Low-drift phase-change material composite matrix

Abstract

The phase-change memory device includes a composite phase-change material layer comprising a mixture of a dispersed phase of a projection material having a first resistivity and a matrix of a phase-change material having a second or third resistivity depending on the phase. The first resistivity of the projection material is greater than the second resistance of the phase-change material and less than the third resistance of the phase-change material. The phase-change memory device further includes a first electrode and a second electrode on opposing surfaces of the composite phase-change material layer. The projection material forms a percolated conductive path from the first electrode to the second electrode.

Description

[Background technology]

[0001] The present invention generally relates to phase change materials, and more particularly to phase change memories having low drift characteristics.

[0002] Phase-change memory (PCM) is a non-volatile solid-state memory technology that utilizes reversible, thermally supported switching of phase-change materials, specifically chalcogenide compounds such as GST (germanium-antimony-tellurium), between states with different electrical resistances. A basic memory unit ("cell") can be programmed to have a number of different states or levels exhibiting different resistance characteristics. Different data values ​​can be represented using s programmable cell states, thereby enabling the storage of information.

[0003] In a single-level PCM device, each cell can be set to one of two states, s=2, which is either the "SET" state or the "RESET" state, thereby enabling 1 bit of memory per cell. In the RESET state, which corresponds to the amorphous state of the phase change material, the electrical resistance of the cell is very high. By heating to a temperature above its crystallization point and then cooling, the phase change material can be converted to a low-resistance crystalline state. This low-resistance state provides the SET state for the cell. Then, if the cell is heated to a temperature above the melting point of the phase change material, the material will return to a sufficiently amorphous RESET state when rapidly cooled. In a multi-level PCM device, cells can be set to programmable states of s>2, thereby enabling memory of more than 1 bit per cell. The different programmable states correspond to different relative proportions of amorphous and crystalline phases within the volume of the phase change material. Specifically, a multi-level cell utilizes intermediate states in addition to the two states used in single-level operation, in which the cell contains varying volumes of amorphous phase within the normally crystalline PCM material. Since the two material phases exhibit a large resistance contrast, changing the size of the amorphous phase within the entire cell volume results in a corresponding variation in the cell resistance.

[0004] Data reading and writing in a PCM cell are achieved by applying an appropriate voltage to the phase change material via a pair of electrodes associated with each cell. During the writing operation, the resulting programming signal causes Joule heating of the phase change material to an appropriate temperature, generating the desired cell state upon cooling. PCM cell reading is performed using cell resistance as a metric for the cell state. The applied read voltage causes current to flow through the cell, and this read current depends on the cell's resistance. Therefore, measuring the cell's read current provides indication of the programmed cell state. A sufficiently low read voltage is used for this resistance metric to ensure that the application of the read voltage does not disturb the programmed cell state. Cell state detection can then be performed by comparing the resistance metric with a predefined reference level for s programmable cell states.

[0005] Phase-change memory (PCM) has been considered a crucial device for low-power interfaces in enterprise artificial intelligence (AI). However, PCM devices face the challenge of overcoming resistance drift, a problem in which the PCM cell resistance increases as a function of time. A unit cell of a PCM often comprises multiple memory-stive devices, e.g., 6T4R, to improve the accuracy of the written weight values. The resistance of each phase-change memory (PCM) cell can drift over time, resulting in increasingly higher resistances. This can lead to fluctuations in the weights corresponding to the assigned data stored within the phase-change memory (PCM), and therefore may require additional hardware and / or software for correction. Several solutions have been proposed to eliminate the effects of drift in phase-change memory (PCM) devices. Some of the proposed solutions include projection liner phase-change memory (PCM), phase-change heterostructure (PCH), and interfacial phase-change memory (iPCM).

[0006] In projection liner phase-change memory (PCM), it is difficult to apply appropriate material compositions that are suitable for integration with functional phase-change memory (PCM). Furthermore, phase-change heterostructures (PCHs) and interfacial phase-change memory (iPCMs) have been found to be difficult to deposit and require precise temperature control. In addition, the application of phase-change heterostructures (PCHs) to memory applications and interfacial phase-change memory (iPCMs) face significant difficulties because they cannot provide high-quality epitaxial growth for forming van der Waals gaps. This often makes it impossible to manufacture phase-change heterostructures (PCHs) and interfacial phase-change memory (iPCMs) for memory applications. The solubility of layers within iPCMs also hinders high durability because they eventually react to form high-drift PCMs. [Overview of the project]

[0007] In some embodiments, the methods and structures described herein can overcome the aforementioned difficulties by forming a lower-drift phase-change memory (PCM) composite material matrix. The phase-change material of the Disclosure may be formed using sputtering. By employing co-sputtering, a slightly conductive material (with resistance about 10 times that of crystalline PCM) can be mixed with the phase-change material (e.g., GST) in the phase-change material layer within the phase-change memory (PCM) element to form a projection matrix composite material. For example, the phase-change material may be Ge2Sb2Te5. Dielectric dopant materials such as Al2O3, Si3N4, SiO2, SiO, TiO2, and HfO2 may be used in PCM materials as non-conductive dopant materials in amounts as high as 50 atomic percent. However, the methods and structures of the Disclosure may replace these non-conductive dopant materials with slightly conductive non-drift materials such as metal nitrides, metal oxides, doped semiconductors, small bandgap semiconductors, semimetals, topological insulators, topological semimetals, van der Waals materials, or combinations thereof. Slightly conductive, non-drift materials may be called projection materials. Replacing non-conductive additives with the aforementioned projection materials can be achieved by co-sputtering methods employing targets for GST and targets for insufficiently conductive materials. When the projection material is integrated into the PCM as a substitute for the non-conductive material, it forms a percolated conductive path through the PCM element from the lower electrode to the upper electrode, thereby providing a path with reduced drift.

[0008] When employing this lower-drift phase-change memory (PCM) composite matrix, the resistance increases during the reset stage by blocking the current so that it passes only through the projection material. Note that in the lower-drift phase-change memory (PCM) composite matrix, only the phase-change material becomes amorphous during reset. In phase-change memory, a reset pulse is realized when the crystalline structure, i.e., the state of the crystalline structure, changes from crystalline to amorphous. This corresponds to logic "0". In some embodiments, the current used to read the resistance of the phase-change memory (PCM) avoids the reset phase-change material volume, which is high-resistance and high-drift, thereby reducing the effective drift measured in the higher-resistance (R) state.

[0009] The lower drift PCM composite matrix provided by the methods and structures of the present disclosure can provide a smaller programming current compared to non-composite and projection-liner type PCMs by limiting the volume of the phase-change material, increasing its electrical resistance, and improving internal Joule-Thomson heating. The lower drift PCM composite matrix provided by the methods and structures of the present disclosure may provide a slightly smaller programming current or an equivalent programming current compared to comparable PCM composites containing non-conductive additives rather than projection material. This is provided that the projection material does not significantly reduce the overall thermal and electrical resistance of the PCM, which would worsen internal Joule-Thomson heating.

