In the past decade,there has been tremendous progress in integrating chalcogenide phase-change materials(PCMs)on the silicon photonic platform for non-volatile memory to neuromorphic in-memory computing applications.I...In the past decade,there has been tremendous progress in integrating chalcogenide phase-change materials(PCMs)on the silicon photonic platform for non-volatile memory to neuromorphic in-memory computing applications.In particular,these non von Neumann computational elements and systems benefit from mass manufacturing of silicon photonic integrated circuits(PICs)on 8-inch wafers using a 130 nm complementary metal-oxide semiconductor line.Chip manufacturing based on deep-ultraviolet lithography and electron-beam lithography enables rapid prototyping of PICs,which can be integrated with high-quality PCMs based on the wafer-scale sputtering technique as a back-end-of-line process.In this article,we present an overview of recent advances in waveguide integrated PCM memory cells,functional devices,and neuromorphic systems,with an emphasis on fabrication and integration processes to attain state-of-the-art device performance.After a short overview of PCM based photonic devices,we discuss the materials properties of the functional layer as well as the progress on the light guiding layer,namely,the silicon and germanium waveguide platforms.Next,we discuss the cleanroom fabrication flow of waveguide devices integrated with thin films and nanowires,silicon waveguides and plasmonic microheaters for the electrothermal switching of PCMs and mixed-mode operation.Finally,the fabrication of photonic and photonic–electronic neuromorphic computing systems is reviewed.These systems consist of arrays of PCM memory elements for associative learning,matrix-vector multiplication,and pattern recognition.With large-scale integration,the neuromorphic photonic computing paradigm holds the promise to outperform digital electronic accelerators by taking the advantages of ultra-high bandwidth,high speed,and energy-efficient operation in running machine learning algorithms.展开更多
Phase-change memory(PCM)has considerable promise for new applications based on von Neumann and emerging neuromorphic computing systems.However,a key challenge in harnessing the advantages of PCM devices is achieving h...Phase-change memory(PCM)has considerable promise for new applications based on von Neumann and emerging neuromorphic computing systems.However,a key challenge in harnessing the advantages of PCM devices is achieving high-speed operation of these devices at elevated temperatures,which is critical for the efficient processing and reliable storage of data at full capacity.Herein,we report a novel PCM device based on Ta-doped antimony telluride(Sb2Te),which exhibits both high-speed characteristics and excellent high-temperature characteristics,with an operation speed of 2 ns,endurance of >106 cycles,and reversible switching at 140℃.The high coordination number of Ta and the strong bonds between Ta and Sb/Te atoms contribute to the robustness of the amorphous structure,which improves the thermal stability.Furthermore,the small grains in the three-dimensional limit lead to an increased energy efficiency and a reduced risk of layer segregation,reducing the power consumption and improving the long-term endurance.Our findings for this new Ta-Sb2Te material system can facilitate the development of PCMs with improved performance and novel applications.展开更多
Sn-doped Ge2Sb2Te5 thin films deposited on Si（100）/SiO2 substrates by rf magnetron sputtering are investigated by a differential scanning calorimeter, x-ray diffraction and sheet resistance measurement. The crystall...Sn-doped Ge2Sb2Te5 thin films deposited on Si（100）/SiO2 substrates by rf magnetron sputtering are investigated by a differential scanning calorimeter, x-ray diffraction and sheet resistance measurement. The crystallization temperatures of the 3.58 at.%, 6.92 at.% and 10.04 at.% Sn-doped Ge2Sb2Te5 thin films have decreases of 5.3, 6.1 and 0.9℃, respectively, which is beneficial to reduce the switching current for the amorphous-to-crystalline phase transition. Due to Sn-doping, the sheet resistance of crystalline Ge2Sb2Te5 thin films increases about 2-10 times, which may be useful to reduce the switching current for the amorphous-to-crystalline phase change. In addition, an obvious decreasing dispersibility for the sheet resistance of Sn-doped Ge2Sb2Te5 thin films in the crystalline state has been observed, which can play an important role in minimizing resistance difference for the phase-change memory cell element arrays.展开更多
Embedded phase-change random-access memory(ePCRAM)applications demand superior data retention in amorphous phase-change materials(PCMs).Traditional PCM design strategies have focused on enhancing the thermal stability...Embedded phase-change random-access memory(ePCRAM)applications demand superior data retention in amorphous phase-change materials(PCMs).Traditional PCM design strategies have focused on enhancing the thermal stability of the amorphous phase,often at the expense of the crystallization speed.While this approach supports reliable microchip operations,it compromises the ability to achieve rapid responses.To address this limitation,we modified ultrafast-crystallizing Sb thin films by incorporating Sc dopants,achieving the highest 10-year retention temperature(~175℃)among binary antimonide PCMs while maintaining a sub-10-ns SET operation speed.This reconciliation of two seemingly contradictory properties arises from the unique kinetic features of the 5-nm-thick Sc12Sb88 films,which exhibit an enlarged fragile-to-strong crossover in viscosity at medium supercooled temperature zones and an incompatible sublattice ordering behavior between the Sc and Sb atoms.By tailoring the crystallization kinetics of PCMs through strategic doping and nanoscale confinement,we provide new opportunities for developing robust yet swift ePCRAMs.展开更多
Although phase-change random-access memory(PCRAM)is a promising next-generation nonvolatile memory technology,challenges remain in terms of reducing energy consumption.This is primarily be-cause the high thermal condu...Although phase-change random-access memory(PCRAM)is a promising next-generation nonvolatile memory technology,challenges remain in terms of reducing energy consumption.This is primarily be-cause the high thermal conductivities of phase-change materials(PCMs)promote Joule heating dissi-pation.Repeated phase transitions also induce long-range atomic diffusion,limiting the durability.To address these challenges,phase-change heterostructure(PCH)devices that incorporate confinement sub-layers based on transition-metal dichalcogenide materials have been developed.In this study,we engi-neered a PCH device by integrating HfTe_(2),which has low thermal conductivity and excellent stability,into the PCM to realize PCRAM with enhanced thermal efficiency and structural stability.HEAT sim-ulations were conducted to validate the superior heat confinement in the programming region of the HfTe_(2)-based PCH device.Moreover,electrical measurements of the device demonstrated its outstanding performance,which was characterized by a low RESET current(∼1.6 mA),stable two-order ON/OFF ratio,and exceptional cycling endurance(∼2×10^(7)).The structural integrity of the HfTe_(2)confinement sub-layer was confirmed using X-ray photoelectron spectroscopy and transmission electron microscopy.The material properties,including electrical conductivity,cohesive energy,and electronegativity,substantiated these findings.Collectively,these results revealed that the HfTe_(2)-based PCH device can achieve significant improvements in performance and reliability compared with conventional PCRAM devices.展开更多
