Patent Application
20170133588
Field of the Disclosure
Embodiments of the present disclosure generally relate to data storage and computer memory systems, and more particularly, to resistive random access memory device structures and methods for making the same.
Description of the Related Art
An important part of any computer is a mass storage device which typically may include rotating magnetic media or a solid state media device. A number of different memory technologies exist today for storing information for use in a computing system.
In recent years there has been a demand for higher density devices, which maintain a relatively low cost per bit, for use in high capacity storage applications. Today, the memory technologies that generally dominate the computing industry are magnetic media and NAND flash; however, these memory technologies may not be able to address the current and future capacity demands of next generation computing systems.
Resistive Random Access Memory (ReRAM) is an emerging technology for next generation non-volatile memory (NVM) devices. The memory structure of a ReRAM device includes an array of cells which each carry one or multiple bits of data. The memory structure of the ReRAM device utilizes resistance values rather than an electric charge to store the data. ReRAM devices are made out of dielectric materials, the resistivity of which can be switched by the application of an electric signal. A typical ReRAM cell comprises one or multiple dielectric layers sandwiched between conductive electrodes. Some existing ReRAM cells work through a filamentary switching mechanism, and a key driver of filament formation is the electric field created by the potential difference applied to the ReRAM cell electrodes. However, controlling the filament location has been shown to be problematic. Maintaining control of the filament location is important in avoiding filament formation near device edges and, therefore, to control the device yield and switching reproducibility. Furthermore, metallic alloys of typical ReRAM devices have various susceptibility to etching and/or milling.
While the switching mechanism in other ReRAM cells may be only partially or not at all mediated by the formation of a filament, all types of ReRAM work by the action of an electric field on a dielectric, thus the need for focusing the electric field arises in any type of ReRAM.
Therefore, there is a need in art for an improved ReRAM memory cell capable of focusing the electric field at the center of the cell.
The present disclosure generally relates to an electrode structure for a resistive random access memory (ReRAM) device cell which focuses the electric field at a center of the cell and methods for making the same. As such, a non-uniform metallic electrode may be deposited onto the ReRAM device which is subsequently exposed to an oxidation or nitrogenation process during cell fabrication. The electrode structure may include at least one layer comprising a first material and a second material, wherein the concentration of the first material and the second material are varied based on location within the electrode. By a process that makes the second material more electrically insulating, a metal electrode profile is formed to favor the center of the cell as the location with the greatest electric field. This profile may be conical or pyramid shaped depending on the shape of the electrode prior to treatment. As such, size scaling and reliability of the non-volatile memory component are each increased.
In one embodiment, a resistive random access memory (ReRAM) device is disclosed. The ReRAM device includes a multilayer metallic electrode structure and a switching medium. The multilayer metallic electrode structure may include a plurality of layers. Each layer of the plurality of layers may include a first material selected from a first group and a second material selected from a second group. The first group consists of Ag, Au, Pt, Pd, Cu, Rh, or alloys or mixtures thereof. The second group consists of Mg, Ta, TaN, Si, Al, Ti, TiN, W, Hf, Nb, Zr, or alloys or mixtures thereof. A first layer of the plurality of layers closest to the switching medium may include the greatest concentration of the second material of the second group. A second layer of the plurality of layers furthest away from the switching medium may include the lowest concentration of the second material of the second group.
In another embodiment, a memory device is disclosed. The memory device may include at least one layer, a switching medium, and a contact. The layer may be located between the switching medium and the contact. At least one layer may include one of an element of a first group and one of an element of a second group. The first element is selected from the first group consisting of Ag, Au, Pt, Pd, Cu, Rh, or alloys or mixtures thereof. The second element is selected from the second group consisting of Mg, Ta, TaN, Si, Al, Ti, TiN, W, Hf, Nb, Zr, or alloys or mixtures thereof. The concentration of the element of the first group may be varied continuously and the concentration of the element of the second group may be varied continuously. The concentration of the element of the second group may be greatest near the switching medium. The concentration of the element of the first group is greatest away from the switching medium.
In yet another embodiment, a method for forming a memory device is disclosed. The method may include forming a first layer. The first layer may include a material from a first group and a material from a second group. The first group may include Ag, Au, Pt, Pd, Cu, Rh, or alloys or mixtures thereof. The second group may include Mg, Ta, TaN, Si, Al, Ti, TiN, W, Hf, Nb, Zr, or alloys or mixtures thereof. The method may further include forming a second layer. The second layer may include a material from a first group and a material from a second group. The first group may include Ag, Au, Pt, Pd, Cu, Rh, or alloys or mixtures thereof. The second group may include Mg, Ta, TaN, Si, Al, Ti, TiN, W, Hf, Nb, Zr, or alloys or mixtures thereof. The second layer may be below the first layer. The second layer may include a greater concentration of the material from the second group than the first layer. The first layer and the second layer may collectively form an electrode. The method may also include etching or ion-milling the memory device. The method may additionally include exposing the memory device to an oxygen-rich or a nitrogen-rich environment to form the layers in a conical structure. The regions of the electrode with the greatest concentration of the material from the second group contain the greatest concentration of an oxide or an insulator material.
