Memory device with adjustable threshold voltage

Abstract

A device includes a first electrode comprising a first electrode material of a type that is electrically insulated if oxidized by an oxidizing agent, a second electrode comprising a second electrode material of a type that is electrically conductive if oxidized by the oxidizing agent, a threshold switch layer between the first electrode and the second electrode, the threshold switch layer includes a material switchable from an electrically insulated state to a conductive state by a voltage across a threshold voltage between the first electrode and the second electrode, a first electrode interface between the threshold switch layer and the first electrode, a second electrode interface between the threshold switch layer and the second electrode, wherein the device comprises an oxidant adapted to be movable between the first electrode and the second electrode, the threshold switch layer providing a channel for moving the oxidant between the first electrode and the second electrode.

Description

Technical Field

[0001] This invention relates to the field of memory technology, and more specifically, to memory-level storage devices utilizing chalcogenide materials. Background Technology

[0002] Memory technology plays a crucial role in the performance and efficiency of modern computing systems. As applications become increasingly data-intensive and demand the rapid processing of large datasets, the requirements for memory solutions become more stringent. Modern computer architectures utilize layered memory structures that combine different types of memory technologies to optimize performance and storage capacity. Dynamic Random Access Memory (DRAM), with its fast access time of approximately 10 nanoseconds, enables rapid data retrieval and processing, making it the primary working memory. In contrast, NAND memory offers larger capacities but slower access times of approximately 100 microseconds for non-volatile storage.

[0003] Despite significant progress over the years, a considerable performance gap remains between volatile memories such as DRAM and non-volatile memory solutions such as NAND flash memory. This gap poses a challenge to achieving seamless system performance, as the slower access times of non-volatile memories can become a bottleneck for data-intensive applications that demand speed and persistence. The need to bridge this gap has spurred interest in developing new memory technologies that can provide the high speed of DRAM while offering the non-volatility and cost advantages of NAND flash memory.

[0004] Storage-class memory (SCM) is a promising memory technology designed to fill this gap. SCM aims to provide a balance of performance, capacity, and endurance, effectively integrating into the existing memory hierarchy between DRAM and traditional memory solutions. Several approaches to realizing SCM are being explored, including the integration of new materials and device architectures that support faster access times and higher data densities.

[0005] Currently, a promising candidate for this role is phase-change memory (PCM) integrated into a crosspoint array (reducing cost by minimizing the footprint of individual memory cells). However, for such an array to function properly, highly nonlinear selector elements (so-called 1S1R cells) are needed in series with the PCM memory elements to suppress the inevitable leakage current through the half-select cells.

[0006] For this purpose, a two-way threshold switch (OTS) was used. For example... Figure 9 As shown, a current-voltage plot of a typical bidirectional threshold switch (OTS) including a chalcogenide layer material is illustrated. This plot demonstrates the highly nonlinear switching behavior of the OTS when the applied voltage exceeds a certain threshold voltage (V).thres When the applied voltage drops to a certain holding voltage (V), the current flowing through the device will suddenly increase. hold When the current through the device drops below a certain threshold, the current decreases abruptly. This nonlinear characteristic allows the OTS to act as a selector device connected in series with memory elements, suppressing leakage current through unselected cells in a crosspoint memory array. Typically, this selector role is played by a chalcogenide-based bidirectional threshold switch (OTS) device.

[0007] However, the development of this type of memory system faces several challenges. One of the main problems with traditional 1S1R memory (which includes an OTS layer stacked on top of a PCM layer) is related to the high aspect ratio of the memory cells. Specifically, the PCM layer is typically much thicker than the OTS layer. The high aspect ratio structure within these cells complicates the manufacturing process, makes precise patterning difficult, and increases manufacturing costs. In fact, variations in layer thickness in some memory cell designs contribute to these manufacturing complexities.

[0008] Advances in materials science and manufacturing technologies continue to address some of these challenges, but obstacles remain in achieving the optimal balance between performance, scalability, and cost-effectiveness. Therefore, further development of memory technologies is still needed to overcome these limitations and fully realize the potential of advanced memory solutions such as SCMs. Summary of the Invention

[0009] The purpose of embodiments of the present invention is to provide a good device, a good memory element including the device, a good memory device including the memory element, and a good programming and reading method applicable to the memory element.

[0010] The above objectives are achieved by the device and method according to the present invention.

[0011] One advantage of this invention is that it can provide a device with an adjustable threshold voltage, which enables online tuning of the threshold voltage.

[0012] One advantage of embodiments of the present invention is that the need for a thick phase-change memory layer can be eliminated, thereby reducing the high aspect ratio and simplifying the patterning process.

[0013] One advantage of this invention is that the threshold switching layer can be used simultaneously as a selector and an oxidant exchange layer.

[0014] One advantage of this invention is that the memory function can be integrated at the interface between the threshold switch layer and the metal electrode, thereby reducing the complexity of the device.

[0015] One advantage of this invention is that, compared to existing solutions based on the conventional 1S1R cell structure, this device concept provides a lower-cost option for memory-class applications.

[0016] One advantage of embodiments of the present invention is that the proposed device structure can realize high-performance memory-class memory, bridging the performance gap in existing memory tiers. In fact, one advantage of embodiments of the present invention is that, compared to NAND flash memory, the high-speed non-volatile memory has shorter access times, and compared to DRAM, it has lower manufacturing complexity.

[0017] In a first aspect, the present invention relates to a device comprising:

[0018] a. A first electrode, comprising a first electrode material of the type that is electrically insulating if oxidized by an oxidizing agent.

[0019] b. A second electrode, comprising a second electrode material of the type that conducts electricity if oxidized by the oxidizing agent, and

[0020] c. A threshold switching layer between the first electrode and the second electrode, the threshold switching layer comprising, or being formed of, a material that can be switched from an electrically insulating state to a conductive state by a voltage across a threshold voltage between the first electrode and the second electrode, and

[0021] d. The first electrode interface between the threshold switch layer and the first electrode, and the second electrode interface between the threshold switch layer and the second electrode.

[0022] The device includes an oxidant adapted to move between a first electrode and a second electrode, and a threshold switching layer provides a channel or path for moving the oxidant between the first electrode and the second electrode.

[0023] The first electrode interface between the threshold switch layer and the first electrode can be an interface where the first electrode faces or contacts the threshold switch layer. The second electrode interface between the threshold switch layer and the second electrode can be an interface where the second electrode faces or contacts the threshold switch layer.

[0024] Typically, the device is arranged such that current moving between the first and second electrodes flows through a threshold switching layer. Typically, the device is arranged such that current moving between the first and second electrodes flows through the first electrode interface. Typically, the device is arranged such that current moving between the first and second electrodes flows through the second electrode interface.

[0025] In embodiments, the first electrode interface is formed of, or substantially composed of, the first electrode material. Specifically, the first electrode interface preferably does not substantially contain electrode material that would remain conductive if oxidized by an oxidizing agent. In embodiments, a first electrode interface comprising oxidized first electrode material means that the first electrode includes an oxidized interface layer at the first electrode interface, the oxidized interface layer comprising or being formed of the oxidized first electrode material, the oxidized interface layer having a thickness of at least 0.3 nm, for example, from 0.3 nm to 10 nm, in the direction from the first electrode interface to the threshold switching layer. In these embodiments, the first electrode interface may include an oxidized interface layer. The oxidized interface layer comprising oxidized first electrode material at the first electrode interface is typically electrically insulating.

[0026] In embodiments, a first electrode interface comprising a first electrode material oxidized by an oxidant means that the first electrode interface comprises a substantially continuous or uniform layer of the oxidized first electrode material. One advantage of these embodiments is that the current flowing between the first electrode and the threshold switch layer efficiently passes through the oxidized first electrode material. In embodiments, the standard deviation of the thickness of the oxidized interface layer throughout the entire oxidized first electrode material is at most 50%, preferably at most 20%, of the thickness.