The Gasbag Phase-change Carbon Dioxide Energy Storage System leverages elastic gasbags to store carbon dioxide under varying geographical conditions.This approach utilizes the phase-change sensible heat effect to effi...The Gasbag Phase-change Carbon Dioxide Energy Storage System leverages elastic gasbags to store carbon dioxide under varying geographical conditions.This approach utilizes the phase-change sensible heat effect to efficiently manage energy storage and release.This technology requires lower pressure and temperature control,resulting in reduced energy consumption and improved efficiency.Additionally,it is less restricted by geographical factors to a certain extent,enabling the formation of a closed-loop system.This contributes to the development of new energy utilization systems.The article examines and compares two experimental energy storage projects employing elastic gasbags to maintain a constant pressure supply of carbon dioxide on the low-pressure side.It further details the precise calculation methods for system cycle efficiency and energy storage density while analyzing energy losses incurred during the storage and release phases.Finally,an economic analysis is conducted using specific data,demonstrating that optimizing temperature and pressure parameters at various nodes enhances overall system efficiency while reducing energy consumption.Furthermore,the study highlights the system's high sensitivity to grid electricity prices.This research is anticipated to contribute to the development of more efficient and reliable energy storage solutions for power systems,addressing the growing energy demands and sustainability challenges.展开更多
To address the limitations of conventional energy systems and optimize the energy conversion pathways and efficiency,a type of“five-in-one”multifunctional phase-change composite with magnetothermal,electrothermal,so...To address the limitations of conventional energy systems and optimize the energy conversion pathways and efficiency,a type of“five-in-one”multifunctional phase-change composite with magnetothermal,electrothermal,solar-thermal,and thermoelectric energy conversion and electromagnetic shielding functions is developed for multipurpose applications.Such a novel phase-change composite is fabricated by an innovative combination of paraffin wax(PW)as a phase-change material and a carbonized polyimide/Kevlar/graphene oxide@ZIF-67 complex aerogel as a supporting material.The carbonized complex aerogel exhibits a unique bidirectional porous structure with high porosity and robust skeleton to support the loading of PW.The reduced graphene oxide and Co NC resulting from high-temperature carbonization are anchored on the aerogel skeleton to generate high thermal conduction and magnetic effect,enhancing the phonon and electron transfer of the aerogel and improving its energy conversion efficiency.The phase-change composite not only exhibits excellent solar-thermal,thermoelectric,electrothermal,and magnetothermal energy conversion performance,but also achieves high electromagnetic interference shielding effectiveness of 66.2 d B in the X-band.The introduction of PW significantly improves the thermal energy-storage capacity during multi-energy conversion.The developed composite exhibits great application potential for efficient solar energy utilization,sustainable power generation,outdoor deicing,human thermal therapy,and electronic device protection.展开更多
Considering the three typical phase-change related rock mechanics phenomena during drilling and production in oil and gas reservoirs,which include phase change of solid alkane-related mixtures upon heating,sand liquef...Considering the three typical phase-change related rock mechanics phenomena during drilling and production in oil and gas reservoirs,which include phase change of solid alkane-related mixtures upon heating,sand liquefaction induced by sudden pressure release of the over-pressured sand body,and formation collapse due to gasification of pore fillings from pressure reduction,this study first systematically analyzes the progress of theoretical understanding,experimental methods,and mathematical representation,then discusses the engineering application scenarios corresponding to the three phenomena and reveals the mechanical principles and application effectiveness.Based on these research efforts,the study further discusses the significant challenges,potential developmental trends,and research approaches that require urgent exploration.The findings disclose that various phase-related rock mechanics phenomena require specific experimental and mathematical methods that can produce multi-field coupling mechanical mechanisms,which will eventually instruct the control on resource exploitation,evaluation on disaster level,and analysis of formation stability.To meet the development needs of the principle,future research efforts should focus on mining more phase-change related rock mechanics phenomena during oil and gas resources exploitation,developing novel experimental equipment,and using techniques of artificial intelligence and digital twins to implement real-time simulation and dynamic visualization of phase-change related rock mechanics.展开更多
Tailoring the degree of structural disorder in Ge-Sb-Te alloys is important for the development of non-volatile phase-change memory and neuro-inspired computing.Upon crystallization from the amorphous phase,these allo...Tailoring the degree of structural disorder in Ge-Sb-Te alloys is important for the development of non-volatile phase-change memory and neuro-inspired computing.Upon crystallization from the amorphous phase,these alloys form a cubic rocksalt-like structure with a high content of intrinsic vacancies.Further thermal annealing results in a gradual structural transition towards a layered structure and an insulator-to-metal transition.In this work,we elucidate the atomic-level details of the structural transition in crystalline GeSb_(2)Te_(4) by in situ high-resolution transmission electron microscopy experiments and ab initio density functional theory calculations,providing a comprehensive real-time and real-space view of the vacancy ordering process.We also discuss the impact of vacancy ordering on altering the electronic and optical properties of GeSb_(2)Te_(4),which is relevant to multilevel storage applications.The phase evolution paths in Ge-Sb-Te alloys and Sb_(2)Te_(3)are illustrated using a summary diagram,which serves as a guide for designing phase-change memory devices.展开更多
