Ultrathin Organic Material Enhances E-Skin Display

E-Skin-Sensor made of polymer light-emitting diodes (PLEDs) and an ultraflexible organic photodetector. (Source: Someya Lab.)

E-skin-sensor made of polymer light-emitting diodes (PLEDs) and an ultraflexible organic photodetector. (Source: Someya Lab.)

University of Tokyo researchers have developed an ultrathin, ultra­flexible, protective layer and demon­strated its use by creating an air-stable, organic light-emitting diode display. This techno­logy will enable creation of electronic 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 Takao Someya and 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 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. 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.” (Source: U Tokyo)

Reference: T. Yokota et al.: Ultraflexible organic photonics skin, Sci. Adv. 2, e1501856, online 15 April 2016, DOI: 10.1126/sciadv.1501856

Link: Organic Transistor Lab (T. Someya), Department of Electric and Electronic Engineering, University of Tokyo, Japan

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