Heat Spreader Materials Research Articles

A laser-based Ångstrom method for in-plane thermal characterization of isotropic and anisotropic materials using infrared imaging.

High heat fluxes generated in electronics and semiconductor packages require materials with high thermal conductivity to effectively diffuse the heat and avoid local hotspots. Engineered heat spreading materials typically exhibit anisotropic conduction behavior due to their composite construction. The design of thermal management solutions is often limited by the lack of fast and accurate characterization techniques for such anisotropic materials. A popular technique for measuring the thermal diffusivity of bulk materials is the Ångstrom method, where a thin strip or rod of material is heated periodically at one end, and the corresponding transient temperature profile is used to infer the thermal diffusivity. However, this method is generally limited to the characterization of one-dimensional samples and requires multiple measurements with multiple samples to characterize anisotropic materials. Here, we present a new measurement technique for characterizing the isotropic and anisotropic in-plane thermal properties of thin films and sheets as an extension of the one-dimensional Ångstrom method and other lock-in thermography techniques. The measurement leverages non-contact infrared temperature mapping to measure the thermal response from laser-based periodic heating at the center of a suspended thin film sample. Uniquely, our novel data extraction method does not require precise knowledge of the boundary conditions. To validate the accuracy of this technique, numerical models are developed to generate transient temperature profiles for hypothetical anisotropic materials with known properties. The resultant temperature profiles are processed through our fitting algorithm to extract the in-plane thermal conductivities without knowledge of the input properties of the model. Across a wide range of in-plane thermal conductivities, these results agree well with the input values. Experiments demonstrate the approach for a known isotropic reference material and an anisotropic heat spreading material. The limits of accuracy of this technique are identified based on the experimental and sample parameters. Further standardization of this measurement technique will enable the development and characterization of engineered heat spreading materials with desired anisotropic properties for various applications.

Pulsed chemical vapor deposition for crystalline aluminum nitride thin films and buffer layers on silicon and silicon carbide

Low temperature aluminum nitride (AlN) deposition has applications ranging from serving as a heat spreading material to serving as a buffer layer for III-V semiconductors on silicon or silicon carbide (SiC) for radio frequency, power, and microLED devices. While crystalline AlN is traditionally deposited at high temperature (>800 °C), in the present study AlN is deposited on Si(100), Si(111), and 4H-SiC substrates by two modest temperature processes using a metal precursor with high thermal stability, tris(dimethylamido) aluminum (III), and a highly reactive nitrogen source, anhydrous hydrazine. A 580 °C pulsed chemical vapor deposition (CVD) process is compared to a more complex 400 °C atomic layer annealing process, in which the same precursors are utilized with periodic ion bombardment to induce film crystallinity. Films deposited by both processes template preferential c-axis orientation in subsequently sputtered AlN on unheated substrates. Both templating techniques demonstrate equivalent enhancements in crystallinity of the sputtered AlN relative to a non-templated sputtered film by x-ray diffraction and transmission electron microscopy studies. On 4H-SiC substrates, a comparison of sputtering directly and templating with the 580 °C pulsed CVD process reveals epitaxial deposition by the 580 °C pulsed CVD process which extends into the low temperature sputtered AlN.

Systematic Investigations on the Thermal Management Performance of Graphite Thin Films for High-Electron-Mobility Transistors

Self-heating is a severe problem for high-electron-mobility transistors (HEMTs). Graphene and thin graphite films are attractive candidates for heat spreader materials at the transistor level due to their ultrahigh in-plane thermal conductivity. However, a realistic and systematic simulation study of how they can improve the thermal management of HEMTs has not been carried out yet and is needed to push the method into practical use and realize industrialization. This study systematically investigated the effect of graphene and thin graphite films, and the most practical boundary condition in the simulations was primarily selected with comparisons. Then, the thermal properties consisting of thermal conductivity and interfacial thermal resistance (ITR) between graphite and other materials were fully investigated, which may bottleneck the actual improvement of the thermal management in applications. Our steady-state results indicated that the ITR between graphite and SiO2 determined the whole improvement in thermal management performance through the added graphite heat bridge. Subsequently, the transient thermal analysis was conducted on the HEMTs to explore the effect of graphene and thin graphite films under repeated joule heating pulses on a microsecond time scale, and we obtained the effect of graphene and thin graphite films on each heating and cooling process. Finally, based on all the results and analysis mentioned above, we can confirm that the graphite-based heat-spreader structures can still offer efficient heat dissipation under near-real conditions, thereby indicating ways of the optimization of HEMTs heat dissipation.

