Magnetically-controlled pixels and related methods for spatial light modulation and memory applications

Abstract

Lateral crystal-differentiated and functional-differentiated structures can be grown in a single epitaxial growth step. Such structures can be used to form integrated magnetically- controlled pixels. The pixels can be implemented as magnetooptic pixels for a spatial light modulator. A controlling magnetic flux can be supplied to active elements in each magnetically-controlled pixel by a magnetic conduit comprising a high-permeability material. Several different magnetically-controlled, integrated-circuit devices are possible.

Description

Magnetically-Controlled Pixels and Related Methods for Spatial Light Modulation and Memory ApplicationsCROSS-REFERENCE TO RELATED APPLICATIONS

[0001] This application claims a priority benefit, under 35 U.S.C. § 119(e), of U.S. Application No. 63 / 594,649, filed on October 31, 2023 titled, “Magnetically-Controlled Pixels and Related Methods for Spatial Light Modulation and Memory Applications,” which application is incorporated herein by reference in its entirety.BACKGROUND

[0002] A pixel in an integrated-circuit (IC) device, such as a memory cell or spatial light modulator (SLM), is typically controlled by applying a voltage or current to an active element in the pixel. The voltage or current can directly change a characteristic of the active element. For example, an applied voltage can change the orientation of liquid crystal molecules in the pixel of a liquid-crystal display (LCD).SUMMARY

[0003] The described implementations relate to integrated devices that include a layer (such as an epitaxial layer) having lateral crystal-differentiated and lateral function-differentiated regions of material that have the same chemical stoichiometry. The functional difference pertains to magnetic, magnetoelectric, piezoelectric, ferroelectric, or magnetooptic functionalities. According to some implementations, the layer and its differentiated regions can be grown in a single epitaxial growth step. One application of the layer is for a spatial light modulator (SLM) in which pixels of the SLM comprise magnetooptic elements formed in the epitaxial layer. The magnetooptic elements can be magnetically controlled. Although the SLM is described in detail, other integrated-circuit devices that operate differently (e.g., using magnetoelectric or piezoelectric properties) can be fabricated.

[0004] Some implementations relate to a magnetically-controlled pixel comprising: a substrate; an active element of the magnetically-controlled pixel, wherein the active element is disposed in, on, or adjacent to a first surface of the substrate; and a backend layer disposed on or adjacent to the first surface of the substrate, the backend layer comprising a magnetic conduit made of high-permeability material extending from a first surface of the backendlayer to a second surface of the backend layer to inject a magnetic flux from the magnetic conduit into the active element of the magnetically-controlled pixel to control the active element.

[0005] Some implementations relate to an integrated device comprising: a layer comprising a lateral crystal-differentiated and lateral function-differentiated structure, wherein the lateral crystal -differentiated and lateral function-differentiated structure comprises: a first region of the layer comprising a first material in a crystal form having a chemical stoichiometry to perform a first function during operation of the integrated device; and a second region of the layer comprising a second material that is not in the crystal form of the first material but has a same chemical stoichiometry, wherein the second region performs a second function different from the first function during operation of the integrated device.

[0006] Some implementations relate to a method of making an integrated device, the method comprising: growing, in a single growth step, an epitaxial layer comprising a lateral crystal- differentiated and lateral function-differentiated structure, wherein the lateral crystal- differentiated and lateral function-differentiated structure comprises: a first epitaxial region of the epitaxial layer comprising a first material in a crystal form having a chemical stoichiometry to perform a first function during operation of the integrated device; and a second epitaxial region of the epitaxial layer comprising a second material that is not in the crystal form of the first material but has a same chemical stoichiometry, wherein the second epitaxial region performs a second function different from the first function during operation of the integrated device.

[0007] Some implementations relate to a method of making a magnetically-controlled pixel, the method comprising: forming an active element of the magnetically-controlled pixel in, on, or adjacent to a first surface of a substrate; forming a backend layer on or adjacent to the first surface of the substrate; and forming a magnetic conduit from a first surface of the backend layer to a second surface of the backend layer, wherein the magnetic conduit is arranged to inject magnetic flux from the magnetic conduit into the active element of the magnetically-controlled pixel to control the active element.

[0008] Some implementations relate to a method of magnetically controlling an active element of a magnetically-controlled pixel, the method comprising: driving a magnetic flux through a magnetic conduit that extends from a first surface of a backend layer through the backend layer to a second surface of the backend layer; injecting at least a portion of themagnetic flux from the magnetic conduit into the active element, wherein the active element is disposed on or adjacent to the backend layer; and changing a characteristic of the active element with at least the portion of the magnetic flux from the magnetic conduit.

[0009] All combinations of the foregoing concepts and additional concepts discussed in greater detail below (provided such concepts are not mutually inconsistent) are contemplated as being part of the inventive subject matter disclosed herein. In particular, all combinations of claimed subject matter appearing at the end of this disclosure are contemplated as being part of the inventive subject matter disclosed herein. The terminology explicitly employed herein that also may appear in any disclosure incorporated by reference should be accorded a meaning most consistent with the particular concepts disclosed herein.BRIEF DESCRIPTION OF THE DRAWINGS

[0010] The skilled artisan will understand that the drawings primarily are for illustrative purposes and are not intended to limit the scope of the inventive subject matter described herein. The drawings are not necessarily to scale; in some instances, various aspects of the inventive subject matter disclosed herein may be shown exaggerated or enlarged in the drawings to facilitate an understanding of different features. In the drawings, like reference characters generally refer to like features (e.g., functionally similar and / or structurally similar components).

[0011] FIG. 1 depicts Faraday rotation.

[0012] FIG. 2A depicts an example of a spatial light modulator (SLM) that includes magnetooptic pixels.

[0013] FIG. 2B depicts the magnetooptic SLM of FIG. 2A mounted on a printed circuit board.

[0014] FIG. 3 depicts further details of the backend layer of the SLM of FIG. 2A. The backend layer includes a plurality of magnetic conduits arranged to inject magnetic flux into each active element of the magnetooptic pixels.

[0015] FIG. 4A illustrates structures associated with a microfabrication process to form active elements in the magnetooptic pixels of the SLM of FIG. 2A.

[0016] FIG. 4B depicts further details of a crystal-differentiated and functional-differentiated structure formed according to the process of FIG. 4A.

[0017] FIG. 4C depicts a crystal-differentiated and functional-differentiated structure formed according to another microfabrication process.

