Fabrication and integration of photonic devices for phase-change memory and neuromorphic computing

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.

Research on microcapsules of phase change materials

Microcapsule technology is a kind of technology wrapping the solid or liquid into minute-sized particles within the field of micrometer or millimeter with film forming materials. This thesis introduces microcapsule technology of phase change materials and its main functions and the structural composition, preparation methods and characterization technology of microcapsule of phase change materials. The microcapsule of phase change materials is small in size and its temperature remains unchanged during the process of heat absorption and heat release. It is of great value in research and application prospect due to these characteristics.

Universal memory based on phase-change materials:From phase-change random access memory to optoelectronic hybrid storage

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.

Paraffin/SiC as a Novel Composite Phase-Change Material for a Lithium-Ion Battery Thermal Management System

A lithium-ion battery thermal management system has always been a hot spot in the battery industry. In this study, a novel high-thermal-conductivity composite phase-change material(CPCM) made by paraffin wax and silicon was adopted to facilitate heat transfer. Moreover, high resistance or even insulation of CPCM is capable of preventing short circuits between the cells. The heat transfer mechanism of CPCMs was determined under a scanning electron microscope. A thermogravimetric analyzer was employed to determine the thermal stability. A diff erential scanning calorimeter was used to explore the thermophysical properties of the composite samples. By comparing the results of the experiment, it was reported that under the silicon carbide content of 5%, the parameters were better than others. The phase-change enthalpy of CPCM was 199.4 J/g, the leakage rate of liquid was 4.6%, and the melting point was 53.6℃. To verify the practicality of CPCM, a three-dimensional layered battery pack model was built in the COMSOL Multiphysics software. By simulating the thermal runaway inside the battery packs of various materials, it was reported that the addition of CPCM significantly narrowed the temperature range of the battery pack from 300–370 to 303–304 K. Therefore, CPCM can eff ectively increase the rate of heat transfer to prevent the chain of thermal runaway reactions. It also enables the battery pack to run at a stable temperature.

Design of broadband achromatic metasurface device based on phase-change material Ge_(2)Sb_(2)Te_(5)

Based on the phase-change material Ge_(2)Sb_(2)Te_(5)(GST),achromatic metasurface optical device in the longer-infrared wavelength is designed.With the combination of the linear phase gradient GST nanopillar and the adjustment of the crystalline fraction m value of GST,the polarization insensitive achromic metalenses and beam deflector metasurface within the longer-infrared wavelength 9.5μm to 13μm are realized.The design results show that the achromatic metalenses can be focused on the same focal plane within the working waveband.The simulation calculation results show that the fullwidth at half-maximum(FWHM)of the focusing spot reaches the diffraction limit at each wavelength.In addition,the same method is also used to design a broadband achromatic beam deflector metasurface with the same deflection angle of 19°.The method proposed in this article not only provides new ideas for the design of achromatic metasurfaces,but also provides new possibilities for the integration of optical imaging,optical coding and other related optical systems.

An artificial synapse by superlattice-like phase-change material for low-power brain-inspired computing

Phase-change material(PCM)is generating widespread interest as a new candidate for artificial synapses in bioinspired computer systems.However,the amorphization process of PCM devices tends to be abrupt,unlike continuous synaptic depression.The relatively large power consumption and poor analog behavior of PCM devices greatly limit their applications.Here,we fabricate a GeTe/Sb2Te3 superlattice-like PCM device which allows a progressive RESET process.Our devices feature low-power consumption operation and potential high-density integration,which can effectively simulate biological synaptic characteristics.The programming energy can be further reduced by properly selecting the resistance range and operating method.The fabricated devices are implemented in both artificial neural networks(ANN)and convolutional neural network(CNN)simulations,demonstrating high accuracy in brain-like pattern recognition.

Melting and Solidification Heat Transfer Characteristics of a Phase-Change Material in a Latent Heat Storage Vessel: Effects of a Perforated Partition Plate and Metal Fiber

Today, latent heat storage technology has advanced to allow reuse of waste heat in the middle-temperature range. This paper describes an approach to develop a latent heat storage system using middle-temperature waste heat (~100oC - 200oC) from factories. Direct contact melting and solidification behavior between a heat-transfer fluid (oil) and a latent heat storage material mixture were observed. The mixture consisted of mannitol and erythritol (Cm = 70 mass %, Ce = 30 mass %) as a phase-change material (PCM). The weight of the PCM was 3.0 kg and the flow rate of the oil, foil, was 1.0, 1.5, or 2.0 kg/min. To decrease the solidified height of the PCM mixture during the solidification process, a perforated partition plate was installed in the PCM region in the heat storage vessel. PCM coated oil droplets were broken by the perforated partition plate, preventing the solidified height of the PCM from increasing. The solidification and melting processes were repeated using metal fiber. It was found that installing the metal fiber was more effective than installing the perforated partition plate to prevent the flow out problem of the PCM.

