Thermal Conductivity Of Silicon Research Articles

Exploration and optimization on thermoelectric conversion of waste heat of blast furnace slag

The iron and steel industry involves processes that generate abundant waste heat resources. The energy utilization rate can be improved by using thermoelectric conversion technology to directly convert waste heat into electric energy through the Seebeck effect. In this study, a special waste heat recovery device, designed according to the production environment characteristics of blast furnace (BF) slag, is proposed. The heat transfer process between the BF slag and thermoelectric generator (TEG) is analyzed, and the heat source temperature field model is constructed. Based on the temperature distribution, the size of the TEG is determined. The heat transfer behavior of the thermoelectric module (TEM) is optimized using a non-contact heat collection mode and a water-cooling device, which improves the temperature gradient. A thermal conductive silicone grease is introduced as the thermal conductive layer to achieve uniform distribution of the hot end temperature and improve the heat transfer capacity of the collector plate. After design optimization, the temperature gradient of the TEM increased by 15.3 °C and 38 % on average. The experimental results show that a single TEM can generate about 3.084 J of electric energy. Using 70 kg of BF slag with an initial temperature of 600 °C, the TEG per unit installed area can generate about 1.23 kJ of electric energy in 1 h. This study provides an important foundation for research in thermoelectric conversion, utilization of BF slag waste heat and sustainable development of the iron and steel industry.

On the importance of Akhiezer damping to thermal conductivity in silicon at elevated temperatures above 300 K

Recently, Chiloyan et al. [Appl. Phys. Lett. 116, 163102 (2020)] have reported that phonon transport could exceed bulk heat conduction if low-frequency phonons with long mean free path (MFP) remain in the nonthermal regime in silicon. To gain a better understanding of their findings, we investigated the effects of temperature-induced anharmonicity on both Landau–Rumer damping and Akhiezer damping, including polarization. To do this, we follow a rigorous procedure for calculating the Akhiezer model and use phonon kinetic theory based on the Boltzmann transport equation. Consequently, we find that in the Akhiezer regime, the longitudinal acoustic phonon modes (LA) are strongly suppressed by phonon anharmonicity compared to the transverse acoustic phonon modes. Therefore, the low-frequency phonons with a long MFP of LA can help to exceed bulk heat conduction if they remain in the regime of nonthermal phonon transport where there are no appreciable scatterings with other phonons. It is also shown that Akhiezer damping eliminates thermal conductivity by 16.8% at 500 K, which is higher than the observed reduction (12.6%) at 300 K in silicon, uncovering a novel regime where the Akhiezer damping, previously deemed insignificant in the thermal conduction of bulk silicon, becomes crucial.

THERMAL CONDUCTIVITY MODELING OF DIELECTRIC OILS-BASED NANOFLUIDS USING THE FINITE ELEMENT METHOD

The enhancement of the thermal conductivity of dielectric oils has a positive effect on the performance of electrical equipment that uses these oils as a cooling medium. Nanofluids (NFs) have inspired high-voltage engineers to use them as alternative fluids in power transformers due to their impressive heat transfer and insulation compared to traditional dielectric oils. The present study is a numerical simulation by COMSOL Multiphysics of the thermal conductivity of NFs based on dielectric oils used in power transformers, to identify the effect of temperature, the concentration of nanoparticles (NPs), type of insulating fluid and NPs on thermal conductivity. The NFs were modeled inside a cube using the finite element method (FEM) by applying a temperature gradient. Several types of NPs were used (SiC, ZnO, TiO2, and Al2O3) in addition to several volume concentrations (0%, 0.001%, 0.002%, 0.01%, and 0.02%). The results showed a significant improvement in the thermal conductivity of the NFs with increasing concentration since the best results were recorded at an estimated volume concentration of 0.02%, while the lowest results were obtained for samples using a volume concentration estimated at 0.001%. The base fluid (BF) type and NPs play a dominant role in the thermal performance of the NFs, as the vegetable oil-based nanofluid provided the highest thermal conductivity values and silicon carbides (SiC) was the best NPs used in this study. However, a decrease in thermal transfer capacities was observed for all samples with increasing temperature.