[0018] FIG. 5 is a scanning electron microscope (SEM) image of magnetooptic pixels formed using the process described in connection with FIG. 4A.

[0019] FIG. 6A illustrates surface reflection from a GGG substrate used in the SLM of FIG. 2A.

[0020] FIG. 6B illustrates cancellation of the surface reflection of FIG. 6A using a singlelayer antireflection coating.

[0021] FIG. 7A, FIG. 7B, FIG. 7C, FIG. 7D, FIG. 7E, and FIG. 7F depict structures associated with a process to form magnetic conduits in the backend layer, as in the SLM of FIG. 2A

[0022] FIG. 8 depicts structure for magnetic recording media.

[0023] FIG. 9 depicts structure for a magnetoelectric device.

[0024] FIG. 10 depicts structure for a spin-wave device.DETAILED DESCRIPTION

[0025] Described herein are integrated circuit (IC) devices, some of which comprise pixels, that include active elements controlled by injected magnetic flux. In some implementations, the magnetic flux can be injected into the pixel’s active element using a magnetic conduit that runs to the active element through a backend layer of the pixel. The injected magnetic flux can change a characteristic and / or property of the active element in the pixel. For an example optical application of a spatial light modulator (SLM), each pixel in an array of magnetooptic pixels can comprise magnetooptic material as an active element of the pixel. The injected magnetic flux at each pixel can change the birefringence (an optical property) of the pixel’s magnetooptic material. This change in birefringence can be used to change the amplitude and / or phase of light passing through the pixel or can be used to rotate the polarization of the light according to Faraday rotation (FR).

[0026] For an example memory application, each pixel in an array of magnetic pixels can comprise a magnetizable material as the active element in the pixel. The injected magnetic flux at each pixel can change the orientation and / or amplitude of the magnetization at each pixel to encode or erase a data bit in the magnetizable material.

[0027] Although the following description is mainly directed to a magnetooptic application relating to SLMs, magnetically-controlled pixels as described herein can be used in other applications such as magnetic memory and magnetoelectric devices.

[0028] An example device described herein is an SLM that is based on magnetooptic material disposed at each pixel of the SLM. The magnetooptic material can provide phase shifting and / or amplitude modulation of light at each pixel of the SLM. In some applications, the SLM can comprise an array of the magnetooptic pixels that is used to encode and process information in optical signals for a neural network. The amount of phase shift at a pixel in the array can represent the computational ‘weight’ for each pixel in the neural network. Preferably, the device has low optical loss (e.g., no greater than 5 dB), provides high-speed reprogramming of the pixels at low power consumption (e.g., pixel switching times no longer than 1 microsecond at energies no larger than 1 picojoule per pixel), and is thin in the light propagation direction (e.g., a die that is no thicker than 1 mm). Further, each pixel can be controlled independently of other pixels in the array.

[0029] 1. Faraday Rotation (FR)

[0030] The inventors have recognized and appreciated that integrated magnetooptic devices can use the FR effect to modulate the phase and / or amplitude of light passing through magnetooptic material in the device. In such implementations, the light propagates parallel to the magnetization direction. FIG. 1 depicts rotation of the propagating light’s linear polarization according to the FR effect which occurs as light is transmitted through the magnetooptic material 110 with magnetization M. Although the magnetooptic Kerr effect (MOKE) and Cotton-Mouton (CM) effect can be used to alter the propagating light, the inventors have found that such devices would exhibit a smaller phase shift compared to the FR effect. Example magnetooptic materials that can be used for FR at visible (VIS) wavelengths and near infrared (NIR) wavelengths include, but are not limited to, partially bismuth-substituted yttrium-iron-garnet (Bi-YIG) and partially cerium-substituted yttrium- iron-gamet (Ce-YIG) which exhibit a suitable amount of FR for an injected magnetic flux.

[0031] According to the FR effect, left-handed (LH) and right-handed (RH) circular polarization components of light passing through the magnetooptic material experience different refractive indices (and therefore incur different phase shifts) due to magnetically- induced birefringence in the material. Changes in the amount of injected magnetic flux changes the amount of birefringence of the magnetooptic material. If the light incident on themagnetooptic material is linearly polarized (which is decomposable into LH and RH circular polarizations), the birefringence causes a rotation of the plane of the linear polarization as the light passes through the magnetooptic material.

[0032] Without being bound to a particular theory, the amount of rotation of the linear polarization (rotation angle P) can be determined from the expressionwhere Lis Verdet’s constant, B is the magnetic flux density, d is the optical path length, An is the difference between refractive indices against LH and RH circular-polarized light, and A is the wavelength of the light passing through the material. To create a phase shift, the rotated linearly polarized light can be resolved into components. Alternatively, circularly polarized light can be used to induce only a phase shift at each pixel.

[0033] 2. Example Spatial Light Modulator

[0034] FIG. 2A depicts an example structure for a spatial light modulator 200 (in partial exploded view) that includes magnetooptic pixels 220. The device includes a substrate 205 (formed from gadolinium gallium garnet (GGG) in this example), though other materials can be used), an array of magnetooptic pixels 220 comprising garnet active elements , a reflective layer 230 (formed from aluminum (Al) in this example), a backend layer 240 comprising magnetic conduits 210, and a complimentary metal-oxide-semiconductor (CMOS) layer 250. The magnetic conduits 210 can be used to carry and inject magnetic flux into the active elements of the magnetooptic pixels 220. The thickness of the reflective layer 230 can be from approximately or exactly 5 microns to approximately or exactly 50 microns, though it could be thinner or thicker in some implementations. The magnetooptic pixels 220 are disposed between the substrate 205 and the reflective layer 230 in the example device.

[0035] The SLM 200 can operate in reflection mode. For operation, light is incident on and passes through the substrate 205, interacts with the magnetooptic pixels 220, reflects from the reflective layer 230, interacts with the magnetooptic pixels 220 again, and exits through the substrate 205. The magnetooptic pixels 220 can be activated independently of each other to control the amount of reflected light from each pixel. FIG. 2B depicts how the SLM 200 can be mounted on a printed circuit board (PCB) 270, which could be packaged for a commercially-marketable device.

[0036] FIG. 3 depicts a perspective view of a portion of a portion of the SLM 200 of FIG. 2A (only four pixels 220 are shown in the 3D rendering of the device but an SLM 200 can have many more pixels). An enlarged plan view of the magnetooptic pixels 220 is also shown. Each pixel 220 comprises an active element 221 and at least a portion of a frame 222 surrounding the pixel.

