Flexible touch sensor with finely patterned Ag nanowires buried at the surface of a colorless polyimide film

Transparent electrodes based on percolated networks of silver nanowires (AgNWs) are known for their good conductivity, transparency, and flexibility. Owing to these intrinsic properties, AgNWs are gaining much attention and are considered potential electrode materials in large-area and flexible devices. However, a major drawback of the AgNWs - poor adhesion to polymers - is holding back their practical usage. The weak bond of AgNWs to polymers limits their fine-pitch patternability, which is one of the most important requirements in the electronics industry. In the study reported here, we irradiated nanowires, attached to the polymer during photolithography and metal etching, with intense pulsed light to improve the adhesion. As a result, a complicated pattern of nanowires was fabricated without any form of damage. For better flexibility, we transferred the patterned AgNWs to the surface of a colorless polyimide film to produce a highly stable electrode under repeated bending cycles. As a result of these developments, a flexible touch panel based on a capacitive sensor was successfully fabricated.