[0027] In embodiments, the second electrode interface is formed of, or substantially composed of, the second electrode material. Specifically, the second electrode interface preferably does not substantially contain electrode material that would become electrically insulating if oxidized by an oxidizing agent. In embodiments, a second electrode interface comprising oxidized second electrode material means that the second electrode includes an oxidized interface layer at the second electrode interface, which comprises or is formed of oxidized second electrode material, having a thickness of at least 0.3 nm, for example, from 0.3 nm to 10 nm, in the direction from the second electrode interface to the threshold switching layer. In these embodiments, the second electrode interface may include an oxidized interface layer. The oxidized interface layer comprising oxidized second electrode material at the second electrode interface is generally conductive.

[0028] In embodiments, a second electrode interface comprising a second electrode material oxidized by an oxidant means that the second electrode interface comprises a substantially continuous or uniform layer of oxidized second electrode material. An advantage of these embodiments is that the current flowing between the second electrode and the threshold switch layer efficiently passes through the oxidized second electrode material. In embodiments, the standard deviation of the thickness of the oxidized interface layer, spanning the entire oxidized second electrode material, is at most 50%, preferably at most 20%, of the thickness.

[0029] Devices incorporating an oxidant suitable for movement between a first electrode and a second electrode typically mean that the oxidant is located at a position from which it can move between the first and second electrodes. In embodiments, the oxidant is positioned along a channel between the first and second electrodes. In embodiments, the first electrode interface comprises the first electrode material oxidized by the oxidant, and / or the second electrode interface comprises the second electrode material oxidized by the oxidant. However, this is not necessary. In embodiments, the threshold switching layer comprises the first electrode material. In particular, the oxidant may be substantially entirely contained in the threshold switching layer immediately after fabrication. In some embodiments, the oxidant may be an ion of the material composition of the threshold switching layer.

[0030] In an embodiment, when the first electrode interface comprises a first electrode material oxidized by an oxidant, essentially the entire first electrode interface is oxidized by the oxidant. When the complete interface between the threshold switch layer and the first electrode interface is formed by the oxidized first electrode material, the only electrical path between the threshold switch layer and the first electrode is through the oxidized first electrode material. As a result, the threshold voltage can be effectively affected by the presence of the oxidized first electrode material.

[0031] In an embodiment, when the second electrode interface comprises a second electrode material oxidized by an oxidant, essentially the entire second electrode interface is oxidized by the oxidant. In another embodiment, when the complete interface between the threshold switch layer and the second electrode interface is formed by the oxidized second electrode material, the only electrical path between the threshold switch layer and the second electrode is through the oxidized second electrode material. As a result, the threshold voltage can be effectively affected by the presence of the oxidized second electrode material.

[0032] The voltage between the first and second electrodes is typically the voltage across at least the first electrode interface (including, if present, the oxidized interface layer containing oxidized first electrode material at the first electrode interface), the threshold switch layer, and the second electrode interface (including, if present, the oxidized interface layer containing oxidized second electrode material at the second electrode interface). Therefore, the magnitude of the device's threshold voltage typically depends on the resistance across the first electrode interface, the resistance across the threshold switch layer, and the resistance across the second electrode interface.

[0033] The second electrode material is conductive or exhibits metallic behavior, regardless of whether it is oxidized by an oxidizing agent.

[0034] However, the conductivity of the first electrode material is strongly dependent on whether it is oxidized by an oxidizing agent. If the first electrode material is not oxidized, it is conductive or exhibits metallic behavior. If the first electrode material is oxidized, it is electrically insulating.

[0035] Therefore, if the second electrode interface includes the second electrode material oxidized by the oxidant, the second electrode interface remains conductive. Similarly, if the first electrode material at the first electrode interface is substantially unoxidized by the oxidant, it is also conductive. This can result in a lower threshold voltage for the device, essentially determined solely by the inherent threshold voltage of the threshold switching layer itself.

[0036] However, if the first electrode interface comprises the first electrode material oxidized by an oxidant, such that the oxidized first electrode material forms at least one continuous (or: closed sub-layer), then the first electrode interface is electrically insulating. An electrically insulating interface effectively increases the voltage between the first and second electrodes required to switch the threshold switching layer, because this voltage must also be sufficient to generate a current through the electrically insulating interface. Therefore, this can result in a very high threshold voltage.

[0037] In one embodiment, the first electrode interface includes the first electrode material oxidized by the oxidant, while the second electrode interface substantially does not contain the second electrode material oxidized by the oxidant. In another embodiment, the second electrode interface includes the second electrode material oxidized by the oxidant, while the first electrode interface substantially does not contain the first electrode material oxidized by the oxidant. In yet another embodiment, the first electrode interface includes the first electrode material oxidized by the oxidant, while the second electrode interface includes the second electrode material oxidized by the oxidant. However, the magnitude of the threshold voltage may depend primarily or substantially only on the amount of oxidant at the first electrode interface. Because the oxidant can move between the first and second electrodes, it can be moved from the first electrode interface to the second electrode interface, and / or from the second electrode interface to the first electrode interface, thus tuning the threshold voltage. This capability allows the threshold voltage to be tuned online (e.g., in situ, in use, or in operation) by simply adjusting the polarity of the applied voltage used to move the oxidant between the electrodes. This feature is advantageous not only for memory storage purposes (where the adjustable voltage can represent data stored in the device) but also for other applications that require dynamic adjustment of the threshold voltage without physically altering the device structure.

[0038] In an embodiment, the threshold switching layer is a bidirectional threshold switching layer, wherein the bidirectional threshold switching layer can switch from a resistive state to a conductive state when the applied voltage crosses (e.g., rises above a threshold voltage), and can switch from a conductive state to a resistive state when the applied voltage crosses (e.g., falls below a certain holding voltage). (See also) Figure 9The threshold voltage typically differs from the holding voltage—in particular, the threshold voltage is usually higher than the holding voltage—due to the negative differential resistance exhibited by the bidirectional threshold switch, resulting in a hysteresis effect on its conductivity. Therefore, at an applied voltage intermediate between the threshold and holding voltage, the threshold switch layer can be in a conductive state if the applied voltage is crossed (e.g., dropped below the threshold voltage) to reach the intermediate applied voltage, or in an insulating state if the applied voltage is crossed (e.g., risen above the holding voltage) to reach the intermediate applied voltage. Bidirectional threshold switches can facilitate robust access to the individual memory elements of a memory array.

[0039] In this embodiment, the switchable material contained in the threshold switching layer is a chalcogenide. In this embodiment, the bidirectional threshold switching layer can be a chalcogenide layer. The chalcogenide layer may include, or be composed of, chalcogenides, which are typically in an amorphous or glassy state. One advantage of these embodiments is that the chalcogenides can be good bidirectional threshold switches. Examples of chalcogenides exhibiting bidirectional threshold switching are germanium sulfide, germanium selenide, germanium telluride, silicon telluride, arsenic telluride, antimony selenide, antimony telluride, indium selenide, indium telluride, and tin selenide. Besides these binary compounds, bidirectional threshold switching can also occur in more complex chalcogenide alloys, where the layers typically contain three, four, or even more elements. Other examples of chalcogenides exhibiting bidirectional threshold switching include alloys such as Si-Ge-S, Si-Ge-As-Te, Si-Ge-As-Se, and Si-Ge-As-Se-Te, as well as many other possible combinations. The chalcogenides in embodiments of the present invention may include or be composed of these materials, or may be formed from other chalcogenides that exhibit a bidirectional threshold switch.