[0037] The perspective view of FIG. 3 shows further details of the backend layer 240 that includes the magnetic conduits 210 (only one is illustrated). According to some implementations, the backend layer 240 comprises a layer of nonmagnetic material 242 (e.g., a polymer, an insulator, a dielectric material, or other non-magnetic material) in which the magnetic conduits 210 are disposed. The nonmagnetic material 242 of the backend layer 240 surrounds the magnetic conduits 210. The magnetic conduits can be formed from a high- permeability material. A high-permeability material is a magnetizable material comprising at least one of nickel (Ni), iron (Fe), cobalt (Co), a nickel-iron (Ni-Fe) alloy, a nickel-cobalt (Ni-Co) alloy, an iron-cobalt (Fe-Co) alloy, and a nickel-iron-cobalt (Ni-Fe-Co) alloy. In some cases, the relative permeability p / p0of a high-permeability material is no less than 10 (e.g., from 10 to 106or any subrange therebetween). In some cases, the relative permeability of a high-permeability material is no less than 100 (e.g., from 102to 106or any subrange therebetween). In some cases, the relative permeability of a high-permeability material is no less than 1000 (e.g., from 103to 106or any subrange therebetween). The magnetic conduits 210 can extend from a first surface 241 of the backend layer 240 to a second surface 249 of the backend layer.

[0038] The active elements of the magnetooptic pixels 220 can be located on or adjacent to the first surface 241. A first electrode 261 and a second electrode 262 can be formed adjacent to the second surface 249 of the backend layer 240. The term “adjacent” as used herein can mean in contact with or near (e.g., within 100 microns), in which case there may or may not be one or more intervening layers between the adjacent components. For example, the electrodes 261, 262 that are formed adjacent to the second surface 249 can be located directly on and in physical contact with the second surface 249 or can be formed within 2 microns of the second surface 249 such that there can be one or more intervening layers between the electrodes 261, 262 and the second surface 249.

[0039] A nanocoil 280 formed from an electrical conductor can be connected between the first electrode 261 and the second electrode 262. The nanocoil 280 can loop around at least aportion of the magnetic conduit 210. The nanocoil 280 can be formed with conductive vias and metal interconnects disposed on one or more metal levels.

[0040] When electrical current (e.g., from the CMOS layer 250) couples to the nanocoil 208 via the electrodes 261, 262 and flows through the nanocoil 280, the current can generate and drive a magnetic flux that flows through the magnetic conduit 210 to the magnetooptic pixel 220. The magnetic conduit 210 can terminate at or near (e.g., within 2 microns) of the magnetooptic pixel 220 such that magnetic flux is injected into the active element of the magnetooptic pixel 220 from the magnetic conduit 210. The injected magnetic flux can alter the birefringence of the magnetooptic active element in the pixel 220 and cause FR of light passing through the pixel. A polarizer can be located in the reflected beam path from the SLM 200 to pass, attenuate, or block reflected light from each magnetooptic pixel 220, depending on the amount of polarization rotation by each magnetooptic pixel 220.

[0041] An advantage of the structure of FIG. 3 is that the pixel electrodes 261, 262 are removed and remote from the immediate vicinity of the active elements of the magnetooptic pixels 220. For example, the active elements within the magnetooptic pixels 220 are disposed on an opposite side of the backend layer 240 than the electrodes 261, 262. By locating the electrodes 261, 262 a distance from the magnetooptic pixels 220 and their active elements, smaller pixel sizes can be achieved.

[0042] An additional advantage is that the magnetic conduits 210 can be spaced farther apart going towards the CMOS layer 250, so that the size of the first electrode 261 and second electrode 262 of the backend layer 240 can be matched in size to mating electrodes that can be commercially fabricated on the CMOS layer 250 in a CMOS foundry. The larger size of the electrodes can relax alignment tolerances between the backend layer 240 and the CMOS layer 250. The backend layer 240 can function, at least in part, as a magnetic interposer between the electrical circuitry of the CMOS layer 250 and the array of magnetooptic pixels 220. By using high permeability materials such as permalloy for the magnetic conduits 210, a large magnetic flux can be generated, driven through the magnetic conduits 210, and injected into the active elements of the SLM’s magnetooptic pixels 220 with a small amount of electrical current. These features can allow reduction of the maximum transverse dimension of each magnetooptic pixel 220 to no greater than 500 nm in some cases and reduce power consumption to no greater than 1 picojoule switching energy per pixel.

[0043] The active elements 221 of the magnetooptic pixels 220 can be separated from each other by frames 222 extending on one or more sides of each pixel. The frames 222 can comprise a material (such as perovskite) to magnetically isolate each magnetooptic pixel 220 from adjacent magnetooptic pixels 220, so that independent control of each pixels is possible.

[0044] 3. Pixel Fabrication

[0045] Magnetooptic pixels 220 can be formed from partially Ce-substituted YIG or partially Bi-substituted YIG as the active element 221 of the pixel. For some implementations, the active element 221 can be grown on a GGG substrate 205, for example. The reflective layer 230 can be disposed adjacent the active elements of the magnetooptic pixels 220 so that light incident on the active elements 221 can be reflected back through the active elements, providing a reflection mode SLM that benefits from two passes through the active elements 221, as described above. Perovskite can be grown for the frames 222 surrounding the active elements 221 at the same time as the magnetooptic material of the active elements 221 is grown, resulting in a single growth step for the two differently functioning materials. Ce- substituted YIG or Bi-substituted YIG in perovskite form are not ferromagnetic or ferrimagnetic materials, so either material in perovskite form can provide a measure of magnetic isolation for each magnetooptic pixel 220, thereby improving independent control and modulation of light by each pixel.

[0046] Perovskite can also have a similar refractive index to the magnetooptic material of the active element 221 so that light can propagate through the pixel’s active elements 221 and surrounding frames 222 filled with perovskite while maintaining better uniformity of the optical phase front across the entire magnetooptic pixel 220 (which includes a portion of the frames 222) and across the SLM array when no magnetic flux are injected into the active elements 221. For example, a plane wave incident on the whole array of magnetooptic pixels 220 (without any injected magnetic flux into the active elements) can reflect from the reflective layer 230 and emerge from the array of magnetooptic pixel 220 having a nearly planar wavefront with little or no phase variations across the wavefront.

