Interfacial Thermal Resistance Research Articles

Thermal characterization of Ge-rich GST/TiN thin multilayers for phase change memories

In the domain of phase change memories (PCMs), intensive research is conducted to reduce the programming cycle cost. The RESET operation is done by melting the PCM and then quenching the liquid phase to put it back to the amorphous state. In most of the devices, the heating is realized by the Joule effect with a titanium nitride (TiN) component put in contact with the PCM itself. One of the crucial points to improve the efficiency of this technology is to characterize the thermal contact between TiN and PCM. Having a low thermal resistance between the heater and the PCM ensures the heat transfer between the two is as efficient as possible. In this work, the interfacial thermal resistance between Ge-doped G2Sb2Te5 (GeGST)/TiN in multilayer systems has been characterized, and the influence of the compressive stress exerted by the TiN layers on the GeGST crystallization has been highlighted.

Conjoint Effect of Boron Nitride and Surface-Enhanced Flake Graphite in Thermal Conductivity of Thermally Conductive Grease

The next generation of high-power electronic devices is expected to exhibit improved heat dissipation capabilities despite their smaller size. Current studies have investigated the utilization of hybrid fillers, our study introduces a novel approach by combining boron nitride (BN) and surface-enhanced flake graphite (G), both of which possess a platelet-like structure, to develop a thermally conductive grease. The grease shows an exceptionally high thermal conductivity of 2.21 W/mK and an extremely low electrical conductivity of 7.3×10-6 S/m. The viscosity of the grease is measured at 149 Pa·s. By incorporating hybrid fillers with a significantly high aspect ratio into EPON 828, a notable reduction of interfacial thermal resistance is observed, which is attributed to the formation of an effective pathway for phonon transfer facilitated by the unique characteristics of the hybrid fillers. Various theoretical models are employed to corroborate the experimental data, which facilitates substantiating the fundamental principles underlying the enhanced thermal conductivity of the prepared thermal grease.

Thermal Modeling and Experimental Validation of Mid-Conductor Winding Cooling

A direct cooling method for windings of electrical machines, mid-conductor winding cooling, is studied. Spaces between the wires are utilized as coolant channels, with a liquid being pumped through the winding along the length. These results in the elimination of thermal interface resistances, a high heat transfer area and heat transfer coefficient while maintaining the same cross-sectional area for the copper winding. A thermohydraulic model is made and validated to analyze the heat transfer rates and pressure drop. Validation measurements with a water-glycol mixture as coolant show that the modeled and measured pressure drop correspond within 0.07 bar and the modeled and measured winding temperature within 3 °C. When made relative to the temperature difference between winding and coolant, the deviation is equal to 12%. The validated model is used to analyze the performance when utilizing oil as coolant. For a winding temperature of 180 °C and a pressure drop of 1 bar, using the novel cooling method results in a maximal attainable current density equal to 39.4 A/mm2 which is 41% higher than that attainable with spray end winding cooling.

A high-performance thermal transistor based on interfacial negative differential thermal resistance

A thermal transistor, which can achieve the smart, flexible, and precisely controlled thermal management, proves to be a promising thermal device. Recently, thermal transistors based on the negative differential thermal resistance (NDTR) have been regarded as the most feasible configuration considering their simple structures. Among the several methods to implement NDTR, the method of reducing the contact pressure between mated surfaces by using the negative thermal expansion material, thus generating a negative temperature dependent interface thermal conductance and accompanied NDTR, is the most likely to be observed experimentally. In this paper, a thermal transistor based on NDTR is designed by engineering the interfacial thermal resistance. Moreover, we optimize the switching function and the amplification function of the transistor by only adjusting the temperature and the length of the source terminal. As an example, a silicon thermal transistor with a high switching ratio as well as an accurately controlled thermal flux amplification function is discussed at low temperature. The design and optimization of macroscopic thermal transistor will promote the rapid development of thermal functional devices and help to control thermal flux in a more flexible and effective way.

Facile and Scalable Strategy for Fabricating Highly Thermally Conductive Epoxy Composites Utilizing 3D Graphitic Carbon Nitride Nanosheet Skeleton.