Preparation of Microcapsules Containing Triple Core Materials with Interfacial Condensation Reaction

In this manuscript, we describe the novel method for preparing the microcapsules containing α-tocopherol oil droplets as the first core material, calcium chloride powder as the second core material and the fine water droplets as the third core material by the interfacial condensation reaction between hydroxyl propyl methyl cellulose and tannic acid. The interfacial condensation reaction was performed between hydroxyl propyl methyl cellulose dissolved in the continuous water phase and tannic acid dissolved in the inner fine water droplets as the third core material. The calcium chloride powder as the second core material was dispersed in the α-tocopherol oil droplet as the first core material beforehand. The α-tocopherol oil containing the second and the third core materials was dispersed in the continuous water phase to form the [(S + W)/O/W] emulsion. The α-tocopherol oil as the first core material was microencapsulated satisfactorily and the contents of the second core material were increased with the concentration of stearic acid as the oil soluble stabilizer. The mechanical strength of microcapsules increased with the concentration of hydroxyl propyl methyl cellulose. Thermal energy could be released by breaking the microcapsules in water and by dissolving calcium chloride in the continuous water phase.

Photothermal phase change material microcapsules via cellulose nanocrystal and graphene oxide co-stabilized Pickering emulsion for solar and thermal energy storage

Phase change materials(PCMs)have attracted significant attention in thermal management due to their ability to store and release large amounts of heat during phase transitions.However,their widespread application is restricted by leakage issues.Encapsulating PCMs within polymeric microcapsules is a promising strategy to prevent leakage and increase heat transfer area with matrices.Moreover,photothermal PCM microcapsules are particularly desirable for solar energy storage.Herein,we fabricated photothermal PCM microcapsules with melamine-formaldehyde resin(MF)as shell using cellulose nanocrystal(CNC)and graphene oxide(GO)co-stabilized Pickering emulsion droplets as templates.CNC displays outstanding Pickering emulsifying ability and can facilitate the fixation of GO at the oil-water interface,resulting in a stable CNC/GO co-stabilized PCM Pickering emulsion.A polydopamine(PDA)layer was coated in-situ on the emulsion droplets via oxidization self-polymerization of dopamine.Meanwhile,GO was reduced to reduced GO(rGO)due to the reducing ability of PDA.The outmost MF shell of the PCM microcapsules was formed in-situ through the polymerization and crosslinking of MF prepolymer.The resulted PCM@CNC/rGO/PDA/MF microcapsules exhibit uniform sizes in the micrometer range,excellent leakage-proof performance,high phase change enthalpy(175.4 J g^(−1))and PCM encapsulation content(84.2%).Moreover,the presence of rGO and PDA endows PCM@CNC/rGO/PDA/MF microcapsules with outstanding photothermal conversion performance.The temperature of PCM@CNC/rGO/PDA/MF microcapsule slurries(15wt.%)can reach 73°C after light irradiation at 1 W cm^(−2).Therefore,photothermal PCM@CNC/rGO/PDA/MF microcapsules are promising for solar energy harvesting,thermal energy storage,and release in various applications,such as energy-efficient buildings and smart textiles.

Experimental Investigation of a Phase-ChangeMaterial’s Stabilizing Role in a Pilot of Smart Salt-Gradient Solar Ponds

Faced with the world’s environmental and energy-related challenges,researchers are turning to innovative,sustainable and intelligent solutions to produce,store,and distribute energy.This work explores the trend of using a smart sensor to monitor the stability and efficiency of a salt-gradient solar pond.Several studies have been conducted to improve the thermal efficiency of salt-gradient solar ponds by introducing other materials.This study investigates the thermal and salinity behaviors of a pilot of smart salt-gradient solar ponds with(SGSP)and without(SGSPP)paraffin wax(PW)as a phase-change material(PCM).Temperature and salinity were measured experimentally using a smart sensor,with the measurements being used to investigate the stabilizing effects of placing the PCM in the solar pond’s lower convective zone.The experimental results show that the pond with the PCM(SGSPP)achieved greater thermal and salinity stability,with there being a lesser temperature and salinity gradient between the different layers when compared to a solar pond without thePCM(SGSP).The use of the PCM,therefore,helped control the maximum and minimum temperature of the pond’s storage zone.The UCZ has been found to operate approximately 4 degrees above the average ambient temperature of the day in the SGSPP and 7 degrees in SGSP.Moreover,an unstable situation is generated after 5 days from starting the operation and at 1.9 m from the bottom,and certain points have the tendency to be neutral from the upper depths in 1,3 m of the bottom.

