WO2022198623A1 - 基于氧掺杂的Sb 2Te 3相变材料、相变存储器及制备方法 - Google Patents

基于氧掺杂的Sb 2Te 3相变材料、相变存储器及制备方法 Download PDF

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WO2022198623A1
WO2022198623A1 PCT/CN2021/083195 CN2021083195W WO2022198623A1 WO 2022198623 A1 WO2022198623 A1 WO 2022198623A1 CN 2021083195 W CN2021083195 W CN 2021083195W WO 2022198623 A1 WO2022198623 A1 WO 2022198623A1
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phase change
shell
core
phase
oxygen
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程晓敏
曾运韬
缪向水
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Huazhong University of Science and Technology
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    • C09K5/00—Heat-transfer, heat-exchange or heat-storage materials, e.g. refrigerants; Materials for the production of heat or cold by chemical reactions other than by combustion
    • C09K5/02—Materials undergoing a change of physical state when used
    • H—ELECTRICITY
    • H10—SEMICONDUCTOR DEVICES; ELECTRIC SOLID-STATE DEVICES NOT OTHERWISE PROVIDED FOR
    • H10N—ELECTRIC SOLID-STATE DEVICES NOT OTHERWISE PROVIDED FOR
    • H10N70/00—Solid-state devices having no potential barriers, and specially adapted for rectifying, amplifying, oscillating or switching
    • H10N70/20—Multistable switching devices, e.g. memristors
    • H10N70/231—Multistable switching devices, e.g. memristors based on solid-state phase change, e.g. between amorphous and crystalline phases, Ovshinsky effect
    • H—ELECTRICITY
    • H10—SEMICONDUCTOR DEVICES; ELECTRIC SOLID-STATE DEVICES NOT OTHERWISE PROVIDED FOR
    • H10N—ELECTRIC SOLID-STATE DEVICES NOT OTHERWISE PROVIDED FOR
    • H10N70/00—Solid-state devices having no potential barriers, and specially adapted for rectifying, amplifying, oscillating or switching
    • H10N70/801—Constructional details of multistable switching devices
    • H10N70/881—Switching materials
    • H10N70/882—Compounds of sulfur, selenium or tellurium, e.g. chalcogenides
    • H10N70/8828—Tellurides, e.g. GeSbTe
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
    • Y02P—CLIMATE CHANGE MITIGATION TECHNOLOGIES IN THE PRODUCTION OR PROCESSING OF GOODS
    • Y02P20/00—Technologies relating to chemical industry
    • Y02P20/10—Process efficiency

Definitions

  • the invention belongs to the technical field of micro-nano electronics, and more particularly relates to a "shell-core" structure phase change material and a phase change memory based on oxygen-doped Sb 2 Te 3 .
  • Phase-change memory is considered by the International Semiconductor Industry Association to be the most likely to replace flash memory and dynamic memory and become the mainstream memory in the future due to its advantages of high integration, fast response, long cycle life and low power consumption.
  • phase change memory The basic principle of phase change memory is to use electrical pulse signals to act on the memory cells, so that the phase change material undergoes a reversible phase transition between amorphous and crystalline states to achieve the storage of "0" and "1".
  • a narrow pulse width, high amplitude electric pulse is applied to the cell to perform RESET operation, the crystalline phase change memory material melts and rapidly cools and transforms into an amorphous disordered state, thereby realizing the transition from a low resistance state "0" to a high resistance state. fast resistive transition of state "1".
  • phase change unit to perform SET operation
  • amorphous phase change memory material undergoes an annealing-like process to crystallize and return to a low-resistance state, realizing "1" erasing and writing. return "0".
  • phase change materials The optimization of the performance of phase change materials is the key to improving the performance of phase change memory, and the microstructure of phase change materials determines its macroscopic properties.
  • the power consumption of the phase-change memory is not only related to the melting point of the phase-change material, but also closely related to the utilization efficiency of the heat generated and dissipated inside the device.
  • the data retention time of the phase change memory is mainly determined by the amorphous stability of the phase change layer material.
  • Sb 2 Te 3 is a phase change material that has received extensive attention in recent years. It has a low crystallization temperature, a growth-dominated crystallization process, and a fast crystallization speed. Therefore, the phase change memory device based on Sb 2 Te 3 has a fast SET speed. specialty. However, its amorphous stability is poor, and the data retention time of the device needs to be further improved.
  • the main performance optimization method for Sb 2 Te 3 phase change materials is doping.
  • the local characteristics of the phase change material are changed to improve the performance of the phase change memory device.
  • the existing mechanism of Sb 2 Te 3 doping to improve its performance is mainly that doping elements (such as Ti, Sc, Y, etc.) form a certain local crystal structure in Sb 2 Te 3 , such as octahedral structure, etc.
  • doping elements such as Ti, Sc, Y, etc.
  • the crystallization process of Sb 2 Te 3 is regulated locally, and the amorphous stability of Sb 2 Te 3 material and the data retention time of the device are improved.
  • the doping process is simple, but it is difficult to accurately control the microstructure of the material.
  • phase change materials and devices can also be optimized by regulating the hetero interface or superlattice interface.
  • the preparation process of heterostructure and superlattice-like structure is more complicated, the selection conditions of another material are more stringent, and the device characteristics are not affected by the structural characteristics and process of the hetero- or superlattice-like/Sb 2 Te 3 interface. The parameters are particularly sensitive and are not conducive to large-scale commercial production.
  • the purpose of the present invention is to provide an oxygen - doped Sb 2 Te 3 phase change material, a phase change memory and a preparation method.
  • a "shell-core" (Core-shell, cs) microstructure
  • the shell layer plays a role in thermal resistance, improves the utilization efficiency of electricity and heat, and reduces the power consumption of RESET; the shell layer can also prevent the atomic migration of elements in the core and improve the reliability of the device.
  • the doping elements form bonds with the core phase change material elements, which can effectively improve the amorphous stability of the core phase change material, and finally achieve an all-round improvement in the overall performance of the device.
  • an oxygen-doped Sb 2 Te 3 phase change material is provided, the chemical formula of which is: O x (Sb 2 Te 3 ) 1-x , wherein O is oxygen, and x represents oxygen in Atomic percentage in the entire chemical composition, 0 ⁇ x ⁇ 40%.
  • oxygen atoms combine with element atoms in Sb 2 Te 3 to form a disordered oxide, which wraps around Sb 2 Te 3 and separates Sb 2 Te 3 into multiple islands to form a shell-core structure, in which the shell part It is the combination of oxygen atoms and element atoms in Sb 2 Te 3 to form disordered oxides, and the core part is Sb 2 Te 3 grains.
  • part of the oxygen element enters the Sb 2 Te 3 crystal grains to improve the amorphous stability of the Sb 2 Te 3 .
  • the properties of the amorphous oxide grain boundaries in the Sb 2 Te 3 are controlled by controlling the doping amount of O to control the O-Sb 2 Te 3 phase
  • the electrochemical properties of the memory-change material, the electrochemical properties include high and low resistance state resistance, crystallization temperature, and the O-Sb 2 Te 3 phase-change memory material refers to the O x (Sb 2 Te 3 ) 1-x material, where 0 ⁇ x ⁇ 40%.
  • oxygen atoms combine with Sb atoms in Sb 2 Te 3 to form disordered oxides, and are concentrated around Sb 2 Te 3 grains to form amorphous grain boundaries.
  • the disordered oxide is a disordered oxide formed by the combination of oxygen atoms and Sb atoms in Sb 2 Te 3 , and has the characteristics of high melting point, low thermal conductivity and stable performance.
  • the high melting point refers to greater than Sb. 2
  • the melting point of Te 3 (890K) the low thermal conductivity means that the thermal conductivity is close to the order of 10 ⁇ 3 , which is almost heat insulating;
  • the stable performance means that the structure is stable, not easily decomposed and not easily melted.
  • the oxide grain boundaries play a role in improving the electrothermal efficiency and preventing atomic migration during the phase change process, and at the same time, they are used to increase the resistance value of the amorphous state of the phase change layer and improve the amorphous stability of the Sb 2 Te 3 material.
  • a simple doping process can be used to realize the method of comprehensively controlling the microstructure and device characteristics of Sb 2 Te 3 and its application, and form a "shell-core" in the Sb 2 Te 3 phase change layer.
  • Microstructure in which the amorphous "shell” grain boundary with low thermal conductivity acts like a hetero interface, physically separating the crystal grains (that is, the "core” part) that has undergone phase transition and acting as a thermal resistance
  • the grain boundary of the amorphous shell layer blocks the atomic migration of Sb 2 Te 3 grains in the phase transition process, improving the reliability of the device and the number of cycles of erasing and writing; at the same time, doping
  • the bond between the hetero elements and the elements of the phase change material can effectively improve the amorphous stability of the phase change material, thereby improving the comprehensive performance of the device in an all-round way.
  • phase change memory based on oxygen-doped Sb 2 Te 3 phase change material, which comprises a bottom electrode, an isolation layer, a phase change memory material thin film layer and a top electrode, wherein the The material of the phase change memory material thin film layer is the oxygen-doped Sb 2 Te 3 phase change material as described above.
  • a method as described above which is prepared by magnetron sputtering, chemical vapor deposition, atomic layer deposition, electroplating or electron beam evaporation.
  • the specific magnetron sputtering method is any one of the following three kinds:
  • O-Sb 2 Te 3 phase change material of the present invention O atoms and Sb atoms combine to form disordered oxides, which are distributed around the grains of the phase change material Sb 2 Te 3 to form amorphous oxide grain boundaries, which separate the phase change material Sb 2 Te 3 into smaller "phase change islands" , the formation of the skin is an adiabatic high-resistance oxide, and the inner layer is a "shell-core" structure of Sb 2 Te 3 .
  • the local disorder and the shrinking of the phase transition core region increase the resistance value of the amorphous state of the phase transition layer and improve the amorphous stability of the Sb 2 Te 3 material.
  • the existence of the "shell-core” heterostructure limits the long-range migration of atoms in the "shell-core” structure due to external electrical operation, thereby improving the overall cycling characteristics of the memory device and effectively inhibiting the device.
  • the resistance drift of the device improves the resistance stability of the device.
  • the thermal insulation properties of the shell material and the encapsulation structure of the shell to the phase change grains make the heat energy more concentrated inside the grains during the phase change process, reducing the heat loss, thereby improving the electrothermal efficiency of the phase change process, effectively Reduce the reset power consumption of the device.
  • Fig. 1 shows the in-situ square resistance and annealing temperature of the O-Sb 2 Te 3 phase change memory material film and pure Sb 2 Te 3 phase change memory material film formed with a "shell-core” structure after grain boundary engineering control according to an embodiment of the present invention
  • the real-time relationship curve of where the heating rate is 12°C/min, where ST stands for pure Sb 2 Te 3 phase change memory material, and OST stands for O-Sb 2 Te 3 phase change memory material with "shell-core” structure.
