JP5520484B2 - Chalcogenide devices and chalcogenide materials with low germanium or tellurium content - Google Patents

Description

Related Application Information The present invention relates to US patent application no. 11 / 200,466, the disclosure of which is hereby incorporated by reference and forms part of the present invention.

  The present invention relates to chalcogenide materials used in electrical memory or switching devices.

More particularly, the present invention relates to non-equilibrium chalcogenide alloys of the Ge-Sb-Te family, which contain a low concentration of Ge and / or a low concentration of Te compared to the widely used Ge ₂ Sb ₂ Te ₅ alloy.

  Most specifically, the present invention relates to electrical chalcogenide materials that exhibit high set speeds from the initial state with high resistance.

  Chalcogenide materials are new commercial electronic materials that exhibit functions such as switching, memory, logic and processing.

The basic principles of chalcogenide materials were developed in the 1960s by S. R. Ovshinsky. Many efforts in the past decades by Obshinsky and other researchers around the world have led to the advancement of the underlying science that governs the structure and properties of chalcogenide materials and the expansion of the practical range of chalcogenide materials . Chalcogenide devices showed switching behavior in early development in which switching from a resistive state to a conductive state is induced in response to application of a voltage above a threshold. Although threshold voltage is formally a property of the device, the response of the active chalcogenide material to the voltage is an important factor that underlies the magnitude of the threshold voltage. The change from resistive to conductive state induced by voltage is the basis of the Obsinsky threshold switch (OTS) and is an important practical feature of chalcogenide materials. OTS provides very reproducible switching at ultra-fast switching speeds over 10 ¹³ cycles. The basic principles and operational characteristics of OTS are described in, for example, Patent Documents 1 to 4 below. These disclosures are cited in the present invention together with non-patent documents 1, 2 and other journal articles, and form part of the present invention.

  Other important applications of chalcogenide materials include electrical and optical memory devices. One type of chalcogenide memory device utilizes its wide range of resistance values as the basis for memory operation. Each resistance value corresponds to a different structural state of the chalcogenide material, and one or more states can be selected and used to define the working memory state. Chalcogenide materials exhibit an amorphous state or phase and a crystalline state or phase. The different structural states of the chalcogenide material differ with respect to the relative proportions of crystalline and amorphous phases in a given volume or region of the chalcogenide material. The range of the resistance value is limited to the set state and the reset state of the chalcogenide material. The set state is a low resistance structural state whose electrical characteristics are mainly controlled by the crystalline portion of the chalcogenide material, and the reset state is a high resistance structural state whose electrical properties are mainly controlled by the amorphous portion of the chalcogenide material.

  Each memory state of the chalcogenide memory material corresponds to a different resistance value, and each memory resistance value indicates the content of unique information. In operation, the chalcogenide material can be programmed to a specific memory state by applying a current pulse of appropriate amplitude and time to change the chalcogenide material to a structural state having a predetermined resistance. By controlling the amount of energy imparted to the chalcogenide material, the relative ratio of crystalline and amorphous phase regions within the volume of the material is controlled, thereby controlling the structural (and memory) state of the chalcogenide material. can do.

  Each memory state can be programmed by applying a current pulse specific to that state, and each state can be read non-destructively by measuring resistance. Programming in different states is completely reversible and the memory device can be written and read with an almost unlimited number of cycles, providing a sound and reliable operation. The variable resistance memory function of chalcogenide materials is currently utilized in Ovonic Universal Memory (OUM) devices, which are beginning to enter the market. The basic principle and operation of the OUM type device are disclosed in Patent Documents 5 to 8, for example. These disclosures are cited in the present invention together with non-patent documents 3, 4 and other journal articles, and form part of the present invention.

  The general behavior (including switching, memory and storage) and chemical composition of chalcogenide materials are described, for example, in US Pat. These patents also describe a proposed mechanism that governs the behavior of chalcogenide materials, including the crystalline state through a series of partial crystal states that underlie many of the operational characteristics of electrical and optical chalcogenide materials. To structural changes from the amorphous state to the amorphous state (and vice versa).

  Current commercial developments of chalcogenide materials and devices are also aimed at making arrays of devices. Chalcogenide materials offer the potential for high density, memory, logic and neural arrays that can operate using either conventional binary data storage protocols or non-binary multilevel protocols. Chalcogenide arrays further provide the prospect of integrating memory and processing functions on a single chip.

  Further expansion of the commercial prospects of chalcogenide phase change memories requires further improvements in the manufacturing process and the chemical and physical properties of the chalcogenide material. With respect to the properties of chalcogenide materials, it is necessary to improve the thermal stability of the materials. Since chalcogenide material data is held as the structural state of the material, any tendency for the structural state to change with temperature implies a potentially undesirable mechanism in which the data is erased or lost. Many chalcogenide memory materials retain their structural state at room temperature for extended periods of time, but as temperature increases, they become sensitive to changes in the structural state. This practically limits the temperature environment in which the chalcogenide memory device can be utilized, as well as the applicable processing or manufacturing temperature. It is desirable to develop new chalcogenide compositions that have a stable structural state over a constantly increasing temperature range.

In most current memory applications, chalcogenide materials are operated in a binary mode where the memory state corresponds to a set state and a reset state. This is because the set state and the reset state provide the largest resistance ratio and facilitate the identification of the material state during reading. In most manufacturing methods intended for commercial production of chalcogenide memory devices, the chalcogenide material is deposited on a substrate, conductive contact layer or other layer. After deposition, the chalcogenide material is in an amorphous or irregular state and is converted to a crystalline state by subsequent processing. In devices that have all been manufactured, it is sometimes necessary to have the chalcogenide material electrically learned or adjusted so that the device operates consistently as a usable memory element material. This conditioning process includes converting the chalcogenide device into a state suitable for product use. In devices that use the widely used Ge ₂ Sb ₂ Te ₅ alloy, the tuning process requires multiple cycles of setting and resetting, so that the set state resistance is the desired reproducible value. To stabilize.

To increase manufacturing efficiency, it is desirable to develop chalcogenide materials and device structures that can be electrically tuned for practical operation in the shortest time. US patent application no. In 11 / 200,466, the inventors have identified a series of novel chalcogenide compositions that require little adjustment. The alloy includes Ge and a Group V element, where the Group V element is preferably Sb. In some embodiments, the alloy further comprises Te. Compared to the widely used Ge ₂ Sb ₂ Te ₅ synthesis, this alloy has less Ge and / or Te. The alloy of this application can be called a non-conjugated alloy because the alloy composition exists on the Ge-Sb-Te ternary phase diagram and away from the conjugate line connecting Sb ₂ Te ₃ and GeTe.

