EHD Printing of PEDOT: PSS Inks for Fabricating Pressure and Strain Sensor Arrays on Flexible Substrates

Robotic skins with multi-modal sensors are necessary to facilitate better human-robotic interaction in non-structured environments. Integration of various sensors, especially onto substrates with non-uniform topographies, is challenging using standard semiconductor fabrication techniques. Printing is seen as a technology with great promise that can be used for sensor fabrication and integration as it may allow direct printing of different sensors onto the same substrate regardless of topology. In this work, we investigate Electro-Hydro-Dynamic (EHD) printing, a method that allows printing of micron-sized features with a wide range of materials, for fabricating pressure sensor arrays using Poly(3,4-ethylenedioxythiophene): Polystyrene Sulfonate (PEDOT:PSS). Fabrication of such sensors has been achieved by prepatterning gold or platinum metallized interdigitated comb electrode arrays on a polyimide substrate, with three custom made PEDOT: PSS based inks printed directly onto the electrode arrays. These three inks include a formulation of PEDOT: PSS and NMP; PEDOT: PSS, PVP, and NMP; and PEDOT: PSS, PVP, Nafion, and NMP. All these inks were successfully printed onto sensor elements. The initial results of bending-induced strain tests on the fabricated sensors display that all the inks are sensitive to strain. This confirms their suitability for pressure and strain sensor applications; however, the behavior of each ink; including sensitivity, linearity, and stability; is unique to the type.