Researchers at the Fraunhofer Institute for Surface Engineering and Thin Films IST, Brunswick, Germany, have developed a process to produce transparent, electrically conductive oxide coatings, which could prove ideal for clearing frosted-over windscreens on cold winter mornings.
In a unique approach, the researchers combined mid-frequency magnetron sputtering with a chemical reaction. The glass substrate is heated in a reactor and coated and then, in the course of magnetron sputtering, accelerated ions of inert gas ‘shoot’ atoms out of a zinc-aluminium plate. The metal atoms are deposited on the substrate in a vacuum.
For this coating to become both electrically conductive and transparent, the zinc needs to be oxidised, so that the aluminium and zinc atoms bond together. ‘We are now working to produce contacts for thin-film solar cells’, comments Dr Bernd Szyszka of the IST. ‘Transparent and electrically conductive coatings are also needed for flat monitor screens and electrically switchable window panes for buildings’.
This brought about the idea for the windshields. ‘A prerequisite for use of these coatings systems’, Szyszka continues, ‘is to convert the operating voltage for cars from 12 to 24 or even 42 volts’ - a conversion that is expected over the next two to four years to improve the configuration of electronic systems in motor vehicles.
Technically, the coatings can also function at low power, but manufacturing costs are then extremely high. With a higher voltage, thinner coatings suffice - which can be produced at substantially lower cost.
The advantage of the IST process is that it is exceptionally stable in operation, and the coatings can be applied rapidly and inexpensively. The IST researchers are presently using an industrial scale plant to coat glass substrates of up to 0.6 to 1m in size.