​​are standardized along the horizontal axis. Additionally, Figure 5 The curve in the graph is through Figure 2D The minimum magnetic reluctance of an exemplary magnetic tunnel junction device is normalized along the vertical axis. If in Figure 2D In an exemplary magnetic tunnel junction device with three magnetoelectric multiferroic portions (148A, 148B, 148C), four magnetoresistive states can be formed based on the applied programming voltage between the top electrode 110 and the bottom electrode 170. In the example shown, the magnetization direction of the reference layers (132A, 132B, 132C) is assumed to be downward, the spin parallel alignment between each reference layer (132A, 132B, 132C) and the underlying free layer (136A, 136B, 136C) is assumed to provide lower magnetoresistive force than antiparallel alignment, and the direction of the arrows indicates the magnetization direction of the three free layers (136A, 136B, 136C).

[0083] The application of positive and negative programming voltages can deterministically switch the magnetization direction of the free layers back and forth without the application of an external magnetic field. Different absolute values ​​(i.e., magnitudes) of the critical positive and negative programming voltages can switch the magnetization direction of one, two, or all three free layers in the device 180.

[0084] For example, the lowest absolute value of the critical positive programming voltage can switch the magnetization direction of only one free layer 136C, which is magnetically coupled to the corresponding multiferroic region 148C with the lowest structural defect density. Therefore, in Figure 5 In this process, the device switches from magnetoresistive state 1 to state 2. The intermediate absolute value of the critical positive programming voltage can switch the magnetization of the two free layers (136B, 136C), which are magnetically coupled to the corresponding multiferroic regions (148B, 148C) with intermediate and lowest structural defect densities. Therefore, in Figure 5In this process, the device switches from magnetoresistive state 2 to state 3. However, the magnetization direction of the free layer 136A, which is magnetically coupled to the corresponding multiferroic region 148A with the highest structural defect density, is not switched. The highest absolute value of the critical positive programming voltage is sufficient to switch the magnetization directions of all three free layers (136A, 136B, 136C), which are magnetically coupled to the corresponding multiferroic regions (148A, 148B, 148C). Therefore, in Figure 5 In this process, the device switches from magnetoresistive state 3 to state 4. Therefore, four magnetoresistive states can be obtained in the device 180, which contains three free layers and three multiferroic regions. The same four states can be achieved in reverse (i.e., from state 4 to state 1) using different absolute values ​​(i.e., magnitudes) of the critical negative programming voltage.

[0085] Typically, at least two magnetoelectric multiferroic portions {(148A, 148B, 148C) or (248_i, 1≤i≤N)} may be disposed within each magnetic tunnel junction device 180. The magnetic resistance between the bottom electrode 170 and the top electrode 110 may have at least three different values ​​depending on the magnetization direction of the plurality of magnetoelectric multiferroic portions in each magnetic tunnel junction device 180 of this disclosure.

[0086] refer to Figure 6 The diagram illustrates an interconnection network of magnetic tunnel junction devices 180 according to embodiments of the present disclosure. The magnetic tunnel junction devices 180 of embodiments of the present disclosure can be connected in a synaptic connection configuration. The magnetic tunnel junction devices 180 can be connected in a synaptic connection configuration in which the output nodes of one set of magnetic tunnel junction devices 180 are connected to a corresponding set of multiple input nodes of another set of magnetic tunnel junction devices 180. The average number of connections for each output node of each magnetic tunnel junction device 180 can be at least three, and can be four or more. Connections within the synaptic connection configuration can be limited to physical proximity of each magnetic tunnel junction device. For example, electrical connections can be limited to physical proximity of a second nearest neighbor magnetic tunnel junction device, a third nearest neighbor magnetic tunnel junction device, a fourth nearest neighbor ferroelectric device, or any other predetermined hierarchy. Such synaptic connection configurations can be advantageously used to provide computing devices in which multiple possibilities are calculated simultaneously, and a probabilistic answer to a given problem is provided. In such synaptic connection configurations, the conductance of each path can be increased within an increase in a corresponding control voltage. Therefore, the path that provides the maximum current under a predetermined set of control voltages (such as a set of bias voltages of a selected subset of the magnetic tunnel junction device 180) can be determined within a nanosecond time frame.

