Apparatus having first and second switching materials

In an example, an apparatus includes an electrically conductive component having a first side and a second side, a first switching material formed on the first side of the electrically conductive component, and a second switching material formed on the second side of the electrically conductive component. The second switching material may include a different material than the first switching material and resistance states of each of the first switching material and the second switching material are to be modified through application of electric fields through the first switching material and the second switching material. The apparatus may also include an electrode in contact with one of the first switching material and the second switching material.

BACKGROUND

Memristors are devices that can be programmed to different resistive states by applying a programming energy, for example, a voltage or current pulse. The programming energy generates a combination of electric field thermal effects, and potentially other effects that are to modulate the conductivity of both non-volatile switch and non-linear select functions in a switching element. After programming, the state of the memristor remains stable over a specified time period and the state is thus readable. Memristor elements can be used in a variety of applications, including non-volatile solid state memory, programmable logic, signal processing, control systems, pattern recognition, and other applications.

DETAILED DESCRIPTION

Disclosed herein is an apparatus that includes an electrically conductive component with a first switching material formed on a first side and a second switching material formed on a second side of the electrically conductive component. The apparatus may also include an electrode that is in contact with one of the first switching material and the second switching material. The first switching material and the second switching material may have different characteristics with respect to each other and thus, application of an electric field through the first switching material may have a different result as compared to application of an electric field through the second switching material. For instance, the first switching material may have a higher current threshold for switching as compared to the second switching material.

The apparatus disclosed herein may be formed of a plurality of electrically conductive components and a plurality of electrodes arranged in a crossbar configuration. Particularly, the electrodes may be positioned with respect to the electrically conductive components such that each of the electrodes alternatingly contacts the first switching material and the second switching material of a number of the electrically conductive components. In other words, the electrodes may be interweaved or interlaced with the electrically conductive components.

In another example, the apparatus disclosed herein may be formed of electrically conductive components formed of sub-components that extend collinearly with each other and are in contact with each other. The sub-components may be formed of different materials with respect to each other. In this example, an electrode may have a switching material formed thereon and the switching material may alternatingly contact a first sub-component and second sub-component on adjacent electrically conductive components. Because the first and the second sub-components may be formed of different materials, properties of switches formed at the alternating junctions between the sub-components and the electrode may differ from each other. The electrodes may also be interweaved or interlaced with the electrically conductive components in this example.

Generally speaking, the interweaved configuration of the electrically conductive components and the electrodes may afford a higher level of strength in the apparatus as compared to merely arranging the electrically conductive components on top of the electrodes. In addition, the apparatus may be supported on a flexible substrate such that the apparatus may be flexed or bent. The apparatus disclosed herein, therefore, may be employed in applications in which flexibility of the apparatus may be desirable, such as, in e-textiles, wearable electronics, etc. Moreover, because the junctions at which the electrodes contact the electrically conductive components may have alternating first and second properties, switches formed at the adjacent junctions may differ from each other. For instance, the switches formed at the adjacent junctions may have opposite polarities from each other. In one regard, therefore, sneak path leakage may be relatively lower as compared to crossbar arrays of electrodes having homogeneous adjacent junctions.

With reference toFIGS. 1 and 2A-2C, there are shown simplified isometric views of a portion of an apparatus100, according to multiple examples. It should be understood that the apparatus100depicted inFIGS. 1 and 2-2Cmay include additional components and that some of the components described herein may be removed and/or modified without departing from a scope of the apparatus100. In addition, although the components of the apparatus100have been depicted as having certain shapes and sizes, it should be clearly understood that the depictions of the components are for purposes of illustration only and that the components of the apparatus100may therefore have other shapes and sizes without departing from a scope of the apparatus100.

As shown inFIG. 1, the apparatus100may include an electrically conductive component102and an electrode120. The electrode120may be positioned in a crossed relationship with respect to the electrically conductive component102. The electrically conductive component102and the electrode120may be formed of a metal or a metallic material that is to conduct electricity. In addition, the electrically conductive component102and the electrode120may be formed of different materials. As described in greater detail herein below, the electrode120may be positioned with a plurality of the electrically conductive component102such that the electrode120alternatively contacts the tops and the bottoms of the electrically conductive components102. In other words, the electrode120may be interweaved, interlaced, entwined, etc., with the electrically conductive component102, or vice versa.