Research Progress in High Thermal Conductivity Silicon Nitride Ceramics Prepared by Non-Oxide Additives

Research Progress in High Thermal Conductivity Silicon Nitride Ceramics Prepared by Non-Oxide Additives

Study on the effects of incremental curing on the thermal conductivity, insulation, and mechanical properties of thermal conductive silicone rubber

With the development of fields such as electronics and telecommunications, electronic devices are becoming more integrated and powerful. Therefore, there is an increasing demand for high thermal conductive and insulating flexible materials. Silicone rubber (SR), as an excellent flexible substrate, is often combined with various thermal conductive fillers to enhance its thermal conductivity (TC). Carbon materials are commonly used as thermally conductive fillers. To improve the insulation performance while maintaining the TC of the material, uncured SR filled with boron nitride (BN) is used as an insulating layer on the same substrate. The TC of the once-cured BN/SR composite and the incremental cured BN/SR composite as a coating are 0.492 W/(mK) and 0.484 W/(mK), respectively, with a BN content of 10 vol%. The TC of carbon fiber (CF)/SR composites before and after surface treatment with BN/SR are 1.760 W/(mK) and 1.682 W/(mK), respectively, with a CF content of 20 vol%. The volume resistivity of the former is less than 104 Ω cm, while the latter is greater than 1014 Ω cm.

Investigation of mesoporous silicon thermal conductivity: Effect of nanographene insertion

In this study, the impact of nanographene incorporation on the thermal properties of mesoporous silicon (PSi) was evaluated using two complementary experimental methods: the temperature gradient (TG) and the photothermal radiometry (MPTR) methods. It is shown that the measured thermal conductivity of the mesoporous silicon (PSi) ranges from 0.10 to 0.68 W/m.K in the case of TG and from 0.37 to 3.02 W/m.K in MPTR and is strongly correlated to the electrochemical etching parameters. These values are much lower than that of crystalline silicon, estimated to be from 100 to 140 W/m.K, depending on the doping rate. They appear to be, however, in the order of magnitude range for the percolation models that also include the in-depth porosity and the crystallite mean radius. This set of experiments on the thermal conductivity was extended to investigate the effect of graphene incorporation in the PSi matrix (G-PSi) as it has seldom been reported in the literature. The results from both methods exhibit significantly higher values (1.7 ± 0.3 W/m.K for TG, and from 0.7 to 2.13 W/m.K for MPTR). This spread of the thermal conductivity values is attributed to the intrinsic working principle of the TG versus the MPTR method as highlighted in the last part of the present paper. Targeting the thermoelectric application of both matrices (PSi, G-PSi), the thermal conductivity remains sufficiently low for them to be considered as very promising materials, keeping in mind the enhancement of the power-factor attributed to the incorporation of graphene.

Experimental research on thermoelectric characteristics of a thermoelectric generator with external influencing factors optimization

The external influencing factors, the thermal interface material, load-bearing brick weight, and temperature difference, of a thermoelectric generator (TEG) device were experimentally examined. The micro heat pipe array (MHPA), as one novel thermal interface material, was investigated. The multi-variable coupling approach is used to analyze the intrinsic coupling correlation of the external influencing factors. The dimensionless synthesis economic factor index was proposed to analyze the improvement of thermoelectric characteristics, which can quickly assess the contact thermal resistance of different thermal interface materials. The results showed that the load power and load voltage generally increase with increased temperature differences. The contact thermal resistance decreases with increased load-bearing brick weight, but the decrement gradually decreases. The thermal interface material plays an important role in thermoelectric characteristics. The load-bearing brick weight performs little impact on the non-thermal interface material (NTIM) scheme. The two thermal conductive silicone grease schemes noticeably reveal better thermoelectric characteristics than those of the graphite paper schemes, although the thermal conductivity of thermal conductive silicone grease are much lower than that of graphite paper. The MHPA scheme exhibit the best thermoelectric characteristics, and its dimensionless synthesis economic factor index can be up to 371.81 %.

