Until now, complex oxide materials have only been manufactured on rigid, millimeter-thick wafers, with limited flexibility and therefore limited energy-generating potential. Kim says the ability to manufacture flexible films of complex oxides could open the door to new energy-havesting devices, such as sheets or coverings that stretch in response to vibrations and produce electricity as a result. Complex oxides are known to have a wide range of electrical and magnetic properties, and some combinations can generate a current when physically stretched or exposed to a magnetic field. As reported in this new paper, the team used remote epitaxy to make flexible semiconducting films from complex oxides - chemical compounds made from oxygen and at least two other elements. Since this realization, Kim and his colleagues have tried a number of increasingly exotic semiconducting combinations. The reason, they found, boiled down to polarity, or the respective charges between the atoms flowing over graphene and the atoms in the underlying wafer. In 2018, the team showed that they could use remote epitaxy to make semiconducting materials from metals in groups 3 and 5 of the periodic table, but not from group 4. The graphene provided a nonstick surface from which the researchers could peel away the new film, leaving the graphene-covered wafer, which they could reuse. They flowed atoms of each metal over the graphene-covered wafer and found the atoms formed a film on top of the graphene, in the same crystal pattern as the underlying wafer.

Then, they were able to produce thin, flexible films of semiconducting material by first placing a layer of graphene on a thick, expensive wafer made from a combination of exotic metals. Kim and his colleagues reported their first results using remote epitaxy in 2017. Kum, Sungkyu Kim, Wei Kong, Kuan Qiao, Peng Chen, Jaewoo Shim, Sang-Hoon Bae, Chanyeol Choi, Luigi Ranno, Seungju Seo, Sangho Lee, Jackson Bauer, and Caroline Ross from MIT, along with collaborators from the University of Wisconsin at Madison, Cornell University, the University of Virginia, Penn State University, Sun Yat-Sen University, and the Korea Atomic Energy Research Institute. вЂњYou can use this technique to mix and match any semiconducting material to have new device functionality, in one flexible chip,вЂќ says Jeehwan Kim, an associate professor of mechanical engineering at MIT. The researchers expect that 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 your car, electronic fabrics that respond to the weather, and other flexible electronics that seemed until now to be the stuff of Marvel movies. More importantly, they can stack films made from these different materials, to produce flexible, multifunctional electronic devices. In a paper published today in the journal Nature, the researchers demonstrate that they can use remote epitaxy to produce freestanding films of any functional material. In this way, the team can copy and peel away any number of thin, flexible semiconducting films, using the same underlying wafer. Once the researchers grow a semiconducting film, they can peel it away from the graphene-covered wafer and then reuse the wafer, which itself can be expensive depending on the type of material itвЂ™s made from. The process is called вЂњremote epitaxyвЂќ and 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. Now a process developed by MIT engineers may be the key to manufacturing flexible electronics with multiple functionalities in a cost-effective way. Because computer chips are rigid, the electronic devices that they power, such as our smartphones, laptops, watches, and televisions, are similarly inflexible. At the heart of any electronic device is a cold, hard computer chip, covered in a miniature city of transistors and other semiconducting elements.

Stacks chips