Metallic bismuth on strontium-bismuth tantalate thin films for ferroelectric memory application

Abstract

Strontium–bismuth tantalate (SBT) has been actively investigated as an attractive candidate for non-volatile ferroelectric random access memories because of its high resistance to fatigue. However, the ferroelectric property of SBT is easily affected by fabrication process parameters. The relationship between the surface chemistry of SBT thin films and the fabrication process parameters, such as crystallization temperature, upper Pt electrode, annealing in oxygen after Pt electrode fabrication (= the second annealing), hydrogen sintering and ion etching, were examined mainly by XPS analysis. In all specimens, metallic Bi, which is one of the main causes for deterioration of their performances, was observed in addition to oxidic Bi, Sr and Ta. The deposition of an upper Pt electrode resulted exclusively in an increase in metallic Bi content. Sintering in a hydrogen atmosphere and ion etching increased the ratio of metallic Bi to total Bi. The second annealing was effective in suppressing the metallic Bi content. Copyright © 2000 John Wiley & Sons, Ltd.