Multi-layered conductive metal oxide structures and methods for facilitating enhanced performance characteristics of two-terminal memory cells

A memory cell including a two-terminal re-writeable non-volatile memory element having at least two layers of conductive metal oxide (CMO), which, in turn, can include a first layer of CMO including mobile oxygen ions, and a second layer of CMO formed in contact with the first layer of CMO to cooperate with the first layer of CMO to form an ion obstruction barrier. The ion obstruction barrier is configured to inhibit transport or diffusion of a subset of mobile ion to enhance, among other things, memory effects and cycling endurance of memory cells. At least one layer of an insulating metal oxide that is an electrolyte to the mobile oxygen ions and configured as a tunnel barrier is formed in contact with the second layer of CMO.

FIELD OF THE INVENTION

Embodiments of the invention relate generally to semiconductors and memory technology, and more particularly, to systems, integrated circuits, and methods to enhance cycling endurance, as well as the memory effect, of memory elements, such as implemented in third dimensional memory technology.

BACKGROUND OF THE INVENTION

Conventional memory architectures and technologies, such as those including dynamic random access memory (“DRAM”) cells and Flash memory cells, typically are not well-suited to resolve issues of manufacturing and operating resistance change-based memory cells. The above-described memory architectures, while functional for their specific technologies, fall short of being able to adequately address the issues of cycling endurance of resistance-based memory elements and the degradation due to repeated program-erase cycles. As the structures of conventional memory cells differ from resistance-based memory elements, there are different requirements and approaches to improve the reliability (e.g., cycling endurance) of two-terminal resistance-based memory elements.

In certain conventional approaches to forming resistance-based memory elements, materials providing mobile ions have been formed on multiple layers to form a reservoir of ions used in transport to another material for modifying the resistance of the memory cell. Typically, the multiple layers are formed with identical materials and compositions and cooperate to operate as an ionic conductor and an electronic insulator. While functional, there are certain performance deficiencies associated with this structure.

FIG. 1depicts sub-optimal performance characteristics associated with a conventional multi-layered structure material operable as an ionic conductor and an electronic insulator. Diagram100depicts various magnitudes of current I through a memory cell over a number of program-erase cycles, the memory cell being formed with a material operable as an ionic conductor and an electronic insulator. As shown, the magnitudes of current I alternate between a first magnitude110associated with an erasing operation and a second magnitude112associated with a programming operation. Over a number of cycles120, the conventional multi-layered structure has its performance characteristics degrade or other otherwise change. In this case, the current “drifts” lower in magnitudes over number of cycles120such that an average current magnitude102between magnitudes110and112decreases over a number of program-erase cycles. Typically, additional circuitry (e.g., sense amp circuitry) and resources are required to accommodate or filter out the current drift, especially when sensing a current representative of a data value, such as a read current generated by application of a read voltage during a read operation to a memory cell, for example. Further, the differences in magnitudes between first magnitudes110and second magnitudes112decrease during a number of cycles122, which are subsequent in time to the number of cycles120. In some cases, the phenomena depicted during number of cycles120can arise after, for example 10,000 program-erase cycles.

It would be desirable to provide improved systems, integrated circuits, and methods that minimize one or more of the drawbacks associated with conventional techniques for facilitating improved cycling endurance and memory effects for two-terminal resistance-based memory elements disposed in, for example, cross-point arrays or other memory structures suitable for two-terminal resistance-based memory elements.

Although the above-described drawings depict various examples of the invention, the invention is not limited by the depicted examples. It is to be understood that, in the drawings, like reference numerals designate like structural elements. Also, it is understood that the drawings are not necessarily to scale.

DETAILED DESCRIPTION

In some examples, techniques such as those described herein enable emulation of multiple memory types for implementation on a single component such as a wafer, substrate, or die. U.S. patent application Ser. No. 11/095,026, filed Mar. 30, 2005, published as U.S. publication no. 2006/0171200, and entitled “Memory Using Mixed Valence Conductive Oxides,” already incorporated by reference herein, describes non-volatile third dimensional memory elements that may be arranged in a two-terminal, cross-point memory array. New memory structures are possible with the capability of this third dimensional memory array. The technology allows for the emulation of other memory technologies by duplicating the interface signals and protocols, while accessing the third dimensional memory array. The third dimensional memory array may emulate other types of memory (e.g., emulation of DRAM, SRAM, ROM, EEPROM, FLASH, NAND FLASH, and NOR FLASH), providing memory combinations within a single component.

