The field of printed electronics has been receiving increasing attention in recent years for the potential it holds for very low-cost flexible electronics on common media such as paper, plastic and textiles.
It is expected to facilitate a wide variety of unconventional applications, moving beyond typical silicon-based electronics such as flexible displays, smart labels, animated posters and active clothing.
However, the full potential of printed electronics has mostly remained untapped due to several design constraints. One such major challenge has been posed by the use of printing processes such as inkjet or screen printing, which limit the capabilities to just planar printing of the microelectrodes.
Researchers from the University of Illinois have now developed a new printing approach that allows omnidirectional printing using a novel concoction of silver nanoparticle inks. This facilitates the microelectrodes to be printed out of plane, thus allowing them to directly cross pre-existing patterned features through the formation of spanning arches. This approach departs from typical techniques where insulating layers or bypass electrode arrays are required in conventional layouts. The research is described in a recent paper published by the online journal, Science Express.
The researchers were able to produce the printed features by first preparing a highly concentrated silver nanoparticle ink, which allows them to write their own silver linings as required. This ink is then extruded through a tapered cylindrical nozzle attached to a three-axis micropositioning stage, which is controlled by computer-aided design software.
The team was able to demonstrate patterned silver microelectrodes by omnidirectional printing of concentrated nanoparticle inks with minimum widths of about 2 micrometres on semiconductor, plastic and glass substrates. To create bonding between the silver nanoparticles, which does not take place when printed, the printed structure is heated to 150°C or higher. During this process of thermal annealing, the nanoparticles fuse into an interconnected structure.
The modest processing temperatures required for this process enable the printed features to be compatible with flexible, organic substrates, which was demonstrated by patterning both planar and out-of-plane silver microelectrodes. The researchers were able to produce spanning interconnects for solar microcell and light emitting diode arrays and bonded silver wires to fragile, three-dimensional devices.
This novel approach, unlike conventional techniques, allows the fine silver wires to be bonded to delicate devices using minimal contact pressure, which makes it ideal for many electronic and optoelectronic applications involving flexible, stretchable electronics. The printed microelectrodes, which carry signals from one circuit element to another, can withstand repeated bending and stretching, without any significant change in their electrical properties.
This novel omnidirectional printing of electronics could pave the way for creating highly integrated systems from diverse classes of electronic materials on a wide variety of substrates.
For more information contact Patrick Cairns, Frost & Sullivan, +27 (0)21 680 3274, [email protected], www.frost.com
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