scholarly journals A new regime of nanoscale thermal transport: Collective diffusion increases dissipation efficiency

2015 ◽  
Vol 112 (16) ◽  
pp. 4846-4851 ◽  
Author(s):  
Kathleen M. Hoogeboom-Pot ◽  
Jorge N. Hernandez-Charpak ◽  
Xiaokun Gu ◽  
Travis D. Frazer ◽  
Erik H. Anderson ◽  
...  
Keyword(s):  
Integrated Circuits ◽  
Free Path ◽  
Thermal Management ◽  
Thermal Transport ◽  
Heat Dissipation ◽  
Mean Free Path ◽  
Heat Sources ◽  
Nanoscale Systems ◽  
Nanoscale Thermal Transport ◽  
Thermal Therapies

Understanding thermal transport from nanoscale heat sources is important for a fundamental description of energy flow in materials, as well as for many technological applications including thermal management in nanoelectronics and optoelectronics, thermoelectric devices, nanoenhanced photovoltaics, and nanoparticle-mediated thermal therapies. Thermal transport at the nanoscale is fundamentally different from that at the macroscale and is determined by the distribution of carrier mean free paths and energy dispersion in a material, the length scales of the heat sources, and the distance over which heat is transported. Past work has shown that Fourier’s law for heat conduction dramatically overpredicts the rate of heat dissipation from heat sources with dimensions smaller than the mean free path of the dominant heat-carrying phonons. In this work, we uncover a new regime of nanoscale thermal transport that dominates when the separation between nanoscale heat sources is small compared with the dominant phonon mean free paths. Surprisingly, the interaction of phonons originating from neighboring heat sources enables more efficient diffusive-like heat dissipation, even from nanoscale heat sources much smaller than the dominant phonon mean free paths. This finding suggests that thermal management in nanoscale systems including integrated circuits might not be as challenging as previously projected. Finally, we demonstrate a unique capability to extract differential conductivity as a function of phonon mean free path in materials, allowing the first (to our knowledge) experimental validation of predictions from the recently developed first-principles calculations.

Directional thermal channeling: A phenomenon triggered by tight packing of heat sources

2021 ◽  
Vol 118 (40) ◽  
pp. e2109056118
Author(s):  
Hossein Honarvar ◽  
Joshua L. Knobloch ◽  
Travis D. Frazer ◽  
Begoña Abad ◽  
Brendan McBennett ◽  
...  
Keyword(s):  
Thermal Transport ◽  
Heat Dissipation ◽  
Materials Science ◽  
Phonon Scattering ◽  
Mean Free Path ◽  
Close Packing ◽  
Heat Sources ◽  
Nanoscale Thermal Transport ◽  
The Mean ◽  
Underlying Mechanisms

Understanding nanoscale thermal transport is critical for nano-engineered devices such as quantum sensors, thermoelectrics, and nanoelectronics. However, despite overwhelming experimental evidence for nondiffusive heat dissipation from nanoscale heat sources, the underlying mechanisms are still not understood. In this work, we show that for nanoscale heat source spacings that are below the mean free path of the dominant phonons in a substrate, close packing of the heat sources increases in-plane scattering and enhances cross-plane thermal conduction. This leads to directional channeling of thermal transport—a novel phenomenon. By using advanced atomic-level simulations to accurately access the lattice temperature and the phonon scattering and transport properties, we finally explain the counterintuitive experimental observations of enhanced cooling for close-packed heat sources. This represents a distinct fundamental behavior in materials science with far-reaching implications for electronics and future quantum devices.

Heat Conduction in Nanostructured Materials Predicted by Phonon Bulk Mean Free Path Distribution

2015 ◽  
Vol 137 (7) ◽  
Author(s):  
Giuseppe Romano ◽  
Jeffrey C. Grossman
Keyword(s):  
Free Path ◽  
Nanostructured Materials ◽  
Thermal Transport ◽  
High Efficiency ◽  
Theoretical Models ◽  
Mean Free Path ◽  
Phonon Transport ◽  
Computational Effort ◽  
Boltzmann Transport ◽  
Computational Framework

