Tech Briefs Magazine - February 2022 - 11

Q & A
A Unique Material Transmits Heat in
One Direction and Blocks it in Another
Professor Jiwoong Park
and his team at the
University
of
Chicago
have made a material that
is crystalline in the X-Y
direction, but amorphous
in
the Z direction.
It
therefore has the unique thermal properties
that it is an excellent transmitter of
heat in the x-y plane but a thermal insulator
in the z plane.
Tech Briefs: How did you get started
on this research?
Jiwoong Park: We started three or
four years ago with our curiosity about a
material we had made. If you look at any
material, let's say metal or glass, it has
similar structural properties in all three
directions. If it's a crystal, it's crystalline
in all three directions. If it's amorphous,
like glass, then it's amorphous in all
three directions. We had grown a very
thin two-dimensional crystal and wondered
what would happen if we stacked
them. It turned out that it was crystalline
in the X-Y direction, but amorphous in
the Z direction.
Tech Briefs: How do you make this
material?
Park: The first step is to grow the individual
layer. We use a technique called
metal organic chemical vapor deposition.
We have a substrate and introduce precursors,
meaning the ingredient atoms
and molecules, and then we control the
temperature. We usually heat it up, then
bring it to low pressure and the molecule
breaks down, releasing the atoms that we
want - in this case molybdenum and sulfur.
They react on the surface of the substrate
and form a mono-layer crystal.
Tech Briefs: How large an area of this
material did you, or can you, make?
Park: We can make it into literally
wafer scale or bigger because we start
Tech Briefs, February 2022
Cov
with a very thin material, about 10 centimeters
in size, but it could be larger.
We then stack them one by one, so in
principle it could be any thickness that
we would like. In our experiment, we
went up to 20 or 30 layers, which
amounts to 10 to 20 nanometers.
Tech Briefs: Do you picture this on
the scale of integrating it into a chip
or a larger electronic assembly?
Park: Introducing any new step or
ingredient to a CMOS process is daunting
because you need to consider so
many processes
that happen before
and after. However, we are in conversation
with the industry to think about a
way to integrate it, but it's at a very
early stage.
Tech Briefs: On a larger scale could it
be mounted on a mechanical
structure, possibly inside an iPhone
or something like that?
Park: I do have to think about it more
because the big question is always how to
separate heat-producing parts from
heat-sensitive parts. One has to do something
to put them together in a tight
space.
Tech Briefs: How close are you to
being able to implement this in an
actual product?
Park: Now, the ratio of the conductive
part to the insulating part is about 1,000.
If we can make it 10,000 or 100,000, it
will become more appealing. And realizing
the same properties with different
materials, will give industry much more
opportunity to think about using this for
a variety of different processes. At the
current stage, we want to make this platform
more general so that more people
can pick up on it.
Read the full transcript of this Q&A at
www.techbriefs.com.
www.techbriefs.com
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Tech Briefs Magazine - February 2022

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