Resistive Characterization of Soft Conductive PDMS Membranes for Sensor Applications

Conductive PDMS is used as an active sensing element in many sensor applications. The resistive characterization of Carbon Black (CB) filled soft conductive PDMS (Poly-Di-Methyl-Siloxane) membranes is reported in this paper. The conductive membranes are fabricated on a measurement template. A simple two point resistance measurement scheme, connected to the measurement template measures the surface resistivity of the fabricated membranes. As expected, the resistivity of the membranes decreases with increase in CB concentration. The surface resistivity of membranes fabricated using CB-PDMS composite and CB-Methanol-PDMS composite is compared. It is observed that dispersion of CB particle in methanol prior to the preparation of conductive PDMS has following advantages. 1) Low percolation threshold 2) Higher conductivity 3) Better surface profile. The CB filled conductive PDMS membranes show piezo resistivity. The resistance of the membranes increases with increased pressure. Higher values of piezo resistivity coefficients are observed at low CB concentration. The effect of the ambient temperature on the membrane resistance is also discussed. The conductive membranes show a Positive Temperature Coefficient (PTC) and the value of the coefficient increases with a decrease in concentration.