[0010] In one embodiment, a phase change device is provided, in which a low-drift phase change composition matrix is ​​provided, which is a phase change material containing additives that provide a projection material having a resistivity greater than that of the crystalline phase of the phase change material and less than that of the amorphous phase of the phase change material. In one embodiment, the phase change material device includes a composite phase change material layer. The composite phase change material layer includes a mixture of a dispersed phase of the projection material having a first resistivity and a matrix phase of the phase change material having a second resistivity or a third resistivity depending on the phase. The first resistivity of the projection material has a resistivity greater than that of the second resistance of the phase change material and less than that of the third resistance of the phase change material. The second resistivity corresponds to the crystalline phase of the phase change material. The third resistivity corresponds to the amorphous phase of the phase change material. The phase change material (PCM) further includes a first electrode and a second electrode on opposing surfaces of the composite phase change material layer.

[0011] In some embodiments, the second resistivity corresponds to the crystalline phase of the phase-change memory, and the third resistivity corresponds to the amorphous phase of the phase-change material. The advantage here is that the first resistivity of the projection material is constant and does not transition like the phase-change memory material. Drift can be mitigated by providing a constant resistance path for the current between electrodes.

[0012] In some embodiments, the third resistivity of the amorphous phase is at least 20 times greater than that of the second resistivity of the crystalline phase. The electrical resistance of the percolated conductive path in the projection material may be more than 5 times greater than the electrical resistance of the percolated current path through the crystalline phase-change material, and has a lower electrical resistance than the resistance through the amorphous phase of the phase-change material. In some embodiments, the resistance of the percolated current path is advantageous because it allows the phase-change memory to function through its transition between the amorphous and crystalline material phases, and also provides a constant resistance path for the current between electrodes, thereby mitigating drift.

[0013] In one embodiment, the phase-change material device includes a matrix of phase-change material comprising alternating layers of phase-change material with layers of confinement material. In some embodiments, an advantage of this embodiment is that the alternating layers of different compositions within the phase-change material matrix can provide a better internal thermal barrier, thereby potentially reducing the programming current.

[0014] In one embodiment, the phase-change material device includes a phase-change material matrix comprising alternating layers of dispersed phases of phase-change material and projection material, with a layer entirely composed of phase-change material. The layer composed entirely of phase-change material may have a different composition from the phase-change material in the matrix phase. This embodiment may provide the absence of a clear pathway between electrodes.

[0015] In another embodiment, a phase-change memory device is provided comprising a composite phase-change material layer having a mixture of a dispersed phase of a projection material having a first resistivity and a matrix of a phase-change material having a second or third resistivity depending on the phase, wherein the first resistivity of the projection material has a resistance greater than the second resistance of the phase-change material and less than the third resistance of the phase-change material. The phase-change memory device further comprises a projection material layer in direct contact with the back surface of the composite phase-change material layer. The back electrode is in direct contact with the projection material layer on the back surface of the composite phase-change material layer. The upper electrode is located on the opposite surface of the composite phase-change material layer, opposite to the surface in direct contact with the projection material layer. This embodiment includes additional elements of the projection material. The projection material liner and the dispersed phase of the projection material provide at least two mechanisms for providing a percolated conductive path from the lower electrode to the upper electrode, and this combination can further reduce the drift effect.

[0016] In another embodiment, a method for mitigating drift effects in a phase-change memory device is described, comprising the steps of forming a composite phase-change material layer comprising a mixture of a dispersed phase of a projection material having a first resistivity and a matrix of a phase-change material having a second or third resistivity depending on the phase. The first resistivity of the projection material has a resistance greater than the second resistance of the phase-change material and less than the third resistance of the phase-change material. The method further comprises the steps of forming a first electrode and a second electrode on opposing surfaces of the composite phase-change material layer, and providing a current between the first and second electrodes. The projection material forms a percolated conductive path from the first electrode to the second electrode through a phase-change region of the composite phase-change material layer. The phase-change region is present in one of the first and second electrodes.

[0017] In one embodiment, the projection material forms percolated conductive paths with constant resistance to reduce drift effects. In one embodiment, the step of forming the composite phase-change material layer includes a co-sputtering method employing a first sputtering target for providing the phase-change material of the matrix of the phase-change material and a second sputtering target for providing the dispersed phase of the projection material. The advantage of using two targets is that it provides control over the amount of dispersion in a manner that can provide percolated conductive paths that reduce drift effects.

[0018] These and other features and advantages will become apparent from the following detailed description of their exemplary embodiments, which should be read in conjunction with the accompanying drawings. [Brief explanation of the drawing]

[0019] The following description provides details of preferred embodiments with reference to the following figures.

[0020] [Figure 1]A side cross-sectional view showing a phase change memory device including a composite phase change material layer comprising a dispersion phase of a projection material and a matrix of a phase change material having a second resistivity or a third resistivity according to a phase.

[0021] [Figure 2] A side cross-sectional view showing a phase change memory device including a composite phase change material layer comprising a mixture of a dispersion phase of a projection material, wherein the projection material forms a percolated conductive path from a first electrode to a second electrode.

[0022] [Figure 3] A side cross-sectional view showing a phase change memory device including a composite phase change material layer comprising a mixture of a dispersion phase of a projection material and a matrix of a phase change material, wherein the phase change memory device further includes a projection material layer in direct contact with a back surface of the composite phase change material layer.

[0023] [Figure 4] A side cross-sectional view showing a phase change memory device including a composite phase change material layer comprising a mixture of a dispersion phase of a projection material and a matrix of a phase change material, wherein the composite phase change material layer further includes alternating layers of a phase change material and a confinement material.

[0024] [Figure 5] A side cross-sectional view showing a phase change memory device including a composite phase change material layer comprising a mixture of a dispersion phase of a projection material and a matrix of a phase change material, wherein the composite phase change material layer further includes alternating layers of a composite phase change material including a projection material and a layer that is solely (as a whole) a phase change material, or layers having phase change materials of different compositions.

[0025] [Figure 6]This is a side cross-sectional view of an initial structure for forming a phase-change memory device according to one embodiment of the present disclosure.

[0026] [Figure 7] This is a side cross-sectional view showing one embodiment in which a composite phase-change material layer comprising a mixture of a dispersed phase of a projection material and a matrix of a phase-change material is formed on the first electrode shown in Figure 6.

[0027] [Figure 8] This is a diagram of a sputtering apparatus, including two sputtering targets for forming a composite phase-change material layer, according to one embodiment of the present disclosure.

[0028] [Figure 9] This is a diagram of a sputtering apparatus that includes two sputtering targets for forming a composite phase-change material layer, further including a collimator.

