Leakage current characteristics of lead-zirconate-titanate thin film capacitors for memory device applications

The leakage cut-rent of ferroelectric thin film capacitors is comprised of electronic conduction current and polarization current. In this work, the origin of these leakage current components in lead-zirconate-titanate (PZT) thin film capacitors is studied by means of two different methods. The first method distinguishes the current components by measuring the leakage current with different delay times. The second method determines the current components by measuring the charging and discharging currents when a specified voltage is turned on and off. Both measurements show that the polarization current is dominant in an electric field lower than 100 kV/cm. The polarization current is modeled using Debye-type electric polarization. The relaxation times and equivalent capacitances of the polarization current are extracted from the discharging current. The electronic conduction current obtained by measuring the leakage current with long delay time can be explained to be due to ohmic conduction in a low field (lower than 40 kV/cm) and Poole-Frenkel emission in a high field (higher than 40 kV/cm). The total leakage current calculated by the sum of the polarization current and the electronic conduction current agrees well with the measured result.