Electric-field-induced polarization enhancement of vinylidene fluoride/trifluoroethylene copolymer ultrathin films

We investigated the polarization enhancement in 60-nm-thick vinylidene fluoride/trifluoroethylene (VDF/TrFE) films without thermal annealing by applying repeated bipolar electric pulses. The remnant polarization was 8.4mC/m² in as-spin-coated films and increased to up to 45mC/m ² when 105 pulses were applied. Although the remnant polarization was half and the coercive field twice those of annealed films, the electrically treated film had a markedly smoother surface than the annealed film. Finally, a 15-nm-thick ferroelectric VDF/TrFE film with low conductivity was fabricated by electric treatment; annealed films with the same thickness experienced a severe short-circuit problem originating from the surface roughness.