MOCVD of Nb Substituted SrBi2Ta2O9 for Integrated Ferroelectric Capacitors

Abstract

AbstractThe Bi layered perovskites are promising materials for ferroelectric random access memories (FeRAM's) because of their inherently high resistance to fatigue. Liquid delivery, flash vaporization metalorganic chemical vapor deposition (LD-MOCVD) is an attractive process for these materials, because it offers the ability to produce high quality, conformal films of controlled composition for both high and low density memory applications. We have developed a well-controlled process to deposit Nb-substituted SrBi2Ta2O9 (SBNT) using a mixed alkoxide-β-diketonate precursor Nb(O-i-Pr)4(thd) that is compatible with a previously developed precursor suite for SBT (Sr(thd)2-pmdeta, Bi(thd)3, and Ta(O-i-Pr)4(thd)). The Nb and Ta precursors behave in the same way in the process, making the Nb substitution level in the film identical to that in the precursor solution. In this study, wavelength dispersive x-ray fluorescence has been used to characterize composition and thickness. As-deposited films are smooth, with a surface roughness of 2 nm RMS. After a post-deposition annealing treatment, a high quality layered perovskite crystal structure was obtained. The resultant ferroelectric hysteresis shows a 50% increase in coercive voltage for 28% Nb substitution at the Ta site with the same switchable polarization. In the 28% Nb containing film, imprint was significantly improved compared to SBT films without substitution.