Surface waves can help nanostructured devices keep their cool

Date:
October 12, 2020
Source:
Institute of Industrial Science, The University of Tokyo
Summary:
A research team has demonstrated that hybrid surface waves called
surface phonon-polaritons provide enhanced thermal conductivity
in nanoscale membranes. These surface waves can aid in the thermal
management of nanostructured devices as conventional cooling methods
reach their material-related limits. Surface phonon-polaritons
will be particularly useful for heat conduction in silicon-based
microelectronics and photonics applications.



FULL STORY ==========================================================================
The continuing progress in miniaturization of silicon microelectronic
and photonic devices is causing cooling of the device structures to
become increasingly challenging. Conventional heat transport in bulk
materials is dominated by acoustic phonons, which are quasiparticles
that represent the material's lattice vibrations, similar to the way
that photons represent light waves. Unfortunately, this type of cooling
is reaching its limits in these tiny structures.


========================================================================== However, surface effects become dominant as the materials in
nanostructured devices become thinner, which means that surface waves may provide the thermal transport solution required. Surface phonon-polaritons (SPhPs) -- hybrid waves composed of surface electromagnetic waves and
optical phonons that propagate along the surfaces of dielectric membranes
-- have shown particular promise, and a team led by researchers from
the Institute of Industrial Science, the University of Tokyo has now demonstrated and verified the thermal conductivity enhancements provided
by these waves.

"We generated SPhPs on silicon nitride membranes with various thicknesses
and measured the thermal conductivities of these membranes over wide temperature ranges," says lead author of the study Yunhui Wu. "This
allowed us to establish the specific contributions of the SPhPs to
the improved thermal conductivity observed in the thinner membranes."
The team observed that the thermal conductivity of membranes with
thicknesses of 50 nm or less actually doubled when the temperature
increased from 300 K to 800 K (approximately 27DEGC to 527DEGC). In
contrast, the conductivity of a 200-nm-thick membrane decreased over the
same temperature range because the acoustic phonons still dominated at
that thickness.

"Measurements showed that the dielectric function of silicon nitride did
not change greatly over the experimental temperature range, which meant
that the observed thermal enhancements could be attributed to the action
of the SPhPs," explains the Institute of Industrial Science's Masahiro
Nomura, senior author of the study. "The SPhP propagation length along
the membrane interface increases when the membrane thickness decreases,
which allows SPhPs to conduct much more thermal energy than acoustic
phonons when using these very thin membranes." The new cooling channel provided by the SPhPs can thus compensate for the reduced phonon thermal conductivity that occurs in nanostructured materials.

SPhPs are thus expected to find applications in thermal management of
silicon- based microelectronic and photonic devices.


========================================================================== Story Source: Materials provided by Institute_of_Industrial_Science,_The_University_of_Tokyo.

Note: Content may be edited for style and length.


========================================================================== Journal Reference:
1. Y. Wu, J. Ordonez-Miranda, S. Gluchko, R. Anufriev, D. De Sousa
Meneses,
L. Del Campo, S. Volz, M. Nomura. Enhanced thermal conduction
by surface phonon-polaritons. Science Advances, 2020; 6 (40):
eabb4461 DOI: 10.1126/ sciadv.abb4461 ==========================================================================

Link to news story: https://www.sciencedaily.com/releases/2020/10/201012115939.htm

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