In addition to less need for adjustment after the manufacturing process is complete, it is also desirable to develop chalcogenide alloys that exhibit high crystallization rates for a range of memory states over a wide dynamic range of resistance.
U.S. Pat. 3,271,591 U.S. Pat. 5,543,737 U.S. Pat. 5,694,146 U.S. Pat. 5,757,446 U.S. Pat. 6,859,390 U.S. Pat. 6,774,387 U.S. Pat. 6,687,153 U.S. Pat. 6,314,014 U.S. Pat. 6,671,710 U.S. Pat. 6,714,954 U.S. Pat. 6.087, 674 U.S. Pat. 5,166,758 U.S. Pat. 5,296,716 U.S. Pat. 5,536,947 U.S. Pat. 5,596,522 U.S. Pat. 5,825,046 U.S. Pat. 5,687,112 U.S. Pat. 5,912,839 U.S. Pat. 3,530,441 SR Ovshinsky, “Reversible Electrical Switching Phenomena in Disordered Structures”, Physical Review Letters, vol. 21, p.1450-1453 (1969) SR Ovshinsky and H. Fritzsche, “Amorphous Semiconductors for Switching, Memory, and Imaging Applications”, IEEE Transactions on Electron Devices, vol.ED-20, p.91-105 (1973) Pirovana et al., “Low Field Amorphous State Resistance and Threshold Voltage Drift in Chalcogenide Materials”, IEEE Transactions on Electron Devices, vol. 51, p.714-719 (2004) Weiss, “Morphing Memory”, IEEE Spectrum, vol. 167, p.363-364 (2005)

  In one embodiment of the present invention, the present invention provides a chalcogenide alloy composition that exhibits favorable tuning characteristics with short crystallization times. In other embodiments, the present invention provides chalcogenide alloy compositions such that the crystallization time varies only slightly for different structural states where the resistance is spread over one to several orders of magnitude. In electrical chalcogenide device applications, the alloys of the present invention provide fast set speeds and / or favorable tuning characteristics for multiple states over a wide range of resistance. The alloys of the present invention provide preferred threshold voltage, reset current, and reset resistance.

  The alloys of the present invention generally contain Ge, Sb and / or Te, where Ge is 11-22 atomic percent, Sb is 22-65 atomic percent, and Te is 28-55 atomic percent. In one embodiment of the present invention, the alloy of the present invention comprises 13-20 atomic percent Ge, 28-43 atomic percent Sb, and 43-55 atomic percent Te. In another embodiment, the alloy of the present invention comprises 15-18 atomic percent Ge, 32-35 atomic percent Sb, and 48-51 atomic percent Te.

The present invention includes an electrical device comprising a chalcogenide material of the present invention, said device comprising a layer of chalcogenide material for electrical connection having two electrical terminals or contacts. The invention further includes an array of such devices. In one embodiment of the present invention, a device comprising one of the alloys of the present invention requires a set pulse time of less than 100 ns when the reset resistance is ≦ 200 kΩ. In other embodiments, a device comprising one of the alloys of the present invention requires a set pulse time of less than 40 ns when the reset resistance is ≦ 100 kΩ. In a preferred embodiment, a device comprising one of the alloys of the present invention requires a set pulse time of less than 20 ns when the reset resistance is ≦ 40 kΩ. In another preferred embodiment, a device comprising one of the alloys of the present invention requires a set pulse time of less than 30 ns when the reset resistance is ≦ 60 kΩ.

  The present invention provides chalcogenide materials and electrical devices comprising the chalcogenide materials of the present invention that exhibit favorable operating characteristics for practical memory and switching applications. Devices comprising the alloys of the present invention exhibit a short set time from a reset state with high resistance. The device provides memory states over a wide range of resistances, each memory state exhibiting a short set time. The device thus enables a rapid conversion between memory states with very different resistances. In particular, the device comprising the chalcogenide alloy of the present invention allows conversion between a high resistance memory state and a low resistance memory state, and has a high conversion speed and a high resistance ratio of the two states. The device of the present invention provides a preferred threshold voltage and reset current.

  The device also has the same preferred adjustment characteristics as described in US Pat. In some embodiments, a device comprising a chalcogenide material of the present invention does not need to be adjusted after fabrication to make the device a practical adjustment. In these embodiments, the set resistance is stable even after cycling the set and reset states immediately after device deposition, and the stabilized set resistance deviates only slightly from the initial resistance value of the device. . As a result, the need to apply electrical learning to the device after completion of the manufacturing process prior to practical use is greatly reduced. Further information regarding this adjustment process can be found in US patent application no. 11 / 200,466.

  Since the principles underlying the improved set speed properties of the alloys of the present invention are related to the structural characteristics of the chalcogenide material, it is useful to review the basic principles of operation of the chalcogenide material. An important feature of chalcogenide materials in the operation of chalcogenide memory devices and device arrays is the ability to make phase changes between two or more structural states. (Some people call chalcogenide materials “phase change materials” because of the importance of phase changes in memory applications, and so on in the present specification.) Chalcogenide materials have a crystalline state, one or more. There are structural states including a partially crystalline state and an amorphous state. The crystalline state may be a single crystalline state or a polycrystalline state. The partially crystalline state refers to a structural state in which a certain volume of chalcogenide material includes an amorphous portion and a crystalline portion. In general, phase change materials have multiple partially crystalline states that can be distinguished by the relative proportions of amorphous and crystalline portions. Partial crystallinity is one way to characterize the structural state of a chalcogenide phase change material. The partial crystal state continuously changes from 0% (amorphous limit) to 100% (crystallization limit). Phase change chalcogenide materials can thus phase change in multiple structural states where the partial crystallinity varies globally between 0% and 100%.

  A phase change in the structural state of the chalcogenide material is induced by supplying energy to the chalcogenide material. Various forms of energy can affect the partial crystallinity of the chalcogenide material and induce structural changes. Suitable forms of energy include other energies such as electrical energy, thermal energy, optical energy or particle beam energy and induce electrical, thermal and optical effects on the chalcogenide material. Combinations of different forms of energy can also induce structural changes. Continuous and reversible variability of partial crystallinity can be achieved by controlling the energy environment of the chalcogenide material. With appropriate control of the energy environment of the chalcogenide material, the crystalline state can change from a partial crystalline state to an amorphous crystalline state, the partial crystalline state can change to a crystalline state, an amorphous state, and a different partial crystalline state, and The amorphous state can change from a partially crystalline state to a crystalline state. Considerations related to the use of thermal, electrical and optical energy to induce structural changes are described below.