  • FIG. 2 is a comparison diagram of XRD characterization of an O-Sb 2 Te 3 phase change memory material film formed with a “shell-core” structure after grain boundary engineering regulation in an embodiment of the present invention and a pure Sb 2 Te 3 phase change memory material film, wherein , the temperature corresponding to each curve represents the annealing temperature of the corresponding thin film, where ST represents pure Sb 2 Te 3 phase change memory material, and OST represents the O-Sb 2 Te 3 phase change memory material of “shell-core” structure.
  • Figure 3 is an in-plane-TEM microscopic analysis diagram of the O-Sb 2 Te 3 phase change memory material film with a "shell-core" structure after grain boundary engineering control, in which the crystalline sample was annealed at 300 °C for 10 min. It can be seen from the figure that the sample microscopically presents a uniform heterostructure.
  • Figure 4 is an HRTEM microscopic analysis diagram of an O-Sb 2 Te 3 phase change memory material film with a "shell-core” structure after grain boundary engineering control, wherein the crystalline sample was annealed at 300 °C for 10 min.
  • the longer solid arrow shows the crystalline part of the "core” structure
  • the shorter dashed arrow shows the amorphous part of the "shell” structure
  • the rectangular box in the right figure represents the Fourier of the corresponding part.
  • Leaf transition diagram It can be seen from the figure that the grains in the sample are wrapped by the randomly distributed amorphous structure.
  • Fig. 5 is the EDX element distribution diagram of the O-Sb 2 Te 3 phase change memory material film formed with "shell-core" structure after grain boundary engineering control
  • Fig. 5(a) is the bright field image of the sampling area
  • Fig. 5( b) is an image of Sb element distribution
  • Fig. 5(c) is an image of Te element distribution. It can be seen from the figure that the distribution of Sb element and Te element are not completely coincident, and there is a wrapping phenomenon.
  • Fig. 6 is the X-ray photoelectron spectrum of the O-Sb 2 Te 3 phase-change memory material film with a "shell-core" structure after grain boundary engineering control.
  • the crystalline sample was annealed at 300 °C for 10 min, and the surface After Ar + treatment to remove the surface oxidation contamination layer,
  • Figure 6(a) is the energy spectrum of Sb element
  • Figure 6(b) is the energy spectrum of Te element
  • the diffraction peaks in the figure correspond to the corresponding chemical bonds.
  • Figure 7 is the supercell model of the amorphous O-Sb-Te phase change material with O atomic content of 5%, 10%, and 20% calculated by using first-principles in the present invention, and Figure 7(a) shows 5% doped amorphous supercell model, Figure 7(b) shows the 10% doped amorphous supercell model, and Figure 7(c) shows the 20% doped amorphous supercell model. It can be seen from the figure that O atoms tend to bond with Sb atoms. With the increase of O atomic concentration, the O-Sb binding species increased and formed the encapsulation structure of Sb2Te3 grains.
  • Figure 8 is the effect of the simplified "shell-core” structure on the motion of atoms in the inner layer (inside the "core") obtained by first-principles calculations in the present invention, wherein the curve line1 corresponds to the conventional phase of pure Sb 2 Te 3 Simulation results of atomic motion of change material (PCM) at high temperature (550K), curve 2 corresponds to the simulation result of atomic motion of pure Sb 2 Te 3 conventional phase change material (PCM) at low temperature (300 K), curve 3 corresponds to O -The simulation results of the atomic motion of the "shell-core” phase change material (cs-PCM) represented by Sb 2 Te 3 at high temperature (550K), curve 4 corresponds to the "shell-core” represented by O-Sb 2 Te 3 Simulation results of the atomic motion of the core-structure phase change material (cs-PCM) at low temperature (300K). It can be seen from the figure that the "shell” layer can effectively inhibit the movement of atoms in the inner "core", and the sensitivity to temperature is significantly reduced.
  • Figure 9 is the effect of the simplified "shell-core” structure on the atomic motion in different regions of the inner layer (inside the "core") calculated by using first principles in the embodiment of the present invention, and curves 1 and 3 correspond to the inner layer "core”
  • curves 1 and 3 correspond to the inner layer "core”
  • curve 2 corresponds to the simulation result of the atomic motion in the middle region of the inner "core” phase change material.
  • the inset is a simplified three-dimensional wrapped structure model of "shell-core” structure O-Sb 2 Te 3
  • region 1 and region 3 correspond to the inner layer "core” phase change material close to the "shell” layer region atoms
  • region 2 corresponds to the inner layer
  • the layer "core” phase change material with atoms in the middle region It can be seen from the figure that the motion of atoms in the middle region is more violent than that in the region near the shell.
  • FIG. 10 is a schematic diagram of the blocking effect of the simplified "shell-core” structure on thermal diffusion obtained by using COMSOL simulation in the present invention. It can be seen from the figure that the heat is mainly concentrated in the inner layer Sb-Te phase change material region.
  • FIG. 11 is a schematic diagram of the phase change memory cell structure with the O-Sb 2 Te 3 phase change memory material having a "shell-core” structure formed after grain boundary engineering control as the functional layer.
  • 1 is the top electrode
  • 2 is a phase change material with a "shell-core” structure
  • 3 is a thermally insulating SiO2 layer
  • 4 is the bottom electrode.
  • Figures 12 to 15 are the phase change memory cells and undoped Sb 2 Te 3 phase change memory cells with the O-Sb 2 Te 3 phase change memory material with "shell-core” structure formed after grain boundary engineering control as the functional layer
  • the electrical performance test comparison chart of the unit Figure 12 is the device IV performance comparison chart
  • Figure 13 is the device RESET performance comparison chart
  • Figure 14 is the device drift resistance performance comparison chart
  • Figure 15 is the O-Sb forming a "shell-core” structure.
  • the invention provides a material and a storage device which can realize the comprehensive regulation of the microstructure and device characteristics of Sb 2 Te 3 by using a simple doping process, and relates to adopting an oxygen doping process and utilizing an amorphous oxide structure for Sb 2 Te 3 .
  • the 2 Te 3 phase change material is controlled to form a unique "shell-core" structure, which narrows its phase change region and blocks long-range atomic migration and thermal diffusion, thereby improving the performance of Sb 2 Te 3 phase change memory.
  • a "shell-core” microstructure is formed in the Sb 2 Te 3 phase transition layer, in which the amorphous low thermal conductivity "shell layer” grain boundary plays a role similar to a hetero interface, and has a Sb 2 Te 3 grains (also called “cores”) are physically separated, and play a role in thermal resistance, improve the efficiency of electric and heat utilization, and reduce RESET power consumption; the grain boundary of the amorphous shell layer blocks the atoms of Sb 2 Te 3 grains in the phase transition process migration, improve the reliability of the device and the number of cycles of erasing and writing; at the same time, the doping elements form bonds with the phase change material elements, which can effectively improve the amorphous stability of the phase change material. comprehensive performance.
  • phase change memory material formed by the control of the amorphous structure of the present invention
  • O is obtained by introducing O into the Sb 2 Te 3 phase change memory material, and its general chemical composition is as follows: O x (Sb 2 Te 3 ) 1-x , where x represents the atomic percentage of O element, and the preferred value range of x is 0 ⁇ x ⁇ 40%.
  • the value of x can be regulated by adjusting the flow rate of oxygen (O 2 ) introduced during preparation.
  • the doped O atoms combine with Sb atoms to form disordered oxides, which are distributed around the grain boundaries of the phase change material to separate the phase change material into A small "phase change island", forming a skin (or “shell") is a high-resistance adiabatic oxide, and the inner layer (or “core” part) is a Sb 2 Te 3 phase change material.
  • “Shell-core” structure Preferably, the thickness of the "shell-core” structure O-Sb 2 Te 3 phase change memory thin film material is 50 nm to 300 nm.
  • the thickness of the "shell-core” structure O-Sb 2 Te 3 phase change memory thin film material measured by the real-time change curve of in-situ thin film square resistance versus annealing temperature is about 50 nm.
  • the thickness of the "shell-core” structure O-Sb 2 Te 3 phase change memory thin film material used for STEM and EDX microscopic analysis and X-ray photoelectron spectroscopy characterization is about 100 nm, and annealed at 300 ° C for 10 min to obtain a crystalline sample, wherein, The surface of the "shell-core” structure O-Sb 2 Te 3 phase-change memory film material used for XPS characterization was treated with Ar + to remove the surface contaminating oxide layer.
  • the high resistance state of the "shell-core” structure O-Sb 2 Te 3 phase change memory film material is 10 4 times that of the low resistance state.
  • the phase transition temperature of the "shell-core” O-Sb 2 Te 3 phase-change memory film material is greatly increased.
  • the skin (“shell”) is an adiabatic and high-resistance oxide
  • the inner layer (“core”) is a Sb 2 Te 3 phase change material.
  • the composition of each part is verified by EDX characterization.
  • the XPS characterization of the "shell-core” structure O-Sb 2 Te 3 phase-change memory film material shows that the doped O atoms mainly form bonds with Sb atoms.
  • First-principles calculations observed the formation of the O-Sb structure in the "shell-core” structured O-Sb 2 Te 3 phase-change memory material, and showed a wrapping trend with increasing O atomic concentration.
  • the physical model was established by simplifying the three-dimensional wrapping structure of the "shell-core” structure. It was observed through simulation calculations that the outer "shell” structure could inhibit the movement of atoms in the inner "core”. At the same time, the electrothermal simulation observed that the "shell-core” structure can effectively block the thermal diffusion during the phase transition.
  • the phase-change memory cell sequentially includes a bottom electrode, an isolation layer, a film layer of a phase-change memory material, and a top electrode.
  • the film layer of the phase change memory material is made of the "shell-core" structure O-Sb 2 Te 3 phase change material regulated by the amorphous structure described in the present invention, which is filled with a diameter of 250 nm and a depth of 100 nm. in the small hole.
  • the bottom electrode material is TiN.
  • the material of the isolation layer is SiO 2 .
  • the material of the top electrode is metal Pt.
  • the invention provides a preparation method of a "shell-core" structure O-Sb 2 Te 3 phase change material for phase change memory, the preparation method includes magnetron sputtering, chemical vapor deposition, atomic layer deposition, electroplating method, electron beam evaporation method, etc.
  • the magnetron sputtering method is the most flexible in preparation. It can be co-sputtered with Sb target and Te target in an oxygen atmosphere, or Sb 2 Te 3 target can be used for sputtering in an oxygen environment, or O-Sb 2 Te 3 alloy target sputtering.
  • These methods can all prepare the "shell-core" structure O-Sb 2 Te 3 phase change memory material of the present invention according to the formula of the formula.