Although not shown, the electrically conductive component102and the electrode120may each be an elongated structure, such as a wire, a thread, a strand, etc. In addition, the electrically conductive component102and the electrode120may each have a thickness that is in the nanometer scale. For instance, the electrically conductive component102may have a thickness that is less than 200 nm, and more particularly, a thickness that is less than about 50 nm. In other examples, the electrically conductive component102and the electrode120may each have a thickness in the micrometer or larger scale. The length of the electrically conductive component102may be substantially larger than the thickness of the electrically conductive component102, e.g., in the micrometer or larger scale. The electrode120may have similar length dimensions.

As also shown inFIG. 1, the electrically conductive component102is depicted as having a first side104and a second side106. The second side106is depicted as being positioned on the side opposite the first side104on the electrically conductive component102. A first switching material108, which is also referred to herein as the first layer108, is depicted as being provided or formed on the first side104of the electrically conductive component102. Additionally, a second switching material110, which is also referred to herein as the second layer110, is depicted as being positioned on the second side106of the electrically conductive component102. Each of the first switching material108and the second switching material110include materials for which resistance states are to change responsive to the application of a sufficiently strong electric field through the switching materials. In addition, the first switching material108and the second switching material110are to retain the resistance states following removal of the electric field. In this regard, the first switching material108and the second switching material110are memristive materials.

The resistance states of the first switching material108and the second switching material110may be read through application of a reading voltage or current across the first switching material108and the second switching material110. In addition, the resistance states of the first switching material108and the second switching material110may be cleared, e.g., reset, through application of rewriting voltages or currents, e.g., in a reverse polarity, to clear the resistance states of the first switching material108and the second switching material110.

The apparatus100may generally be defined as an electrically actuated apparatus formed of the electrically conductive component102, the first switching material108, the second switching material110, and the electrode120. As shown, the electrode120is in contact with the first switching material108, however, depending on the position at which contact is formed in the interweaving, the electrode120may alternatively be in contact with the second switching material110as shown inFIG. 2A. Thus, the electrode120may be in contact with one of the first switching material108and the second switching material110, such that an electric field may be created in one of the first switching material108and the second switching material110through application of a voltage or current through either or both of the electrically conductive component102and the electrode120.

According to an example, the electrically conductive component102may be formed of a different material than the electrode120. By way of particular example, the electrically conductive component102may be formed of platinum, tantalum, or the like, and the electrode120may be formed of copper or the like. In other examples, the electrically conductive component102may be formed of an electrically conductive material, such as AlCu, AlCuSi, AlCuSi with a barrier layer, such as TiN, Cu, Ag, Ti, Ta, or the like.

The first switching material108and the second switching material110may be formed of different switching oxides, such as a metal oxides. Specific examples of switching oxide materials may include magnesium oxide, titanium oxide, zirconium oxide, hafnium oxide, vanadium oxide, niobium oxide, tantalum oxide, chromium oxide, molybdenum oxide, tungsten oxide, manganese oxide, iron oxide, cobalt oxide, copper oxide, zinc oxide, aluminum oxide, gallium oxide, silicon oxide, germanium oxide, tin dioxide, bismuth oxide, nickel oxide, yttrium oxide, and gadolinium oxide, among other oxides. In addition to the binary oxides presented above, the switching oxides may be ternary and complex oxides such as silicon oxynitride. The oxides presented above may be formed using any of a number of different processes such as sputtering from an oxide target, reactive sputtering from a metal target, atomic layer deposition (ALD), evaporation from oxide sources, oxidizing a deposited metal or alloy layer, etc.

According to an example, the first switching material108and the second switching material110are formed of different switching materials such that, for instance, the first switching material108exhibits a different switching characteristic as compared to the second switching material110. For instance, the first switching material108may have a higher threshold for changing its resistance level then the second switching material110. In this regard, a lower strength electric field applied through the first switching material108and the second switching material110may result in the second switching material110changing its resistance state and the resistance state of the first switching material108remains unchanged. As another example, the polarity of a first switch formed with the first switching material108may be opposite the polarity of a second switch formed with the second switching material110. This may happen, for instance, when the oxygen vacancy concentration at the interface of the electrically conductive component102/first switching material108is much higher than the concentration at the interface of the electrically conductive component102/second switching material110.

