Hysteresis in ultrathin ferroelectric polymer films observed by capacitance versus voltage measurements

Abstract

Capacitance-Voltage measurements have been used to observe switching in 50 nm, spun-cast films of polyvinylidene fluoride and its copolymers with trifluoroethylene. As the capacitance measurement frequency is increased to 1 MHz, the C-V characteristics change. At 1 MHz, the maximum in capacitance at the coercive field is not observed, but a small increase in capacitance occurs at the highest fields. This increase could be due to an electrostrictive contraction of the films. DC currents show a slow relaxation which persists for times in excess of one hour. The quasi-steady state values are consistent with a space charge limited process and the currents are large enough to significantly distort hysteresis loops measured with periods in excess of a few seconds.