Deuterium in (Ba,Sr)TiO3 thin films: Kinetics and mechanisms of incorporation and removal during annealing

Abstract

The kinetics of deuterium doping of and removal from polycrystalline (Ba,Sr)TiO3 (BST) thin films during annealing were investigated using secondary ion mass spectrometry depth profiling, and the data were correlated to changes in the electrical behavior of the films. Results for deuterium doping of exposed BST films on a Pt bottom electrode layer are consistent with incorporation of deuterium interstitial defects at the BST/Pt interface and “upward” diffusion toward the film surface. The incorporation kinetics of deuterium in Pt/BST/Pt capacitors are more complex and are greatly enhanced by the presence of the Pt top electrode. Removal of deuterium from D2/N2-exposed Pt/BST/Pt specimens during oxygen recovery anneals appears to be limited by the rate of an interfacial reaction at low temperatures (200–250 °C). The pre-D2 exposure leakage current properties of the BST capacitors were found to be largely recovered when the deuterium concentration in the films was reduced to ∼1019 cm−3 during post-D2 oxygen recovery anneals. Recovery annealing in vacuum, although it removed deuterium from the films, was found to result in an increase in leakage current density for annealing temperatures greater than 300 °C. These results suggest that introduction of large amounts of positive space charge into the BST films has a pronounced effect on the electrical properties of the Pt/BST interface.