A flexible active-matrix cells with selectively poled bi-functional polymer-ceramic nanocomposite for pressure and temperature sensing skin has been developed in a joint research by the Universities of Cambridge, Linz and Princeton along with the Joanneum Weiz and the University of Applied Science Jena.
Human skin is a sensitive detector of both pressure and temperature. Continuous efforts to develop similar sensors for electronics have resulted in the development. Piezoelectrical materials generate electrical signals in response to changes in applied pressure, and pyroelectrics are sensitive to changes in temperature. Unfortunately, almost all materials from each of those groups also fall into the other, which makes it difficult to discriminate between changes in pressure and temperature. The research team has developed a nanocomposite able to differentiate between the two sensitivities. Nanoparticles from lead titanium, embedded in a ferroelectric polymer, are the characteristic feature of this bifunctional material. Both components’ electric polarization can be configured independently. Thus, the polymer’s polarization can be oriented by alternating voltage with respect to the ceramic’s. When adjusting the polarizations parallel, the piezoelectric coefficients of the polymer and the ceramic cancel each other out, whereas the pyroelectric response is increased. When antiparallel, the material shows a piezoelectrical response only. By selecting the phase of the last cycle of the AC voltage applied to different parts of their composite film, the scientists have defined areas sensitive to either pressure or temperature only. The films thus prepared have been mounted onto a flexible foil containing silicon or organic transistors. Initial results show linear responses of the pressure- and temperature-sensitive regions with only limited cross-sensitivities.