Phase change storage material and device based on two-dimensional elemental bismuthene

Abstract

The invention discloses a phase change storage material and device based on two-dimensional elementary bismuthene. The chemical component of the phase change storage material is bismuth elementary substance, and the melting point is lt; 300 DEG C; an amorphous phase of the material is of a long-range disordered atom arrangement structure, a local structure is mainly a defective octahedron and has a four-membered ring and five-membered ring structure, the coordination number of most atoms is 3, and an energy band structure has no band gap; a crystal phase of the two-dimensional bismuthene material has a buckling hexagonal honeycomb layered structure, adjacent layers are connected with each other through Van der Waals force, and an energy band structure has a band gap. According to the invention, the two-dimensional elemental bismuthene is used as a phase change functional layer material, so that the component segregation phenomenon in the use process of the device can be physically and essentially eliminated, and meanwhile, the ultrathin size and the low melting point characteristic of the material have the advantages in the aspects of high-density integration and low-power-consumption operation of the phase change memory device.

Description

Technical Field

[0001] This invention relates to the field of phase change memory technology, and specifically to a phase change memory material and device based on two-dimensional elemental bismuthene. Background Technology

[0002] Phase-change memory (PCM) is a non-volatile memory device that stores information based on the physical property changes of phase-change materials. These devices utilize the differences in electrical or optical properties caused by the reversible transitions between different phases of the material to represent different storage states. Compared to existing dynamic random access memory (DRAM) and flash memory technologies, PCM offers advantages such as non-volatility, fast read / write speeds, simple device structure, and good scalability, and is widely considered an important candidate technology for storage-class memory and novel computing architectures.

[0003] However, existing mainstream phase-change memory technologies still face certain challenges in achieving longer cycle life, ultra-high density integration, and low power consumption. Traditional phase-change materials mainly rely on ternary or quaternary chalcogenide alloys such as germanium-antimony-tellurium (Ge-Sb-Te). During multiple write-erase cycles, huge thermal gradients and electric fields are generated inside the device. Different atoms migrate and redistribute under the drive of thermal and electric fields, causing deviations in the stoichiometry of the active region and ultimately leading to device failure. Furthermore, the phase-change material layer in traditional phase-change memory devices is usually in bulk form, with a thickness on the order of tens of nanometers, limiting further increases in the integration density of memory cells in the three-dimensional vertical stacking direction. In addition, the melting point of traditional phase-change materials is relatively high (typically above 600°C), requiring more power for write and erase operations. The heat accumulation during multiple write and erase processes can lead to excessively high temperatures in localized areas, causing data stored in those areas to become invalid. This high power consumption also limits further increases in the integration density of memory cells in the chip. Summary of the Invention

[0004] To overcome the shortcomings of the existing technology, the present invention provides a phase change memory material and device based on two-dimensional elemental bismuthene. The device uses two-dimensional elemental bismuthene as a phase change functional layer material, which can eliminate the component segregation phenomenon during the use of the device from a physical point of view. At the same time, its ultra-thin size and low melting point characteristics have advantages in realizing high-density integration and low-power operation of phase change memory devices.

[0005] To achieve the above objectives, the technical solution adopted by the present invention is as follows: A phase change storage material based on two-dimensional elemental bismuthene, wherein the chemical composition of the phase change storage material is elemental bismuth and the melting point is <300℃; The amorphous phase of the material has a long-range disordered atomic arrangement structure, with the local structure dominated by defect octahedra, and has four-membered and five-membered ring structures. The coordination number of most atoms is 3, and the band structure has no band gap. The crystalline phase of two-dimensional bismuthene materials has a buckled hexagonal honeycomb layered structure, with adjacent layers interconnected by van der Waals forces, and the band structure has a band gap.

[0006] A phase change memory device based on two-dimensional elemental bismuthene, wherein the memory device is arranged in a three-dimensional vertical stacking manner and the structure includes four layers, from bottom to top: a substrate layer, a bottom electrode layer, a phase change functional layer and a top electrode layer. The phase change functional layer is a phase change storage material based on two-dimensional elemental bismuthene with a thickness of ≤1nm. When it is in the amorphous phase, the band structure has no band gap, and when it is in the crystalline phase, the band structure has a band gap. Correspondingly, when the phase change functional layer is in the amorphous phase, the device is in a low-resistivity state, and when it is in the crystalline phase, the device is in a high-resistivity state.