[0029] [Figure 10] This is a side cross-sectional view showing a second electrode formed on the upper surface of a composite phase-change material layer comprising a mixture of a dispersed phase of a projection material and a matrix of a phase-change material, according to one embodiment of the present disclosure. [Modes for carrying out the invention]

[0030] Detailed embodiments of the claimed structure and method are disclosed herein; however, it should be understood that the disclosed embodiments are merely illustrative of the claimed structure and method, which may be embodied in various forms. Furthermore, each example shown in relation to the various embodiments is intended to be illustrative and not limiting. In addition, each figure is not necessarily to scale, and some features may be exaggerated to show details of particular components. Accordingly, the specific structural and functional details disclosed herein should be interpreted not as limiting, but merely as representative grounds to teach those skilled in the art how to employ the methods and structures of this disclosure in various ways. For the purposes of the following description, the terms “top,” “bottom,” “right,” “left,” “vertical,” “horizontal,” “upper,” “lower,” and their derivatives refer to embodiments of this disclosure in which they are oriented in the drawings. The term “positioned on” means that a first element, such as a first structure, is located on a second element, such as a second structure, where intervening elements, such as an interface structure, e.g., an interface layer, may be located between the first and second elements. The term "direct contact" means that a first element, such as a first structure, and a second element, such as a second structure, are connected without any intermediate conductive, insulating, or semiconductor layer at the interface between the two elements.

[0031] The development of phase-change memory (PCM) faces several challenges. One of these is that the amorphous phase of the phase-change material exhibits undesirable attributes such as low-frequency noise and drift. This drift causes the resistance value of the amorphous phase to increase over time. As a result, the readout measurements of programmed cell states tend to fluctuate over time. This complicates the retrieval of stored information, and if there is a large variability in the drift exhibited by different cell states, and therefore the distribution of readout measurements for adjacent cell states interferes with each other, it can even corrupt the information. The more cell states there are, and therefore the closer the initial intervals between the resistance levels being read out, the more susceptible the cell becomes to this problem.

[0032] The method and structure overcome the aforementioned problems by using a lower drift phase-change memory composite material matrix. In some embodiments, the phase-change memory (PCM) cell is a matrix of phase-change material and a "bad" metal (TiN x , HaN x WN x WO x These include slightly conductive materials such as doped semiconductors (doped Si, SiGe, SiC, Ge), small bandgap semiconductors (Te, Se, etc.), semimetals (e.g., Bi, Sn), topological insulators (Bi2Se3, BiSb, BiSbTe), topological semimetals, and van der Waals materials (WTe2, MoTe2, TiTe2). The slightly conductive materials form percolated conductive pathways from the lower electrode to the upper electrode. The slightly conductive materials that form percolated conductive pathways may be called projection materials or projection additives.

[0033] The methods and structures of this disclosure will be discussed in more detail below with reference to Figures 1 to 10.

[0034] The term "phase-change memory (PCM)" refers to a memory technology based on phase-change materials, such as chalcogenide materials, where data is read as "0" or "1" based on the electrical resistivity that changes depending on whether the phase-change material in the cell is in a crystalline or amorphous phase, after a phase change induced by a heater (or electric current). The chalcogenide materials used in PCM include numerous binary, ternary, and quaternary alloys of many metals and metalloids. Phase-change memory (PCM) is a non-volatile solid-state memory technology that utilizes phase-change materials that have different electrical properties in their crystalline and amorphous phases. Specifically, the amorphous phase has higher resistance than the crystalline phase. The term "amorphous phase" refers to a solid that lacks the long-range order characteristic of crystals. "Crystalline phase" is a type of solid whose basic three-dimensional structure consists of a highly regular pattern of atoms or molecules forming a crystal lattice.

[0035] PCM cells are often programmed using heat generated by electric current to control the state of the phase-change material. Key parameters of PCM technology include the reset current and the set speed. The reset current affects the overall power consumption of the memory array, while the set speed controls the overall speed of the memory array.

[0036] The phase-change memory (PCM) of this disclosure incorporates a phase-change material with a projection material within a composite material. A “composite material” is a material composed of two or more distinct phases, e.g., a matrix phase and a dispersed phase, having bulk properties distinct from any of its constituent elements themselves. As used herein, the term “matrix phase” refers to a phase of the composite material, including and sharing a load with the dispersed phase. In some embodiments, the matrix phase may be the primary component of the composite material. As used herein, the term “dispersed phase” refers to a second phase (or more phases) embedded within the matrix phase of the composite material.

[0037] Figures 1 and 2 show one embodiment of a phase-change memory device 100, which includes a composite phase-change material layer 50 comprising a mixture of a dispersed phase of projection material 53 having a first resistivity and a matrix of phase-change material having a second or third resistivity depending on the phase. The phase-change memory device 100 further includes a first electrode 45 and a second electrode 46 on opposing surfaces of the composite phase-change material layer 50. The first electrode 45 may in some cases be called a heater.

[0038] The composite phase-change material layer 50 contains a phase-change material, a portion of which contains a high-resistance amorphous phase and a portion of which contains a low-resistance polycrystalline phase. The projection material 53 forms its own volume / phase containing one or more of the following: metal nitrides, conductive oxides, antimonides, semiconductors, and metalloids. The resistance of the projection material 53 does not drift significantly. The projection material forms paths (called percolated conductive paths 55) using the electrical resistance between the resistances of the phase-change memory layer when the phase-change material is crystalline or amorphous. The high-resistance amorphous phase-change material 51 provides a drifting high-resistance conductive path 57, but due to its higher resistance, conductivity preferentially occurs along path 55.

[0039] The composite phase-change material layer 50 undergoes a phase change between a crystalline stage and an amorphous stage. In some embodiments, the crystalline stage phase-change material 52 has lower resistance, while the amorphous stage phase-change material 51 has higher resistance. In some embodiments, the first resistivity of the projection material 53 is greater than the second resistivity of the phase-change material (crystalline stage phase-change material 52) and less than the third resistivity of the phase-change material (amorphous stage phase-change material 51). In some embodiments, the third resistivity of the amorphous phase is at least 20 times greater than that of the second resistivity of the crystalline phase of the phase-change material providing the matrix to the composite phase-change material layer 50, for example, GST.

[0040] Phase-change-based memory materials, such as chalcogenide-based materials and similar materials, can be transitioned between amorphous and crystalline phases by applying an electric current at a level suitable for implementation within integrated circuits. The amorphous phase is characterized by a higher electrical resistivity than the crystalline phase, which allows for easy reading of data. These properties make them applicable for use as programmable resistive materials in forming non-volatile memory circuits that can be read and written using random access.

[0041] The transition from amorphous to crystalline phase is generally a lower current operation. The transition from crystalline to amorphous, referred to herein as RESET, is generally a higher current operation, which involves a short-duration, high-current-density pulse to melt or break the crystalline structure, after which the phase-change material is rapidly cooled to quench the phase-change process, allowing at least a portion of the phase-change material to stabilize in the amorphous phase.

