Phase Change Material Device Research Articles

Post-processing of phase change material in a zero-change commercial silicon photonic process

Integration of phase change material (PCM) with photonic integrated circuits can transform large-scale photonic systems by providing non-volatile control over phase and amplitude. The next generation of commercial silicon photonic processes can benefit from the addition of PCM to enable ultra-low power, highly reconfigurable, and compact photonic integrated circuits for large-scale applications. Despite all the advantages of PCM-based photonics, today’s commercial foundries do not provide them in their silicon photonic processes yet. We demonstrate the first-ever electrically programmable PCM device that is monolithically post-processed in a commercial foundry silicon photonics process using a few fabrication steps and coarse-resolution photolithography. These devices achieved 1.4 dB/μm of amplitude switching contrast using a thin layer of 12.5 nm GeSbTe in this work. We have also characterized the reconfiguration speed as well as repeatability of these devices over 20,000 switching cycles. Our solution enables non-volatile photonic VLSI systems that can be fabricated at low cost and high reliability in a commercial foundry process, paving the way for the development of non-volatile programmable photonic integrated circuits for a variety of emerging applications.

Experimental Study on the Transient Behaviors of Mechanically Pumped Two-Phase Loop with a Phase Change Energy Storage Device for Short Time and Large Heat Power Dissipation of Spacecraft

For the purpose of dissipating large heat power with cyclical operating modes of satellite, one mechanically pumped two-phase loop (MPTL) coupled with a novel phase change energy storage device was designed and constructed. The phase change energy storage device integrating with filament tube heat exchanger and form-stable phase change material (PCM) with expanded graphite (EG) was designed and employed to increase the conductivity. The two-phase change behavior of liquid-vapor change for MPTL and solid-liquid transition for PCM was used to acquire, transport and store the heat. Results indicated that the time of heat storage for PCM device was more than 598.0 s, and the temperature at the outlet of the device increased from −2.0 °C to 15.0 °C under the heating power of 6.7 kW. The flowrate decreased from 0.059 kg/s to 0.034 kg/s due to the length increase of two-phase section during the melting process of PCM device. Lowering the rotation speed of pump increased the oscillating amplitude of flowrate, and its maximum value reached to 0.008 kg/s. The total working period for PCM device for lower rotation speed of 8000 r/min was 48.0 s longer than that for higher speed of 10000 r/min due to decreased heat transfer coefficient.

Gas extraction hood modeling in a steel converter for energy recovery using phase change materials

The steel industry is characterized by its energy-intensive processes. The steel forming process stands out, where the oxidation of carbon, when reacting, generates incomplete combustion gases at high temperature through the process basic oxygen injection in the furnace (BOF). A model of intermittent process and high temperature gas collection system is proposed and validated through experimental measurements. Through it, energy improvement opportunities are analyzed, highlighting energy recovery from high temperature flue gases by incorporating a phase change material (PCM) method for temporary energy storage. It was estimated that the fumes inside the hood could provide 77 GJ of available energy during the 15 min of oxygen injection (blowdown). With the use of a PCM device, between 13% and 32% residual energy recovery is obtained, equivalent to 10–25 GJ. In this way, a continuous heat flow could be generated during the whole process for steam generation through a cooling system in the gas collection system, with an electricity generation potential with a Rankine cycle of 14.5 MW.

Experimental and numerical study on performance enhancement of photovoltaic panel by controlling temperature with phase change material

In order to enhance the electricity generation performance of photovoltaic (PV) panel, experimental and numerical studies were carried out to control the temperature by using phase change material (PCM). The PV combined with PCM (PV-PCM) device and PV-PCM with foam copper were designed, and their temperature, voltage, and output power were measured and compared with those of PV panel. The mathematical model of heat transfer for PV-PCM was established and verified by experiment. And the influences of PV-PCM tilt angle, PCM properties and thickness, and ambient temperature on the temperature control effect were studied numerically. The results illuminate that the PV panel's temperature decreases significantly with the using of PCM, which correspondingly enlarges its open circuit voltage and output power. And the PCM with foam copper has a better effect. The temperature control effect of the PV-PCM system is better with the increase of the tilt angle, the PCM thermal conductivity and thickness, and the decrease of PCM phase change temperature. But there are limited conditions for them. The higher the ambient temperature, the worse the temperature control effect. The present study has important reference value for PV performance enhancement.