Experimental study of ice melting of concrete permeable brick sidewalks using embedded carbon fibre heating wire

Electric heating methods have been proven to be effective means to melt ice on sidewalks and bridge decks. However, sidewalks are covered with permeable concrete bricks separated by gaps, which differ from surfaces of roads and bridge decks. Therefore, it is necessary to study methods of melting ice on sidewalks. In this paper, a method for melting ice on sidewalks based on carbon fibre heating wire (CFHW) is proposed. The experiments compare the effects of various environment temperatures, wind speeds, and energising voltages and spacings of CFHW on the surface temperature and melting of ice on sidewalk specimens. The transfer law of heat energy produced by CFHW inside the specimen and the effect of sealing concrete brick holes with a thermal conductive silicone grease in ice melting sidewalks are analysed. The results show that the proposed method has good ice melting performance on sidewalks.

Waffle-inspired thermal conductive silicone rubber composites with excellent electromagnetic shielding performance based on three-dimensional filler networks

Improving the thermal conductivity and electromagnetic shielding performance of silicone rubber composites is crucial for their application in electronic devices. In this work, inspired by the structure of waffle, a novel approach combining ice templating and mechanical vibration was employed to prepare reduced graphene oxide (rGO)/silicon carbide whisker (SiC) filler networks arranged in both horizontal and vertical directions. Silicone rubber composites were prepared by vacuum impregnation of silicone rubber into the three-dimensional filler networks. At the hybrid filler content of 3.88 vol%, the through-plane thermal conductivity reached 5.24 W/(m·K), exhibiting about 31 times higher than that of silicone rubber, and the anisotropy of thermal conductivity of the composite was only 1.35 due to the structural arrangement of the filler network in both vertical and horizontal directions. The total electromagnetic interference (EMI) shielding effectiveness of the composite with 3.88 vol% hybrid filler was 35.2 dB with low electromagnetic reflection, exhibiting good EMI shielding performance.

Preparation and properties of highly thermal conductive C/C-SiC

A kind of highly thermal conductive silicon carbide matrix composites (c-1000/C-SiC, c-600/C-SiC) reinforced with chopped mesophase pitch-based carbon fibers (c-MPCF) including 1000 W/(m·K) and 600 W/(m·K) were successfully prepared by the phenolic resin precursor impregnation pyrolysis and liquid silicon infiltration (LSI) method. Quasi-isotropic c-MPCF/C-SiC composites demonstrate excellent thermophysical properties, including average flexure strength of 111.5 MPa of c-1000/C-SiC and 123.0 MPa of c-600/C-SiC, average high thermal conductivity of 101.33 W/(m·K) and 93.94 W/(m·K) at room temperature, low coefficient of thermal expansions of 2.942 ppm/K and 3.147 ppm/K at room temperature, which provides a new strategy for preparing isotropic silicon carbide ceramic matrix composites with comprehensive properties and dimensional stability.

Lattice Thermal Conductivity of Silicon and Germanium Core/Shell and Segmented Nanowires

Lattice Thermal Conductivity of Silicon and Germanium Core/Shell and Segmented Nanowires

Depth-dependent recovery of thermal conductivity after recrystallization of amorphous silicon

The depth-dependent recovery of silicon thermal conductivity was achieved after the recrystallization of silicon that had been partially amorphized due to ion implantation. Transmission electron microscopy revealed nanoscale amorphous pockets throughout a structurally distorted band of crystalline material. The minimum thermal conductivity of as-implanted composite material was 2.46 W m−1 K−1 and was found to be uniform through the partially amorphized region. X-ray diffraction measurements reveal 60% strain recovery of the crystalline regions after annealing at 450 °C for 30 min and almost full strain recovery and complete recrystallization after annealing at 700 °C for 30 min. In addition to strain recovery, the amorphous band thickness reduced from 240 to 180 nm after the 450 °C step with nanoscale recrystallization within the amorphous band. A novel depth-dependent thermal conductivity measurement technique correlated thermal conductivity with the structural changes, where, upon annealing, the low thermal conductivity region decreases with the distorted layer thickness reduction and the transformed material shows bulk-like thermal conductivity. Full recovery of bulk-like thermal conductivity in silicon was achieved after annealing at 700 °C for 30 min. After the 700 °C anneal, extended defects remain at the implant projected range, but not elsewhere in the layer. Previous results showed that high point-defect density led to reduced thermal conductivity, but here, we show that point defects can either reform into the lattice or evolve into extended defects, such as dislocation loops, and these very localized, low-density defects do not have a significant deleterious impact on thermal conductivity in silicon.

