Analysis of the degradation mechanism of Pt/SrBi₂(Ta/Nb)₂O₉/Pt capacitors during reductive annealing

Degradation mechanism of the Pt/SrBi₂Ta_2xO₉/Pt and Pt/SrBi₂(Ta_1.x/Nb_x)₂O₉/Pt capacitors exposed to the hydrogen attack has been analyzed. The capacitors were fabricated from thin-films consisting of SrBi₂Ta_2xO₉ (1 ≃ x ≃ 1.1) and SrBi₂(Ta_1.x/Nb_x)₂O₉ (0 ≃ x ≃ 1) (SBTN) that were formed using a sol-gel process. In most capacitors, SBTN thin-films were short-circuited while annealing in the reducing atmosphere. In contrast, excessive Ta addition could hold back the short circuit. Analysis of the degradation mechanism were carried out by means of the XRD, TEM and XPS, which revealed that the most significant alteration took place in the vicinity of crystal grain boundaries. It was also found that the film with excessive Ta concentration contains the pyrochlore phase in the grain boundary layers. These findings suggest that the stabilization of grain boundary layers is effective to realize capacitors resistant to process conditions.