The application of high-performance thermal interface materials (TIMs) for thermal management is commonly used to tackle the problem of heat accumulation, which influences the performance and reliability of microelectronic devices. Herein, a novel three-dimensional (3D) carbon nitride nanosheet (CNNS)/epoxy composite with high thermal conductivity was developed by introducing 3D CNNS skeleton fillers prepared by a facile and scalable strategy assisted by a salt template. Benefiting from the continuous heat transfer pathways formed in the CNNS skeleton, 17.0 wt % 3D CNNS/epoxy composites achieve a superior thermal conductivity of 1.27 W/m·K, which is 6.35 and 1.57 times higher than those of epoxy resin and convention CNNS/epoxy, respectively. With the aid of theoretical model analysis and finite element simulation, the pronounced enhancement effect of the 3D CNNS skeleton on the thermal conductivity of epoxy composites is found to be attributed to the continuous 3D CNNS thermally conductive network, the diminished CNNS-CNNS interfacial thermal resistance, and the effective interfacial interactions between epoxy and CNNS. In addition, the 3D CNNS/epoxy composites possess high electrical insulation and desirable mechanical strength. Therefore, 3D CNNS/epoxy composites are promising TIMs for advanced electronic thermal management.

Design of Silicon Rubber/BN Film with High Through-plane Thermal Conductivity and Ultra-low Contact Resistance

Polymer-hexagonal boron nitride (BN) composite has become an ideal thermal interface material (TIM) for electronic devices because of its high thermal conductivity and superior electronic insulation. However, owing to the 2D shape and chemical inertness of BN filler, the vertical alignment of BN and the huge thermal resistance are current challenges, which hinder the efficient heat transfer of polymer/BN composites. Herein, by a novel non-solvent induced phase separation process combined “in-situ welding” strategy, we present the fabrication of silicone rubber film with finger-like continuous BN-welded filler skeleton, which reveals a high through-plane thermal conductivity of 15.4 W m−1K−1 at only ∼ 15 wt% BN. Finite element simulation and nonlinear model analyses theoretically confirm that the filler-to-filler interfacial thermal resistance (ITR) is halved after in-situ welding process. In addition, thanks to the excellent compressibility and conformability of silicon rubber matrix, the contact thermal resistance (<70 Kmm2W−1) of this composite film is much lower than that of the commercial thermal pad under different pressure. The proposed strategy opens up a novel and high-throughput preparation strategy for the high-performance TIM for modern electronic devices.

Vertically Aligned Boron Nitride Nanosheets Films for Superior Electronic Cooling.

Thermally conductive and electrically insulating thermal interface materials (TIMs) are highly desired for electronic cooling. To improve heat transfer efficiency, thermally conductive fillers with a high loading content have been incorporated into the polymer-based TIMs. However, this is usually at the expense of the interfacial thermal resistance reduction and reliability. In this study, vertically aligned boron nitride nanosheet films (VBNFs) have been prepared by a scalable microfluidic spinning process and template-assisted chemical vapor deposition conversion method. A further high-temperature annealing was applied to achieve high crystallinity. VBNFs have been applied as fillers to fabricate TIMs and achieve a superior through-plane thermal conductivity of 6.4 W m-1 K-1 and low modulus of 2.2 MPa at low BN loading of 9.85 vol %, benefitting from the well-aligned vertical sheet structure and high crystallinity. In addition, the fabricated TIMs present high-volume resistivity and breakdown strength, satisfying the electrical insulation demands. The high thermal conductivity and low modulus contribute an outstanding cooling performance to the TIMs in the heat dissipation application for high-power LEDs. This template-assisted conversion technology for the fabrication of orientated BN nanosheets structure and the prepared high-performance TIMs pave the way for efficient thermal management of high-power electronics.

The Thermal Time Constant of an Electrothermal Microcantilever Resonator

Background: The thermal time constant is the core parameter for determining the dynamic response of the electrothermal actuators and the corresponding maximum operational frequency. Aim: Since it is necessary to determine how the thermal actuation is taking place within the cantilever, this paper presents two models for the thermal time constant of bimetal microcantilevers. One model was based on the bimetallic effect, and the second was based on temperature gradients in layers Methods: In order to investigate and check the validity of the two roposed model, the device was actuated electrothermally and the thermal time response was estimated. A driving voltage was applied to the platinum electrode. The first model is based on the interface thermal resistance between the base and the top electrode layer. The second model assumes that the temperature gradients within the base layer are responsible for thermal actuation. Results: The microcantilever was excited electrothermally with a resonance frequency of 1.89 MHz. The bimetallic effect was found to be less able to stimulate the microcantilever at this resonance frequency. Therefore, the conclusion was that thermal actuation occurred as a result of temperature variation within the SiC base layer. Conclusion: The results also indicated that temperature variations within one of the two materials in contact may be responsible for thermal actuation, especially if the material has high thermal conductivity.