The use of thermal energy to induce structural changes exploits thermodynamics and dynamics associated with phase changes from the crystalline state to the amorphous state or from the amorphous state to the crystalline state. Amorphous state, for example, by cooling the chalcogenide material at a sufficient speed so as not crystalline phase generated from the heating to the melting point than any precursor state from (partially crystalline state, crystalline state, comprising amorphous state) Can be formed. Crystalline state, for example, sufficient time to allow the growth of the nucleation and / or crystal region, by heating the crystallization temperature than the chalcogenide material, any precursor to (partially crystalline state, crystalline state, an amorphous state Including). The crystallization temperature is below the melting point and corresponds to the temperature at which crystallization occurs. The driving force for crystallization is typical in that the overall energy of the chalcogenide material decreases as the degree of partial crystallinity increases because the free energy of the crystalline or partially crystalline state is lower than the free energy of the amorphous state. Thermodynamic. Formation of crystal states or crystal regions (nucleation and growth) in the partial crystal state is kinetically possible. Thus, when heated below the melting point, crystallization is promoted by providing energy that facilitates the reorganization of the atoms necessary to form a crystalline phase or crystalline region. Partial crystallinity of the partially crystalline state is controlled by adjusting the temperature or time of heating of the previously amorphous chalcogenide material, or by adjusting the cooling rate of the previously amorphous chalcogenide material can do.

  The use of electrical energy to induce structural changes typically relies on the application of electrical (current or voltage) pulses to the chalcogenide material. By adjusting the magnitude and / or time of the electrical pulse applied to the chalcogenide material, it is possible to change the partial crystallinity continuously. The effect of electrical energy on the structure of the chalcogenide material is often represented by changes in the low field electrical resistance of the chalcogenide material due to the magnitude of the current or voltage pulse applied to the chalcogenide material. A representative example of the low field electrical resistance (R) of a chalcogenide material as a function of electrical energy or current pulse magnitude (energy / current) is shown in FIG. FIG. 1 shows the low field electrical resistance change of a chalcogenide material resulting from various magnitudes of electrical energy or current pulses, commonly referred to as a resistance plot.

  The resistance plot includes two types of response characteristics of chalcogenide materials to electrical energy. These molds are substantially delimited by the vertical dashed line 10 shown in FIG. The mold to the left of the dashed line 10 can be referred to as a storage chalcogenide material. The storage type is characterized in that the electrical resistance is almost constant or gradually changes with increasing electrical energy and suddenly decreases above a certain threshold energy. In this way, the accumulation type passes through a plateau region (generally indicated by reference numeral 30) corresponding to a range in which the resistance change is small or gradual from the left end point 20 of the resistance plot in the direction of increasing energy. And extends to point 40, where the electrical resistance suddenly decreases. The plateau 30 is horizontal or inclined. The structural state of the chalcogenide material when energy is applied continuously changes depending on the partial crystallinity of the structural state that correlates with the total amount of applied energy, so the left side of the resistance plot is called the accumulation type. The leftmost point 20 corresponds to the accumulation type structural state with the lowest partial crystallinity. This state is either completely amorphous or contains some residual crystals. As energy is added, the degree of partial crystallinity increases and the chalcogenide material changes among the plurality of partial crystal states that follow the plateau 30 in the direction of increasing applied energy. The selected accumulation state (structural state of the accumulation region) is indicated by square marks in FIG. By accumulating a threshold amount of applied energy, the partial crystallinity of the chalcogenide material increases sufficiently to perform a change to the set state characterized by a dramatic decrease in electrical resistance and stabilization of the set state 40. The structural changes in the storage region are unidirectional in that they proceed only in the direction of increasing applied energy in the plateau region 30 and are only reversible by first amorphizing or resetting the chalcogenide material. It is sex. The behavior shown in FIG. 1 is reproducible even when the required energy or current is applied and the device containing the chalcogenide material is cycled into the set and reset states many times. Once the reset condition is obtained, a lower amplitude current pulse can be reapplied and the chalcogenide material accumulation response can be retraced. It is thus possible to cycle the set and reset states many times, which is a necessary feature for a high lifetime of memory cycles.

  Without wishing to be bound by theory, the inventor has found that the application of energy to a storage chalcogenide material can cause partial crystallinity by nucleation of new crystalline regions or growth of existing crystalline regions or combinations thereof. I believe it will increase. In order to prevent the formation of an adjacent crystal network that bridges the chalcogenide material between the two device electrodes, the crystal regions are formed or grown relatively isolated from each other, so that a portion along the plateau 30 is formed. It is believed that the electrical crystallinity changes very slowly, although the mechanical crystallinity increases. This type of crystallization can be referred to as subpercolation crystallization. The change in set state is consistent with a percolation threshold such that an adjacent, interconnected crystal network is formed in the chalcogenide material between the two device electrodes. For example, this type of network can be formed if the size is large enough to cause a crystallization region to hit an adjacent region. Since the electrical resistance of the chalcogenide material in the crystallization phase is lower than in the amorphous phase, the percolation threshold corresponds to the formation of an adjacent low resistance conductive path by the chalcogenide material. As a result, the percolation threshold is characterized by a dramatic decrease in the resistance of the chalcogenide material. The leftmost position of the accumulation type is an amorphous state or a partially crystallized state without an adjacent crystal network. Subpercolation crystallization begins with an initial amorphous or partially crystallized state, and includes multiple partially crystallized states that increase in partial crystallinity until the percolation threshold is reached and a change to the set state occurs. Proceed through.

  The mold on the right side of the broken line 10 in FIG. 1 is called a gray scale mold or a gray scale region. The gray scale mold extends from the set state 40 through a plurality of intermediate states (generally indicated at 50) to a reset position or reset state 60. The various positions of the gray scale type are referred to as the gray scale state of the chalcogenide material. The selected gray scale state is indicated by a circle in FIG. As shown in FIG. 1, grayscale structural changes are induced by applying a current or electrical energy pulse to the chalcogenide material. In the gray scale type, the resistance of the chalcogenide material varies with the magnitude of the applied electrical pulse. The grayscale specific state resistance is characteristic of the structural state of the chalcogenide material, and the structural state of the chalcogenide material depends on the magnitude of the current pulse applied in the grayscale region. As the magnitude of the current pulse increases, the partial crystallinity of the chalcogenide material decreases. Partial crystallinity is high near the set point 40 and gradually decreases as the reset state 60 is approached. The chalcogenide material varies from a structural state with an adjacent crystal network in the set state 40 to an amorphous or substantially amorphous or partially crystallized structural state without an adjacent crystal network in the reset state. Applying a current pulse while increasing the size has the effect of converting a portion of the crystal network into an amorphous phase, ultimately resulting in the destruction or interruption of the adjacent highly conductive crystal path of the chalcogenide material. As a result, the resistance of the chalcogenide material increases as the magnitude of the applied current pulse increases in the gray scale region.

