Heat Dissipation Channel Research Articles

Enhanced thermal conduction by surface phonon-polaritons.

Improving heat dissipation in increasingly miniature microelectronic devices is a serious challenge, as the thermal conduction in nanostructures is markedly reduced by increasingly frequent scattering of phonons on the surface. However, the surface could become an additional heat dissipation channel if phonons couple with photons forming hybrid surface quasiparticles called surface phonon-polaritons (SPhPs). Here, we experimentally demonstrate the formation of SPhPs on the surface of SiN nanomembranes and subsequent enhancement of heat conduction. Our measurements show that the in-plane thermal conductivity of membranes thinner than 50 nm doubles up as the temperature rises from 300 to 800 kelvin, while thicker membranes show a monotonic decrease. Our theoretical analysis shows that these thickness and temperature dependencies are fingerprints of SPhP contribution to heat conduction. The demonstrated thermal transport by SPhPs can be useful as a previously unidentified channel of heat dissipation in a variety of fields including microelectronics and silicon photonics.

Thermal coupling parameters between electron, phonon, and magnon of Nickel

Thermal interaction in an electron-phonon-magnon system in a ferromagnetic Ni film is investigated using a time-resolved pump-probe technique with thermoreflectance and magneto-optical Kerr effect. A nanoscale Au/Ni bilayer is used to induce thermal excitation of Ni in two ways: direct heating of Ni and indirect heating of Ni via Au. By comparing experiments and thermal modeling, we obtain the coupling parameters for electron-phonon, electron-magnon, and phonon-magnon pairs: 8.55 × 1017, 1.0–1.3 × 1017, and 0.8–1.1 × 1017 W m−3 K−1, respectively. In particular, we find that the phonon-magnon coupling parameter plays a significant role as a fast heat dissipation channel from magnon to phonon during the initial few picoseconds. In addition, both direct and indirect heating can be explained by similar coupling parameters with a variation less then 30%. Consequently, we conclude that the heat exchange between electron, phonon, and magnon is the dominant mechanism for the ultrafast demagnetization.

Design of Single-Turn Air-Core Integrated Planar Inductor for Improved Thermal Performance of GaN HEMT-Based Synchronous Buck Converter

Gallium nitride (GaN) high electron mobility transistor (HEMT) has a lateral device structure with wafer-level packaging, which is advantageous in minimizing parasitic parameters and overall device size. This type of packaging also has better thermal performance than conventional packaging due to low junction-to-bottom thermal resistances. It indicates copper layers in printed circuit boards can effectively serve as heat dissipation channels for the switching devices. When these copper traces and pours in the vicinity of the switching devices are carefully designed and shaped, they can also be utilized as an integrated output filter. In this article, a synchronous buck converter with a single-turn air-core integrated planar inductor is proposed to achieve both zero-voltage switching and high thermal performance of the GaN HEMTs. A new planar inductor design flowchart is introduced, and analytically estimated inductance and resistance are verified with simulation and experiment. Three different inductors are designed and fabricated to prove the improved thermal performance of the proposed converters.

Phonon Engineering to Modify Acoustic Phonon Velocity in Hexagonal Layered Superlattices

This letter presents the possibility of using the effective medium model coupled with the piezoelectric stiffening to quantitatively explain and engineer acoustic phonons as a heat dissipation channel in GaN-based devices. These effects will be described for a GaN/AlN superlattice that exhibits enhanced acoustic phonon velocities as compared with bulk GaN. We numerically calculate the stiffened elastic constant values and apply them within the effective medium model for elastic constants. With the recent advances in epitaxial GaN growth technology, it may be possible to consider this phonon engineering option to investigate the effect on the longitudinal sound velocity to increase the rate of heat transport in GaN/AlN superlattice.

Dioxygen Activation by Iron Complexes: The Catalytic Role of Intersystem Crossing Dynamics for a Heme-Related Model

Enzymes containing heme, nonheme iron, or copper active sites play an essential role in the dioxygen binding and activation for substrate oxidation. The conceptual challenges to the quantitative modeling of this primary catalytic step arise from (1) instrinsic electronic nonadiabaticity of the spin flip events of the triplet dioxygen molecule (3O2), mediated by spin–orbit coupling and (2) possible heat dissipation channels, due to the high exothermicity of dioxygen binding processes. Herein, the spin-forbidden dioxygen binding dynamics of a reduced heme model was directly investigated in terms of the nonadiabatic trajectory surface-hopping dynamics, involving the coupled singlet, triplet and quintet states. This work reveals the complexity of this elemental reaction, and the binding/dissociation dynamics of iron peroxo species is important to interpret the subsequent H atom abstraction reaction step. Furthermore, we identify nonadiabatic dynamical effects that could not be observed through traditional cal...