By controlling the amorphous-to-crystalline relative volume,chalcogenide phase-change memory materials can provide multi-level data storage(MLS),which offers great potential for high-density storageclass memory and ne...By controlling the amorphous-to-crystalline relative volume,chalcogenide phase-change memory materials can provide multi-level data storage(MLS),which offers great potential for high-density storageclass memory and neuro-inspired computing.However,this type of MLS system suffers from high power consumption and a severe time-dependent resistance increase(‘‘drift")in the amorphous phase,which limits the number of attainable storage levels.Here,we report a new type of MLS system in yttriumdoped antimony telluride,utilizing reversible multi-level phase transitions between three states,i.e.,amorphous,metastable cubic and stable hexagonal crystalline phases,with ultralow power consumption(0.6–4.3 p J)and ultralow resistance drift for the lower two states(power-law exponent<0.007).The metastable cubic phase is stabilized by yttrium,while the evident reversible cubic-to-hexagonal transition is attributed to the sequential and directional migration of Sb atoms.Finally,the decreased heat dissipation of the material and the increase in crystallinity contribute to the overall high performance.This study opens a new way to achieve advanced multi-level phase-change memory without the need for complicated manufacturing procedures or iterative programming operations.展开更多
Further improvement of storage density is a key challenge for the application of phase-change memory(PCM)in storage-class memory.However,for PCM,storage density improvements include feature size scaling down and multi...Further improvement of storage density is a key challenge for the application of phase-change memory(PCM)in storage-class memory.However,for PCM,storage density improvements include feature size scaling down and multilevel cell(MLC)operation,potentially causing thermal crosstalk issues and phase separation issues,respectively.To address these challenges,we propose a high-aspect-ratio(25:1)lateral nanowire(NW)PCM device with conventional chalcogenide Ge_(2)Sb_(2)Te_(5)(GST-225)to realize stable MLC operations,i.e.,low intra-and inter-cell variability and low resistance drift(coefficient=0.009).The improved MLC performance is attributed to the high aspect ratio,which enables precise control of the amorphous region because of sidewall confinement,as confirmed by transmission electron microscopy analysis.In summary,the NW devices provide guidance for the design of future high-aspect-ratio threedimensional PCM devices with MLC capability.展开更多
Phase-change memory(PCM)has been developed for three-dimensional(3D)data storage devices,posing huge challenges to the thermal stability and reliability of PCM.However,the low thermal stability of Ge2Sb2Te5(GST)limits...Phase-change memory(PCM)has been developed for three-dimensional(3D)data storage devices,posing huge challenges to the thermal stability and reliability of PCM.However,the low thermal stability of Ge2Sb2Te5(GST)limits further application.Here,we demonstrate PCM based on In0.9Ge2Sb2Te5(IGST)alloy,showing 180C 10-years data retention,6 ns set speed,one order of magnitude longer life time,and 75%reduced power consumption compared to GST-based device.The In can occupy the cationic positions and the In-Te octahedrons with good phase-change properties can geometrically match well with the host Ge-Te and Sb-Te octahedrons,acting as nucleation centers to boost the set speed and enhance the endurance of IGST device.Introducing stable matched phase-change octahedrons can be a feasible way to achieve practical PCMs.展开更多
Chalcogenide phase-change materials(PCMs),in particular,the flagship Ge2Sb2Te5(GST),are leading candidates for advanced memory applications.Yet,GST in conventional devices suffer from high power consumption,because th...Chalcogenide phase-change materials(PCMs),in particular,the flagship Ge2Sb2Te5(GST),are leading candidates for advanced memory applications.Yet,GST in conventional devices suffer from high power consumption,because the RESET operation requires melting of the crystalline GST phase.Recently,we have developed a conductive-bridge scheme for low-power phase-change application utilizing a self-decomposed Ge-Sb-O(GSO)alloy.In this work,we present thorough structural and electrical characterizations of GSO thin films by tailoring the concentration of oxygen in the phase-separating GSO system.We elucidate a two-step process in the as-deposited amorphous film upon the introduction of oxygen:with increasing oxygen doping level,germanium oxides form first,followed by antimony oxides.To enable the conductive-bridge switching mode for femtojoule-level RESET energy,the oxygen content should be sufficiently low to keep the antimony-rich domains easily crystallized under external electrical stimulus.Our work serves as a useful example to exploit alloy decomposition that develops heterogeneous PCMs,minimizing the active switching volume for low-power electronics.展开更多
Phase-change line memory cells with different line widths are fabricated using focused-ion-beam deposited C-Pt as a hard mask. The electrical performance of these memory devices was characterized. The current^oltage ...Phase-change line memory cells with different line widths are fabricated using focused-ion-beam deposited C-Pt as a hard mask. The electrical performance of these memory devices was characterized. The current^oltage （I-V） and resistance-voltage （RV） characteristics demonstrate that the power consumption decreases with the width of the phase-change line. A three-dimensional simulation is carried out to further study the scaling properties of the phase- change line memory. The results show that the resistive amorphous （RESET） power consumption is proportional to the cross-sectional area of the phase-change line, but increases as the line length decreases.展开更多
In the design of phase-change memory（PCM）,it is important to perform numerical simulations to predict the performances of different device structures.This work presents a numerical simulation using a coupled system ...In the design of phase-change memory（PCM）,it is important to perform numerical simulations to predict the performances of different device structures.This work presents a numerical simulation using a coupled system including Poisson＇s equation,the current continuity equation,the thermal conductivity equation,and phase-change dynamics to simulate the thermal and electric characteristics of phase-change memory.This method discriminates the common numerical simulation of PCM cells,from which it applies Possion＇s equation and current continuity equations instead of the Laplace equation to depict the electric characteristics of PCM cells,which is more adoptable for the semiconductor characteristics of phase-change materials.The results show that the simulation agrees with the measurement,and the scalability of PCM is predicted.展开更多
By way of periphery circuit design of the phase-change memory,it is necessary to present an accurate compact model of a phase-change memory cell for the circuit simulation.Compared with the present model,the model pre...By way of periphery circuit design of the phase-change memory,it is necessary to present an accurate compact model of a phase-change memory cell for the circuit simulation.Compared with the present model,the model presented in this work includes an analytical conductivity model,which is deduced by means of the carrier transport theory instead of the fitting model based on the measurement.In addition,this model includes an analytical temperature model based on the 1D heat-transfer equation and the phase-transition dynamic model based on the JMA equation to simulate the phase-change process.The above models for phase-change memory are integrated by using Verilog-A language,and results show that this model is able to simulate theⅠ-Ⅴcharacteristics and the programming characteristics accurately.展开更多