In yet another embodiment, a method for forming a memory device is disclosed. The method may include forming a first layer, a second layer, a third layer, a fourth layer, and a fifth layer. The first layer may include a material from a first group and a material from a second group. The first group may include Ag, Au, Pt, Pd, Cu, Rh, or alloys or mixtures thereof. The second group may include Mg, Ta, TaN, Si, Al, Ti, TiN, W, Hf, Nb, Zr, or alloys or mixtures thereof. The second layer may include a material from a first group and a material from a second group. The first group may include Au, Pt, Pd, Cu, Rh, or alloys or mixtures thereof. The second group may include Mg, Ta, TaN, Si, Al, Ti, TiN, W, Hf, Nb, Zr, or alloys or mixtures thereof. The second layer may be below the first layer. The second layer may include a greater concentration of the material from the second group than the first layer. The first layer and the second layer may collectively form a first electrode. The third layer may include a material from a third group. The third group may include Mg, Ta, TaN, Si, Al, Ti, TiN, W, Hf, Nb, Zr, or alloys or mixtures thereof. The fourth layer may include a material from the first group and a material from the second group. The fifth layer may include a material from the first group and a material from the second group. The fifth layer may be below the fourth layer. The fifth layer may include a lower concentration of the material from the second group than the fourth layer. The fourth layer and the fifth layer may collectively form a second electrode. The third layer may be between the first electrode and the second electrode. The method may further include etching or ion-milling the memory device. The method may also include exposing the first electrode, the second electrode, and the third layer to an oxygen-rich or a nitrogen-rich environment to form the first electrode and the second electrode in a conical structure. Regions of the first electrode and the second electrode with the greatest concentration of the material from the second group may contain the greatest concentration of an oxide or an insulator material. The exposing may form the third layer into a switching medium.
So that the manner in which the above recited features of the present disclosure can be understood in detail, a more particular description of the disclosure, briefly summarized above, may be had by reference to embodiments, some of which are illustrated in the appended drawings. It is to be noted, however, that the appended drawings illustrate only typical embodiments of this disclosure and are therefore not to be considered limiting of its scope, for the disclosure may admit to other equally effective embodiments.
To facilitate understanding, identical reference numerals have been used, where possible, to designate identical elements that are common to the figures. It is contemplated that elements disclosed in one embodiment may be beneficially utilized on other embodiments without specific recitation.
In the following, reference is made to embodiments of the disclosure. However, it should be understood that the disclosure is not limited to specific described embodiments. Instead, any combination of the following features and elements, whether related to different embodiments or not, is contemplated to implement and practice the disclosure. Furthermore, although embodiments of the disclosure may achieve advantages over other possible solutions and/or over the prior art, whether or not a particular advantage is achieved by a given embodiment is not limiting of the disclosure. Thus, the following aspects, features, embodiments and advantages are merely illustrative and are not considered elements or limitations of the appended claims except where explicitly recited in a claim(s). Likewise, reference to “the disclosure” shall not be construed as a generalization of any inventive subject matter disclosed herein and shall not be considered to be an element or limitation of the appended claims except where explicitly recited in a claim(s).
The present disclosure generally relates to an electrode structure for a resistive random access memory (ReRAM) device cell which focuses the electric field at a center of the cell and methods for making the same. As such, a non-uniform metallic electrode may be deposited onto the ReRAM device which is subsequently exposed to an oxidation or nitrogenation process during cell fabrication. The electrode structure may comprise at least one layer comprising a first material and a second material, wherein the concentration of the first material and the second material are varied based on location within the electrode. By a process that makes the second material more electrically insulating, a metal electrode profile is formed which favors the center of the cell as the location with the greatest electric field. This profile may be conical or pyramid shaped depending on the shape of the electrode prior to treatment. As such, size scaling and reliability of the non-volatile memory component are each increased.
