In the same way that texts and images are printed on paper nowadays, in the future printers will be able to be used for manufacturing all types of electronic circuits. That technology will require new inks, such as the one which was just presented at the industrial fair in Hannover, the largest in the world, by researchers from the Leibniz Institute for New Materials (INM, Germany).
“This ink can be loaded into the cartridge of a fountain pen and used to draw an electronic circuit to light up a LED,” points out Lola González García, the Spanish scientist who participated in its development, to SINC. The details are published in the journal ´Chemical Science´.
The components of this innovative product are gold nanoparticles coated with a conductive organic polymer. The resulting nanostructures are very stable when diluted in alcohols and water, the usual ingredients of conventional inks. In fact, the idea is to apply the method to inkjet printers.
The components of this innovative product are gold nanoparticles coated with a conductive organic polymer
“The nanometric size of the metallic particles and their good stability make it possible to print very fine lines of ink (measuring a few microns),” explains González, who reminds us that minimising the width of these lines as much as possible is one of the highlights of current printed electronics.
Another advantage of the ink –which becomes conductive upon drying– is that it allows electronic circuits to be drawn on flexible materials, such as paper or plastic, utilising tools as common as a pen and without the need for any additional processes.
This is possible thanks to the properties of polymers, whose function is three-fold. On the one hand, they work as ‘ligands’ that stabilise the metallic particles and make sure that they remain suspended in the solvent (if they bound together too much they would ruin the printing process). Second, they help to package the metallic particles while they dry, improving the quality of the printed lines. They additionally act as a ´hinge´: when the material is bent, they maintain the connectivity among the metallic particles and, thus, their electrical conductivity.
Other inks already existed before with metallic nanoparticles and organic ligands, but the main problem is that organic molecules are insulating –they do not conduct electricity,– which makes using them impossible unless a sintering process is applied (treating a metallic compact or powder with heat to increase its resistance) after printing the material.
This process presents a number of disadvantages, such as having to use high temperatures that are not compatible with all types of substrates (paper, plastics or textiles, for instance), as well as deterioration in the quality of the printed lines.
“But our new inks do not require sintering, apart from being particularly flexible and conductive as soon as they dry,” concludes Tobias Kraus, director of the Structure Formation group at INM.
Other gold nanowire research
This study is part of NanoSpekt, a project for the development of materials for printed electronics, in which the researchers have also manufactured another product: extremely thin gold nanowires (less than 2 nanometres) which are very asymmetrical (between 4 and 8 micrometres long). The technique has allowed for printing motifs with a line width of less than 1 micron, another step forward in the miniaturisation of printed electronic circuits.
The materials they present in this other article, published in the journal ‘Nano Letters’, are very transparent (up to 92% transparency) and maintain good conductivity when bent. “This means they are flexible, transparent and conductive, ideal for markets like flexible displays and medical implants,” points out González.