Semiconductor memories and memory material may be fabricated using the described techniques to create a single-layer or multiple-layer three-terminal memory and a single-layer or multiple-layer two-terminal memory, such as a cross-point memory described in U.S. patent application Ser. No. 11/095,026 (incorporated above). Using materials including but not limited to silicon oxide (SiO2), platinum (Pt), titanium nitride (TiN), yttria-stabilized zirconia (YSZ), tungsten (W), conductive metal oxide (CMO), perovskites (e.g., PCMO), and others, a memory may be formed with at least one layer of continuous and memory material (e.g., unetched) sandwiched between two or more electrodes. As part of the formation of a memory cell, for example, a discrete bottom electrode of a memory cell may be formed by etching one or more layers of material. The etched layers may be filled with material and planarized. Above the bottom electrode, one or more layers of memory material may be deposited but not etched (i.e., continuous, unetched layers of memory material). Above the unetched layer(s) of memory material (e.g., the uppermost layer of continuous and unetched memory material), additional layers of material, including a material for a top electrode, and optionally a selection device (“SD”) such as a non-ohmic device (“NOD”), for example, may be deposited and etched to form an implantation mask that, when implanted using ion implantation techniques, creates an insulating layer of conductive metal oxide (“CMO”) (e.g., praseodymium calcium manganese oxide—PCMO) in regions of the CMO that are not covered by the implantation mask. The implantation mask may or may not include the NOD, that is, the NOD may be formed after the layers that comprise the implantation mask. The continuous and unetched layer(s) of CMO may include perovskite-based structures and materials (e.g., PCMO) that, when exposed to argon (Ar), xenon (Xe), titanium (Ti), zirconium (Zr), aluminum (Al), silicon (Si), oxygen (O2), silicon and oxygen, or other types of ion implantation techniques and materials, creates regions of material that are electrically insulating and may be referred to as insulating metal oxide (“IMO”). Depending on the type of CMO material selected, its thickness, and processing conditions, the IMO regions can have an amorphous structure that is electrically insulating or a crystalline structure that is electrically insulating. The described techniques enables the formation of memories with small feature sizes and matrices of top and bottom electrodes that are electrically insulated from one another with a greater degree of fabrication reliability and decreased defect or degradation rates. The described fabrication techniques may be varied and are not limited to the examples provided.

In some embodiments, an IMO structure, such as an electrolytic tunnel barrier, and one or more mixed valence conductive oxide structures (e.g., one or more layers of a conductive oxide material) need not operate in a silicon substrate, and, therefore, can be fabricated above circuitry being used for other purposes. That is, the active circuitry portion can be fabricated front-end-of-the-line (“FEOL”) on a substrate (e.g., a Silicon (Si) wafer, Si die, or other semiconductor substrate) and one or more layers of two-terminal cross-point memory arrays that include the non-volatile memory elements can be fabricated back-end-of-the-line (“BEOL”) directly on top of the substrate and electrically coupled with the active circuitry in the FEOL layer using an inter-level interconnect structure, at least a portion of which, is also fabricated FEOL. Manufacturing process for forming FEOL circuitry on a semiconductor wafer followed by subsequent BEOL vertically memory fabrication above the FEOL circuitry is described in pending U.S. patent application Ser. No. 12/454,322, filed May 15, 2009, and titled “Device Fabrication”, already incorporated herein by reference. Further, a two-terminal memory element can be arranged as a cross-point such that one terminal is electrically coupled with an X-direction line (or an “X-line”) and the other terminal is electrically coupled with a Y-direction line (or a “Y-line”). A third dimensional memory can include multiple memory elements vertically stacked upon one another, sometimes sharing X-direction and Y-direction lines in a layer of memory, and sometimes having isolated lines. When a first write voltage, VW1, is applied across the memory element (e.g., by applying ½ VW1 to the X-direction line and ½−VW1 to the Y-direction line), the memory element can switch to a low resistive state. When a second write voltage, VW2, is applied across the memory element (e.g., by applying ½ VW2 to the X-direction line and ½−VW2 to the Y-direction line), the memory element can switch to a high resistive state. Memory elements using electrolytic tunnel barriers and mixed valence conductive oxides can have VW1 opposite in polarity from VW2.

FIG. 2illustrates a portion of a memory cell including a memory element in accordance with various embodiments. As shown, a portion200of a memory cell201includes an electrode209(e.g., a top electrode), a memory element205, and an electrode208(e.g., a bottom electrode). Memory element205includes, but is not limited to, a layer of insulating metal oxide (IMO)202formed on multiple layers of conductive metal oxide (CMO), which is depicted as including a layer of CMO Type 2 Material204formed on a layer of CMO Type 1 material206. In this example, the materials in layer of CMO Type 2 Material204and layer of CMO Type 1 material206have different compositions. Layers of CMO provide mobile oxygen ions207for ion transport225when various write voltage potentials are applied to electrodes208and209(e.g., from an external source) and those potentials generate an electric field EW227within the layers202,204, and206during write operations. Here, mobile oxygen ions (e.g., O2−) 207 will be denoted as O−. Transport225of the mobile oxygen ions207is in a direction opposite that of the generated electric field EW227. A magnitude and direction of the electric field EW227will depend on the magnitude and polarities of the write voltage potentials applied to electrodes208and209.