An optimized device structure for reducing the RESET current of phase-change random access memory （PCRAM） with blade-type like （BTL） phase change layer is proposed. The electrical thermal analysis of the BTL cell ...An optimized device structure for reducing the RESET current of phase-change random access memory （PCRAM） with blade-type like （BTL） phase change layer is proposed. The electrical thermal analysis of the BTL cell and the blade heater contactor structure by three-dimensional finite element modeling are compared with each other during RESET operation. The simulation results show that the programming region of the phase change layer in the BTL cell is much smaller, and thermal electrical distributions of the BTL cell are more concentrated on the TiN/GST interface. The results indicate that the BTL cell has the superiorities of increasing the heating efficiency, decreasing the power consumption and reducing the RESET current from 0.67mA to 0.32mA. Therefore, the BTL cell will be appropriate for high performance PCRAM device with lower power consumption and lower RESET current.展开更多
The era of information explosion is coming and information need to be continuously stored and randomly accessed over long-term periods,which constitute an insurmountable challenge for existing data centers.At present,...The era of information explosion is coming and information need to be continuously stored and randomly accessed over long-term periods,which constitute an insurmountable challenge for existing data centers.At present,computing devices use the von Neumann architecture with separate computing and memory units,which exposes the shortcomings of“memory bottleneck”.Nonvolatile memristor can realize data storage and in-memory computing at the same time and promises to overcome this bottleneck.Phase-change random access memory(PCRAM)is called one of the best solutions for next generation non-volatile memory.Due to its high speed,good data retention,high density,low power consumption,PCRAM has the broad commercial prospects in the in-memory computing application.In this review,the research progress of phase-change materials and device structures for PCRAM,as well as the most critical performances for a universal memory,such as speed,capacity,and power consumption,are reviewed.By comparing the advantages and disadvantages of phase-change optical disk and PCRAM,a new concept of optoelectronic hybrid storage based on phase-change material is proposed.Furthermore,its feasibility to replace existing memory technologies as a universal memory is also discussed as well.展开更多
Recent years, optically controlled phase-change memory draws intensive attention owing to some advanced applications including integrated all-optical nonvolatile memory, in-memory computing, and neuromorphic computing...Recent years, optically controlled phase-change memory draws intensive attention owing to some advanced applications including integrated all-optical nonvolatile memory, in-memory computing, and neuromorphic computing. The light-induced phase transition is the key for this technology. Traditional understanding on the role of light is the heating effect. Generally, the RESET operation of phase-change memory is believed to be a melt-quenching-amorphization process. However, some recent experimental and theoretical investigations have revealed that ultrafast laser can manipulate the structures of phase-change materials by non-thermal effects and induces unconventional phase transitions including solid-to-solid amorphization and order-to-order phase transitions. Compared with the conventional thermal amorphization,these transitions have potential superiors such as faster speed, better endurance, and low power consumption. This article summarizes some recent progress of experimental observations and theoretical analyses on these unconventional phase transitions. The discussions mainly focus on the physical mechanism at atomic scale to provide guidance to control the phase transitions for optical storage. Outlook on some possible applications of the non-thermal phase transition is also presented to develop new types of devices.展开更多
Si-doped Ge2Sb2Te5 films have been prepared by dc magnetron co-sputtering with Ge2Sb2Te5 and Si targets. The addition of Si in the Ge2Sb2Te5 film results in the increase of both crystallization temperature and phasetr...Si-doped Ge2Sb2Te5 films have been prepared by dc magnetron co-sputtering with Ge2Sb2Te5 and Si targets. The addition of Si in the Ge2Sb2Te5 film results in the increase of both crystallization temperature and phasetransition temperature from face-centred-cubic （fcc） phase to hexagonal （hex） phase. The resistivity of the Ge2Sb2Te5 film shows a significant increase with the Si doping. When doping 11.8 at.% of Si in the film, the resistivity after 460℃ annealing increases from 1 to 11 mΩ.cm and dynamic resistance increase from 64 to 99Ω compared to the undoped Ge2Sb2Te5 film. This is very helpful to writing current reduction of phase-change random access memory.展开更多
基金the support of the National Natural Science Foundation of China(Grant No.62204201)。
文摘In the past decade,there has been tremendous progress in integrating chalcogenide phase-change materials(PCMs)on the silicon photonic platform for non-volatile memory to neuromorphic in-memory computing applications.In particular,these non von Neumann computational elements and systems benefit from mass manufacturing of silicon photonic integrated circuits(PICs)on 8-inch wafers using a 130 nm complementary metal-oxide semiconductor line.Chip manufacturing based on deep-ultraviolet lithography and electron-beam lithography enables rapid prototyping of PICs,which can be integrated with high-quality PCMs based on the wafer-scale sputtering technique as a back-end-of-line process.In this article,we present an overview of recent advances in waveguide integrated PCM memory cells,functional devices,and neuromorphic systems,with an emphasis on fabrication and integration processes to attain state-of-the-art device performance.After a short overview of PCM based photonic devices,we discuss the materials properties of the functional layer as well as the progress on the light guiding layer,namely,the silicon and germanium waveguide platforms.Next,we discuss the cleanroom fabrication flow of waveguide devices integrated with thin films and nanowires,silicon waveguides and plasmonic microheaters for the electrothermal switching of PCMs and mixed-mode operation.Finally,the fabrication of photonic and photonic–electronic neuromorphic computing systems is reviewed.These systems consist of arrays of PCM memory elements for associative learning,matrix-vector multiplication,and pattern recognition.With large-scale integration,the neuromorphic photonic computing paradigm holds the promise to outperform digital electronic accelerators by taking the advantages of ultra-high bandwidth,high speed,and energy-efficient operation in running machine learning algorithms.
