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EP-4736608-A1 - LOW DRIFT PHASE CHANGE MATERIAL COMPOSITE MATRIX

EP4736608A1EP 4736608 A1EP4736608 A1EP 4736608A1EP-4736608-A1

Abstract

A phase change memory device that includes a composite phase change material layer comprising a mixture of a dispersed phase of a projection material of a first resistivity, and a matrix of a phase-change material of a second resistivity or third resistivity dependent on phase. The first resistivity of the projection material has a resistance that is greater than the second resistance for the phase change material, and is 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 faces of the composite phase change material layer. The projection material forms a percolated conducting path from the first electrode to the second electrode.

Inventors

  • BREW, Kevin, Wayne
  • PHILIP, Timothy, Matthew
  • HAN, JIN PING
  • CHEN, CHING-TZU

Assignees

  • International Business Machines Corporation

Dates

Publication Date
20260506
Application Date
20240531

Claims (20)

  1. 1 . A phase change memory device comprising: a composite phase change material layer comprising a mixture of a dispersed phase of a projection material of a first resistivity, and a matrix of a phase-change material of a second resistivity or third resistivity dependent on phase, wherein the first resistivity of the projection material has a resistance that is greater than the second resistance for the phase change material, and is less than the third resistance of the phase change material; a first electrode; and a second electrode on opposing faces of the composite phase change material layer, wherein the projection material forms a percolated conducting path from the first electrode to the second electrode.
  2. 2. The phase change memory device of claim 1 , wherein the second resistivity corresponds to a crystalline phase of the phase change memory, and the third resistivity corresponds to an amorphous phase of the phase change material.
  3. 3. The phase change memory device of claim 1 or claim 2, wherein the projection material comprises a metal nitride, metal oxide, doped semiconductor, small bandgap semiconductor, topological insulator, topological semimetals, a Van der Waal material or a combination thereof.
  4. 4. The phase change memory device of any preceding claim, wherein the projection material comprises a metal nitride selected from the group consisting of titanium nitride (TiNx), tantalum nitride (TaNx), tungsten nitride (WNx), aluminum nitride (AINx) and combinations thereof.
  5. 5. The phase change memory device of any of claims 1 to 3, wherein the projection material comprises a doped semiconductor selected from the group consisting of doped Si, doped SiGe, doped silicon carbide (SIC), doped germanium (Ge), and combinations thereof.
  6. 6. The phase change memory device of any of claims 1 to 3, 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. 7. The phase change memory device of any of claims 1 to 3, wherein the projection material is a semimetal selected from the group consisting of bismuth, tin (Sn), mercury telluride, graphite and combinations thereof.
  8. 8. The phase change memory device of any of claims 1 to 3, wherein the projection material comprises a topological material selected from the group consisting of Bi2Se3, BiSb, BISbTe, graphene, TaAs, WTe2, NasBi, CdaAs2 and combinations thereof.
  9. 9. The phase change memory device of any of claims 1 to 3, wherein the projection material comprises a Van der Waal material selected from the group consisting of Te2, MoTe2, TITe2 and combinations thereof.
  10. 10. The phase change memory device of any preceding claim, wherein: the second resistivity corresponds to a crystalline phase of the phase change memory, and the third resistivity corresponds to an 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.
  11. 11 . The phase change memory device of claim 10, wherein the electrical resistance of the percolated conducting path of the projection material has greater than 5 times more electrical resistance than percolated current path through the crystalline phase change material and has less electrical resistance than the resistance through the amorphous phase change material of the phase change material.
  12. 12. The phase change memory device of any preceding claim, wherein the matrix of the phase-change material includes alternating layers of the phase change material with layers of conductive material.
  13. 13. The phase change memory device of any of claims 1 to 11 , wherein the matrix of the phase-change material includes alternating layers of the phase change material and dispersed phase of a projection material with layers entirely of the phase change material.
  14. 14. The phase change memory device of any preceding claim, wherein the composition phase change material layer further comprises a non-conducting additive selected from the group consisting of AI2O3, SisN4, Si O2, SIO, TO2, HfO2, and combinations thereof.
  15. 15. The phase change memory device of any preceding claim, comprising: a projection material layer in direct contact with a backside surface of the composite phase change material layer; a backside electrode in direct contact with the projection material layer at the backside surface of the composite phase change material layer; and a top electrode on an opposing face of the composite phase change material layer that is opposite the face of the composite phase change material layer that is in direct contact with the projection material layer, wherein the projection material forms a percolated conducting path from the first electrode to the second electrode.
  16. 16. A phase change memory device comprising: a composite phase change material layer comprising a mixture of a dispersed phase of a projection material of a first resistivity, and a matrix of a phase-change material of a second resistivity or third resistivity dependent on phase, wherein the first resistivity of the projection material has a resistance that is greater than the second resistance for the phase change material, and is less than the third resistance of the phase change material; a projection material layer in direct contact with a backside surface of the composite phase change material layer; a backside electrode in direct contact with the projection material layer at the backside surface of the composite phase change material layer; and a top electrode on an opposing face of the composite phase change material layer that is opposite the face of the composite phase change material layer that is in direct contact with the projection material layer, wherein the projection material forms a percolated conducting path from the first electrode to the second electrode.
  17. 17. A method for reducing drift effects in a phase change memory device comprising: forming phase change memory device according to any of claims 1 to 15; and applying a current across the first and second electrode, wherein the projection material forms a percolated conducting path from the first electrode to the second electrode through a phase change region of the composite phase change material layer at one of the first and second electrode, wherein the projection material forms a percolated conducting path from the first electrode to the second electrode.
  18. 18. A method for reducing drift effects in a phase change memory device comprising: forming a composite phase change material layer comprising a mixture of a dispersed phase of a projection material of a first resistivity, and a matrix of a phase-change material of a second resistivity or third resistivity dependent on phase, wherein the first resistivity of the projection material has a resistance that is greater than the second resistance for the phase change material, and is less than the third resistance of the phase change material; forming a first electrode and a second electrode on opposing faces of the composite phase change material layer; and applying a current across the first and second electrode, wherein the projection material forms a percolated conducting path from the first electrode to the second electrode through a phase change region of the composite phase change material layer at one of the first and second electrode, wherein the projection material forms a percolated conducting path from the first electrode to the second electrode.
  19. 19. The method of claim 18, wherein the forming of the composite phase change material layer comprises a co-sputtering method that employs a first sputter target to provide the phase-change material of the matrix of the phase-change material, and a second sputter target to provide the dispersed phase of a projection material.
  20. 20. The method of claim 18 or claim 19, wherein the second resistivity corresponds to a crystalline phase of the phase change memory, and the third resistivity corresponds to an amorphous phase of the phase change material.