  • the "shell-core” structure O-Sb 2 Te 3 phase-change memory material and device preparation process of the present invention are mature, and are easy to achieve compatibility with the existing microelectronic process technology.
  • the unique "shell-core” structure formed reduces the size of the phase transition region, inhibits atomic migration and blocks thermal diffusion.
  • the "shell-core” structure O-Sb 2 Te 3 phase change memory device of the present invention reduces the DC set operating current by an order of magnitude, reduces the reset power consumption by more than 95%, and reduces the resistance value by more than 95%. Drift is significantly reduced and cycle characteristics are greatly improved.
  • the O-Sb 2 Te 3 phase change memory film material is prepared by magnetron sputtering method; high-purity argon gas is used as the sputtering gas during preparation, and a small amount of oxygen is introduced to provide an oxygen atmosphere.
  • the sputtering pressure is 0.5Pa, Sb
  • the 2 Te 3 target uses an AC power supply with a power supply of 60W.
  • the specific preparation process includes the following steps:
  • acetone-treated substrate was vibrated with ultrasonic waves of 40W power for 10 minutes in an ethanol solution, rinsed with deionized water, and dried with high-purity N2 gas on the surface and back to obtain a substrate to be sputtered.
  • the substrate After the pre-sputtering is completed, rotate the substrate to be sputtered above the Sb 2 Te 3 target, open the baffle, and sputter O-Sb 2 Te 3 phase change memory film materials with different thicknesses according to the predetermined sputtering time .
  • the sputtering time is 3 min
  • the thickness of the prepared film is about 50 nm, which is used to measure the real-time change curve of the square resistance of the in-situ film with the annealing temperature.
  • the sputtering time is 6 min
  • the thickness of the prepared film is about 100 nm, which is used for XRD characterization.
  • the pure Sb 2 Te 3 phase - change memory film material was prepared by magnetron sputtering method ; high-purity argon gas was used as sputtering gas during preparation, and the sputtering pressure was 0.5Pa. 60W.
  • the specific preparation process includes the following steps:
  • the SiO 2 /Si(100) substrate was placed in an acetone solution with ultrasonic vibration of 40 W for 10 minutes, and rinsed with deionized water.
  • the acetone-treated substrate was vibrated with ultrasonic waves of 40W in an ethanol solution for 10 minutes, rinsed with deionized water, and the surface and back of the substrate were dried with high-purity N 2 gas to obtain a substrate to be sputtered.
  • the substrate After the pre-sputtering is completed, rotate the substrate to be sputtered above the Sb 2 Te 3 target, open the baffle, and sputter Sb 2 Te 3 phase-change memory film materials with different thicknesses according to the predetermined sputtering time.
  • the sputtering time is 3 min
  • the thickness of the prepared film is about 50 nm, which is used to measure the real-time change curve of the square resistance of the in-situ film with the annealing temperature.
  • the sputtering time is 6 min
  • the thickness of the prepared film is about 100 nm, which is used for XRD characterization.
  • Fig. 1 shows the in-situ square resistance and annealing temperature of the O-Sb 2 Te 3 phase change memory material film and pure Sb 2 Te 3 phase change memory material film formed with a "shell-core” structure after grain boundary engineering control according to an embodiment of the present invention
  • the real-time relationship curve of where the heating rate is 6°C/min, ST stands for pure Sb 2 Te 3 phase change memory material, and OST stands for O-Sb 2 Te 3 phase change memory material with "shell-core” structure.
  • the comparison shows that the formation of the "shell-core” structure increases the resistance value of the amorphous state of the material, and the window between the resistance value of the amorphous state and the crystalline state increases, the phase transition temperature is greatly increased to 250 °C, and the amorphous state of the material increases. Stability is significantly improved.
  • Figure 2 shows the phase transition between the O-Sb 2 Te 3 phase change memory material film (abbreviated as OST in the figure) and pure Sb 2 Te 3 (abbreviated as ST in the figure) after the control of grain boundary engineering to form a "shell-core" structure Comparison of XRD characterization of memory material thin films.
  • the square corresponds to the diffraction peak of the Sb-Te material
  • the inverted triangle corresponds to the diffraction peak of the Sb-O material.
  • the "shell-core" structure Sb 2 Te 3 phase change memory material film has no other diffraction peaks except the base peak, and is in an amorphous state.
  • the pure ST film at annealing temperature of 200 °C showed an obvious polycrystalline diffraction peak pattern, indicating that the formation of the "shell-core” structure improved the amorphous stability of the material system, which was consistent with the in-situ RT curve of the film.
  • the diffraction peak of weaker Sb-O material appeared in the spectrum of the "shell-core” structure Sb 2 Te 3 phase change memory material film at 300 °C annealing temperature, which confirmed the existence of the shell Sb-O oxide.
  • the O-Sb 2 Te 3 phase-change memory thin film material was prepared by magnetron sputtering. During preparation, high-purity argon gas was introduced as sputtering gas, and a small amount of oxygen was introduced to provide an oxygen atmosphere. The sputtering pressure was 0.5Pa. The Sb 2 Te 3 target was powered by AC power with a power of 60W.
  • the specific preparation process includes the following steps:
  • acetone-treated substrate was vibrated with ultrasonic waves of 40W power for 10 minutes in an ethanol solution, rinsed with deionized water, and dried with high-purity N2 gas on the surface and back to obtain a substrate to be sputtered.
  • the substrate After the pre-sputtering is completed, rotate the substrate to be sputtered above the Sb 2 Te 3 target, open the baffle, and sputter O-Sb 2 Te 3 phase change memory film materials with different thicknesses according to the predetermined sputtering time .
  • the sputtering time is 6 min
  • the thickness of the prepared film is about 100 nm, which is used for TEM, HRTEM, EDX microscopic analysis and X-ray photoelectron spectroscopy characterization.
  • the O-Sb 2 Te phase change memory thin film material in this example is tested.
  • FIG. 3 is an in plane-TEM microscopic analysis diagram of an O-Sb 2 Te 3 phase-change memory material film with a "shell-core" structure after grain boundary engineering regulation according to an embodiment of the present invention.
  • the as-deposited samples were annealed at 300 °C for 10 min. It can be found that the sample microscopically presents a uniform heterostructure.
  • FIG. 4 is an HRTEM microscopic analysis diagram of an O-Sb 2 Te 3 phase change memory material film with a "shell-core” structure in this embodiment, wherein the as-deposited sample is annealed at 300° C. for 10 min.
  • the longer solid arrow shows the crystalline part of the "core” structure
  • the shorter dashed arrow shows the amorphous part of the "shell” structure
  • the rectangular box in the right figure represents the Fourier of the corresponding part.
  • Leaf transition diagram It can be found from the figure that the grains are wrapped by randomly distributed amorphous structures, which are separated into nano-sized "crystal islands", forming "shells” which are amorphous substances with low thermal conductivity and low electrical conductivity, and the inner "core” is crystalline. shell-core” structure.
  • Fig. 5 is the EDX element distribution diagram of the O-Sb 2 Te 3 phase-change memory material film with "shell-core" structure in this embodiment
  • Fig. 5(a) is the bright field image of the sampling area
  • Fig. 5(b) is the Sb element distribution image
  • Fig. 5(c) is the Te element distribution image. It can be seen from the figure that the distribution of Sb element and Te element are not completely coincident, and there is a wrapping phenomenon.
  • Figure 6 is the X-ray photoelectron spectrum of the O-Sb 2 Te 3 phase-change memory material film with the "shell-core" structure in this example, wherein the as-deposited sample was annealed at 300 °C for 10 min, and the surface was subjected to Ar + Treatment to remove the surface oxidation contamination layer
  • Figure 6 (a) is the energy spectrum of Sb element
  • Figure 6 (b) is the energy spectrum of Te element
  • the diffraction peaks in the figure correspond to the corresponding chemical bonds.
  • the results of element distribution characterization show that Sb element is not only distributed in the Te element distribution area to form Sb-Te compound, but also distributed in the periphery of Te element.
  • the Materials Studio software is used to model the Sb 2 Te 3 phase-change memory thin film materials with O doping concentrations of 5%, 10%, and 20%, respectively, and the three models are randomized by first-principles.
  • the simulation of the melting and quenching process obtains the amorphous model of the OST phase change memory thin film material with O doping concentrations of 5%, 10% and 20%, respectively.
  • the results are shown in Figure 7.
  • the simplified "shell-core” structure O-Sb 2 Te 3 and pure Sb 2 Te 3 were modeled by Materials Studio software, and the "shell-core” structure O-Sb 2 Te 3 at different temperatures was simulated by first-principles The atomic motion of the model and pure Sb 2 Te 3 as well as the motion of atoms in the middle region and the atoms near the shell region in the "shell-core” structure O-Sb 2 Te 3 model at the same temperature, through data processing to form an intuitive image, Fig.
  • curve 8 is the effect of the simplified "shell-core” structure on the motion of atoms in the inner layer (inside the "core") at different temperatures calculated by using first principles in the present invention, wherein curve 1 corresponds to the conventional phase transition of pure Sb 2 Te 3
  • curve 2 corresponds to the simulation results of the atomic motion of pure Sb 2 Te 3 conventional phase change material (PCM) at low temperature (300 K)
  • curve 3 corresponds to O-
  • curve 4 corresponds to the "shell-core” structure represented by O-Sb 2 Te 3 "Simulation results of atomic motion in structural phase change material (cs-PCM) at low temperature (300K).
  • Figure 9 is the effect of the simplified "shell-core” structure on the atomic motion in different regions of the inner layer (inside the "core") calculated by using first principles in the embodiment of the present invention, and curves 1 and 3 correspond to the inner layer "core”
  • curves 1 and 3 correspond to the inner layer "core”
  • curve 2 corresponds to the simulation result of the atomic motion in the middle region of the inner "core” phase change material.
  • the inset is a simplified three-dimensional wrapped structure model of "shell-core” structure O-Sb 2 Te 3 , region 1 and region 3 correspond to the inner layer “core” phase change material close to the "shell” layer region atoms, region 2 corresponds to the inner layer The layer “core” phase change material with atoms in the middle region.
  • Fig. 7 is an amorphous model of the OST phase change memory film material with O doping concentrations of 5%, 10% and 20% in the embodiment of the present invention. It can be found that the doped O atoms tend to combine with Sb atoms to form bonds . With the increase of O atom concentration, the O-Sb bound species increased and appeared randomly at the unit cell boundary. When the concentration of O atoms is 20%, the Sb-O bonding substances at the boundary are connected to form a wrapping structure for the inner layer of Sb-Te substances, that is, the "shell” is the Sb-O oxide with low thermal conductivity and low conductivity, and the inner layer “core” " is the "shell-core” structure of traditional Sb-Te phase change materials.
