Compositional Dependence of Electrical Characteristics in SrBi2Ta2-xNbxO9 Ferroelectric Capacitor Reduced by H2 Annealing

Degradation of electrical properties by annealing in hydrogen ambient is one of the most significant problems associated with ferroelectric oxides used in mainstream nonvolatile memory. A decrease in the degradation of the remanent polarization and the breakdown voltage of a ferroelectric SrBi2Ta2-x Nb x O9 (SBTN) capacitor has been attempted by controlling the Ta/Nb ratio, adding excess Bi oxide and adding excess Nb oxide. Substituting Nb for Ta improves the remanent polarization, however, it also leads to a decrease in the breakdown voltage. Excess Bi and Nb oxide both decrease the remanent polarization. Regarding the breakdown voltage, the addition of excess Bi and Nb oxide decrease the amount of the degradation caused by short-time H2-annealing, although it is not enough to prevent the degradation caused by long-time H2 annealing. Furthermore, the reduction path in the ferroelectric capacitor by low-temperature H2 annealing is discussed.