[0007] The substrate layer is selected from silicon carbide, sapphire, or a silicon substrate covered with an oxide layer, and is used to provide mechanical support and thermal diffusion channels for the phase change memory device.

[0008] The materials of the bottom electrode layer and the top electrode layer are selected from one of the following: metal electrode materials (such as Au, TiN), two-dimensional conductive materials (such as graphene), or transparent conductive electrodes (such as ITO).

[0009] The phase change functional layer is prepared by one of the following methods: physical vapor deposition, chemical vapor deposition, molecular beam epitaxy, and electron beam evaporation.

[0010] The amorphous and crystalline phases of the phase change functional layer are switched by applying an electrical pulse between the top and bottom electrodes of the device. Applying a high-amplitude narrow pulse will drive the phase change functional layer to become amorphous, while applying a medium-to-low amplitude long pulse will drive the phase change functional layer to become crystallized.

[0011] When performing a write operation to switch to the low-resistivity amorphous phase, a high-amplitude narrow pulse is applied to the device, with a voltage amplitude of 1.5V~3.0V and a pulse width of 5ns~500ns; when performing an erase operation to switch to the high-resistivity crystalline phase, a medium-low amplitude long pulse is applied to the device, with a voltage amplitude of 0.6V~1.2V and a pulse width of 50ns~1000ns.

[0012] The phase-change memory device is applied to high-density storage-class memory or in-memory computing chips.

[0013] The beneficial effects of this invention are: This invention employs a two-dimensional elemental bismuthene phase change storage material. Since the material contains only one element, there is no thermodynamic driving force for element separation or component drift during the cyclic "write-erase" process, thus avoiding device failure caused by component segregation and improving the cycle life of phase change storage devices.

[0014] This invention utilizes the two-dimensional characteristics of two-dimensional elemental bismuthene phase change memory materials with a thickness of ≤1nm. The ultra-thin thickness can greatly improve the thermal stability of the amorphous phase and reduce the size of the device in the vertical direction, which is conducive to three-dimensional stacking and high-density integration, meeting the integration needs of the post-Moore era.

[0015] The two-dimensional elemental bismuthene phase change memory material proposed in this invention has a low melting point (<300℃), which is beneficial to reduce operating power consumption, thereby reducing data storage failure caused by local heat accumulation effect and improving the integration density of memory cells in the chip. Attached Figure Description

[0016] Figure 1 This is a schematic diagram of the crystal phase structure of two-dimensional bismuthene.

[0017] Figure 2 This is a schematic diagram of the amorphous phase structure of two-dimensional bismuthene.

[0018] Figure 3 This is a density of states analysis diagram of the two-dimensional bismuthene crystalline and amorphous phases.

[0019] Figure 4 This is a schematic diagram of a phase change memory device unit structure based on two-dimensional bismuthene material. Detailed Implementation

[0020] The present invention will now be described in further detail with reference to the accompanying drawings.

[0021] Figure 1 This is a schematic diagram of the crystal structure of a two-dimensional bismuthene material. Bismuth atoms form a buckled hexagonal honeycomb layered structure, with adjacent layers connected by van der Waals interactions.

[0022] Figure 2 This is a schematic diagram of the amorphous phase structure of two-dimensional bismuthene. The amorphous phase is a long-range disordered atomic arrangement structure, with its local structure dominated by defect octahedra, forming a large number of four-membered and five-membered ring structures, and the coordination number is mainly 3.

[0023] Figure 3 This is a density of states analysis diagram of the crystalline and amorphous phases of two-dimensional bismuthene. The crystalline and amorphous phases of two-dimensional bismuthene materials have different density of states characteristics and differ in electronic structure.

[0024] The density of states in a crystalline phase is essentially zero at the Fermi level, exhibiting a clear band gap and displaying semiconductor properties. In contrast, the density of states band gap in an amorphous phase narrows significantly, approaching closure, and the density of states curve broadens and smooths, exhibiting tail states and displaying metallic properties. Electronic states in a crystalline phase are delocalized, while those near the Fermi level in an amorphous phase exhibit localization. Therefore, the two phases have significant differences in electrical properties, which can be used for data storage and erasure.

