Japanese researchers developed a polymer membrane with an electric conductivity of 1,200S/cm or higher, which they claim is twice as high as that of existing products.
The membrane was developed jointly by Sanyo Electric Co Ltd and a research group led by Takakazu Yamamoto, a professor at the Tokyo Institute of Technology. It also features a high reproducibility, according to the company.
The new polymer membrane is expected to be used for transparent electrodes of touch panels, LCD TVs, etc. Its sheet resistance should be 300-500Ω/〈 for use in a touch panel, and 10 to several tens of Ω/〈 for an LCD TV, according to Sanyo Electric. The polymer membrane can have a sheet resistance suitable for use in touch panels thanks to its high conductivity, the company said.
Specifically, the new conductive membrane has a sheet resistance of only 68Ω/〈 when it is formed with a thickness of 120nm, Sanyo said. And the average sheet resistance is about 100Ω/〈, though it depends on the membrane thickness, the company said.
Transmittance is another important index when a membrane is used as a transparent electrode. A 100nm-thick prototype of the new membrane has a transmittance of about 75% for light having a wavelength of 550nm.
"The improvement of transmittance is one of the challenges we are facing because, currently, it is lower than that of existing ITO films," Sanyo said.
Another hurdle for the commercialization is degradation caused by oxygen, UV light, etc. It is necessary to prevent the degradation and ensure sufficient reliability of the membrane.
"We are now preparing to evaluate the reliability," the company said.
Innovations in material, formation process
The prototype is made of a polymer material called "polyethylenedioxythiophene (PEDOT)," which has a stable molecular structure. The key to a high conductivity is an additive used to control the reaction speed of the materials in the PEDOT production.
This time, the researchers used a new additive and optimized its quantity to achieve the high conductivity. The improvement of the membrane orientation supposedly increased the conductivity.
A chemical oxidation polymerization method was adopted to produce PEDOT. Film formation processes suitable for cost reduction, such as spin coating, printing and dipping, can be utilized, according to Sanyo. Dipping is a method to produce a membrane by dipping a substrate in a solution and then pulling it up.
Because the new membrane is so thin, the amount of materials used can be reduced and the cost of production equipment can be cut down. Thus, once it is commercialized, it "may be produced at a cost lower than that of existing ITO electrodes," the company said.
Sanyo plans to look for specific applications of the membrane as well as to further increase its conductivity to double that of the prototype.