[0042] Referring to Figures 1 and 2, the matrix of the phase transition material providing the crystalline stage phase transition material 52 and the amorphous stage phase transition material 51 within the active region of the composite phase transition material layer 50 may be a germanium (Ge), antimony (Sb), and tellurium (Te) (GST) composition. For example, the matrix phase transition material of a memory device may include Ge2Sb2Te5. Other phase transition materials, including Ge(x)Sb(2y)Te(x+3y), may be used, where x and y are integers (including 0). Other basic phase transition materials other than GeSbTe-based materials may also be used, including the GaSbTe system which can be described as Ga(x)Sb(x+2y)Te(3y), where x and y are integers. Alternatively, the basic phase transition material may be selected from the Ag(x)In(y)Sb2Te3 system, where x and y are decimals which may be less than 1. In some embodiments, the matrix of the phase material may include additional additives to the Ge2Sb2Te5 base. However, many other phase-change-based memory materials, including alloys such as Ga / Sb, In / Sb, In / Se, Sb / Te, Ge / Te, Ge / Sb / Te, In / Sb / Te, Ga / Se / Te, Sn / Sb / Te, In / Sb / Ge, Ag / In / Sb / Te, Ge / Sn / Sb / Te, Ge / Sb / Se / Te, and Te / Ge / Sb / S, are intended with respect to the matrix of the composite phase-change material layer 50. In one embodiment, the matrix of the composite phase-change material layer 50 has an average Te concentration of less than 70%, typically less than about 60%, and generally ranging from as low as about 23% to as high as about 58% Te. The concentration of Ge can exceed about 5%, ranging from as low as about 8% to an average of about 30% in the material. In some examples, the germanium (Ge) content is less than 50%. The remaining main constituent element in this composition was Sb. These percentages are atomic percentages where the atoms of the constituent elements total 100%.

[0043] As shown in Figure 2, the projection material 53 forms a percolated conductive path 55 from the first electrode 45 to the second electrode 46. The percolated conductive path 55 can extend through the amorphous phase of the matrix phase change material that may be present within the active region of the phase change memory (PCM) device 100, providing a constant current electrical path between the first and second electrodes 45, 46 that can reduce drift. Figure 2 shows a phase change memory device 100 including a composite phase change material layer 50 comprising a mixture of dispersed phases of the projection material 53, where the projection material 53 forms a percolated conductive path 55 from the first electrode 45 to the second electrode 46. The percolated conductive path 55 means that even if the current cannot pass through the amorphous region of the phase change material, the current can still travel through the composition phase change material 50 between the electrodes 45, 46 along the percolated conductive path 55 of the projection material 53. It should be noted that the matrix of the phase change material has resistance that varies depending on the degree of its amorphous properties. This occurs within the active region of the phase change memory (PCM) device 100, which is in direct contact with one of the first and second electrodes, and the active region undergoes a phase change as part of the operation of the memory device for storing data and the RESET operation. Prior to the structures and methods of the present disclosure, the variation in resistance between different crystalline states was a mechanism that could thereby require additional hardware and / or programming to mitigate drift effects. However, the programmability of conductance is subject to drift, which has so far hindered the ability to program the analog states of phase change memory. The percolated conductive path 55 of the projection material 53 has constant resistance between the amorphous phase of the phase change material and the crystalline phase of the phase change material, and surprisingly, and unexpectedly, this has been found to mitigate the drift effect. The constant resistance of the percolated conductive path 55 is inverse to the variability of the crystalline stage phase change material 52 and amorphous stage phase change material 51 within the active region of the composite phase change material layer 50 directly above the first electrode 45. The active region of the composite phase change material layer, identified by reference numeral 65, is shown in Figures 3 to 6.

[0044] In some embodiments, the projection material 53 is a metal nitride, metal oxide, doped semiconductor, small bandgap semiconductor, topological insulator, topological semimetal, van der Waals material, or a combination thereof. The electrical resistance of the percolated conductive path 55 of the projection material 53 is more than five times greater than the electrical resistance of the percolated current path 55 through the crystalline phase change material 52, and is less than the electrical resistance through the amorphous phase of the phase change material 51.

[0045] In some embodiments, when the projection material 53 is a metal nitride, the metal nitride is titanium nitride (TiN x ), tantalum nitride (TaNx), tungsten nitride (WNx), aluminum nitride (AlNx), and combinations thereof may be selected. In some embodiments, if the projection material 53 is a doped semiconductor, the doped semiconductor may be selected from doped Si, doped SiGe, doped silicon carbide (SiC), doped germanium (Ge), and combinations thereof.

[0046] In some embodiments, the projection material 53 is a narrow-bandgap semiconductor. A narrow-bandgap semiconductor is a semiconductor material having a relatively small bandgap compared to that of silicon, i.e., less than 1.11 eV at room temperature. In some embodiments, when the projection material 53 is a narrow-bandgap semiconductor, the composition may be selected from tin telluride, titanium telluride, germanium, selenium, InSb, InAs, GaSb, AlSb, and combinations thereof.

[0047] In some embodiments, the projection material 53 may be a semimetal. A semimetal is a material in which the overlap between the lower conduction band and the upper valence band is very small. In some examples, when the projection material 53 is a semimetal, it may be selected from bismuth, tin (Sn), mercury, graphite, and combinations thereof.

[0048] In other examples, the projection material 53 may be a topological insulator. Topological insulators are quantum materials characterized by a bulk gap and an odd number of relativistic Dirac fermions on their surfaces. While their bulk is insulating, their surfaces can conduct electric current using a distinct spin texture. In some examples, the topological insulators for the projection material 53 may be Bi2Se3, BiSb, BiSbTe, and combinations thereof.

[0049] In further examples, the projection material 53 may be a topological semiconductor. Topological semiconductors are quantum materials characterized by a bulk gap and an odd number of relativistic Dirac fermions on their surfaces. While their bulk is insulating, their surfaces can conduct electric current using a distinct spin texture. In some examples, topological insulators for the projection material 53 may be Bi2Se3, BiSb, BiSbTe, and combinations thereof.

[0050] In some examples, projection material 53 can be a topological semiconductor. Topological semimetals define a class of gapless electronic phases that exhibit topologically stable crossovers of energy bands. Topological semimetals such as Dirac, Weyl, or Rhein-node semimetals are gapless materials characterized by their nodal band structure and surface states. Some suitable examples of topological semiconductors may include graphene, Weyl semimetals such as TaAs and WDe2, and Dirac semimetals such as Na3Bi or Cd3As. 。 .

[0051] In further examples, the projection material includes van der Waals materials selected from the group consisting of WTe2, MoTe2, TiTe2, and combinations thereof.

[0052] In some further embodiments, the composite material layer may further include an additional dispersed phase of nonconductive additives, such as a dielectric. For example, the nonconductive additives may be selected from the group consisting of Al2O3, Si3N4, SiO2, SiO, TiO2, HfO2, and combinations thereof.