Improvement the flame retardancy, thermal conductivity and mechanical properties of silicone rubber via silane coupling agent modified CNTs‐β‐FeOOH

AbstractSilicone rubber with its odorless and non‐toxic, high and low temperature resistance and other advantages is widely used in many fields, but its shortcomings of flammability and low thermal conductivity limit its application and development. Therefore, the research on flame retardant and thermal conductive silicone rubber is practically valueable. In this study, iron oxyhydroxide (β‐FeOOH) was synthesized on carbon nanotubes (CNTs) by in situ growth and added to silicone rubber after surface modification with γ‐aminopropyltriethoxysilane (KH550). The results showed that the limiting oxygen index (LOI) of methyl vinyl silicone rubber (VMQ) with the addition of one part of KH550@CNTs‐β‐FeOOH increased to 29.8%, its peak heat release rate (pHRR) and total heat release (THR) decreased by 40.1% and 30.2%, respectively, and its thermal conductivity increased to 0.3680 W/m·k. The flame‐retardant performance and thermal conductivity of the VMQ composite were significantly improved. The improvement of its flame retardancy was mainly due to the catalytic carbonization of CNTs and β‐FeOOH, which promoted the formation of dense carbon layers. The carbon layer insulates the exchange of oxygen and combustible gases. In addition, the thermal conductive network constructed by KH550@CNTs‐β‐FeOOH in the composite effectively improved the thermal conductivity of VMQ.

Effects of spherical Al2O3 grades on crack initiation of thermal conductive silicone pads under high-temperature aging

ABSTRACT In this paper, the rule and mechanisms of crack initiation and propagation in the aging process of thermal conductive silicone pads (TCSP) were investigated by designing Al2O3 particle grading schemes with different particle sizes and mass ratios. Scanning electron microscope and energy dispersive spectrometer analysis showed that TCSP prepared with Al2O3 particles of various sizes according to the gradation ratio had the best anti-aging effect at high temperatures. At this time, the aging was mainly due to the aging degradation of the polymer matrix; When the proportion of small-size Al2O3 particles increases, aggregates and pore defects appear in TCSP. At this time, the main reason for its aging is that the high-temperature expansion of gas in pore defects accelerates the aging degradation of the polymer matrix; When the proportion of small-sized Al2O3 particles decreases, a large number of holes appear in TCSP and the coverage rate of the polymer matrix on Al2O3 particles decreases. The main reason for the high-temperature aging crack is that the gas between the holes expands at high temperature, resulting in the rapid extension of the crack and the polymer matrixes falling.

Multiphysics Numerical Simulation and Geometric Optimization of a Micronozzle for the MEMS Thruster

This paper reports a numerical research on MEMS (microelectromechanical system) micronozzles through multiphysics coupling simulation along with design optimization based on simulation results. The micronozzle, which is a core component of the electrothermal microthruster, features a micron-scale geometry, a 2-dimensional (2D) Laval configuration, a rectangular cross section, and a highly thermal conductive silicon wall due to MEMS fabrication. As a result, viscous loss in the flow field and heat transfer to the nozzle wall can strongly influence nozzle performance, namely, thrust force and specific impulse. To accurately understand the flow field inside the micronozzle and how the highly thermal conductive silicon wall interacts with gas flow, a numerical simulation that couples fluid dynamics field and solid heat transfer field is employed in the research. The influence of different structural parameters on micronozzle performance is then investigated to set a basis for design optimization. The optimum design of the linear expander micronozzle is obtained through constrained optimization by linear approximation. To further improve micronozzle performance, the bell-shaped expander is adapted. The optimization result shows that the bell-shaped expander is not suitable for micronozzle featuring 2D Laval configuration, and the reason behind the phenomenon is thoroughly discussed.

