Surface-energy patterning for ink-jet printed flexible electronics

Abstract

Ink-jet printing is a desirable manufacturing technique for electronic devices as this additive method should allow for integration of different electronic components over large substrate areas at low cost. Drop placement and structure of the dried film are critical factors when using ink-jet printing as a deposition method, and can be reliably controlled through surface energy patterning of the substrate. For example, print resolution and reliability of drop placement can be improved considerably by using a surface energy pattern to direct the printed drops. Additionally, printing of field-effect transistors (FETs) typically requires the deposited material to span an area of surface energy contrast (electrodes and channel region), which can often be difficult due to preferential wetting on one of the surfaces. This effect can be suppressed through the use of a surface energy pattern, improving device performance and device-to-device variability. We have investigated different photolithographically defined anti-wetting materials to form the surface energy pattern, including an alkyl functionalized polysilsesquioxane (PSSQ), and perfluoropolymers such as polytetrafluoroethylene (PTFE). FETs incorporating an ink-jet printed small molecule, n-type, organic semiconductor confined by these anti-wetting structures will be described. The effect of the wetting region geometry on the film morphology and device properties will also be discussed. Using these techniques we show ink-jet printed, n-type organic transistors with a field-effect mobility of >0.2 cm2 V-1 s-1, and have fabricated flexible QVGA (320240 pixel) reflective displays with a 250250 m pixel size.