Just as a ten-floor apartment building can offer more living space than a one-story house for the same amount of real estate, so too could microchips that stretch up into three dimensions instead of just the conventional two lead to dramatically more powerful computers. Now Harvard researchers say they have a simple way to create three-dimensional circuitry that assembles itself. In addition, the scientists can merge these extraordinarily porous devices with a wide variety of substances to make “smart matter” that can respond to and control its surroundings, or fuse these electronics with living cells to produce what they dub “cyborg tissues.”
The researchers started with silicon wires only nanometers or billionths of a meter in diameter printed as a sheet onto an epoxy surface. Electron beams or ultraviolet rays were then used to sketch patterns onto these layers, hardening the epoxy. Dissolving the unhardened epoxy then left behind flexible 2-D circuits. These could then be rolled up like scrolls by hand to create 3-D stacks — curly metal wires integrated with these devices could even make them roll up themselves. Metal spots deposited on the circuits could in principle serve as bridges between multiple layers of these scrolls.
These novel structures are more than 99 percent empty space, voids the investigators could readily fill with a wide variety of conventional materials. The resulting hybrid compounds are what the nanoscientists call smart matter — for example, sensors can help reveal when and where acidic or alkaline solutions infiltrated the materials, or when and how they got squeezed, twisted or stretched. Possible applications might include contact lenses that can record and display images, said researcher Jia Liu at Harvard University.
These electronic networks could also in principle be integrated with living cells for cyborg tissues. These could lead to implants with novel capabilities not seen in regular tissues, such as new senses or enhanced strength, Liu said. He, with Charles Lieber and their colleagues, detailed their findings online April 8 in the Proceedings of the National Academy of Sciences.