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.

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.

New Math Model for Designing Engine Radiator

Aim To raise the H-NE math model for designing engine radiators.Methods Thismodel was founded on multi-nonlinear regression technology,and the quadratic equatingmethod was used to smooth original data.Through the sensitivity analysis about radiatoroptimization designing,some major restraints were obtained.Results Type 1301C radiator wasoptimizingly renwed by use o this model,and the new radiator is more excellent than theold one in respect of the heat transfer factor and the manufacturing cost.Conclusion Theradiation performance can be improved,the area can be reduced,and the fitting scope can bewidened if this model is used in designing radiators.

Ta-Doped Sb2Te Allows Ultrafast Phase-Change Memory with Excellent High-Temperature Operation Characteristics

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.

Preparation of composite aluminum automobile radiator by inversion casting

The inversion casting technics of producing three ply Al Mn/Al Si composite strap used in automobile radiator was studied. The physical processes of inversion casting, including the flux supporting reacting and volatilizing at high temperature, the melting and solidification when the elements of solid and liquid fresh alloys meet with each other, the mutual diffusion of elements in solid and liquid, the crystallization and forming of metallurgical combination and the following rolling process, were analyzed. At the same time, the composite mechanism of this technique was also discussed. [

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.

Unconventional phase transition of phase-change-memory materials for optical data storage

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.

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.

Thin film design for advanced thermochromic smart radiator devices

This paper describes the research on the materials and design methods for advanced smart radiator devices （SRDs） on large-area flexible substrates utilized on spacecraft. The functional material is thermochromic vanadium dioxide. The coating design of SRD is similar to the design of broadband filter coatings in a mid-infrared region. The multilayer coatings have complex structures. Coating materials must be highly transparent in a required spectrum region and also mechanically robust enough to endure the influence from the rigorous environments of outer space. The number of layers must be very small, suitable for the deposition on large-area flexible substrates. All the coatings are designed initially based on optical calculation and practical experience, and then optimized by the TFCALC software. Several designs are described and compared with each other. The results show that the emittance variability of the designed SRDs is great than 400%, more advanced than the reported ones.

DEVELOPMENT OF SINGLE-PHASED WATER-COOLING RADIATOR FOR COMPUTER CHIP

In order to cool computer chip efficiently with the least noise, a single phase water-cooling radiator for computer chip driven by piezoelectric pump with two parallel-connection chambers is developed. The structure and work principle of this radiator is described. Material, processing method and design principles of whole radiator are also explained. Finite element analysis （FEA） software, ANSYS, is used to simulate the heat distribution in the radiator. Testing equipments for water-cooling radiator are also listed. By experimental tests, influences of flowrate inside the cooling system and fan on chip cooling are explicated. This water-cooling radiator is proved more efficient than current air-cooling radiator with comparison experiments. During cooling the heater which simulates the working of computer chip with different power, the water-cooling radiator needs shorter time to reach lower steady temperatures than current air-cooling radiator.

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.

Forming technology of boiling structure on evaporation surface of phase-change heat sink for high-power light emitting diode

Boiling structures on evaporation surface of red copper sheet with a diameter （D） of 10 mm and a wall thickness （h） of 1 mm were processed by the ploughing-extrusion （P-E） processing method, which is one part of the phase-change heat sink for high power （HP） light emitting diode （LED）. The experimental results show that two different structures of rectangular- and triangular-shaped micro-grooves are formed in P-E process. When P-E depth （ap）, interval of helical grooves （dp） and rotation speed （n） are 0.12 ram, 0.2 mm and 100 r/min, respectively, the boiling structures of triangular-shaped grooves with the fin height of 0.15 mm that has good evaporation performance are obtained. The shapes of the boiling structures are restricted by dp and ap, and dp is determined by n and amount of feed （f）. The ploughing speed has an important influence on the formation of groove structure in P-E process.

Three-Dimensional Simulations of RESET Operation in Phase-Change Random Access Memory with Blade-Type Like Phase Change Layer by Finite Element Modeling

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.

Neutron Capture Therapy (NCT) & In-Hospital Neutron Irradiator (IHNI)——a new technology on binary targeting radiation therapy of cancer

BNCT is finally becoming ＂a new option against cancer＂. The difficulties for its development progress of that firstly is to improve the performance of boron compounds, secondly, it is the requirements of quantification and accuracy upon radiation dosimetry evaluation in clinical trials. Furthermore, that is long anticipation on hospital base neutron sources. It includes dedicated new NCT reactor, accelerator based neutron sources, and isotope source facilities. In ad- dition to reactors, so far, the technology of other types of sources for clinical trials is not yet completely proven. The In- Hospital Neutron lrradiator specially designed for NCT, based on the MNSR successfully developed by China, can be installed inside or near the hospital and operated directly by doctors. The Irradiator has two neutron beams for respective treatment of the shallow and deep tumors. It is expected to initiate operation in the end of this year. It would provide a safe, low cost, and effective treatment tool for the NCT routine application in near future.

