IMF2017

Solution casting of thin films of the ferroelectric copolymer poly(vinylidene fluoride-co-trifluoroethylene) (P(VDF-TrFE)) under ambient conditions is highly attractive for cost-effective production of flexible ferroelectric memory devices. However, due to the typically rough and porous films obtained under ambient, the yield of functional devices is low. A major challenge is ambient water vapor condensing into the drying solution, causing vapor-induced phase separation (VIPS). In this contribution we have used a combined experiment-modeling approach and show that the hydrophilicity of solvent is a decisive factor in the morphology of the final film, as it determines the ingress rate of water into the drying polymer solution during the film formation process. We present our numerical study, to study the ternary phase diagram of the polymer/water/solvent blend. Our calculation show that how VIPS is influenced by the change in composition due to simultaneous solvent evaporation and water condensation. The numerical simulations render morphologies consistent with the experimentally observed structures. Furthermore, the model shows that how the domain size and the early-stage phase composition principally depend on the relative humidity of the environment. Based on the gained insight, we have processed transparent, closely packed smooth films under ambient and outside cleanroom conditions, and demonstrate functional device yield of 100% for devices operating at voltages compatible with flexible electronics.