The effect of ZrO 2 buffer layer on electrical properties in Pt/SrBi 2Ta 2O 9/ZrO 2/Si ferroelectric gate oxide structure

Abstract

We have investigated metal/ferroelectric/insulator/semiconductor (MFIS) structure with strontium bismuth tantalate (SBT) as ferroelectric thin film and ZrO 2 as the insulating buffer layer. Sr 0.8Bi 2.4Ta 2O 9 thin films were prepared by metal organic deposition (MOD) method and ZrO 2 films were deposited by r.f.-sputtering. Coercive field that decisively affects the memory window was increased greatly by inserting the ZrO 2 insulator between SBT and SiO 2 and, thus, the memory window also increases with an electric field to the SBT. Memory windows of MFIS structure were in the range of 0.3–2.6 V when the gate voltage varied from 3 to 10 V. Memory windows of MFIS structure were found to be dependent on the thickness of the buffer layer. We observed the maximum memory window in MFIS with a 28-nm thickness of ZrO 2 layer. Auger electron spectroscopy (AES) depth profile and high resolution transmission electron microscopy (HRTEM) of SBT/ZrO 2 (28 nm)/Si structure showed that the ZrO 2 thin films as a buffer layer helped to prevent the formation of interfacial layer and interdiffusion between SBT and Si.