Optical phase-change memory material based on arsenic telluride compound, device and preparation method thereof

Abstract

The application discloses an optical phase change storage material based on arsenic tellurium compound, a device and a preparation method thereof, which comprises arsenic (As) elements and tellurium (Te) elements, and the chemical formula of the phase change material is As x Te y , wherein 1

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of phase change storage material and device, in particular to an optical phase change storage material based on arsenic tellurium compound, a device and a preparation method thereof. BACKGROUND

[0002] The rapid rise and development of advanced data-intensive technologies such as artificial intelligence, big data, and cloud computing have posed great challenges to the data storage and processing capabilities of computing devices. In the face of the imminent data storage crisis, academia and industry are actively developing non-volatile storage and brain-like computing technologies with fast speed, large capacity, and low energy consumption, in order to achieve stable storage and rapid processing of data in the same unit. Among them, phase change memory based on phase change material has the advantages of non-volatility and fast running speed. Phase change memory represented by Intel Optane chips has entered the market first, filling the performance gap between dynamic random access memory and flash-based solid state drives.

[0003] Phase change memory utilizes the rapid reversible phase change and large resistance / reflection rate difference between crystalline and amorphous phases of phase change materials based on chalcogenides (such as germanium antimony tellurium alloy) to achieve non-volatile storage of data, where the amorphous state with high resistance / low reflectivity is called logic state "0", and the crystalline state with low resistance / high reflectivity is called logic state "1". In the SET operation, the phase change storage material realizes the transition from amorphous to crystalline phase, while in the RESET operation, the phase change storage material realizes the transition from crystalline to amorphous phase.

[0004] Antimony tellurium compound Sb2Te3 is a key parent material for realizing high-performance phase change storage and brain-like computing, with the advantages of fast phase change speed and large resistance / reflection rate difference. Ge2Sb2Te5 (abbreviated as GST) developed based on it has been widely used in phase change memory. However, the crystallization temperature of Sb2Te3 compound is relatively low (about 85℃), and the amorphous stability is poor, which poses a risk of data loss in actual service environment. This shortcoming to some extent restricts the performance of related phase change materials developed based on it. Therefore, exploring a new type of phase change parent material with good amorphous stability is one of the important research directions in the field. SUMMARY

[0005] In order to overcome the shortcomings of the prior art, the present application aims to provide an optical phase change storage material based on arsenic tellurium compound, a device and a preparation method thereof, which has good amorphous stability and significant optical reflectivity difference, and is expected to become an important new type of phase change parent material and break through the binary logic recognition of "0" and "1".

[0006] To achieve the above purpose, the technical scheme adopted by the present application is:

[0007] An optical phase-change storage material based on arsenic-tellurium compound, which is an arsenic-tellurium compound phase-change storage material with a chemical formula of As x Te y , wherein 1 < x < 3, 2 < y < 4, and the amorphous phase structure thereof contains a large number of homopolar chemical bonds and five-membered ring structures.

[0008] The homopolar chemical bond refers to a chemical bond formed by two atoms of the same kind, such as an As-As chemical bond; and the five-membered ring structure refers to a ring-shaped local structure formed by five As and Te atoms in sequence.

[0009] The crystal phase structure of the arsenic-tellurium compound phase-change storage material contains two phases, i.e., an alpha crystal phase and a beta crystal phase, both of which have a similar van der Waals layer structure, and the local structure has a similar atomic configuration, i.e., an octahedral or defective octahedral configuration; the difference between the two phases mainly lies in that, in the alpha crystal phase, a part of the As atoms has a coordination number of 6, the rest of the As atoms are in a defective octahedral configuration, and each adjacent Te atom has five adjacent As atoms, while in the beta crystal phase, the As atoms form a coordination octahedral structure with six adjacent Te atoms.