[0040] Unlike phase change materials, which can switch between amorphous and crystalline states during operation, bidirectional threshold-switching layers containing chalcogenide materials typically remain amorphous after the switching event or removal of the electrical excitation. While the mechanism behind this reversible switching remains under debate, explanations can be found in the metastable formation of newly introduced metallogenic bonds when the applied voltage is above the threshold voltage, and the termination of these newly introduced metallogenic bonds when the applied voltage is below the holding voltage (see, for example, Noé et al., “Towards the ultimate nonvolatile resistive memory: revealing the mechanism behind bidirectional threshold switching,” Science Advances 6 (2020) eaay2830).

[0041] Therefore, when the threshold voltage of a chalcogenide is exceeded, the chalcogenide transitions from an electrically insulating state to a conductive state. This state transition involves the breaking and rearrangement of interatomic bonds, which requires energy provided by applying the voltage. Thus, this state change is typically associated with heating the chalcogenide.

[0042] The heat generated may induce the release of oxidant from the interface. Therefore, the first electrode interface and the second electrode interface are located near the chalcogenide and are preferably in direct contact with it.

[0043] Another advantage of the heat generated is that the permeability of chalcogenides to oxidants typically increases with increasing temperature. However, chalcogenides generally conduct to oxidants in both conductive and electrically insulating states.

[0044] Although the threshold switching layer comprises or is preferably a chalcogenide, other threshold switching materials, such as other bidirectional threshold switching materials, may also be used. In embodiments, the threshold switching layer may be provided or switchable to a stage in which the threshold switching layer is permeable to the oxidant to provide the channel, for example, by heating the threshold switching layer, and / or the threshold switching layer may be provided or switchable to a material form in which it is permeable to the oxidant.

[0045] In an embodiment, the threshold switching layer providing a channel for the movement of oxidant between the first and second electrodes means that the device is arranged to provide a channel from the first electrode through the threshold switching layer to the second electrode for the movement of oxidant between the first and second electrodes. In an embodiment, the threshold switching layer providing a channel for the movement of oxidant between the first and second electrodes means that, although in principle, additional layers may exist between the first electrode and the threshold switching layer, and / or between the second electrode and the threshold switching layer, such additional layers are permeable to the oxidant or do not obstruct it. In an embodiment, the threshold switching layer providing a channel for the movement of oxidant between the first and second electrodes means that the threshold switching layer can be a material in which it is, or can be heated, made permeable to the oxidant. Chalcogenides generally allow the oxidant to move through them in both electrically insulating and conductive states, although the permeability of chalcogenides is typically greatly enhanced when the layer is heated.

[0046] Suitable oxidants that are mobile between the first and second electrodes generally mean that the oxidant is of a type that is mobile between the first and second electrodes. Typically, the oxidant is an anion. In embodiments, the oxidant may include or may be selected from oxides, sulfides, selenides, tellurides, or combinations thereof. These ions can form stable oxide electrode materials. In embodiments, the oxidant may be an oxide. Oxides can form stable bonds with the electrode interface, providing good memory functionality, while being highly mobile through threshold switching layers, such as chalcogenides.

[0047] In embodiments, the threshold switching layer may include a catalyst for facilitating the decomposition of the oxidant from the electrode interface. The catalyst can lower the energy barrier for bond breaking between the oxidant and the electrode interface. The catalyst is typically mobile through the threshold switching layer, which is often the case where the threshold switching layer comprises a chalcogenide. Preferably, for example, when the threshold switching layer is a chalcogenide, the threshold switching layer is permeable to the catalyst after being heated by a state transition from an electrically insulating state to a conductive state. In embodiments, the catalyst has a charge of a first sign, opposite to the second sign of the oxidant charge. In embodiments, the catalyst is cationic. In these embodiments, when an electric field is applied to induce oxidant movement, the catalyst can flow in the opposite direction to the reducing agent (typically an anion). As a result, during programmed operation, the catalyst may accumulate at the interface where a thermal decomposition reaction occurs to release the oxidant from the interface oxidized by the oxidant. These catalysts can alter the local structure and bonding environment, making the oxidant energy-favorable as it moves from the interface into the chalcogenide. The catalyst may be a transition metal. In embodiments, the catalyst is selected from nickel, indium, cobalt, platinum, or combinations thereof. In an embodiment, the threshold switching layer, such as a chalcogenide, may include 5% atomic percentage of catalyst as part of the total atomic content of the threshold switching layer. When the threshold switching layer is heated, for example by switching from its electrically insulating state to its conductive state, its permeability to the catalyst can be greatly enhanced.

[0048] In an embodiment, within the threshold switching layer, the concentration of chemical elements from Group 15 or 16 and from Period 3 or higher is higher in a first region of the electrode interface in contact with the first and second electrode interfaces containing the oxidant than in a second region separated from the electrode interface containing the oxidant by the first region. In an embodiment, chemical elements from Group 15 or 16 and from Period 3 or higher may include tellurium (Te), sulfur (S), selenium (Se), or combinations thereof, or constitute thereof. Preferably, for example, when the threshold switching layer is a chalcogenide, the threshold switching layer is permeable to the chemical elements after being heated by a state transition from an electrically insulating state to a conductive state.

[0049] In an embodiment, the first electrode may be composed of a first electrode material. In an embodiment, the first electrode material may include molybdenum, tantalum, titanium, or titanium nitride. In an embodiment, the first electrode material may be selected from molybdenum, tantalum, titanium, titanium nitride, or combinations thereof. When oxidized by an oxidizing agent, these materials become electrically insulating.

[0050] In embodiments, the second electrode may be composed of a second electrode material. In embodiments, the second electrode material may include indium tin oxide, ruthenium, or tungsten. In embodiments, the second electrode material may be selected from a list consisting of indium tin oxide, ruthenium, tungsten, or combinations thereof. When oxidized by an oxidizing agent, these materials remain conductive; in particular, these materials form conductive oxides or conductive substoichiometric oxides.

[0051] Any feature of any embodiment of the first aspect may be described independently corresponding to any embodiment of any other aspect of the invention.

[0052] In a second aspect, the present invention relates to memory elements of devices including any embodiment of the first aspect.

[0053] In an embodiment, an electrically insulating oxidized first electrode material (oxidized by an oxidizing agent) can mean that the oxidized first electrode material (and optionally a first electrode interface, if including the oxidized first electrode material) is an insulator. In an embodiment, a conductive oxidized second electrode material (oxidized by an oxidizing agent) can mean that the oxidized second electrode material (and optionally a second electrode interface, if including the oxidized second electrode material) is a conductor. Typically, both the first and second electrode materials (not oxidized by an oxidizing agent) are also conductors.

[0054] In some embodiments, an electrically insulating oxidized first electrode material and a conductive oxidized second electrode material may be associated with each other. For example, the oxidized first electrode material may be "more insulating" or have "lower conductivity" compared to the oxidized second electrode material (e.g., both may be conductors (or both may be insulators), but with a difference in conductivity). In embodiments, the conductivity (and / or conductivity) of the first electrode interface containing the oxidized first electrode material (e.g., the conductivity of the oxidized interface layer at the first electrode interface) may be lower than the conductivity (and / or conductivity) of the second electrode interface containing the oxidized second electrode material (e.g., the conductivity of the oxidized interface layer at the second electrode interface). This asymmetry or difference in conductivity and / or conductivity may make the threshold voltage dependent on whether the oxidant is at the first electrode interface or the second electrode interface. Thus, at least some or all of the oxidant can move between the first and second electrode interfaces to tune the threshold voltage. The conductivity of the oxidized first electrode material is also typically lower than that of the first electrode material and / or the (unoxidized) second electrode material. Typically, the first and second electrode materials are different, for example, having different chemical compositions.

[0055] In an embodiment, the memory element may be associated with an adjustable threshold voltage representing data stored in the memory element. For example, a high threshold voltage or a value of the threshold voltage may indicate that a binary "0" is stored in the memory element, while a low threshold voltage or a value of the threshold voltage may indicate that a binary "1" is stored in the memory element.