The multilayer electrode structure 202 may include a plurality of layers 204, 206, 208, 210, 212. Each layer of the plurality of layers 204, 206, 208, 210, 212 may be an electrode. Although five layers 204, 206, 208, 210, 212 are shown, it is contemplated that any number of layers may be utilized. In one embodiment, the plurality of layers 204, 206, 208, 210, 212 may include between about two layers and about ten layers. In another embodiment, the plurality of layer 204, 206, 208, 210, 212 may include more than ten layers. Each layer 204, 206, 208, 210, 212 may be a metallic layer. Each layer may maintain a thickness of between about 0.05 nm and about 4 nm. In some embodiments, each layer 204, 206, 208, 210, 212 of the plurality of layers may have a different thickness.
Each layer 204, 206, 208, 210, 212 of the plurality of layers may comprise a first material selected from a first group and a second material selected from a second group. The first group may consist of Ag, Au, Pt, Pd, Cu, Rh, or alloys or mixtures thereof. The second group may consist of Mg, Ta, TaN, Si, Al, Ti, TiN, W, Hf, Nb, Zr, or alloys or mixtures thereof. The second material may be made semiconducting or insulating by an oxidation or nitration process.
The layers 204, 206, 208, 210, 212 closest to the switching medium 216 may contain the greatest concentration of material from the second group. The layer 204, 206, 208, 210, 212 furthest away from the switching medium 216 may contain the lowest concentration of material from the second group. In some embodiments, the layers 204, 206, 208, 210, 212 furthest away from the switching medium 216 may contain no material from the second group. The layers 204, 206, 208, 210, 212 may contain progressively higher concentrations of material from the second group as the layers 204, 206, 208, 210, 212 become closer to the switching medium 216. As such, the composition of the material from the first group and the composition of the material from the second group within each layer may vary depending on the location of the layer 204, 206, 208, 210, 212. In some embodiments, the layer, for example layer 204, coupled to the contact 214 may contain material only from the first group. Furthermore, in some embodiments, the layer, for example layer 212, coupled to the switching medium 216 may contain only material from the second group. By way of example only, if X represents a material of the first group, Y represents a material of the second group, and B, C, D, and E represent a percentage of concentration wherein E %>D %>C %>B %, then each layer may be represented by the following equations:
X (1) (Layer 204)
X100-BYB (2) (Layer 206)
X100-CYC (3) (Layer 208)
X100-DYD (4) (Layer 210)
X100-EYE (5) (Layer 212)
The switching medium 216 may be an insulator material and/or a semiconductor material. In some embodiments, the switching medium 216 may be deposited as a metal and/or the switching medium may consist of Mg, Ta, TaN, Si, Al, Ti, TiN, W, Hf, Nb, Zr, or alloys or mixtures thereof.
The plurality of layers 204, 206, 208, 210, 212 of the ReRAM device 200 may be etched during fabrication to define the electrodes therein. In some embodiments, the plurality of layers 204, 206, 208, 210, 212 may be ion-milled to define the electrodes therein. Subsequent to the etching and/or ion-milling each layer 204, 206, 208, 210, 212 may be exposed to an oxygen-rich and/or nitrogen-rich environment, such as, for example, a gas and/or a plasma. The gas and/or plasma may oxidize and/or nitrogenize each layer 204, 206, 208, 210, 212 to a concentration which may be dependent on the concentration of the material from the second group present in each layer 204, 206, 208, 210, 212. The deposition of the plurality of layers 204, 206, 208, 210, 212 may gradually increase susceptibility to etching and/or milling at an exposed side of the layers 204, 206, 208, 210, 212.
In some embodiments, the switching medium 216 may be exposed to the oxygen-rich and/or nitrogen-rich environment at the same time as each of the layers 204, 206, 208, 210, 212. As such, in some embodiments, the switching medium may be a metallic multilayer switching medium in the ReRAM device and may be fully oxidized and/or nitrogenized. Oxidizing and/or nitrogenizing the switching medium may allow for the entire ReRAM device to be exposed to an oxygen-rich and/or a nitrogen-rich environment in a single step.
The varying degree of oxidation, and/or nitrogenization, may create layers 204, 206, 208, 210, 212 with a cone-like or a pyramid-like metallic electrode structure within each layer 204, 206, 208, 210, 212, as shown in
The lower electrode 230 may be a second multilayer electrode structure 280, comprising a second plurality of layers 240, 242, 244, 246, 248, wherein each layer of the second plurality of layers 240, 242, 244, 246, 248 comprises a first material selected from a first group and a second material selected from a second group. The first group may consist of Ag, Au, Pt, Pd, Cu, Rh, or alloys or mixtures thereof. The second group may consist of Mg, Ta, TaN, Si, Al, Ti, TiN, W, Hf, Nb, Zr, or alloys or mixtures thereof. A first layer 248 of the second plurality of layers 240, 242, 244, 246, 248 that is closest to the switching medium 216 may comprise the greatest concentration of the second material of the second group. A second layer 240 of the second plurality of layers 240, 242, 244, 246, 248 that is furthest away from the switching medium 216 may comprise the lowest concentration of the first material of the second group.
