Ferroelectric strontium bismuth tantalate thin films deposited by metalorganic chemical vapour deposition (MOCVD)

Thin films of Sr1-xBi2+xTa2O9 (SBT) have been deposited by metalorganic chemical vapor deposition (MOCVD) on 150 mm Si wafers with Pt/Ti electrodes. The choice of Bi precursor significantly affects the process; film homogeneity is significantly improved when using a beta-diketonate Bi precursor in combination with compatible Sr and Ta precursors. A highly repeatable process has been developed, with good run-to-run composition and thickness control. Effects of Bi volatility have been investigated in annealing experiments that show the onset of Bi loss at similar to 570 degrees C at reduced pressure (1-10 Torr). Film properties relevant to integrated ferroelectric random access (Fe RAMS) memories have also been characterized. Remenant polarizations (2P(r)) up to 24 mu C cm(-2) have been obtained at 5 V, with 90% saturation of 2P(r) at 1.5 V and a coercive voltage of 0.52 V for a 140 mn film. Electrical leakage current density values were <2x10(-8) A cm(-2) at 1.5 V. Fatigue endurance has been measured to 10(11) cycles with < 10% degradation in switched charge. (C) 1999 Elsevier Science Limited. All rights reserved.