Japanese Researchers Move One Step Closer To Making Electronic Skin

Photo: The red seven-segment PLED display in operation on the back of a hand. / Credit: Someya Laboratory

Researchers at University of Tokyo have developed an ultrathin, ultra flexible, and protective layer that creates an air-stable, organic light-emitting diode (OLED) display.

This new technology will enable scientists to create electronic skin –e-skin– displays of blood oxygen level, e-skin heart rate sensors for athletes and many other applications.

Professor Takao Someya and Dr. Tomoyuki Yokota from the university’s Graduate School of Engineering were able to develop a high-quality protective film less than two micrometers thick that enables the production of ultrathin and ultraflexible wearable electronic displays and other devices.

To minimize impact of devices integrating with the human body, wearable electronics need be thin and flexible. Most devices developed so far require 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.

This new technology looks an answers to these problems.

The protective film was developed by researchers 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. They 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, researchers created polymer light-emitting diodes (PLEDs) and organic photodetectors (OPDs), which can be attached to the skin, and were 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. With reduce heat generation and power consumption, these can be directly attached to the body for medical applications such as displays for blood oxygen concentration or pulse rate.

Researchers were also able to combine red and green PLEDs with a photodetector to demonstrate a blood oxygen sensor.

Top left: System outline of a blood oxygen level monitor. Top right: Red and green polymer light-emitting diodes (PLEDs) are directed to shine into the finger. Reflected light from inside the finger is caught by an ultraflexible organic photodetector. This reflected light provides a measure of blood oxygen and pulse rate. Bottom: The output of the sensor can be shown on a PLED display. / Credit: Someya Laboratory

Someya said that “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.”

“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,” he added.