Research on performance of heat sink with no dielectric copper-aluminum connection

Air-cooled copper-aluminum composite heat sink is generally used for heat dissipation of electronic components. If the traditional copper-aluminum connection mode is used, such as welding, copper plugging and locking, bad phenomena such as pores, impurities and interface thermal resistance easily occur on the bonding surface, resulting in decreased heat conduction efficiency, heat dissipation efficiency and lower strength of the bonding surface. Therefore, we introduce a mortise-tenon connected heat sink, and optimize the honeycomb structure of the heat dissipation fin to design a new type of air cooled heat sink with no dielectric copper-aluminum connection. CFD simulation software is used to study the heat dissipation performance of the traditional and new heat sink, and the obtained data are comparatively analyzed to verify feasibility of the process. The result shows that the mass of the honeycomb heat sink is reduced by 37.1%, the surface area is increased by 47.8%, and the heat dissipation performance of the new copper-aluminum heat sink is 60% higher than that of pure copper integrated heat sink. It is concluded that heat sink with mortise-tenon connection has superior performance than traditional integrated air cooled heat sink, and honeycomb heat sink has superior performance than solid plate heat sink.

Analytical integration of the heater and sensor 3ω signals of anisotropic bulk materials and thin films

We derive and analytically integrate the models for the heater and sensor 3ω signals of the temperature field of anisotropic bulk materials and thin films. This integration is done by using the Fourier transform and expressing the frequency dependence of temperature in terms of the modified Bessel and Struve functions, which are well-implemented in major computation software. The effects of the radiative losses and interface thermal resistance are also evaluated for different frequency regimes. Further, by fitting the 3ω model integrated over the heater and sensor widths to experimental data recorded up to 31 kHz, the thermal conductivity and thermal diffusivity of a quartz glass wafer are determined for temperatures ranging from 300 to 800 K. The obtained results show that the usual log-linear approximation can induce an uncertainty of about 5% on the thermal conductivity values. The exact integrated models are thus expected to facilitate the accurate determination of the thermal conductivity and thermal diffusivity of anisotropic materials through a wide spectrum of modulation frequencies and without time-consuming numerical integration.

Fractional derivative modelling for rheological characteristics of multilayered saturated porous rock with interfacial thermal contact resistance

AbstractIn this paper, the one‐dimensional rheological characteristics of multilayered saturated porous rock subjected to a ramp‐type heating is investigated. By introducing the fractional order parameter and material parameters, a viscoelastic constitutive model is proposed to describe the rheological characteristics of multilayered saturated porous rock. The general incomplete thermal contact model is established to predict the interfacial thermal contact resistance of multilayered saturated porous rock. Based on the coupled thermo‐hydro‐mechanical theory, the semi‐analytical solutions of the excess pore water pressure, temperature increment and displacement are obtained by using the Laplace transform method. The accuracy of the present solutions is verified by comparing with the classic elastic and viscoelastic models, and existing solutions. In addition, the influence of fractional order parameter, material parameter ratio, thermal contact transfer coefficient and thermal partition coefficient on the excess pore water pressure, temperature increment and displacement of multilayered saturated porous rock are investigated.

Numerical and analytical modelling of effective thermal conductivity of multi-walled carbon nanotubes polymer nanocomposites including the effect of nanotube orientation and interfacial thermal resistance

Multi-walled carbon Nanotube (MWCNT) fillers are extensively used to improve the thermomechanical properties of polymers. In this study, five different weight fractions (0%, 0.25%, 0.50%, 0.75%, and 1%) of MWCNT-polymer nanocomposites were prepared by the solution mixing technique. The thermal conductivity of MWCNT-polymer nanocomposites was investigated using the laser flash method. The closed-form solution of the modified Mori-Tanaka homogenization method was developed for the accurate estimation of the thermal conductivity of nanocomposite materials after considering the influence of interfacial thermal resistance (ITR). The finite element simulation of RVE modelling was utilized to predict the thermal conductivity of nanocomposites with and without consideration of the interfacial thermal resistance effect. A perfect bond was assumed between MWCNT and polymer for both numerical and analytical studies. The thermal conductivity results obtained from the closed-form solution of the modified Mori-Tanaka method were in good agreement with both the finite element simulation (FEM) and experimental results.