Further, layer of CMO Type 2 Material204and a portion of layer of CMO Type 1 material206include an ion-implanted material. The ion-implanted material is disposed within the crystalline structures of the different compositions of layers204and206to form an ion obstruction barrier210. Ion obstruction barrier210is configured to inhibit transport or diffusion of other mobile ions203aand203b(e.g., a cation or positively charged “+” ion) when a data operations voltage (e.g., a write voltage or a read voltage) is not being applied across electrodes208and209, such that there is no electric field being generated that could cause transport of the other mobile ions203aand203b. Note, the other mobile ions203aand203bare not the mobile oxygen ions207and the mobile oxygen ions207are only transported225when a write voltage is applied across electrodes (208,209) and electric field EW227is generated. Examples of other mobile ions203aand203binclude metal ions and other like ions that can diffuse or otherwise transfer between IMO202and layers of CMO Type 2204and CMO Type 1206. Note also, that mobile oxygen ions207are not transported225when a read voltage is applied across electrodes (208,209). In some embodiments, memory element205constitutes a portion201of a two-terminal re-writeable non-volatile memory cell.

In view of the foregoing, the structures and/or functionalities of layers of CMO Type 2204and CMO Type 1206of different compositions can facilitate implementation of ion obstruction barrier210(and structures and/or functionalities thereof). In accordance with various embodiments, ion obstruction barrier210can provide for enhanced memory effect for re-writeable nonvolatile memory cells, enhanced cycling endurance over a number of write and erase cycles, and/or the stabilization of current magnitudes over the number of write and erase cycles. Examples of enhanced performance characteristics are depicted inFIGS. 3A and 3B.

FIG. 3Ais a diagram300illustrating current magnitudes generated during program and erase cycles of a memory cell including portion200of a memory cell ofFIG. 2, according to some embodiments. The current magnitudes range between a first magnitude310associated with an erase operation and a second magnitude312associated with a programming operation. Over a number of program-erase cycles320, ion obstruction barrier210and/or the layers of CMO Type 2204and CMO Type 1206of different compositions facilitate stabilization of the current magnitudes, thereby reducing or eliminating current drift. In particular, ion obstruction barrier210provides for an average current magnitude302between magnitudes310and312that remains stable and is substantially the same over number of program-erase cycles320. Stabilized current magnitudes obviate the necessity for additional circuitry (e.g., FEOL sense amp circuitry) and resources to accommodate current drift denoted by a current magnitude304that decreases over time as a function of the number of program-erase cycles320. Also, the difference301between magnitudes310and312remains relatively constant from a first number of cycles320to a second number of cycles322. According to some embodiments, the difference301represents a greater amount of current (or current density) available to flow through portion200of a memory cell ofFIG. 2over a number of cycles324that otherwise might not be available. A greater write or erase current facilitates increases in thickness in a tunnel oxide (not shown), which, in turn, enables miniaturization or scaled down dimensions of a memory cell.

Further, ion obstruction barrier210and/or the layers of CMO Type 2204and CMO Type 1206cooperate to enhance the number of program and erase cycles to extend over a first number of cycles320and a second number of cycles322. For example, first number of cycles320can represent 10,000 cycles (10K), whereas a memory cell including portion200of the memory cell depicted inFIG. 2can achieve a number of cycles324that is 100,000 cycles (100K). In some cases, number of cycles324can range from about 100,000 (100K) to about 1,000,000 cycles (1000K), or greater.

FIG. 3Bis a diagram350illustrating an example of the on/off ratios for a memory cell including portion200of a memory cell ofFIG. 2, according to some embodiments. As shown, ion obstruction barrier210and/or the layers of CMO Type 2204and CMO Type 1206of different compositions can establish an on/off ratio352of about two orders of magnitude (102). More preferably, an on/off ratio355of about three orders of magnitude (103) or greater357is desired. The on-off ratio is the ratio between the currents when a memory cell including portion200ofFIG. 2is switched on or switched off, thereby establishing a non-volatile memory effect. Another way of stating the on-off ratio is to divide a resistance value of a low resistance state (e.g., a high current erased state) by a resistance value of the highest resistant state (e.g., a low current programmed state). For the same magnitude of read voltage applied across the electrodes (208,209) the read current will be low when the memory element205stores data in the programmed high resistance state and the read current will be higher when the memory element205stores data in the erased low resistance state. In that it is easier to measure or sense read current than it is to measure or sense resistance, on/off ratios based on current are typically used because the magnitude of the current is a function of the resistance value stored in the memory element205. The memory effect of a memory cell including memory element205can increase to greater than about 10 to about 100 times than otherwise might be the case when either ion obstruction barrier210or the layers of CMO Type 2204and CMO206of different compositions, or both, are absent. According to some alternate embodiments, on/off ratio352can be greater than three orders of magnitude. In view of the above, ion obstruction barrier210and/or the layers of CMO Type 2204and CMO Type 1206ofFIG. 2can cooperate to enhance the reliability of memory cells that include memory element205.