[0087] While a magnetic tunnel junction device 180 comprising a tunnel blocking layer 134 (e.g., an MgO layer) has been described above, other types of spintronic (e.g., MRAM) devices with different magnetic junctions can alternatively be formed. For example, spin valve or pseudo-spin valve giant magnetoresistive (GMR) devices can be formed instead. In spin valve devices, the tunnel blocking layer is replaced with a conductive, non-magnetic spacer layer. Spin valve devices typically include a SAF structure with a fixed reference layer. The SAF structure can be omitted in pseudo-spin valve devices, and different ferromagnetic materials with different coercivities can be used for the free layer and the reference layer. Spin valve and pseudo-spin valve devices can be formed above or below the multiferroic portion coupled to the respective free layer.

[0088] Referring to all the accompanying drawings and according to various embodiments of this disclosure, the magnetic device 180 includes a first electrode 170, a second electrode 110, a plurality of magnetic junctions 140 located between the first and second electrodes, each comprising a ferromagnetic reference layer 132 and a ferromagnetic free layer 136, and a plurality of magnetoelectric multiferroic portions {(148A, 148B, 148C) or (248_i)} with different structural defect densities located between the first and second electrodes. Each of the plurality of magnetoelectric multiferroic portions is magnetically coupled to the ferromagnetic free layer 136 of a corresponding one of the plurality of magnetic junctions 140.

[0089] In one embodiment, the plurality of magnetic junctions 140 include a plurality of magnetic tunnel junctions {(140A, 140B, 140C) or (140_i, 1≤i≤N)}, each including a corresponding reference layer (a portion of 132A, 132B, 132C, or 132L), a corresponding tunnel blocking layer (a portion of 134A, 134B, 134C, or 134L), and a corresponding ferromagnetic free layer (a portion of 136A, 136B, 136C, or 136L).

[0090] In one embodiment, the plurality of magnetoelectric multiferroic portions {(148A, 148B, 148C) or (248_i)} comprise materials selected from and / or are substantially composed of 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, or Ni3B7O 13 I.

[0091] In one embodiment, each of the plurality of magnetoelectric multiferroic portions {(148A, 148B, 148C) or (248_i)} has a corresponding tilted magnetic moment direction Mc and a corresponding ferroelectric polarization direction P. The relative spatial orientation between the corresponding tilted magnetic moment direction and the corresponding ferroelectric polarization direction within each magnetoelectric multiferroic portion is the same. Each magnetoelectric multiferroic portion {(148A, 148B, 148C) or (248_i)} contacts a corresponding ferromagnetic free layer (a portion of 136A, 136B, 136C, or 136L) and has a corresponding out-plane (e.g., (001)) component of the tilted magnetic moment magnetically coupled to the corresponding free layer via exchange coupling or bias.

[0092] In one embodiment, the magnetoresistance between the first electrode 170 and the second electrode 110 has at least three different values, which depend on the respective tilted magnetic moment direction Mc of the plurality of magnetoelectric multiferroic portions and the magnetization direction of the respective magnetically coupled free layers relative to the magnetization direction of the reference layer in the same magnetic junction.

[0093] In one embodiment, the first electrode 170 includes a bottom electrode, the second electrode 110 includes a top electrode located above the bottom electrode, and a plurality of magnetic junctions 140 are located above or below a plurality of magnetoelectric multiferroic portions.

[0094] In one embodiment, different structural defect densities may include different densities of fractured joints in different magnetoelectric multiferroic regions, different densities of displaced atoms in the lattice of different magnetoelectric multiferroic regions, and / or different densities of gallium or helium atoms in different magnetoelectric multiferroic regions.

[0095] In one embodiment, the plurality of magnetoelectric multiferroic portions include a first magnetoelectric multiferroic portion 148A having a first structural defect density and a first ferroelectric coercivity, and a second magnetoelectric multiferroic portion 148B having a second structural defect density higher than the first structural defect density and a second ferroelectric coercivity higher than the first ferroelectric coercivity.

[0096] exist Figure 2D , Figure 2E and Figure 2F In the first embodiment shown, the plurality of magnetic junctions 140 include discrete magnetic tunnel junctions (140A, 140B, 140C) that are not in direct contact with each other, and the plurality of magnetoelectric multiferroic portions (148A, 148B, 148C) are separated by a distinct boundary 146.

[0097] exist Figure 3CIn the second embodiment shown, the plurality of magnetoelectric multiferroic portions 248_i lack distinct boundaries within a single continuous magnetoelectric multiferroic layer 248 and have a graded structural defect density that monotonically changes laterally from one side to the other, and the plurality of magnetic junctions 140_i include a continuous polycrystalline ferromagnetic free layer 136L having a plurality of grains separated by domain wall grain boundaries.