The resistance levels or states of the first switching material108and the second switching material110may be changed in response to various programming conditions and the first switching material108and the second switching material110are able to exhibit a memory of past electrical conditions. For instance, the first switching material108and the second switching material110may be programmed to have one of a plurality of distinct resistance levels. Particularly, the resistance level of the first switching material108may be changed through application of a voltage or current, in which the voltage or current may cause mobile dopants in the first switching material108to move, which may alter the electrical operation of the first switching material108. That is, for instance, the distinct resistance levels of the first switching material108may correspond to different current levels applied to the first switching material108. By way of example, the first switching material108may be programmed to have a higher resistance level through application of a higher current level. The resistance level of the second switching material110may be changed through implementation of similar operations.

After removal of the current, the locations and characteristics of the dopants in the first switching material108and the second switching material110are to remain stable until the application of another programming electric field. That is, the first switching material108and the second switching material110are to remain at the programmed resistance level following removal of the current. The programmed resistance level may correspond to a value, such as the bit “1” or “0.”

Turning now toFIG. 2A, the apparatus100is depicted as including all of the same features as those described above with respect toFIG. 1. However, the apparatus100depicted inFIG. 2Adiffers from the apparatus100depicted inFIG. 1in that the electrode120is depicted as being in contact with the second switching material110. In addition, the electrically conductive component102is depicted as being formed of a first sub-component202and a second sub-component204. Particularly, the first switching material108is shown as being provided or formed on the first sub-component202and the second switching material110is shown as being provided or formed on the second sub-component204.

According to an example, the first sub-component202may be formed of a material on which the first switching material108may grow, for example, TaOx growth from a Ta material, and the second sub-component204may be formed of the material on which the second switching material110may grow, for example, TiOx growth from a Ti material. Alternatively, an additional metal layer (not shown) may be provided on either or both the first sub-component202and the second sub-component204, from which the first switching material108and/or the second switching material110may grow. By way of particular example, the materials for the first sub-component202and the second sub-component204may be selected to be materials that respectively facilitate the growth of the first switching material108and the second switching material110through a thermal oxidation process. For instance, the first sub-component202may be platinum (Pt), the second sub-component204may be tantalum (Ta), and the electrode120may be copper (Cu). In this example, the first sub-component202and the electrode120may undergo thermal oxidation to form a switching oxide (Ox) between the first sub-component202and the electrode120. In addition, the second sub-component204and the electrode120may undergo thermal oxidation to form a switching oxide (Ox) between the second sub-component204and the electrode120. The apparatus100may thus have a Pt/CuOx/Cu and a Ta/TaOx:CuOx/Cu configuration.

Turning now toFIGS. 2B and 2C, the apparatus100is depicted as including all of the same features as those described above with respect toFIGS. 1 and 2A. However, the apparatus100depicted inFIG. 2Bdiffers from the apparatus100depicted inFIGS. 1 and 2Ain that the electrically conductive component102is depicted as not having a switching layer formed on the electrically conductive component102. Instead, as shown inFIG. 2B, a third switching material206is depicted as being formed on electrode120. Additionally,FIG. 2Bshows a portion of another electrically conductive component102in which the third switching material206is in contact with the first sub-component202of the electrically conductive component102. InFIG. 2C, the electrically conductive component102is depicted as including the first switching material108and the second switching material110and the electrode120is depicted as including the third switching material206. In addition, the third switching material206is depicted is alternatingly contacting the first switching material108and the second switching material108. In bothFIGS. 2B and 2C, it should be understood that the third switching material206may include any of the materials described above with respect to the first switching material108and the second switching material110.FIGS. 2A-2Cthus show that the apparatus100may include a single or dual oxide switching materials and that either or both of the electrically conductive component102and the electrode120may include switching materials formed thereon.