Returning back toFIG. 2, a grain orientation of the material of an electrode, such as electrode208can facilitate the crystalline structures of layer of CMO Type 1 material206and/or layer of CMO Type 2 Material204, according to some embodiments. Electrodes208and209can be formed from an electrically conductive material, such as a metal (e.g., a noble metal or a combination of noble metals). In a specific example, electrodes208and209can be formed of platinum (Pt) and may be deposited to a thickness of, for example, from about 50 Angstroms to about 1250 Angstroms. In other embodiments, electrodes208and209can be formed from a conductive metal oxide (CMO), a doped CMO, or from a metal or metal alloy that has been completely or partially oxidized. Actual thicknesses for electrodes208and209will be application specific and are not limited to the examples set forth herein.

IMO material202can include a material to form a tunnel oxide-based structure or an electrolytic tunnel barrier. In various embodiments, the IMO202can include but is not limited to a material for implementing a tunnel barrier layer is also an electrolyte that is permeable to the mobile oxygen ions207at voltages for write operations. Suitable materials for IMO202include but are not limited to one or more of the following: high-k dielectric materials, rare earth oxides, rare earth metal oxides, yttria-stabilized zirconium (YSZ), zirconia (ZrOX), zirconium oxygen nitride (ZrOxNy), yttrium oxide (YOX), erbium oxide (ErOX), gadolinium oxide (GdOX), lanthanum aluminum oxide (LaAlOX), hafnium oxide (HfOX), aluminum oxide (AlOx), silicon oxide (SiOx), cerium oxide (CeOX), gadolinium doped cerium oxide (CeOX), titanium oxide (TiOx), tantalum oxide (TaOx), and equivalent materials. IMO material202can have a thickness of approximately 50 Angstroms or less. Actual IMO thickness will be application specific and can be a function of the material selected and voltage magnitudes chosen for data operations to memory cells (e.g., read voltages, write voltages, program and erase voltages) that facilitate electron tunneling.

CMO Type 1 material206and CMO Type 2 material204can include different compositions of conductive metal oxide (CMO) or other perovskite material that typically exhibits memory characteristics. CMOs can be formed from a variety of perovskite materials and may include a mixed valence conductive oxide having substantially mixed crystalline or polycrystalline perovskite structure. Perovskite materials, such as CMO, may include two or more metals being selected from a group of transition metals, alkaline earth metals and rare earth metals. Examples of other perovskite materials may include, but are not limited to, manganites, titanates (e.g., strontium titanate STO, reduced STO), zirconates (SZO:Cr, CNO:Cr, TaO:Cr), LSCO, and high Tc superconductors (e.g., YBCO). Other examples of perovskites include but are not limited to PrCaMnOX(PCMO), LaNiOX(LNO), SrRuOX(SRO), LaSrCrOX(LSCrO), LaCaMnOX(LCMO), LaSrCaMnOX(LSCMO), LaSrMnOX(LSMO), LaSrCoOX(LSCoO), and LaSrFeOX(LSFeO), where x is nominally 3 for perovskites (e.g., x≦3 for perovskites) or the one or more CMO layers can be a conductive binary metal oxide structure comprised of a conductive binary metal oxide having the form AXOY, where A represents a metal and O represents oxygen. The conductive binary oxide material may optionally be doped (e.g., with niobium Nb, fluorine F, and/or nitrogen N) to obtain the desired conductive properties for a CMO. Other suitable CMO materials are described in U.S. patent application Ser. No. 12/653,836, filed Dec. 18, 2009, and published as U.S. publication no. 2010/0157658, and titled “Conductive Metal Oxide Structures In Non-Volatile Re-Writable Memory Devices”, already incorporated herein by reference. Layers of CMO Type 1 material206and CMO Type 2 material204can include two or more layers of CMO materials, at least two of which comprise CMO material of different compositions. Regardless, a CMO layer adjacent to and in contact with IMO layer202is thinner than other CMO layers. For example, layer of CMO Type 2 material204, which is adjacent layer of IMO202, can be formed to have a thickness between about 10% and about 20% of the thickness of CMO Type 1 material206, according to some embodiments.

According to various embodiments, memory element205is a resistive memory element configured to maintain a resistive state representative of a data stored therein. Stored data is retained in the absence of electrical power (i.e., is non-volatile). As used herein, the term “discrete memory element” can refer, at least in some examples, to a memory cell having a structure that includes no more than memory element205, and electrodes208and209. For example, a discrete memory element can be a gateless two-terminal device. Examples of a non-discrete memory cell and/or memory element include but are not limited to one or more transistors or diodes configured to implement a selection device (SD) such as a non-ohmic device (NOD) or the like. Typical variations include 1T1R, 2T1R, 1D1R, and 2D1R devices where one (1T) or two (2T) transistors or one (1D) or two (2D) diodes are included in the memory cell and electrically coupled with the memory element.

