Microelectronics technology

Eyeing up a new technology

A “bionic” eye lens points to a completely new way of building microelectronic circuits

CONVENTIONAL contact lenses are good at correcting vision. That, however, is not enough for Babak Parviz. Dr Parviz, who works at the University of Washington, in Seattle, wants to get them to provide information, too. His model is the “head-up” displays on the windscreens of aircraft that are also becoming popular in cars. Shrinking the technology used in these applications to the point where it can be employed in tiny, flexible lenses has proved challenging. But last week, at a conference in Tucson, Arizona, organised by the Institute of Electrical and Electronics Engineers, Dr Parviz announced that he was getting close.

The lenses themselves are made out of polyethylene terephthalate (PET), a substance similar to that used in overhead projection sheets. Dr Parviz uses PET because his previous research has shown that metal circuits can be safely and effectively attached to it. The trick is building that circuitry in the first place, because the components—most notably, light-emitting diodes, or LEDs—have to be manufactured at high temperatures using processes that involve corrosive liquids.

The usual trick of doing this in situ on a piece of silicon that also serves as the circuit board would not work on a piece of PET, which would be destroyed almost instantly. Instead, Dr Parviz employs a technique he developed the year before last, and for which this is the first practical use.

It works by etching small, precisely shaped holes in the PET. The shapes of the holes match those of particular components. Those components are manufactured elsewhere, using the traditional, plastic-hostile techniques. They are then mixed together to create a grey powder that is floated in alcohol over the surface of the lens.

When a component floats over an appropriately shaped hole in the PET, it slips into position. In this way, not only can LEDs be laid down, but also tiny solar panels and antennae that convert radio waves into electrical energy. Everything is thus in place for a display unit that can extract power from the outside world, and also receive signals from it. All that need then be done is to encapsulate the result in Perspex (chosen because, being the material from which hard contact lenses are routinely made, it can protect the circuitry with harming the wearer’s eye) and shape the whole thing on a heated aluminium mould, so that it fits the eyeball of the wearer.

At the moment, Dr Parviz’s prototype does not produce a useful image. That would require much more complicated circuitry than he has built so far. But he can make the LEDs flash on and off, so the principle seems to work.

The next stage is to get someone to try one of the lenses on. That, in today’s risk-averse world, requires regulatory approval. But even by getting his self-assembled screen of LEDs to flash, Dr Parviz has shown that circuits can be built at room temperature this way. And that, rather than the specifics of this particular bionic eye lens, is the real point of the exercise.