[0010] The arsenic-tellurium compound phase-change storage material has a crystallization temperature higher than 150℃, good amorphous stability, and an optical reflectance / transmittance contrast between the crystal phase and the amorphous phase of more than 25%.

[0011] The arsenic-tellurium compound phase-change storage material can realize reversible conversion between the amorphous phase and the crystal phase under the action of a laser pulse, and the optical reflectance / transmittance changes accordingly, and the structure and the optical reflectance / transmittance can remain stable without loading the pulse, wherein the wavelength of the laser pulse ranges from 300 nm to 1000 nm, the power is greater than or equal to 5 mW, and the pulse width is greater than or equal to 10 ns.

[0012] The arsenic-tellurium compound phase-change storage material has at least three stable and identifiable optical reflectance / transmittance states under the action of a laser pulse, wherein the amorphous state is a low reflectance / transmittance state, the alpha crystal phase is a medium reflectance / transmittance state, and the beta crystal phase is a high reflectance / transmittance state.

[0013] The arsenic-tellurium compound phase-change storage material is an arsenic-tellurium thin film material with a thickness of 5 nm to 1 μm.

[0014] A device unit prepared based on an optical phase-change storage material based on an arsenic-tellurium compound, which comprises a substrate layer, a waveguide material layer, and a phase-change material layer, the three material layers are stacked in order from bottom to top, and during the operation of the device unit, a laser passes through the waveguide material layer, induces the phase-change material layer above to change phase, and then changes the transmittance of the laser, thereby realizing the recognition of logic values.

[0015] A method for preparing a device unit based on an arsenic-tellurium compound optical phase change memory material, comprising the following steps:

[0016] 1) preparing a substrate layer;

[0017] 2) preparing a waveguide material layer on the substrate layer;

[0018] 3) preparing a phase change material layer on the waveguide material layer, the phase change material layer being an arsenic-tellurium compound phase change material.

[0019] The arsenic-tellurium compound phase change material is prepared by a magnetron sputtering method, a chemical vapor deposition method, an atomic layer deposition method, or an electron beam evaporation method, and has a chemical general formula of As x Te y , wherein 1 < x < 3, 2 < y < 4, the arsenic-tellurium compound phase change material is prepared by using an As target and a Te target or an As x Te y alloy target.

[0020] Advantages of the present application:

[0021] The arsenic-tellurium compound phase change material provided by the present application has a small difference in electronegativity between two elements, a large number of homopolar chemical bonds in an amorphous phase structure, and a large number of five-membered ring structures. The two crystal phase structures do not contain homopolar chemical bonds and five-membered ring structures. The local atomic structures of the amorphous phase and the crystal phase are significantly different, resulting in a large energy barrier that needs to be overcome during crystallization of the arsenic-tellurium compound phase change material, thereby having good amorphous stability, and the crystallization temperature can be above 150℃. The amorphous phase and the crystal phase of the phase change material also have good optical reflectivity / transmittance contrast. In the visible light range, the average optical reflectivity / transmittance contrast between the beta crystal phase and the amorphous phase is more than 25%, and the average optical reflectivity / transmittance contrast between the alpha crystal phase and the amorphous phase is more than 15%. Based on the above two advantages, the arsenic-tellurium compound phase change material can be used as an important phase change matrix material for developing new phase change materials with more excellent performance. The preparation method of the phase change material provided by the present application is simple and easy to accurately control the content of each element. The optical phase change memory provided by the present application has the advantages of strong data retention and stable performance. BRIEF DESCRIPTION OF DRAWINGS

[0022] Figure 1 The left figure is an alpha crystal phase (monoclinic) structure, and the right figure is a beta crystal phase (rhombohedral) structure.

[0023] Figure 2 The figure is a statistical diagram of the primitive ring structure in the amorphous phase of the arsenic-tellurium compound.

[0024] Figure 3The figure is a representative pentatomic ring structure in the amorphous phase of arsenic-tellurium.

