Streamlining touchscreen prod'n using photometallisation

A team of researchers at Leibniz Institute for New Materials (INM) in Germany are using photometallisation to develop microscopic and macroscopic conductor tracks that are used in touchscreens for detecting the position of a user's finger. According to the team, benefits of the low-cost process are that it is quick, flexible, scalable and environmentally friendly.

As part of the process, foils or glass are coated with a photoactive layer of metal oxide nanoparticles. A colourless, UV-stable silver compound is then applied. After exposure to UV light, the silver compound decomposes and the silver ions are reduced to metallic, electrically conductive silver. Tracks of varying sizes, down to a 1000th of a millimetre, can be created this way. Corresponding conductor tracks are then produced by exposure to UV light.

"There are three different options that we can use," said Peter William de Oliveira, head of INM's optical materials programme division. "'Writing' using a UV laser is particularly good for the first customised production and testing of a new conductor strip design, but this method is too time-consuming for mass production."

Photomasks that are UV permeable only at the desired positions can also be used for structuring, but they are expensive and have a high environmental impact. "For a semi-continuous process they are particularly suitable for solid substrates such as glass," said de Oliveira, but they are not flexible and mainly composed of quartz glass and so are not a fit for a roll-to-roll process.

The INM researchers are focusing on a third option that uses "transparent stamps."

"These stamps mechanically displace the silver complex, and where there is no silver there is also no conductor strip," de Oliveira noted. "So we can form structures measuring just a few micrometres. Since the stamps are made of a flexible polymer, we have the possibility of arranging them on a roll." In addition, because the stamps are transparent, the researchers are working to incorporate the UV source in the roll, so the first steps would be done for a roll-to-roll process. The result: Conductor strip structures of different sizes could be produced on a large scale on substrates such as polyethylene or polycarbonate film.

- Amy Norcross
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