All of the three panels support multi-touch input. The first and third panels can detect up to two points at the same time while the second panel can detect up to five points at the same time. The first and third methods are suited to realize a simple manufacturing process, which is the advantage of CNTs. But the third method, especially, has a problem.
Specifically, with the third method, there is a large anisotropic nature in electric resistance due to the orientation of CNTs on the CNT film. For example, it might occur that the x-coordinate of a finger can be detected with a high accuracy while the detection accuracy for its y-coordinate is low.
"When two points having the same x-coordinate and different y-coordinates are touched at the same time, it is possible that they cannot be distinguished," Chimei Innolux said.
To address this problem, the company developed the second method, which combines a simply patterned ITO film and a CNT film. The electric resistance of the ITO film is isotropic and, thus, mitigates the problem of the CNT film.
It takes time to replace ITO film
This time, Chimei Innolux applied the CNT film to a touch panel, not to the transparent electrodes of a display.
"As a replacement for an ITO film, the CNT film has a high electric resistance," the company said. "A high electric resistance is not a serious problem for a touch panel. So, it is much easier to use the CNT film for a touch panel than to use it for replacing an ITO film."