Memory element205can as a discrete memory element constitute a memory cell, according to at least some embodiments. In some examples, a programmed state is a high resistance state (e.g., a logic “0”), and an erased state is a low resistance state (e.g., a logic “1”), thereby establishing a magnitude of an access current that is relatively lower for the programmed state and is relatively higher for the erased state. When only two resistive states are stored, the memory cell can be referred to as a single level cell (SLC). A range of resistive states (e.g., two-bits as “00”, “01”, “10”, or “11”) can represent more than two memory states (i.e., multiple bits per memory cell can be stored as a multi-level cell—MLC).

Note that in alternate embodiments, other materials and layers can be disposed between those structures shown inFIG. 2. While the term “bottom electrode” can refer to an electrode that is formed closer to a substrate (not shown) than other electrodes, the description of structures and techniques relating to a bottom electrode can apply to a top electrode.

FIG. 4illustrates a memory element in accordance with some embodiments. As shown, a memory element400includes, but is not limited to, including a layer of insulating metal oxide (IMO)402formed on multiple layers of conductive metal oxide (CMO), which is depicted as including a layer of CMO Type 2 Material404formed on a layer of CMO Type 1 material406. Memory element400is formed on electrode408. In this example, the materials in layer of CMO Type 2 Material404and layer of CMO Type 1 material406have different compositions. At least one of layer of CMO Type 1 material406and layer of CMO Type 2 Material404can include an atomic layer deposited (ALD) layer of material or a plasma enhanced atomic layer deposited (PEALD) layer of material. Here, deposition of one or more of the CMO layers may occur in whole or in part using ALD or PEALD. In other embodiments, one or more of the CMO layers may be deposited in whole or in part using a nano-deposition process. Note that the layers of CMO provide mobile oxygen ions407for ion transport when various electric fields are applied across electrodes408and409(e.g., from an external source as described in regard toFIG. 2). Further, layer of CMO Type 2 Material404and a portion of layer of CMO Type 1 material406include an ion-implanted material. The ion-implanted material is disposed within the crystalline structures of the different compositions of layers404and406to form an ion obstruction barrier.

CMO Type 1 material406can be formed from relatively large-sized grains in relatively crystalline structures, whereas CMO Type 2 material404can be formed from relatively fine-sized grains in relatively irregular crystalline structures. According to various embodiments, layer of CMO Type 1 material406is formed with grains440bhaving an orientation414and a grain size 442. CMO Type 2 material404is deposited as a layer in which grains440aadopt similar grain orientations414and grain dimensions or sizes442from layer of CMO Type 1 material406(e.g., grain size and grain orientation are replicated or mimicked in CMO Type 2 material404). Here, replication of the grain size and/or grain orientation in CMO Type 2 material404may be identical to or substantially identical to the grain size and/or grain orientation in CMO Type 1 material406. In some embodiments, CMO Type 2 material404may be formed first followed by CMO Type 1 material406being formed on layer404. The replication of the grain size and/or grain orientation in CMO Type 1 material406may be identical to or substantially identical to the grain size and/or grain orientation in CMO Type 2 material404(seeFIG. 9B) upon which layer406is formed. Therefore, replication is from layer404to layer406. According to some embodiments, layer of CMO Type 1 material406is formed to have a thickness420from about 50 to about 250 Angstroms, and layer of CMO Type 2 material404is formed to have a thickness422from about 5 to about 25 Angstroms. As another example, layer of CMO Type 2 material404can be formed to have a thickness422from about 10 to about 20 Angstroms. IMO402has a thickness432that is approximately 50 Angstroms or less. For example, thickness432can be 27 Angstroms. Actual thicknesses for 420 and 422 will be application specific and are not limited to the examples set forth herein. Although IMO402is depicted not connected with CMO Type 2 material404for purposes of illustration, in actuality an upper surface440tand a bottom surface402bwill be in direct contact with each other.

Although only one layer of IMO material402is depicted, the present invention is not limited to a single layer of IMO and additional IMO layers may be formed in contact with one another and having a combined thickness that is approximately 50 Angstroms or less. A memory element including multiple IMO layers (i.e., at least two IMO layers) their composition, and formation is described in pending U.S. patent application Ser. No. 13/250,772, filed Sep. 30, 2011, and titled “Memory Device Using Multiple Tunnel Oxide Layers”, already incorporated herein by reference.

FIGS. 5A to 5Cillustrate various multi-layer CMO structures having different compositions, according to various embodiments. Layers of CMO Type 1 material506and CMO Type 2 material504include different compositions, such as different elements, different stoichiometries, and different concentrations of oxygen ions.FIG. 5Adepicts a dual-layers CMO structure500whereby layers of CMO Type 1 material506and CMO Type 2 material504have different compositions due to implementations of different elements (e.g., Element 1 and Element 2).FIG. 5Bdepicts a dual-layers CMO structure520whereby layers of CMO Type 1 material506and CMO Type 2 material504have different compositions due to implementations of different stoichiometries (e.g., Stoichiometry 1 and Stoichiometry 2), whereas the compositions have identical elements.FIG. 5Cdepicts a dual-layers CMO structure540whereby layers of CMO Type 1 material506and CMO Type 2 material504have different compositions due to implementations of different concentrations or diffusion rates of mobile oxygen ions (e.g., O−concentration 1 and O−concentration 2), whereas the compositions have identical elements and identical stoichiometries.