[0025] Figure 4 This is a schematic diagram of a phase change memory device unit structure based on two-dimensional bismuthene material. The structure in the figure, from bottom to top, consists of substrate layer 1, bottom electrode layer 2, phase change functional layer 3, and top electrode layer 4.

[0026] The present invention will be further illustrated below with specific embodiments.

[0027] Example 1 This embodiment describes a phase change storage material based on two-dimensional bismuthene. The phase change material is a single layer of elemental bismuthene with a melting point <300℃. In the crystalline phase, bismuth atoms are arranged in a buckled hexagonal honeycomb layered structure with a coordination number of 3, a bond length of 3.04 Å, a bond angle of 90 degrees, and a thickness of 1 nm. Its crystal structure is as follows. Figure 1 As shown.

[0028] The phase change material has a significant band gap in its crystalline phase, exhibiting semiconductor properties. Due to the two-dimensional quantum confinement effect, it is in a high-resistivity state at room temperature.

[0029] The phase change material exhibits long-range order in its amorphous phase structure, possessing numerous four- and five-membered ring structures, with local structures differing from the crystalline phase. Due to the breaking of lattice symmetry, the long-range disordered structure leads to a significant contraction of the band gap in the amorphous phase, and the electronic states near the Fermi level become localized, exhibiting low-resistivity states.

[0030] The phase change material is elemental bismuth, containing no other elements. During the reversible transformation between the crystalline and amorphous phases, there is no migration or separation of chemical components, fundamentally overcoming the problem of component segregation in traditional alloy materials.

[0031] The phase change material is ultrathin, with a thickness ≤1nm. Compared to traditional bulk phase change materials, this significantly reduces the thickness of the phase change functional layer, thereby increasing the stacking density. The phase change material can achieve reversible switching of its storage state through external electrical pulse excitation: during a write operation (Reset), a high-amplitude narrow pulse is applied to the material, using Joule heating to instantly heat the bismuthene layer above its melting point, followed by rapid quenching. This freezes the atomic arrangement into a long-range disordered amorphous phase, transforming the material into a low-resistivity state (corresponding to logic "1"). In the erase operation (Set), a long pulse of medium to low amplitude is applied to heat the material to the crystallization temperature range and hold it for a certain time, driving the atoms to undergo short-range diffusion and rearrange to restore the thermodynamically stable buckled honeycomb crystal phase, and the material is restored to a high-resistivity state (corresponding to logic "0"); the read operation is completed by applying a weak signal far below the threshold to detect the resistance state.

[0032] When an external stimulus is applied between the top and bottom electrode layers, a high-amplitude narrow pulse (voltage amplitude of 1.5V and pulse width of 5ns) is applied to the device during a write operation to switch to the low-resistivity amorphous phase; and a medium-to-low amplitude long pulse (voltage amplitude of 0.6V and pulse width of 50ns) is applied to the device during an erase operation to switch to the high-resistivity crystalline phase.

[0033] Example 2 This embodiment is a phase change memory device unit based on two-dimensional elemental bismuthene material. The phase change device unit includes at least a substrate layer, a bottom electrode layer, a phase change functional layer, and a top electrode layer, with the four layers stacked sequentially from bottom to top to form a multilayer structure.

[0034] In the phase change memory device unit, the phase change functional layer is the two-dimensional elemental bismuthene phase change material described in the invention above, and the thickness of this layer is 0.7 nm. When the phase change functional layer is in the amorphous phase, the device is in a low-resistance state; when it is in the crystalline phase, the device is in a high-resistance state. The switching between the high and low resistance states is achieved by applying an electrical pulse between the amorphous and crystalline phases.

[0035] When an external stimulus is applied between the top electrode layer and the bottom electrode layer, and a write operation is performed to switch to the low-resistivity amorphous phase, a high-amplitude narrow pulse (preferably a voltage amplitude of 3.0V and a pulse width of 500ns) is applied to the device; when an erase operation is performed to switch to the high-resistivity crystalline phase, a medium-to-low amplitude long pulse (a voltage amplitude of 1.2V and a pulse width of 1000ns) is applied to the device.

