Tech Briefs Magazine - May 2024 - Sensor-28

Utilization of persistent photocurrent
of oxide semiconductor nanoparticles
Light
EC
eEF
Decrease
of
barner height
eeEF
EW
Grain
Au
boundary
ZnO
NPs
Au
4 -bit pulse patterns
Handwriting digit recognition
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0123456789
Inferred output digital
Disposable and flexible paper-based optoelectronic synaptic devices for physical reservoir computing. (Image: Ikuno Laboratory, Dept. of Applied
Electronics, Graduate School of Advanced Engineering, Tokyo University of Science)
for prolonged use, should be capable of
handling rapidly changing biological signals
for real-time monitoring, be flexible
enough to attach comfortably to the
human body, and be easy to make and
dispose of due to the need for frequent
replacements for hygiene reasons.
NASA Low Outgassing Approved
One Part Silicone Adhesive
MasterSil 920-LO
■ Non-corrosive cures
■ Fast set up time
■ Ideal for sensitive
components
■ Refractive index 1.43
Considering these criteria, researchers
from Tokyo University of Science (TUS)
led by Associate Professor Takashi Ikuno
have developed a flexible paper-based
sensor that operates like the human
brain. Their findings were published online
in the journal Advanced Electronic
Materials on February 22, 2024.
" A paper-based optoelectronic synaptic
device composed of nanocellulose
and ZnO was developed for realizing
physical reservoir computing. This device
exhibits synaptic behavior and cognitive
tasks at a suitable timescale for
health monitoring, " said Dr. Ikuno.
In the human brain, information travels
between networks
of neurons
through synapses. Each neuron can process
information on its own, enabling
the brain to handle multiple tasks at the
same time. This ability for parallel processing
makes the brain much more efficient
compared to traditional computing
systems. To mimic this capability, the
researchers fabricated a photo-electronic
artificial synapse device composed
of gold electrodes on top of a 10 µm
transparent film consisting of zinc oxide
(ZnO) nanoparticles and cellulose
nanofibers (CNFs).
The transparent film serves three main
purposes. First, it allows
through, enabling it
light
to pass
to handle optical
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+1.201.343.8983 * main@masterbond.com
www.masterbond.com
28
input signals representing biological information.
Second, the cellulose nanofibers
impart flexibility and can be easily disposed
of by incineration. Third, the ZnO
nanoparticles are photoresponsive and
generate a photocurrent when exposed to
pulsed UV light and a constant voltage.
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This photocurrent mimics the responses
transmitted by synapses in the human
brain, enabling the device to interpret and
process biological information received
from optical sensors.
The film was able to distinguish 4-bit
input optical pulses and generate distinct
currents in response to time-series
optical input, with a response time on
the order of sub-seconds. This quick response
is crucial for detecting sudden
changes or abnormalities in health-related
signals. Furthermore, when exposed
to two successive light pulses, the
electrical current response was stronger
for the second pulse. This behavior,
termed post-potentiation facilitation,
contributes to short-term memory processes
in the brain and enhances the
ability of synapses to detect and respond
to familiar patterns.
To test this, the researchers converted
MNIST images, a dataset of handwritten
digits, into 4-bit optical pulses. They then
irradiated the film with these pulses and
measured the current response. Using this
data as input, a neural network was able to
recognize handwritten numbers with an
accuracy of 88%.
This handwritten digit-recognition capability
remained unaffected even when the
device was repeatedly bent and stretched
up to 1,000 times, demonstrating its ruggedness
and feasibility for repeated use.
" This study highlights the potential of embedding
semiconductor nanoparticles in
flexible CNF films for use as flexible synaptic
devices for PRC, " concluded Dr. Ikuno.
For
more
information,
mediaoffice@admin.tus.ac.jp.
Sensor Technology, May 2024
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Easily disposed of
by incineration
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Classification of
4bit optical pulses
contact
Desired output digital
Readout current (µA)
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Tech Briefs Magazine - May 2024

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