  • the three-dimensional wrapping structure of the "shell-core” structure O-Sb 2 Te 3 is simplified, and the inset in Figure 9 is obtained. Studying the motion of atoms in the confined direction (Z direction) can reflect and infer the confinement pair in the three-dimensional direction. Influence of "nuclear" Sb-Te atomic motion.
  • Figure 8 is a comparison of the Z-direction atomic motions of the "shell-core" O-Sb 2 Te 3 model and pure Sb 2 Te 3 at low and high temperatures, respectively.
  • Curve 1 corresponds to the simulation results of atomic motion of pure Sb 2 Te 3 conventional phase change material (PCM) at high temperature (550K)
  • curve 2 corresponds to pure Sb 2 Te 3 conventional phase change material (PCM) at low temperature (300 K)
  • Simulation results of atomic motion curve 3 corresponds to the simulation results of atomic motion of the "shell-core” phase change material (cs-PCM) represented by O-Sb 2 Te 3 at high temperature (550K)
  • curve 4 corresponds to O- Simulation results of the atomic motion of the "shell-core” phase change material (cs-PCM) represented by Sb 2 Te 3 at low temperature (300K).
  • FIG. 9 is a comparison diagram of the movement of atoms in the middle region of the inner "core” phase change material and atoms in the region close to the shell layer at the same temperature, in which curve 1 and curve 3 correspond to the movement of atoms in the region near the shell layer of the inner "core” phase change material The simulation results of the situation, curve 2 corresponds to the simulation results of the atomic motion in the middle region of the inner "core” phase change material.
  • the motion of atoms in the middle region is more violent than that in the region near the shell.
  • the "shell-core” structure can effectively suppress the motion of atoms close to the oxide interface, and has limited influence on the motion of atoms in the central region of the inner "core”. That is, the "shell-core” structure can inhibit the long-range migration of material atoms in the inner "core”, but does not affect the mutual movement of the material atoms in the inner "core” in the inner region of the shell.
  • Figure 10 is a thermal simulation diagram of the simplified "shell-core” structure obtained by using COMSOL software. It can be found that when the current is operated, the heat is mainly concentrated in the Sb-Te phase change material region of the core, which illustrates the shell layer of the "shell-core” structure. It has obvious blocking effect on thermal diffusion, and effectively improves the utilization efficiency of electricity and heat in the phase change process.
  • the O-Sb 2 Te 3 phase-change memory thin film material with the "shell-core” structure is used as the phase change layer material to prepare the memory device, wherein the O-Sb 2 Te 3 phase change layer with the "shell-core” structure adopts magnetic Controlled sputtering method.
  • high-purity argon gas was introduced as sputtering gas, and a small amount of oxygen was introduced to provide an oxygen atmosphere.
  • the sputtering pressure was 0.5Pa.
  • the Sb 2 Te 3 target was powered by AC power with a power of 60W.
  • the specific preparation process includes the following steps:
  • acetone-treated substrate was vibrated with ultrasonic waves of 40W power for 10 minutes in an ethanol solution, rinsed with deionized water, and dried with high-purity N2 gas on the surface and back to obtain a substrate to be sputtered.
  • the 100nm TiN lower electrode was prepared by DC power sputtering.
  • step 3 Use chemical vapor deposition to deposit a 100 nm SiO2 insulating layer on the TiN lower electrode in step 2.
  • a through hole with a depth of 100 nm and a diameter of 250 nm is formed in the SiO 2 insulating layer in step 3 by processes such as electron beam lithography and etching.
  • the memory array is formed by a photolithography process.
  • step 6 Fill the through hole formed in step 4 with O-Sb 2 Te 3 phase-change memory film material using the AC power sputtering method
  • the substrate After the pre-sputtering is completed, rotate the substrate to be sputtered above the Sb 2 Te 3 target, open the baffle, and sputter O-Sb 2 Te 3 phase change memory film materials with different thicknesses according to the predetermined sputtering time .
  • the sputtering time is 6 min
  • the thickness of the prepared phase change layer is about 100 nm.
  • the 100nm Pt upper electrode was prepared by DC power sputtering method, and a complete phase change memory device array based on the "shell-core" structure O-Sb 2 Te 3 phase change layer was obtained.
  • pure Sb 2 Te 3 memory device is prepared by using pure Sb 2 Te 3 phase-change memory thin film material as the phase change layer.
  • acetone-treated substrate was vibrated with ultrasonic waves of 40W power for 10 minutes in an ethanol solution, rinsed with deionized water, and dried with high-purity N2 gas on the surface and back to obtain a substrate to be sputtered.
  • the 100nm TiN lower electrode was prepared by DC power sputtering.
  • step 3 Use chemical vapor deposition to deposit a 100 nm SiO2 insulating layer on the TiN lower electrode in step 2.
  • a through hole with a depth of 100 nm and a diameter of 250 nm is formed in the SiO 2 insulating layer in step 3 by processes such as electron beam lithography.
  • the memory array is formed by a photolithography process.
  • the 100nm Pt upper electrode was prepared by DC power sputtering to obtain a complete phase change memory device array based on the Sb 2 Te 3 phase change layer.
  • FIG. 11 is a schematic diagram of the phase change memory cell structure using the “shell-core” structure O-Sb 2 Te 3 phase change memory material as the functional layer in the present embodiment.
  • 1 is the top electrode
  • 2 is a Phase change material of "shell-core” structure
  • 3 is the thermally insulating SiO2 layer
  • 4 is the bottom electrode.
  • FIGS. 12 to 15 are comparison diagrams of the electrical performance of the phase change memory cell with the O-Sb 2 Te 3 phase change memory material of the "shell-core” structure as the functional layer and the undoped Sb 2 Te 3 phase change memory cell.
  • Figure 12 is the device IV performance comparison chart
  • Figure 13 is the device RESET performance comparison chart
  • Figure 14 is the device drift resistance performance comparison chart
  • Figure 15 is the "shell-core" structure O-Sb 2 Te 3 device cycle performance chart.
  • Figure 12 is a comparison diagram of the IV characteristics of the devices. Obviously, both have undergone phase transition, and the operating threshold currents I th are 1.64 ⁇ A and 12 ⁇ A, respectively. It can be seen that the “shell-core” structure O-Sb 2 Te 3 phase change storage Phase-change memory cells with thin-film materials as functional layers reduce operating current by an order of magnitude.
  • Figure 13 is the RV test chart of the device, which reflects the RESET performance of the device.
  • the phase change memory cell with the "shell-core" structure O-Sb 2 Te 3 phase change memory film material as the functional layer can be operated with a pulse width of 10ns. Successful reset.
  • the high and low resistance ratios of the two devices are both greater than 10 2 , which is beneficial to improve the anti-interference ability of the device. Comparing the two devices under the same operating pulse width, as shown by the dotted line in Figure 13, the traditional Sb 2 Te 3 phase transition is used.
  • phase change memory cell with the storage film material as the functional layer can achieve a reset voltage of 2.8V at a pulse width of 10ns, compared with the phase change memory cell with the "shell-core" structure O-Sb 2 Te 3 phase change memory film material as the functional layer. There is a 3 to 4 times difference in the 0.95V of the cell.
  • phase change memory unit with the "shell-core” structure O-Sb 2 Te 3 phase change memory thin film material as the functional layer has low power consumption, which can solve the heat dissipation problem in the compact three-dimensional stacked array, and provide a good solution for three-dimensional storage. a possible material system.
  • Figure 14 is a measurement and comparison graph of device resistance drift. Resistance drift can be described by the power equation (1) with time:
  • R is the test resistance
  • R0 and ⁇ 0 are constants that depend on the initial state of the material.
  • the exponential factor ⁇ is the resistance drift coefficient, which represents the resistance drift speed. Higher values of ⁇ indicate faster drift.
  • the drift exponent ⁇ is independent of temperature and increases only with the initial resistance value. As shown in Fig.
  • the drift index ⁇ 0.005 of the phase change memory cell with the "shell-core” structure O-Sb 2 Te 3 phase change memory film material as the functional layer, compared with the traditional Sb 2 Te 3 phase change memory cell
  • Figure 15 is the test result of the cycle characteristics of the phase change memory cell with the "shell-core” structure O-Sb 2 Te 3 phase change memory film material as the functional layer.
  • the identification standard is Repeatedly applying the set pulse (600ns on the rising edge, 1us on the falling edge, 600 ns on the falling edge; 2.5V) and reset pulse (8ns on the rising edge, 50ns on the falling edge, 8ns on the falling edge; 2.8V), the cycle times of the device can reach the order of 10 8 .
  • the O atoms in the sputtering atmosphere It combines with Sb atoms to form amorphous oxides, which are distributed around the SbTe grains of the phase change material to form grain boundaries, which separate the phase change material Sb 2 Te 3 into smaller "phase change islands", in which the skin "
  • the "shell” layer is an oxide with low thermal conductivity and low electrical conductivity
  • the inner layer “core” is the "shell-core” structure of the phase change material Sb 2 Te 3 .
  • the local disorder increases the resistance value of the amorphous state of the phase change material and improves the amorphous stability of the Sb 2 Te 3 material.
  • the existence of the "shell-core” heterostructure limits the long-range migration of atoms in the "core” in the “shell-core” structure due to external electrical operations, thereby improving the overall cycling characteristics and resistance of the memory device. Value drift characteristics.
  • the low thermal conductivity of the "shell” oxide material also has a significant effect on reducing the RESET power consumption of the device.