Technical and commercial viability assessment of liquid-cooled heat sinks for a circuit board with discrete heat loads

In this contribution, existing gaps in the design process of liquid-cooled heat sinks, i.e., the lack of overall performance assessment metrics and commercial viability analyses, are addressed. This work focused on the design of a cost-effective cooling system for a commercial circuit board with multiple and asymmetric heat sources designed and manufactured by an electronics company. The analysis was performed using 3-D computational fluid dynamics simulations across sixteen different cases, focusing on the effect on performance and manufacturing cost of two primary design features of liquid-cooled heat sinks: the inlet and outlet manifolds and heat transfer enhancing features, where pin fins and minichannels were considered. Specifically, the effect of diameter and spacing of the pin fins and the effect of the distribution and length of the mini channels over an unevenly heated surface were parametrically investigated. The tradeoff between thermal and hydraulic performance of the heat sinks was reconciled using an overall performance parameter, which allowed for a single numerical evaluation of the heat sinks’ global performance spanning several operating flow conditions. Likewise, the tradeoff between cost and performance was investigated by comparing the manufacturing cost of the different heat sink designs, including two heat spreader materials. Lastly, a comprehensive assessment of the potential cooling solutions for the circuit board was done by combining the overall performance and manufacturing cost per prototype through a novel parameter proposed herein. The broader liquid-cooled heat sink design approach reported in this work is a missing aspect in similar contributions, as the focus is solely on technical performance parameters, while commercial implementation issues (manufacturability and production cost) are neglected.

High-Performance RF Power Amplifier Module Using Optimum Chip-Level Packaging Structure

This article presents a high-performance radio frequency (RF) power amplifier (PA) module for which an optimum chip-level packaging structure is proposed to reduce the operating temperature of the RF PA monolithic microwave integrated circuit (MMIC). Because the output power ( <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">P</i> <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">out</sub> ) and the efficiency of an RF PA module are strongly affected by the thermal characteristics of the PA MMIC, various types of heat spreader materials and thermal interface materials have been examined to implement the PA chip-level packaging structure, and the optimum combination is proposed for a performance enhancement of the PA module in this article. In addition, the optimum form-factor of the heat spreader was suggested based on a thermal simulation. To verify the proposed PA chip-level packaging structure, a 10 W 6–18 GHz RF PA MMIC using a commercial 0.25- <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">μ</i> m gallium nitride high electron mobility transistor process was designed and implemented for radar applications. The operating temperature of the PA MMIC on the proposed chip-level packaging structure shows a dramatic reduction of 24.8 °C, and accordingly, the average <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">P</i> <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">out</sub> and average power-added efficiency are enhanced by up to 9.2% and 2.8%, respectively, when compared with a PA module using the conventional chip-level packaging structure.

Quantum-Dot Based Vertical External-Cavity Surface-Emitting Lasers With High Efficiency

We demonstrate an optically pumped vertical external-cavity surface-emitting laser (VECSEL) based on quantum dots (QDs) with a high optical gain. The photoluminescence (PL) emission of the QDs at the operating wavelength of 1030 nm has been optimized towards a high integrated intensity by using a dot density in the range of 10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">11</sup> cm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-2</sup> and a narrow PL linewidth of around 30 meV due to an improved size homogeneity. Additionally, post-growth rapid thermal annealing at 650 °C for 45 s was found to reduce the non-radiative recombination centers and further improve the output power efficiency. During this study, the number of QD layers, the heat sink temperature and the heat spreader material were analyzed. The best results with a record slope-efficiency of 35% and a maximum continuous-wave output power of 5.7 W could be achieved with an RTA treated QD based VECSEL containing 24 QD layers in the gain section. The laser was processed with a solder-based flip-chip bonding technique on a diamond heat sink and temperature stabilized at 4 °C. Furthermore, an excellent symmetric beam profile with M <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> = 1.12 was achieved.