We develop a computational framework, based on the Boltzmann transport equation (BTE), with the ability to compute thermal transport in nanostructured materials of any geometry using, as the only input, the bulk cumulative thermal conductivity. The main advantage of our method is twofold. First, while the scattering times and dispersion curves are unknown for most materials, the phonon mean free path (MFP) distribution can be directly obtained by experiments. As a consequence, a wider range of materials can be simulated than with the frequency-dependent (FD) approach. Second, when the MFP distribution is available from theoretical models, our approach allows one to include easily the material dispersion in the calculations without discretizing the phonon frequencies for all polarizations thereby reducing considerably computational effort. Furthermore, after deriving the ballistic and diffusive limits of our model, we develop a multiscale method that couples phonon transport across different scales, enabling efficient simulations of materials with wide phonon MFP distributions length. After validating our model against the FD approach, we apply the method to porous silicon membranes and find good agreement with experiments on mesoscale pores. By enabling the investigation of thermal transport in unexplored nanostructured materials, our method has the potential to advance high-efficiency thermoelectric devices.

scholarly journals Tuning the Anisotropic Thermal Transport in {110}-Silicon Membranes with Surface Resonances

Nanomaterials ◽  
2021 ◽  
Vol 12 (1) ◽  
pp. 123
Author(s):  
Keqiang Li ◽  
Yajuan Cheng ◽  
Maofeng Dou ◽  
Wang Zeng ◽  
Sebastian Volz ◽  
...  
Keyword(s):  
Thermal Conductivity ◽  
Thermal Transport ◽  
Heat Dissipation ◽  
Mean Free Path ◽  
Dynamic Simulations ◽  
Resonant Structures ◽  
Thermoelectric Energy ◽  
Thin Membranes ◽  
The Mean ◽  
Equilibrium Molecular Dynamic

Understanding the thermal transport in nanostructures has important applications in fields such as thermoelectric energy conversion, novel computing and heat dissipation. Using non-homogeneous equilibrium molecular dynamic simulations, we studied the thermal transport in pristine and resonant Si membranes bounded with {110} facets. The break of symmetry by surfaces led to the anisotropic thermal transport with the thermal conductivity along the [110]-direction to be 1.78 times larger than that along the [100]-direction in the pristine structure. In the pristine membranes, the mean free path of phonons along both the [100]- and [110]-directions could reach up to ∼100 µm. Such modes with ultra-long MFP could be effectively hindered by surface resonant pillars. As a result, the thermal conductivity was significantly reduced in resonant structures, with 87.0% and 80.8% reductions along the [110]- and [100]-directions, respectively. The thermal transport anisotropy was also reduced, with the ratio κ110/κ100 decreasing to 1.23. For both the pristine and resonant membranes, the thermal transport was mainly conducted by the in-plane modes. The current work could provide further insights in understanding the thermal transport in thin membranes and resonant structures.

Experimental Analysis Model of an Active Cooling Method for 3D-ICs Utilizing Multidimensional Configured Thermoelectric Coolers

2010 ◽  
Vol 132 (2) ◽  
Author(s):  
Huy N. Phan ◽  
Dereje Agonafer
Keyword(s):  
Integrated Circuits ◽  
Thermal Management ◽  
Heat Dissipation ◽  
Three Dimensional ◽  
Analysis Model ◽  
Thermoelectric Coolers ◽  
Active Cooling ◽  
3D Ics ◽  
Cooling Method ◽  
Memory Applications

Presently, stack dice are used widely as low-power memory applications because thermal management of 3D architecture such as high-power processors inherits many thermal challenges. Inadequate thermal management of three-dimensional integrated circuits (3D-ICs) leads to reduction in performance, reliability, and ultimately system catastrophic failure. Heat dissipation of 3D systems is highly nonuniform and nonunidirectional due to many factors such as power architectures, transistors packing density, and real estate available on the chip. In this study, the development of an experimental model of an active cooling method to cool a 25 W stack-dice to approximately 13°C utilizing a multidimensional configured thermoelectric will be presented.

scholarly journals Atypical thermal transport in Cu nanorods in the diffusive–ballistic crossover

2016 ◽  
Vol 94 (11) ◽  
pp. 1241-1244
Author(s):  
P.K. Karmakar ◽  
D. Mohanta
Keyword(s):  
Thermal Transport ◽  
Small Amplitude ◽  
Path Length ◽  
Heat Dissipation ◽  
Free Path Length ◽  
Mean Free Path ◽  
Hot Electrons ◽  
Axial Heat ◽  
Electron Mean Free Path ◽  
Electronic Scattering