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Abstract

本发明提供一种基于氧掺杂的Sb 2Te 3相变材料、相变存储器及制备方法，属于微纳电子技术领域，其采用简单的掺杂工艺实现对Sb 2Te 3的微观结构及器件特性进行全面调控的方法及其应用，在Sb 2Te 3相变层中形成"壳-核"微观结构，其中，非晶低热导率的"壳层"晶界起到类似于异质界面的作用，对发生相变的晶粒也即"核"部进行物理隔断，并起到热阻作用，改善电热利用效率，降低RESET功耗。其中，非晶壳层晶界阻隔Sb 2Te 3晶粒在相变过程中的原子迁移，提高器件的可靠性及循环擦写次数。同时，掺杂元素与核部相变材料元素成键，可有效提高相变材料的非晶稳定性，以上方面综合作用，从而全方位地改善器件的综合性能。

Description

基于氧掺杂的Sb 2Te 3相变材料、相变存储器及制备方法 【技术领域】
本发明属于微纳电子技术领域，更具体地，涉及一种基于氧掺杂Sb 2Te 3的“壳-核”结构相变材料及相变存储器。
【背景技术】
在当今电子技术以及信息产业飞速发展的时代，随着数据的爆炸式增长，人们对非易失性存储器的性能要求也越来越高。相变存储器(PCM)凭借其集成度高、响应速度快、循环寿命长和低功耗等优点被国际半导体工业协会认为最有可能取代闪存和动态存储器而成为未来主流存储器。
相变存储器的基本原理是用电脉冲信号作用于存储单元上，使相变材料在非晶态与晶态之间发生可逆相变来实现“0”和“1”的存储。在单元上施加一个窄脉宽、高幅值的电脉冲对其进行RESET操作，晶态相变存储材料熔化快冷转变为非晶无序态，从而实现从低阻态“0”到高阻态“1”的快速阻变。反之，在相变单元上施加一个宽脉宽、低幅值的电脉冲对其进行SET操作，非晶态相变存储材料经历一个类退火过程结晶，返回低阻态，实现“1”擦写回“0”。
相变材料性能的优化是提升相变存储器性能的关键，而相变材料的微观结构决定着其宏观特性。研究发现，相变存储器的可靠性和循环擦写特性主要与相变材料在反复升温降温过程中的内部原子迁移机制有关。相变存储器的功耗不仅与相变材料的熔点有关，还与器件内部涉及产热及散热过程的电热利用效率密切相关。相变存储器的数据保持时间主要由相变层材料的非晶稳定性决定。
Sb 2Te 3是近年来受到广泛关注的相变材料，其晶化温度低且具有生长主导型晶化过程，晶化速度快，因此，基于Sb 2Te 3的相变存储器件具有SET速度快的特点。但是，其非晶稳定性较差，器件的数据保持时间需要进一步提升。
目前，对Sb 2Te 3相变材料的主要性能优化手段是掺杂。通过在Sb 2Te 3相变材料中引入其他元素形成不同的微观结构，改变相变材料的局域特性从而改善 相变存储器件的性能。已有的Sb 2Te 3掺杂对其性能的改善机制主要是，掺杂元素(如Ti、Sc、Y等)在Sb 2Te 3中形成一定的局域晶体结构，如八面体结构等，局域调控Sb 2Te 3的晶化过程，提高Sb 2Te 3材料的非晶稳定性及器件的数据保持时间。掺杂工艺简单，但难以实现对材料微观结构的精确调控，在器件高阻稳定性得到改善的同时会一定程度上牺牲晶化速度，很难实现器件性能的全面提升。另外，在Sb 2Te 3中插入异质层或不同相变材料形成类超晶格结构，通过对异质界面或超晶格界面的调控也可实现相变材料及器件性能的优化。然而，异质结构及类超晶格结构的制备工艺较复杂，另一种材料的选择条件较严苛，且器件特性对异质或类超晶格/Sb 2Te 3界面的结构特性及工艺参数尤其敏感，不利于大规模商业化生产。
因此，需要开发一种新型的改性Sb 2Te 3的方法，以实现对其微观结构的精确、灵敏、简单地调控，从而使其能作为商业化的相变存储材料应用。
【发明内容】
针对现有技术的缺陷，本发明的目的在于，提供一种基于氧掺杂的Sb 2Te 3相变材料、相变存储器及制备方法，通过氧掺杂，在Sb 2Te 3相变层中形成“壳-核”(Core-shell，cs)微观结构，壳层起到热阻作用，改善电热利用效率，降低RESET功耗；壳层还能阻止核内元素的原子迁移，提高器件的可靠性；此外，掺杂元素与核部相变材料元素成键，可有效提高核部相变材料的非晶稳定性，最终全方位地实现改善器件的综合性能。
按照本发明一个方面，提供一种基于氧掺杂的Sb 2Te 3相变材料，其化学式为：O x(Sb 2Te 3) 1-x，其中，O为氧元素，x代表氧元素在整个化学组成中的原子百分比，0<x<40％。
进一步的，氧原子与Sb 2Te 3中的元素原子结合形成无序氧化物，包裹在Sb 2Te 3周围，将Sb 2Te 3分隔成多个岛状，形成壳核结构，其中，壳部是氧原子与Sb 2Te 3中的元素原子结合形成无序氧化物，核部为Sb 2Te 3晶粒。
进一步的，部分氧元素进入Sb 2Te 3晶粒中，用于提高Sb 2Te 3的非晶稳定性。
进一步的，O x(Sb 2Te 3) 1-x材料中，通过控制O的掺入量来控制所述Sb 2Te 3 中非晶氧化物晶界的性质从而调控O-Sb 2Te 3相变存储材料的电化学性质，电化学性质包括高低阻态电阻、晶化温度，O-Sb 2Te 3相变存储材料是指O x(Sb 2Te 3) 1-x材料，其中，0<x<40％。
进一步的，氧原子与Sb 2Te 3中Sb原子结合形成无序氧化物，并集中在Sb 2Te 3晶粒周围形成非晶晶界。
进一步的，无序氧化物为氧原子与Sb 2Te 3中Sb原子结合形成的无序氧化物具有熔点较高，热导率较低底，性能稳定的特点，所述熔点高是指大于Sb 2Te 3的熔点(890K)；所述热导率较低是指热导率接近10 -3量级，几乎隔热；所述性能稳定是指结构稳定，不易分解不易熔化。
进一步的，氧化物晶界在相变过程中起到提高电热效率、阻止原子迁移的作用，同时用于提高相变层非晶状态的电阻值，改善Sb 2Te 3材料的非晶稳定性。
在以上发明构思中，采用简单的掺杂工艺即能实现对Sb 2Te 3的微观结构及器件特性进行全面调控的方法及其应用，在Sb 2Te 3相变层中形成“壳-核”微观结构，其中非晶低热导率的“壳层”晶界起到类似于异质界面的作用，对发生相变的晶粒(即为“核”部)进行物理隔断，并起到热阻作用，改善电热利用效率，降低RESET功耗，此外，非晶壳层晶界阻隔Sb 2Te 3晶粒在相变过程中的原子迁移，提高器件的可靠性及循环擦写次数；同时，掺杂元素与相变材料元素成键，可有效提高相变材料的非晶稳定性；从而全方位地改善器件的综合性能。
按照本发明的另一个方面，还提供一种基于氧掺杂的Sb 2Te 3相变材料的相变存储器，其包括底电极、隔离层、相变存储材料薄膜层和顶电极，其中，所述相变存储材料薄膜层材质为如上所述的基于氧掺杂的Sb 2Te 3相变材料。
按照本发明的第三个方面，还提供一种如上所述方法，采用磁控溅射法、化学气相沉积法、原子层沉积法、电镀法或电子束蒸发法制备。
进一步的，具体的磁控溅射方法为以下三种中的任意一种：
(1)Sb靶和Te靶在有氧环境下共溅射；
(2)Sb 2Te 3靶在有氧环境下溅射；
(3)O掺杂后的Sb 2Te 3合金靶溅射。
总体而言，通过本发明所构思的以上技术方案与现有技术相比，具有以下有益效果：
与现有技术中未经氧化物晶界非晶组织调控的Sb 2Te 3相变存储材料相比，本发明的“壳-核”结构O-Sb 2Te 3相变材料中，O原子与Sb原子结合形成无序氧化物，分布在相变材料Sb 2Te 3晶粒周围形成非晶氧化物晶界，将相变材料Sb 2Te 3分隔成一个个体积较小的“相变岛”，形成表皮是绝热高阻的氧化物，里层是Sb 2Te 3的“壳-核”结构。局部无序态以及相变核区域的缩小提高了相变层非晶状态的电阻值，改善了Sb 2Te 3材料的非晶稳定性。另外，“壳-核”异质结构的存在在三维结构上限制了“壳-核”结构里层原子由于外加电操作引起的长程迁移，从而提高存储器件的整体循环特性，并有效抑制了器件的阻值漂移，改善了器件阻值稳定性。此外，壳层材料的绝热特性及壳层对相变晶粒的包裹结构，使得相变过程中热量能更集中在晶粒内部，减少热量的散失，从而提高了相变过程的电热效率，有效减小器件的reset功耗。
【附图说明】
图1是本发明实施例经过晶界工程调控过后形成“壳-核”结构的O-Sb 2Te 3相变存储材料薄膜与纯Sb 2Te 3相变存储材料薄膜原位方阻与退火温度的实时关系曲线，其中升温速率为12℃/min，其中，ST代表纯Sb 2Te 3相变存储材料，OST代表“壳-核”结构的O-Sb 2Te 3相变存储材料。
图2是本发明实施例中经过晶界工程调控过后形成“壳-核”结构的O-Sb 2Te 3相变存储材料薄膜与纯Sb 2Te 3相变存储材料薄膜XRD表征对比图，其中，每条曲线处对应的温度表示相应薄膜的退火处理温度，其中，ST代表纯Sb 2Te 3相变存储材料，OST代表“壳-核”结构的O-Sb 2Te 3相变存储材料。
图3是经过晶界工程调控过后形成“壳-核”结构的O-Sb 2Te 3相变存储材料薄膜的in plane-TEM微观分析图，其中，晶态样品在300℃下退火10min。由图可知，样品微观呈现均匀的异质结构。
图4是经过晶界工程调控过后形成“壳-核”结构的O-Sb 2Te 3相变存储材料薄 膜的HRTEM微观分析图，其中，晶态样品在300℃下退火10min。图中，较长的实线箭头所示是“核”结构晶体部分，较短的虚线箭头所示为“壳”结构非晶体部分，右侧图中的矩形方框表示为对应部分的傅里叶转换图。由图可知，样品中晶粒被随机分布的非晶组织包裹。
图5是经过晶界工程调控过后形成“壳-核”结构的O-Sb 2Te 3相变存储材料薄膜的EDX元素分布图，图5(a)为取样区域明场图象，图5(b)为Sb元素分布图象，图5(c)为Te元素分布图象。由图可知，Sb元素和Te元素分布不完全重合，有包裹现象。
图6是经过晶界工程调控过后形成“壳-核”结构的O-Sb 2Te 3相变存储材料薄膜的X射线光电子能谱图，其中，晶态样品在300℃下退火10min，并且表面经过Ar +处理以去除表面氧化污染层，图6(a)为Sb元素能谱图，图6(b)为Te元素能谱图，图中衍射峰对应相应的化学键。