[0036] The preparation methods of the phase change functional layer include, but are not limited to, physical vapor deposition, molecular beam epitaxy, and electron beam evaporation.

[0037] In this example, magnetron sputtering is preferably used to prepare the phase change functional layer. The sputtering process is carried out in an ultra-high vacuum chamber with a background vacuum level better than 1x10⁻⁶. -5 Torr uses high-purity bismuth targets.

[0038] In the phase-change memory device unit, the substrate layer serves to support the entire device structure, providing a flat supporting interface for the formation of the subsequent phase-change functional layer, and also participating in thermal management during the phase-change process. The substrate layer material can be, but is not limited to, SiC and high-resistivity Si materials.

[0039] In the phase change memory cell, the bottom electrode layer material can be, but is not limited to, TiN, W, and graphene. The top electrode layer can be, but is not limited to, Ti, Au, and ITO.

Claims

1. A phase change storage material based on two-dimensional elemental bismuthene, characterized in that, The phase change storage material is composed of elemental bismuth and has a melting point of <300℃. The amorphous phase of the material has a long-range disordered atomic arrangement structure, with the local structure dominated by defect octahedra, and has four-membered and five-membered ring structures. The coordination number of most atoms is 3, and the band structure has no band gap. The crystalline phase of two-dimensional bismuthene materials has a buckled hexagonal honeycomb layered structure, with adjacent layers interconnected by van der Waals forces, and the band structure has a band gap.

2. A phase change storage device based on two-dimensional elemental bismuthene, characterized in that, The storage device is arranged in a three-dimensional vertical stacking manner, and the structure includes four layers, which are, from bottom to top, a substrate layer, a bottom electrode layer, a phase change functional layer and a top electrode layer. The phase change functional layer is the phase change storage material based on two-dimensional elemental bismuthene as described in claim 1, with a thickness of ≤1nm. When it is in the amorphous phase, the band structure has no band gap, and when it is in the crystalline phase, the band structure has a band gap. Correspondingly, when the phase change functional layer is in the amorphous phase, the device is in a low-resistivity state, and when it is in the crystalline phase, the device is in a high-resistivity state.

3. A phase change memory device based on two-dimensional elemental bismuthene according to claim 2, characterized in that, The substrate layer is selected from silicon carbide, sapphire, or a silicon substrate covered with an oxide layer, and is used to provide mechanical support and thermal diffusion channels for the phase change memory device.

4. A phase change storage device based on two-dimensional elemental bismuthene according to claim 2, characterized in that, The materials used for the bottom electrode layer and the top electrode layer are selected from one of the following: metal electrode material, two-dimensional conductive material, or transparent conductive electrode.

5. A phase change memory device based on two-dimensional elemental bismuthene according to claim 2, characterized in that, The phase change functional layer is prepared by one of the following methods: physical vapor deposition, chemical vapor deposition, molecular beam epitaxy, and electron beam evaporation.

6. A phase change memory device based on two-dimensional elemental bismuthene according to claim 2, characterized in that, The amorphous and crystalline phases of the phase change functional layer are switched by applying an electrical pulse between the top and bottom electrodes of the device. Applying a high-amplitude narrow pulse will drive the phase change functional layer to become amorphous, while applying a medium-to-low amplitude long pulse will drive the phase change functional layer to become crystallized.

7. A phase change memory device based on two-dimensional elemental bismuthene according to claim 6, characterized in that, When performing a write operation to switch to the low-resistivity amorphous phase, a high-amplitude narrow pulse is applied to the device, with a voltage amplitude of 1.5V~3.0V and a pulse width of 5ns~500ns; when performing an erase operation to switch to the high-resistivity crystalline phase, a medium-low amplitude long pulse is applied to the device, with a voltage amplitude of 0.6V~1.2V and a pulse width of 50ns~1000ns.

8. The application of a phase change memory device based on two-dimensional elemental bismuthene according to any one of claims 2-7, characterized in that, The phase-change memory device is applied to high-density storage-class memory or in-memory computing chips.

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