Description

LOW DRIFT PHASE CHANGE MATERIAL COMPOSITE MATRIX BACKGROUND [0001] The present invention generally relates to phase change materials, and more particularly to phase change memory having low drift characteristics. [0002] Phase-change memory (PCM) is a non-volatile solid-state memory technology that exploits the reversible, thermally-assisted switching of phase-change materials, in particular chalcogenide compounds such as GST (Germanium-Antimony-Tellurium), between states with different electrical resistance. The fundamental storage unit (the "cell”) can be programmed into a number of different states, or levels, which exhibit different resistance characteristics. The s programmable cell-states can be used to represent different data values, permitting storage of information. [0003] In single-level PCM devices, each cell can be set to one of s=2 states, a "SET” state and a "RESET” state, permitting storage of one bit per cell. In the RESET state, which corresponds to an amorphous state of the phasechange 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 transformed into a low-resistance, crystalline state. This low-resistance state provides the SET state of the cell. If the cell is then heated to a high temperature, above the melting point of the phase-change material, the material reverts to the fully-amorphous RESET state on rapid cooling. In multilevel PCM devices, the cell can be set to s>2 programmable states permitting storage of more than one bit per cell. The different programmable states correspond to different relative proportions of the amorphous and crystalline phases within the volume of phase-change material. In particular, in addition to the two states used for single-level operation, multilevel cells exploit intermediate states in which the cell contains different volumes of the amorphous phase within the otherwise crystalline PCM material. Since the two material phases exhibit a large resistance contrast, varying the size of the amorphous phase within the overall cell volume produces a corresponding variation in cell resistance. [0004] Reading and writing of data in PCM cells is achieved by applying appropriate voltages to the phasechange material via a pair of electrodes associated with each cell. In a write operation, the resulting programming signal causes Joule heating of the phase-change material to an appropriate temperature to induce the desired cellstate on cooling. Reading of PCM cells is performed using cell resistance as a metric for cell-state. An applied read voltage causes a current to flow through the cell, this read current being dependent on resistance of the cell. Measurement of the cell read current therefore provides an indication of the programmed cell state. A sufficiently low read voltage is used for this resistance metric to ensure that 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 predefined reference levels for the s programmable cell-states. [0005] Phase change memory (PCM) have been considered to be a fundamental device for a low power interface towards enterprise artificial intelligence (Al). However, phase-change memory (PCM) devices face challenges for overcoming resistance drift, an issue where PCM cell resistance increases as a function of time. Unit cells of PCM often comprise multiple memristive devices, e.g., 6T4R, to improve accuracy of the written weight value. The resistance of each phase change memory PCM) cell can drifts over time leading to higher and higher resistance. This can result in creating volatility in the weight corresponding to the assigned data stored in the phase change memory (PCM), which can require additional hardware and/or software to correct. Several solutions have been proposed to resolve the impact of drift in phase change memory (PCM) devices. Some of the proposed solutions include projection liner phase change memory (PCM), phase change heterostructures (PCH), and interfacial phase change memory (IPCM). [0006] Projection liner phase change memory (PCM) is difficult to apply the appropriate material compositions that will be compatible with functional phase change memory (PCM) integration. Further, it has been determined that phase change heterostructures (PCH), and interfacial phase change memory (IPCM) are difficult to deposit and require precise temperature control. Additionally, the application of phase change heterostructures (PCH) to memory applications, and interfacial phase change memory (IPCM) have faced significant difficulty for failing to provide quality epitaxial grown for Van der Waals gap formation. This has often rendered phase change heterostructures (PCH) in memory applications and interfacial phase change memory (IPCM) non-manufacturable. Solubility of the layers in IPCM also