First-principles study and experimental characterization of metal incorporation in germanium telluride

Germanium telluride is a well-known phase change material (PCM) used in non-volatile memory cells and radio frequency switches. Controlling the properties of GeTe for improved PCM device performance has sometimes been achieved by doping and/or alloying with metals, often at concentrations greater than 10 at. % and using non-equilibrium methods. Since switching PCMs between the low-resistance crystalline and high-resistance amorphous states requires a heating cycle, the stability of metal-incorporated GeTe (Ge0.5−xMxTe0.5) films is also critical to practical implementation of these materials in electronic and optoelectronic devices. In this work, we use both density-functional theory and experimental characterization methods to probe the solubility and critical properties of Ge0.5−xMxTe0.5 films. Using first-principles calculations, we determine the enthalpy of formation for GeTe with 2.08, 4.17, and 6.25 at. % of Cu, Fe, Mn, Mo, and Ti and show trends between the stability of the Ge0.5−xMxTe0.5 systems and the atomic position, composition, and distribution of the metal atoms in the GeTe matrix. Out of all the studied systems, Mo was the only metal to cluster within GeTe. Analysis of the Ge–Te bond lengths and volumes of the Ge0.5−xMxTe0.5 supercells shows that increasing the atomic concentration (2.08, 4.17, 6.25 at. %) of the different metals causes varied distortions of the crystal structure of GeTe that are accompanied by significant changes in the projected density of states. Computational predictions concerning metal solubility and the effect of metal incorporation on critical properties of GeTe are compared to experimental results in the literature (Cu, Mn, Mo, and Ti) and to transmission electron microscopy and transport data from newly characterized co-sputtered Ge0.5−xFexTe0.5 films. The computational predictions of decreasing solubility (Mn > Cu, Fe > Ti, Mo) shows good agreement with experimental observations (Mn, Cu > Fe > Ti, Mo), and Ge0.5−xFexTe0.5 films exhibited increased crystallization temperatures from pure GeTe.

An artificial synapse by superlattice-like phase-change material for low-power brain-inspired computing**Project supported by the National Science and Technology Major Project of China (Grant No. 2017ZX02301007-002), the National Key R&D Plan of China (Grant No. 2017YFB0701701), and the National Natural Science Foundation of China (Grant Nos. 61774068 and 51772113). The authors acknowledge the support from Hubei Key Laboratory of Advanced Memories

Phase-change material (PCM) is generating widespread interest as a new candidate for artificial synapses in bio-inspired 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.

2D Conduction Simulation of a PCM Storage Coupled with a Heat Pump in a Ventilation System

Efforts to simulate heat transfer in a PCM (Phase Change Material) storage device are generally led by considerations of Biot number and material thickness, of 2D versus 1D representation, and of possible hysteresis effects arising from the characterisation of the PCM using differential scanning calorimetry (DSC). In this paper we present a numerical treatment of heat conduction in a paraffin-based storage brick, based on experimental data for a full scale, heat storage component studied under laboratory conditions. The PCM was modelled adopting equivalent thermophysical properties during the phase change. An equivalent heat capacity and thermal conductivity were provided for an appropriate description of energy release and storage in the process of solidification and melting. The geometry of the metal container induces 2D effects that are generally neglected in numerical modelling. The thickness of the plates (about 2 cm) is sufficiently large to require the modelling of conduction in the PCM, but can also induce convection that has been neglected in this study. Experimental results are presented and compared for both a 1D and 2D model of the PCM device. It was concluded that a 2D representation is essential for configurations; like the case study and geometry we had; with a large difference in thermal conductivity between PCM and metal casing. Two curves of equivalent heat capacity (measured via DSC) were introduced for heating and cooling phases. Comparisons to experimental results indicated significant errors in the models during melting and solidification of the PCM, which could be reduced by instead adopting the mean of the two heat capacity curves. The rate of temperature change during the experiments and for the DSC characterisation was analysed and found to explain well the observations. In particular, as novelty, two peaks of equivalent heat capacity have been observed with DSC when the rate is very low instead of only one peak using current rate: and that explains the real behaviour in the experiments.

Study of solar heated biogas fermentation system with a phase change thermal storage device

A new technique of solar heating biogas fermentation system integrated with a phase change thermal storage device is introduced for improving the low efficiency of the traditional biogas fermentation devices during winter. For a designed solar heated biogas system, its performance of anaerobic fermentation process under the different natural cooling conditions has been assessed by varying the thicknesses of insulation materials. And the optimum relative proportion between the heat supplied by solar and that stored in phase change heat storage device has been also investigated. The preliminary results based on the numerical simulations performed with meteorological data from Anhui Province, China show that the proposed PCM device with 3 m3 paraffin wax as phase change material (PCM) and 20 m2 solar collector areas can satisfy the heat required by producing 5 m3 biogas per day corresponding to a solar fraction (f) of 0.8 in winter. It indicates that the proposed solar heating system could be a promising approach for promoting biogas technology applications in cold rural regions of China.

