Oxidative and initiated chemical vapor deposition for application to organic electronics

Abstract

Since the first discovery of polymeric conductors in 1977, the research area of "organic electronics" has grown dramatically. However, methods for forming thin films comprised solely of conductive polymers are limited by the rigid nature of the conjugated backbone. Neither spin casting from solution nor melt processing can be used. To answer to this challenge, a solvent-free method of oxidative chemical vapor deposition (oCVD) to synthesize conductive poly (3, 4-ethylenedioxythiophene) (PEDOT) films was demonstrated. The substrate temperature systemically controls the conjugation length, resulting in films with conductivity of 9.1 x 10-4 to 348 S/cm. The highest conductivity was about 1000 S/cm. The doping level could also be tuned with substrate temperature. Consequently, the work function was varied from 5.1 to 5.4 eV. The polymerization rate could be modulated with various oxidants, which significantly affects the surface morphology of PEDOT film. With milder oxidant, the surface morphology was highly nano-porous. Conformal coverage of PEDOT was also observed on trench structures and paper mats. Furthermore, with this one-step method, PEDOT film could be grafted on various kinds of organic substrates. Huge increase in adhesion strength was consistently observed. With this grafting technique, nanometer-scale PEDOT pattern was firstly obtained on flexible substrates down to 60 nm.

(cont.) A click chemistry functionalizable poly (propargyl methacrylate) (PPMA) films also were prepared via initiated chemical vapor deposition (iCVD). PPMA itself exhibits e-beam sensitivity and hence can be directly patterned via electron beam (e-beam) lithography without requiring a conventional resist layer. With this PPMA layer, a nanopatterned multi-functional surface was also fabricated and we demonstrated the covalent functionalization of two independent components in a one-pot, self-sorted area-selective process, performed in an aqueous solution at room temperature, having conditions which are bioompatible. Finally, we report a novel nano-adhesive layer deposited by the iCVD process. An epoxy-containing polymer, poly (glycidyl methacrylate) (PGMA) was used as a nano-adhesive layer. No leakage was observed up to the test pressure of 50 psia from the resulting microfluidic devices.