Microscopic characterization of polarization fatigue in ferroelectric vinylidene fluoride and trifluoroethylene copolymer films

Recently studies on electric fatigue in ferroelectric polymers have drawn much attention due to the potential application of ferroelectric polymers in nonvolatile memory devices. Compared to inorganic ferroelectrics, ferroelectric polymers are mostly semi-crystalline with a coexistence of crystalline phase and amorphous phase. To well understand electric fatigue in ferroelectric polymers, it is necessary to determine the different contributions from crystallites, amorphous phase and even boundaries between crystallites to polarization fatigue. Here we introduce a SPM-based technique to characterize electric fatigue in nanometer scale. Microscopic fatigue is determined by the attenuation of voltage-excited local vibration amplitudes at two kinds of local structures (the crystallites and the boundaries between crystallites), and, for comparison, macroscopic electric fatigue characteristics are also recorded by a standard Sawyer–Tower circuit. Our observations indicate that the attenuation rate of vibration amplitude on crystallites is much slower than that at boundaries. Abnormal increase of vibration amplitude and slim local butterfly loops are observed at some of boundaries in deeply fatigued films.