Flexible electronics will enable engineers to develop various devices, from roll-up displays to ultra-rugged field equipment.  (Source: Beckman Institute, University of Illinois)
Scientists working with carbon nanotubes and flexible circuitry continue to push reality towards fantasy.

One of the next gaps between science fiction and reality that electronics engineers are hoping to bridge is that of flexible displays and computers. While various groups have come up with ways to create flexible displays, like LG.Philips' electrophoretic display, mass production of any kind is still far off. Great strides have been made towards flexible circuitry as shown by Northwestern University's flexible dielectric material. The nanodielectric is not only flexible, but printable, which could tie into future integrated circuit production techniques.

As seen in last week's issues of the journal Nature, work at the University of Illinois at Urbana-Champaign (UIUC) has brought engineers closer to mass production quality flexible ICs. Utilizing the popular carbon nanotube (CNT), UIUC's circuit is not only flexible, but much faster than typical organic circuitry. Organics have previously been too slow for use in devices like high speed displays.

The UIUC circuits are made using a combination of transfer printing and lithography techniques. First, the CNTs are deposited over the surface of a flexible substrate. The nanotubes are not forcefully aligned in any way, but due to their dispersion, form a conductive mat, similar to the University of Warwick's CNT microelectrode. Next, gold electrodes and various circuit components are applied over the substrate and CNT coating. Finally, to prevent the CNTs from bridging connections and short circuiting the network, soft lithography is used to cut channels between the electrodes, severing any nanotube connections that may bridge them.

One hurdle that organic circuitry has faced is a much lower operating speed than standard silicon devices. In order to be useful in high-speed circuitry, transistors must be capable of switching on and off thousands or millions of times per second. While the UIUC circuits haven't breached the megahertz barrier, their current speed of several kilohertz is more than enough for simple devices and RFID sensors and on par with that of current LCD circuitry.

There are no “high tech” processes involved in UIUC's circuits. Transfer printing and simple lithography techniques have been around for decades. While creating uniform nanotubes is difficult outside of a laboratory, it is certainly not an uncommon procedure at this time. The simplicity of the fabrication process favors mass production, should a few small developments be made.

Jet printed nanotubes made headlines back in 2006 when Rensselaer Polytechnic Institute and University of Oulu scientists used a standard ink jet printer to print a popular picture of Albert Einstein using ink made of dissolved CNTs. Since then, jet printing has become widely used in CNT research. Further refinement to printing processes could benefit the UIUC circuits by virtue of printing a more precise pattern of nanotubes. This could eliminate the need for the lithography step of fabrication entirely.

The nanotube printing process is not alone in areas that could see improvement. High precision methods of nanotube production are needed to insure that the nanotubes used are of high purity and similar mechanical dimensions. In conjunction with a refined printing process, this could benefit the UIUC circuits both in ease of production and in quality management.

Mass produced flexible displays and wearable computers are not far off. Technological advances like those at the University of Illinois are moving these futuristic devices further from books and movies and closer to our homes and pockets.

"If you can find a PS3 anywhere in North America that's been on shelves for more than five minutes, I'll give you 1,200 bucks for it." -- SCEA President Jack Tretton

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