Imagine printing with inexpensive plastic inks that detect light. Imagine using the same inkjet process to combine these substances with printable electric switches - transistors - that can transmit the collected information. You could print out entire digital imagers this way.
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The EU-funded IPPIA project has developed the basic building blocks of a promising technology. It has designed a photosensor element — a light-detecting pixel — that can be produced entirely using inkjet printing techniques. This achievement could permit the development of fully printable imagers.
“This type of imager is essentially a digital camera on a foil,” says Mario Caironi of the Italian Institute of Technology (Fondazione Istituto Italiano di Tecnologia), who led the research. It could, he adds, be manufactured quickly, affordably and on many types of support, including plastic foils and textiles.
Printed digital imagers would be much lighter than current camera technology and, depending on the support, they could even be foldable. In addition, they could be offered in different shapes and sizes to suit specific applications.
It would be possible, for example, to supply imaging tubes or moulds matching the dimensions of specific manufactured parts. This type of equipment could facilitate various industrial quality control processes.
It would also be possible to produce particularly large imagers, potentially covering entire walls, to inspect big objects in a single go. This option would, for instance, be handy for vehicle security checks.
Foldable cameras large and small
“Basically, to build a pixel, you need to combine a photodetector with a switch, a transistor; these pixels can then be arranged in arrays to build an imager,” Caironi explains. “In IPPIA, we wanted to produce pixels that are fully inkjet-printed.”
Printable components for these photosensor elements already existed, Caironi adds. “We knew we could print photodetectors, we knew we could print transistors, so we wanted to integrate the two to show that it is possible to produce pixels,” he notes. Transistors, increasingly miniaturised, underpin the electronics on which we have come to rely.
IPPIA’s mission was accomplished by the time the project ended in August 2014, delivering the printable pixels that constitute the main building blocks of a new type of digital imager and opening up a whole new range of possibilities.
The tiny photosensors developed by IPPIA are produced by building up successive layers of liquid plastic materials using an inkjet printing process. As these inks are applied at low temperatures, a thin sheet of plastic can be used as a support — and it does not actually have to be flat. It would, for example, be possible to produce imaging tubes for the inspection of round or hollow parts on an assembly line.
Caironi benefited from EU-funding for IPPIA, in the form of a Marie Curie grant awarded to help him re-establish his career in Italy at the end of a temporary post-doc position in the UK. He has since received a sizeable grant from the European Research Council for work building on the outcomes of the project.
Caironi’s printable photodetectors can be tuned to detect various types of light. At the moment, his research focuses on the visible to near-infrared range and X-rays, where he is exploring options for promising applications. These notably include plastic, digital X-ray imaging technology.
Access to inexpensive, light, thin X-ray imagers would, for instance, be of great interest in medicine, Caironi explains. This innovation could significantly reduce costs, along with the weight and size of digital radiology equipment based on silicon technology.
There are many possibilities, he adds, but it is still early days. “We are still developing the technology, obviously. We are now moving towards building small demonstrators, pixel by pixel.” So it may be a while yet before the full potential of inkjet-printed cameras can be tapped, but they could revolutionise the way we look at the world.