[0053] It should be noted that the above examples are provided for illustrative purposes only and the disclosure is not intended to be limited to such examples. Other materials suitable for providing conductive paths between electrodes and having resistance between the amorphous and crystalline phase transition materials of the matrix may also be suitable for the projection material 53. For example, the electrical resistance (i.e., first resistivity) of the percolated conductive path 55 of the projection material 53 is more than five times greater than the electrical resistance of the percolated current path 55 through the crystalline phase transition material of the matrix, and is less than the electrical resistance through the amorphous phase of the phase transition material of the matrix. The resistivity (i.e., third resistivity) of the amorphous phase of the phase transition material in the matrix of the composite phase transition material layer 50 is at least 20 times greater than that of the resistivity (i.e., second resistivity) of the crystalline phase of the phase transition material in the matrix of the composite phase transition material layer 50.

[0054] It should be noted that the structures and methods of this disclosure are not limited to the embodiments shown in Figures 1 and 2. For example, Figure 3 shows one embodiment of a memory device comprising a composite phase-change material layer 50 having a mixture of dispersed phases of projection material 53, combined with a further layer of projection material similar to a projection liner positioned between the composite phase-change material layer 50 and the first electrode 45. Figures 4 and 5 show another embodiment of a phase-change heterostructure memory layer 50 comprising alternating composite phase-change memory layers 70 including phase-change material, projection material, and confinement layers 71 and 72.

[0055] Figure 3 is a side cross-sectional view showing a phase-change memory device 100 including a composite phase-change material layer 50 comprising a mixture of a dispersed phase of projection material 53 and a matrix of phase-change material 70. More specifically, in one embodiment, the phase-change memory device 100 includes a composite phase-change material layer 70 comprising a mixture of a dispersed phase of projection material having a first resistivity and a matrix of phase-change material having a second or third resistivity depending on the phase, wherein the first resistivity of the projection material has a resistance greater than the second resistance of the phase-change material and less than the third resistance of the phase-change material. The phase-change memory device 100 further includes a projection material layer 60 in direct contact with the back surface of the composite phase-change material layer 70. In some embodiments, a back electrode 45 is in direct contact with the projection material layer 60 on the back surface of the composite phase-change material layer 70. The phase-change memory device 100 further includes an upper electrode 46 on the opposite surface of the composite phase-change material layer 70, which is opposite to the surface of the composite phase-change material layer 70 that is in direct contact with the projection material layer 60.

[0056] In some embodiments, the matrix of the phase-change material 70 includes a portion of the material containing a high-resistance amorphous phase and a portion of the material containing a low-resistance polycrystalline phase. The matrix of the phase-change material is similar to that of the phase-change material described above with reference to Figures 1 and 2, and includes a phase change that generates a crystalline-stage phase-change material 52 and an amorphous-stage phase-change material 51 within the active region of the composite phase-change material layer 50.

[0057] Referring to Figure 3, the dispersed phase of the projection material 53 forms its own volume / phase composed of one or more of the following: metal nitrides, conductive oxides, antimonide metals, semiconductors, and semimetals. The above description of the projection material 53 shown in Figures 1 and 2 is suitable for the description of the projection material 53 shown in Figure 3. The projection material 53 present in the matrix of the phase transition material 70 forms paths with electrical resistance between the resistances of the phase transition memory material when the phase transition material is crystalline or amorphous. These paths may be called percolated conductive paths 55. The resistance of the projection material 53 in the percolated projection paths 55 does not drift significantly.

[0058] Still referring to Figure 3, the device further includes a projection material layer 60 in direct contact with the back surface of the composite phase-change material layer 70. The projection material layer 60 is located between the composite phase-change material layer 70 and the first electrode 45. The projection material layer 60 may consist of the same material composition as the projection material 53 described above with reference to Figures 1 and 2. The dispersed phases of the projection material liner 60 and the projection material 53 provide at least two mechanisms for providing a percolated conductive path from the lower electrode 45 to the upper electrode 46, and this combination may further reduce the drift effect.

[0059] Figure 4 shows another embodiment of a phase-change memory device 100, which includes a composite phase-change material layer 50 comprising a mixture of a dispersed phase of projection material and a matrix of phase-change material, where the composite phase-change material layer further comprises alternating layers of composite phase-change material 70 and conductive material 71. The alternating structure may be called a heterostructure. In some embodiments, an advantage of this embodiment is that the alternating layers of different compositions within the phase-change material matrix 70 and conductive material layer 71 can provide a better internal thermal barrier, thereby potentially reducing the programming current. The layers of composite phase-change material 70 have the composition of phase-change material 51, 52 and projection material 53, as described above with reference to Figures 1 and 2. The conductive material layer 71 may also be called a confinement layer. The confinement layer can form a van der Waals gap with the phase-change material (PCM). The conductive material layer 71 may consist of Sb2Te3 or TiTe2. Note that the above compositions are provided for illustrative purposes only. For example, the confinement layer (also called the conductive material layer 71) may be composed of one or more of the following materials: metal nitrides, conductive oxides, antimonide metals, semiconductors, metalloids, and combinations thereof, having a resistance equivalent to the crystalline resistance of the phase change material (approximately 1 / 10 to 10 times the resistance).

[0060] Figure 5 shows another embodiment of the phase-change memory device 100, which includes a composite phase-change material layer comprising a mixture of a dispersed phase of projection material and a matrix of phase-change material. In the embodiment shown in Figure 5, the composite phase-change material layer 50 further includes alternating layers of composite phase-change material 70 and layer 72 which is exclusively phase-change material. The composite phase-change material 70 includes the projection material 53 described above with reference to Figures 1 and 2. The composite phase-change material 70 employs the phase-change material as the matrix of the composite material, and the projection material is the dispersed phase. Layer 72, which is composed exclusively of phase-change material, does not contain projection material. The composition of the phase-change material in the layer identified by reference number 72 may be the same as that in the composite phase-change material 70. In other embodiments, the composition of the phase-change material in the layer identified by reference number 72 may differ from the composition in the composite phase-change material 70. Note that the compositions of the phase-change material described above with reference to Figures 1 and 2 may provide the compositions of the phase-change material in the embodiment shown in Figure 5. The dispersed phase of the projection material forms a percolated conductive path from the first electrode 45 to the second electrode 46. The percolated conductive path 55 can extend through the amorphous phase of the matrix phase change material, which may be present within the active region of the phase change memory (PCM) device 100, providing a constant current electrical path between the first and second electrodes 45, 46 that can reduce drift.