  In contrast to the accumulation region, the structural changes that occur in the grayscale region are reversible and bidirectional. For this reason, the gray scale region is also referred to as the direct overwriting region of the resistance plot. As described above, each state of the gray scale region can be confirmed by its resistance and the magnitude of the current pulse. When a current pulse of a certain magnitude is applied, a change in partial crystallinity is induced, Produces a certain resistance value. When a current pulse is subsequently applied, the partial crystallinity can be increased or decreased with respect to the initial partial crystallinity of the chalcogenide material. If the magnitude of the subsequently applied current pulse is greater than that used to establish the initial state, the partial crystallinity of the chalcogenide material will decrease and the structural state will be higher resistance along the grayscale resistance curve. Conversion from the initial state in the direction of the reset state. Similarly, when the magnitude of the next applied current pulse is smaller than that used to establish the initial state, the partial crystallinity of the chalcogenide material increases and the structural state is a resistance along the grayscale resistance curve. It changes from the initial state in the direction of the set state where becomes lower.

  In OUM applications, the grayscale state of the chalcogenide material is used to determine the memory state of the memory device. Most commonly, the memory device is a binary memory device that utilizes two of the grayscale states as memory states. Here, different information values (for example, “O” or “1”) relate to the respective states. Each memory state corresponds to a different structural state of the chalcogenide material, and each structural state is characterized by a different resistance value, eg, as shown in the gray scale state of FIG. The state can be read or identified by measuring the resistance. The operation of converting a chalcogenide material into a structural state associated with a particular memory state can be referred to as programming the chalcogenide material, writing to the chalcogenide material, or storing information in the chalcogenide material.

In order to facilitate reading and minimize read errors, it is desirable to select the memory state of the binary memory device so that the ratio of the resistances of the two states is large. In general, a set state (or a state in the vicinity of the set state) and a reset state (or a state in the vicinity of the reset state) are selected as memory states in a binary memory application. The ratio of resistance depends on the chemical composition of the chalcogenide, the thickness of the chalcogenide material of the device, the placement of the device, and the like. In a standard two-terminal device structure, a layer of phase change material having a composition of Ge ₂₂ Sb ₂₂ Te ₅₆ , a thickness of 600 ridges, and a pore size of less than about 0.1 μm, for example, the resistance in the reset state is about 100-1000 kΩ and the resistance in the set state is less than about 10 kΩ. Phase change materials generally exhibit a resistance in the range of 100 kΩ to 1000 kΩ in the reset state and a resistance in the range of 0.5 kΩ to about 50 kΩ in the set state. In preferred phase change materials, the resistance in the reset state is at least twice, typically more than an order of magnitude greater than the resistance in the set state. In addition to binary (single bit / device) memory applications, chalcogenide materials can select non-binary, ie, by selecting more than two states from grayscale states and associating information values with each state. It can be used as a memory device of a multi-value bit / device. Here, each memory state corresponds to a different structural state of the chalcogenide and is characterized by a different resistance value.

  One embodiment of the present invention provides a chalcogenide material that enables a device with improved operating speed, where the device speed is related to the time required to induce changes between structural states. As described above, accumulating information in the chalcogenide material involves a process such as applying energy to the chalcogenide material to induce a structural change to a memory state that represents the information item that the user desires to accumulate. The speed of the device is governed by the rate at which the structural change occurs, which ultimately depends on the dynamics of the change between the crystalline state and the amorphous state of the chalcogenide material (or vice versa). From a phenomenological point of view, structural changes that induce an increase in partial crystallinity are considered to be slower than structural changes that induce a decrease in partial crystallinity. As described above, the formation of a crystalline phase from an amorphous phase requires the confirmation of an ordered phase from an irregular phase, and the achievement of an ordered phase entails a large atomic rearrangement over one or more interatomic distances. Can be considered. The required atomic motion and periodic rearrangement of interatomic bonds in a periodic regular array requires a time scale, and the crystallization process is necessarily an equilibrium process.

  In contrast, structural changes leading to a decrease in partial crystallinity are essentially non-equilibrium processes that occur on a time scale shorter than the equilibrium time scale associated with crystallization of the same material. The reduction in the degree of partial crystallinity includes a change of the ordered crystal region to a disordered amorphous region. The crystalline region first melts and then is quenched to form an amorphous phase. The melting process is not limited by the time scale associated with the atomic motion of the material, and the quench process generally occurs on a shorter time scale than the crystallization process. The time scale of change is determined by the rate of application of energy that causes melting and the rate of removal of energy to quench the molten state. Both speeds can be controlled by external experimental conditions and can occur on a very short time scale. For standard chalcogenide materials, the equilibrium time scale associated with the crystallization process is typically 10-1000 nanoseconds, while the amorphization (melt-quenching) process is a sub-nanosecond to 10 nanosecond time scale. By adjusting the experimental conditions, it can be made to occur on a picosecond or even femtosecond time scale.

  From the above description, the speed of operation of the chalcogenide memory device will be determined in part by the rate at which the partial crystallinity changes from the low partial crystallinity state to the high partial crystallinity state. In a typical binary device, the two memory states are a reset state (low partial crystallinity state) and a set state (high partial crystallinity state), and the operating speed is from the reset state to the set state. It is thought to be significantly affected by the time scale of change. In addition to the rate of change from the amorphous phase to the crystalline phase, the time required to place the chalcogenide device in the set state depends on the initial crystallization volume fraction of the device. As described above, in connection with FIG. 1, the memory state of the chalcogenide device can be selected from among the grayscale states 50 that extend from the set state 40 to the reset state 60. The set state 40 can be formed from either the reset state 60 or the grayscale state 50 by applying energy to accumulate the increment to achieve the percolation state as described above. The magnitude of the energy increment required to put one of the grayscale states into the set state is less than the energy required to induce a change from the reset state in region 60 of FIG.

  The gray scale state very close to the set state has a resistance and partial crystallinity similar to the set state. These states have a relatively low resistance and require a relatively low net energy storage to make a change to the set state. That the partial crystallinity of the low-resistance grayscale state is similar to the set state means that the structural arrangement or conditions of the low-resistance grayscale state are not significantly deviated from the percolation arrangement of the set state. Since only a small change in the structural arrangement is required to achieve the set state, the time required to induce the set state change is even shorter, so there is more between the low resistance grayscale state and the set state. Rapid changes are possible.