With reference now toFIG. 3, there is shown a simplified isometric view of a portion of an apparatus100, according to another example. It should be understood that the apparatus100depicted inFIG. 3may include additional components and that some of the components described herein may be removed and/or modified without departing from a scope of the apparatus100. In addition, although the components of the apparatus100have been depicted as having certain shapes and sizes, it should be clearly understood that the depictions of the components are for purposes of illustration only and that the components of the apparatus100may therefore have other shapes and sizes without departing from a scope of the apparatus100. Moreover, it should be understood that the apparatus100may include any number of electrically conductive components102and electrodes120arranged in a crossbar configuration and that the electrically conductive components102and electrodes120may be configured in any of the manners depicted inFIGS. 1 and 2A-2C.

As shown inFIG. 3, the apparatus100includes a plurality of electrically conductive components102interweaved with a plurality of electrodes120in a crossbar array configuration. That is, each of the electrodes120is depicted as being interweaved with a number of electrically conductive components102such that an electrode120alternatingly contacts a top and a bottom of adjacent electrically conductive components102.

In the example depicted inFIG. 1, each of the electrodes120alternatingly contacts the first switching material108and the second switching material110of the number of electrically conductive components102. Reference numeral304indicates a junction at which an electrode120contacts the first switching material108of an electrically conductive component102. Additionally, reference numeral306, which refers to all of the dashed boxes shown inFIG. 3, indicates a junction at which an electrode120contacts the second switching material110of an electrically conductive component102. The junctions304and306are the locations in the apparatus100at which the resistance states of the first switching material108and the second switching material110may be set and read.

As may be seen by the interweaved or interlaced structure of the array of electrically conductive components102and electrodes120, each of the nearest junctions to any of the junctions304are the junctions306. As such, junctions304having the same switching materials and thus the same characteristics as a particular junction304are located relatively farther away from the junction304than the junctions306, which have different switching materials. In one regard, therefore, occurrences of sneak path currents through the crossbar array may be reduced as the characteristics of the switching materials in nearby junctions may be different from each other. In addition, the occurrences of sneak path currents may be reduced because the polarities of the first switching material108and the second switching material110may be opposite each other.

In other examples, the junctions304and306may have configurations as shown inFIGS. 2A-2C. In these examples, the junctions304and306may be formed to have a different characteristic with respect to each other through formation of the electrodes120and/or the electrically conductive components102in manners discussed above with respect toFIGS. 2A-2C.

The apparatus100is further depicted as including a substrate302upon which the crossbar array configuration of the electrically conductive components102and the electrodes120are positioned. According to an example, the array of electrically conductive components102and electrodes120may be attached to the substrate302such that the substrate302supports the array. In addition, the substrate302may be formed of a flexible material, such as a polymer, such that the array of electrically conductive components102and electrodes120may be flexed. In one regard, the combination of the substrate302and the interweaved configuration of the electrically conductive components102with the electrodes120may result in a relatively strong apparatus100.

Although not shown, the apparatus100may include or may be connected to electronics that enable each of the junctions304,306to be individually addressable, such as, a voltage source, a reader device, a controller, etc. In this regard, each of the electrically conductive components102and the electrodes120may be connected to a voltage source such that electric fields may be generated at the junctions304and306.

With reference now toFIG. 4, there is shown a flow diagram of a method for fabricating an apparatus100, according to an example. It should be understood that the method400depicted inFIG. 4may include additional operations and that some of the operations described herein may be removed and/or modified without departing from the scope of the method400. The description of the method400is made with reference to the features depicted inFIGS. 1-3for purposes of illustration and thus, it should be understood that the method400may be implemented in apparatuses having architectures different from those shown in those figures.

With reference toFIG. 4, at block402, a plurality of electrically conductive components102may be formed. Particularly, for instance, each of the electrically conductive components102may be formed to have a respective first side104and second side106. The electrically conductive components102may be formed through any suitable process such as sputtering, atomic layer deposition, formation of nanoparticle stripe patterns through dewetting, 3D printing, etc. In addition, the electrically conductive components102may be formed of a single structure as shown inFIG. 1or may be formed to have a first sub-component202and a second sub-component204as shown inFIG. 2.

At block404, the plurality of electrodes120may be formed. The electrodes120may be formed through any suitable fabrication process, such as sputtering, atomic layer deposition, formation of nanoparticle stripe patterns through dewetting, 3D printing, etc.

