Rapid Thermal Annealing of Oxide Electrodes for Nonvolatile Ferroelectric Memory Structures

Abstract

We report on the properties of a ferroelectric stack comprising (La0.5Sr0.5)CoO3 (LSCO)/Pb(Nb,Zr,Ti)O3 (PNZT)/LSCO deposited on 4 inch diameter platinized Si wafers (Pt/Ti/SiO2/Si). The LSCO electrodes were deposited at room temperature by pulsed laser ablation and the ferroelectric layer was deposited by the sol-gel technique. Rutherford backscattering was performed to confirm the uniformity in composition, thickness and stoichiometry of LSCO across the wafers. Conventional furnace or rapid thermal annealing was performed to crystallize the electrodes. The oxidation resistance of the conducting barrier layers, Pt/Ti, was found to be dependent on the annealing procedure adopted for the bottom electrode. In the case where the bottom LSCO was crystallized by rapid thermal annealing, Rutherford backscattering analysis and transmission electron microscopy studies revealed that there was no oxidation of the Pt/Ti conducting barrier composite. This is in contrast to the observations for in-situ deposition or conventional furnace annealing of the bottom electrode. The resistivity, coercive field and polarization of the ferroelectric stack were uniform across the 4-inch wafers. The ferroelectric capacitors showed no fatigue up to 1011 cycles and no imprint at 100°C. The ferroelectric properties were independent of the annealing procedure used for crystallizing the electrodes.