  However, as the resistance in the gray scale state increases, the structural arrangement becomes less crystalline and deviates significantly from the set percolation arrangement. Achieving the set state requires greater energy storage and a greater amount of structural configuration change. Therefore, the time scale of change to the set state increases. For this reason, the operation speed of the memory device using the high-resistance gray scale state as the memory state becomes slower.

  From the above discussion, two important factors governing the rate of change between memory states and the speed of operation of the memory device are the inherent characteristics of a working chalcogenide material from an amorphous or partially crystalline state. It was shown that this is the initial state of the crystallization rate and the crystallinity of the chalcogenide material. While it is true that fast operating speed can be achieved by selecting a memory state with a structural arrangement that does not deviate much from the set state percolation arrangement, this method is often insufficient. The main drawback is that in such a method, the resistance ratio between the different memory states is low and the resistances of the different states are similar, making it more difficult to distinguish among the different memory states at the time of reading. That's what it means.

  In the present invention, chalcogenide compositions that exhibit improved intrinsic crystallization rates provide a more effective way of achieving higher operating speeds. The chalcogenide alloys of the present invention enable chalcogenide memory devices that exhibit a rapid change from grayscale to set states over a wider range of resistance compared to conventional alloys. Due to the rapid crystallization, the initial deviation of the gray scale structure from the set percolation arrangement is less important in determining the rate of change, so the higher the intrinsic crystallization speed, the higher the resistance. It is possible to change rapidly from a gray scale state to a set state. The high crystallization rate can compensate for the increase in structural configuration shift between the high resistance memory state and the set state. The chalcogenide alloys of the present invention thus enable memory devices that provide high operating speeds and high resistance ratios between memory states.

  While not wishing to be bound by theory, the inventor believes that the crystallization process of chalcogenide materials is based on the mechanisms of nucleation of crystalline regions from amorphous regions, growth of nucleated phases, and growth of existing crystalline regions. We recognize that it can be caused by one or more of It is believed that the crystallization rate increases as the rate of one or more of these mechanisms increases. High nucleation rates increase the concentration of crystalline nuclei, and crystalline nuclei are seeds for the crystallization process, resulting in faster crystallization rates. Growth is a process in which the size of an existing crystalline region is increased by interfacial conversion from an amorphous material to a crystalline material at the crystalline region boundary. Increasing the growth rate promotes the expansion of the crystal region and promotes the change to the percolation structure arrangement.

  Formation of the crystalline phase from the amorphous phase is usually thermodynamically supported but kinetically suppressed. At temperatures below the melting point, the free energy of the crystalline phase is lower than the free energy of the amorphous phase, so there is a thermodynamic driving force for crystallization. However, as described above, in order to crystallize, it is necessary to perform atomic rearrangement necessary for realizing a crystallized state in which the material is ordered. In order to induce the necessary rearrangement, the energy barrier must be overcome, which acts to suppress crystallization. Both nucleation and growth processes are associated with energy barriers. As the energy barrier size increases, the kinetic probability of the crystallization process decreases. The high crystallization rate observed in the alloys of the present invention can be explained by the reduced energy barrier associated with either or both of the nucleation process and the growth process. The energy barrier reduction occurs in chalcogenide compositions that readily exhibit atomic rearrangement at temperatures between the crystallization temperature and the melting point. Easy rearrangement is expected in compositions with low structural rigidity, especially in the amorphous phase.

  The relative atomic concentration of different elements in the composition of the present invention can explain the improved crystallization rate. The material of the present invention generally includes Ge, Sb and Te. These elements are tetravalent, trivalent, and divalent, respectively. In many amorphous chalcogenide phases, Te promotes the formation of extended chain structures, and Ge and Sb function as improving elements that act to promote interchain cross-linking. Ge is an element that strongly promotes crosslinking, but Sb is an element that is only moderately crosslinked. Since cross-linking acts to increase the rigidity of the structure of the amorphous phase, when the Ge and / or Sb concentration decreases, the rigidity of the amorphous phase tends to decrease. However, when the Ge and / or Sb concentration is decreased, the Te concentration is increased, which has the effect of increasing the chain length. Long chains are disadvantageous from a crystallization point of view because long chains are difficult to rearrange in order to create an ordered state that promotes crystallization. The chalcogenide material of the present invention has a lower atomic concentration of Ge and Te and a higher atomic concentration of Sb than the prior art material. The decrease in Ge shows a tendency to reduce the formation of bridges in the amorphous phase and acts to promote crystallization by reducing the structural rigidity. Reduction of Te acts to reduce the number and / or length of chains, such as the structure of the amorphous phase, and can facilitate crystallization by facilitating atomic rearrangement. Sb is a cross-linking promoting element, but is less effective than Ge. Considering the decrease in Te concentration, the effect of increasing Sb concentration on structural rigidity is not significant. The chalcogenide composition of the present invention thus shows that the balance of the factors underlying the crystallization tendency of the chalcogenide material is optimal.

  In one embodiment of the invention, the alloy is a material having a Ge concentration in the range of 11-22 atomic percent, an Sb concentration in the range of 22-65 atomic percent, and a Te concentration in the range of 28-55 atomic percent. is there. In other embodiments, the alloy has a Ge concentration in the range of 13-20 atomic percent, an Sb concentration in the range of 28-43 atomic percent, and a Ge concentration in the range of 43-55 atomic percent, 32-35 A material having an Sb concentration in the atomic percent range and a Te concentration in the 48-51 atomic percent range.

  Specific examples of chalcogenide compositions within the scope of the present invention and the properties of devices comprising the chalcogenide compositions of the present invention are described in the following examples.

Example 1
This example describes the fabrication of a memory device having an active chalcogenide layer according to the present invention. This device structure is a commonly used two-terminal device design and has an active chalcogenide layer with holes in electrical contact with the upper and lower electrodes. Two different device configurations were used, and similar results were achieved for each. Both designs were deposited on Si wafers with a thick SiO ₂ surface oxide layer.

In one design, a chalcogenide layer having a thickness of 500 mm was deposited on a circular lower electrode having a dimension of <1000 mm and a surrounding SiO ₂ layer. Next, as it is, a 400-cm carbon layer was deposited on the chalcogenide layer, and one or more conductive layers were deposited on the carbon layer to deposit an upper electrode. The conductive layer typically consists of a 300Å TiN layer and a 500Å Ti layer.

