Stretchable electronic devices have been garnering increasing interest over the past decade.
Recently, Finland-based Nokia announced the Morph device concept, which uses stretchable electronics for a next-generation transparent and flexible mobile phone.
Researchers hope that in the near future, the fabrication of electronic devices will move beyond the traditional flat bed wafer onto flexible substrates. They envision incorporating them in clothing, surgical gloves, electronic paper and so on. But ensuring that the electrical wiring does not snap or get damaged when the material is stretched or twisted is still a challenge that has not been satisfactorily addressed.
A team of researchers from the Massachusetts Institute of Technology (MIT) has now stumbled upon a radically new approach for designing flexible electronic circuits without damaging the wires. The team was involved in an analysis of the wrinkling and delamination of stickers, such as the ones usually stuck on windows and car bumpers. Eventually their understanding of how the blisters are formed in these stickers led to the idea that by having partial separation of wires from the surface material and intentionally creating delamination in them, they could ensure that the wires are insulated from the stress caused by stretching. This novel concept is described by the researchers in a recent paper published in the Proceedings of the National Academy of Sciences.
Delamination of a thin film from the flat surface to which it is attached is known to occur commonly, either due to differing rates of expansion induced by heat, or due to compression of the substrate surface. The researchers developed a theory explaining the formation and evolution of the blisters, and found that the blister size can be predicted through models.
Most significantly though, the researchers were able to control the blister size by modifying the elasticity of the film and the substrate, and the strength of adhesion between them. Thus, by carefully designing the parameters of the substrate and the film, wires could be partially attached to a surface and made to move with the material without breaking under stress due to twisting and stretching of the substrate.
It is believed that this work differs remarkably from similar approaches toward creating stretchable electronics through blistering of materials, in that it does not rely on complex microfabrication techniques to force the delamination blisters to appear. Such approaches may typically cause the blisters to become larger than their intrinsic size. This novel approach allows delamination to be precisely modelled and controlled, paving the way for a well designed stretchable electronic device with complete prior knowledge about how the blisters will appear when stretched.
This work also indicates that materials such as graphene, which are ultra thin and flexible, may be ideal for stretchable electronic devices. The researchers collaborated with the French National Centre for Scientific Research for this work, which was funded by the European Union’s New and Emerging Science and Technology (EU-NEST) programme.
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