Flexible Pressure Sensors Based on Screen-Printed P(VDF-TrFE) and P(VDF-TrFE)/MWCNTs

This paper presents large-area-printed flexible pressure sensors developed with an all screen-printing technique. The 4 x 4 sensing arrays are obtained by printing polyvinylidene fluoride-trifluoroethylene P(VDF-TrFE) and their nanocomposite with multi-walled carbon nanotubes (MWCNTs) and are sandwiched between printed metal electrodes in a parallel plate structure. The bottom electrodes and sensing materials are printed sequentially on polyimide and polyethylene terephthalate (PET) substrates. The top electrodes with force concentrator posts on backside are printed on a separate PET substrate and adhered with good alignment to the bottom electrodes. The interconnects, linking the sensors in series, are printed together with metal electrodes and they provide the expandability of the cells. Different weight ratios of MWCNTs are mixed in P(VDF-TrFE) to optimize the percolation threshold for a better sensitivity. The nanocomposite of MWCNTs in piezoelectric P(VDF-TrFE) is also explored for application in stretchable interconnects, where the higher conductivity at lower percolation ratios are of significant importance compared to the nanocomposite of MWCNTs in an insulator material. To examine the functionality and sensitivity of sensor module, the capacitance-voltage analysis at different frequencies, and the piezoelectric and piezoresistive response of the sensor are presented. The whole package of foldable pressure sensor is completely developed by screen-printing and is targeted toward realization of low-cost electronic skin.