Producing electric circuits that are actually printed on paper is not straightforward and usually requires some type of mask or stencil. Paper as a substrate is flexible, cheap, lightweight, and environmentally friendly. Flexible circuits of this type could be used, e.g., in radio frequency identification (RFID) tags.

Hong-Mei Xiao, Chinese Academy of Sciences, Beijing, Shao-Yun Fu, Chinese Academy of Sciences, Beijing, and Chongqing University, China, and colleagues have developed a process that uses laser printing to make multilayer circuits from silver nanowires (Ag NWs) on paper. The team first printed the desired circuit with a common laser printer, using the usual toner. In a second step, the printed paper is laminated at elevated temperatures with a polyimide (PI) film that has been coated with silver nanowires. The Ag NWs “stick” to the toner and remain on the paper only in the previously printed areas. The process can be repeated to form multilayered circuits.

The possible size of the circuits depends mainly on the resolution of the laser printer. In contrast to liquid printing processes, the method does not require wetting of the paper, which can lead to distortions. As a proof a concept, a working two-layered RFID tag was printed. According to the team, the approach is promising for the preparation of highly integrated paper-based circuits with optimized performance.

• Rapid Laser Printing of Paper-Based Multilayer Circuits,
  Gui-Wen Huang, Qing-Ping Feng, Hong-Mei Xiao, Na Li, Shao-Yun Fu,
  ACS Nano 2016.
  DOI: 10.1021/acsnano.6b04830