Optimal Design of Multi-channel Water Cooled Radiator for Motor Controller of New Energy Vehicle

In order to improve the heat dissipation capability of motor controller for new energy vehicles,the water cooled radiator with multiple channels is optimized in this paper.The heat conduction between the heat source IGBT and the radiator,the convective heat transfer between the radiator and the coolant,the mechanical strength and the manufacturing cost are comprehensively considered during the optimization process.The power loss and thermal resistance of the IGBT unit are calculated at first,and finite element model of the radiator is established.On this basis,multi-physics coupling analysis of the water cooled radiator is carried out.Secondly,the sensitivity analysis is applied to verify the influence of structural parameters on the heat dissipation performance of the radiator system.The influence of coolant inlet velocity v,number of cooling ribs n,height of radiator ribs H on the maximum temperature rise T,the temperature difference ΔT between phase U and W,and the coolant pressure lossΔP are analyzed in depth,and the optimal range of the structural parameters for heat dissipation is obtained.Finally,an experimental platform was set up to verify the performance of the proposed structure of water cooled radiator for motor controller of new energy vehicle.The results show that the heat dissipation capability of the proposed radiator is improved compared with the initial design.

Influence of the Coolant Flow Containing Silver Nanoparticles (Ag) from an Aqueous Solution Based on Ethylene Glycol (EG50%) on the Thermal-Hydraulic Performance of an Automotive Radiator

A theoretical analysis of the influence of the flow of a coolant containing silver nanoparticle (Ag) in an automotive radiator is presented. The coolant fluid is composed of water or an aqueous solution of Ethylene-Glycol (EG50%) and silver nanoparticles. Ethylene glycol (EG) has been used in automobile radiators for many years due to its compatibility with metals and its anti-cooling properties. Silver nanoparticles are being incorporated into the development of high-precision surgical equipment. It is shown that the rate of heat transfer increases significantly using silver nanoparticles and ethylene glycol and water. There is a maximum for heat exchange between fluids in all analyzed coolant flows—the maximum moves to higher airflow rates when the coolant flow rate is increased. However, the energy dissipation in the stream also increases, but the relationship between the energy dissipated in the flow and the energy transferred in the form of heat is low, which justifies the use of silver nanoparticles and ethylene glycol, or silver nanoparticles and water as a coolant in the automotive vehicle radiator.

Thermal analysis of an innovative flat heat pipe radiator

An innovative flat heat pipe radiator was put forward, and it has the features of high efficiency of heat dissipation, compact construction, low thermal resistance, light weight, low cost, and anti-dust-deposition. The thermal analysis of the flat heat pipe radiator for cooling high-power light emitting diode （LED） array was conducted. The thermal characteristics of the flat heat pipe radiator under the different heat loads and incline angles were investigated experimentally in natural convection. An electro-thermal conversion method was used to measure the junction temperature of the LED chips. It is found that the integral temperature distribution of the flat heat pipe radiator is reasonable and uniform. The total thermal resistance of the flat heat pipe radiator varies in the range of 0.38-0.45 K/W. The junction temperatures of LED chips with the flat heat pipe radiator and with the aluminum board at the same forward current of 0.35 A are 52.5 and 75.2 ℃, respectively.

Numerical Study on Application of CuO-Water Nanofluid in Automotive Diesel Engine Radiator

Application of CuO-water nanofluid with size of the nanoparticles of 20 nm and volume concentrations up 2% is numerically investigated in a radiator of Chevrolet Suburban diesel engine under turbulent flow conditions. The heat transfer relations between airflow and nanofluid coolant have been obtained to evaluate local convective and overall heat transfer coefficients and also pumping power for nanofluid flowing in the radiator with a given heat exchange capacity. In the present study, the effects of the automotive speed and Reynolds number of the nanofluid in the different volume concentrations on the radiator performance are also investigated. The results show that for CuO-water nanofluid at 2% volume concentration circulating through the flat tubes with Renf = 6000 while the automotive speed is 70 km/hr, the overall heat transfer coefficient and pumping power are approximately 10% and 23.8% more than that of base fluid for given conditions, respectively.

CFD Analysis and Optimization of Automobile Radiator based on STAR-CCM+

This research talks about the radiator cooling system of the automobile engine,the radiator’ s fluidstructure interaction dynamics based on computational fluid dynamics( CFD) STAR-CCM+ software. The linear regression model of coolant determined by MATLAB software was imported into the user-defined field function of the software,using the standard K-Epsilon turbulence model to analyze temperature,pressure and velocity changes of the coolant in the radiator channel. In order to improve the efficiency of the radiator,it is necessary to analyze the structure of two kinds of heat sinks,and get better heat transfer effect.