[0056] When data is programmed into a memory element, the memory element can be adapted to move an oxidant between a bottom electrode and a top electrode to change the amount of oxidized first material at the first electrode interface and / or the amount of oxidized second material at the second electrode interface for tuning the threshold voltage.

[0057] Any feature of any embodiment of the second aspect may be described independently corresponding to any embodiment of any other aspect of the invention.

[0058] In a third aspect, the present invention relates to a method for programming data into a memory element of any embodiment of the second aspect, comprising applying a programming voltage to the memory element to induce movement of the oxidant between a first electrode and a second electrode to change the amount of oxidized first material at the first electrode interface and / or the amount of oxidized second electrode material at the second electrode interface, thereby tuning a threshold voltage.

[0059] The programming voltage is typically applied between the first and second electrodes. In an embodiment, the programming voltage may be applied to tune the threshold voltage to at least 0.1 V, preferably at least 0.3 V, more preferably at least 0.5 V, and even more preferably at least 1.0 V.

[0060] In embodiments, a programming voltage can be applied to set the threshold switching layer from an electrically insulating state to a conductive state. Particularly for chalcogenides, the transition from an electrically insulating to a conductive state is associated with heating the threshold switching layer. Heat can lead to increased mobility of the oxidant through the threshold switching layer and, moreover, can induce the release of the oxidant from the interface. In embodiments, a programming voltage can be applied to heat the threshold switching layer such that the threshold switching layer is permeable to the oxidant. In embodiments, a programming voltage can be applied to heat the threshold switching layer such that the oxidant is released from the first electrode interface and / or the second electrode interface.

[0061] Any feature of any embodiment of the third aspect may be described independently corresponding to any embodiment of any other aspect of the invention.

[0062] In a fourth aspect, the present invention relates to a method for reading data from a memory element of any embodiment of the second aspect, comprising applying a read voltage to the memory element to determine a value representing a threshold voltage.

[0063] A read voltage is typically applied between the first and second electrodes. The read voltage is usually adjusted so that the oxidant at the interface of the first or second electrode is essentially not released, thus enabling non-destructive reading. For example, the read voltage can be applied for a sufficiently short time that the oxidant does not move substantially between the electrodes.

[0064] In an embodiment, the value representing the threshold voltage can be (or, for example, based on) the current between the first and second electrodes sensed by a controller. This sensed current can depend on the position of the read voltage relative to the threshold voltage. For example, when a read voltage is applied and the current is above a certain predetermined current, it can be assumed that the read voltage is above the threshold voltage (representing the value of the threshold voltage). Similarly, when a read voltage is applied and the current is below a certain predetermined current, it can be assumed that the read voltage is below the threshold voltage (representing the value of the threshold voltage). In an embodiment, the value representing the threshold voltage can be a binary value that depends on whether the threshold voltage is below or above the read voltage. Binary values ​​are typically represented using two discrete states, usually denoted as "0" and "1". This allows for simple binary data storage. However, this is not necessary; instead, the read voltage can be tuned to determine a precise value for the threshold voltage, which can result in multi-level memory elements providing dense data storage.

[0065] Any feature of any embodiment of the fourth aspect may be described independently corresponding to any embodiment of any other aspect of the invention.

[0066] In a fifth aspect, the present invention relates to a memory device comprising:

[0067] a. The memory element of any embodiment of the second aspect, and

[0068] b. The controller, configured to:

[0069] If instructed to program data into a memory element, then perform the method of any embodiment of the third aspect on the memory element, and

[0070] If instructed to read data from a memory element, the method of any embodiment of the fourth aspect is performed on the memory element.

[0071] In the absence of operations such as reading or programming, or between such operations, the magnitude of the voltage applied to the device by the controller may be lower than the holding voltage, causing the threshold switch to be in an electrically insulating state. Therefore, when a reading or programming operation is performed, this typically means a shift in the voltage applied to the device, from a voltage magnitude lower than the holding voltage to the reading or programming voltage.

[0072] The controller may include instructions to apply a predetermined or pre-programmed read voltage to the memory element, i.e., between the first and second electrodes, when instructed to read data. The magnitude of the predetermined read voltage may be between the magnitude of a threshold voltage in its high state (e.g., when the first electrode interface comprises a first electrode material oxidized by an oxidant) and the magnitude of a threshold voltage in its low state (e.g., when the second electrode interface comprises a second electrode material oxidized by an oxidant, and typically the first electrode interface substantially does not contain an oxidant). The controller may be adapted to sense current through the memory element in response to the applied read voltage. When the sensed current is high, it may be assumed that the applied read voltage causes a crossing of the threshold voltage, such that the threshold switching layer is in a conductive state, and the threshold voltage is low. When the sensed current is low, it may be assumed that the applied read voltage does not cause a crossing of the threshold voltage, such that the threshold switching layer remains in an electrically insulating state, and the threshold voltage is high.

[0073] In an embodiment, when instructed to program data into a memory element, a programming voltage is applied by a controller to the memory element, i.e., between the first and second electrodes. The magnitude of the programming voltage is typically greater than the magnitude of a threshold voltage, causing the threshold switching layer to switch from an electrically insulating state to a conductive state. When the threshold voltage is high, the magnitude of the programming voltage is preferably greater than the magnitude of the threshold voltage, for example, representing binary "0", causing the threshold switching layer to switch from an electrically insulating state to a conductive state, regardless of whether the threshold voltage is high or low.

[0074] In an embodiment, the controller may include a first programming (e.g., one of set and reset) instruction for applying the programming voltage to induce movement of the oxidant in a direction from the first electrode to the second electrode when instructed to program first data (e.g., one of binary "1" and "0") into the memory element. In an embodiment, the controller may include a second programming (e.g., the other of set and reset) instruction for applying the programming voltage—when instructed to program second data (e.g., the other of binary "0" and "1") different from the first data into the memory element—to induce movement of the oxidant in a direction from the second electrode to the first electrode. Specific examples of setting and resetting memory elements are provided throughout the specification; however, the terms "set" and "reset" are interchangeable or generalized to the programming of the first or second data, which may be binary data but is not required. Similarly, "1" and "0" are interchangeable or generalized to the first or second data, which may be binary data but is not required.

[0075] When the memory element is used to store binary data, write data, or set a position, the memory element may include an applied programming voltage, which in this case may be referred to as a set voltage, for inducing the movement of an oxidant from a first electrode to a second electrode. When the memory element is used to store binary data, erasing data from the memory element or resetting the memory element may include applying a programming voltage, which in this case may be referred to as a reset voltage, for inducing the movement of an oxidant from the second electrode to the first electrode. The set voltage may have an opposite polarity to the reset voltage.

[0076] Typically, the programming voltage is applied independently of the data already stored in the memory element. Thus, when a programming voltage is applied to program data into the memory element already present, the threshold voltage can remain substantially the same because the oxidant is already located at the electrode interface, and the applied programming voltage induces the oxidant to move towards that electrode interface. For example, in an embodiment where the memory element is used to store binary data, when the memory element includes stored data representing binary "1", i.e., in a low threshold voltage state, where the second electrode interface comprises a second electrode material oxidized by the oxidant, and the threshold voltage can remain substantially the same when the programming voltage is a write or set voltage, and therefore can remain low. Similarly, when the memory element includes stored data representing binary "0", i.e., in a high threshold voltage state, where the first electrode interface comprises a first electrode material oxidized by the oxidant, and the threshold voltage can remain substantially the same when the programming voltage is an erase or reset voltage, and therefore can remain high.