The multilayer electrode structure 202 of the upper electrode 232 may include layers 204, 206, 208, 210, 212. The second multilayer electrode structure 280 of the lower electrode 230 may include layers 240, 242, 244, 246, 248 which may be substantially similar to the layers 204, 206, 208, 210, 212 of the multilayer electrode structure 202, however the layers 240, 242, 244, 246, 248 of the second multilayer electrode structure 280 may be a mirror image of the layers 204, 206, 208, 210, 212 of the upper electrode 232. In the embodiment shown in
The varying degree of oxidation, and/or nitrogenization, may create layers 204, 206, 208, 210, 212 of the multilayer electrode structure 202 of the upper electrode 232 and layers 240, 242, 244, 246, 248 of the second multilayer electrode structure 280 of the lower electrode 230 with a cone-like or a pyramid-like metallic electrode structure within each layer 204, 206, 208, 210, 212, 240, 242, 244, 246, 248 as shown in
Each layer 204, 206, 208, 210, 212, 240, 242, 244, 246, 248 as shown in
The single layers 270 of the ReRAM device 200 may be etched during fabrication to define the electrodes therein. In some embodiments, the single layers 270 may be ion-milled to define the electrodes therein. Subsequent to the etching and/or ion-milling the single layers 270 may be exposed to an oxygen-rich and/or nitrogen-rich environment, such as, for example, a gas and/or a plasma. The gas and/or plasma may oxidize and/or nitrogenize each single layer 270 to a concentration which may be dependent on the concentration of the material from the second group present in each single layer 270.
The ReRAM device 200 of
As compared to the electric field of
At operation 320 a second layer may be formed. The second layer may comprise a material from a first group and a material from a second group. The first group may comprise Ag, Au, Pt, Pd, Cu, Rh, or alloys or mixtures thereof. The second group may comprise Mg, Ta, TaN, Si, Al, Ti, TiN, W, Hf, Nb, Zr, or alloys or mixtures thereof. The second layer may be below the first layer. The second layer may comprise a greater concentration of the material from the second group than the first layer. The first layer and the second layer may collectively form and electrode.
At operation 330 the memory device may be etched or ion-milled. At operation 340 the memory device may be exposed to an oxygen-rich or a nitrogen-rich environment to form the electrode in a conical structure. The regions of the electrode with the greatest concentration of the material from the second group may contain the greatest concentration of an oxide or an insulator material.
In some embodiments, the method 300 may also include forming a third layer. The third layer may comprise a material from a first group and a material from a second group, wherein the first group comprises Ag, Au, Pt, Pd, Cu, Rh, or alloys or mixtures thereof, and wherein the second group comprises Mg, Ta, TaN, Si, Al, Ti, TiN, W, Hf, Nb, Zr, or alloys or mixtures thereof. The method 300 may further include forming a fourth layer comprising a material from a first group and a material from a second group. The first group may comprise Ag, Au, Pt, Pd, Cu, Rh, or alloys or mixtures thereof, and the second group may comprise Mg, Ta, TaN, Si, Al, Ti, TiN, W, Hf, Nb, Zr, or alloys or mixtures thereof. The fourth layer may be below the third layer. The third layer may comprise a greater concentration of the material from the second group than the fourth layer. The third layer and the fourth layer may collectively form a second electrode. The second electrode may be formed prior to the exposing of the first electrode to an oxygen-rich or a nitrogen-rich environment. The method 300, in some embodiments, may also include exposing the second electrode to an oxygen-rich or a nitrogen-rich environment to form the second electrode in a conical structure. Regions of the second electrode with the greatest concentration of the material from the second group contain the greatest concentration of an oxide or an insulator material. In certain embodiments, the exposing of the first electrode and the second electrode to the oxygen-rich or the nitrogen-rich environment may occur at the same time.
At operation 420 a second layer may be formed. The second layer may comprise a material from a first group and a material from a second group. The first group may comprise Ag, Au, Pt, Pd, Cu, Rh, or alloys or mixtures thereof. The second group may comprise Mg, Ta, TaN, Si, Al, Ti, TiN, W, Hf, Nb, Zr, or alloys or mixtures thereof. The second layer may be below the first layer. The second layer may comprise a greater concentration of the material from the second group than the first layer. The first layer and the second layer may collectively form a first electrode.
