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 (approximate to 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 (T-sub) and film thickness (t(PEDOT)) are used as parameters to alter properties of the PEDOT thin films; increased T-sub and t(PEDOT) 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 approximate to 1/3. Regarding the piezoresistive properties of the devices, acid treatment, higher T-sub and t(PEDOT) (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.