图7是本发明中利用第一性原理计算得到的O原子含量依次为5％、10％、20％的非晶态O-Sb-Te相变材料的超胞模型，图7(a)表示掺杂5％的非晶态超胞模型，图7(b)表示掺杂10％的非晶态超胞模型，图7(c)表示掺杂20％的非晶态超胞模型。由图可知，O原子倾向于和Sb原子结合成键。随着O原子浓度的增加，O-Sb结合物质增加，并形成对Sb2Te3晶粒的包裹结构。
图8是本发明中利用第一性原理计算得到的不同温度下简化“壳-核”结构对里层(“核”内部)原子运动的影响，其中，曲线line1对应纯Sb 2Te 3常规相变材料(PCM)在高温(550K)下的原子运动情况模拟结果，曲线2对应纯Sb 2Te 3常规相变材料(PCM)在低温(300K)下的原子运动情况模拟结果，曲线3对应O-Sb 2Te 3所代表的“壳-核”结构相变材料(cs-PCM)在高温(550K)下的原子运动情况模拟结果，曲线4对应O-Sb 2Te 3所代表的“壳-核”结构相变材料(cs-PCM)在低温(300K)下的原子运动情况模拟结果。由图可知，“壳”层可以有效抑制里层“核”内原子的运动，且对温度的敏感程度明显降低。
图9是本发明实施例中利用第一性原理计算得到的简化“壳-核”结构对里层(“核”内部)不同区域原子运动的影响，曲线1和曲线3对应里层“核”相变材 料靠近壳层区域原子运动情况模拟结果，曲线2对应里层“核”相变材料中间区域原子运动情况模拟结果。其中，插图为简化后的“壳-核”结构O-Sb 2Te 3三维包裹结构模型，区域1和区域3对应里层“核”相变材料靠近“壳”层区域原子，区域2对应里层“核”相变材料中间区域原子。由图可知，中间区域原子运动比靠近壳层区域原子更剧烈。
图10是本发明中利用COMSOL仿真得到的简化“壳-核”结构对热扩散的阻挡作用示意图。由图可知，热量主要集中于里层Sb-Te相变材料区域。
图11是以经过晶界工程调控过后形成“壳-核”结构的O-Sb 2Te 3相变存储材料为功能层的相变存储单元结构的示意图。其中，1为顶电极，2为具有“壳-核”结构的相变材料，3为绝热绝缘SiO 2层，4为底电极。
图12至图15是以经过晶界工程调控过后形成“壳-核”结构的O-Sb 2Te 3相变存储材料为功能层的相变存储单元与未掺杂Sb 2Te 3相变存储单元的电学性能测试对比图，图12是器件I-V性能对比图，图13是器件RESET性能对比图，图14是器件阻漂性能对比图，图15是形成“壳-核”结构的O-Sb 2Te 3相变存储材料为功能层的相变存储器件(cs-OST)循环性能图。
【具体实施方式】
为了使本发明的目的、技术方案及优点更加清楚明白，以下结合附图及实施例，对本发明进行进一步详细说明。应当理解，此处所描述的具体实施例仅仅用以解释本发明，并不用于限定本发明。
本发明提供了一种采用简单的掺杂工艺即可实现对Sb 2Te 3的微观结构及器件特性进行全面调控的材料及其存储器，涉及采用氧掺杂工艺，利用非晶氧化物组织对Sb 2Te 3相变材料进行调控，形成独特的“壳-核”结构，缩小其相变区域并阻挡原子长程迁移以及热扩散，从而改进Sb 2Te 3相变存储器性能。具体的，在Sb 2Te 3相变层中形成“壳-核”微观结构，其中非晶低热导率的“壳层”晶界起到类似于异质界面的作用，对发生相变的晶粒(也称为“核”)进行物理隔断，并起到热阻作用，改善电热利用效率，降低RESET功耗；非晶壳层晶界阻隔Sb 2Te 3晶粒在相变过程中的原子迁移，提高器件的可靠性及循环擦写次数；同时，掺 杂元素与相变材料元素成键，可有效提高相变材料的非晶稳定性，以上综合作用，从而能全方位地改善器件的综合性能。
更具体的，本发明的通过非晶组织调控形成的“壳-核”结构相变存储材料(csPCM)中，将O引入Sb 2Te 3相变存储材料中得到的，其化学组成通式为O x(Sb 2Te 3) 1-x，其中x代表O元素的原子百分比，较佳的x取值范围为0<x<40％。通过调整制备时通入氧气(O 2)的流量，可以调控x的取值。所述的“壳-核”结构O-Sb 2Te 3相变存储材料中，掺入的O原子与Sb原子结合形成无序氧化物，分布在相变材料晶界周围将相变材料分隔成一个个体积较小的“相变岛”，形成表皮(或称为“壳”)是绝热高阻的氧化物，里层(或称为“核”部)是Sb 2Te 3相变材料的“壳-核”结构。优选的，“壳-核”结构O-Sb 2Te 3相变存储薄膜材料厚度为50nm～300nm。
本发明中，采用原位薄膜方阻随退火温度实时变化曲线测量的所述“壳-核”结构O-Sb 2Te 3相变存储薄膜材料的厚度为50nm左右。用于STEM和EDX微观分析以及X射线光电子能谱表征的所述“壳-核”结构O-Sb 2Te 3相变存储薄膜材料厚度大约100nm，在300℃退火10min得到晶态样品，其中，用于XPS表征的所述“壳-核”结构O-Sb 2Te 3相变存储薄膜材料表面经Ar +处理以去除表面污染氧化层。所述“壳-核”结构O-Sb 2Te 3相变存储薄膜材料高阻态是低阻态的10 4倍。所述“壳-核”结构O-Sb 2Te 3相变存储薄膜材料相变温度较纯Sb 2Te 3得到大幅提高。所述“壳-核”结构O-Sb 2Te 3相变存储薄膜材料STEM观察到：Sb 2Te 3晶粒被随机分布的非晶组织隔成一个个纳米尺寸的“相变岛”，形成表皮(“壳”)的是绝热高阻的氧化物，形成里层(“核”部)的是Sb 2Te 3相变材料，各个部分的成分通过EDX表征加以验证。所述“壳-核”结构O-Sb 2Te 3相变存储薄膜材料XPS表征说明掺入的O原子主要和Sb原子成键。第一性原理计算观察到“壳-核”结构O-Sb 2Te 3相变存储材料中O-Sb结构的形成，并随着O原子浓度增加而呈现包裹趋势。简化“壳-核”结构三维包裹结构建立物理模型，通过模拟计算观察到外层“壳”结构可以抑制里层“核”内原子的运动。同时电热仿真观察到“壳-核”结构可以有效阻挡相变过程中的热扩散。
本发明一个实施例中相变存储单元依次包括底电极、隔离层、相变存储材料薄膜层、顶电极。所述相变存储材料薄膜层材质为本发明所述的通过非晶组织进行调控的“壳-核”结构O-Sb 2Te 3相变材料，其被填充在直径为250nm、深度为100nm的小孔中。所述底电极材质为TiN。所述隔离层材质为SiO 2。所述顶电极材质为金属Pt。
本发明提供了一种用于相变存储器的“壳-核”结构O-Sb 2Te 3相变材料的制备方法，制备方法包括磁控溅射法、化学气相沉积、原子层沉积法、电镀法、电子束蒸发法等。其中，磁控溅射法制备最为灵活，可以采用Sb靶和Te靶在有氧氛围下共溅射，也可以采用Sb 2Te 3靶在有氧环境下溅射，还可以采用O-Sb 2Te 3合金靶溅射。这些方法都能按照化学通式的配比制备本发明的”壳-核”结构O-Sb 2Te 3相变存储材料。
本发明的“壳-核”结构O-Sb 2Te 3相变存储材料以及器件制备工艺成熟，易于实现与现有微电子工艺技术的兼容。形成的独特的“壳-核”结构缩小了相变区域大小，抑制了原子迁移以及阻挡了热扩散。本发明的“壳-核”结构O-Sb 2Te 3相变存储器件相较于纯Sb 2Te 3相变存储器件直流set操作电流减小一个数量级，reset功耗降低超过95％，阻值漂移明显降低，循环特性得到大幅改善。
为了更加详细的阐述本发明方法，下面结合更加具体的实施例进一步详细说明。
实施例1
本实施例中制备的用于相变存储器件的O-Sb 2Te 3相变存储薄膜材料化学通式为(ST) 1-xO x，其中ST代表Sb 2Te 3，本实施例中x＝0.1。
O-Sb 2Te 3相变存储薄膜材料采用磁控溅射法制得；制备时通入高纯氩气作为溅射气体，并通入少量氧气提供有氧氛围，溅射气压为0.5Pa，Sb 2Te 3靶采用交流电源，电源功率为60W。具体制备工艺包括以下步骤：
1.选取尺寸为1cm×1cm的SiO 2/Si(100)基片，清洗表面、背面，去除灰尘颗粒、有机和无机杂质。
a)将SiO 2/Si(100)基片放置在丙酮溶液中用40W功率的超声振动10分 钟，去离子水冲洗。
b)将丙酮处理后的基片在乙醇溶液中用40W功率的超声振动10分钟，去离子水冲洗，高纯N 2气吹干表面和背面，得到待溅射基片。
2.采用交流电源溅射方法制备O-Sb 2Te 3相变存储薄膜材料
a)放置好Sb 2Te 3合金靶材，其纯度达到99.99％(原子百分比)，将其本底真空抽至10 -4Pa。
b)使用高纯Ar气作为溅射气体，并通入少量O 2气，将溅射气压调节至0.5Pa，靶材和基片距离为120mm。
c)设定功率为60W。
d)将空基托旋转到Sb 2Te 3靶上方，对Sb 2Te 3靶材进行10min预溅射，清洁靶材表面。
e)预溅射完成后，将待溅射基片旋转到Sb 2Te 3靶上方，开启挡板，依照预定的溅射时间，溅射不同厚度的O-Sb 2Te 3相变存储薄膜材料。溅射时间为3min时，制备的薄膜厚度为50nm左右，用于原位薄膜方阻随退火温度实时变化曲线测量。溅射时间为6min时，制备的薄膜厚度为100nm左右，用于XRD表征。
对比例1
本对比例1中制备纯Sb 2Te 3相变存储薄膜材料。
纯Sb 2Te 3相变存储薄膜材料采用磁控溅射法制得；制备时通入高纯氩气作为溅射气体，溅射气压为0.5Pa，Sb 2Te 3靶采用交流电源，电源功率为60W。具体制备工艺包括以下步骤：
1.选取尺寸为1cm×1cm的SiO 2/Si(100)基片，清洗表面、背面，去除灰尘颗粒、有机和无机杂质。
a.将SiO 2/Si(100)基片放置在丙酮溶液中用40W功率的超声振动10分钟，去离子水冲洗。
b.将丙酮处理后的基片在乙醇溶液中用40W功率的超声振动10分钟，去离子水冲洗，高纯N 2气吹干表面和背面，得到待溅射基片。
2.采用交流电源溅射方法制备纯Sb 2Te 3相变存储薄膜材料
a.放置好Sb 2Te 3合金靶材，其纯度达到99.99％(原子百分比)，将其本底真空抽至10 -4Pa。