基金supported by the National Key Research and Development Program of China(2017YFA0206101,2017YFB0701703,2017YFA0206104,2017YFB0405601,2018YFB0407500)the National Natural Science Foundation of China(91964204,61874178,61874129)+1 种基金the Science and Technology Council of Shanghai(20501120300,18DZ2272800)the Shanghai Sailing Program(19YF1456100).
文摘Phase-change memory(PCM)has considerable promise for new applications based on von Neumann and emerging neuromorphic computing systems.However,a key challenge in harnessing the advantages of PCM devices is achieving high-speed operation of these devices at elevated temperatures,which is critical for the efficient processing and reliable storage of data at full capacity.Herein,we report a novel PCM device based on Ta-doped antimony telluride(Sb2Te),which exhibits both high-speed characteristics and excellent high-temperature characteristics,with an operation speed of 2 ns,endurance of >106 cycles,and reversible switching at 140℃.The high coordination number of Ta and the strong bonds between Ta and Sb/Te atoms contribute to the robustness of the amorphous structure,which improves the thermal stability.Furthermore,the small grains in the three-dimensional limit lead to an increased energy efficiency and a reduced risk of layer segregation,reducing the power consumption and improving the long-term endurance.Our findings for this new Ta-Sb2Te material system can facilitate the development of PCMs with improved performance and novel applications.
文摘Sn-doped Ge2Sb2Te5 thin films deposited on Si（100）/SiO2 substrates by rf magnetron sputtering are investigated by a differential scanning calorimeter, x-ray diffraction and sheet resistance measurement. The crystallization temperatures of the 3.58 at.%, 6.92 at.% and 10.04 at.% Sn-doped Ge2Sb2Te5 thin films have decreases of 5.3, 6.1 and 0.9℃, respectively, which is beneficial to reduce the switching current for the amorphous-to-crystalline phase transition. Due to Sn-doping, the sheet resistance of crystalline Ge2Sb2Te5 thin films increases about 2-10 times, which may be useful to reduce the switching current for the amorphous-to-crystalline phase change. In addition, an obvious decreasing dispersibility for the sheet resistance of Sn-doped Ge2Sb2Te5 thin films in the crystalline state has been observed, which can play an important role in minimizing resistance difference for the phase-change memory cell element arrays.
基金the National Natural Science Foundation of China(52032006)the Basic and Applied Basic Research Foundation of Guangdong(2020B1515120008)+1 种基金the Science and Technology Foundation of Shenzhen(ZDSYS20210623091813040)Shenzhen University 2035 Program for Excellent Research(00000203)。
文摘Embedded phase-change random-access memory(ePCRAM)applications demand superior data retention in amorphous phase-change materials(PCMs).Traditional PCM design strategies have focused on enhancing the thermal stability of the amorphous phase,often at the expense of the crystallization speed.While this approach supports reliable microchip operations,it compromises the ability to achieve rapid responses.To address this limitation,we modified ultrafast-crystallizing Sb thin films by incorporating Sc dopants,achieving the highest 10-year retention temperature(~175℃)among binary antimonide PCMs while maintaining a sub-10-ns SET operation speed.This reconciliation of two seemingly contradictory properties arises from the unique kinetic features of the 5-nm-thick Sc12Sb88 films,which exhibit an enlarged fragile-to-strong crossover in viscosity at medium supercooled temperature zones and an incompatible sublattice ordering behavior between the Sc and Sb atoms.By tailoring the crystallization kinetics of PCMs through strategic doping and nanoscale confinement,we provide new opportunities for developing robust yet swift ePCRAMs.
基金financially supported by a National Research Foundation of Korea(NRF)grant funded by the Korean government(No.2016R1A3B1908249,RS202400407199).
文摘Although phase-change random-access memory(PCRAM)is a promising next-generation nonvolatile memory technology,challenges remain in terms of reducing energy consumption.This is primarily be-cause the high thermal conductivities of phase-change materials(PCMs)promote Joule heating dissi-pation.Repeated phase transitions also induce long-range atomic diffusion,limiting the durability.To address these challenges,phase-change heterostructure(PCH)devices that incorporate confinement sub-layers based on transition-metal dichalcogenide materials have been developed.In this study,we engi-neered a PCH device by integrating HfTe_(2),which has low thermal conductivity and excellent stability,into the PCM to realize PCRAM with enhanced thermal efficiency and structural stability.HEAT sim-ulations were conducted to validate the superior heat confinement in the programming region of the HfTe_(2)-based PCH device.Moreover,electrical measurements of the device demonstrated its outstanding performance,which was characterized by a low RESET current(∼1.6 mA),stable two-order ON/OFF ratio,and exceptional cycling endurance(∼2×10^(7)).The structural integrity of the HfTe_(2)confinement sub-layer was confirmed using X-ray photoelectron spectroscopy and transmission electron microscopy.The material properties,including electrical conductivity,cohesive energy,and electronegativity,substantiated these findings.Collectively,these results revealed that the HfTe_(2)-based PCH device can achieve significant improvements in performance and reliability compared with conventional PCRAM devices.
