University researchers develop ultra-thin silver film to improve touch-screen technology

A researcher holds a piece of silver alloy film as a transparent electrode that is six inches in diameter.

A researcher holds a piece of silver alloy film as a transparent electrode that is six inches in diameter. Buy this photo
Courtesy of Cheng Zhang

 

Tuesday, March 28, 2017 - 9:31pm

A research team in the University of Michigan College of Engineering succeeded in creating a tarnish-proof silver film whose properties allow for various uses such as high-tech screens. The team’s paper, published last Monday, details the film’s versatility.

As the silver film is ultra-thin, it can be used for displays such the touch screens on cell phones. The film is also transparent, which is why it can be directly applied to solar cells or organic LED displays — increasing efficiencies as the film allows more light to enter solar cells and to leave the LEDs.

Cheng Zhang, a former Engineering Ph.D. student, currently works at the National Institute of Standards and Technology and is the first writer listed on the paper. Zhang highlighted the advantages of film, especially when used for future flexible screens. So far, he explained, the material indium tin oxide is widely used for touch screens. However, it cracks very easily when moved, which interferes with the materials’ conductivity. Since silver films have a much better stability, even when moved, they are more suitable for flexible screens.

Another material currently used as a transparent conductor for flexible displays is graphene. However, the silver film shows major advantages compared to this material; namely, its conductivity is much better than the conductivity of graphene.

Zhang said silver films might be a better future alternative to ITO for economic reasons, as prices for indium are likely to rise in the future, whereas the price of silver compared to that is more likely to stay stable.

“Indium itself is a rare element,” Zhang said. “In addition, most of the supply of indium is in China and in Canada, so it is not everywhere in the world, only a few places.”

L. Jay Guo, a professor of electrical engineering and computer science, supervised the research team, and explained there were previous difficulties in producing ultra-thin silver films. Previous techniques to overcome these technical difficulties included adding other films beneath the silver film.

“It is known in the scientific community that if you want to form a silver film like this that is thin, it is not going to be continuous,” Guo said. “But adding another film would inevitably impact the performance of the silver film.”

Guo and his team set out to solve the problem by combining the silver with a small amount of aluminum. This allowed for them to create an ultra-thin, seven-nanometer silver film, smooth, transparent and resistant to tarnish.

Chengang Ji, a Ph.D. student in electrical engineering and computer science, was also part of the research team. Ji pointed out the market possibilities of the silver film given all its advantages compared to currently used materials.

“We are trying to commercialize this product because it has very good potential for the next generation,” Ji said. “So we are trying to a find a way for mass production of this silver film.”