b.使用高纯Ar气作为溅射气体，将溅射气压调节至0.5Pa，靶材和基片距离为120mm。
c.设定功率为60W。
d.将空基托旋转到Sb 2Te 3靶上方，对Sb 2Te 3靶材进行10min预溅射，清洁靶材表面。
e.预溅射完成后，将待溅射基片旋转到Sb 2Te 3靶上方，开启挡板，依照预定的溅射时间，溅射不同厚度的Sb 2Te 3相变存储薄膜材料。溅射时间为3min时，制备的薄膜厚度为50nm左右，用于原位薄膜方阻随退火温度实时变化曲线测量。溅射时间为6min时，制备的薄膜厚度为100nm左右，用于XRD表征。
将上述实施例1和对比例1中的O-Sb 2Te 3、纯Sb 2Te 3相变存储薄膜材料进行测试。图1是本发明实施例经过晶界工程调控过后形成“壳-核”结构的O-Sb 2Te 3相变存储材料薄膜与纯Sb 2Te 3相变存储材料薄膜原位方阻与退火温度的实时关系曲线，其中，升温速率为6℃/min，ST代表纯Sb 2Te 3相变存储材料，OST代表“壳-核”结构的O-Sb 2Te 3相变存储材料。对比可知，“壳-核”结构的形成提高了材料非晶态的电阻值，且非晶态阻值与晶态阻值之间的窗口增大，相变温度大幅提高至250℃，非晶稳定性得到明显改善。
图2是经过晶界工程调控过后形成“壳-核”结构的O-Sb 2Te 3相变存储材料薄膜(图中缩写为OST)与纯Sb 2Te 3(图中缩写为ST)相变存储材料薄膜XRD表征对比图。图中，方块对应Sb-Te物质衍射峰，倒三角对应Sb-O物质衍射峰。200℃退火后，“壳-核”结构Sb 2Te 3相变存储材料薄膜除了基底峰之外没有其他衍射峰，处于非晶状态。然而，200℃退火温度下的纯ST薄膜呈现明显的多晶衍射峰图，说明“壳-核”结构的形成提高了材料体系的非晶稳定性，与薄膜原位R-T关系曲线图相吻合。同时300℃退火温度下“壳-核”结构Sb 2Te 3相变存储材料薄 膜谱图中出现强度较弱的Sb-O物质的衍射峰，印证了壳层Sb-O氧化物的存在。
实施例2
本实施例中制备的用于相变存储器件的O-Sb 2Te 3相变存储薄膜材料化学通式为(ST) 1-xO x，其中ST代表Sb 2Te 3，本实施例中x＝0.1。
O-Sb 2Te 3相变存储薄膜材料采用磁控溅射法制得。制备时通入高纯氩气作为溅射气体，并通入少量氧气提供有氧氛围，溅射气压为0.5Pa，Sb 2Te 3靶采用交流电源，电源功率为60W。具体制备工艺包括以下步骤：
1.选取尺寸为1cm×1cm的SiO 2/Si(100)基片，清洗表面、背面，去除灰尘颗粒、有机和无机杂质。
a)将SiO 2/Si(100)基片放置在丙酮溶液中用40W功率的超声振动10分钟，去离子水冲洗。
b)将丙酮处理后的基片在乙醇溶液中用40W功率的超声振动10分钟，去离子水冲洗，高纯N 2气吹干表面和背面，得到待溅射基片。
2.采用交流电源溅射方法制备O-Sb 2Te 3相变存储薄膜材料
a)放置好Sb 2Te 3合金靶材，其纯度达到99.99％(原子百分比)，将其本底真空抽至10 -4Pa。
b)使用高纯Ar气作为溅射气体，并通入少量O 2气，将溅射气压调节至0.5Pa，靶材和基片距离为120mm。
c)设定功率为60W。
d)将空基托旋转到Sb 2Te 3靶上方，对Sb 2Te 3靶材进行10min预溅射，清洁靶材表面。
e)预溅射完成后，将待溅射基片旋转到Sb 2Te 3靶上方，开启挡板，依照预定的溅射时间，溅射不同厚度的O-Sb 2Te 3相变存储薄膜材料。溅射时间为6min时，制备的薄膜厚度为100nm左右，用于TEM、HRTEM、EDX微观分析以及X射线光电子能谱表征。
将本实施例中的O-Sb 2Te相变存储薄膜材料进行测试。
图3本发明实施例的经过晶界工程调控过后形成”壳-核”结构的O-Sb 2Te 3相 变存储材料薄膜的in plane-TEM微观分析图。沉积态样品在300℃下退火10min。可以发现样品微观呈现均匀的异质结构。
图4是本实施例中“壳-核”结构的O-Sb 2Te 3相变存储材料薄膜的HRTEM微观分析图，其中，沉积态样品在300℃下退火10min。图中，较长的实线箭头所示是“核”结构晶体部分，较短的虚线箭头所示为“壳”结构非晶体部分，右侧图中的矩形方框表示为对应部分的傅里叶转换图。由图发现，晶粒被随机分布的非晶组织包裹，分隔成一个个纳米尺寸的“晶体岛”，形成“壳”是低热导低电导的非晶物质，里层“核”为晶体的”壳-核”结构。
图5是本实施例中“壳-核”结构的O-Sb 2Te 3相变存储材料薄膜的EDX元素分布图，图5(a)为取样区域明场图象，图5(b)为Sb元素分布图象，图5(c)为Te元素分布图象。由图可知，Sb元素和Te元素分布不完全重合，有包裹现象。
图6是本实施例中“壳-核”结构的O-Sb 2Te 3相变存储材料薄膜的X射线光电子能谱图，其中，沉积态样品在300℃下退火10min，并且表面经过Ar +处理以去除表面氧化污染层，图6(a)为Sb元素能谱图，图6(b)为Te元素能谱图，图中衍射峰对应相应的化学键。通过元素分布表征结果说明Sb元素除了分布在Te元素分布区域形成Sb-Te化合物外，还在Te元素外围分布，结合Sb原子和Te原子的成键状态可以说明，通过引入O原子形成了“壳”是低热导低电导的Sb iO j氧化物，里层“核”是传统Sb-Te相变材料的“壳-核”结构相变存储材料。
实施例3
本实施例利用Materials Studio软件对O元素掺入浓度分别为5％、10％和20％的Sb 2Te 3相变存储薄膜材料进行建模，利用第一性原理对三个模型进行随机化，熔化，淬火过程的模拟仿真得到O元素掺入浓度分别为5％、10％和20％的OST相变存储薄膜材料的非晶模型，结果如图7所示。利用Materials Studio软件对简化的“壳-核”结构O-Sb 2Te 3以及纯Sb 2Te 3进行建模，利用第一性原理模拟不同温度下“壳-核”结构O-Sb 2Te 3模型和纯Sb 2Te 3的原子运动以及同一温度下“壳-核”结构O-Sb 2Te 3模型中中间区域原子和靠近壳层区域原子的运动情况，通过数据处理形成直观图象，图8是本发明中利用第一性原理计算得到的不同温 度下简化“壳-核”结构对里层(“核”内部)原子运动的影响，其中，曲线1对应纯Sb 2Te 3常规相变材料(PCM)在高温(550K)下的原子运动情况模拟结果，曲线2对应纯Sb 2Te 3常规相变材料(PCM)在低温(300K)下的原子运动情况模拟结果，曲线3对应O-Sb 2Te 3所代表的“壳-核”结构相变材料(cs-PCM)在高温(550K)下的原子运动情况模拟结果，曲线4对应O-Sb 2Te 3所代表的“壳-核”结构相变材料(cs-PCM)在低温(300K)下的原子运动情况模拟结果。图9是本发明实施例中利用第一性原理计算得到的简化“壳-核”结构对里层(“核”内部)不同区域原子运动的影响，曲线1和曲线3对应里层“核”相变材料靠近壳层区域原子运动情况模拟结果，曲线2对应里层“核”相变材料中间区域原子运动情况模拟结果。其中，插图为简化后的”壳-核”结构O-Sb 2Te 3三维包裹结构模型，区域1和区域3对应里层“核”相变材料靠近“壳”层区域原子，区域2对应里层“核”相变材料中间区域原子。
图7是本发明实施例中O元素掺入浓度分别为5％、10％和20％的OST相变存储薄膜材料的非晶模型，可以发现掺入的O原子倾向于和Sb原子结合成键。随着O原子浓度的增加，O-Sb结合物质增加并且在晶胞边界随机出现。当O原子浓度为20％的时候，边界处Sb-O结合物质连接形成对里层Sb-Te物质的包裹结构，即“壳”是低热导低电导的Sb-O氧化物，里层“核”是传统Sb-Te相变材料的“壳-核”结构。
对“壳-核”结构O-Sb 2Te 3三维包裹结构进行简化，得到如图9中的插图，研究被限制方向(Z方向)原子的运动可以反映并推测三维方向上的限制对里层“核”Sb-Te原子运动的影响。图8是分别在低温和高温下“壳-核”结构O-Sb 2Te 3模型和纯Sb 2Te 3的Z方向原子运动对比图。曲线1对应纯Sb 2Te 3常规相变材料(PCM)在高温(550K)下的原子运动情况模拟结果，曲线2对应纯Sb 2Te 3常规相变材料(PCM)在低温(300K)下的原子运动情况模拟结果，曲线3对应O-Sb 2Te 3所代表的“壳-核”结构相变材料(cs-PCM)在高温(550K)下的原子运动情况模拟结果，曲线4对应O-Sb 2Te 3所代表的“壳-核”结构相变材料(cs-PCM)在低温(300K)下的原子运动情况模拟结果。可以看出壳层可以有效抑制里层 “核”内原子的运动，且对温度的敏感程度明显降低，即温度增加原子运动剧烈程度变化较纯Sb 2Te 3有明显减小。图9是同一温度下里层“核”相变材料中间区域原子和靠近壳层区域原子的运动情况对比图，其中曲线1和曲线3对应里层“核”相变材料靠近壳层区域原子运动情况模拟结果，曲线2对应里层“核”相变材料中间区域原子运动情况模拟结果。可以看出中间区域原子运动比靠近壳层区域原子更剧烈。通过第一性原理计算模拟仿真，可以发现“壳-核”结构可以有效抑制靠近氧化物界面的原子的运动，对里层“核”中心区域原子运动的影响有限。即“壳-核”结构可以抑制里层“核”内材料原子的长程迁移，但不影响里层“核”内材料原子在壳内区域的相互运动。
图10是简化的“壳-核”结构利用COMSOL软件得到的热仿真图，可以发现电流操作时，热量主要集中于核部Sb-Te相变材料区域，说明“壳-核”结构的壳层对热扩散有明显的阻挡作用，有效提高了相变过程中的电热利用效率。
实施例4
本实施例中采用“壳-核”结构的O-Sb 2Te 3相变存储薄膜材料作为相变层材料制备存储器件，其中“壳-核”结构O-Sb 2Te 3相变层采用磁控溅射法制得。制备时通入高纯氩气作为溅射气体，并通入少量氧气提供有氧氛围，溅射气压为0.5Pa，Sb 2Te 3靶采用交流电源，电源功率为60W。具体制备工艺包括以下步骤：