A systematic design to develop high-performance sintered particulate copper-composite as heat spreader material

A computational framework built on an effective-medium theory and mean-field homogenization is used to design particulate copper (Cu) composite for high-performance heat spreaders for electronic devices. Several potential particulate types as a second-phase are considered based on their intrinsic properties to design various Cu-composite heat-spreaders leading to desirable properties such as low coefficient of thermal expansion (CTE), low density, and improved structural response without compromising on required thermal conductivity. Based on computational predictions, the thermal interface of matrix-particulate is found to be the dominant factor for maintaining required thermal conductivity (~300 W m−1 K−1), which suggested ceramic particles, particularly Beo, SiC, and AlN, as preferred candidates when loaded up to 30 vol%. Due to very high thermal conductivity and low CTE, diamond particles demonstrated the best results provided its wettability with copper is improved as a result of the surface coating. To validate the model results, numerous Cu composites with diamond as a second-phase are sintered using the spark plasma sintering technique, and the experimental data is found in close agreement with the predictions. The Cu composites containing Ni-coated diamond particles exhibited thermal conductivity more than the value of pure Cu at extremely low volume concentration (5%). The effect of particle size is also studied and it is found that the composites sintered with sub-micron particles resulted in more porosity as compared to micron-sized particles, which displayed direct bearing on thermal and mechanical properties as demonstrated by experimental data. The measured data on densification and particle–matrix interface condition is used in calibrating the models for establishing their effect on resulting thermal and structural properties. The presented integrated computational design methodology is validated using experimental data, which is expected to help the researchers and electronic industry develop high-performance heat spreaders with tailored properties.

Effect of SiC formation temperature on improvement in thermal conductivity of electrodeposited SiC-coated diamond/Cu composite plating

ABSTRACT Diamond/Cu composites are considered promising heat spreader materials; however, improving the interfacial adhesion between diamond and Cu is a challenge in manufacturing these composites. We focused on the surface modification of diamonds and previously reported that the formation of a SiC on the diamond surface effectively enhances the diamond/Cu interfacial adhesion, as well as thermal conductivity. In this study, the optimum treatment temperature to form SiC on diamond to apply to SiC-coated diamond/Cu composite platings for improving the interfacial adhesion and thermal conductivity is investigated. The formation of SiC on the diamond surface was greatly affected by the treatment temperature, and the coverage of the SiC coating on the diamonds increased with treatment temperature. The formation of a more uniform SiC coating contributed to improved interfacial adhesion between the diamond and electrodeposited Cu matrix. The thermal conductivity of the SiC-coated diamond/Cu composite plating generally increased with an increase in temperature; however, excessive heat treatment at 1450°C decreased the thermal conductivity. The composite platings using SiC-coated diamond prepared at 1400°C showed a maximum thermal conductivity of 454 Wm−1K−1, which was higher than that of pure Cu platings (373 Wm−1K−1) and pristine diamond/Cu composite platings (375 Wm−1K−1).

Special Topic on Monolithic 3-D Integration for Energy-Efficient Computing

As the traditional 2-D scaling is approaching its physical limit, there is a great motivation to explore the third dimension for future integrated circuit design. The memory industry has already adopted monolithic 3-D integration (e.g., in 176-layer 3-D NAND Flash), while the 3-D vertical integration structure of logic transistors (e.g., 3-D stacked nanosheets, NMOS on top of PMOS) is emerging for sub-3-nm logic nodes. The other trend is to stack the embedded nonvolatile memories [e.g., resistive random access memory (RRAM), phase change memory (PCM), magnetic random access memory (MRAM), and ferroelectric field-effect-transistor (FeFET)] on top of CMOS using the back-end-of-line (BEOL) processing. Taking one step further, the integration of multiple tiers of active transistors with embedded memories is expected to offer significant improvements in the throughput and energy efficiency thanks to the massive connectivity between logic and memories. Besides the technological breakthroughs, circuit design automation methodologies have become key enablers to optimize the tier partitioning in monolithic 3-D architectures. In addition, heat dissipation should be taken care of by accurate thermal modeling in these monolithic 3-D architectures. New heat spreading materials and advanced embedded cooling techniques are also important.