[0098] Various embodiments of this disclosure provide a magnetic junction device 180 comprising three or more magnetoresistive states. The magnetic junction device 180 may be configured as a single, independent device. Alternatively, multiple magnetic junction devices 180 may be arranged in an array configuration or a synaptic connection configuration to provide a random access memory (e.g., magnetoresistive memory) device or a synaptic computing device.

[0099] According to one embodiment, a method for forming a plurality of magnetoelectric multiferroic portions in a continuous magnetoelectric multiferroic layer includes structurally damaging different portions of the continuous magnetoelectric multiferroic layer with different structural defect densities. In one embodiment, structurally damaging different portions of the continuous magnetoelectric multiferroic layer includes performing different focused ion beam irradiation processes in each of the plurality of magnetoelectric multiferroic portions to provide different structural defect densities in each of the plurality of magnetoelectric multiferroic portions. Different focused ion beam irradiation processes can result in at least one of the following: different densities of fractured junctions in the different magnetoelectric multiferroic portions, different densities of displaced atoms in the lattice of the different magnetoelectric multiferroic portions, or different densities of gallium or helium atoms in the different magnetoelectric multiferroic portions. In a first embodiment, the method includes forming discrete magnetic tunnel junctions that are not in direct contact with each other, formed above or below magnetoelectric multiferroic portions separated by clearly defined boundaries. In a second embodiment, focused ion beam irradiation generates a monotonically laterally varying structural defect density within the continuous magnetoelectric multiferroic layer from one side to the other. A continuous magnetic tunnel junction stack is formed above a continuous magnetoelectric multiferroic layer, wherein different regions of the continuous magnetic tunnel junction stack include multiple magnetic junctions.

[0100] 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 device, comprising: First electrode; Second electrode; Multiple magnetic junctions, each of which includes a ferromagnetic reference layer and a ferromagnetic free layer and is located between the first electrode and the second electrode; Multiple magnetoelectric multiferroic portions, each having a different structural defect density and located between the first and second electrodes, wherein each of the multiple magnetoelectric multiferroic portions is magnetically coupled to the ferromagnetic free layer of a corresponding one of the multiple magnetic junctions; and It also includes at least one of the following features: (1) First feature, in which: Different structural defect densities include varying densities of fracture joints in different magnetoelectric multiferroic regions; or (2) Second feature, in which: Different structural defect densities include different densities of displaced atoms in the lattice of the different magnetoelectric multiferroic regions; or (3) The third feature, in which: Different structural defect densities include different densities of gallium or helium atoms in the different magnetoelectric multiferroic portions; or (4) The fourth feature, in which: The plurality of magnetoelectric multiferroic components include: The first magnetoelectric multiferroic portion has a first structural defect density and a first ferroelectric coercivity. and The second magnetoelectric multiferroic portion has a second structural defect density higher than the first structural defect density, and a second ferroelectric coercivity higher than the first ferroelectric coercivity; or (5) The fifth feature, in which: The plurality of magnetoelectric multiferroic portions include portions without distinct boundaries within a single continuous magnetoelectric multiferroic layer having a graded structural defect density that monotonically changes laterally from one side to the other; and The plurality of magnetic junctions comprise a continuous polycrystalline ferromagnetic free layer having a plurality of grains separated by domain wall grain boundaries.

2. The magnetic device of claim 1, wherein the magnetic device includes a magnetoresistive memory device, and the plurality of magnetic junctions include a plurality of magnetic tunnel junctions, each of the plurality of magnetic tunnel junctions including a tunnel blocking layer.

3. The magnetic device according to claim 2, wherein the plurality of magnetoelectric multiferroic portions comprise materials selected from 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.

4. The magnetic device according to claim 3, wherein the plurality of magnetoelectric multiferroic portions comprise BiFeO3.

5. The magnetic device according to claim 1, wherein: The first electrode includes a bottom electrode; The second electrode includes a top electrode located above the bottom electrode; and The plurality of magnetic junctions are located above or below the plurality of magnetoelectric multiferroic portions.

6. The magnetic device according to claim 1, wherein the at least one feature includes the first feature.

7. The magnetic device according to claim 1, wherein the at least one feature includes the second feature.

8. The magnetic device according to claim 1, wherein the at least one feature includes the third feature.

9. The magnetic device according to claim 1, wherein the at least one feature includes the fourth feature.

10. The magnetic device of claim 1, wherein the plurality of magnetic junctions comprises discrete magnetic tunnel junctions that are not in direct contact with each other, and wherein the plurality of magnetoelectric multiferroic portions are separated by distinct boundaries.