  In the second design, a 350 mm lower electrode layer (eg, TiAlN) was deposited on the surface oxide layer and an insulating layer (eg, SiO 2) was deposited on the lower electrode. A hole having a diameter of approximately 800 mm was formed in the insulating layer. Subsequently, a chalcogenide layer having a thickness of 500 mm was deposited. The chalcogenide layer coats the holes and extends horizontally on the surrounding insulating layer. Next, as it is, a 400-cm carbon layer was deposited on the chalcogenide layer, and one or more conductive layers were deposited on the carbon layer to deposit an upper electrode. The conductive layer typically included a 300 Ｔｉ TiN layer and a 500 Ｔｉ Ti layer.

Appropriate lithography and patterning was performed on each design of the device to allow device addressing and the device was annealed at 300 ° C. for 30 minutes. Both device designs are well known in the prior art, and further information regarding, for example, chalcogenide phase change memory cells can be found, for example, in US Pat. No. 5,166,758, US Pat. No. 5,296,716, US Pat. No. 5,414,271, US Pat. No. 5,359,205, US Pat. 5,166,758.

The chalcogenide layer of each memory device of Example 1 was deposited at 200 ° C. using a Ge ₂ Sb ₂ Te ₅ , Ge, and Sb target by RF co-sputtering. By controlling the input, ion energy, exposure time, use of different targets, etc. in the sputtering process, chalcogenide films of different compositions were made. A memory device having a chalcogenide layer having the composition shown in Table 1 was produced. The composition is given in atomic percent of the elements contained in the chalcogenide material. The atomic percent is also referred to as atomic concentration in the present invention. In Example 1, many devices having a chalcogenide layer having the composition shown in Table 1 were manufactured. The chalcogenide material and the device comprising it are now referred to by the composition in Table 1 or the symbols shown in the left column.

  The device of Example 1 is an electrical device including a chalcogenide material, a first terminal in electrical connection with the chalcogenide material, and a second terminal in electrical connection with the chalcogenide material, wherein the chalcogenide composition described above One or more devices were fabricated using each of the above. Each device can operate in multiple reset states (state on the right side of FIG. 1), multiple storage states (state on the left side of FIG. 1), or a combination of reset and storage states, so that the operating characteristics of the device are It is qualitatively similar to the behavior shown in FIG. Different chalcogenide compositions result in different device operating characteristics, which are described in Example 2 below.

(Example 2)
Example 2 describes the improved crystallization rate of a device comprising a chalcogenide material according to the present invention. The device structure used in Example 2 corresponds to the above structure described in Example 1. The crystallization rate of a device containing some of the chalcogenide compositions shown in Example 1 was measured. In the measurement, a current pulse was applied to the device to change the chalcogenide to the initial state of the gray scale portion of the response curve. The initial resistance was recorded. In the next step of the experiment, energy was applied to the device and the time required to set the device in the set was recorded. The applied energy is in the form of a current pulse having a constant amplitude and fluctuation range. The energy of the pulse is such that the device operates in the accumulation response type of the device's resistance-current plot (see FIG. 1). The device resistance was monitored as a function of time when pulses were applied to the device with varying pulse widths from 20 ns to 5 μs. The change to the set state was indicated by a decrease in resistance as described above in connection with FIG. The pulse time required to achieve the set state was recorded. For each device, repeat the experiment with several different initial states in a grayscale type over a wide range of resistors, and determine the relationship between the initial state resistance and the pulse time required to set the device. Were determined.

FIG. 2 shows the dependence of the pulse time required to set the device on the initial state resistance used in the experiment. The pulse time required to set the device in a set state is also called a set pulse width, and is represented by W _set in FIG. The set pulse time is reported in seconds. The initial resistance used in the experiment is also referred to as the device's reset resistance because it represents the grayscale resistance of the device that is reset prior to the start of the experiment. (In the scope of this terminology, the reset state with the greatest resistance is called the saturated reset state.) The initial state resistance is denoted R _rs in FIG. 2 and is reported in ohms. FIG. 2 shows several data curves. Each data curve corresponds to a device containing a different chalcogenide composition, and a point on each curve corresponds to a different reset state of the device. The legend of FIG. 2 identifies the chalcogenide composition associated with each data curve by the display in Table 1. The data curve represented by “ control ” refers to a device comprising a composition of prior art Ge ₂ Sb ₂ Te ₅ .

The control device data curve is typical of the response of prior art chalcogenide materials. If the reset resistance of the control device is less than about 4.5 kΩ, the set pulse time is about 20 ns. However, if this resistance is higher than about 4.5 kΩ, the set pulse time increases dramatically, reaching a value of about 400 ns with a resistance of about 11.9 kΩ. For memory states where the resistance is slightly greater than twice, the set pulse time is about 20 times greater. In actual memory applications, it is desirable that the resistance ratio between memory states be greater than 2 so that different states can be reliably distinguished during reading. For the control device, the data show that a large increase in set pulse time is accompanied by a two-fold increase in resistance. With respect to operating speed, a longer set pulse time with a higher resistance state becomes a control factor.

Considering the data curve of the device containing the alloy according to the invention, a much more favorable relationship is shown between the set pulse time and the reset resistance. The data curve of the device containing the alloy of the present invention is generally much lower than the data curve of the control device. Devices comprising the alloys of the present invention exhibit the beneficial feature of providing short set pulse times for conditions with higher reset resistance. Representative data points from the data curve selected from FIG. 2 are summarized in Table 2.

The data points clearly demonstrate the advantages of the alloys of the present invention over prior art control alloys. In devices containing the alloys of the present invention, a short set pulse time is observed with a much higher reset resistance (and a much wider range of reset resistance). For example, in a device comprising Ge _17.8 Sb _33.3 Te _48.9 alloy, increasing the resistance by more than 20 times only involves an increase in set pulse time of only 4.3 times. Similar favorable results were observed for other alloys disclosed in this invention, including the alloys listed in Table 2.

Thus, devices that operate with the alloys of the present invention exhibit a faster transition to the set state for a wider range of reset resistance than similar devices that operate with prior art alloys. From an application point of view, the change to a fast set state observed over a wide range of resistors allows the operation of a binary device using memory states with very different resistances without sacrificing operating speed. So it is beneficial. For example, the control device allows operation with a set pulse time of 400 ns between memory states where the resistances differ slightly more than twice. On the other hand, devices including Ge _17.8 Sb _33.3 Te _48.9 can be operated with a set pulse time of only 86 ns between memory states with resistances differing by a factor of 20 or more. Operation between states with significantly different resistances is preferred because such states facilitate identification during reading and allow for programming variations between cells. Larger resistor ratios reduce read errors.

