What’s in a word? Call it a membrane and most people associate it with something scientific. Call it skin and there are definite human associations. So when the engineers at the University of California Berkeley (USA) developed a pressure sensitive electronic material made of nanowires, is it a membrane or skin?
They’d like to call it skin. Sort of…it’s a material that is touch sensitive ‘like skin.’ It’s not skin at all in the sense that it’s not organic. The material is composed of nanowires made of germanium and silicon (inorganic) and its functioning is electro-mechanical. Eventually the researchers think it could become part of a material/organic system that can be used as skin, first on robots, and then on people. But for now, in these very early stages, they’re calling it e-skin (electronic skin) – the first such material constructed from the inorganic single crystalline semiconductors known as nanowire.
Scientists have been working on artificial skin for decades. Most of the work has been done with organic materials. That seems natural. The organics are flexible and not difficult to work with. Unfortunately, they are also (mostly) lousy for electronic purposes. Organic material has poor semiconductor properties, which means making it work in an electronic environment requires relatively high voltages. Power supply, especially from batteries, is a problem.
Inorganic materials, such as silicon can have very good electrical properties and don’t need much power. (That’s one big reason why most of our electronics are made with silicon-based semiconductors.) However, most inorganic semiconductors are inflexible and either wear out quickly or crack. Not good properties for skin. The nanowire material gets around this problem by the flexibility of the many very tiny ‘wires.’
The research team invented new techniques for creating the material, including rolling the nanowires from a cylinder onto a sticky film (a substrate of polyimide). The pattern of nanowires laid down on the film creates transistors. On top of the transistors a rubber touch-sensitive film provides the sensor capability. The completed e-skin requires less than 5 volts of power, can detect pressures from 1-15 kilopascals (that’s about the range of typing to holding something with a few pounds of force), and could withstand more than 2,000 bending cycles.
“This is the first truly macroscale integration of ordered nanowire materials for a functional system – in this case, an electronic skin,” said study lead author Kuniharu Takei, post-doctoral fellow in electrical engineering and computer sciences. “It’s a technique that can be potentially scaled up. The limit now to the size of the e-skin we developed is the size of the processing tools we are using.”
[Source: Nanotechnology Today]
The next steps for ‘e-skin’ are the classic technological problems of scaling – making the material in quantity – and of integrating the material with other technology, for example robotics. Along the way, which is likely to be a matter of many months if not years, other developments in nanotechnology may come along and overshadow this work – or possibly augment it. In a field of research that is as dynamic as nanotech, the pace of innovation is both difficult to predict and relatively rapid.
The research is published online at Nature Materials Nanowire active-matrix circuitry for low-voltage macroscale artificial skin