Solution-processible electrode materials for a heat-sensitive piezoelectric thin-film sensor

Piezoelectric sensors are needed in a wide range of applications from physiological measurement applications to industrial monitoring systems. Custom-designed, highly integratable and cost-effective sensor elements can be manufactured by using flexible materials in combination with high-throughput printing for fabrication. This would also enable the embedding of ubiquitous sensors in our living environment to improve the common welfare. Here, we have fabricated flexible piezoelectric sensor elements using printing methods. We demonstrated that alternative, printable electrode materials are compatible with temperature-sensitive functional substrates. Low-temperature curable electrodes were printed on both sides of unmetallized, polyvinylidene fluoride film. Various solution-processible materials – for example, carbon nanotube–cellulose composite, poly(3,4-ethylenedioxythiophene):poly(styrene sulfonate), carbon ink and silver flake ink – were used. DC sheet resistances of the electrodes and sensitivities of the sensor elements were measured. Sheet resistance varied from 10−1 to 106 Ω/□ and sensitivities varied from 23 to 29 pC/N. Evaporated metal electrodes as well as commercially available sensor elements were used as reference sensors. The sensing capability of printed sensors was quite insensitive to the sheet resistance of the electrodes. Further, the electrode conformation was studied by microscopy; reliability of the sensors was studied by vibration tests. In addition, sensors were tested for measuring physiological signals.