1.选取尺寸为1cm×1cm的SiO 2/Si(100)基片，清洗表面、背面，去除灰尘颗粒、有机和无机杂质。
a)将SiO 2/Si(100)基片放置在丙酮溶液中用40W功率的超声振动10分钟，去离子水冲洗。
b)将丙酮处理后的基片在乙醇溶液中用40W功率的超声振动10分钟，去离子水冲洗，高纯N 2气吹干表面和背面，得到待溅射基片。
2.采用直流电源溅射方法制备100nm TiN下电极。
3.采用化学气相沉积法在步骤2中的TiN下电极上沉积100nm SiO 2绝缘层。
4.通过电子束光刻刻蚀等工艺在步骤3中的SiO 2绝缘层形成深度为100 nm、直径为250nm的通孔。
5.通过光刻工艺形成存储阵列。
6.采用交流电源溅射方法在步骤4中形成的通孔内填充O-Sb 2Te 3相变存储薄膜材料
a)放置好Sb 2Te 3合金靶材，其纯度达到99.99％(原子百分比)，将其本底真空抽至10 -4Pa。
b)使用高纯Ar气作为溅射气体，并通入少量O 2气，将溅射气压调节至0.5Pa，靶材和基片距离为120mm。
c)设定功率为60W。
d)将空基托旋转到Sb 2Te 3靶上方，对Sb 2Te 3靶材进行10min预溅射，清洁靶材表面。
e)预溅射完成后，将待溅射基片旋转到Sb 2Te 3靶上方，开启挡板，依照预定的溅射时间，溅射不同厚度的O-Sb 2Te 3相变存储薄膜材料。溅射时间为6min时，制备的相变层厚度为100nm左右。
7.采用直流电源溅射方法制备100nm Pt上电极，得到完整的基于“壳-核”结构O-Sb 2Te 3相变层的相变存储器件阵列。
对比例4
本对比例中使用纯Sb 2Te 3相变存储薄膜材料作为相变层制备纯Sb 2Te 3存储器件。
1.选取尺寸为1cm×1cm的SiO 2/Si(100)基片，清洗表面、背面，去除灰尘颗粒、有机和无机杂质。
a)将SiO 2/Si(100)基片放置在丙酮溶液中用40W功率的超声振动10分钟，去离子水冲洗。
b)将丙酮处理后的基片在乙醇溶液中用40W功率的超声振动10分钟，去离子水冲洗，高纯N 2气吹干表面和背面，得到待溅射基片。
2.采用直流电源溅射方法制备100nm TiN下电极。
3.采用化学气相沉积法在步骤2中的TiN下电极上沉积100nm SiO 2绝缘 层。
4.通过电子束光刻刻蚀等工艺在步骤3中的SiO 2绝缘层形成深度为100nm、直径为250nm的通孔。
5.通过光刻工艺形成存储阵列。
6.采用交流电源溅射方法在步骤4中形成的通孔内采用磁控溅射填充纯Sb 2Te 3相变存储薄膜材料
7.采用直流电源溅射方法制备100nm Pt上电极，得到完整的基于Sb 2Te 3相变层的相变存储器件阵列。
将上述实施例4和对比例4中的分别基于“壳-核”结构的O-Sb 2Te 3相变存储器和纯Sb 2Te 3相变存储器件进行电学特性测试。
图11是本实施例中以“壳-核”结构O-Sb 2Te 3相变存储材料为功能层的相变存储单元结构的示意图，由图可知，其中，1为顶电极，2为具有“壳-核”结构的相变材料，3为绝热绝缘SiO 2层，4为底电极。
图12至图15是以“壳-核”结构的O-Sb 2Te 3相变存储材料为功能层的相变存储单元与未掺杂Sb 2Te 3相变存储单元的电学性能测试对比图，图12是器件I-V性能对比图，图13是器件RESET性能对比图，图14是器件阻漂性能对比图，图15是“壳-核”结构的O-Sb 2Te 3器件循环性能图。
图12是器件I-V特性对比图，明显地，两者都发生了相转变，操作阈值电流I th分别为1.64μA和12μA，可知，以“壳-核”结构O-Sb 2Te 3相变存储薄膜材料为功能层的相变存储单元操作电流减小一个数量级。
图13是器件的R-V测试图，反映的是器件RESET性能，以“壳-核”结构O-Sb 2Te 3相变存储薄膜材料为功能层的相变存储单元在10ns宽的脉冲操作下能成功reset。另外，两个器件高低阻值比均大于10 2，有利于提高器件的抗干扰能力；比较相同操作脉冲宽度下的两个器件，如图13中虚线所示，以传统Sb 2Te 3相变存储薄膜材料为功能层的相变存储单元在10ns脉宽下reset电压达到2.8V，相较于以“壳-核”结构O-Sb 2Te 3相变存储薄膜材料为功能层的相变存储单元的 0.95V有3到4倍的差异。用欧姆定律计算功耗
Figure PCTCN2021083195-appb-000001
结果如下表所示：
表1.器件reset功耗比较
  U RESET R SET t Energy
ST器件 2.8V 9673.322746ohm 10ns 8.105PJ
OST器件 0.95V 26941.8068ohm 10ns 0.335PJ
可知，以“壳-核”结构O-Sb 2Te 3相变存储薄膜材料为功能层的相变存储单元具有较低的功耗，可以解决紧凑三维堆叠阵列中的散热问题，为三维存储提供了一种可能的材料体系。
图14是器件电阻漂移的测量和比较图。电阻漂移可以通过带时间的幂次方程(1)进行描述：
Figure PCTCN2021083195-appb-000002
其中，R是测试电阻，R 0和τ 0是取决于材料初始状态的常数。指数因子α是电阻漂移系数，它表示阻值漂移速度。α的值越高表示漂移越快。对于无序硫族化物材料，漂移指数α与温度无关，并且仅随初始电阻值而增加。如图14所示，以“壳-核”结构O-Sb 2Te 3相变存储薄膜材料为功能层的相变存储单元的漂移指数α＝0.005，相较于以传统Sb 2Te 3相变存储薄膜材料为功能层的相变存储单元α＝0.03有很大的改善，同时插图中的数据离散柱形图也说明前者阻值更稳定，波动更小。
图15是以“壳-核”结构O-Sb 2Te 3相变存储薄膜材料为功能层的相变存储单元循环特性的测试结果，在认定标准为高低阻值差异大于10倍的情况下，重复施加set脉冲(上升沿600ns,1us,下降沿600ns；2.5V)和reset脉冲(上升沿8ns,50ns,下降沿8ns；2.8V)，器件Cycle次数可以达到10 8数量级别。
与现有技术中未经非晶组织调控的Sb 2Te 3相变存储材料相比，本发明的“壳-核”结构O-Sb 2Te 3相变材料中，溅射氛围内的O原子与Sb原子结合形成非晶氧 化物，分布在相变材料SbTe晶粒周围形成晶界，将相变材料Sb 2Te 3分隔成一个个体积较小的“相变岛”，其中，形成表皮“壳”层的是低热导低电导的氧化物，里层“核”内的是相变材料Sb 2Te 3的“壳-核”结构。局部无序态提高了相变材料非晶状态的电阻值，改善了Sb 2Te 3材料的非晶稳定性。另外，“壳-核”异质结构的存在在三维结构上限制了“壳-核”结构里层“核”内原子由于外加电操作引起的长程迁移，从而提高存储器件的整体循环特性以及阻值漂移特性。“壳”层氧化物材料的低热导特性对减小器件RESET功耗也效果显著。
本领域的技术人员容易理解，以上所述仅为本发明的较佳实施例而已，并不用以限制本发明，凡在本发明的精神和原则之内所作的任何修改、等同替换和改进等，均应包含在本发明的保护范围之内。

Claims (10)

  1. 一种基于氧掺杂的Sb 2Te 3相变材料，其特征在于，其化学式为：O x(Sb 2Te 3) 1-x，其中，O为氧元素，x代表氧元素在整个化学组成中的原子百分比，0<x<40％。
  2. 如权利要求1所述的一种基于氧掺杂的Sb 2Te 3相变材料，其特征在于，氧原子与Sb 2Te 3中的元素原子结合形成无序氧化物，包裹在Sb 2Te 3周围，将Sb 2Te 3分隔成多个岛状，形成壳-核结构，其中，壳部是氧原子与Sb 2Te 3中的元素原子结合形成无序氧化物，核部为Sb 2Te 3晶粒。
  3. 如权利要求2所述的一种基于氧掺杂的Sb 2Te 3相变材料，其特征在于，部分氧元素进入Sb 2Te 3晶粒中，用于提高Sb 2Te 3的非晶稳定性。
  4. 如权利要求3所述的一种基于氧掺杂的Sb 2Te 3相变材料，其特征在于，O x(Sb 2Te 3) 1-x材料中，通过控制O的掺入量来控制所述Sb 2Te 3中非晶氧化物晶界的性质从而调控O-Sb 2Te 3相变存储材料的电化学性质，电化学性质包括高低阻态电阻、晶化温度，O-Sb 2Te 3相变存储材料是指O x(Sb 2Te 3) 1-x材料，其中，0<x<40％。
  5. 如权利要求4所述的一种基于氧掺杂的Sb 2Te 3相变材料，其特征在于，氧原子与Sb 2Te 3中Sb原子结合形成无序氧化物，并集中在Sb 2Te 3晶粒周围形成非晶晶界。
  6. 如权利要求5所述的一种基于氧掺杂的Sb 2Te 3相变材料，其特征在于，无序氧化物为氧原子与Sb 2Te 3中Sb原子结合形成的无序氧化物，具有熔点较高、热导率较低的特点，所述熔点高是指比Sb 2Te 3熔点高20～30K，所述热导率较低是指热导率接近10 -3量级，接近完全隔热程度。
  7. 如权利要求6所述的一种基于氧掺杂的Sb 2Te 3相变材料，其特征在于，氧化物晶界在相变过程中起到提高电热效率、阻止原子迁移的作用，同时用于提高相变层非晶状态的电阻值，改善Sb 2Te 3材料的非晶稳定性。
  8. 一种基于氧掺杂的Sb 2Te 3相变材料的相变存储器，其特征在于，其包括 底电极、隔离层、相变存储材料薄膜层和顶电极，其中，所述相变存储材料薄膜层材质为如权利要求1-4之一所述的基于氧掺杂的Sb 2Te 3相变材料。
  9. 制备如权利要求1-7之一所述的基于氧掺杂的Sb 2Te 3相变材料的方法，其特征在于，采用磁控溅射法、化学气相沉积法、原子层沉积法、电镀法或电子束蒸发法制备。
  10. 如权利要求9所述的方法，其特征在于，具体的磁控溅射方法为以下三种中的任意一种：
    (1)Sb靶和Te靶在有氧环境下共溅射；
    (2)Sb 2Te 3靶在有氧环境下溅射；
    (3)O掺杂后的Sb 2Te 3合金靶溅射。
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