Effect of bismuth oxide as a buffer layer on metal-lanthanum-substituted bismuth titanate-insulator-semiconductor structures

Abstract

We have investigated metal/ferroelectric/insulator/s'emiconductor (MFIS) structures with lanthanum-substituted bismuth titanate (BLT) as a ferroelectric layer and bismuth oxide as an insulating buffer layer between BLT and Si substrate. BLT films and Bi oxide films were prepared by the direct liquid injection metal organic chemical vapor deposition process. The morphology of the Bi oxide film was changed with the increase of its thickness and the annealing temperature. Bi oxide on silicon was converted into Bi silicate during annealing at 750 degreesC. The morphology of the BLT films deposited on Bi oxide depended on the morphology of the Bi oxide film and on the reaction with Bi oxide during the annealing process, which was confirmed by transmission electron microscopy and energy dispersive x-ray spectroscopy. The maximum memory window was 0.83 V at the sweep voltage of 5 V with the Bi oxide film annealed at 650 degreesC and with a thickness of 5 nm. With BLT/Bi oxide annealed at 750 degreesC, the window was decreased due to the reaction between the BLT film, Bi oxide film, and Si substrate, and the leakage current density was increased. By inserting the buffer layer, the MFIS structure had a lower leakage current density than metal/ferroelectric/semiconductor structure. (C) 2003 American Vacuum Society.