[0061] In another embodiment, a method for mitigating drift effects within a phase-change memory device 100 is described, comprising the steps of forming a composite phase-change material layer 50 comprising a mixture of a dispersed phase of a projection material 53 having a first resistivity and matrices of phase-change materials 51, 52 having a second or third resistivity depending on the phase. The first resistivity of the projection material has a resistance greater than the second resistance of the phase-change material and less than the third resistance of the phase-change material. The method further includes the steps of forming a first electrode 45 and a second electrode 46 on opposing surfaces of the composite phase-change material layer 50, and providing a current between the first and second electrodes 45, 46. The projection material 53 forms a percolated conductive path 55 from the first electrode 45 to the second electrode 46 through the phase-change region of the composite phase-change material layer 50. The phase-change region 65 is present in one of the first and second electrodes. In one embodiment, the projection material forms a percolated conductive path 55 having a certain resistance to reduce the drift effect. The method is further described with reference to Figures 6 to 10.

[0062] Figure 6 shows one embodiment of an initial structure for forming a phase-change memory device 100. According to one embodiment of the present application, in one embodiment, the initial structure includes a lower electrode 45 embedded in an insulating substrate 10. Although a single lower electrode 45 is described and shown, multiple lower electrodes may be formed in the insulating substrate 10. In some embodiments, the lower electrode 45 extends only partially through the insulating substrate 10, as shown. In other embodiments of the present application, the lower electrode 45 extends throughout the entire insulating substrate 10.

[0063] The insulating substrate 10 may include any dielectric material, such as silicon dioxide, silicon nitride, silicon oxynitride, silsesquioxane, or a carbon-doped oxide (i.e., organic silicate) containing atoms of Si, C, and H. The insulating substrate 10 may be formed using a deposition process, such as chemical vapor deposition (CVD), plasma-enhanced chemical vapor deposition (PECVD), spin-on coating, vapor deposition, or chemical solution deposition. The insulating substrate 10 may be formed on a base substrate not shown. The base substrate may include semiconductor materials, insulating materials, and / or conductive materials.

[0064] In some embodiments, an opening is then formed within the insulating layer 10, and then a lower electrode 45 is formed within the opening. The lower electrode 45 may also be called the first electrode. The opening can be formed using lithography and etching. After the opening is formed within the insulating substrate 10, the lower electrode 45 is formed by depositing a conductive metallic material within the opening. The conductive metallic material providing the lower electrode 45 may include, but is not limited to, titanium nitride (TiN), tungsten (W), silver (Ag), gold (Au), aluminum (Al), or multilayer stacks thereof. The conductive metallic material can be formed by a deposition process such as CVD, PECVD, physical vapor deposition (PVD), sputtering, atomic layer deposition (ALD), or plating. A planarization process or etch-back process may follow the deposition of the conductive metallic material providing the lower electrode 45. As shown, the lower electrode 45 has an upper surface that is coplanar with the uppermost surface of the insulating substrate 10. The exemplary semiconductor structure shown in Figure 6 can also be formed by first providing a lower electrode 45 on the surface of a base substrate (not shown) by depositing a conductive metallic material and then patterning the deposited conductive metallic material by lithography and etching. Subsequently, an insulating substrate 10 can be formed by depositing a dielectric material and then performing a planarization or etch-back process.

[0065] Figure 7 shows one embodiment in which a composite phase change material layer 50 is formed on the first electrode (also called the lower electrode) 45 shown in Figure 6, comprising a mixture of a dispersed phase of projection material 53 and a matrix of phase change material 52.

[0066] In one embodiment, the step of forming the composite phase-change material layer 50 includes a co-sputtering method employing a first sputtering target for providing the phase-change material, which is the matrix of the phase-change materials 51, 52, and a second sputtering target for providing the dispersed phase of the projection material 53. The advantage of using two targets is that it can provide control over the amount of dispersion in a way that can provide percolated conductive paths 55 that reduce drift effects. For example, the dispersed phase of the projection material 53 may be present in the matrix of the phase-change material at a concentration ranging from 5% to 40%.

[0067] As used herein, “sputtering” refers to a method of depositing a film of material onto a semiconductor surface. The desired material, i.e., the source target, is irradiated with particles, such as ions, which knock atoms out of the target, and the displaced target material is deposited onto the deposition surface. Examples of sputtering techniques suitable for depositing the metal adhesive layer 16 include, but are not limited to, DC diode sputtering (also known as DC sputtering), radio frequency (RF) sputtering, magnetron sputtering, and ionized metal plasma (IMP) sputtering. Co-sputtering uses two sputtering targets.

[0068] Figure 8 shows a sputtering apparatus including two sputtering targets 149 and 151 for forming a composite phase-change material layer 50 containing a dispersed phase of projection material 53. The sputtering system includes a chamber 150 in which the sputtering targets 149, 151 and a substrate 152 are mounted. The sputtering targets 149, 151 and the substrate 152 are coupled to a power supply and controller 156 used to apply a bias voltage during the sputtering process. The applied bias voltage may be DC, pulsed DC, radio frequency, or a combination thereof, and may be turned on and off and adjusted by the controller to suit a particular sputtering process. The sputtering chamber 150 is equipped with a vacuum pump 155 or other means for evacuating the chamber and removing exhaust gases. The chamber is also configured with a source 153 of an inert gas such as argon, and a source 154 of a reactive gas such as oxygen or nitrogen in the example described herein. The system has the ability to dynamically control the gas flow from sources 153 and 154 so as to have an effect on the composition of the layer formed by the sputtering process. The sputtering target identified by reference numeral 151 has the composition of the phase change material and serves as a source of material used to form the matrix of the composite phase change material layer 50 on the substrate 152. The substrate includes a first electrode 45 (also called the lower electrode 45). The sputtering target identified by reference numeral 149 has the composition of the projection material 53 and serves as a source of material for forming the dispersed phase within the composite phase change material layer 50.

[0069] It will be understood that this is a simplified diagram sufficient for the purposes of explanation in this specification.

[0070] Figure 9 is a simplified diagram of an alternative sputtering system that may be used with the composite material targets also described herein. Figure 9 differs from Figure 8 in that a collimator 157 is positioned between the targets 149, 151 and the substrate 152. The collimator 157 may be used when sputtering substrates containing high aspect ratio features to improve the uniformity of coverage on high aspect ratio features. Some sputtering systems have the ability to move the collimator in and out of the sputtering chamber as needed.

[0071] In some embodiments, the composite phase-change material layer 50 is deposited using one of the sputtering apparatuses shown in Figures 8 and 9. In some embodiments, the phase-change material of the phase-change material layer 50 may be deposited in a crystalline phase. However, this is merely an example and is not necessary in some embodiments.

[0072] Figure 10 shows the formation of a second electrode 46 on the upper surface of a composite phase-change material layer 50 comprising a mixture of a dispersed phase of projection material and a matrix of phase-change material. The second electrode 46 (also called the upper electrode) may include one of the conductive metallic materials mentioned above in providing the first electrode 45 (lower electrode). In some embodiments, the second electrode 46 and the first electrode 45 include the same conductive metallic material. In other embodiments, the second electrode 46 and the lower electrode 45 include different conductive metallic materials. The second electrode 46 may be formed using other deposition methods, including plating, electroplating, sputtering, or forms such as physical vapor deposition and chemical vapor deposition.