[0077] However, when a programming voltage is applied to program data into a memory element and the memory element contains data other than the data to be programmed, applying the programming voltage can cause the threshold voltage to be tuned. In this case, the threshold voltage of the memory element can be tuned to cross a predetermined read voltage (typically not applied when the programming voltage is applied, but its value is usually pre-programmed or stored in the controller). For example, if the threshold voltage is higher than the predetermined read voltage before the programming is performed, a programming voltage can be applied such that the threshold voltage is tuned to cross the predetermined read voltage, or tuned to be lower than the predetermined read voltage. This is typically achieved by moving an oxidant from the first electrode interface to the second electrode interface, where the oxidant oxidizes the second electrode material. In this case, the programming voltage can be a set voltage, allowing the memory element to switch from binary "0" to binary "1". For example, if the threshold voltage is lower than the predetermined read voltage before the programming is performed, a programming voltage can be applied such that the threshold voltage is tuned to cross the predetermined read voltage, or tuned to be higher than the predetermined read voltage. This is typically achieved by moving an oxidant from the second electrode interface to the first electrode interface, where the oxidant oxidizes the first electrode material. In this case, the programming voltage can be a reset voltage, which allows the memory element to switch from binary "1" to binary "0".

[0078] Any feature of any embodiment of the fifth aspect may be described independently corresponding to any embodiment of any other aspect of the invention.

[0079] Specific and preferred aspects of the invention are set forth in the appended independent and dependent claims. Features of the dependent claims may be suitably combined with features of the independent and other dependent claims, not merely those expressly set forth in the claims.

[0080] Although devices in the field are constantly being improved, changed, and developed, it is believed that the concepts of this invention represent a sufficiently novel and original advancement, including deviations from prior practice, thereby providing devices with this property that are more efficient, stable, and reliable.

[0081] The above and other features, characteristics, and advantages of the present invention will become apparent from the following detailed description taken in conjunction with the accompanying drawings, which illustrate the principles of the invention by way of example. This description is given for illustrative purposes only and does not limit the scope of the invention. The accompanying drawings are referenced below. Attached Figure Description

[0082] Figure 1A This is a vertical cross-sectional view of a first exemplary device according to an embodiment of the present invention.

[0083] Figure 1B According to an embodiment of the present invention Figure 1A The current of the device depends on the voltage.

[0084] Figure 2A yes Figure 1A A vertical cross-sectional view of the device, in which a set voltage is applied to the device.

[0085] Figure 2B According to an embodiment of the present invention Figure 2A The current of the device depends on the voltage.

[0086] Figure 3A This is a vertical cross-sectional view of the device in Figure 2, where the device has been set, and therefore data has been written to the device.

[0087] Figure 3B According to an embodiment of the present invention Figure 3A The current of the device depends on the voltage.

[0088] Figure 4A yes Figure 3A A vertical cross-sectional view of the device, in which a reset voltage is applied to the device.

[0089] Figure 4B According to an embodiment of the present invention Figure 4A The current of the device depends on the voltage.

[0090] Figure 5This is a vertical cross-sectional view of a second exemplary device according to an embodiment of the present invention.

[0091] Figure 6 It is a vertical cross-sectional view of the device of claim 5, wherein a set voltage is applied to the device.

[0092] Figure 7 It is a vertical cross-sectional view of the device of claim 5, wherein the device has been positioned so that data has been written into the device.

[0093] Figure 8 This is a schematic perspective view of a memory device according to an embodiment of the present invention.

[0094] Figure 9 It is a current-voltage relationship diagram based on existing bidirectional threshold switches.

[0095] In different accompanying drawings, the same reference numerals refer to the same or similar elements. Detailed Implementation

[0096] The invention will be described with reference to specific embodiments and certain accompanying drawings, but is not limited thereto; rather, it is defined solely by the claims. The described drawings are merely illustrative and not restrictive. In the drawings, some elements may be enlarged and not drawn to scale for illustrative purposes. Dimensions and relative dimensions do not correspond to an actual reduction in scale for the practice of the invention.

[0097] Furthermore, the terms first, second, third, etc., used in the specification and claims are used to distinguish similar elements and are not necessarily used to describe a temporal, spatial, ranking, or any other order of precedence. It should be understood that the terms thus used are interchangeable where appropriate, and the embodiments of the invention described herein can operate in an order different from that described or illustrated herein.

[0098] Furthermore, the terms top, bottom, above, below, etc., used in the specification and claims are for descriptive purposes and not necessarily for describing relative positions. It should be understood that such terms are interchangeable where appropriate, and the embodiments of the invention described herein can operate in orientations different from those described or illustrated herein.

[0099] It should be noted that the term "comprising" as used in the claims should not be construed as limiting itself to the means listed thereafter; it does not exclude other elements or steps. Therefore, the term should be interpreted as specifying the presence of the stated features, integers, steps, or components as mentioned, but does not exclude the presence or addition of one or more other features, integers, steps, or components, or groups thereof. Thus, the term "comprising" covers both cases where only the stated features are present and cases where these features are present along with one or more other features. The term "comprising" according to the invention therefore also includes an embodiment where no other components are present. Therefore, the scope of the statement "device comprising means A and B" should not be construed as limiting it to a device consisting only of components A and B. This means that for the present invention, the only relevant components of the device are A and B. However, the term "comprising" can also include the term "by" under the limitation of "no other elements or steps are present," and therefore, the term "comprising" can be understood to also provide a basis for replacing the term "comprising" with "by" or "comprising."

[0100] Similarly, it should be noted that the term "coupling" should not be interpreted as limited to direct connection. The terms "coupling" and "connection" can be used together with their derivatives. It should be understood that these terms are not intended to be synonyms. Therefore, the scope of the phrase "device A coupled to device B" should not be limited to devices or systems where the output of device A is directly connected to the input of device B. This implies the existence of a path between the output of device A and the input of B, which can include other devices or apparatuses. "Coupling" can mean two or more elements in direct physical or electrical contact, or it can mean two or more elements that are not in direct contact but still cooperate or interact with each other.

[0101] Throughout this specification, the reference to "an embodiment" or "an embodiment" means that a specific feature, structure, or characteristic described in connection with that embodiment is included in at least one embodiment of the invention. Therefore, the appearance of the phrase "an embodiment" or "an embodiment" in various places throughout this specification does not necessarily refer to the same embodiment, but may refer to different embodiments. Furthermore, in one or more embodiments, specific features, structures, or characteristics may be combined in any suitable manner, as will be apparent to those skilled in the art from this disclosure.

[0102] Similarly, it should be understood that in the description of exemplary embodiments of the invention, various features of the invention are sometimes grouped together in a single embodiment, drawing, or description for the purpose of simplification and to aid in understanding one or more of the various inventive aspects. However, this approach to the disclosure should not be construed as reflecting an intention to claim more features than are expressly recited in each claim. Rather, as reflected in the appended claims, inventive aspects lie in fewer features than all the features of a single foregoing disclosed embodiment. Thus, the claims appended to the Detailed Description are thereby explicitly incorporated into this Detailed Description, wherein each claim itself represents a separate embodiment of the invention.

[0103] Furthermore, while some embodiments described herein include features that are included in other embodiments but not others, it will be understood by those skilled in the art that combinations of features from different embodiments are intended to fall within the scope of the invention and form different embodiments. For example, any embodiment of the claimed embodiments in the appended claims may be used in any combination.

[0104] Furthermore, some embodiments described herein are described as methods or combinations of method elements that can be implemented by a processor of a computer system or by other means of implementing the functionality. Thus, a processor having the necessary instructions for performing the elements of such methods or methods forms means for performing the elements of methods or methods. Furthermore, the elements described herein in the apparatus embodiments are examples of means for implementing the functionality performed by elements that achieve the objectives of the present invention.

[0105] Numerous specific details are set forth in the description provided herein. However, it should be understood that embodiments of the invention can be practiced without these specific details. In other instances, well-known methods, structures, and techniques have not been shown in detail so as not to obscure the understanding of this specification.