[0047] Taking YIG as an example, the Y-Fe-0 system has a garnet structure represented by YsFesOn (YIG) and a perovskite structure represented by YFeCh (YFO). Since the constituent elements are the same for the garnet and perovskite, the refractive index will be essentially the same value for each material, as is the case with quartz (SiCh) and amorphous silicon dioxide SiCh. This similarity in refractive index can provide uniform propagation ofincident light through the active elements 221 and the surrounding frames 222 with negligible phase difference between the two materials. Published literature gives the refractive index n = 2.2 for both YIG and YFO at 1550 nm.

[0048] FIG. 4A depicts structures associated with an example process to fabricate active elements 221 for magnetooptic pixels 220. The process can include patterning a resist 410 and using a lift-off lithography process to form a patterned seed layer 420 for the perovskite frames that will surround the magnetooptic active elements 221. The seed layer material can be barium titanate (BaTiCh), strontium titanate (SrTiCh), lanthanum strontium manganite (Lai-xSrxMnCh), or strontium ruthenate (SRuCh) that is deposited on patterned resist (for a lift-off process) using a pulsed laser deposition (PLD) process. Other possible seed layers for perovskite include PbTiO3(PT), Pb(ZrTi)O3(PZT), and Pb(MgNb)TiO3(PMN-PT). The resist can be patterned by electron beam lithography (EBL) or by photolithography.

[0049] For PLD of the SrTiOs seed layer, the substrate temperature can be between 20 °C and 28 °C. The laser pulse energy can be between 250 mJ and 400 mJ, and its fluence at samples can be between 1.0 and 2.5 mJ / cm2per pulse. The chamber pressure can be between 5* 10'5millitorr and 2* 10'2millitorr, and the thickness of the deposited seed layer can be from 8 nm to 50 nm. For PLD and growth of the magnetooptic material, the substrate temperature can be between 550 °C and 650 °C. The laser pulse energy can be between 350 mJ and 550 mJ. The chamber pressure can be between 5 millitorr and 100 millitorr, and the thickness of the deposited active layer can be from 30 nm to 3000 nm.

[0050] When a Y-Fe-0 precursor target with a Y :Fe composition in the range of 3 :5 to 1 : 1 is used to grow material in contact with garnet or perovskite seed layer for epitaxial growth, the material will epitaxially grow or crystallize in a structure that matches the contact material (seed layer or underlying material). This behavior also occurs in Bi-YIG and can be used to fabricate the magnetooptic active elements 221 and non-magnetic surrounding frames 222 on garnet substrates 205 using a patterned perovskite seed layer as depicted in FIG. 4A. The magnetooptic active elements 221 and perovskite frames 222 can be grown at the same time using the PLD process, for example. After growth of the magnetooptic active elements 221 and perovskite frames 222, the structure can be planarized (e.g., using a chemical mechanical polishing step) and the reflective layer 230 deposited on the polished surface.

[0051] FIG. 4B depicts further details of a structure formed according to the process of FIG. 4A. In a single growth step, a lateral crystal-differentiated and functional -differentiatedstructure is formed. The structures comprises a first material 430 in a first region having a first crystalline form (garnet: YsFesOn in this example) and a second material 440 in a second adjacent region having a second crystalline form (perovskite: 4{(Y3 / 4Fei / 4)FeO3} in this example). The two grown materials according to such a process can have the same stoichiometry, though have different forms or phases, at least one of which is a crystalline form (garnet or YIG in this example). In some cases, one of the materials of the lateral crystal -differentiated structure can comprise an amorphous form of the material. In the example of FIG. 4B, the YsFesOn (YIG) crystal is grown on a gadolinium gallium garnet (GGG) substrate 205. The (Y3Fei)Fe40i2 (YFO) crystal is grown on a strontium titanate (STO) seed layer 420 that is patterned on the GGG substrate 205.

[0052] Material systems other than Y and Fe can be used to form lateral crystal-differentiated structures following the process of FIG. 4A and FIG. 4B. More generally, a rare earth (RE) element can be used for Y (another example being bismuth Bi). Other metals (M) can be used for iron, such as aluminum Al. A lateral crystal-differentiated structure can then comprise, for example, a first material of RE-M-0 garnet formed in a first region and a second material of RE-M-0 perovskite formed in an adjacent second region. Additionally, other crystal forms can be included, such as spinel. In some implementations, at least one of the grown materials can comprise an amorphous or polycrystalline form of the grown material that may or may not be subsequently annealed into a crystal form.

[0053] In the example of FIG. 4B, the iron garnet exhibits strong magnetoopic response (e.g., greater than 500 deg / cm) and the perovskite does not. This difference in properties yields a lateral functional-differentiated structure for the grown lateral crystal-differentiated structure. In this case, the garnet can be used for an optical modulation function while the perovskite is used to magnetically isolate the garnet active elements 221 of the magnetooptic pixels 220. Using other material systems can yield different lateral crystal-differentiated structures and different lateral functional -differentiated structures. For example, the first grown material 430 can have one of the following magnetic properties whereas the second grown material 440 does not have the magnetic property: magnetooptic, ferromagnetism, antiferromagnetism, and ferrimagnetism. Examples of materials that can exhibit or not exhibit the magnetic property are materials of a RE-Fe-0 system where RE is Bi or any rare earth element such as Y. Iron Fe can be substituted partially or fully with Al, In, Ga, or Sc to adjust the magnetic property.

[0054] In some cases, the first grown material 430 can have one of the following electrical properties whereas the second grown material 440 does not have the electrical property: ferroelectricity, piezoelectricity, and pyroelectricity. Examples of materials that can exhibit or not exhibit the electrical property are materials of a RE-Fe-0 system where RE is Bi or any rare earth element such as Y. Iron Fe can be substituted partially or fully with Al, In, Ga, or Sc to adjust the electrical property.

[0055] In some cases, the first grown material 430 can be ferroelastic whereas the second grown material 440 does not have the ferroelastic property. Examples of materials that can exhibit or not exhibit the ferroelastic property are materials of a RE-Fe-0 system where RE is Bi or any rare earth element such as Y. Iron Fe can be substituted partially or fully with Al, In, Ga, or Sc to adjust the ferroelastic property.

[0056] In some cases, the first grown material 430 can support laser oscillations (e.g., a grown yttrium aluminum garnet (YAG) laser gain medium) whereas the second grown material 440 does not support laser oscillations. Examples of materials that can support laser oscillations include YAG, YIG, YGaG, and YScG. Nd can be doped into these materials to adjust the band structure of the material.

