Fundamental Understanding of Thermal Transport



A new device which measures the distance between phonon collisions has been developed by engineers from MIT. This device provides a nuanced picture of heat production in microelectronics.


In today’s world, computer chips have billions of tiny transistors placed onto a plate of silicon. These are placed within the width of a fingernail. Each transistor acts as a switch that carries out a computer’s computations. The transistor is tens of nanometers wide. The transistors signal back and forth as dense forests. They give off heat which can fry the electronics if a chip gets too hot. In a computer chip, the transistor’s temperature rise can be altered through a classical  diffusion theory. MIT engineers have suggested that the theory doesn’t hold up to extreme small length scales.

Fundamental Understanding of Thermal Transport

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The transistor’s have a different diffusion theory which is underestimated by the temperature rise. The temperature alteration values are given by the nanoscale heat sources. The reliability and performance of the device and the chips could be affected through the miscalculation. The diffusion theory cannot be used to calculate the temperature rise of the device when the heat source is very small. The temperature rise can be higher than diffusion prediction which is not feasible.


Path distribution of phonon

Heat typically flows in the form of phonons in dielectrics and semiconductors. Wavelike particles carry heat which is immense through the material. It experiences various scattering during the propagation. The distance a phonon carries heat before colliding with other phonon particles is known as phonon’s free path. It will be able to conduct heat or carry when it has longer phonon’s free path. The mean free path varies from phonon to phonon in different materials. It ranges from several nanometers to microns.


A more detailed picture of a material’s heat-carrying capability has been given by researchers in power engineering at MIT. The detailed structure enables the researchers to study on engineer materials. Nanostructures have the ability to limit the distance that phonon’s travel. Some of the phonon’s do not contribute much to material’s thermal conductivity. The phonon’s tend to collide with other when they have larger heat sources acting on them. The diffusion theory can be valid in these cases.


Detailed transport picture

Each material has a different distribution plotted for mean free paths. These are reconstructed depending upon the thermal ability and heater size. A new picture of heat conduction has been anticipated through this. The desired conditions can be obtained by varying the size of heat sources. The electrically conducting and thermally insulating materials are desired for the applications. This research was funded by U.S. Department of Energy. It was funded in the part by MIT’s Solid-State Solar Thermal Energy Conversion Center.

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