Printed electronics from lab to fab

Whilst the electronics industry and its gadget-addled followers obsess over computer and mobile device processors and advanced graphics capabilities, the more interesting advances are being made in relatively simple technologies that should vastly expand the economic, geographical and cultural scope of microelectronics. I am thinking for example of the use of age-old printing techniques to lay down electronic circuits on flexible materials such as fabrics and paper.

Novalia press used for printing electronic circuits on paper (photo: Kate Stone)

Back in 2008 I had a feature article in the industry journal +Plastic Electronics on the high-technology hub known as the Cambridge Cluster. Silicon Fen, as it is otherwise known, was at the time the recipient of some 9% of Europe’s venture capital investment, and 24% of UK high-tech investment. With such a large amount of money sloshing around, the markets clearly had confidence in the technologies being developed in Cambridge’s university and commercial laboratories.

Flexible electronics is one such technology, and in this emerging field Europe is competing hard with the big players in the United States. The research effort generally comes under the banner of nanotechnology, but it goes much further than that.

One of the subjects of my 2008 study was the Cambridge-based printed electronics startup Novalia, founded by former academic Kate Stone. In that article I included a photograph of a lithographic press used by Novalia to print electronic circuits on paper, and the illustration is reproduced here. When we think of microelectronics processing the common image is of whiter than white clean rooms staffed by technicians dressed like surgeons. With Novalia we have in stark contrast a printing press in a factory-like environment with dust on the floor.

Printed electronics fabrication remains a primitive technology, but not for long. Microelectronic components are three-dimensional albeit relatively flat objects, whilst ink is a liquid that dries rapidly when deposited in very thin layers on a porous substrate. How is it possible to print detailed microelectronic circuits onto paper? The challenge is in developing metal inks with a fine control over their electrical conductivity, viscosity, surface tension and adhesion properties. This is as much classical chemistry and engineering as it is nanoscience.

One approach to the problem is described by Tsinghua University nanotechnologist Jing Liu and his colleagues. In their Nature paper first author Yi Zheng et al. detail a process for modifying the adhesion properties of liquid metal ink, overcoming the material’s naturally high surface tension through the use of a dispensing machine with a brush-like porous pinhead aperture, and slightly oxidised inks adapted for particular paper substrates.

The Chinese approach may be some way from the rough and ready presses used to print millions of red-top daily newspapers, but like lithography it is based on established mechanical engineering principles. Furthermore, it is a “desktop” technique that can be carried out under everyday environmental conditions.

This is the key to transferring cutting edge nanotech from the laboratory to the shop floor.