[0057] In some cases, the first grown material 430 can optically scintillate whereas the second grown material 440 does not scintillate. Examples of materials that can scintillate include YAG, YIG, YGaG, and YScG. Any rare earth element can be doped into these materials to adjust the band structure of the material.

[0058] An alternative fabrication method involves patterning trenches to define the pixels in a uniformly thick garnet layer of the first material 430 (e.g., YsFesOn) that is grown on the substrate 205. The trenches can be formed by reactive ion etching, for example, and can be etched through the layer to form pixels in any shape (round, oval, square, rectangular, hexagonal, etc.). The trenches can then be filled with a non-magnetic material (e.g., a spin- on glass) as the second material 440 having a refractive index that may or may not essentially match the refractive index of garnet. The surface can be planarized and / or polished back to the unetched portions of the garnet surface using chemical mechanical polishing prior to depositing the aluminum reflective layer. The resulting structure is shown in FIG. 4C.

[0059] Such fabrication processes can be used to form an array of magnetizable memory pixels. Instead of depositing or etching garnet, a ferromagnetic material can be deposited oretched for the first material 430. In a memory application, the trenches may or may not be filled with the second material 440.

[0060] FIG. 5 is an SEM image of magnetooptic active elements formed on a GGG substrate following the fabrication process outlined in FIG. 4A. The magnetooptic pixels (15 shown) formed in garnet as the first material 430 have transverse dimensions of approximately 200 nm and are surrounded by perovskite as the second material 440.

[0061] As may be appreciated, an unwanted surface reflection (of more than 11% of the incident light) can occur at the air / gamet interface for each pixel of the SLM, as depicted in FIG. 6A. This surface reflection arises from the large difference in refractive index between air (na=l) and the garnet substrate 205 ( / / <;=2.0). This reflection can be significantly mitigated by an antireflection coating 610, as depicted in FIG. 6B. According to some implementations, the antireflection coating 610 can consist of a single layer of different material having a lower refractive index than the substrate 205, such as silicon dioxide (nsiO2 = 1.5). The thickness of the antireflective coating 610 can be chosen such that radiation reflecting from the air / SiCh interface cancels radiation reflecting from the SiCh / garnet interface, as illustrated in FIG. 6B. For the materials of this example SLM structure, the thickness of the SiCh is 88 nm for a 530 nm wavelength of the incident radiation 620. Different thicknesses can be used for different materials and / or incident wavelengths to reduce or essentially eliminate the unwanted surface reflection.

[0062] Referring again to FIG. 3, there are at least two processes that can be used to form the magnetic conduits 210 and nanocoils 280 in the backend layer 240. Two of these processes comprise 3D pattern formation in a material and subsequent reduction in size of the patterned features. A first process comprises volumetric deposition and controlled shrinkage of patterned scaffolds, as described in U.S. patent No. 11,214,661 issued Jan. 4, 2022, which is incorporated herein by reference in its entirety. FIG. 7A through FIG. 7F depict how this process can be adapted to form magnetic conduits 210 and nanocoils 280. A hydrogel 710 that is swollen (depicted in FIG. 7A) can be patterned with 3D structures 720 (e.g., the conduits 210 and / or nanocoils 280). The patterning can be done using two-photon laser lithography. In a later step, depicted in FIG. 7B, the hydrogel and patterned structures are shrunk to a smaller size (e.g., by exposing the swollen hydrogen to an acid or salt).

[0063] In further detail, a laser is focused to a high-intensity spot 730 in the swollen hydrogel, as depicted in FIG. 7C. The high-intensity spot 730 can be at or near thediffraction limit Di of light for the laser. The high intensity in the hydrogel causes a two- photon reaction to occur in which polymers 740 of the hydrogel scaffold crosslink and chromophores 750 added into the hydrogel matrix combine with the hydrogel scaffold. The laser spot 730 can be scanned in three dimensions to form an extended, 3D structure. In a subsequent development step, unbound chromophores 750 are washed out of the hydrogel matrix, leaving only the bound chromophores 750, as depicted in FIG. 7D. The hydrogel matrix can be exposed to a solution containing metal nanoparticles that will bind to the chromophores 750, and subsequently rinsed, leaving bound metal nanoparticles 760. The bound metal nanoparticles 760 form seed locations for subsequent growth of conductive material 770 for the conduits 210 or nanocoils 280, as depicted in FIG. 7E. Nickel and / or iron could be used for the magnetic conduits and gold or silver could be used for the nanocoils 280, though other materials may be used in addition to or instead of these materials. Finally, the structure is shrunk as described above and depicted in FIG. 7F, resulting in minimum feature sizes dmin that can be smaller than the diffraction limit Di for the light used to pattern the structure.

[0064] A second process is an additive manufacturing process as described by Andrey Vyatskikh et al. in “Additive manufacturing of 3D nano-architected metals,” Nature Communications, (2018) 9:593, which is herein incorporated by reference in its entirety. In this process, nickel acrylate and iron acrylate can be used as metal precursors in the metalcontaining photoresist to form high-permeability magnetic conduits. A 3D structure formed in the metal-containing photoresist can be reduced in size using a pyrolysis step in the process to arrive at the magnetic conduits and / or nanocoils in the backend layer.

[0065] Another process, mentioned above, is to use conventional lithography techniques for forming conductive vias and metal layer interconnects to pattern the magnetic conduits 210 and / or the nanocoils 280.

[0066] 4. Device Applications

[0067] There are a variety of devices that can be fabricated with lateral crystal-differentiated and lateral functional-differentiated structures using the processes described herein. One example structure is magnetic recording media shown in FIG. 8. The structure comprises a substrate 205 (which may be GGG, gadolinium scandium gallium garnet (GSGG), or substituted gadolinium gallium garnet (SGGG)), and memory pixels 810 (only four shown but there could be millions or more on a chip). The memory pixels 180 are formed from afirst material 430 of garnet (Bi-YsFesOn in this example) surrounded by a frame of a second material 440 (STO perovskite in this example). Both materials can be grown at the same time, as described above. As depicted in FIG. 4A, the second material 440 can be patterned using an STO seed layer to allow any desired shape of the magnetic pixels. When a rare earth element or bismuth is used for an RE-Fe-0 grown perovskite, the resulting grown perovskite can be paramagnetic or antiferromagnetic and serve as the frame for each pixel. However, the grown garnet is ferrimagnetic and is magnetizable for read / write memory. The magnetizable ferrimagnetic regions of each pixel are isolated from one another by regions of antiferromagnetic perovskite. In some implementations, each pixel can be magnetized out of the plane of the chip (generally in the z direction). In some implementations, the structure includes a template layer 808 of garnet (e.g., essentially pure YsFesOn) which serves as a template for subsequent crystal growth of the magnetizable ferrimagnetic regions. The template layer 808 may be magnetized in the plane of the chip (in the x-y plane) and provide magnetic flux paths for the pixels.