Devices comprising the alloys of the present invention are also advantageous when applied to memories having multiple states. The fact that the alloy of the present invention undergoes a change to a set state at a high speed with respect to a wide range of resistance states means that the device speed can be reduced and operation by other memory states is possible. For example, for a sufficiently accurate memory state readability, if a minimum resistance ratio of about 2 is desired, and if it is desired to operate at a speed limited by a set pulse time of 400 ns, the memory state in the control device is Only two are available. On the other hand, in the case of a device comprising Ge _17.8 Sb _33.3 Te _48.9 , five consecutive memory states exhibiting a resistance ratio of 2 can be operated at a faster rate defined by the set pulse time 86 ns. Can be determined.

  The present invention provides an electrical device comprising a chalcogenide material for electrical connection having at least two terminals, wherein the device operates between a plurality of states determined by structural features of the chalcogenide material. can do. In one embodiment of the invention, the operating state of the device includes more than one reset state, the resistance of one reset state being more than three times greater than the resistance of the other reset state, and the higher resistance state is required. The set pulse time is less than 20 times greater than the required set pulse time for the lower resistance state. In other embodiments, the operational state of the device includes more than one reset state, the resistance of one reset state being more than three times greater than the resistance of the other reset state, and the required set pulse time of the higher resistance state. Is less than 10 times greater than the required set pulse time for the lower resistance state. In yet another embodiment, the operating state of the device includes more than one reset state, the resistance of one reset state being more than three times greater than the resistance of the other reset state, and the required set pulse of the higher resistance state. The time is less than 5 times greater than the required set pulse time for the lower resistance state. In yet another embodiment, the operating state of the device includes more than one reset state, the resistance of one reset state being more than three times greater than the resistance of the other reset state, and the required set pulse of the higher resistance state. The time is less than twice as long as the required set pulse time for the lower resistance state.

  In one embodiment, the operating state of the device includes more than one reset state, the resistance of one reset state is more than 10 times greater than the resistance of the other reset state, and the set pulse required for the higher resistance state The time is less than 20 times greater than the set pulse time required for the lower resistance state. In other embodiments, the operating state of the device includes more than one reset state, the resistance of one reset state being more than 10 times greater than the resistance of the other reset state, and the set required for the higher resistance state The pulse time is less than 10 times greater than the set pulse time required for the lower resistance state. In other embodiments, the operating state of the device includes more than one reset state, the resistance of one reset state being more than 10 times greater than the resistance of the other reset state, and the set required for the higher resistance state The pulse time is less than 5 times greater than the set pulse time required for the lower resistance state.

  In one embodiment, the operating state of the device includes more than one reset state, the resistance of one reset state is more than 20 times greater than the resistance of the other reset state, and the set pulse required for the higher resistance state The time is less than 20 times greater than the set pulse time required for the lower resistance state. In other embodiments, the operating state of the device includes more than one reset state, the resistance of one reset state being more than 20 times greater than the resistance of the other reset state, and the set required for the higher resistance state The pulse time is less than 10 times greater than the set pulse time required for the lower resistance state. In still other embodiments, the operating state of the device includes more than one reset state, the resistance of one reset state being more than 20 times greater than the resistance of the other reset state, and required for the higher resistance state. The set pulse time is less than 5 times greater than the set pulse time required for the lower resistance state.

FIG. 3 is extracted from FIG. 2 and summarizes the set pulse width data selected for a control device and a device comprising an alloy of the present invention. FIG. 3 illustrates the set pulse time from a reset state having a resistance greater than 100 kΩ for a device comprising a prior art control alloy and a device comprising some of the alloys of the present invention. The set state at each device change has a resistance of less than 5 kΩ. In FIG. 3, the set pulse width is plotted as a function of the Ge, Sb and Te atomic percent in the active chalcogenide layer of the device. The atomic percentages of Ge, Sb and Te are represented by rhombus symbols, triangle symbols and square symbols, respectively. Since the atomic percent of each element is shown for each of several compositions, each composition is represented by the three symbols in FIG. Since one set pulse width is reported for each composition in FIG. 3, the three symbols representing each composition are arranged horizontally. The top set of three symbols corresponds to the set pulse width of the control device using Ge ₂₂ Sb ₂₂ Te ₅₅ as the active chalcogenide material. This configuration shows the longest set pulse width displayed in FIG.

Although three ellipses are shown in FIG. 3, each ellipse represents the preferred atomic percent of each element of the chalcogenide material. The neighborhood range associated with the ellipse is based on the desirability of achieving a short set pulse width and fast device operation. The left ellipse represents the preferred atomic percent range of Ge, extending from about 13.5 atomic percent to about 18 atomic percent. In this Ge composition range, the set pulse width of the device is significantly shorter than the set pulse width of the control device consisting of a chalcogenide material with 22 atomic percent Ge and the device consisting of Ge ₂₀ Sb ₃₀ Te ₅₀ as the active chalcogenide material.

The middle ellipse represents the preferred atomic percent range of Sb, extending from about 33.0 atomic percent to about 41 atomic percent. In this Sb composition range, the set pulse width of the device is a control device consisting of a chalcogenide material with 22 atomic percent of Sb and a set of devices consisting of Ge _20.0 Sb _25.5 Te _54.5 as the active chalcogenide material. It is significantly shorter than the pulse width.

The right ellipse represents the preferred atomic percent range of Te and extends from about 37 atomic percent to about 48 atomic percent. In this Te composition range, the set pulse width of the device is a control device consisting of a chalcogenide material with 55 atomic percent Te, and a set of devices consisting of Ge _20.0 Sb _25.5 Te _54.5 as the active chalcogenide material. It is significantly shorter than the pulse width.

  FIG. 4 is also extracted from the results shown in FIG. 2 and summarizes the required reset current of the device. The reset current is expressed as a function of the atomic percent of the elements contained in the active chalcogenide layer of the device. As in FIG. 3, atomic percentages of Ge, Sb, and Te are shown for each composition, and each composition is represented by three horizontally arranged symbols. The atomic percentages of Ge, Sb and Te are represented by rhombus symbols, triangle symbols and square symbols, respectively. The reset current is expressed in amps (A) and corresponds to the current required to change the device to a saturated reset state. As described above, the saturated reset state of the device is the reset state having the maximum resistance. In order to minimize the power required to operate the device, it is desirable for the device to have a low reset current.

