Printing organic transistors
High-speed low-power printed transistors could lead to new display technologies

Date:
October 7, 2020
Source:
University of Tokyo
Summary:
Researchers successfully print and demonstrate organic transistors,
electronic switches, which can operate close to their theoretical
speed limits. They showed high-speed operation only requires low
voltages to work, which would reduce the power consumption of
their applications.

These kinds of transistors are used in display technology such as
liquid crystal display (LCD) screens and e-ink. This is the first
time this kind of transistor has been printed and it could lead
to new curved, flexible and even wearable low power devices.



FULL STORY ==========================================================================
The chances are you are reading these words on a smartphone or computer
screen.

For around the last 10 years, these types of screens have been based on
a display technology composed of so-called thin film transistors. These
are inorganic transistors which require very little power, and they have
proven themselves very capable given their widespread adoption. But they
have some limits which researchers have been busy trying to overcome.


==========================================================================
"We explore new ways to improve upon thin film transistors, such as new
designs or new methods of manufacture," said Gyo Kitahara, a Ph.D. student
from the Department of Applied Physics. "Organic thin film transistors,
for example, have a bright future in LCD screen devices. Compared to the inorganic kind currently used, we expect the organic kind to be useful
in low-cost, large- area, lightweight and wearable electronic products, especially by using printing-based production technologies." The idea
of organic thin film transistors itself is not new, but the ability
to print such devices, which would allow for a design revolution, has
eluded industry and academics, until now. Professor Tatsuo Hasegawa of
the Department of Applied Physics, Kitahara and their team came up with a
way to print organic semiconductor films, the basis of these transistors,
on a special surface that is highly solution-repellent, or lyophobic. This means ordinarily the surface would repel the materials required to print
the structure of the transistor, which seems counterintuitive as to why
such a surface would be useful at all.

But lyophobic surfaces are responsible for creating transistor structures
that are finely tuned for high performance. So how did the researchers
overcome their repellent nature? "We made use of a fluidic property
you probably see every time you wash your hands with soap," said
Kitahara. "Soap bubbles can hold a shape by lowering the surface tension
of liquid. We presume that the soap-film mechanism should be effective
for formation of a thin liquid layer on lyophobic surfaces in spite of
the repellent forces. Solid semiconductor films can be formed and grown
via the formation of thin liquid layers during the printing processes."
With this hurdle of how to print organic transistors overcome, other researchers can build on the team's findings and find ways to scale this
method up. With a proliferation of large, flexible or wearable devices, Hasegawa's team dreams of seeing a convergence between the real world
and virtual world in ways we've never seen before.

"After having experimented by trial and error, we eventually found
that the use of a special U-shaped metal-film pattern seems to be
effective for uniform film growth thanks to the way it creates a thin
liquid layer on lyophobic surfaces," said Kitahara. "We anticipated the
results beforehand to some extent, but the success of these findings was finally demonstrated and obtained after overcoming several difficulties,
which brought great pleasure and happiness to me."

========================================================================== Story Source: Materials provided by University_of_Tokyo. Note: Content
may be edited for style and length.


========================================================================== Journal Reference:
1. Gyo Kitahara, Satoru Inoue, Toshiki Higashino, Mitsuhiro Ikawa,
Taichi
Hayashi, Satoshi Matsuoka, Shunto Arai, Tatsuo Hasegawa. Meniscus-
controlled printing of single-crystal interfaces showing extremely
sharp switching transistor operation. Science Advances, 2020; 6
(41): eabc8847 DOI: 10.1126/sciadv.abc8847 ==========================================================================

Link to news story: https://www.sciencedaily.com/releases/2020/10/201007182345.htm

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