Materials scientists at the University of Illinois at Urbana-Champaign, US, have developed ultra-thin sheets of stretchable silicon that could be used to construct high-performance electronic devices with complex shapes.
Silicon is normally rigid, which is fine for computer chips, but not so for wearable electronics and flexible displays. For this reason there is much interest in organic films for flexible electronics. The problem with organic polymers, however, is that they do not offer the same level of performance as silicon, and therefore cannot be used for computationally-intensive tasks.
Building on their earlier success with one-dimensional ribbons of stretchy silicon, John Rogers and his Illinois colleagues have now developed two-dimensional sheets of silicon, which they say could make it possible to put electronics on spheres and surfaces with complicated geometries.
The sheets, which range in area from 3–5 mm2, and in thickness from 55–320 nm, are fixed to a stretched-out sheet of rubber. When the tension is released the silicon buckles to form a herringbone-like pattern, and it is these snaking patterns of waves that allow the sheets of silicon to stretch in two dimensions.
“Stretchable is fundamentally different from flexible,” says Rogers. “Flexibility only allows the system to be rolled into a cylinder or wrapped around a cone. Stretchability is required for anything else – e.g., integration on a surgical glove, conformal shaping to a sphere, etc.”
The researchers have so far made functional diodes out of the two-dimensional stretchy silicon, and are currently working on developing an electronic eye. “We will have a working prototype – at the resolution of a few hundred pixels and the form factor of a human eye – before the end of the summer, probably sooner,” says Rogers.
Rogers recently founded a company – Semprius – to commercialise systems that use printed silicon and other semiconductors, and provide an outlet for stretchable silicon.
Further reading: Biaxially Stretchable Wavy Silicon Nanomembranes, Choi et al., Nano Lett. 7, 1655 (2007).
Article first published in Nanomaterials News.