  FIG. 4 includes an ellipse to show the preferred atomic percent range for Ge, Sb, and Te. This preferred range corresponds to an atomic percent of different elements that results in a low reset current. The left ellipse represents the preferred atomic percent range for Ge, extending from about 14 atomic percent to about 18 atomic percent. In this Ge composition range, the device reset current typically decreases as the atomic percent of Ge increases or decreases. The middle ellipse represents the preferred atomic percent range of Sb, extending from about 17 atomic percent to about 33 atomic percent. In this Sb composition range, the device reset current typically decreases as the atomic percent of Sb increases or decreases. The right ellipse represents the preferred atomic percent range of Te and extends from about 43 atomic percent to about 55 atomic percent. In this Te composition range, the device reset current typically decreases as the atomic percentage of Te increases or decreases.

In addition to the results described in Example 2 above, further experiments were performed using the devices and compositions described in Example 1. In these experiments, the set pulse width required to change the device from a reset state having a resistance of 50 kΩ to a set state having a resistance of less than 5 kΩ, the threshold voltage of the device in a saturated reset state, the holding voltage of the device, and The initial resistance of the device was measured. The set of parameters included in these experiments and the experiment described in Example 2 corresponds to some of the more important device characteristics for practical memory applications. The results generally show a small variation in the optimum range of atomic percent of Ge, Sb and Te for different properties. Thus, in the design of new devices, the importance of different properties is weighted relative to each other in order to achieve an overall optimum level of performance.

  The present invention generally provides chalcogenide materials comprising Ge and Sb. In one embodiment, the atomic concentration of Ge is between 11 atomic% and 21 atomic%. In a preferred embodiment, the atomic concentration of Ge is between 13% and 20%. In another preferred embodiment, the atomic concentration of Ge is between 15 atomic% and 18 atomic%. In one embodiment, the atomic concentration of Sb is between 22 atomic% and 65 atomic%. In a preferred embodiment, the atomic concentration of Sb is 28 atomic% to 43 atomic%. In another preferred embodiment, the atomic concentration of Sb is between 32 atomic% and 35 atomic%. In each of the foregoing embodiments, the composition range of each element includes the composition at both ends.

  The present invention further provides a chalcogenide material containing Te as well as Ge and Sb in the above composition range. In one embodiment, the atomic concentration of Te is 28 atomic% to 55 atomic%. In a preferred embodiment, the atomic concentration of Te is 43 atomic% to 55 atomic%. In another preferred embodiment, the atomic concentration of Te is 48 atomic% to 51 atomic%. In each of the foregoing embodiments, the composition range of each element includes the composition at both ends.

  The present invention further includes embodiments that are functionally equivalent to the above-described embodiments. As described in some of the above-cited US patents, chalcogenide materials generally include a chalcogen element and one or more chemical or structural modifying elements. The chalcogen element (eg Te, Se) is selected from group VI of the periodic table, and the modifying element is group III (eg Ga, Al, In), group IV (eg Si, Ge, Sn) or V of the periodic table. It can be selected from the group (eg P, As, Sb). The role of the modifying element includes providing a position for branching or crosslinking between chains of chalcogen elements. The group IV modifying element can function as a tetracoordinate modifying element and has two coordination positions within the chalcogenide chain and two coordination positions that allow branching or crosslinking away from the chalcogenide chain. Including. The group III and group V modifying elements can function as tricoordinate modifying elements, with one coordination allowing two coordination positions within the chalcogenide chain and branching or crosslinking away from the chalcogenide chain. Includes position. In the above embodiment, the feature of the present invention that the chalcogenide material containing Ge, Sb, and / or Te is used has been described. However, all or a part of Ge is replaced with another group IV element (for example, Si), and One skilled in the art will appreciate that all or a portion can be replaced with another group V element (eg, As) and all or a portion of Te can be replaced with another group VI element (eg, Se). It can be done.

  In addition to individual devices, the present invention further extends to an array of devices. The chalcogenide materials and devices of the present invention are described in US Pat. No. 5,694,146, US Pat. No. 5,912,839 and U.S. Pat. Can be integrated into an XY array as described in US Pat. Chalcogenide device arrays can be used for both memory and processing capabilities, including logic and parallel operations.

  The foregoing discussion and description are not meant to be limiting of the practice of the invention, but rather are illustrative. One skilled in the art will appreciate that there are many equivalents of the embodiments disclosed herein. The claims are intended to include all equivalents and obvious variations thereof, as well as the foregoing disclosure, which defines the scope of the invention.

FIG. 1 is a schematic diagram of the resistance of a chalcogenide material as a function of energy or current. FIG. 2 shows the change in set pulse width as a function of the reset resistance of several two-terminal electrical devices comprising different chalcogenide alloys according to the present invention. FIG. 3 shows the set pulse width of a two-terminal electrical device from a reset state having a resistance greater than 100 kΩ to a set state of less than 5 kΩ as a function of the atomic concentration of Ge, Sb and Te present in the active chalcogenide material of the device. FIG. 4 shows the reset current of a two-terminal electrical device up to a saturation reset state as a function of the atomic concentration of Ge, Sb and Te present in the active chalcogenide material of the device.

Claims (10)

A chalcogenide material comprising 15 to 18 atomic percent of Ge, 33 to 41 atomic percent of Sb, and 43 to 49 atomic percent of Te. A chalcogenide material according to claim 1;
A first electrode in electrical connection with the chalcogenide material;
An electrical device comprising a second electrode in electrical connection with the chalcogenide material. An electrical device comprising the chalcogenide material according to claim 1, a first terminal electrically connected to the chalcogenide material, and a second terminal electrically connected to the chalcogenide material,
The device has a first reset state and a second reset state;
The resistance in the first reset state is more than three times greater than the resistance in the second reset state;
The electric device according to claim 1, wherein the set pulse time in the first reset state is less than 20 times the set pulse time in the second reset state. The electric device according to claim 3 , wherein the set pulse time in the first reset state is less than five times the set pulse time in the second reset state. The electrical device according to claim 3 , wherein the resistance in the first reset state is 10 times or more larger than the resistance in the second reset state. 6. The electric device according to claim 5 , wherein the set pulse time in the first reset state is less than 10 times the set pulse time in the second reset state. 6. The electrical device according to claim 5 , wherein the set pulse time in the first reset state is less than five times the set pulse time in the second reset state. The electrical device according to claim 3 , wherein the resistance in the first reset state is 20 times or more larger than the resistance in the second reset state. 9. The electric device according to claim 8 , wherein the set pulse time in the first reset state is less than 10 times the set pulse time in the second reset state. 9. The electric device according to claim 8 , wherein the set pulse time in the first reset state is less than five times the set pulse time in the second reset state.

Images