Polarity dependent DC resistance degradation and electrical breakdown in Nb doped PZT films

The role of interfacial defect chemistry in time dependent breakdown and associated charge transport mechanisms was investigated for Pb-0.99(Zr0.52Ti0.48)(0.98)Nb0.02O3 (PNZT) films. Electrical degradation was strongly dependent on the sign of the electric field; a significant increase in the median time to failure from 4.8 +/- 0.7 to 7.6 +/- 0.4 h was observed when the top electrode was biased negatively compared to the bottom electrode. The improvement in the electrical reliability of Pt/PNZT/Pt films is attributed to (1) a VO center dot center dot distribution across the film due to PbO nonstoichiometry and (2) Ti/Zr segregation in PNZT films. Compositional mapping indicates that PbO loss is more severe near the bottom electrode, leading to a VO center dot center dot gradient across the film thickness. Upon degradation, VO center dot center dot migration toward the bottom Pt electrode is enhanced. The concentration of VO center dot center dot accumulated near the bottom Pt interface (6.2 x 10(18)/cm(3)) after degradation under an electric field of 350 kV/cm for 12 h was two times higher than that near the top Pt/PNZT interface (3.8 x 10(18)/cm(3)). The VO center dot center dot accumulation near the bottom Pt/PNZT interface causes severe band bending and a decrease in potential barrier height, which in turn accelerates the electron injection, followed by electron trapping by Ti4+. This causes a dramatic increase in the leakage current upon degradation. In contrast to the bottom Pt/PNZT interface, only a small decrease in potential barrier height for electron injection was observed at the top Pt/PNZT interface following degradation. It is also possible that a Zr-rich layer near the top interface reduces electron trapping by Ti4+. (c) 2019 Author(s). All article content, except where otherwise noted, is licensed under a Creative Commons Attribution (CC BY) license (http://creativecommons.org/licenses/by/4.0/).