Experimental Evaluation of a Latent Heat Storage Module with a Heat Spreader for Thermal Management of a Tablet Computer

The objective of this work was to experimentally determine the feasibility of using a phase change material (PCM)-based temperature control module, in conjunction with a heat spreader and thermal interface material, to improve the thermal management of a tablet computer. An experimental apparatus was designed to be representative of a tablet computer. This mock tablet was used to perform a series of transient heating and cooling experiments to compare the impact of the PCM module on the thermal response of the system. The PCM module consisted of n-eicosane encapsulated with heat-sealable laminated film forming a 2 mm thick sheet of encapsulated PCM. A full comparison, including the use of a heat spreader and a thermal interface material (TIM), was conducted at heat generation rates of 4.5 and 7 W. The temperature control module was able to reduce the mean and peak temperatures of the internal components and at a heat generation rate of 7 W it extended its operating time by 30% before it reached a critical threshold temperature.

Thermal and mechanical characterization of high performance polymer fabrics for applications in wearable devices

With advances in flexible and wearable device technology, thermal regulation will become increasingly important. Fabrics and substrates used for such applications will be required to effectively spread any heat generated in the devices to ensure user comfort and safety, while also preventing overheating of the electronic components. Commercial fabrics consisting of ultra-high molecular weight polyethylene (UHMW-PE) fibers are currently used in personal body armor and sports gear owing to their high strength, durability, and abrasion resistance. In addition to superior mechanical properties, UHMW-PE fibers exhibit very high axial thermal conductivity due to a high degree of polymer chain orientation. However, these materials have not been widely explored for thermal management applications in flexible and wearable devices. Assessment of their suitability for such applications requires characterization of the thermal and mechanical properties of UHMW-PE in the fabric form that will ultimately be used to construct heat spreading materials. Here, we use advanced techniques to characterize the thermal and mechanical properties of UHMW-PE fabrics, as well as other conventional flexible materials and fabrics. An infrared microscopy-based approach measures the effective in-plane thermal conductivity, while an ASTM-based bend testing method quantifies the bending stiffness. We also characterize the effective thermal behavior of fabrics when subjected to creasing and thermal annealing to assess their reliability for relevant practical engineering applications. Fabrics consisting of UHMW-PE fibers have significantly higher thermal conductivities than the benchmark conventional materials while possessing good mechanical flexibility, thereby showcasing great potential as substrates for flexible and wearable heat spreading application.

Applications and Impacts of Nanoscale Thermal Transport in Electronics Packaging

Abstract This review introduces relevant nanoscale thermal transport processes that impact thermal abatement in power electronics applications. Specifically, we highlight the importance of nanoscale thermal transport mechanisms at each layer in material hierarchies that make up modern electronic devices. This includes those mechanisms that impact thermal transport through: (1) substrates, (2) interfaces and two-dimensional materials, and (3) heat spreading materials. For each material layer, we provide examples of recent works that (1) demonstrate improvements in thermal performance and/or (2) improve our understanding of the relevance of nanoscale thermal transport across material junctions. We end our discussion by highlighting several additional applications that have benefited from a consideration of nanoscale thermal transport phenomena, including radio frequency (RF) electronics and neuromorphic computing.