[0025] Figure 4 The figure is a schematic diagram of optical reflectance index analysis of the crystal phase and amorphous phase of arsenic-tellurium compound.

[0026] Figure 5 The figure is a schematic diagram of the structure of an optical phase change memory device unit based on arsenic-tellurium compound. DETAILED DESCRIPTION

[0027] The application will be further described in detail below with reference to the accompanying drawings.

[0028] Figure 1 The figure is a schematic diagram of the crystal structure of arsenic-tellurium compound. The left figure is the α phase (monoclinic) structure, and the right figure is the β phase (rhombohedral) structure. Both phases are layered structures, and the total energy of the α phase is slightly lower than that of the β phase. In the α phase, part of the As atoms has a coordination number of 6, and the rest of the As atoms is in a defective octahedron, and the adjacent Te atoms have 5. In the β phase, the As atoms usually form a coordination octahedron with 6 adjacent Te atoms. In the α phase and the β phase, there is a Peierls distortion in the As-Te bond near the 6-coordinated As atoms. In the defective octahedron of the α phase, the central As atom has two pairs of long and short As-Te bonds (respectively and ), one As-Te short bond and one very long As-As interatomic distance In the α phase and the β phase, the Te atoms at the edge of the atomic layer block form a triple-defective octahedron model, and the rest of the Te atoms form 5-coordination and 6-coordination in the α phase and the β phase, respectively.

[0029] Figure 2 and Figure 3 The figures are a statistical schematic diagram of the primitive ring structure in arsenic-tellurium compound and a representative pentatomic ring structure in the amorphous phase of arsenic-tellurium. Unlike the Sb2Te3 amorphous phase, which is mainly composed of tetatomic rings, the amorphous phase of arsenic-tellurium compound is mainly composed of pentatomic rings, and at least one homopolar bond exists in the pentatomic ring. Therefore, the proportion of homopolar bonds in the amorphous phase of arsenic-tellurium compound exceeds 40%, which is significantly higher than that of other phase change storage materials. For comparison, the proportion of homopolar bonds in Sb2Te3 is only 17%. At the same time, the crystal phase of arsenic-tellurium compound does not contain pentatomic ring structure and homopolar bond. The great difference between the two structures increases the crystallization energy barrier of arsenic-tellurium compound, and thus improves its amorphous stability and crystallization temperature. Therefore, the optical phase change storage material of arsenic-tellurium compound has good amorphous stability.

[0030] Figure 4The figure is an optical reflectivity index analysis diagram of arsenic-tellurium compound crystal phase and amorphous phase. In a wide spectral range, the reflectivity of α phase, β phase and amorphous phase has a large difference. In the visible light range (1.64-3.19 eV), the reflectivity of β phase is the highest, that of α phase is the second, and that of amorphous phase is the smallest. The reflectivity index contrast of β phase and amorphous phase is more than 25%, which is due to the large 1 and 2 (real part and imaginary part of dielectric function) of β phase. Due to the reduction of coordination number and the enhancement of Peierls distortion, the resonance bond of α phase is weakened, and the reflectivity index contrast of α phase and amorphous phase is more than 15%.

[0031] Figure 5 The figure is a structure diagram of an optical phase change memory device unit based on arsenic-tellurium compound phase change material. The optical phase change memory unit at least includes a substrate layer, a waveguide material layer and a phase change material layer, and the three material layers are stacked from bottom to top. During the working process of the device unit, laser passes through the waveguide material layer, and the near-field coupling effect between the electromagnetic mode propagating in the waveguide and the phase change unit at the top of the waveguide is used to absorb enough energy to realize crystallization and amorphization phase change, so as to realize information writing and erasing. Based on the good amorphous stability and large optical contrast of arsenic-tellurium compound phase change material, the optical phase change memory device unit has the advantages of strong data retention and stable performance.