[0073] The method further includes the step of applying a current between first and second electrodes 45, 46, where the projection material 53 forms a percolated conductive path 55 from the first electrode 45 to the second electrode 46, passing through a phase transition region 65 of the composite phase transition material layer 50 in one of the first and second electrodes 45, 46. The active region (also called the phase transition region 65) includes a region of the composite material layer 50 that has undergone a phase transition between an amorphous phase 51 and a crystalline phase 52 of the phase transition material. The amorphous region is highly resistive. The degree of amorphous crystalline properties affects the resistivity of the phase. This results in variability that causes drift. The projection material 53 forms a percolated conductive path with constant resistance that mitigates the drift effect.

[0074] Please understand that the use of any of the following " / ", "and / or", and "at least one of" is intended to include, for example, "A / B", "A and / or B", and "at least one of A and B", the selection of only the first enumerated option (A), or only the second enumerated option (B), or the selection of both options (A and B). As a further example, in the case of "A, B, and / or C", and "at least one of A, B, and C", such phrasing is intended to include the selection of only the first enumerated option (A), or only the second enumerated option (B), or only the third enumerated option (C), or only the first and second enumerated options (A and B), or only the first and third enumerated options (A and C), or only the second and third enumerated options (B and C), or the selection of all three options (A, B, and C). This may be extended to the same number of items as listed, as will be readily apparent to those skilled in the art.

[0075] Preferred embodiments of the system and method (intended to be illustrative and not limiting) have been described, but it should be noted that modifications and variations may be made by those skilled in the art in light of the above teachings. Therefore, it should be understood that changes within the scope of the invention outlined by the attached claims may be made in the specific embodiments disclosed. Thus, aspects of the invention have been described with the details and specificity required by patent law, but what is claimed and desired to be protected by the patent certificate is described in the attached claims.

[0076] Exemplary embodiments include the following: [Item (1)] A composite phase-change material layer comprising a mixture of a dispersed phase of a projection material having a first resistivity and a matrix of a phase-change material having a second or third resistivity depending on the phase, wherein the first resistivity of the projection material is greater than the second resistance of the phase-change material and less than the third resistance of the phase-change material; First electrode; and A second electrode on the opposing surface of the composite phase-change material layer, wherein the projection material forms a percolated conductive path from the first electrode to the second electrode. A phase-change memory device comprising the above features. [Item (2)] The phase-change memory device according to item (1), wherein the second resistivity corresponds to the crystalline phase of the phase-change memory, and the third resistivity corresponds to the amorphous phase of the phase-change material. [Item (3)] The phase-change memory device according to item (1), wherein the projection material includes metal nitrides, metal oxides, doped semiconductors, small bandgap semiconductors, topological insulators, topological semimetals, van der Waals materials, or combinations thereof. [Item (4)] The aforementioned projection material is titanium nitride (TiN x ), tantalum nitride (TaN x) Tungsten nitride (WN x ) Aluminum nitride (AlN x ) and a metal nitride selected from the group consisting of combinations thereof, the phase change memory device according to item (1). [Item (5)] The projection material includes a doped semiconductor selected from the group consisting of doped Si, doped SiGe, doped silicon carbide (SiC), doped germanium (Ge), and combinations thereof, the phase change memory device according to item (1). [Item (6)] The projection material is a narrow bandgap semiconductor selected from the group consisting of tin telluride, titanium telluride, gallium germanium, selenium, InSb, InAs, GaSb, AlSb, and combinations thereof, the phase change memory device according to item (1). [Item (7)] The projection material is a semimetal selected from the group consisting of bismuth, tin (Sn), mercury telluride, graphite, and combinations thereof, the phase change memory device according to item (1). [Item (8)] The projection material includes a topological material selected from the group consisting of Bi2Se3, BiSb, BiSbTe, graphene, TaAs, WTe2, Na3Bi, Cd3As2, and combinations thereof, the phase change memory device according to item (1). [Item (9)] The projection material includes a van der Waals material selected from the group consisting of WTe2, MoTe2, TiTe2, and combinations thereof, the phase change memory device according to item (1). [Item (10)] The third resistivity of the amorphous phase is at least 20 times greater than that of the second resistivity of the crystalline phase, the phase change memory device according to item (2). [Item 11] The phase change memory device according to item (10), wherein the electrical resistance of the percolated conductive path in the projection material is more than five times greater than the electrical resistance of the percolated current path through the crystalline phase change material, and is less than the electrical resistance of the phase change material through the amorphous phase change material. [Item 12] The phase change memory device according to item (1), wherein the matrix of the phase change material includes alternating layers of the phase change material having a layer of conductive material. [Item (13)] The phase-change memory device according to item (1), wherein the matrix of the phase-change material includes alternating layers of dispersed phases of the phase-change material and the projection material, with a layer that is entirely made of the phase-change material. [Item (14)] The phase-change memory device according to item (1), wherein the compositional phase-change material layer further comprises a non-conductive additive selected from the group consisting of Al2O3, Si3N4, SiO2, SiO, TiO2, HfO2, and combinations thereof. [Item (15)] A composite phase-change material layer having a mixture of a dispersed phase of a projection material having a first resistivity and a matrix of a phase-change material having a second or third resistivity depending on the phase, wherein the first resistivity of the projection material is greater than the second resistance of the phase-change material and less than the third resistance of the phase-change material; A projection material layer in direct contact with the back surface of the composite phase change material layer; The back electrode of the composite phase change material layer that is in direct contact with the projection material layer on the back surface; and An upper electrode on the opposite surface of the composite phase-change material layer to the surface in direct contact with the projection material layer, wherein the projection material forms a percolated conductive path from the first electrode to the second electrode. A phase-change memory device comprising the above features. [Item (16)] A step of forming a composite phase-change material layer comprising a mixture of a dispersed phase of a projection material having a first resistivity and a matrix of a phase-change material having a second or third resistivity depending on the phase, wherein the first resistivity of the projection material is greater than the second resistance of the phase-change material and less than the third resistance of the phase-change material; The steps of forming a first electrode and a second electrode on opposing surfaces of the composite phase change material layer; and In the step of applying a current between the first and second electrodes, the projection material forms a percolated conductive path from the first electrode to the second electrode, passing through the phase change region of the composite phase change material layer in one of the first and second electrodes. A method for reducing drift effects in a phase-change memory device, comprising the features described above. [Item 17] The method according to Item (16), wherein the step of forming the composite phase change material layer comprises a co-sputtering method employing a first sputtering target for providing the phase change material of the matrix of the phase change material and a second sputtering target for providing the dispersed phase of the projection material. [Item (18)] The method according to item (16), wherein the second resistivity corresponds to the crystalline phase of the phase-change memory, and the third resistivity corresponds to the amorphous phase of the phase-change material. [Item (19)] The method according to item (16), wherein the projection material includes metal nitrides, metal oxides, doped semiconductors, small bandgap semiconductors, topological insulators, topological semimetals, van der Waals materials, or combinations thereof. [Item (20)] The method according to item (20), wherein the third resistivity of the amorphous phase is at least 20 times greater than that of the second resistivity of the crystalline phase.