[0106] The following items are provided separately to aid in understanding the invention.

[0107] As used herein, any property of a material, including electrical and ionic conductivity or conductivity and threshold voltage, can be determined under standard conditions, such as 25°C and / or 101325 Pa (=1 atm). Alternatively, the property can be determined under various conditions of the material (e.g., the temperature of the material and / or the pressure of the environment). For example, when the property is associated with a state transition occurring at a heated temperature, the property can be a property at said heated temperature. For example, during a method, the property is typically determined as the method is performed. Where the property is oriented, it can be determined along the relevant direction, for example, along the direction between the first and second electrodes for conductivity and conductivity and threshold voltage. Conductivity can be determined by any technique known in the art, such as the Van der Pauw method, or two-point or four-point probe methods.

[0108] As used herein, unless otherwise stated, when a material is referred to as “electrically insulating,” it exhibits high resistance. For example, when a threshold switch layer is referred to as being in an electrically insulating state, the threshold switch layer effectively prevents the flow of current at normal operating voltage. In embodiments, the electrically insulating material may have a resistance of up to 1 S / m, preferably up to 10 S / m. -1 S / m, preferably up to 10 -2 S / m, or even more preferably up to 10 -3 S / m, and more preferably up to 10 -4 The conductivity is S / m. Specifically, when the material is referred to as "electrically insulating," the conductivity can be at most 1 S / m. In an embodiment, the oxidized first electrode material can have a conductivity of at most 1 S / m. In an embodiment, the oxidized interface layer at the first electrode can have a conductivity of at most 1 S / m. In an embodiment, the switchable material of the threshold switch layer in an electrically insulating state can have a conductivity of at most 1 S / m.

[0109] As used herein, unless otherwise stated, when a material is referred to as “conductive,” it exhibits low resistance. For example, when a threshold switch layer is referred to as being in a conductive state, the threshold switch layer effectively allows current to flow under an applied voltage. In embodiments, the conductive material may have at least 10 2 S / m, preferably at least 10 3 S / m, more preferably at least 10 4 Conductivity in S / m. Specifically, when a material is described as "conductive," its conductivity can be at least 10. 2 S / m. In an embodiment, the first electrode (unoxidized) may have at least 10. 2 The conductivity is S / m. In the embodiments, the first electrode material (unoxidized) may have a conductivity of at least 10. 2The conductivity is S / m. In an embodiment, the second electrode (unoxidized) may have a conductivity of at least 10. 2 The conductivity is S / m. In the embodiments, the second electrode material (unoxidized) may have a conductivity of at least 10. 2 The conductivity is S / m. In the embodiments, the oxidized second electrode material may have a conductivity of at least 10. 2 In the embodiment, the conductivity S / m of the oxidized interface layer at the second electrode can have at least 10. 2 The conductivity is S / m. In an embodiment, the switchable material of the threshold switch layer can have a conductivity of at least 10 when in a conductive state. 2 The conductivity in S / m can be measured under conditions where the material is in its conductive state, i.e., under the elevated local temperature achieved during switching operations. However, in general, as those skilled in the art will know, threshold switches, especially bidirectional threshold switches, may be more likely to be associated with a strong shift or change in conductivity across the threshold voltage than with a specific conductivity.

[0110] As used herein, unless otherwise stated, when a material is described as being ion-permeable, such as a catalyst or oxidant, the material can effectively conduct ions. In the embodiments, when the material exhibits at least 10 ions permeability... -5 S / m, preferably at least 10 -3 S / m, more preferably at least 10 -1 When a material has a conductivity of at least 1 S / m, or even more preferably at least 1 S / m, it is considered to be ion-permeable. Specifically, when a material is considered to be ion-permeable, its conductivity can be at least 10. -5 S / m.

[0111] As used herein, unless otherwise stated, when a material is referred to as an ion-blocking material, the material may be substantially non-conductive to ions. In embodiments, when a material exhibits at most 10 ions... -6 S / m, preferably up to 10 -8 S / m, preferably up to 10 -10 When the conductivity is S / m, the material is considered to block ions. Specifically, when a material is considered to block ions, the conductivity can be at most 10. -6 S / m.

[0112] The invention will now be described in detail through several embodiments thereof. It will be apparent that other embodiments of the invention can be configured based on the knowledge of those skilled in the art without departing from the technical teachings of the invention, which is limited only by the terms of the appended claims.

[0113] In a first aspect, the present invention relates to a device comprising:

[0114] a. A first electrode, comprising a first electrode material that is electrically insulating if oxidized by an oxidizing agent.

[0115] b. A second electrode, comprising a second electrode material that is conductive if oxidized by the oxidant, and

[0116] c. A threshold switching layer between the first electrode and the second electrode, the threshold switching layer comprising a material that can be switched from an electrically insulating state to a conductive state by a voltage across a threshold voltage between the first electrode and the second electrode, and

[0117] d. The first electrode interface between the threshold switch layer and the first electrode, and the second electrode interface between the threshold switch layer and the second electrode.

[0118] The device includes an oxidant adapted to move between a first electrode and a second electrode, and a threshold switching layer provides a channel for moving the oxidant between the first electrode and the second electrode.

[0119] In a second aspect, the present invention relates to a memory element of a device comprising any embodiment of the first aspect. In embodiments, the memory element may be associated with an adjustable threshold voltage representing data stored in the memory element. When data is programmed into the memory element, the memory element may be adapted to move an oxidant between a bottom electrode and a top electrode to change the amount of oxidized first material at a first electrode interface and / or the amount of oxidized second material at a second electrode interface for tuning the threshold voltage.

[0120] In a third aspect, the present invention relates to a method for programming data into a memory element of any embodiment of the second aspect, comprising applying a programming voltage to the memory element to induce movement of the oxidant between a first electrode and a second electrode to change the amount of oxidized first material at the first electrode interface and / or the amount of oxidized second electrode material at the second electrode interface, thereby tuning a threshold voltage.

[0121] In a fourth aspect, the present invention relates to a method for reading data from a memory element of any embodiment of the second aspect, comprising applying a read voltage to the memory element to determine a value representing a threshold voltage.

[0122] This invention provides a memory and operating method that relies on the reversible oxidation of asymmetric electrode interfaces (due to the use of asymmetric stacks) to achieve binary or multi-level data storage capabilities. The simple device structure enables low-cost, high-density memories suitable for memory-class memory applications.

[0123] like Figure 1AThe diagram shows a vertical cross-section of a first exemplary device (1) of the present invention. The device (1) includes a stack. The stack includes a bottom diffusion barrier layer (51) and a first electrode (4) above or on the bottom diffusion barrier layer (51). The first electrode (4) includes a first electrode interface (40) between the first electrode (4) and a threshold switching layer (3). The first electrode interface (40) adjacent to (e.g., in contact with) the threshold switching layer (3) includes a first electrode material oxidized by an oxidant to make it electrically insulating. In other words, the device (1) may include an electrically insulating oxidized interface layer (40) including a first electrode material oxidized by an oxidant at the first electrode interface (40). Preferably, substantially the entire interface (40) is oxidized, i.e., includes the first electrode material oxidized by an oxidant. Preferably, the oxidized first electrode material at the first electrode interface (40) separates the remaining portion of the first electrode (4) (e.g., a conductive or unoxidized portion) from the threshold switching layer (3).

[0124] The stack also includes a threshold switching layer (3) on or above the first electrode (4), and a second electrode (2) on or above the threshold switching layer (3). Thus, the first electrode (4) and the second electrode (2) are separated from each other by the threshold switching layer (3). The second electrode (2) includes a second electrode interface (20) between the second electrode (2) and the threshold switching layer (3). The second electrode interface (20) does not contain an oxidizing agent. However, this is not strictly required, and the second electrode interface (20) can be oxidized instead, since the second electrode interface (20) is conductive regardless of whether it is oxidized.