Highly Thermal Conductive Silicon Carbide Ceramics Matrix Composites for Thermal Management: a Review

Highly Thermal Conductive Silicon Carbide Ceramics Matrix Composites for Thermal Management: a Review

Ultrathin and Flexible Thermal Perception Sensor for Matter and Pressure Detection

In this article, an ultrathin and flexible thermal perception (FTP) sensor with a fingerprint-like sensing structure is proposed. The developed FTP sensor features a sandwich structure formed by biocompatible polyimide (PI), gold thermistors, and Parylene C layers with a total thickness of <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$8~\mu \text{m}$ </tex-math></inline-formula> . Meanwhile, multisensory functions including temperature and pressure sensing, as well as matter recognition are realized. Specifically, the FTP sensor shows an ultrafast response time of less than 0.12 s and 52 ms for matter and temperature detection, respectively, while various matters information such as PI, rubber, and steel, can be easily distinguished. Besides, the ultrathin design allows the sensor to gain signal stability of less than 0.3% even at a curvature up to 0.25 mm−1. Furthermore, the FTP sensor achieved a sensitivity of 812 mV/kPa for pressure sensing after being partially covered with a thermal conductive powder-doped silicone film. In short, the demonstrated functionality of this ultrathin FTP sensor combined with its simple fabrication holds the prospect of further advancing and deploying this device as a promising sensory system for mimicking human interaction.

Transposable, highly thermal conductive silicone rubber/boron nitride composites with enhanced orientation of BN by multilayer stacked hot pressing according to rheological control

Composites with high out-plane thermal conductivity (TC) and great insulation are essential for thermal management in electronic devices. Herein, a transposable, highly thermal conductive silicone rubber (SR)/boron nitride (BN) composite was fabricated by multi-layer stacked hot pressing, in which the orientation of BN was enhanced based on rheological characterizations. Then the pre-pressed films were stacked under 180 °C to get a full-cured and thick composite. The enhanced orientation of BN and the excellent heat transfer capability of the composites were well verified by SEM, XRD, 2D WAXS, finite element analysis (FEA) and infrared thermography, which resulted in a wonderful thermal pathway and low interfacial thermal resistance. The TC of the composite reached 22.08 W/(m·K), and the high in-plane TC could be converted to high out-plane TC after simple vertically cut due to the flexibility and large thickness of composite. Meanwhile, for the first time, the excellent heat transfer capability of the composite was quantitatively characterized by the characteristic temperature rise time constant (τg). The rheological control was an efficient and potential strategy to get highly thermal conductive composites.

