Strategies for High Resolution Patterning of Conducting Polymers

The discovery of conducting polymers by MacDiarmid, Shirakawa and Heeger in 1977 has generated enormous interest in π-conjugated macromolecules.[1] Since then, their unique properties such as the metal-insulator transition induced by doping-undoping process, controllable optoelectronic property through molecular design and attractive mechanical properties and processing advantages have stimulated many progresses in researches and technically relevant applications. They have been extensively studied allowing the demonstration of different functional devices including organic light emitting diodes (OLED),[2] electrochromic devices,[3] field effect transistors[4] and integrated circuits,[5] batteries,[6] photodetectors[7] and sensors.[8] In microelectronic-related device fabrication, conducting polymers need to be patterned into microand nanostructures. For example, conducting polymer microstructures are used as interconnects and as source, drain and gate electrodes in all-polymer integrated circuits[5] or as red, green, blue (RGB) pixels in multicolor OLED displays.[9] In contrast to the striking achievements in conducting polymer microelectronic devices, the application of conducting polymer nanostructures in nanoelectronic devices is still under development due to the current limitation of nanofabrication. However, their applications in other less demanding areas such as optics, sensors and biotechnology have been demonstrated. For example, Boroumand et al. demonstrated a series of electrically driven nanoscale light sources, which might be used in near-field optical communication system and storage devices.[10] Roman et al. gave strong evidence that nanopatterning of conducting polymer was capable of improving the performance of photodiodes.[11] Matterson demonstrated the increasing efficiency and controllable light output from structured LEDs.[12] Recently, several groups reported the use of conducting polymer nanostructures as chemical or biological sensors, which show higher sensitivity than conventional sensors.[13] For instance, Craighead and co-workers have reported a polyaniline nanowire chemical sensor more sensitive than the traditional filmbased sensors for the detection of ammonium gas. [14] Huang et al. reported a nanofiber film sensor that responds much faster than the conventional film sensor to HCl gas. [15] Apart from the detection of chemical vapors, improved sensing behaviour is also observed when detecting biological molecules, such as glucose[16] and biotin. [17]