Cu/Diamond Interfacial Adhesion Improved By Using Amino Group Modified Diamonds to Electroplating of Cu/Diamond Composite

Introduction Heat spreaders are used to ensure operation of electronic devices, such as smart phones, pads, LED and screen displays, by dissipating heat generated form integrated circuits. The ideal material working as heat spreaders should have high thermal conductivity. Cu and Cu alloys have been used as heat spreader materials from this point of view, but their heat dissipation performances are approaching their upper limit. Therefore, a heat dissipation material exhibiting even higher thermal conductivity is required for future electronics. Meanwhile, carbon materials are expected as next-generation heat spreader materials due to their extremely high thermal conductivities. Our group has previously reported on electroplating of Cu/carbon composites. In this study, we focused on electroplating of Cu/diamond composites because diamond is an interesting filler material that do not require orientation control due to its isotropic thermal conductivity.Typically, it has been suggested that the major issue for Cu/diamond composites is the adhesion at Cu/diamond interface because Cu and diamonds show low affinity. Surface modification with a silane coupling agent has been reported to be effective for improving the affinity of the interface, leading to improvement in thermal conductivity by reducing the thermal barrier at the interface [1]. Amino groups (-NH2) are expected to be attracted to the cathode side along with Cu2+ because it is positively charged in acidic solutions and to improve the Cu/diamond interface by forming complex with Cu. In addition, it has been reported that the -NH2 modification of BN improves the thermal conductivity of BN/epoxy resin composites [2]. In this study, we performed electroplating of Cu/diamond composites using -NH2 modified microdiamonds and investigated its effect on adhesion at Cu/diamond interface.ExperimentalThe -NH2 modified diamonds were prepared beforehand by the following procedure. As a pretreatment, the microdiamonds (MDs: average diameter of 180 μm) were heated at 1350 ℃ for 2 hours in a vacuum (5 Pa or less), and subsequently heated at 425 ℃ in air. The pretreated MDs were added to 50 cm³ of toluene solution containing 5 wt% of 3-aminopropyltrimethoxysilane (APTMS) and stirred for 6 h at 65 ℃ for silanization. Then, 30 ml of methanol was added to prevent further reaction of unreacted APTMS molecules. -NH2 modified MDs were collected by filtration, sequentially washed with methanol, water and acetone and dried at 80 °C in a vacuum oven over night. Existence of -NH2 on diamond surface was confirmed by using ninhydrin reaction.Electroplating was performed at room temperature. The bath composition was 1.0 mol/dm3 CuSO4.5H2O aqueous solution adjusted to pH 2.0 using H2SO4. The -NH2 modified MDs were added to the bath. The cathode used was Cu and the anode used was Pt coil, the reference electrode was Ag/AgCl. Galvanostat was used to apply a constant current of 10 mA/cm2. The quantity of electricity was 250 C (theoretical film thickness of 92 μm). The adhesion at the Cu/diamond interface in the composite plating was evaluated by observing the surface and cross section using a scanning electron microscope (SEM).Results and DiscussionProtrusions were formed on the surface of microdiamond after silanization. Silane oligomer aggregates formed by the self-condensation reaction of APTMS may have bonded to the diamond surface as reported elsewhere [3]. The ninhydrin solution turned from colorless to purple by ninhydrin reaction, implying the presence of -NH2 on modified MDs. From observation of Cu/diamond interface in the composite plating, well adhesion was obtained when using -NH2 modified MDs while an obvious void was observed when using pristine MDs. The result indicated that modification of diamond surface by -NH2 was effective to improve the adhesion at Cu/diamond interface.ConclusionsMD surface was modified by -NH2 groups through silanization. Surface and cross-sectional observation of Cu/diamond composite platings using -NH2 modified MDs showed well adhesion at Cu/diamond interface. It was found that -NH2 modification of diamond surface was effective to improve the adhesion between Cu and diamond.AcknowledgementThis work was partially supported by the JST-OPERA Program, Japan [grant number JPMJOP1843] and “Knowledge Hub Aichi”, Priority Research Project and Aichi Prefecture Research, Development Subsidy from Aichi Prefectural Government. Reference Y. Yamada, M. Miki, NIPPON GOMU KYOUKAISHI, 2013,86,5,133-139K. C. Yung, H. Liem, J. Appl. Polym. Sci.,2007,106,3587-3591Y. Nakamura, N. Karyu, M. Noda, S. Fujii, Journal of the Adhesion Society of Japan, 2016,52,1,9-15