基金funded by the Natural Science Foundation of Heilongjiang Province,China(Grant No.PL2024E027)。
文摘The Gasbag Phase-change Carbon Dioxide Energy Storage System leverages elastic gasbags to store carbon dioxide under varying geographical conditions.This approach utilizes the phase-change sensible heat effect to efficiently manage energy storage and release.This technology requires lower pressure and temperature control,resulting in reduced energy consumption and improved efficiency.Additionally,it is less restricted by geographical factors to a certain extent,enabling the formation of a closed-loop system.This contributes to the development of new energy utilization systems.The article examines and compares two experimental energy storage projects employing elastic gasbags to maintain a constant pressure supply of carbon dioxide on the low-pressure side.It further details the precise calculation methods for system cycle efficiency and energy storage density while analyzing energy losses incurred during the storage and release phases.Finally,an economic analysis is conducted using specific data,demonstrating that optimizing temperature and pressure parameters at various nodes enhances overall system efficiency while reducing energy consumption.Furthermore,the study highlights the system's high sensitivity to grid electricity prices.This research is anticipated to contribute to the development of more efficient and reliable energy storage solutions for power systems,addressing the growing energy demands and sustainability challenges.
基金supported by the Beijing Natural Science Foundation(Grant No.:2242049)。
文摘To address the limitations of conventional energy systems and optimize the energy conversion pathways and efficiency,a type of“five-in-one”multifunctional phase-change composite with magnetothermal,electrothermal,solar-thermal,and thermoelectric energy conversion and electromagnetic shielding functions is developed for multipurpose applications.Such a novel phase-change composite is fabricated by an innovative combination of paraffin wax(PW)as a phase-change material and a carbonized polyimide/Kevlar/graphene oxide@ZIF-67 complex aerogel as a supporting material.The carbonized complex aerogel exhibits a unique bidirectional porous structure with high porosity and robust skeleton to support the loading of PW.The reduced graphene oxide and Co NC resulting from high-temperature carbonization are anchored on the aerogel skeleton to generate high thermal conduction and magnetic effect,enhancing the phonon and electron transfer of the aerogel and improving its energy conversion efficiency.The phase-change composite not only exhibits excellent solar-thermal,thermoelectric,electrothermal,and magnetothermal energy conversion performance,but also achieves high electromagnetic interference shielding effectiveness of 66.2 d B in the X-band.The introduction of PW significantly improves the thermal energy-storage capacity during multi-energy conversion.The developed composite exhibits great application potential for efficient solar energy utilization,sustainable power generation,outdoor deicing,human thermal therapy,and electronic device protection.
基金Supported by the National Natural Science Foundation of China(NSFC)Major Project(51991362).
文摘Considering the three typical phase-change related rock mechanics phenomena during drilling and production in oil and gas reservoirs,which include phase change of solid alkane-related mixtures upon heating,sand liquefaction induced by sudden pressure release of the over-pressured sand body,and formation collapse due to gasification of pore fillings from pressure reduction,this study first systematically analyzes the progress of theoretical understanding,experimental methods,and mathematical representation,then discusses the engineering application scenarios corresponding to the three phenomena and reveals the mechanical principles and application effectiveness.Based on these research efforts,the study further discusses the significant challenges,potential developmental trends,and research approaches that require urgent exploration.The findings disclose that various phase-related rock mechanics phenomena require specific experimental and mathematical methods that can produce multi-field coupling mechanical mechanisms,which will eventually instruct the control on resource exploitation,evaluation on disaster level,and analysis of formation stability.To meet the development needs of the principle,future research efforts should focus on mining more phase-change related rock mechanics phenomena during oil and gas resources exploitation,developing novel experimental equipment,and using techniques of artificial intelligence and digital twins to implement real-time simulation and dynamic visualization of phase-change related rock mechanics.
基金support of National Natural Science Foundation of China(61774123)support of National Natural Science Foundation of China(52150710545)+4 种基金support of their work at CAID.J.-J.W.and M.W.acknowledges financial support from Alexander von Humboldt Foundationfunding from Deutsche Forschungsgemeinschaft within SFB 917“Nanoswitches”support of 111 Project 2.0(BP2018008)the International Joint Laboratory for Micro/Nano Manufacturing and Measurement Technologies of Xi'an Jiaotong Universityprovided by the HPC platform of Xi'an Jiaotong University and the Hefei Advanced Computing Center,and the National Supercomputing Center in Xi'an.
文摘Tailoring the degree of structural disorder in Ge-Sb-Te alloys is important for the development of non-volatile phase-change memory and neuro-inspired computing.Upon crystallization from the amorphous phase,these alloys form a cubic rocksalt-like structure with a high content of intrinsic vacancies.Further thermal annealing results in a gradual structural transition towards a layered structure and an insulator-to-metal transition.In this work,we elucidate the atomic-level details of the structural transition in crystalline GeSb_(2)Te_(4) by in situ high-resolution transmission electron microscopy experiments and ab initio density functional theory calculations,providing a comprehensive real-time and real-space view of the vacancy ordering process.We also discuss the impact of vacancy ordering on altering the electronic and optical properties of GeSb_(2)Te_(4),which is relevant to multilevel storage applications.The phase evolution paths in Ge-Sb-Te alloys and Sb_(2)Te_(3)are illustrated using a summary diagram,which serves as a guide for designing phase-change memory devices.