[0068] FIG. 9 illustrates how a RE-Fe-0 perovskite can be used to electrically control magnetism of RE-Fe-0 garnet. The illustration is a cross section and elevation view of the structure of FIG. 8. The RE-Fe-0 perovskite (RE is a rare earth element of bismuth) can be piezoelectric and induce strain on the ferrimagnetic RE-Fe-0 garnet in response to an applied voltage to the perovskite material, since the two regions are atomically connected at their boundaries. The applied voltage and strain can be out of the plane of the substrate (e.g., in the z direction in the drawing). The strain on the garnet region can generate a magnetoelectric effect (ME) to control the magnetism of the garnet region. This property can be used in reverse for ME energy harvesting and magnetic field sensors. The structure of FIG. 9 can be used in different magnetoelectric devices, such as low power, switchable magnetic devices, radio-frequency and high-frequency devices, magnetic field sensors, and magnetoelectric energy-harvesting devices. Such devices are described in “A review on current status and mechanisms of room temperature magnetoelectric coupling in multiferroics for device applications,” R. Gupta and R. Kotnala, J. Mater. Sci. (2022) 57: 12710- 12737, which is incorporated herein by reference in its entirety.

[0069] FIG. 10 depicts a spin-wave (SW) device 1000 that can be fabricated using lateral crystal-differentiated and lateral functional-differentiated structures described herein. The device comprises two spin-wave generators 1010 that prepare spin waves in two waveguides 1020, 1022 of a Y-branch waveguide structure. The Y-branch waveguides can comprise afirst material 430 (such as garnet). The surrounding region can comprise a second material 840 which may or may not be a perovskite. In some implementations, the second material 840 has a lower refractive index than the first material 430 so that optical waves are guided in the Y-branch waveguides.

[0070] The SW generators prepare the two optical waves in two desired polarization states which can then be combined and interfered in the single waveguide 1024 of the Y-branch. The polarization states of the prepared waves can represent 0 and 1 logic states. A detector 1040 arranged to receive light from the single waveguide can determine the resulting polarization of the combined optical waves. Such a SW device can be used for optical computing. Further details and applications of SW devices are described in “Demonstration of a robust magnonic spin wave interferometer,” N. Kanzana et al.. Scientific Reports (2016) 6:30268, and in “Static and Dynamic Magnetic Properties of Single-Crystalline Yttrium Iron Garnet Films Epitaxially Grown on Three Garnet Substrates,” T. Yoshimoto etal., Adv.Electron. Mater., (2018) 4: 1800106, and in “Three port logic gate using forward volume spin wave interference in a thin yttrium iron garnet film,” T. Goto et al., Scientific Reports (2019) 9: 16472, which publications are herein incorporated by reference in their entirety.

[0071] The SW device 1000 can operate with low power consumption since there is no Joule heating for signal transmission. There is no significant electrical load on an antenna, so the device can operate with low driving power. Further, the spin-wave frequency can be in the gigahertz frequency band. In some implementations, the Y-branch can be fabricated from garnet as the first material 430 and bonded atomically with a ferroelectric perovskite as the surrounding second material 440. Such a structure could allow voltage-driven SW devices rather than conventional current-driven SW devices.