Thermal Conductivity of Graphene and Its Applications on Heat Spreading Materials

Graphene consists of a single layer of carbon atoms arranged in two-dimensional hexagonal lattice. This research set up model of graphene with heat source and sinks to visualize the movement of carbon atoms. Moreover, molecular dynamics simulations were tools to study the thermal conductivity of graphene and other properties of a material. The result shows that the thermal conductivity of graphene in the room temperature is relatively high among the existing materials. Various possibilities for its application will be briefly discussed, mainly focused on heat spreading materials. At last, there will be a discussion about graphene’s future development.

Performance analysis of MgO/ZnO multilayer thin film as heat spreader on Al substrates for high-power LED thermal management applications

Towards improving structural, surface, and thermal properties of MgO heat spreader, ZnO thin film was interstacked into MgO. This would improve heat dissipation and keeping the temperature as well as the junction temperature of LEDs in safe operating conditions and make the MgO/ZnO multilayer thin film as a reliable heat spreader material in thermal management application. XRD measurements, FESEM, and AFM analysis were employed in examining the structure, morphology, particle size, and topography of the spin-coated monolithic MgO and multilayer MgO/ZnO thin films, respectively. Improvement in crystal size, reduction in residual stress, lattice strain, and dislocation density were recorded for MgO/ZnO multilayer films. Similarly, introduction of ZnO into MgO resulted an improvement in surface morphology with large particle size (76 nm) and decrease in surface roughness from 19.1 to 9.6 nm. From thermal transient analysis, a noticeable difference in junction temperature raise (ΔTJ = 27.07 °C) and high difference in total thermal resistance (ΔRth-tot = 5.3 K/W) were recorded for LED fixed on 6:4 L MgO:ZnO thin film-coated aluminum substrate. Introduction of ZnO into MgO improves the structure and surface qualities as well as thermal performance of MgO thin film and LEDs mounted on them. The optimized multilayer MgO/ZnO ceramic-ceramic composite thin film could be employed for efficient, reliable, and longer life LEDs thermal management as heat spreader.

Ultrathin thermally conductive yet electrically insulating exfoliated graphene fluoride film for high performance heat dissipation

Abstract With the development of portable and flexible electronic devices, demends for high-performance thermal management materials with high thermal conductivity and electrical insulation are growing. Recently, graphene fluoride has received numerous attention from science community due to its high thermal conductivity and electrical insulation. Here, we report an advanced exfoliated graphene fluoride (EGF) film as a high performance heat spreader and thermal interface material for flexible electronic devices, which simultaneously exhibits ultrahigh thermal conductivity, excellent electrical insulation, and satisfactory flexibility. Commercially available graphite fluoride was directly exfoliated into graphene fluoride solution using ball milling method, followed by preparing ultrathin graphene fluoride films to take full advantage of graphene fluoride properties for heat dissipating applications. The resultant films show a tunable thermal conductivity by altering the thickness of films and show a superior in-plane thermal conductivity of 242 W m−1 K−1 and exceptional through-plane thermal conductivity of 21.8 W m−1 K−1 at the thickness of 10 μm. More interestingly, the graphene fluoride films possess excellent flexibility. The newly developed EGF film provides a creative opportunity for fabrication of multifunctional highly flexible materials, which may promote the development of heat dissipation materials in next generation flexible electronics.

Aerogel Perfusion-Prepared h-BN/CNF Composite Film with Multiple Thermally Conductive Pathways and High Thermal Conductivity.

