All electronic devices feature a hard computer chip, covered in many transistors and other semiconducting elements. Because computer chips are rigid, the electronic devices they power — such as smartphones, laptops, watches, and televisions — are similarly inflexible. A process was developed for manufacturing flexible electronics with multiple functionalities in a cost-effective way.
The “remote epitaxy” process involves growing thin films of semiconducting material on a large, thick wafer of the same material, which is covered in an intermediate layer of graphene. Once the semiconducting film grows, it can be peeled away from the graphene-covered wafer. The wafer can be reused, enabling any number of thin, flexible semiconducting films to be copied and peeled away using the same underlying wafer.
Remote epitaxy can produce freestanding films of any functional material. More importantly, films made from these different materials can be stacked to produce flexible, multifunctional electronic devices. The process could be used to produce stretchy electronic films for a wide variety of uses including virtual reality-enabled contact lenses, solar-powered skins that mold to the contours of a car, electronic fabrics that respond to the weather, and other flexible electronics.
The researchers used remote epitaxy to make flexible semiconducting films from complex oxides — chemical compounds made from oxygen and at least two other elements — that are known to have a wide range of electrical and magnetic properties. Some of these combinations can generate a current when physically stretched or exposed to a magnetic field. Until now, complex oxide materials have only been manufactured on rigid, millimeter-thick wafers, with limited flexibility and therefore limited energy-generating potential.
The researchers used the process to make films from multiple complex oxide materials, peeling off each 100-nanometer-thin layer as it was made. They were also able to stack together layers of different complex oxide materials and effectively glue them together by heating them slightly, producing a flexible, multifunctional device.
Traditional epitaxy techniques that grow materials at high temperatures on one wafer can only combine materials if their crystalline patterns match. With remote epitaxy, researchers can make any number of different films using different, reusable wafers and then stack them together, regardless of their crystalline pattern. A thin, flexible device could be made from layers that include a sensor, computing system, battery, and solar cell, producing a flexible, self-powering, Internet of Things stacked chip.