Tech Briefs Magazine - October 2021 - ST-22

Tech Briefs
Ultra-High Performance Flexible Ultraviolet Sensors for
Use in Wearables
To enable the development of wearable devices that possess advanced ultraviolet (UV)
detection functions, scientists have created a new type of light sensor that is both
flexible and highly sensitive.
Nanyang Technological University, Singapore
hile invisible to the human eye,
UV rays surround us in our environment,
and excessive exposure can
cause health issues including skin cancer
and premature skin aging. The intensity
of UV rays is typically reported through
an index during weather reports. A
wearable device, such as a T-shirt or
watch that monitors the actual personal
UV exposure throughout the day, would
be a useful and more accurate guide for
people seeking to avoid sun damage.
NTU researchers have reported that
their flexible UV light sensors were 25
times more responsive, and 330 times
more sensitive than existing sensors,
exceeding the performance level re -
quired for optoelectronic applications -
light-based electronics.
W
UV light sensors, also known as photodetectors,
are used in a wide range of
systems, from smartphones to biomedical
imaging. Over the past decades, gallium
nitride (GaN) has gained prominence
as the ideal material to fabricate
UV light sensors, largely due to its superior
properties in emitting, regulating,
transmitting, and sensing light. However,
most GaN-based UV sensors today are
built on rigid layers, limiting their use in
flexible and wearable products.
While researchers elsewhere have
developed flexible GaN-based UV sensors,
they have not attained the level of
performance required for state-of-theart
use. Two of their biggest challenges
are low responsivity and low sensitivity.
The NTU team overcame these constraints
by creating flexible UV light sensors
on a semiconductor wafer 8 inches
in diameter, using free-standing singlecrystalline
layers of GaN and aluminum
gallium nitride (AlGaN), arranged using
membranes that consist of two different
thin semiconductor layers (heterostructure
membranes).
This type of semiconductor structure,
which can be fabricated using existing
industrial-compatible methods, allows
the material to be easily bent, making it
ideal for use in flexible sensors. At the
same time, the chemical composition of
The NTU research team created flexible UV light sensors that were 25 times more responsive, and
330 times more sensitive, than existing sensors. (Courtesy of the researchers)
22
Cov
www.techbriefs.com
ToC
the material changes with depth, meaning
that high performance is maintained
even when it comes under strain.
In lab tests, the NTU flexible UV light
sensors operated at high levels of
responsivity and sensitivity even while
being subjected to multiple bending and
high temperature tests. Under a range
of external strains (compressive, flat,
and tensile), the sensors recorded a
responsivity level of between 529 - 1340
Ampere/Watt (unit used to measure the
ability of a device to convert an optical
signal to an electrical signal), which is
about 100 times higher than existing UV
sensors. This responsivity remained stable
after 100 cycles of repetitive bending,
demonstrating its potential to be
integrated into wearables.
" The high-performance flexible UV
light sensors we have created pave the
way forward for a wide range of future
wearable applications, such as in personal
smart health monitoring, where people
can accurately measure their UV
exposure levels throughout the day to
reduce their risk of skin cancer, " said
Professor Kim Munho. Skin cancer, one
of the most common types of cancer
globally, is primarily caused by overexposure
to UV radiation from the sun. In
regions such as Australia, which has the
highest rate of skin cancer in the world,
it is estimated that approximately 2 in 3
people will be diagnosed with skin cancer
by the time they reach the age of 70,
according to data compiled by the
World Cancer Research Fund.
" Skin cancer can be prevented by protecting
the skin from excessive sun exposure.
So, a reliable wearable device that
could track UV exposure could be a
handy tool to help monitor one's recommended
exposure, particularly for those
who spend a lot of time outdoors, " the
research team said.
For more information, contact
MediaEnquiry@ntu.edu.sg.
Sensor Technology, October 2021

http://www.techbriefs.com http://info.hotims.com/79418-936

Tech Briefs Magazine - October 2021

Table of Contents for the Digital Edition of Tech Briefs Magazine - October 2021