[0072] 5. Example Implementations

[0073] The inventive apparatus and methods described above can be implemented in various ways, some of which are listed below.(1) A magnetically-controlled pixel comprising: a substrate; an active element of the magnetically-controlled pixel, wherein the active element is disposed in, on, or adjacent to a first surface of the substrate; and a backend layer disposed on or adjacent to the first surface of the substrate, the backend layer comprising a magnetic conduit comprising a high- permeability material extending from a first surface of the backend layer to a second surfaceof the backend layer to inject a magnetic flux from the magnetic conduit into the active element of the magnetically-controlled pixel to control the active element.(2) The magnetically-controlled pixel of configuration (1), wherein the active element comprises a magnetooptic material and the magnetically-controlled pixel is a magnetooptic pixel.(3) The magnetooptic pixel of configuration (1) or (2) included in a spatial light modulator.(4) The magnetically-controlled pixel of any one of configurations (1) through (3), wherein: the active element comprises a magnetizable material, and the magnetically- controlled pixel is a magnetically-controlled memory pixel.(5) The magnetically-controlled memory pixel of any one of configurations (1) through (4) included in a memory chip.(6) The magnetically-controlled pixel of any one of configurations (1) through (5), further comprising: a first electrode disposed on or adjacent to the first surface of the backend layer; a second electrode disposed on or adjacent to the first surface of the backend layer; and an electrical conductor connected between the first electrode and the second electrode, wherein the electrical conductor is arranged to drive a magnetic field through the magnetic conduit.(7) An integrated device comprising: a layer comprising a lateral crystal-differentiated and lateral functional-differentiated structure, wherein the lateral crystal-differentiated and lateral functional-differentiated structure comprises: a first region of the layer comprising a first material in a crystal form having a chemical stoichiometry to perform a first function during operation of the integrated device; and a second region of the layer comprising a second material that is not in the crystal form of the first material but has a same chemical stoichiometry, wherein the second region performs a second function different from the first function during operation of the integrated device.(8) A method of making an integrated device, the method comprising: growing, in a single growth step, an epitaxial layer comprising a lateral crystal -differentiated and lateral functional-differentiated structure, wherein the lateral crystal -differentiated and lateral functional-differentiated structure comprises: a first epitaxial region of the epitaxial layer comprising a first material in a crystal form having a chemical stoichiometry to perform afirst function during operation of the integrated device; and a second epitaxial region of the epitaxial layer comprising a second material that is not in the crystal form of the first material but has a same chemical stoichiometry, wherein the second epitaxial region performs a second function different from the first function during operation of the integrated device.(9) A method of making a magnetically-controlled pixel, the method comprising: forming an active element of the magnetically-controlled pixel in, on, or adjacent to a first surface of a substrate; forming a backend layer on or adjacent to the first surface of the substrate; and forming a magnetic conduit comprising a high-permeability material from a first surface of the backend layer to a second surface of the backend layer, wherein the magnetic conduit is arranged to inject magnetic flux from the magnetic conduit into the active element of the magnetically-controlled pixel to control the active element.(10) The method of (9), wherein forming the magnetic conduit comprises forming the magnetic conduit by an additive manufacturing process in the backend layer.(11) The method of (9), wherein forming the magnetic conduit comprises forming the magnetic conduit by volumetric deposition and controlled shrinkage of patterned scaffolds.(12) The method of any one of (9) through (11), wherein forming the active element comprises: forming a seed layer that is patterned for growth of non-magnetic material in frames around each active element in an array of active elements that includes the active element, wherein each active element in the array of active elements is separated from immediately adjacent active elements in the array of active elements by at least a portion of the frames; depositing a magnetooptic material on the substrate; and depositing the nonmagnetic material on the seed layer that is patterned for growth of the non-magnetic material.(13) A method of magnetically controlling an active element of a magnetically-controlled pixel, the method comprising: driving a magnetic flux through a magnetic conduit comprising a high-permeability material that extends from a first surface of a backend layer through the backend layer to a second surface of the backend layer; injecting at least a portion of the magnetic flux from the magnetic conduit into the active element, wherein the active element is disposed on or adjacent to the backend layer; and changing a characteristic of the active element with at least the portion of the magnetic flux from the magnetic conduit.(14) The method of (13), wherein the magnetically-controlled pixel is one pixel in an array of magnetically-controlled pixels and a maximum size of each active element of each magnetically-controlled pixel in the array of magnetically-controlled pixels is no larger than 500 microns.(15) The method of (13) or (14), wherein the magnetically-controlled pixel is one pixel in an array of magnetically-controlled pixels comprising a plurality of active elements, the method further comprising: driving a plurality of magnetic fluxes through a plurality of magnetic conduits that extends from the first surface of the backend layer through the backend layer to the second surface of the backend layer; injecting at least portions of the plurality of magnetic fluxes from the plurality of magnetic conduits into the plurality of active elements, wherein the plurality of active elements is disposed on or adjacent to the backend layer; and changing a characteristic in each active element of the plurality of active elements with at least the portions of the plurality of magnetic fluxes injected from the plurality of magnetic conduits.(16) The method of any one of (13) through (15), wherein driving the magnetic flux comprises driving an electrical current through an electrical conductor to create and drive the magnetic flux in the magnetic conduit.(17) The method of any one of (13) through (16), wherein changing the characteristic of the active element comprises changing an optical property of the active element to rotate polarization of light passing through the active element.(18) The method of any one of (13) through (17), wherein changing the characteristic of the active element comprises changing a magnetization direction of the active element.

[0074] 6. Conclusion

[0075] While various inventive embodiments have been described and illustrated herein, those of ordinary skill in the art will readily envision a variety of other means and / or structures for performing the function and / or obtaining the results and / or one or more of the advantages described herein, and each of such variations and / or modifications is deemed to be within the scope of the inventive embodiments described herein. More generally, those skilled in the art will readily appreciate that all parameters, dimensions, materials, and configurations described herein are meant to be exemplary and that the actual parameters, dimensions, materials, and / or configurations will depend upon the specific application orapplications for which the inventive teachings is / are used. Those skilled in the art will recognize or be able to ascertain, using no more than routine experimentation, many equivalents to the specific inventive embodiments described herein. It is, therefore, to be understood that the foregoing embodiments are presented by way of example only and that, within the scope of the appended claims and equivalents thereto, inventive embodiments may be practiced otherwise than as specifically described and claimed. Inventive embodiments of the present disclosure are directed to each individual feature, system, article, material, kit, and / or method described herein. In addition, any combination of two or more such features, systems, articles, materials, kits, and / or methods, if such features, systems, articles, materials, kits, and / or methods are not mutually inconsistent, is included within the inventive scope of the present disclosure.

[0076] Also, various inventive concepts may be embodied as one or more methods, of which an example has been provided. The acts performed as part of the method may be ordered in any suitable way. Accordingly, embodiments may be constructed in which acts are performed in an order different than illustrated, which may include performing some acts simultaneously, even though shown as sequential acts in illustrative embodiments.

[0077] All definitions, as defined and used herein, should be understood to control over dictionary definitions, definitions in documents incorporated by reference, and / or ordinary meanings of the defined terms.

[0078] The indefinite articles “a” and “an,” as used herein in the specification and in the claims, unless clearly indicated to the contrary, should be understood to mean “at least one.”

[0079] The phrase “and / or,” as used herein in the specification and in the claims, should be understood to mean “either or both” of the components so conjoined, i.e., components that are conjunctively present in some cases and disjunctively present in other cases. Multiple components listed with “and / or” should be construed in the same fashion, i.e., “one or more” of the components so conjoined. Other components may optionally be present other than the components specifically identified by the “and / or” clause, whether related or unrelated to those components specifically identified. Thus, as a non-limiting example, a reference to “A and / or B”, when used in conjunction with open-ended language such as “comprising” can refer, in one embodiment, to A only (optionally including components other than B); in another embodiment, to B only (optionally including components other than A); in yet another embodiment, to both A and B (optionally including other components); etc.

[0080] As used herein in the specification and in the claims, “or” should be understood to have the same meaning as “and / or” as defined above. For example, when separating items in a list, “or” or “and / or” shall be interpreted as being inclusive, i.e., the inclusion of at least one, but also including more than one, of a number or list of components, and, optionally, additional unlisted items. Only terms clearly indicated to the contrary, such as “only one of’ or “exactly one of,” or, when used in the claims, “consisting of,” will refer to the inclusion of exactly one component of a number or list of components. In general, the term “or” as used herein shall only be interpreted as indicating exclusive alternatives (i.e. “one or the other but not both”) when preceded by terms of exclusivity, such as “either,” “one of,” “only one of,” or “exactly one of.” “Consisting essentially of,” when used in the claims, shall have its ordinary meaning as used in the field of patent law.