Claims

1. A composite phase-change material layer having a mixture of a dispersed phase of a projection material having a first resistivity and a matrix of a phase-change material having a second or third resistivity depending on the phase, wherein the first resistivity of the projection material is greater than the second resistance of the phase-change material and less than the third resistance of the phase-change material; First electrode; and A second electrode on the opposing surface of the composite phase-change material layer, wherein the projection material forms a percolated conductive path from the first electrode to the second electrode. A phase-change memory device comprising the above features.

2. The phase-change memory device according to claim 1, wherein the second resistivity corresponds to the crystalline phase of the phase-change memory, and the third resistivity corresponds to the amorphous phase of the phase-change material.

3. The phase-change memory device according to claim 1 or 2, wherein the projection material includes a metal nitride, a metal oxide, a doped semiconductor, a small bandgap semiconductor, a topological insulator, a topological semimetal, a van der Waals material, or a combination thereof.

4. The aforementioned projection material is titanium nitride (TiN ｘ ), tantalum nitride (TaN ｘ ), tungsten nitride (WN ｘ ), aluminum nitride (AlN ｘ A phase-change memory device according to claim 1 or claim 2, comprising a metal nitride selected from the group consisting of ), and combinations thereof.

5. The phase-change memory device according to claim 1 or 2, wherein the projection material includes a doped semiconductor selected from the group consisting of doped Si, doped SiGe, doped silicon carbide (SiC), doped germanium (Ge), and combinations thereof.

6. The phase change memory device according to claim 1 or claim 2, wherein the projection material is a small bandgap semiconductor selected from the group consisting of tin telluride, titanium telluride, gallium germanium, selenium, InSb, InAs, GaSb, AlSb, and combinations thereof.

7. The phase change memory device according to claim 1 or claim 2, wherein the projection material is a metalloid selected from the group consisting of bismuth, tin (Sn), mercury telluride, graphite, and combinations thereof.

8. The projection material is Bi ２ Se ３ , BiSb, BiSbTe, graphene, TaAs, WTe ２ , Na ３ Bi, Cd ３ As ２ The phase change memory device according to claim 1 or claim 2, comprising a topological material selected from the group consisting of and combinations thereof.

9. The aforementioned projection material is WTe ２ MoTe ２ TiTe ２ A phase-change memory device according to claim 1 or claim 2, comprising a van der Waals material selected from the group consisting of the following, and combinations thereof.

10. The second resistivity corresponds to the crystalline phase of the phase-change memory, and the third resistivity corresponds to the amorphous phase of the phase-change material; and The third resistivity of the amorphous phase is at least 20 times greater than that of the second resistivity of the crystalline phase. The phase-change memory device according to claim 2.

11. The phase change memory device according to claim 10, wherein the electrical resistance of the percolated conductive path in the projection material is more than five times greater than that of the percolated current path through the crystalline phase change material, and is less than that of the amorphous phase change material of the phase change material.

12. The phase-change memory device according to claim 1 or claim 2, wherein the matrix of the phase-change material includes alternating layers of the phase-change material having a layer of conductive material.

13. The phase-change memory device according to claim 1 or claim 2, wherein the matrix of the phase-change material includes alternating layers of dispersed phases of the phase-change material and the projection material, with a layer that is entirely made of the phase-change material.

14. The compositional phase change material layer is Al ２ O ３ Si ３ N ４ SiO ２ SiO, TiO ２ , HfO ２ The phase-change memory device according to claim 1 or claim 2, further comprising a non-conductive additive selected from the group consisting of the and combinations thereof.

15. A projection material layer in direct contact with the back surface of the composite phase change material layer; The back electrode of the composite phase change material layer that is in direct contact with the projection material layer on the back surface; and An upper electrode on the opposite surface of the composite phase-change material layer to the surface in direct contact with the projection material layer, wherein the projection material forms a percolated conductive path from the first electrode to the second electrode. A phase-change memory device according to claim 1 or claim 2, comprising:

16. A composite phase-change material layer having a mixture of a dispersed phase of a projection material having a first resistivity and a matrix of a phase-change material having a second or third resistivity depending on the phase, wherein the first resistivity of the projection material is greater than the second resistance of the phase-change material and less than the third resistance of the phase-change material; A projection material layer in direct contact with the back surface of the composite phase change material layer; The back electrode of the composite phase change material layer that is in direct contact with the projection material layer on the back surface; and An upper electrode on the opposite surface of the composite phase-change material layer to the surface in direct contact with the projection material layer, wherein the projection material forms a percolated conductive path from the first electrode to the second electrode. A phase-change memory device comprising the above features.

17. A step of forming a phase-change memory device according to any one of claims 1 to 15; and In the step of applying a current between the first and second electrodes, the projection material forms a percolated conductive path from the first electrode to the second electrode, passing through the phase change region of the composite phase change material layer in one of the first and second electrodes. A method for reducing drift effects in a phase-change memory device, comprising the features described above.

18. A step of forming a composite phase-change material layer comprising a mixture of a dispersed phase of a projection material having a first resistivity and a matrix of a phase-change material having a second or third resistivity depending on the phase, wherein the first resistivity of the projection material is greater than the second resistance of the phase-change material and less than the third resistance of the phase-change material; The steps of forming a first electrode and a second electrode on opposing surfaces of the composite phase change material layer; and In the step of applying a current between the first and second electrodes, the projection material forms a percolated conductive path from the first electrode to the second electrode, passing through the phase change region of the composite phase change material layer in one of the first and second electrodes. A method for reducing drift effects in a phase-change memory device, comprising the features described above.

19. The method according to claim 18, wherein the step of forming the composite phase change material layer includes a co-sputtering method employing a first sputtering target for providing the phase change material of the matrix of the phase change material and a second sputtering target for providing the dispersed phase of the projection material.

20. The method according to claim 18 or claim 19, wherein the second resistivity corresponds to the crystalline phase of the phase change memory, and the third resistivity corresponds to the amorphous phase of the phase change material.

21. The method according to claim 18 or 19, wherein the projection material includes a metal nitride, a metal oxide, a doped semiconductor, a small bandgap semiconductor, a topological insulator, a topological semimetal, a van der Waals material, or a combination thereof.

22. The second resistivity corresponds to the crystalline phase of the phase-change memory, and the third resistivity corresponds to the amorphous phase of the phase-change material; and The third resistivity of the amorphous phase is at least 20 times greater than that of the second resistivity of the crystalline phase. The method according to claim 18 or claim 19.

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