Near‐Room‐Temperature Thermoelectric Performance Enhancement Via Phonon Spectra Mismatch in Mg3(Sb, Bi)2‐Based Material by Incorporating Multi‐Walled Carbon Nanotubes

AbstractAlthough a high figure of merit (zT) over a wide range of temperatures has been shown in n‐type Zintl Mg3(Sb, Bi)2, further improvement of its near‐room‐temperature performance is still required to promote its application in next‐generation thermoelectric coolers and power generators. Here, a novel strategy of phonon spectra mismatch for enhancing the thermoelectric performance of Mg3(Sb, Bi)2 is reported by incorporating multi‐walled carbon nanotubes (MWCNT). The introduction of very small amounts of MWCNT generates a large interfacial thermal resistance and thus significantly reduces the lattice thermal conductivity of the resulting composites, while maintaining a high power factor. As a result, a zT of ≈1.5 at 573 K and an average zT of 1.14 between 323 and 573 K can be achieved in the 0.5 wt% MWCNT composite. Moreover, a high conversion efficiency of ≈8.1% under a temperature difference of 283 K is realized in a resulting single‐leg device, making it a promising candidate material for low‐grade heat recovery. This study provides not only a material with a high near‐room‐temperature zT but also a unique insight into the design of high‐performance thermoelectric materials via compositing to exploit the large difference in phonon spectra between the components of the composite.

Acoustic Wave Generation in Nanofluids: Effect of the Kapitza Resistance on the Thermophone to Mechanophone Generation Mechanism Transition

High frequency, short wavelength acoustic wave generation in fluids, by means of immersed nanotransducers, is key to applications ranging from the biomedical to the ICT sector, all the way to investigating fundamental aspects of the mechanics of fluids. In this context, the commonly adopted generation mechanism is the thermophone, where the nanotransducer serves as a nanoheater for the surrounding fluid and the acoustic wave is launched by water thermal expansion. Its performance, however, is severely degraded when reaching up to hypersonic frequencies. We analytically investigate the thermoacoustic response in the frequency domain for the case of a gold nanofilm transducer in contact with water. We prove that another generation mechanism, the mechanophone, sets in this critical frequency range, widening the acoustic generation bandwidth. In the mechanophone, it is the nanotransducer thermal expansion that launches pressure waves in water. We find a threshold frequency discriminating between these two regimes, which can be tuned by acting on the Kapitza resistance at the solid–liquid interface. We then show how the mechanophone mechanism can be activated in the frame of photoacoustic generation with pulsed laser sources. The unveiled physics bears generality beyond the specific system and explains the acoustic generation mechanisms in nanofluids.

Rapid boiling of ultra-thin liquid argon film on patterned wettability surface with nanostructure: A molecular dynamics investigation

Surface wettability and structure have been proved as two important influential factors to the thermal transport at the solid-liquid interface at nano scale, however, the combined enhancement mechanism has not been clearly understood till now. In this study, the rapid boiling behaviors of nano thin liquid argon film on the heterogeneous wetting surfaces were examined with the non-equilibrium molecular dynamics (MD) method. Meanwhile, the ring-patterned and stripe-patterned surfaces were designed and analyzed, respectively. By analyzing the trajectory of argon atoms, the bubble nucleation behavior, heat flux and interfacial thermal resistance, it is found that the lower hydrophobic area fraction is favorable for the bubble formation and the ring-patterned surface shows an advantage in the nucleate boiling compared with the stripe-patterned one. Meanwhile, the nanostructure has a great influence on the boiling phenomena, which accelerates the development of bubble nuclei and improves the maximum heat flux compared with the planar one. In present simulations, the ring-patterned surface with nanostructure of 40% hydrophobic area fraction is the optimal design for the efficiency enhancement of explosive boiling process. The findings in this work contribute to the design of the coating nanostructured surface to enhance the boiling heat transfer performance under the high heat fluxes.

Structural Design and Research Progress of Thermally Conductive Polyimide Film - A Review.

Currently, heat accumulation has seriously affected stabilities and life of electronic devices. Polyimide (PI) film with high thermal conductivity coefficient (λ) has long been held up as an ideal solution for heat dissipation. Based on the thermal conduction mechanisms and classical thermal conduction models, this review presents design ideas of PI films with microscopically ordered liquid crystalline structure which are of great significance for breaking the limit of λ enhancement and describes the construction principles of thermal conduction network in high-λ filler strengthened PI films. Furtherly, the effects of filler type, thermal conduction paths and interfacial thermal resistances (ITR) on thermally conductive behavior of PI film are systematically reviewed. Meanwhile, this paper summaries the reported research and provides an outlook on the future development of thermally conductive PI films. Finally, it is expected that this review will give some guidance to the future studies in thermally conductive PI film. This article is protected by copyright. All rights reserved.

