DC ELECTRICAL BEHAVIOR OF POLYMERS USED IN ELECTROOPTIC DEVICES

We have measured the temperature and electric field dependence of the direct current (dc) electrical resistivity of several electro-optic polymers, in addition to pure polymethyl methacrylate (PMMA) and a commercial acrylate, UV-15. All the polymers exhibit a decrease in resistivity, to different degrees, with increasing temperature between room temperature and 130-degrees-C. The results show that in a sandwich of multiple layers, the high temperature resistivity mismatch between individual layers results in field concentration in the layer with the highest electrical resistivity. This can be used to explain the enhanced electro-optic coefficient measured in electro-optic devices consisting of a sandwich of UV-15/copolymer/UV-15. In PMMA, we observed a saddle region in the temperature dependence of resistivity between 67 and 78-degrees-C. Outside the saddle region, the resistivity of PMMA follows an Arrhenius relationship, with an activation energy of 1.0 eV. This saddle region is broadened in the nitro and DCV copolymers. A mechanism in which the motion of side chains hinders the interchain hopping of conducting species is proposed to explain our data.