We propose a simple theoretical calculation scheme based on the phenomenological Fourier heat-flow formalism to study thermal transport behaviors in nanoscale copper rods. The axial heat transport is characterized by a new super-oscillatory feature along with small-amplitude heat spikes. It is anticipated that these atypical spikes are generated by accumulation of localized “hotspots” that have low heat dissipation characteristics. In the case of radial transport, we witness the existence of three distinct heat regimes owing to buildup of hot electrons after experiencing ballistic scattering events. It is important to note that, even though the nanorod diameter is comparable to or smaller than the electron mean free path length, λmfp ∼ 30 nm; multiple ballistic electronic scattering from the outer surface of the nanorods and subsequent accrual into several layers through secondary collisional events has led to concentric heat zones. The hotspots disappear when the nanorod diameter exceeds λmfp.

Phonon Transport in Asymmetric Sawtooth Nanowires

2011 ◽  
Author(s):  
N. A. Roberts ◽  
D. G. Walker
Keyword(s):  
Monte Carlo ◽  
Aspect Ratio ◽  
Monte Carlo Simulations ◽  
Free Path ◽  
Thermal Management ◽  
Strong Dependence ◽  
Mean Free Path ◽  
Phonon Transport ◽  
Specular Reflections ◽  
Size Scales

Thermal transport in asymmetric sawtooth nanowires was investigated. The boundaries reflect phonons differently depending on the frequency and momentum of the phonon. These systems show thermally rectifying behavior when the boundary reflections are a function of both the direction the phonon is traveling and the frequency of the phonon. This rectifying effect could be useful for thermal management applications at all size scales, but would have to be built up from the nanoscale because of a strong dependence on the device aspect ratio and the Knudsen number of the system. Monte Carlo simulations show an accumulation of phonons at the boundary which emits phonons in a perceived rough direction where those phonons have some probability of diffuse reflections at the boundary while phonons emitted in the smooth direction only experience specular reflections at the boundary and are eventually thermalized at the opposite boundary. In this study the level of rectification of the system was linearly dependent on the device aspect ratio as long as the length of the device was near or below the phonon mean free path of the phonons.

Thermal transport through fishbone silicon nanoribbons: unraveling the role of Sharvin resistance

Nanoscale ◽  
2019 ◽  
Vol 11 (17) ◽  
pp. 8196-8203 ◽  
Author(s):  
Lin Yang ◽  
Yang Zhao ◽  
Qian Zhang ◽  
Juekuan Yang ◽  
Deyu Li
Keyword(s):  
Free Path ◽  
Thermal Transport ◽  
Mean Free Path

The phonon mean free path increases with the fin width, boosting the Sharvin resistance at the constrictions.

Phase Change Material for Thermal Management in 3D Integrated Circuits Packaging

2015 ◽  
Vol 2015 (1) ◽  
pp. 000649-000653 ◽  
Author(s):  
Mingli Li ◽  
Na Gong ◽  
Jinhui Wang ◽  
Zhibin Lin
Keyword(s):  
Integrated Circuits ◽  
Phase Change ◽  
Phase Change Material ◽  
Thermal Management ◽  
Electronic Packaging ◽  
Heat Dissipation ◽  
Thermal Control ◽  
Study Phase ◽  
3D Integrated Circuits ◽  
Change Material

Effective thermal control and management in three-dimensional electronic packaging are desirable to ensure the heat generated in integrated circuits can be dissipated. Conventional base materials in electronics from substrate to protective layers, due to low coefficient of thermal conductivity, cannot help to cool down the circuits, while such elevated temperature could highly impact the performance of the chips. In this study, phase change material (PCM) is selected for potential applications in thermal management of electronic packaging due to its isothermal nature and high thermal storage capability. PCM based composite is developed through the impregnation technology using highly porous expanded graphite. Heat transfer test results reveal that the PCM based composite displays superior heat storage capacity, while maintaining the favorable feature of thermal and chemical stabilization for electronic applications. Toward the end, the concept of implementation of PCM based composite is proposed in thermal control of 3D integrated circuits. It is expected the proposed composite will improve heat dissipation, and ultimately enhance the performance of the chips.

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