[0032] The following will be further illustrated by specific examples:

[0033] Example 1

[0034] The embodiment provides an optical phase change storage material and device unit based on arsenic-tellurium compound, the phase change material includes arsenic (As) element and tellurium (Te) element, and the chemical formula is As x Te y , wherein 1 < x < 3, 2 < y < 4. The phase change material used in the embodiment has a chemical formula of As2Te3. The crystal structure includes α phase and β phase. In the α crystal phase, a part of As atoms has a coordination number of 6, and the rest of As atoms are in a defective octahedron, and adjacent Te atoms have 5. In the β crystal phase, As atoms usually form a coordination octahedron with 6 adjacent Te atoms. The crystal structure is shown in Figure 1 .

[0035] The phase change material has a large number of homopolar bonds and five-membered ring structures in the amorphous phase, and the local structure is greatly different from the crystal phase structure. The crystallization temperature of the As2Te3 phase change material used in the example is about 180°C, and the amorphous stability is good. The statistics of the number of base rings in the amorphous structure is shown in Figure 2 , and the typical five-membered ring structure is shown in Figure 3 .

[0036] The phase change material has the highest reflectivity in the beta phase, the second highest in the alpha phase, and the lowest in the amorphous phase in the visible light range (1.64-3.19 eV). The average optical reflectivity / transmissivity contrast of the beta phase and the amorphous phase of the As2Te3 phase change material used in the case is about 29%, and the average optical reflectivity / transmissivity contrast of the alpha phase and the amorphous phase is about 18%. The optical reflectivity is shown in Figure 4 .

[0037] The phase change material can realize reversible conversion between the amorphous phase and the crystal phase under the action of a laser pulse, and the optical reflectivity / transmissivity changes accordingly. In the case, the pulse wavelength is 630 nm, the pulse power is 70 mW, and the pulse width is 10 4 ns. The structure and optical reflectivity / transmissivity can remain stable without loading the pulse, and at least two stable and identifiable optical reflectivity / transmissivity states are provided.

[0038] The thickness of the phase change material film is between 5 nm and 1 μm. The thickness of the As2Te3 film used in the case is about 50 nm.

[0039] The As2Te3 phase change material used in the case has a high crystallization temperature, good amorphous stability, large optical reflectivity / transmissivity contrast between the crystal phase and the amorphous phase, and better data retention and a larger optical signal identification window compared with a typical Sb2Te3 phase change material.

[0040] Example 2

[0041] The application provides an optical phase change memory device unit based on an arsenic tellurium compound phase change material. The optical phase change memory unit at least includes a substrate layer, a light waveguide material layer, and a phase change material layer, which are stacked in order from bottom to top. The phase change material layer is the arsenic tellurium compound phase change material described in the application. The phase change material layer includes the arsenic tellurium compound phase change storage material provided in Example 1, and has a chemical formula of As x Te y , wherein 1 < x < 3 and 2 < y < 4.

[0042] In the optical phase change memory device unit, the substrate layer material needs to have characteristics such as not absorbing light and low refractive index, and can use but is not limited to SiO2 and Al2O3 materials. The light waveguide material layer can use but is not limited to Si3N4, InP, and Si waveguide materials. As shown in Figure 5 , during the working process of the device unit, the laser passes through the waveguide material layer, and the near-field coupling effect between the electromagnetic mode propagating in the waveguide and the phase change unit at the top of the waveguide is used to absorb enough energy to perform crystallization and amorphization phase change, thereby changing the transmissivity of the laser and realizing information writing and erasing.

[0043] The application provides a preparation method of an optical phase change memory unit, and the preparation method comprises at least the following steps: 1) preparing a substrate layer; 2) preparing a waveguide material layer on the substrate layer;

[0044] 3) preparing a phase change material layer on the waveguide material layer, wherein the phase change material layer is an arsenic-tellurium compound phase change material according to the application. x Te y , wherein 1 < x < 3 and 2 < y < 4. The phase change material layer can be prepared by using a magnetron sputtering method, a chemical vapor deposition method, an atomic layer deposition method or an electron beam evaporation method, and using an As target and a Te target or an As x Te y Te alloy target to prepare the arsenic-tellurium compound phase change thin film material.

