Japan's National Institute of Advanced Industrial Science and Technology (AIST) developed a transistor that it claims is as soft and strong as clothes.
Most of the components of the transistor are made of rubber or gel and flexible. As a result, the transistor has a high tensile strength and is highly resistant to bending and stretching.
Even when it is stepped on by a high heel or washed, it will not be broken, AIST said. Because of this advantage, AIST expects that the transistor will be used for a variety of large-area sensors to be attached to human body and clothes.
The transistor is made by forming gate electrodes, source electrodes, drain electrodes, gate dielectric film and channels in silicon rubber whose thickness is about 1mm or less. It measures 1 x 1mm. The length and width of the channel are about 50μm and 700μm, respectively.
For each electrode, a composite material whose electrical conductivity was improved by mixing single-walled carbon nanotubes with rubber was used. The layer corresponding to a gate dielectric film is made of a gel-like material made by impregnating a polymer material with an ionic fluid. And the channel consists of randomly-aligned single-walled carbon nanotubes whose properties are similar to those of semiconductors.
The gel is not an insulator such as an oxide. When a voltage is applied to it, ions inside the gel move. As a result, it functions like an electric double layer capacitor and plays a role of a dielectric material.
The ratio of the on-state current to the off-state current of the transistor is as high as 104. The gate voltage to be applied at that time is -2 to 1V.
The properties of the transistor did not change much even after repeatedly stretching the transistor to increase its length by 40-50% about 1,000 times, indicating that it is resistant to bending and twisting.
"It functions even when it is folded to an acute angle by hand," said Atsuko Sekiguchi, one of the researchers who developed the transistor and senior researcher, CNT Application Team, Nanotube Research Center, AIST.
When an object is stepped on by a high heel, a pressure of about 25kgf/cm2 (about 245N/cm2) is applied to it. It is about 70% stronger than a pressure applied by an auto tire. Still, the operating characteristics of the transistor did not change much, AIST said.