University of Houston researchers have developed a nanomesh electrical conductor that is both stretchable and transparent, thus potentially usable for developing a fully foldable cell phone or a flat-screen television.
A material that is transparent and has both the necessary flexibility and conductivity has proved elusive. Some materials have two of the components but, until now, finding one with all three has remained difficult, according to Zhifeng Ren, physicist at the University of Houston and principal investigator at the Texas Center for Superconductivity.
The nanomesh, a network of fully interconnected gold nanowires, has good electrical conductivity and transparency and has "ultrahigh stretchability," according to the research team. The researchers, who were assisted by two colleagues at Harvard University, found gold nanomesh electrodes increase resistance only slightly, even at a strain of 160 percent, or after 1,000 cycles at a strain of 50 percent.
The material also has potential applications for biomedical devices, said Ren.
And unlike silver or copper, gold nanomesh does not easily oxidize, which Ren said causes a sharp drop in electrical conductivity in silver and copper nanowires. According to research associate Chuan Fei Guo, the group is the first to create a material that is transparent, stretchable and conductive, as well as the first to use grain boundary lithography to process it. “More importantly, it is the first to offer a clear mechanism to produce ultrahigh stretchability,” he said.
The grain boundary lithography involved a bilayer liftoff metallization process, which included an indium oxide mask layer and a silicon oxide sacrificial layer and offers good control over the dimensions of the mesh structure.
"This is very useful to the field of foldable electronics," said Guo. "It is much more transportable."
Research associate Tianyi Sun noted that while Korean electronics maker Samsung demonstrated a cellphone with a bendable screen in October and LG Electronics introduced a curved cellphone available in Asia, neither is truly foldable or stretchable, instead curving slightly to better fit against the user's face. "For that kind of device, we need something flexible, transparent," Sun said of a foldable phone. "If we want to further that technology, we need something else, and the something else could be the technology we are developing."
Ren noted that, although gold nanomesh is superior to other materials tested, even it broke and electrical resistance increased when it was stretched. But he said conductivity resumed when it was returned to the original dimensions. That didn't prove to be the case with silver, he said, presumably because of high oxidation.
The work at the University of Houston was funded by the Department of Energy, while that at Harvard was funded by a National Science Foundation grant.
The research work is reported in Nature Communications.