Polymer thin-film transistor arrays for display backplanes patterned by stamping
Recent progresses in polymer thin-film transistors (TFTs) have led to the fabrication of devices with carrier mobilities up to 0.1 cm2/V.s and good sub-threshold swing (~1V/dec on 100 nm SiO2). The next step towards commercial application of polymer TFTs in large-area electronics consists in the ability to efficiently fabricate arrays of TFTs at low cost. Array fabrication must include patterning of the semiconductor in order to isolate adjacent devices and minimize leakage. Semiconducting polymers enable the use of solution-based techniques, such as ink-jet printing. It is desirable to develop other patterning techniques compatible with roll-to-roll processing. We have developed a process similar to relief printing that allows us to stamp semiconducting polymer on a variety of surfaces. The stamp is molded from polydimetylsiloxane (PDMS) onto a master reproducing the negative of the desired pattern. During the stamping process, the semiconducting solution previously coated on the substrate penetrates the stamp. The raised features of the stamp remain in conformal contact with the substrate and actively absorb the solvent causing the polymer to rapidly precipitate and form a patterned film. The stamping process was successfully used to pattern two polymer semiconductors: a poly(fluorene) (F8T2) and a high-performance regioregular polythiophene. 1-D and 2-D thin film patterns were created over ~cm2 areas on a variety of substrates (oxidized Si wafers, glass, kapton, parylene-coated Si wafers). Patterning the polymers on arrays of predefined electrodes allowed to fabricate by hand full TFT arrays on glass in seconds. The TFT island separation (~few tens of microns) was designed to be appropriate for the fabrication of TFT arrays and minimize registration requirements. The stamped devices showed good electrical characteristics, comparable to those obtained by spin coating.
Salleo, A. ; Wong, W. S. ; Paul, K. ; Chabinyc, M. ; Apte, R. B. ; Street, R. A. Polymer thin-film transistor arrays for display backplanes patterned by stamping. Materials Research Conference Fall 2003; 2003 December; Boston; MA.