A multi-scale analysis of the impact of pressure on melting of crystalline phase change material germanium telluride

The impact of the moderate pressure (about 100 GPa) on the melting of crystalline (c-) phase change material (PCM) germanium telluride (GeTe) is analyzed, by combining the heat transfer equation in the PCM device scale (101–102 nm and beyond), and the ab initio molecular dynamics and the nudged elastic band simulations in the atomistic scale (10−1–100 nm). The multi-scale analysis unravels that a pressure P = 1.0 GPa can increase the melting temperature of c-GeTe and the PCM device “reset” operation energy consumption by 6%–7%. It is shown that the melting temperature increase originates from the pressure-induced raise of the energy barrier of the umbrella-flip transition of the Ge atom from the octahedral symmetry site to the tetrahedral symmetry site. It is revealed that when P > 1.0 GPa, which is normal in PCM devices, the “reset” energy will be increased even by more. Based on the analysis, suggestions to alleviate pressure-induced raise of melting temperature and “reset” energy are provided.

Role of inelastic electron–phonon scattering in electron transport through ultra-scaled amorphous phase change material nanostructures

The electron transport through ultra-scaled amorphous phase change material (PCM) GeTe is investigated by using ab initio molecular dynamics, density functional theory, and non-equilibrium Green's function, and the inelastic electron---phonon scattering is accounted for by using the Born approximation. It is shown that, in ultra-scaled PCM device with 6 nm channel length, $$<$$ < 4 % of the energy carried by the incident electrons from the source is transferred to the atomic lattice before reaching the drain, indicating that the electron transport is largely elastic. Our simulation results show that the inelastic electron---phonon scattering, which plays an important role to excite trapped electrons in bulk PCM devices, exerts very limited influence on the current density value and the shape of current---voltage curve of ultra-scaled PCM devices. The analysis reveals that the Poole---Frenkel law and the Ohm's law, which are the governing physical mechanisms of the bulk PCM devices, cease to be valid in the ultra-scaled PCM devices.

Role of Inelastic Electron-Phonon Scattering in Ultra-Scaled Phase Change Material Nanostructures

ABSTRACTThe electron transport properties of ultra-scaled amorphous phase change material (PCM) GeTe are studied using non-equilibrium Green’s function (NEGF). The inelastic electron-phonon scattering is included using Born approximation. It is shown that, in ultra-scaled PCM device with 6 nm channel length, less than 4% of the energy carried by the incident electrons from the source is transferred to the atomic lattice before reaching the drain, indicating that the electron transport is largely elastic. Our simulation results show that the inelastic electron-phonon scattering, which plays an important role to excite trapped electrons in bulk PCM devices, exerts very limited influence on the current density value and the shape of current-voltage curve of ultra-scaled PCM devices. The analysis reveals that the Poole-Frenkel law and the Ohm’s law, which are the governing physical mechanisms of the bulk PCM devices, cease to be valid in the ultra-scaled PCM devices.

Numerical study of the spacecraft thermal control hardware combining solid–liquid phase change material and a heat pipe

A new spacecraft thermal control hardware composed of two parallel channels working for heat pipe (HP) and solid–liquid phase change material (PCM), respectively, is suggested for the high heat dissipating component which works intermittently with short duty. In present study the honeycomb structure radiator embedded with the device combining HP and PCM is designed, and the detailed thermal math models are developed for numerical analysis. The comparison of computational results between with and without PCM shows that the HP–PCM device redistributes temporal peak heat around a whole orbit period through alternate melting and freezing of PCM, and, as a result, the maximum and minimum temperatures are effectively alleviated. The drawback of PCM application due to low thermal conductivity can be successfully resolved by means of parallel arrangement of the HP channel. The suggested HP–PCM device can be a kind of off-the-shelf component and it does not require any case dedicated configuration. Therefore, it can be used with less impact on the program cost and schedule different from most of the PCM applications.

Thermal Management of an Avionics Module Using Solid-Liquid Phase-Change Materials

A combined experimental and computational investigation of transient thermal control of an avionics module using phase-change material (PCM) is reported. The cone guration examined was a honeycomb core e lled with an organic PCM, n-triacontane, heated from the bottom. Experiments were conducted to evaluate the thermal performance of the PCM device by measuring temperatures at various locations as functions of time until the module temperature reached an acceptable maximum limit. An analysis of melting inside a single honeycomb cell, considering effects of natural convection, showed that, for the power levels and the cell geometry considered, the effect of natural convection on melting was negligible. A system-level analysis of the PCM-e lled device followed. Timewise variations of temperatures at various locations from the model were in good agreement with the experimental data. Times for complete melting, maximum temperature variations within the honeycomb, and evolution of melt shapes are presented as functions of power levels.