FIG. 6is a diagram600depicting formation of an ion obstruction barrier for a two-terminal resistive memory element, according to various embodiments. While not shown, an electrode can be formed upon which a layer of CMO Type 1 material606is formed. Layer of CMO Type 1 material606can serve as a reservoir for mobile oxygen ions607. Layer of CMO Type 2 material604can be formed to have similar crystalline structures, including similar orientations and/or dimensions to layer of CMO Type 1 material606. Next, a mask609can optionally be used to expose portions of layer of CMO Type 2 material604to the environs. One or more elements601can be implanted via ion implantation techniques at an implantation depth D through layer of CMO Type 2 material604to reach a portion of layer of CMO Type 1 material606to form an “active region” as ion obstruction barrier610. Examples of elements601include argon and other suitable elements. Ion obstruction barrier610is configured to inhibit transport or diffusion of other mobile ions (not shown) between layer of CMO Type 1 material606and a layer of insulating metal oxide (IMO), which is not shown. The term active region, according to some embodiments, can refer to an ion obstruction barrier. Other mobile ions may refer to ions other than the mobile oxygen ions607, such as metal ions, for example.

FIG. 7Aillustrates a configuration including a memory cell in accordance with various embodiments. In configuration700, a memory cell701includes a top electrode702, a memory element704, and a bottom electrode706, which can be formed on an optional support layer708. Support layer708can influence the structure and/or functionality of IMO material718. In some embodiments, support layer708is configured to facilitate formation of IMO material718with a uniform thickness or a substantially uniform thickness. Support layer708can serve as a “template” (e.g., a growth template) to promote the formation of bottom electrode706in a manner that propagates the smoothness of a substantially planar upper surface708tof support layer708to an upper surface706tof bottom electrode706, thereby providing for a smooth surface or a substantially smooth upper surface706tof bottom electrode706to establish a relatively smooth interface between CMO 2 Material720band IMO material718, or other layers of the memory element704. Memory cell701also includes portions of array line722and array line724as terminals. Array line722and array line724may be the conductive array lines of a cross-point array with memory cell701positioned between a cross-point of its respective pair of conductive array lines (722,724) and electrically in series with its respective pair of conductive array lines. In configuration700, support layer708is made from an electrically conductive material such that a current I can flow thorough the memory cell701and memory element704during data operations (e.g., a read current) on the memory element704when appropriate voltage potentials (e.g., write voltages or read voltages) are applied to nodes728and730. As such, memory cell701and memory element704can be two-terminal memory structures. Memory element704is shown to include, but is not limited to, structures710aand710b. Memory element structure710aincludes a first substructure including IMO material718, upon which a second substructure including multiple layers of CMO materials720aand720bis formed. Memory element structure710bincludes a first substructure including multiple layers of CMO materials720aand720b, upon which a second substructure including IMO material718is formed. Memory element704can include different and/or additional structures. Multiple layers of CMO materials720aand720bin substructures710aand710binclude ion obstruction barriers (not shown) as described above.

FIG. 7Billustrates another configuration including a memory cell in accordance with various embodiments. In configuration750, a memory cell701includes a top electrode702, a memory element704, and a bottom electrode706, a conductive structure754(e.g., an array line) which can be formed on an optional support layer758. Support layer758can influence the structure and/or functionality of IMO material718. In some embodiments, support layer758is configured to facilitate formation of IMO material718with a uniform thickness or a substantially uniform thickness. Support layer758can serve as a “template” (e.g., a growth template) to promote the formation of conductive structure754and subsequent layers formed above the conductive structure754in a manner that propagates the smoothness of a substantially planar upper surface758tof support layer708to upper surfaces754tand706tof the conductive structure754and bottom electrode706, respectively, thereby providing for a smooth surface or a substantially smooth upper surface706tof bottom electrode706to establish a relatively smooth interface between CMO 2 Material720band IMO material718, or other layers of memory element704. Memory cell701also includes portions of array line722and array line724as terminals. Array line722and array line724may be the conductive array lines of a cross-point array with memory cell701positioned between a cross-point of its respective pair of conductive array lines (722,724) and electrically in series with its respective pair of conductive array lines. In configuration700, support layer758is made from an electrically non-conductive material. Here, a current I can flow thorough the memory cell701and memory element704during data operations (e.g., a read current) on the memory element704when appropriate voltage potentials (e.g., write voltages or read voltages) are applied to nodes760and762. Unlike, configuration700ofFIG. 7A, current I does not flow through support layer758because it is electrically non-conductive. As such, memory cell701and memory element704can be two-terminal memory structures. Memory element704is shown to include, but is not limited to, structures710aand710b. Memory element structure710aincludes a first substructure including IMO material718, upon which a second substructure including multiple layers of CMO materials720aand720bis formed. Memory element structure710bincludes a first substructure including multiple layers of CMO materials720aand720b, upon which a second substructure including IMO material718is formed. Memory element704can include different and/or additional structures. Multiple layers of CMO materials720aand720bin substructures710aand710binclude ion obstruction barriers (not shown) as described above.