Study on the Heat Conduction of Phase-Change Material Microcapsules

The 3ω approach was used to measure the effective thermal conductivity of phase-change material microcapsules (PCMMs) based on urea formaldehyde and sliced paraffin. The effective thermal conductivities of PCMMs with different densities were measured within the phase-change temperature range. The relationships between effective thermal conductivity, density and temperature were analysed. The effective thermal conductivity reached peak values within the phase-change temperature range and the temperature peak value was consistent with the peak value of the phase-change temperature. The effective thermal conductivity increased with increasing density due to the decreased porosity of samples and their increased solid-phase conduction.

Preparation and Characterization of Poly(melamine-urea-formaldehyde) Tetradecanol Microcapsules Coated with Silver Particles

A novel type of microencapsulated phase change materials(microPCMs)based on 1-tetradecanol(TD)core and silver-coated poly(melamine-urea-formaldehyde)(MUF)shell was successfully synthesized by in situ polymerization method followed by silver reduction.Fourier-transform infrared spectroscopy(FTIR),X-ray diffraction(XRD),scanning electron microscopy with energy dispersive X-ray spectrometry(SEM/EDS),thermogravimetric analysis(TGA)and differential scanning calorimetry(DSC)were used to characterize the chemical structure,morphology and thermal properties of the as-prepared silver-coated microPCMs.FTIR analysis confirmed the successful encapsulation of TD with MUF wall materials.The SEM and EDS results indicated that the prepared silver-coated MUF microPCMs exhibited uniform spherical shape with a perfect silver outer layer.From XRD analysis,the Ag metal dispersed on the surface of microcapsules presented the form of elementary substance.The deposition weight of silver particles on the microcapsule surface increased with increasing the amount of silver nitrate,as indicated by EDS tests.The DSC results indicated that the melting temperature and the melting latent heat of microPCMs modified with 0.7g of silver nitrate in 150mL aqueous solution were 39.2°C and 126.6J·g^-1,respectively.Supercooling of the microPCMs coated with silver particles was effectively suppressed,compared with that of microPCMs without Ag.Thus,the encapsulation of TD with silver-coated MUF shell developed by this work can be an effective method to prepare the microPCMs with enhanced thermal transfer performance and phase change properties.

The Application of Microcapsule in the Infrared Stealth Camouflage

Infrared radiation is one of the main exposure symptoms of military targets. Infrared radiation differences between targets and backgrounds should be eliminated to the greatest extent to fight against all kinds of infrared reconnaissance. In addition to the employment of the camouflage paint with low emissivity, reducing the surface temperature of targets is an urgent and difficult challenge. PCM (phase-change material) can be used to effectively solve this problem. The application of microcapsule in the infrared stealth materials greatly promotes the development of infrared stealth technology.

Electrochemical behavior of different shelled microcapsule composite copper coatings

Copper/liquid microcapsule composite coatings with polyvinyl alcohol （PVA）, gelatin or methyl cellulose （MC） as shell materials were prepared by electrodeposition. The influence of shell materials on the corrosion resistance of the composite coatings in 0.1 M H2SO4 was investigated by means of electrochemical techniques, scanning electron microscopy （SEM）, and energy dispersion spectrometry （EDS）. The results show that the participation of microcapsules can enhance the corrosion resistance of the composite coatings compared with the traditional copper layer. Based on the analysis of electrochemical test results, the release ways of microcapsules were deduced. Gelatin and MC as the shell materials of microcapsules are easy to release quickly in the composite coating. On the contrary, the releasing speed of PVA microcapsules is relatively slow due to their characteristics.

Characteristics of Self-Healing Microcapsules for Cementitious Composites

Urea formaldehyde/epoxy resin microcapsules were prepared by an in situ polymerization method and the effect of emulsifier on the syntheses process of the microcapsules was discussed. The surface morphology of the microcapsules was observed by optical microscopy and scanning electron microscopy（SEM）. Chemical structure was characterized by Fourier transform infrared spectroscopy（FTIR）. Thermal stability was obtained using simultaneous thermal analysis（STA）. The microcapsules were composed of urea-formaldehyde resin shell and epoxy resin core. Emulsifier played an important role in the polymerization process when the core material was packed by pre-polymer, so the effects of different emulsifiers（OP-10, SDS and SDBS） were discussed respectively. Results showed that the particle size of the microcapsules was uniform when SDBS as an emulsifier. Microcapsules showed good thermal stability below 240 ℃ and the initial decomposition temperature of the microcapsules was 265 ℃. The core materials released after microcapsules rupturing, which could be proven by the images of SEM. When implanted in cementitious composites, complete shape of microcapsules and good interface between microcapsules and cement specimen substrate could also be observed.