基金the National Key Research and Development Program of China(2017YFB0701700)the National Natural Science Foundation of China(51872017)the High-Performance Computing(HPC)Resources at Beihang University。
文摘By controlling the amorphous-to-crystalline relative volume,chalcogenide phase-change memory materials can provide multi-level data storage(MLS),which offers great potential for high-density storageclass memory and neuro-inspired computing.However,this type of MLS system suffers from high power consumption and a severe time-dependent resistance increase(‘‘drift")in the amorphous phase,which limits the number of attainable storage levels.Here,we report a new type of MLS system in yttriumdoped antimony telluride,utilizing reversible multi-level phase transitions between three states,i.e.,amorphous,metastable cubic and stable hexagonal crystalline phases,with ultralow power consumption(0.6–4.3 p J)and ultralow resistance drift for the lower two states(power-law exponent<0.007).The metastable cubic phase is stabilized by yttrium,while the evident reversible cubic-to-hexagonal transition is attributed to the sequential and directional migration of Sb atoms.Finally,the decreased heat dissipation of the material and the increase in crystallinity contribute to the overall high performance.This study opens a new way to achieve advanced multi-level phase-change memory without the need for complicated manufacturing procedures or iterative programming operations.
基金supported by the National Natural Science Foundation of China(62174065)the Key Research and Development Plan of Hubei Province(2020BAB007)+1 种基金Hubei Provincial Natural Science Foundation(2021CFA038)the support from Hubei Key Laboratory of Advanced Memories&Hubei Engineering Research Center on Microelectronics。
文摘Further improvement of storage density is a key challenge for the application of phase-change memory(PCM)in storage-class memory.However,for PCM,storage density improvements include feature size scaling down and multilevel cell(MLC)operation,potentially causing thermal crosstalk issues and phase separation issues,respectively.To address these challenges,we propose a high-aspect-ratio(25:1)lateral nanowire(NW)PCM device with conventional chalcogenide Ge_(2)Sb_(2)Te_(5)(GST-225)to realize stable MLC operations,i.e.,low intra-and inter-cell variability and low resistance drift(coefficient=0.009).The improved MLC performance is attributed to the high aspect ratio,which enables precise control of the amorphous region because of sidewall confinement,as confirmed by transmission electron microscopy analysis.In summary,the NW devices provide guidance for the design of future high-aspect-ratio threedimensional PCM devices with MLC capability.
基金Genetic Engineering of Precious Metal Materials in Yunnan Province(I)-Construction and Application of Precious Metal Materials Professional Database(I),Grant/Award Number:202002AB080001-1National Natural Science Foundation of China,Grant/Award Numbers:91964204,61874129,61874178,61904189+2 种基金Science and Technology Council of Shanghai,Grant/Award Numbers:20501120300,18DZ2272800Shanghai Sailing Program,Grant/Award Number:19YF1456100the National Key Research and Development Program of China,Grant/Award Numbers:2017YFA0206101,2018YFB0407500。
文摘Phase-change memory(PCM)has been developed for three-dimensional(3D)data storage devices,posing huge challenges to the thermal stability and reliability of PCM.However,the low thermal stability of Ge2Sb2Te5(GST)limits further application.Here,we demonstrate PCM based on In0.9Ge2Sb2Te5(IGST)alloy,showing 180C 10-years data retention,6 ns set speed,one order of magnitude longer life time,and 75%reduced power consumption compared to GST-based device.The In can occupy the cationic positions and the In-Te octahedrons with good phase-change properties can geometrically match well with the host Ge-Te and Sb-Te octahedrons,acting as nucleation centers to boost the set speed and enhance the endurance of IGST device.Introducing stable matched phase-change octahedrons can be a feasible way to achieve practical PCMs.
基金The authors thank Miss Dan He and Miss Chenyu Liang at Instrument Analysis Center of Xi’an Jiaotong University for their assistance with Raman and XPS measurements.E M acknowledges the National Natural Science Foundation of China(Grant No.52150710545)The authors acknowledge the 111 project 2.0(BP2018008)the International Joint Laboratory for Micro/Nano Manufacturing and Measurement Technologies of XJTU.W Z and E M also acknowledge the support of XJTU for their work at CAID.X M acknowledges the National Natural Science Foundation of China(Grant No.62174060)and the funding for Hubei Key Laboratory of Advanced Memories.
文摘Chalcogenide phase-change materials(PCMs),in particular,the flagship Ge2Sb2Te5(GST),are leading candidates for advanced memory applications.Yet,GST in conventional devices suffer from high power consumption,because the RESET operation requires melting of the crystalline GST phase.Recently,we have developed a conductive-bridge scheme for low-power phase-change application utilizing a self-decomposed Ge-Sb-O(GSO)alloy.In this work,we present thorough structural and electrical characterizations of GSO thin films by tailoring the concentration of oxygen in the phase-separating GSO system.We elucidate a two-step process in the as-deposited amorphous film upon the introduction of oxygen:with increasing oxygen doping level,germanium oxides form first,followed by antimony oxides.To enable the conductive-bridge switching mode for femtojoule-level RESET energy,the oxygen content should be sufficiently low to keep the antimony-rich domains easily crystallized under external electrical stimulus.Our work serves as a useful example to exploit alloy decomposition that develops heterogeneous PCMs,minimizing the active switching volume for low-power electronics.
基金Project supported by the National Integrate Circuit Research Program of China (Grant No. 2009ZX02023-003)the National Key Basic Research Program of China (Grant Nos. 2010CB934300, 2011CBA00602, and 2011CB932800)+1 种基金the National Natural Science Foundation of China (Grant Nos. 60906003, 60906004, 61006087, and 61076121)the Science and Technology Council of Shanghai of China (Grant No. 1052nm07000)
文摘Phase-change line memory cells with different line widths are fabricated using focused-ion-beam deposited C-Pt as a hard mask. The electrical performance of these memory devices was characterized. The current^oltage （I-V） and resistance-voltage （RV） characteristics demonstrate that the power consumption decreases with the width of the phase-change line. A three-dimensional simulation is carried out to further study the scaling properties of the phase- change line memory. The results show that the resistive amorphous （RESET） power consumption is proportional to the cross-sectional area of the phase-change line, but increases as the line length decreases.
