Oxidative Chemical Vapor Deposition of Conducting Polymer Films on Nanostructured Surfaces for Piezoresistive Sensor Applications

In this study, a novel, fully polymeric setup for piezoresistive sensing is prepared and tested. Monolayers of polystyrene (PS) nanospheres are assembled on flexible polyethylene naphthalate substrates. Subsequently, thin layers (≈50–100 nm) of poly(3,4-ethylenedioxythiophene) (PEDOT) are deposited conformally around the spheres by oxidative chemical vapor deposition (oCVD). Voltage−current characteristics and direct resistance measurements are performed to test the electrical properties of the samples in their unstrained state and their piezoresistive response during bending. Substrate deposition temperature (Tsub) and film thickness (tPEDOT) are used as parameters to alter properties of the PEDOT thin films; increased Tsub and tPEDOT lead to samples exhibiting lower intrinsic resistance. The electrical conductivity of the samples is estimated to range as high as tens of S cm−1. Dopant exchange of the oCVD-PEDOT layer (intrinsically, chlorine-doped) is performed by putting the samples in 0.5 m sulfuric acid, which decreases their resistance by ≈1/3. Regarding the piezoresistive properties of the devices, acid treatment, higher Tsub and tPEDOT (thus, lower intrinsic resistance) yield samples with increased response. As a result, gauge factors as high as 11.4 are achieved. Due to their flexibility and low-cost, the proposed structures can be readily employed as skin-inspired or wearable electronic devices.