Void Formation and Growth at Solder-Bonded Interfaces in HP LEDs

Heat flux inside the HP LED chip is also increasing with the increasing drive current, integration and miniaturization of LED chips. The junction temperature of LED strongly depended on the heat transmission capacity of die attach layer, which provided the heat dissipation channel between the heat generating LED chips and the heat slug. The voids, interrmetallic compounds or a small delamination would lead to the increasing thermal resistance in the die attach layer. In this paper, the reliability of soldered-bonded interfaces was studied in high-brightness LEDs, which were prepared by Cree and currently available on the market. Results revealed that the higher drive currents would lead to the accelerated degradation or failure of treated LEDs. Additionally, the injection current had an important effect on void formation and growth at the solder-bonded interfaces. The larger drive current would induce the delamination between LED die and heat slug. This study provided some guidance for the end users and a theoretical basis for solder-bonded technologies.

Fabrication of Cu-riched W–Cu composites by combustion synthesis and melt-infiltration in ultrahigh-gravity field

Unadulterated Cu-riched W–Cu composites of W27–Cu73, W34–Cu66, W40–Cu60, W49–Cu51 and W56–Cu44 have been prepared by a novel method called combustion synthesis and melt-infiltration in ultrahigh-gravity field, of which W27–Cu73 and W34–Cu66 showed good ductility and W40–Cu60, W49–Cu51 and W56–Cu44 were brittle. In this technique, Cu melt accompanied with a great amount of heat was produced by thermit reaction and infiltrated into W–Cu powder bed. When the powder bed was Cu-riched powder bed such as W50–Cu50 or W60–Cu40, Cu melt would go through the powder bed, reach the bottom of the graphite crucible and then form a heat dissipation channel. Thus the cooling rate was so fast that the product was mixed up with impurity. The problem can be solved by putting some W powders under W50–Cu50 or W60–Cu40 powder bed to prevent the formation of heat dissipation channel.

Temperature Distribution Analysis of a Switched Reluctance Linear Launcher

A thermal model of a switched reluctance linear launcher is presented in this paper. The accuracy of the thermal model is verified by comparing experimental data with those results derived from finite-element method simulation. The temperature distribution of a switched reluctance linear launcher is derived based on the stator copper losses as the main heat power with measured stator winding current by the current sensor. The maximum temperature rise curves under different ambient temperature and different heat power of winding A are studied. The heat dissipation power of four air convection surfaces under different ambient temperature and the different heat power of winding A is also studied. Furthermore, this paper achieves optimization in thickness of the stator plate and in adding fins to the stator plate for heat dissipation with the present model. It is shown that the stator plate is the maximum heat dissipation power surface so that it can be adopted as the main heat dissipation channel and the effect of heat dissipation is obvious by adding fins to the stator plate.

Thermal analysis for fast thermal-response Si waveguide wrapped by SiN

A new type of Si waveguide wrapped by silicon nitride (SiN) is designed, and its optical and thermal analysis are presented. The thickness of SiN up-cladding should be larger than 1 μm in order to prevent the absorption of optical field by metal heater. Thermal response of the proposed waveguide structure is enhanced by the high thermal conductivity of SiN. Moreover, this thermal response can be further improved by a fast heat dissipation channel created in this structure. Our simulation results indicate that a rise time of about 110 ns can be achieved for the proposed waveguide structure, which is about two orders of magnitude less than that of the conventional Si waveguide. The influences of the thickness of up-cladding and the stretching width and etching depth on the thermal performance are also discussed. The simulation shows thin up-cladding, large stretching width and etching depth are critical to enhance the thermal response speed.

Heat Transfer across the Interface between Nanoscale Solids and Gas

When solid materials and devices scale down in size, heat transfer from the active region to the gas environment becomes increasingly significant. We show that the heat transfer coefficient across the solid-gas interface behaves very differently when the size of the solid is reduced to the nanoscale, such as that of a single nanowire. Unlike for macroscopic solids, the coefficient is strongly pressure dependent above ∼10 Torr, and at lower pressures it is much higher than predictions of the kinetic gas theory. The heat transfer coefficient was measured between a single, free-standing VO(2) nanowire and surrounding air using laser thermography, where the temperature distribution along the VO(2) nanowire was determined by imaging its domain structure of metal-insulator phase transition. The one-dimensional domain structure along the nanowire results from the balance between heat generation by the focused laser and heat dissipation to the substrate as well as to the surrounding gas, and thus serves as a nanoscale power-meter and thermometer. We quantified the heat loss rate across the nanowire-air interface, and found that it dominates over all other heat dissipation channels for small-diameter nanowires near ambient pressure. As the heat transfer across the solid-gas interface is nearly independent of the chemical identity of the solid, the results reveal a general scaling relationship for gaseous heat dissipation from nanostructures of all solid materials, which is applicable to nanoscale electronic and thermal devices exposed to gaseous environments.