Lighter, Flexible Stretchy Electronics

The prospect of making “smart” wearable electronic devices, including ones integrated into clothing and others worn by people directly on their skin, drove scientists in 2013 to develop thinner, lighter, and ever more flexible and stretchable circuitry. Researchers aim to capitalize on these technology advances by making next-generation communication devices and nearly imperceptible medical sensors and monitors. The advances also underpin development of longer-lasting and less obtrusive medical implants. In one example, the University of Tokyo’s Martin Kaltenbrunner and Takao Someya and colleagues demonstrated that large sheets of organic-transistor-based integrated circuitry can be fabricated on polymer foils. The test devices, which set records for their thinness and low weight, withstood repeated bending and crumpling and could be stretched by up to 230% of their original dimensions without losing electrical connectivity (C&EN, July 29, page 28; Nature 2013, DOI: 10.1038/nature12314). In a related study, a team led by Keon Jae Lee of the Korea Advanced Institute of Science & Technology developed a method for quickly separating ultrathin sheets of silicon-based integrated circuits from the traditional rigid substrates on which they are fabricated and encapsulating the sheets in a flexible support—a biocompatible liquid-crystal polymer. The team applied the process to integrated circuits used for radio-frequency wireless communication with implanted medical devices. They report that the circuits withstood 1,000 bending cycles and functioned properly throughout a six-week period in which they were implanted in rats (C&EN Online Latest News, May 7; ACS Nano 2013, DOI:10.1021/nn401246y). These encapsulated devices should last for at least two years inside the human body, the researchers predict.