At block406, the plurality of electrically conductive components102may be interweaved with the plurality of electrodes120such that the plurality of electrically conductive components102across the plurality of electrodes to form an array of junctions. Each of the plurality of electrodes120may be interwoven or interlaced with a number of the electrically conductive components102such that an electrode120alternatingly contacts the top and the bottom of adjacent electrically conductive components102, as shown inFIG. 3. In addition, the interwoven or interlaced electrically conductive components102and electrodes120may be supported on a flexible substrate, for instance, the substrate302depicted inFIG. 3.

According to an example, the electrodes120may be interwoven with the electrically conductive components102following formation of the electrodes120and the electrically conductive components102. In this example, the electrically conductive components102and the electrodes120may be formed of wires and may be woven together through a weaving process that is similar to weaving processes employed to weave other types of strands together. According to another example, the electrodes120may be interwoven with the electrically conductive components102during formation of the electrically conductive components102, the electrodes120, and a switching layer or layers. In this example, a three-dimensional (3-D) printer may be implemented to “print” the electrically conductive components102and the electrodes120into a crossbar arrangement, for instance, as shown inFIG. 3. In either of these examples, the switching layer or layers may be formed on either or both of the electrodes120and the electrically conductive components102through any of the processes described above, for instance, through a thermal oxidation process.

According to an example, forming of the plurality of electrically conductive components102and the plurality of electrodes120includes forming the plurality of conductive components102and the plurality of electrodes120to cause the junctions in the array of junctions to have a different characteristic than neighboring junctions. The junctions may be caused to have a different characteristic than neighboring junctions in any of the manners described above with respect toFIGS. 1 and 2A-2C.

In a first example corresponding toFIG. 1, a first layer108may be formed on the first side104of each of the electrically conductive components102. As discussed above, the first layer108may be grown from the first switching material108or another metal material. The first layer108may also be formed through any suitable process including, chemical vapor deposition (CVD), physical vapor deposition (PVD), plasma-enhanced chemical vapor deposition (PECVD), atomic layer deposition (ALD), or the like. According to a particular example, the first layer108may be formed through thermal oxidation of the electrically conductive component102and the electrode120. In another example, the first layer108may be formed through thermal oxidation of the first sub-component202of the electrically conductive component102and the electrode120.

In addition, a second layer110may be formed on the second side106of the electrically conductive component102. As discussed above, the second layer110may be formed of the second switching material110. The second layer110may be formed through any suitable process including, CVD, PVD, PECVD, ALD, or the like. According to a particular example, the second layer110may be formed through thermal oxidation of the electrically conductive component102. In another example, the second layer110may be formed through thermal oxidation of the second sub-component204of the electrically conductive component102.

In a second example corresponding toFIG. 2A, the electrically conductive components102may each be formed of first and second sub-components202,204. In this example, the first layer108may be formed on the first sub-component202and the second layer110may be formed on the second sub-component204of each of the electrically conductive components102. In addition, the electrodes120may alternatingly contact the first layer108and the second layer110of adjacent electrically conductive components102to form the junctions304,306.

In an example in which the first layer108and the second layer110are formed on the sub-components202,204after the electrodes120are interwoven with the electrically conductive components102, the first layer108may be formed on the first sub-component202through a thermal oxidation process of the first sub-component202and the electrode120. Additionally, the second layer110may be formed on the second sub-component204through a thermal oxidation process of the second sub-component204and the electrode120. As described above, because the first sub-component202and the second sub-component204are different materials, thermal oxidation of the first sub-component202and the second sub-component204are to result in switching materials, e.g., oxides, having different characteristics with respect to each other. According to an example, a thermal oxidation process may be performed concurrently on the first and second sub-components202,204.

In a third example corresponding toFIG. 2B, the electrically conductive components102may each be formed of first and second sub-components202,204and switching materials206may be formed on the electrodes120. In this example, the switching materials206may alternatingly contact the first sub-component202and the second sub-component204of adjacent electrically conductive components102to form the junctions304,306.

In a fourth example corresponding toFIG. 2C, the electrically conductive components102may each be formed of first and second sub-components202,204and switching materials108,110, and206may be formed on the first sub-component202, the second sub-component204, and the electrodes120, respectively. In this example, the switching materials206may alternatingly contact the first switching material (layer)108and the second switching material (layer)110of adjacent electrically conductive components102to form the junctions304,306.