At operation 430 a third layer may be formed. The third layer may comprise a material from a third group. The third group may comprise Mg, Ta, TaN, Si, Al, Ti, TiN, W, Hf, Nb, Zr, or alloys or mixtures thereof.
At operation 440 a fourth layer may be formed. The fourth layer may comprise a material from the first group and a material from the second group.
At operation 450 a fifth layer may be formed. The fifth layer may comprise a material from the first group and a material from the second group. The fifth layer may be below the fourth layer. The fifth layer may comprise a lower concentration of the material from the second group than the fourth layer. The fourth layer and the fifth layer may collectively form a second electrode. The third layer may be between the first electrode and the second electrode. In some embodiments, the first layer, the second layer, the fourth layer, and the fifth layer may each have a thickness of between about 0.05 nm and about 4 nm. In some embodiments, the first layer and the second layer may each have a different thickness, and/or the fourth layer and the fifth layer may each have a different thickness.
At operation 460 the memory device may be etched or ion-milled.
At operation 470, the first electrode, the second electrode, and the third layer may be exposed to an oxygen-rich or a nitrogen-rich environment. The exposing may form the first electrode and the second electrode in a conical structure. Regions of the first electrode and the second electrode with the greatest concentration of the material from the second group may contain the greatest concentration of an oxide or an insulator material. The exposing may form the third layer into a switching medium. In some embodiments, the oxide or insulator material may be formed on an outside edge of each of the first layer, the second layer, the fourth layer, and/or the fifth layer.
In some embodiments, the method 400 may further include combining the first layer and the second layer to form a first multilayer electrode structure. In some embodiments, the method 400 may further include combining the fourth layer and the fifth layer to form a second multilayer electrode structure. The first and/or second multilayer electrode structure may be a top electrode, a bottom electrode, and/or both the top electrode and the bottom electrode within the memory device.
In some embodiments, the method 400 may further include, forming a sixth layer. The sixth layer may include a material from the first group and a material from the second group.
In some embodiments, the method 400 may further include forming a seventh layer. The seventh layer may include a material from the first group and a material from the second group. The seventh layer may be below the sixth layer. The seventh layer may comprise a greater concentration of the material from the second group than the sixth layer. The sixth layer and the seventh layer may collectively form a third electrode.
In some embodiments, the method 400 may further include forming an eighth layer comprising a material from the third group. The method 400 may also include forming a ninth layer. The ninth layer may include a material from the first group and a material from the second group. The method 400 may also include forming a tenth layer. The tenth layer may comprise a material from the first group and a material from the second group. The tenth layer may be below the ninth layer. The tenth layer may comprise a lower concentration of the material from the second group than the ninth layer. The ninth layer and the tenth layer may collectively form a fourth electrode. The eighth layer may be between the third electrode and the fourth electrode. The third electrode and the fourth electrode may be formed prior to the exposing of the first electrode and the second electrode to an oxygen-rich or a nitrogen-rich environment.
In some embodiments, the method 400 may also include exposing the third electrode, the fourth electrode, and the eighth layer to an oxygen-rich or a nitrogen-rich environment to form the third electrode and the fourth electrode in a conical structure. Regions of the third electrode and the fourth electrode with the greatest concentration of the material from the second group may contain the greatest concentration of an oxide or an insulator material.
In some embodiments, the exposing of the first electrode, the second electrode, the third electrode, and the fourth electrode to the oxygen-rich or the nitrogen-rich environment may occur at the same time.
Benefits of the present disclosure include a ReRAM filamentary device with improved filament location predictability. As such, the filament location is controlled and filament formation near device edges is avoided. The formation of a filament near the point of the conical structure of pyramid-like structure may improve device yield, lower forming voltages necessary for filament formation, and improve reproducibility.
The present disclosure provides a materials stack and method for creating an improved filamentary ReRAM non-volatile memory cell by focusing the electric field at the center of the cell. By depositing a non-uniform metallic electrode, either compositionally modulated or multilayer, which is subsequently exposed to, for example, an oxidation process during cell fabrication, a metal electrode profile is automatically created which favors the center of the cell as the location with the highest electric field. For ReRAM cells in which filament creation/dissolution is the switching mechanism, for example OxRAM or CBRAM, the apparatus and method of the present disclosure increases the probability of filament formation near the center of the cell, which is favorable for size scaling and reliability of the non-volatile memory component.
While the foregoing is directed to embodiments of the present disclosure, other and further embodiments of the disclosure may be devised without departing from the basic scope thereof, and the scope thereof is determined by the claims that follow.