Film Thicknesses Influence on the Interfacial Thermal Resistances within Ge‐Rich Ge2Sb2Te5/Ge2Sb2Te5 Multilayers

Phase change memories (PCRAM) are often made of chalcogenide alloys in the form of multilayer systems (MLS). The mostly used alloys are Ge2Sb2Te5 and Ge‐rich Ge2Sb2Te5. The current article reports on the thermal characterization of very thin (&lt;5 nm) Ge‐rich Ge2Sb2Te5/Ge2Sb2Te5 MLS by modulated photothermal radiometry (MPTR). The MPTR method allows for the investigation of such samples by determining, with an inverse method, the total thermal resistance of the stack deposited on the substrate. With the measurement of the total thermal resistance, it is possible to determine the thermal conductivity of the deposit and the interfacial thermal resistances between layers. The interfacial thermal resistance between Ge‐rich Ge2Sb2Te5/Ge2Sb2Te5 is characterized, which is an important parameter to reduce the energy cost of the PCRAM functioning. It is also possible to highlight a decrease in interface quality inside the MLS after the beginning of the phase transition around 250 °C.

An experimental study on anisotropy of thermal conductivity in shale

Thermal conductivity plays a crucial role in heat transfer and geothermal field distribution in the lithosphere. Understanding the anisotropy of thermal conductivity in shale and its influencing factors is significant for resource evaluation in shale oil and gas areas. In this study, the thermal conductivity of shales in the Songliao and Sichuan basins was measured by laser scanning method. The relationship between thermal conductivity and mineral composition, burial depth and stratigraphy was analyzed to investigate the anisotropy of shale thermal conductivity and its influencing factors. The results show that the thermal conductivity of shale ranges from 1.000 to 2.500 W/(m·K) at different angles. The thermal conductivity of shale is positively correlated with the content of high thermal conductivity minerals such as quartz and increases with burial depth. The anisotropy index of shale thermal conductivity ranges from 0.96 to 2.40. As heat flows through multiple laminae, the interfacial thermal resistance and the influence of the medium cause a decrease in the shale thermal conductivity as the angle between the heat flow direction and the laminae increases. The insights obtained are of reference significance for the accurate modeling of the thermal properties of shale sequences and the study of the geothermal field in shale oil and gas areas.

Interface stress calculation and failure behavior of TBCs on the surface of aluminum alloy with anodic oxidation

Aluminum protective coatings have poor performance due to the significant difference in coefficient of thermal expansion (CTE) between the substrate and the coating. In this study, porous anodic aluminum layer, which have high bonding, well matching and grew in situ on the substrate of aluminum alloy (4032) using anodic oxidation, and then thermal barrier coatings were produced on the surface by laser surface modification and atmospheric plasma spraying (APS). The aim of this way is to improve the interface thermal shock resistance (TSR) of the coatings. The results showed that the coatings with anodic aluminum layer (highest group average of 444 cycles) have a much higher number of thermal shock cycles than metallic bond coatings. Furthermore, the failure analysis suggested that the bonding stability of the coatings is influenced by the surface state, surface mosaic structure, as well as such as CTE and surface roughness. Eventually, a double-layer mismatch stress model was developed to characterize the residual stresses caused by deformation mismatch in the coatings. After performing calculations，from a force perspective τa≈10τb, and from a work perspective Wfa≈3.34Wfb.

High Out-of-Plane Thermally Conductive Polyimide Film for Electronic Thermal Management by the Incorporation of Core–Shell Ag/Polyimide Microparticles

Polyimide (PI) films with high out-of-plane thermal conductivity are highly desirable for effectively alleviating thermal failure in advanced flexible electronics. However, it is still a great challenge to achieve high out-of-plane thermal conductivity with a low filler content by a simple method. Herein, an Ag-coated PI microsphere (PIM@Ag) as a thermally conductive filler with a considerable heat-transfer path in the out-of-plane direction is prepared to improve the out-of-plane thermal conductivity of the PI film. Because of the introduction of thermal welding between Ag nanoparticles during thermal imidization further eliminating the interface thermal resistance, the resultant PI/PIM@Ag composite film exhibits a high out-of-plane thermal conductivity of 1.2 Wm–1K–1 with an ultralow Ag content of 6.08 wt % and a superior tensile strength of 124.0 MPa compared to 78.9 MPa of a pure PI film. Practical application and comsol simulation results verify that the PI/PIM@Ag composite film has excellent heat dissipation ability for a chip. This work provides an idea for improving the out-of-plane thermal conductivity of polymers with low filler contents.