University of Tokyo researchers have
developed an ultrathin, ultraflexible, protective layer and demonstrated
its use by creating an air-stable, organic light-emitting diode (OLED)
display. This technology will enable creation of electronic skin
(e-skin) displays of blood oxygen level, e-skin heart rate sensors for
athletes and many other applications.
Integrating electronic devices with the human
body to enhance or restore body function for biomedical applications is
the goal of researchers around the world. In particular, wearable
electronics need to be thin and flexible to minimize impact where they
attach to the body. However, most devices developed so far have required
millimeter-scale thickness glass or plastic substrates with limited
flexibility, while micrometer-scale thin flexible organic devices have
not been stable enough to survive in air.
The research group of Professor Takao Someya and Dr.
Tomoyuki Yokota at the University of Tokyo's Graduate School of
Engineering has developed a high-quality protective film less than two
micrometers thick that enables the production of ultrathin,
ultraflexible, high performance wearable electronic displays and other
devices. The group developed the protective film by alternating layers
of inorganic (Silicon Oxynitrite) and organic (Parylene) material. The
protective film prevented passage of oxygen and water vapor in the air,
extending device lifetimes from the few hours seen in prior research to
several days. In addition, the research group were able to attach
transparent indium tin oxide (ITO) electrodes to an ultrathin substrate
without damaging it, making the e-skin display possible.
Using the new protective layer
and ITO electrodes, the research group created polymer light-emitting
diodes (PLEDs) and organic photodetectors (OPDs). These were thin enough
to be attached to the skin and flexible enough to distort and crumple
in response to body movement. The PLEDs were just three micrometers
thick and over six times more efficient than previously reported
ultrathin PLEDs. This reduced heat generation and power consumption,
making them particularly suitable for direct attachment to the body for
medical applications such as displays for blood oxygen
concentration or pulse rate. The research group also combined red and
green PLEDs with a photodetector to demonstrate a blood oxygen sensor.
"The advent of mobile phones has changed the way we
communicate. While these communication tools are getting smaller and
smaller, they are still discrete devices that we have to carry with us,"
says Someya. He continues, "What would the world be like if we had
displays that could adhere to our bodies and even show our emotions or
level of stress or unease? In addition to not having to carry a device
with us at all times, they might enhance the way we interact with those
around us or add a whole new dimension to how we communicate."
More information:
Tomoyuki Yokota, Peter Zalar, Martin Kaltenbrunner, Hiroaki Jinno,
Naoji Matsuhisa, Hiroki Kitanosako, Yutaro Tachibana, Wakako Yukita,
Mari Koizumi, Takao Someya, "Ultraflexible organic photonic skin," Science Advances 2:e1501856, 15 April 2016. DOI: 10.1126/sciadv.1501856
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