The Effect of Forming Gas Annealing on Pt/(Ba,Sr)TiO 3 /Pt Thin Film Capacitors for Future Dram Applications: Electrical Properties and Degradation Mechanisms

We have used electrical characterization and secondary ion mass spectroscopy (SIMS) to investigate the influence of hydrogen or deuterium (H/D) on the degradation of the electrical properties of Pt/Ba0.7Sr0.3TiO3/Pt thin film capacitors after forming gas exposure. Deuterium SIMS depth profiling shows that high deuterium concentrations can be incorporated into Pt/BSTO/Pt capacitors after forming gas annealing. The increase in H/D concentration in the film is accompanied by an increase in the leakage and dielectric relaxation current density. Voltage offsets in the capacitance-applied voltage (C-VA) characteristics after forming gas exposure at lower temperatures (20 °C) and a suppression in the capacitance density near zero applied D.C. bias after forming gas exposure at higher temperatures, suggests that one effect of forming gas exposure to Pt/BSTO/Pt thin film capacitors is to introduce positive space charge into the BSTO film. Using an equivalent model for a ferroelectric thin film capacitor, which incorporates lower permittivity interfacial layers and a nonlinear electric field-electric displacement relationship for the film interior, the effects of a uniform distribution of positive space charge on the theoretical C-VA and current density applied voltage (J-VA) characteristics are investigated. It is shown the model can account for many of the observed changes that occur in the experimental C-VA and J-VA characteristics after forming gas exposure.