Negative capacitance in epitaxial ferroelectric capacitors evidenced by dynamic dielectric characterization

Abstract A simple dynamic method was developed to evaluate the components in the equivalent circuit of a ferroelectric capacitor. The method is based on the application of short trapezoidal voltage pulses of variable amplitude and the analysis of the resulting current by considering the ferroelectric capacitor as a parallel Rp-Cp equivalent circuit. The values of Rp and Cp components are obtained in relation to different stages of polarization switching as the amplitude of the applied pulses increases. The most important result obtained by applying the present method is the evidence of an abrupt decrease of the Rp value (about 2 orders of magnitude) at the coercive voltage, while the equivalent Cp does not present a dramatic variation during polarization switching. This is interpreted in the context of negative capacitance obtained for ferroelectrics when polarization passes through zero value. The results obtained by using the proposed dynamic characterization method that will be referred to as “dynamic dielectric characterization”, are in good agreement with those obtained by classic capacitance-voltage measurements. A method to stabilize the negative capacitance for longer periods of time is also presented by adding an external resistance in series with the ferroelectric capacitor.