Claims

1. An optical phase-change storage material based on arsenic telluride compounds, characterized in that, For arsenic telluride compound phase change memory material, the chemical formula is As x Te y , wherein 1 < x < 3, 2 < y < 4; The phase change memory material comprises an amorphous phase structure containing a large number of homopolar bonds and five-membered ring structures, wherein the homopolar bond refers to a chemical bond formed by two atoms of the same kind, and the five-membered ring structure is a ring-shaped local structure formed by five As and Te atoms in sequence. The crystal phase structure of the arsenic-tellurium compound phase change memory material comprises an alpha crystal phase and a beta crystal phase, both of which have a similar van der Waals layer structure, and the local structure has a similar atomic configuration, mainly octahedral or defective octahedral; the difference between the two structures mainly lies in that in the alpha crystal phase, a part of As atoms has a coordination number of 6, the rest of the As atoms are in a defective octahedral structure, and there are 5 adjacent Te atoms, while in the beta crystal phase, the As atoms form a coordination octahedron with 6 adjacent Te atoms. The arsenic-tellurium compound phase change memory material has a crystallization temperature higher than 150°C and good amorphous stability, and in the visible light range, the average optical reflectance / transmittance contrast of the beta crystal phase to the amorphous phase is more than 25%, and the average optical reflectance / transmittance contrast of the alpha crystal phase to the amorphous phase is more than 15%. The arsenic-tellurium compound phase change memory material can realize reversible conversion between the amorphous phase and the crystal phase under the action of a laser pulse, and its optical reflectance / transmittance changes accordingly, and its structure and optical reflectance / transmittance can remain stable without loading the pulse, wherein the wavelength range of the laser pulse is 300-1000 nm, the power is ≥5 mW, and the pulse width is ≥10 ns.

2. The optical phase change storage material based on arsenic telluride compound according to claim 1, characterized in that, The arsenic-tellurium compound phase change memory material has at least three stable and identifiable optical reflectance / transmittance states under the action of a laser pulse, wherein the amorphous state is a low reflectance / transmittance state, the alpha crystal phase is a medium reflectance / transmittance state, and the beta crystal phase is a high reflectance / transmittance state.

3. The optical phase change storage material based on arsenic telluride compound according to claim 1, characterized in that, The arsenic-tellurium compound phase change memory material is an arsenic-tellurium thin film material with a thickness of 5 nm-1 μm.

4. A device cell fabricated from an optical phase change material based on arsenic telluride compounds according to any one of claims 1 to 3, characterized in that The device comprises a substrate layer, a waveguide material layer, and a phase change material layer, which are stacked in order from bottom to top, and during the working process of the device unit, laser passes through the waveguide material layer, induces the phase change of the phase change material layer above, changes the transmittance of the laser, and realizes the recognition of logic values.

5. A method of fabricating a device cell based on an optical phase change material of arsenic telluride compound according to claim 4, characterized in that, The method comprises the following steps: 1) preparing a substrate layer; 2) preparing a waveguide material layer on the substrate layer; 3) preparing a phase change material layer on the waveguide material layer, wherein the phase change material layer is an arsenic-tellurium compound phase change material.

6. A method of fabricating a device cell based on an optical phase change material of arsenic telluride compound according to claim 5, characterized in that, The arsenic-tellurium compound phase change material is prepared by a magnetron sputtering method, a chemical vapor deposition method, an atomic layer deposition method or an electron beam evaporation method, and has a chemical general formula of As x Te y , wherein 1 < x < 3, 2 < y < 4, the arsenic-tellurium compound phase change material is prepared by using an As target and a Te target or an As x Te y Te alloy target.

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