FIG. 8depicts an example of arrayed memory cells according to various embodiments. In this example, a memory cell800includes a memory element802, which, in turn, includes dual-layered CMO material870including different compositions and IMO material880. Memory cell800further includes two terminals854and856. Terminals854and856can be electrically coupled with or can be formed as electrodes812and816. The electrodes (812,816) can be made from an electrically conductive material including but not limited to, platinum (Pt), gold (Au), silver (Ag), iridium (Ir), iridium oxide (IrOX), ruthenium (Ru), palladium (Pd), aluminum (Al), alloys of those materials, combinations of those materials, and the like. Optionally, memory cell800can include a support layer818, upon which electrode816, or some other layer is formed. As described above in regards toFIGS. 7A and 7B, the support layer818may or may not be electrically conductive.

In at least some embodiments, memory cell800can include optionally a selection device (SD) (e.g., a NOD)814, which, in turn, can be formed on the memory element802(e.g., either above or below memory element802). SD814can be a “metal-insulator-metal” (MIM) type structure that includes one or more layers of electronically insulating material that are in contact with one another and sandwiched between metal layers (e.g., electrodes), or SD814can be a non-linear device (e.g., one or more diodes or one or more transistors). U.S. Pat. No. 7,995,371, issued on Aug. 9, 2011, and titled “Threshold Device For A Memory Array and U.S. Pat. No. 7,884,349, issued on Feb. 8, 2011, and titled “Selection Device for Re-Writable Memory”, both of which are already incorporated herein by reference. Memory cell800can be formed between conductive array lines, such as array lines892and894. Thus, memory cell800can be formed in an array with other memory cells, and the array can be a cross-point array899with groups of conductive array lines892and894. For example, array line892acan be electrically coupled with the electrode812of the memory cells800and/or may be in contact with a surface of the electrode812. Array line894acan be electrically coupled via support layer818with the electrode816of the memory cells800and/or may be in contact via support layer818with a surface of electrode816.

FIG. 9Adepicts an example of a memory element oriented at an angle with a substrate, according to various embodiments. Diagram900depicts a memory element903including a layer of insulating metal oxide (IMO)902formed on multiple layers of conductive metal oxide (CMO), which is depicted as including a layer of CMO Type 2 Material904formed on a layer of CMO Type 1 material906. In this example, the materials in layer of CMO Type 2 Material904and layer of CMO Type 1 material906have different compositions. Layer of CMO Type 1 material906is formed on electrode908. Further, multiple layers of CMO Type 1 material906and CMO Type 2 Material904include an ion obstruction barrier910. In this example, memory element903is formed in a trench901with surfaces of layer of CMO Type 2 Material904and layer of IMO902being oriented at an angle920relative to substrate surface922(e.g., a FEOL silicon substrate with active circuitry). Structures (e.g., memory element903) above an upper surface922scan be formed BEOL above substrate922. Other orientations are possible.

FIG. 9Bdepicts another example of a memory element oriented at an angle with a substrate, according to various embodiments. Diagram950depicts a memory element953including multiple layers of conductive metal oxide (CMO), which are depicted as including a layer of CMO Type 1 Material906formed on a layer of CMO Type 2 material904, with the layer904formed on a layer of insulating metal oxide (IMO)902. In this example, the materials in layer of CMO Type 2 Material904and layer of CMO Type 1 material906have different compositions. Layer of insulating metal oxide (IMO)902is formed on electrode908. Further, multiple layers of CMO Type 1 material906and CMO Type 2 Material904include an ion obstruction barrier910. In this example, memory element953is formed in a trench951with surfaces of layer of CMO Type 2 Material904and layer of IMO902being oriented at an angle920relative to substrate surface922(e.g., a FEOL silicon substrate with active circuitry). Structures (e.g., memory element953) above an upper surface922scan be formed BEOL above substrate922. Other orientations are possible.

Trenches901and951ofFIGS. 9A and 9Bcan be implemented in a vertical cross-point array configuration as described in pending U.S. patent application Ser. No. 13/210,292, Filed Aug. 15, 2011, and titled “Vertical Cross-Point Arrays For Ultra-High-Density Memory Applications”, already incorporated by reference herein. Electrode908may be a common electrode shared by at least one other memory element903(e.g., on a common word line—WL or common bit line—BL).