基金supported by the National Natural Science Foundation of China(No.61176099)the Open Project of the State Key Laboratory of Functional Materials for Informatics,China
文摘In the design of phase-change memory（PCM）,it is important to perform numerical simulations to predict the performances of different device structures.This work presents a numerical simulation using a coupled system including Poisson＇s equation,the current continuity equation,the thermal conductivity equation,and phase-change dynamics to simulate the thermal and electric characteristics of phase-change memory.This method discriminates the common numerical simulation of PCM cells,from which it applies Possion＇s equation and current continuity equations instead of the Laplace equation to depict the electric characteristics of PCM cells,which is more adoptable for the semiconductor characteristics of phase-change materials.The results show that the simulation agrees with the measurement,and the scalability of PCM is predicted.
基金supported by the National Natural Science Foundation of China(Nos.61176099,61006032,60925015)
文摘By way of periphery circuit design of the phase-change memory,it is necessary to present an accurate compact model of a phase-change memory cell for the circuit simulation.Compared with the present model,the model presented in this work includes an analytical conductivity model,which is deduced by means of the carrier transport theory instead of the fitting model based on the measurement.In addition,this model includes an analytical temperature model based on the 1D heat-transfer equation and the phase-transition dynamic model based on the JMA equation to simulate the phase-change process.The above models for phase-change memory are integrated by using Verilog-A language,and results show that this model is able to simulate theⅠ-Ⅴcharacteristics and the programming characteristics accurately.
基金Supported by the Strategic Priority Research Program of the Chinese Academy of Sciences under Grant No XDA09020402the National Integrate Circuit Research Program of China under Grant No 2009ZX02023-003+1 种基金the National Natural Science Foundation of China under Grant Nos 61261160500,61376006,61401444 and 61504157the Science and Technology Council of Shanghai under Grant Nos 14DZ2294900,15DZ2270900 and 14ZR1447500
文摘An optimized device structure for reducing the RESET current of phase-change random access memory （PCRAM） with blade-type like （BTL） phase change layer is proposed. The electrical thermal analysis of the BTL cell and the blade heater contactor structure by three-dimensional finite element modeling are compared with each other during RESET operation. The simulation results show that the programming region of the phase change layer in the BTL cell is much smaller, and thermal electrical distributions of the BTL cell are more concentrated on the TiN/GST interface. The results indicate that the BTL cell has the superiorities of increasing the heating efficiency, decreasing the power consumption and reducing the RESET current from 0.67mA to 0.32mA. Therefore, the BTL cell will be appropriate for high performance PCRAM device with lower power consumption and lower RESET current.
基金the National Natural Science Foundation of China(Grant Nos.21773291,61904118,and 22002102)the Natural Science Foundation of Jiangsu Province,China(Grant Nos.BK20190935 and BK20190947)+3 种基金the Natural Science Foundation of the Jiangsu Higher Education Institutions of China(Grant Nos.19KJA210005,19KJB510012,19KJB120005,and 19KJB430034)the Fund from the Suzhou Key Laboratory for Nanophotonic and Nanoelectronic Materials and Its Devices(Grant No.SZS201812)the Science Fund from the Jiangsu Key Laboratory for Environment Functional Materialsthe State Key Laboratory of Transducer Technology,Shanghai Institute of Microsystem and Information Technology,Chinese Academy of Sciences.
文摘The era of information explosion is coming and information need to be continuously stored and randomly accessed over long-term periods,which constitute an insurmountable challenge for existing data centers.At present,computing devices use the von Neumann architecture with separate computing and memory units,which exposes the shortcomings of“memory bottleneck”.Nonvolatile memristor can realize data storage and in-memory computing at the same time and promises to overcome this bottleneck.Phase-change random access memory(PCRAM)is called one of the best solutions for next generation non-volatile memory.Due to its high speed,good data retention,high density,low power consumption,PCRAM has the broad commercial prospects in the in-memory computing application.In this review,the research progress of phase-change materials and device structures for PCRAM,as well as the most critical performances for a universal memory,such as speed,capacity,and power consumption,are reviewed.By comparing the advantages and disadvantages of phase-change optical disk and PCRAM,a new concept of optoelectronic hybrid storage based on phase-change material is proposed.Furthermore,its feasibility to replace existing memory technologies as a universal memory is also discussed as well.
基金Project supported by the National Natural Science Foundation of China(Grant Nos.61922035 and 11904118)
文摘Recent years, optically controlled phase-change memory draws intensive attention owing to some advanced applications including integrated all-optical nonvolatile memory, in-memory computing, and neuromorphic computing. The light-induced phase transition is the key for this technology. Traditional understanding on the role of light is the heating effect. Generally, the RESET operation of phase-change memory is believed to be a melt-quenching-amorphization process. However, some recent experimental and theoretical investigations have revealed that ultrafast laser can manipulate the structures of phase-change materials by non-thermal effects and induces unconventional phase transitions including solid-to-solid amorphization and order-to-order phase transitions. Compared with the conventional thermal amorphization,these transitions have potential superiors such as faster speed, better endurance, and low power consumption. This article summarizes some recent progress of experimental observations and theoretical analyses on these unconventional phase transitions. The discussions mainly focus on the physical mechanism at atomic scale to provide guidance to control the phase transitions for optical storage. Outlook on some possible applications of the non-thermal phase transition is also presented to develop new types of devices.
文摘Si-doped Ge2Sb2Te5 films have been prepared by dc magnetron co-sputtering with Ge2Sb2Te5 and Si targets. The addition of Si in the Ge2Sb2Te5 film results in the increase of both crystallization temperature and phasetransition temperature from face-centred-cubic （fcc） phase to hexagonal （hex） phase. The resistivity of the Ge2Sb2Te5 film shows a significant increase with the Si doping. When doping 11.8 at.% of Si in the film, the resistivity after 460℃ annealing increases from 1 to 11 mΩ.cm and dynamic resistance increase from 64 to 99Ω compared to the undoped Ge2Sb2Te5 film. This is very helpful to writing current reduction of phase-change random access memory.