11. The magnetic device according to claim 1, wherein the at least one feature includes the fifth feature.

12. A magnetic device, comprising: First electrode; Second electrode; Multiple magnetic junctions, each of which includes a ferromagnetic reference layer and a ferromagnetic free layer and is located between the first electrode and the second electrode; Multiple magnetoelectric multiferroic portions, the multiple magnetoelectric multiferroic portions having different structural defect densities and located between the first electrode and the second electrode, wherein each of the multiple magnetoelectric multiferroic portions is magnetically coupled to the ferromagnetic free layer of a corresponding one of the multiple magnetic junctions. in: Each of the plurality of magnetoelectric multiferroic components has a corresponding tilted magnetic moment direction and a corresponding ferroelectric polarization direction; and The relative spatial orientation between the corresponding tilted magnetic moment direction and the corresponding ferroelectric polarization direction within each magnetoelectric multiferroic portion is the same.

13. The magnetic device of claim 12, wherein each magnetoelectric multiferroic portion contacts a corresponding ferromagnetic free layer and has a corresponding out-of-plane component of the tilted magnetic moment direction magnetically coupled to the corresponding ferromagnetic free layer via exchange coupling or bias.

14. The magnetic device of claim 13, wherein the magnetic resistance between the first electrode and the second electrode has at least three different values, the at least three different values ​​depending on the respective tilting magnetic moment direction of the plurality of magnetoelectric multiferroic portions and the magnetization direction of the respective magnetically coupled free layer relative to the magnetization direction of the reference layer in the same magnetic junction.

15. An interconnection network of magnetic devices connected in a synaptic connection configuration, wherein the magnetic devices include: First electrode; Second electrode; Multiple magnetic junctions, each of which includes a ferromagnetic reference layer and a ferromagnetic free layer and is located between the first electrode and the second electrode; and Multiple magnetoelectric multiferroic portions, having different structural defect densities and located between the first electrode and the second electrode, wherein each of the multiple magnetoelectric multiferroic portions is magnetically coupled to the ferromagnetic free layer of a corresponding one of the multiple magnetic junctions.

16. A method of forming a magnetic device, comprising: Form the bottom electrode; A continuous magnetoelectric multiferroic layer is formed above the bottom electrode; By structurally damaging different portions of the continuous magnetoelectric multiferroic layer with different structural defect densities, multiple magnetoelectric multiferroic portions are formed in the continuous magnetoelectric multiferroic layer. Multiple magnetic junctions are formed above or below the plurality of magnetoelectric multiferroic portions, each of the magnetic junctions including a corresponding reference layer and a corresponding free layer contacting a corresponding one of the magnetoelectric multiferroic portions; and A top electrode is formed above the bottom electrode, the plurality of magnetoelectric multiferroic portions, and the plurality of magnetic junctions.

17. The method of claim 16, wherein structurally damaging different portions of the continuous magnetoelectric multiferroic layer comprises performing different focused ion beam irradiation processes in each of the plurality of magnetoelectric multiferroic portions to provide the different structural defect densities in each of the plurality of magnetoelectric multiferroic portions.

18. The method of claim 17, wherein: The different focused ion beam irradiation processes result in at least one of the following: different densities of fractured bonds in different magnetoelectric multiferroic regions, different densities of displaced atoms in the lattice of the different magnetoelectric multiferroic regions, or different densities of gallium or helium atoms in the different magnetoelectric multiferroic regions. and The different focused ion beam irradiation processes are performed on the different exposed magnetoelectric multiferroic portions or by the plurality of magnetic junctions covering the different magnetoelectric multiferroic portions.

19. The method of claim 18, wherein forming the plurality of magnetic junctions comprises forming discrete magnetic tunnel junctions that are not in direct contact with each other, and wherein the plurality of magnetoelectric multiferroic portions are separated by distinct boundaries.

20. The method of claim 18, wherein: The focused ion beam irradiation generates a monotonically transversely varying structural defect density from one side to the other within the continuous magnetoelectric multiferroic layer without a clear boundary. and Forming the plurality of magnetic junctions includes forming a continuous magnetic tunnel junction stack over the continuous magnetoelectric multiferroic layer, wherein different regions of the continuous magnetic tunnel junction stack include a plurality of magnetic junctions.

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