FIG. 10graphically depicts one example of a non-linear I-V characteristic1000for a discrete re-writeable non-volatile two-terminal resistive memory element (e.g.,205,704,802,903,953) having integral selectivity due to its non-linear I-V characteristics and the non-linear I-V characteristic is maintained regardless of the value of the data stored in the memory cell, that is the I-V characteristic of the memory element does not change from non-linear to linear as a function of the resistive state stored in the memory element. Therefore, the non-linear I-V characteristic of the memory element is non-linear for all values of stored data (e.g., resistive states). Voltage V applied across the memory element is plotted on the Y-axis and current density J through the memory element is plotted on the X-axis. Here, current through the memory element is a non-linear function of the applied voltage across the memory element. Accordingly, when voltages for data operations (e.g., read and write voltages) are applied across the memory element, current flow through the memory element does not significantly increase until after a voltage magnitude of about 2.0V (e.g., at ≈0.2 A/cm2) is reached (e.g., a read voltage of about 2.0V across the memory element). An approximate doubling of the voltage magnitude to about 4.0V does not double the current flow and results in a current flow of ≈0.3 A/cm2. The graph depicted is only an example and actual non-linear I-V characteristics will be application dependent and will depend on factors including but not limited to an area of the memory element (e.g., area determines the current density J) and the thin-film materials used in the memory element, just to name a few. The area of the memory element will be application dependent. Here, the non-linear I-V characteristic of the discrete memory element applies to both positive and negative values of applied voltage as depicted by the non-linear I-V curves in the two quadrants of the non-linear I-V characteristic1000. One advantage of a discrete re-writeable non-volatile two-terminal resistive memory element that has integral selectivity due to a non-linear I-V characteristic is that when the memory element is half-selected (e.g., one-half of the magnitude of a read voltage or a write voltage is applied across the memory element) during a data operation to a selected memory cell(s), the non-linear I-V characteristic is operative as an integral quasi-selection device and current flow through the memory element is reduced compared to a memory cell with a linear I-V characteristic. Therefore, a non-linear I-V characteristic can reduce data disturbs to the value of the resistive state stored in the memory element when the memory element is un-selected or is half-selected. In other embodiments, the memory element has a non-linear I-V characteristic for some values of the resistive state stored in the memory element and a linear I-V characteristic for other values of the resistive state stored in the memory element.

Thin-film layers for the CMO, IMO, electrodes, or other layers for the memory element (ME) and selection device (SD) described herein can be formed using a variety of microelectronics thin-film layer deposition techniques used for nanometer and sub-nanometer device fabrication, examples of which include, but are not limited to, physical vapor deposition (PVD), sputtering, reactive sputtering, co-sputtering, chemical vapor deposition (CVD), plasma enhanced chemical vapor deposition (PECVD), nano-deposition, atomic layer deposition (ALD), plasma enhanced atomic layer deposition (PEALD), gas cluster ion beam deposition (GCIB), combinations of those techniques, and the like, just to name a few. Further, some or all of the electrode structures can be formed using a plating process, such as electroless plating, for example.

For ALD or PEALD, a thin-film layer, such as an IMO layer and/or a CMO layer can be deposited in whole using ALD or PEALD, or can be deposited in part using ALD or PEALD and some other process, such as PVD or CVD can be used to in conjunction with the ALD or PEALD to deposit the IMO and/or CMO. Therefore, the CMO layer(s) can be deposited in whole or in part using ALD or PEALD and the IMO layers can be deposited in whole or in part using ALD or PEALD. Doping of one or more of the IMO layers and/or doping of the one or more layers of CMO can also be accomplished using the above deposition techniques or combination of those techniques. Doping can occur insitu as part of the deposition process (e.g., doping ceria oxide with gadolinium during the deposition of the ceria oxide).

In some embodiments, some or all of the IMO layers or one or more of the CMO layers are deposited insitu without a chamber break. That is, if there are three layers of IMO, than some or all of those three layers can be deposited insitu in the same deposition chamber. Similarly, if there are multiple layers of CMO, then some or all of those layers can be deposited insitu in the same deposition chamber. Variations in stoichiometry in general or as a function of layer thickness can also be accomplished using the above deposition techniques and the deposition can be accomplished insitu.

The foregoing description, for purposes of explanation, uses specific nomenclature to provide a thorough understanding of the invention. However, it will be apparent to one skilled in the art that specific details are not required in order to practice the invention. In fact, this description should not be read to limit any feature or aspect of the present invention to any embodiment; rather features and aspects of one embodiment can readily be interchanged with other embodiments. Notably, not every benefit described herein need be realized by each embodiment of the present invention; rather any specific embodiment can provide one or more of the advantages discussed above. In the claims, elements and/or operations do not imply any particular order of operation, unless explicitly stated in the claims. It is intended that the following claims and their equivalents define the scope of the invention.