Given the low costs and extensive applications that could be possible with flexible paper circuit boards, we've seen many ideas for their production, from printing with silver ink to embedding chips within paper. Now, however, scientists have developed an elegant method for selectively changing the very nature of the paper itself into conductive graphite. Unlike polymer-based flexible circuits, these paper circuits are, ironically, able to withstand the high temperatures generally used in the production of electronics.
Using an ordinary inkjet printer loaded with a cartridge of an iron nitrate catalyst, the team at Germany's Max Planck Institute prints their target designs onto ordinary paper. When the paper is heated to 800°C (1,472°F) in an oxygen-free environment (which is presumably why the paper doesn't burn), the catalyst changes the composition of the paper's cellulose fibers into pure conductive graphite, while the unprinted paper remains unchanged.
The scientists proved that the resulting "carbon electronics" were selectively conductive by electroplating the paper with copper. As shown in the image below, only the printed design became copper-coated. They also demonstrated how to create a 3D conductive structure by subjecting, whimsically, an origami paper crane to the same catalytic process.
The mechanism of creating graphite from cellulose is still not fully understood, though iron is already also used in the manufacturing of carbon nanotubes. More experimentation and a better understanding could potentially lead to transforming paper-based structures into the atom-thick wonder nanomaterial, graphene.
Source: Max Planck Institute