Preparation of Microcapsules Containing Erythritol with Interfacial Polycondensation Reaction by Using the (W/O) Emulsion

It was tried to microencapsulate erythritol as a phase change material with the interfacial polycondensation reaction method by using the (W/O) emulsion and to characterize the microcapsules prepared. In the experiment, toluene diisocyanate, diphenyl methane diisocyanate and hexamethylenediisocyanate were used to form the polyurethane shell and the effects of them on the heat storage density and the microencapsulation efficiency were investigated. Furthermore, the effect of supercooling prevention agent on the phase change behavior of erythritol was investigated. The microcapsules prepared with toluendiisocyanate monomer showed the highest heat storage density and the higher microencapsulation efficiency. Considerable supercooling phenomenon in the microcapsule was observed and prevented to a certain degree by addition of potassium dihydrogen phosphate and calcium sulfate as the supercooling prevention agent.

Research Status and Development Direction of Smart Clothing Materials

With the continuous development of technology and society, smart devices have filled people’s lives and become an indispensable part of people’s lives. At the same time, smart clothing has also been greatly developed. This article introduces several smart clothing materials, analyzes the current research status of smart clothing materials, and further discusses the applications of smart clothing materials in military, medical, intelligent decoration, and sports and leisure fields. Then the problems of smart clothing in safety, environmental protection, and industrial technology are analyzed, and the corresponding solutions to these problems are proposed, so as to provide reference and guidance for the future development of smart clothing in China. And the research shows that smart clothing will develop in the direction of fashion and diversification, function and comfort, safety and environmental protection, convenience and low cost in the future.

Preparation and characterization of silica microcapsules containing butyl-stearate via sol-gel method

For thermal energy storage application in energy-saving building materials,silica microcapsules containing phase change material were prepared using sol-gel method in O/W emulsion system. In the system droplets in microns are formed by emulsifying an organic phase consisting of butyl-stearate as core material. The silica shell was formed via hydrolysis and condensation from tetraethyl silicate with acetate as catalyst. The SEM photographs show the particles possess spherical morphology and core-shell structure. The as-prepared silica microcapsules mainly consist of microsphere in the diameter of 3-7 μm and the median diameter of these microcapsules equals to 5.2 μm. The differential scanning calorimetry(DSC) curves indicate that the latent heat and the melting point of microcapsules are 86 J/g and 22.6 ℃,respectively. The results of DSC and TG further testify the microcapsules with core-shell structure.

Preparation and Characterization of Poly(divinylbenzene) Microcapsules Containing Octadecane

Poly(divinylbenzene) (PDVB) microcapsules containing octadecane (OD) (PDVB/OD) used as heat storage material were synthesized by suspension polymerization at 70 Microencapsulation, Microcapsule, Heat Storage Material, Octadecane, Suspension Polymerization, Poly(Divinylbenzene)C using benzoyl peroxide and polyvinyl alcohol as initiator and stabilizer, respectively. Thermal properties and stability of PDVB/OD microcapsules were determined using differential scanning calorimeter (DSC) and thermogravimetric analyzer. The morphology and structure of microcapsules were characterized by optical microscope, scanning electron microscope and fourier transform infrared spectrophotometer. From DSC analysis, the melting temperature of encapsulated OD (28oC) was almost the same as that of bulk OD (30oC) while it was quite different in the case of the solidification temperature (19oC and 25oC for encapsulated and bulk OD, respectively). The latent heats of melting (184.0 J/g-OD) and solidification (183.2 J/g-OD) of encapsulated OD were reduced from those of bulk OD (241.7 and 247.0 J/g, respectively). However, the prepared PDVB/OD microcapsules are able to be used for heat storage applications.

不同壁材对ARA微胶囊理化性质和稳定性的影响

为了筛选更优的壁材包埋花生四烯酸(arachidonic acid, ARA),该研究以ARA为芯材,乳清蛋白(whey protein, W)、乳清蛋白-葡萄糖浆(whey protein-glucose syrup, WG)和乳清蛋白-葡萄糖浆-乳糖(whey protein-glucose syrup-lactose, WGL)为壁材制备微胶囊,并对ARA微胶囊的包埋率、含水率、溶解度、堆积密度、休止角、粒径分布、微观形貌和氧化稳定性及热稳定性进行比较分析。结果表明,WGL的包埋率为98.64%,含水率为2.85%,溶解度为89.83%,堆积密度为0.54 g/mL,休止角为35.87°,粒径分布较均匀,其理化性质优于W和WG;表面结构呈完整球形、结构致密,有利于微胶囊的贮藏;采用碘滴定法测定过氧化值,在25和50℃贮藏条件下WGL的过氧化值分别为19.92和32.75 mmol/kg,均显著低于W和WG(P<0.05),表明WGL具有较高的氧化稳定性;由差示扫描量热法和热重法可知WGL的熔解温度和质量保留率最高分别为107℃和27.55%,表明WGL具有良好的热稳定性。综上,WGL的综合性质优于W和WG,表明WGL对ARA有较好的包埋和保护作用,该研究结果对选择合适的壁材包埋ARA微胶囊具有一定的参考意义。