Hexagonal boron nitride (h-BN)-based heat-spreading materials have drawn considerable attention in electronic diaphragm and packaging fields because of their high thermal conductivity and desired electrical insulation properties. However, the traditional approach to fabricate thermally conductive composites usually suffers from low thermal conductivity, and cannot meet the requirement of thermal management. In this work, novel h-BN/cellulose-nano fiber (CNF) composite films with excellent thermal conductivity in through plane and electrical insulation properties are fabricated via an innovative process, i.e., the perfusion of h-BN into porous three dimensional (3D) CNF aerogel skeleton to form the h-BN thermally conductive pathways by filling the CNF aerogel voids. When at an h-BN loading of 9.51 vol %, the thermal conductivity of h-BN/CNF aerogel perfusion composite film is 1.488 W·m−1·K−1 at through plane, an increase by 260.3%. The volume resistivity is 3.83 × 1014 Ω·cm, superior to that of synthetic polymer materials (about 109~1013 Ω·cm). Therefore, the resulting h-BN/CNF film is very promising to replace the traditional synthetic polymer materials for a broad spectrum of applications, including the field of electronics.

Thermal expansion coefficients of high thermal conducting BAs and BP materials

Recently reported very high thermal conductivities in cubic boron arsenide (BAs) and boron phosphide (BP) crystals could potentially provide a revolutionary solution in the thermal management of high power density devices. To fully facilitate such an application, the compatible coefficient of thermal expansion (CTE) between the heat spreader and the device substrate, in order to minimize the thermal stress, needs to be considered. Here, we report our experimental CTE studies of BAs and BP in the temperature range from 100 K to 1150 K, through a combination of X-ray single crystal diffraction and neutron powder diffraction. We demonstrated that the room temperature CTEs, 3.6 ± 0.15 × 10−6/K for BAs and 3.2 ± 0.2 × 10−6/K for BP, are more compatible with most of the semiconductors including Si and GaAs, in comparison with diamond, and thus could be better candidates for the future heat spreader materials in power electronic devices.

Influence of Molar Concentration: Sol-Gel Synthesized Magnesium Oxide Thin Films for High Power Light Emitting Diode Thermal Management

Sol-gel technique was used to synthesize 0.6 M and 0.8 M molar concentrations of magnesium oxide thin on aluminium substrate and enforced into heat spreader material in thermal management of lighting devices. X-ray diffraction analysis confirm the films to be polycrystalline cubic in nature with (200), (220) and (222) orientations. 20 layers from 0.8 M showed higher intensity from the X-ray analysis. Relative thermal conductivity measurement of 20 layers from 0.6 M showed a value of (26.3 W/mK) which appears to improve over other layers. At 700 mA operating current, 20 layers from 0.6 M showed higher junction temperature difference of 37.16 °C as well as higher thermal resistance difference of 5.9 K/W when compared to bare aluminium substrate. All coated films are within the accepted color correlated temperature safe operating range (< 3300 K) of light emitting diodes, addition to this, 20 layers MgO thin films from 0.6 M displayed a recommendable illuminance as well as color correlate temperature performance from optical characterization. Atomic force microscope surface analysis for both molar concentrations showed an improvement in surface smoothness over bare substrate. Overall, magnesium oxide thin films can be perfectly enforced as heat spreader for high power light emitting diodes.

Fabrication of low cost and scalable carbon-based conductive ink for E-textile applications

In this work, we demonstrate a simple, highly scalable and cost-effective fabrication process of functional carbon black (CB) ink from burned charcoal of dry woods. Our process consists of both dry and wet medium blending of burned charcoals which reduces the consumption of high processing time and uses of sophisticated instruments to manufacture functional CB. The process includes formulation of functional CB ink prepared with poly-vinyl alcohol (PVA) binder, which is applied to the textile fabric using a simple pad-dry process. The sheet resistance and the loading percentage of carbon ink on the cotton fabric are saturated to ∼(25–28) kΩ/sq. and ∼(115–130) wt.% of the native fabric, respectively after 7 repeated padding cycles. The carbon-coated fabrics are demonstrated durable and reliable with repeated bending cycles. Although the resistance of the conductive fabric increases after the first wash cycle, interestingly, the resistance of the fabric tends to decrease in the following 11 consecutive wash cycles. The coated conductive fabrics are used as bend-sensors since it is able to detect very low bending angle for at least 1000 repeated bending cycles. Additionally, we demonstrate the use of carbon coated cotton fabric as heat-spreading materials of a textile heater.