[0081] As used herein in the specification and in the claims, the phrase “at least one,” in reference to a list of one or more components, should be understood to mean at least one component selected from any one or more of the components in the list of components, but not necessarily including at least one of each and every component specifically listed within the list of components and not excluding any combinations of components in the list of components. This definition also allows that components may optionally be present other than the components specifically identified within the list of components to which the phrase “at least one” refers, whether related or unrelated to those components specifically identified. Thus, as a non-limiting example, “at least one of A and B” (or, equivalently, “at least one of A or B,” or, equivalently “at least one of A and / or B”) can refer, in one embodiment, to at least one, optionally including more than one, A, with no B present (and optionally including components other than B); in another embodiment, to at least one, optionally including more than one, B, with no A present (and optionally including components other than A); in yet another embodiment, to at least one, optionally including more than one, A, and at least one, optionally including more than one, B (and optionally including other components); etc.

[0082] In the claims, as well as in the specification above, all transitional phrases such as “comprising,” “including,” “carrying,” “having,” “containing,” “involving,” “holding,” “composed of,” and the like are to be understood to be open-ended, i.e., to mean including but not limited to. Only the transitional phrases “consisting of’ and “consisting essentially of’ shall be closed or semi-closed transitional phrases, respectively, as set forth in the United States Patent Office Manual of Patent Examining Procedures, Section 2111.03.

Claims

CLAIMS1. A magnetically-controlled pixel comprising: a substrate; an active element of the magnetically-controlled pixel, wherein the active element is disposed in, on, or adjacent to a first surface of the substrate; and a backend layer disposed on or adjacent to the first surface of the substrate, the backend layer comprising a magnetic conduit comprising a high-permeability material extending from a first surface of the backend layer to a second surface of the backend layer to inject a magnetic flux from the magnetic conduit into the active element of the magnetically- controlled pixel to control the active element.

2. The magnetically-controlled pixel of claim 1, wherein the active element comprises a magnetooptic material and the magnetically-controlled pixel is a magnetooptic pixel.

3. The magnetooptic pixel of claim 2 included in a spatial light modulator.

4. The magnetically-controlled pixel of claim 1, wherein: the active element comprises a magnetizable material, and the magnetically-controlled pixel is a magnetically-controlled memory pixel.

5. The magnetically-controlled memory pixel of claim 4 included in a memory chip.

6. The magnetically-controlled pixel of claim 1, further comprising: a first electrode disposed on or adjacent to the first surface of the backend layer; a second electrode disposed on or adjacent to the first surface of the backend layer; and an electrical conductor connected between the first electrode and the second electrode, wherein the electrical conductor is arranged to drive a magnetic field through the magnetic conduit.

7. An integrated device comprising: a layer comprising a lateral crystal-differentiated and lateral functional-differentiated structure, wherein the lateral crystal-differentiated and lateral functional-differentiated structure comprises:a first region of the layer comprising a first material in a crystal form having a chemical stoichiometry to perform a first function during operation of the integrated device; and a second region of the layer comprising a second material that is not in the crystal form of the first material but has a same chemical stoichiometry, wherein the second region performs a second function different from the first function during operation of the integrated device.

8. A method of making an integrated device, the method comprising: growing, in a single growth step, an epitaxial layer comprising a lateral crystal- differentiated and lateral functional-differentiated structure, wherein the lateral crystal- differentiated and lateral functional-differentiated structure comprises: a first epitaxial region of the epitaxial layer comprising a first material in a crystal form having a chemical stoichiometry to perform a first function during operation of the integrated device; and a second epitaxial region of the epitaxial layer comprising a second material that is not in the crystal form of the first material but has a same chemical stoichiometry, wherein the second epitaxial region performs a second function different from the first function during operation of the integrated device.

9. A method of making a magnetically-controlled pixel, the method comprising: forming an active element of the magnetically-controlled pixel in, on, or adjacent to a first surface of a substrate; forming a backend layer on or adjacent to the first surface of the substrate; and forming a magnetic conduit comprising a high-permeability material from a first surface of the backend layer to a second surface of the backend layer, wherein the magnetic conduit is arranged to inject magnetic flux from the magnetic conduit into the active element of the magnetically-controlled pixel to control the active element.

10. The method of claim 9, wherein forming the magnetic conduit comprises: forming the magnetic conduit by an additive manufacturing process in the backend layer.

11. The method of claim 9, wherein forming the magnetic conduit comprises: forming the magnetic conduit by volumetric deposition and controlled shrinkage of patterned scaffolds.

12. The method of claim 9, wherein forming the active element comprises: forming a seed layer that is patterned for growth of non-magnetic material in frames around each active element in an array of active elements that includes the active element, wherein each active element in the array of active elements is separated from immediately adjacent active elements in the array of active elements by at least a portion of the frames; depositing a magnetooptic material on the substrate; and depositing the non-magnetic material on the seed layer that is patterned for growth of the non-magnetic material.

13. A method of magnetically controlling an active element of a magnetically-controlled pixel, the method comprising: driving a magnetic flux through a magnetic conduit comprising a high-permeability material that extends from a first surface of a backend layer through the backend layer to a second surface of the backend layer; injecting at least a portion of the magnetic flux from the magnetic conduit into the active element, wherein the active element is disposed on or adjacent to the backend layer; and changing a characteristic of the active element with at least the portion of the magnetic flux from the magnetic conduit.

14. The method of claim 13, wherein the magnetically-controlled pixel is one pixel in an array of magnetically-controlled pixels and a maximum size of each active element of each magnetically-controlled pixel in the array of magnetically-controlled pixels is no larger than 500 microns.

15. The method of claim 13, wherein the magnetically-controlled pixel is one pixel in an array of magnetically-controlled pixels comprising a plurality of active elements, the method further comprising: driving a plurality of magnetic fluxes through a plurality of magnetic conduits that extends from the first surface of the backend layer through the backend layer to the second surface of the backend layer;injecting at least portions of the plurality of magnetic fluxes from the plurality of magnetic conduits into the plurality of active elements, wherein the plurality of active elements is disposed on or adjacent to the backend layer; and changing a characteristic in each active element of the plurality of active elements with at least the portions of the plurality of magnetic fluxes injected from the plurality of magnetic conduits.

16. The method of claim 13, wherein driving the magnetic flux comprises: driving an electrical current through an electrical conductor to create and drive the magnetic flux in the magnetic conduit.

17. The method of claim 13, wherein changing the characteristic of the active element comprises changing an optical property of the active element to rotate polarization of light passing through the active element.

18. The method of claim 13, wherein changing the characteristic of the active element comprises changing a magnetization direction of the active element.

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