Selective vapor deposition of poly(3,4-ethylenedioxythiophene) thin film on an n-octadecyltrichlorosilane monolayer oxidized by ultraviolet photolithography

We developed a new patterning method of PEDOT thin film particularly having strong adhesion to an oxide surface. An n-octadecyltrichlorosilane (OTS) monolayer was self-assembled on an oxidized Si wafer surface, masked with a Cr-patterned quartz, and then irradiated with ultraviolet (UV) light to introduce oxidized functional groups on top of photo-dissociated hydrocarbons. Since 3,4-ethylenedioxythiophene (EDOT) monomers are polymerized only in the presence of an oxidizing agent such as FeCl₃, PEDOT thin film can grow only on the area onto which FeCl₃ is adsorbed. In fact, in this study, only the oxidized OTS pattern directly adsorbed FeCls, and highly pure PEDOT thin film successfully grew on the pattern via vapor-phase polymerization method. This newly developed process significantly improved adhesion between PEDOT film and Si wafer surface and successfully patterned PEDOT thin film, as ascertained by contact angle, XPS, optical and atomic force microscopic measurements. Therefore, we strongly believe that the new patterning process considerably heightens the potential of PEDOT to be used as an OTFT electrode or active layer in the very near future.