Tech Briefs Magazine - June 2021 - 30

Electrical/Electronics
Synapse-Like Phototransistor
The technology could help computers process visual information more like the human brain.
National Renewable Energy Laboratory, Golden, Colorado
esearchers developed energy-efficient
phototransistors that could help computers
process visual information more
like the human brain and be used as sensors
in things like self-driving vehicles.
The structures rely on a new type of semiconductor
- metal-halide perovskites -
that has proven to be highly efficient at
converting sunlight into electrical energy
and has shown tremendous promise in a
range of other technologies.
The researchers combined perovskite
nanocrystals with a network of singlewalled
carbon nanotubes to create a
material combination for photovoltaics
or detectors. When they shined a laser at
it, they found a surprising electrical
response. Normally, after absorbing the
light, an electrical current would briefly
flow for a short period of time. In this
case, however, the current continued to
flow and did not stop for several minutes,
even when the light was switched off.
R
Such behavior is referred to as persis -
tent photoconductivity and is a form of
optical memory where the light energy
hitting a device can be stored in memory
as an electrical current. The phenomenon
can also mimic synapses in the brain
that are used to store memories. Often,
however, persistent photoconductivity
requires low temperatures and/or high
operating voltages and the current spike
would only last for small fractions of a
second. In the new technology, the persistent
photoconductivity produces an
electrical current at room temperature
and flows current for more than an hour
after the light is switched off. In addition,
only low voltages and low light
intensities were found to be needed,
highlighting the low energy needed to
store memory.
The research provides previously lacking
design principles that can be incorporated
into optical memory and neuromorphic
computing applications. Visual
perception accounts for the vast majority
of input the brain collects about the
world and these artificial synapses could
be integrated into image recognition systems.
Such systems could potentially im -
prove energy efficiency, performance,
and reliability in applications such as
self-driving vehicles.
The researchers tried three different
types of perovskites - formamidinium
lead bromide, cesium lead iodide, and
cesium lead bromide - and found each
was able to produce a persistent photoconductivity.
To build a neural network
requires integrating an array of these
junctions into more complex architectures
where more complex memory
applications and image processing applications
can be emulated.
For more information, contact David
Glickson at David.Glickson@nrel.gov; 303275-4097.
Biodegradable
Displays for Sustainable Electronics
Thanks to its flexibility and adhesion, the biodegradable display can be worn directly on the hand.
Karlsruhe Institute of Technology, Karlsruhe, Germany
ncreasing use of electronic devices in
consumables and new technologies for
the Internet of Things will increase the
amount of electronic scrap. To save
resources and minimize waste volumes, an
eco-friendlier production and more sustainable
lifecycle will be needed.
Researchers have demonstrated that it
is possible to produce sustainable displays
that are largely based on natural materials
with the help of industrially relevant
production methods. After use, these displays
are not electronic scrap; they can be
composted. In combination with recycling
and reuse, this could help minimize
or completely prevent some environmental
impacts of electronic scrap.
The display is based on the electrochromic
effect of the initial organic
material. When voltage is applied, light
absorption is modified and the material
I
Due to its flexibility and adhesion, the biodegradable display can be worn directly on the hand.
(Photo: Manuel Pietsch, KIT)
changes its color. Electrochromic displays
have low energy consumption and simple
component architecture compared to
commercially available displays such as
LED, LCD, and E-paper. Another advan30
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tage
is that these displays can be produced
by inkjet printing in a customized, inexpensive,
and material-efficient way. More -
over, this process is suited for scaling with
a high throughput.
Tech Briefs, June 2021

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Tech Briefs Magazine - June 2021

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