Challenges for Sige Bicmos in Advanced-Node SOI

D-band (110-170GHz) spectrum is gaining attention for various applications, including 6G mm-Wave, sub-THz sensing, and radar. These systems require lattice spacing for antenna elements at sub-1mm and a very low loss signal path from antenna to integrated chip. A highly efficient front-end in a very small form factor will be required for these systems. This drives the requirement for a monolithically integrated high-gain, high-efficiency front-end that also leverages the benefits of a high-speed / high-density digital CMOS. Silicon germanium (SiGe) heterojunction bipolar transistors (HBT) integrated along with a high-density CMOS provide such an all-silicon monolithic solution.The US government is fostering the expansion of “unique and differentiated domestic manufacturing” with funding through DARPA’s Technologies for Mixed-mode Ultra Scaled Integrated Circuits (T-MUSIC) [1] program to enable disruptive RF mixed-mode technologies by developing high performance RF analog integrated with advanced digital CMOS. Through the T-MUSIC program, DARPA seeks to: 1) advance RF and mixed-mode devices to support ultra-wideband RF frontends from HF to 100 GHz; 2) integrate those devices with high density digital CMOS electronics at the wafer scale to enable embedded digital intelligence; 3) develop and explore ultra-high resolution broadband mixed-mode circuit building blocks for DoD-relevant applications; 4) explore innovative device topologies and materials to form THz devices in an advanced digital CMOS fabrication platform; and 5) establish a domestic ecosystem that facilitates enduring DoD access to differentiated capabilities for high performance RF mixed-mode SoCs.Under T-MUSIC, GlobalFoundries is demonstrating BiCMOS on 45nm PDSOI, which is the focus of this paper, and 22nm FDSOI CMOS with goals of increasing HBT performance of fT/fMAX from 350/500 GHz to 400/600 GHz and 600/700 GHz. HBTs with fT/fMAX of 380/550GHz GHz have been demonstrated building upon previously published results [2]. This paper will touch on some of the challenges that were encountered in achieving that result and discuss those anticipated in future work.Achieving these results required scaling transistor dimensions. Vertical scaling of the emitter, base and collector layers, with higher doping concentrations, reduces transit time but results in higher current densities and higher electric fields. Lateral scaling of the transistor structure reduces parasitic capacitance and resistance but concentrate the power dissipation in a smaller area. The thermal conductivity of silicon is 148W/m-K whereas that of silicon dioxide is ~1.4W/m-K. Even a thin layer of oxide will significantly increase the self-heating of the HBT. Therefore, we replace the SOI with coplanar epitaxy in regions where the HBTs are formed.The vertical scaling of the HBT requires limiting the thermal cycles that the HBT will experience during processing and suggests forming the HBT as late as possible in the CMOS process. However, the thermal cycles associate with the epitaxy and film depositions to form the HBT impact the CMOS transistors which suggests forming the HBT early in the process. We found a point in the process that offers the best compromise minimizing the impact to the doped-channel PDSOI CMOS while achieving the HBT performance goals. Work is just beginning on integration tradeoffs for FDSOI with metal gate and high-K dielectrics.Advanced-node CMOS processes can form components having smaller dimensions which offers advantages for lateral scaling but also presents challenges for forming the HBT. The contact height in 45nm is significantly less than the height of the HBT structure used in GF’s 9HP process. We changed the formation of the emitter and base so that the emitter and base contacts are almost coplanar in contrast to 9HP where the emitter was almost twice the height of the base. This problem is being further exasperated as we migrate to 22nm.The shrinking of BEOL wiring dimensions, along with the ability of the HBT to drive high currents, presents challenges in designing within limits imposed by electromigration. The use of wider wires is constrained by metal density rules. The use of stacked metal levels and redundant vias impact the parasitic capacitances and resistances of the interconnects.The paper and presentation will review these, and other challenges encountered in achieving BiCMOS integration of SiGe HBTs with fT/fMAX of 380/550GHz GHz [see figure] on a 45nm PDSOI CMOS and touch future work.This research was developed with funding from the Defense Advanced Research Projects Agency (DARPA) and is Approved for Public Release, Distribution Unlimited. The views, opinions and/or findings expressed are those of the author and should not be interpreted as representing the official views or policies of the Department of Defense or the U.S. Government.[1] https://www.darpa.mil/attachments/T-MUSIC_Proposers%20Day_Presentations_Combined.pdf [2] J. Pekarik et al., 2021 IEEE BCICTS, 2021, pp. 1-4, Figure 1

Thermal-enhanced nanofluidic osmotic energy conversion with the interfacial photothermal method

Nanofluidic osmotic energy conversion is widely considered a promising technology that converts sustainable salinity-gradient energy. Current studies on temperature regulation require extra electrical consumption to raise the solution temperature, causing the deterioration of the net power generation. In this study, a thermal-enhanced nanofluidic osmotic energy conversion with photothermal conversion structure (PCS-TOEC) integrated device is proposed to utilize sustainable solar energy as the heat source. This device is a reformation by adding photothermal conversion structure (PCS) into a salinity gradient utilization component. PCS is composed of a high solar-absorption cupric oxide film and a high thermal-conductive silicon carbide porous foam, and it can efficiently convert solar energy into solution heat. In addition, PCS can promote bulk heating at a high rate. The experiment shows that the solution temperature is raised from 25 ℃ to 68 ℃ after 240 min under one sun illumination, and the output power density achieves 8.6 W/m2 with 0.5 M/0.01 M NaCl solution, exhibiting a 188 % increase compared to that at room temperature. The increased bulk solution temperature under the photothermal effect can improve the ion diffusion coefficient and electrolyte convection, as well as reduce the electrolyte viscosity, resulting in the enhancement of the associated ion flux. The underlying mechanism of thermally enhanced osmotic power is primarily attributed to the elevated ion flux at increased bulk solution temperatures. Finally, the environmental adaptability of this device is verified over a wide range of concentration gradients (from 10-fold to 100-fold) and pH (from 4 to 10) conditions. In this work, a sustainable solution that enhances osmotic power generation is provided, and a novel method that achieves hybrid renewable energy cooperative utilization is developed.