[0125] The stack also includes a top diffusion barrier layer (52) above or on the second electrode (2). The bottom diffusion barrier layer (51) and the top diffusion barrier layer (52) are substantially oxidizing or impermeable to oxidizing agents. Read and programming voltages can be applied to the first electrode (4) and the second electrode (2) respectively through the bottom diffusion barrier layer (51) and the top diffusion barrier layer (52), thereby preventing oxidizing agents from diffusing out of the device (1). The bottom diffusion barrier layer (51) and the top diffusion barrier layer (52) are typically formed of a conductive material. The bottom diffusion barrier layer (51) and the top diffusion barrier layer (52) can be formed, for example, of amorphous carbon.

[0126] Preferably, the first electrode interface (40) is the interface between the first electrode (4) and the threshold switch layer (3). Similarly, the second electrode interface (20) is preferably the interface between the second electrode (2) and the threshold switch layer (3). In other words, preferably, the threshold switch layer (3) is in direct contact with the first electrode interface (40) and the second electrode interface (20). This direct contact can provide good thermal coupling between the threshold switch layer (3) and the electrode interfaces (20, 40). When the threshold switch layer (3) is heated, good thermal coupling may facilitate the release of oxidant from the electrode interfaces (20, 40). Furthermore, this direct contact allows the oxidant between the electrode interfaces (20, 40) to move directly into the threshold switch layer (3) when the oxidant is released from the electrode interfaces (20, 40), which may be advantageous for providing good mobility of the oxidant between the first electrode (4) and the second electrode (2).

[0127] In this example, the threshold switch layer (3) includes a catalyst for promoting the decomposition of the oxidant from the electrode interfaces (20, 40). The direct contact between the threshold switch layer (3) and the interfaces (20, 40) allows the catalyst in the threshold switch layer (3) to reach the electrode interfaces (20, 40), wherein the catalyst can lower the energy barrier for bond breaking between the oxidant and the electrode interfaces (20, 40).

[0128] In this example, the threshold switching layer (3) is a chalcogenide. In the embodiment, the catalyst has a charge of a first sign, which is opposite to the second sign of the charge of the oxidant. The oxidant is typically negatively charged; therefore, the catalyst is preferably positively charged.

[0129] refer to Figure 1B It depicts Figure 1A Current-voltage characteristics of device (1) in the diagram. Threshold voltage (V) thres The threshold voltage (V) is high because the insulating layer at the first electrode interface (40) restricts current injection. Therefore, the threshold voltage (V) is high. thres The voltage is higher than the predetermined reading voltage (V). read ), so that when a read voltage (V) is applied read When ), the threshold voltage (V) thres The threshold switch layer (3) remains electrically insulated and is therefore in a resistive state. Thus, in response to the applied read voltage (V... read The sensed current will be very low. This state of the device can, for example, correspond to binary "0".

[0130] In the absence of any operation such as reading or programming on the device (1), or between said operations, the amount of voltage applied to the device (1) can typically be lower than the holding voltage (V). holdThe magnitude of the voltage applied to the device (1) is 0 when no read, reset or set voltage is applied, or such that no electric field is applied across the device (1) so as not to induce the movement of the oxidant.

[0131] Also refer to Figure 2A and Figure 2B Perform a write or set operation (V) on device (1). prog Programming voltage (V) prog The electrode is applied between the first electrode (4) and the second electrode (2).

[0132] Applied programming voltage (V) prog ) greater than the threshold voltage (V thres This causes the threshold switching layer (3) to switch from an electrically insulating state to its conductive state.

[0133] This state change is associated with the heating of chalcogenides. Specifically, the state transition involves the breaking and rearrangement of interatomic bonds. This bond rearrangement requires energy, which is derived from an applied voltage. Therefore, chalcogenides become hot during the state change.

[0134] The heat can promote the release of the oxidant from the first electrode interface (40) because the heat can break the bond between the oxidant and the first electrode material of the first electrode (4).

[0135] Furthermore, the heated threshold switch layer (3) can have good permeability to oxidants. In addition, chalcogenides generally have high permeability to oxidants, especially in the conductive state, due to the large number of free charge carriers (electrons / holes) in the conductive state.

[0136] In addition, a programming voltage (V) is applied. prog This causes the electric field across the threshold switching layer (3) to induce the oxidant to move from the first electrode (4) to the second electrode (2) (e.g., due to electrophoresis).

[0137] Thus, the applied electric field causes the oxidant to be effectively released and moved from the first electrode interface (40) to the second electrode interface (20). The movement of the negatively charged oxidant is indicated by arrows. Simultaneously, the catalyst moves toward the first electrode interface (40) in the direction opposite to the arrows, where it catalyzes the release of the oxidant from the first electrode interface (40).

[0138] As a result of the oxidant migration, where the oxidant is removed from the first electrode interface (40) and moves to the second electrode interface (20), where the oxidant now oxidizes the second electrode material, the threshold voltage decreases, as... Figure 2B As shown by the arrow in the image.

[0139] After the set operation, such as Figure 3A As shown, the device (1) has an oxidant located at the second electrode interface (20). In other words, the device (1) may include a conductive oxidized interface layer (20) at the second electrode interface (20), which includes a second electrode material oxidized by the oxidant. Preferably, the oxidized second electrode material at the second electrode interface (20) separates the remaining portion (i.e., the unoxidized portion) of the second electrode (2) from the threshold switch layer (3). The programming voltage can be stopped, and a voltage lower than the holding voltage (V) can be applied. hold The voltage of the threshold switch layer (3) causes it to switch back to an electrically insulating state. The first electrode interface (40) can now be substantially free of oxidants and therefore can be conductive. Accordingly, Figure 3B Presented Figure 3A The current-voltage characteristics of the device (1) in the middle. Due to the effective current injection from the first electrode interface (40) without oxidant, the threshold voltage (V thres The threshold voltage (V) is now low, while the second electrode interface (20) remains conductive. thres The voltage is now below the predetermined read voltage (V). read Thus, it can be determined that device (1) is in a low-resistance state. This state of the device can, for example, correspond to binary "1".

[0140] Also refer to Figure 4B ,exist Figure 4A The erase or reset operation is described, including applying a reset voltage (-V). prog The symbol ; indicates its absolute value, but with a negative sign to indicate relative to the value in the equation. Figure 2A and 2B The programming voltage V applied to device (1) prog The opposite polarity. Reset voltage (-V) prog ) has a set voltage (V) prog The opposite sign or polarity is because it generates electric fields in opposite directions between the first electrode (4) and the second electrode (2) (relative to the polarity). Figure 2A and 2B Reset voltage (-V) prog The value of ) is again greater than the threshold voltage (V thres The value of the programming voltage (V) causes the threshold switching layer (3) to switch back to the conductive state. Typically, the programming voltage (V) prog The value of ), i.e., the set voltage (V prog The magnitude of the reset voltage (-V) and the reset voltage (-V) progEach of the values ​​of the threshold voltage is greater than the value of the high threshold voltage, i.e., the value of the threshold voltage in the high state (therefore, when the first interface includes the first electrode material oxidized by the oxidant). In this case, the threshold switching layer switches from an electrically insulating state to a conductive state. In this example, the reset voltage (-V) prog ) and set voltage (V prog The same magnitude is required; however, this is not necessary, and different magnitudes can be used instead. Since the applied field is now generated in the opposite direction, the oxidant released from the second electrode material at the second electrode interface (20) moves back from the second electrode interface (2) to the first electrode interface (4) (its direction is from...). Figure 4A (The arrow in the image indicates this). This resets device (1) to... Figure 1A The state shown is attributed to the insulating oxide layer at the first electrode interface (40), which restored the high threshold voltage (V). thres ).

