Evaluation of Ferroelectric/Silicon Interface State Density in Ferroelectric-Gate Transistors Using a Charge Pumping Method

Abstract

Interface state density between a ferroelectric SrBi2Ta2O9 (SBT) and a silicon substrate was investigated by applying the charge pumping method to the n-channel metal-ferroelectric-silicon field effect transistors (MFS FETs). It was found from the frequency dependence of the surface recombination charge that the mean interface state density of the SBT/Si structure annealed at 675°C was about 4.3 × 1011 cm−2 eV−1, while that the density was higher than 3 × 1012 cm−2 eV−1, when the SBT films were annealed at 700°C and higher. It was also found from the drain current vs. gate voltage characteristics of the MFS FETs that the maximum value of the effective channel mobility was about 180 cm2/Vs when the SBT film was annealed at 675°C.