Layer-by-layer self-assembled conductive thin films for MEMS applications

A layer-by-layer self-assembly process is investigated based on the alternate deposition of polyanion and polycation polymer materials onto oxidized silicon substrates for anti-static and electrical applications in MEMS devices. The polyanion and polycation in this study are sulfonated polystyrene and polypyrrole, respectively. The influence of FeCl3 oxidant concentration is examined. It is found that the films prepared with higher oxidant concentrations exhibit lower resistivity; films prepared at 30 mM FeCl3 show a resistivity of 0.05 Omega cm while those prepared at 6 mM FeCl3 have values on the order of 0.15 Omega cm. The influence of doping with p-toluene sulfonic acid on the resistivity is found to be quite small, although the use of the dopant remains highly desirable for increased structural and thermal stability. Using atomic and electric force microscopy, the film morphology is found to exhibit nodular structures with an approximate grain size of 28 nm and 60 mV surface potential distribution. Finally, through reaction with octadecyl-sulfate sodium, the water contact angle of the pyrrole films have been shown to increase from 46 degrees to 85 degrees. (C) 2005 Elsevier B.V. All rights reserved.