[0141] Although this example uses device (1) to store binary data, this is not required by the present invention. Instead, in embodiments of the invention, a programming voltage can be applied for a specific time to achieve a specific threshold voltage. The read voltage can be tuned to determine a value representing the specific threshold voltage.

[0142] Figure 5 A second exemplary device (1) is shown, which has a concentration gradient within a threshold switching layer (3) from elements of group 15 or 16 and elements of period 3 or higher. For example, the element could be tellurium (Te), sulfur (S), or selenium (Se). The concentration of this element is higher in a first region (32) near an electrode interface containing an oxidant, compared to a more distant second region (31). Figure 5 The first electrode interface (40) is located in the middle. The element can promote the release of the oxidant from the interface (20, 40) by promoting the breaking of the bond between the oxidant and the interface (20, 40). In fact, elements from Group 15 or 16 have high electronegativity, and since the element comes from Period 3 or higher, it usually reacts with oxidants, especially when the oxidant is oxygen.

[0143] like Figure 6As shown, during programming operations, such as write or set operations similar to those in Figure 2, the programming voltage moves the oxidant to the opposite electrode interface (20). The arrows indicate the direction of movement of the oxidant, i.e., from the first electrode (4) to the second electrode (2). Unlike the catalyst in the first exemplary embodiment described above, the element has the same charge as the oxidant (e.g., both the oxidant and the element can be anions), and therefore moves in the same direction as the oxidant when an electric field is applied through the threshold switch layer (3). Thus, the element also moves in the direction of the arrow.

[0144] After the set operation, such as Figure 7 As shown, the first region (32) with a higher concentration of Group 15 or 16 elements has also moved to the second electrode interface (20) along with the oxidant. As a result, the first region (32) has shifted its position within the threshold switch layer (3) and is now located on the side of the threshold switch layer (3) that is in contact with the second electrode interface (20), thereby enhancing the performance of the device (1) by facilitating the effective release of the oxidant and thus aiding migration during subsequent reset operations.

[0145] In a fifth aspect, the present invention relates to a memory device comprising:

[0146] a. The memory element of any embodiment of the second aspect, and

[0147] b. The controller, configured to:

[0148] If instructed to program data into a memory element, then perform the method of any embodiment of the third aspect on the memory element, and

[0149] If instructed to read data from a memory element, the method of any embodiment of the fourth aspect is performed on the memory element.

[0150] Figure 8 A schematic diagram of a memory device (6) incorporating the disclosed memory element (7) is presented. The device includes four parallel column lines (12) forming bit lines and four parallel row lines (11) forming word lines. The column lines (12) and row lines (11) are conductive and connected to a controller (not shown) for selectively and independently applying voltage.

[0151] According to the invention, each intersection of the column line (12) and the row line (11) is electrically coupled through a memory element (7), thereby forming an array of memory elements (7). In this example, for each memory element (7), the lower electrode interface is oxidized by an oxidant. By applying appropriate voltages V1 and V2 to specific column lines (121) and specific row lines (111) respectively, a programming voltage is applied to a specific memory element (71) at their intersection, allowing selective programming or reading of individual memory elements (71) in the array of memory elements (7). In fact, selective programming and reading of individual memory elements (7) is facilitated by the use of a threshold switch layer, that is, a bidirectional threshold switch in this example, particularly a chalcogenide, which can be used as a selector. The selection voltages V1 and V2 are such that only the threshold voltage of a specific memory element (71) is crossed, thereby only the specific memory element (71) is effectively addressed. For example, V1 and V2 may have opposite signs.

[0152] exist Figure 8 In this process, a programming voltage is applied to a specific memory element (71), causing an oxidant to move between the bottom and top electrodes of the memory element (71) (similar to what has been described above for the first and second exemplary devices).

[0153] It is understood that although preferred embodiments, specific structures and configurations, and materials have been discussed herein with respect to the device according to the invention, various changes or modifications in form and detail may be made without departing from the scope of the invention. Steps may be added to or removed from the method within the scope of the invention.

Claims

1. A device (1), comprising: The first electrode (4) comprises a first electrode material that is electrically insulating if oxidized by an oxidizing agent. The second electrode (2) comprises a second electrode material that is conductive if oxidized by the oxidant, and A threshold switching layer (3) is provided between the first electrode (4) and the second electrode (2), the threshold switching layer (3) including a threshold voltage (V) that can be crossed between the first electrode (4) and the second electrode (2). thres The voltage of a material that switches from an electrically insulating state to a conductive state, and The first electrode interface (40) between the threshold switch layer (3) and the first electrode (4), and the second electrode interface (20) between the threshold switch layer (3) and the second electrode (2). The device (1) includes an oxidant that is movable between the first electrode (4) and the second electrode (2), and the threshold switch layer (3) provides a channel for moving the oxidant between the first electrode (4) and the second electrode (2).

2. The device (1) according to claim 1, characterized in that, The threshold switching layer (3) therein is a chalcogenide layer.

3. The device (1) according to claim 1 or 2, characterized in that, Within the threshold switching layer (3), the concentration of chemical elements from Group 15 or 16 and from Period 3 or higher is higher in the first region (32) than in the second region (31), wherein the first region (32) contacts the electrode interfaces (20, 40) of the first electrode interface containing the oxidant and the second electrode interface, and the second region (31) is separated from the electrode interfaces (20, 40) containing the oxidant through the first region (32).

4. The device (1) according to any one of the preceding claims, characterized in that, The oxidant mentioned herein includes oxygen, sulfur, selenium, or tellurium, preferably oxygen.

5. The device (1) according to any one of the preceding claims, characterized in that, The threshold switching layer (3) includes a catalyst for promoting the decomposition of the oxidant from the electrode interface, the catalyst having a first charge with a second sign opposite to the charge of the oxidant.

6. The device (1) according to any one of the preceding claims, characterized in that, The first electrode interface (40) includes the first electrode material oxidized by the oxidant, and / or The second electrode interface (20) includes the second electrode material oxidized by the oxidant.

7. The device (1) according to any one of the preceding claims, characterized in that, The first electrode material includes molybdenum, tantalum, titanium, or titanium nitride.

8. The device (1) according to any one of the preceding claims, characterized in that, The second electrode material includes indium tin oxide, ruthenium, or tungsten.

9. A memory element (7), comprising the device (1) of any of the preceding claims.

10. A method for programming data into a memory element (7) of claim 9, comprising applying a programming voltage to the memory element (7) for: The oxidant is induced to move between the first electrode (4) and the second electrode (2), thereby changing the amount of oxidized first material at the first electrode interface (40) and / or the amount of oxidized second electrode material at the second electrode interface (20), thereby adjusting the threshold voltage (V). thres ).

11. The method according to claim 10, characterized in that, The programming voltage is applied to tune the threshold voltage to at least 0.1 V, preferably at least 0.3 V, more preferably at least 0.5 V, and even more preferably at least 1.0 V.

12. The method according to claim 10 or 11, characterized in that, The programming voltage is applied to set the threshold switch layer (3) from the electrically insulating state to the conductive state.

13. A method for reading data from the memory element (7) of claim 9, comprising applying a read voltage to the memory element (7) to determine a threshold voltage (V) representing the threshold voltage. thres The value of ).

14. The method according to claim 13, characterized in that, Wherein represents the threshold voltage (V) thres The value of ) depends on the threshold voltage (V thres The binary value that is lower or higher than the read voltage.

15. A memory device (6), comprising: The memory element (7) of claim 9, and The controller is configured to: If instructed to program data into the memory element (7), the method of any one of claims 10 to 12 is performed on the memory element (7), and If instructed to read data from the memory element (7), the method of claim 13 or 14 is performed on the memory element (7).

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