Lateral Microstructuring of oCVD PEDOT Nanolayers Fabricated by EDOT/SbCl₅ Chemistry and Photoresist-Based Lift-Off

Oxidative chemical vapor deposition (oCVD) converts coevaporated monomer and oxidant species into conductive polymer thin films with high surface conformity to the topology of the substrate. FeCl3 as the traditional oCVD oxidant, however, also has drawbacks, like the requirement of a postrinsing to remove nonreacted particles from the substrate surface or the need to install the crucible inside the deposition chamber, which leads to an increase in reactor volume, higher precursor consumption, and eventually higher cost. We present a self-designed compact oCVD reactor and demonstrate the synthesis of homogeneous oCVD PEDOT coatings on silicon oxide substrates of up to 5 cm in size without any postprocessing by employing the more volatile liquid SbCl5 oxidant and EDOT monomer chemistry. The growth rate, sheet resistance, and optical transmittance of as-deposited PEDOT layers are systematically investigated by screening the influence of various oCVD reactor parameters (substrate temperature, monomer temperature, deposition time, and nitrogen carrier gas flow). We use a photoresist-based lift-off process to obtain oCVD PEDOT stripes of 10 to 2000 μm in width and integrate metal contact electrodes for subsequent transfer length method (TLM) characterization. Upon comparing TLM-derived conductivities of two different fabrication schemes, i.e., “PEDOT last” (∼312 S/cm) and “PEDOT first” (∼306 S/cm), with four-point probe measurements taken on nonpatterned PEDOT references (∼350 S/cm), we suggest that the micropatterning process has negligible influence on the electrical properties of oCVD PEDOT. Our TLM analysis also reveals that the patterned PEDOT/metal interfaces exhibit very low contact resistivities (ρc < 10–2 Ω cm2), which in the best case (ρc = 7.1·10–4 ± 2.5·10–4 Ω cm2) is about 1 order of magnitude below the current record reported for PEDOT:PSS. Our results demonstrate that the combination of a compact oCVD reactor with EDOT/SbCl5 chemistry and photolithography processing is a promising route toward microfabrication of highly integrated conductive polymer devices.