Printing electronics requires “inks” with electrical properties that can act as conductors, resistors or semiconductors. These inks are becoming more versatile. One example comes from Xerox, an American firm which makes office equipment and commercial printing systems. Its research centre in Canada has developed a silver ink which can be used to print flexible electronic circuits directly onto materials like plastic or fabrics.
Silver is a better conductor of electricity than copper, which is typically used in circuits, but silver is expensive and tricky to print because it melts at 962°C. However, by making silver into particles just five nanometres (billionths of a metre) in size, Xerox has produced a silver ink which melts at less than 140°C. That allows it to be printed using inkjet and other processes relatively cheaply, says Paul Smith, the director of research at the laboratory. Only minuscule quantities of silver are used and there is no waste, unlike chemical-etching processes.
Xerox’s PARC research centre in Palo Alto, California, is developing ways to use such inks. These can print circuits for various components, including flexible display screens, sensors and antennae for radio-frequency security tags. With the emergence of additive-manufacturing techniques, it starts to become possible to print such things directly onto the product itself, says Janos Veres, the manager of PARC’s printed-electronics team. That includes products with complex shapes. Optomec, based in Albuquerque, New Mexico, has developed additive-manufacturing systems for a variety of industries. It can print electronics directly onto a pair of glasses, for “augmented reality”; it can make a plastic water tank that uses embedded electronics to measure how full it is and turn pumps on or off; it can print sensors on military armour; or an antenna on the case of a mobile phone.