Decrease In Potential Barrier Height Research Articles

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 Pb0.99(Zr0.52Ti0.48)0.98Nb0.02O3 (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•• 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•• gradient across the film thickness. Upon degradation, VO•• migration toward the bottom Pt electrode is enhanced. The concentration of VO•• accumulated near the bottom Pt interface (6.2 × 1018/cm3) 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 × 1018/cm3). The VO•• 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+.

Effects of reducing and oxidizing atmospheres on the PTCR characteristics of porous n-BaTiO3ceramics by adding polyethylene glycol

Donor doped BaTiO3 (n-BaTiO3) ceramics were fabricated by adding polyethylene glycol (PEG) at 20 wt %. The effects of reducing and oxidizing atmospheres on the PTCR characteristics of the porous n-BaTiO3 ceramics were investigated. The PTCR characteristics of the porous n-BaTiO3 ceramics is strongly affected by chemisorbed oxygen at the grain boundaries and are recovered as the atmosphere is changed from the reducing gas to oxidizing gas. The low room-temperature resistivity of the porous n-BaTiO3 ceramics in reducing atmospheres may be caused by the decrease in potential barrier height, which originates from an increase in the number of electrons owing to the desorption of chemisorbed oxygen atoms at the grain boundaries. In addition, the high room-temperature resistivity of the porous n-BaTiO3 ceramics in oxidizing atmospheres may be caused by the increase in potential barrier height, which results from the adsorption of chemisorbed oxygen atoms at the grain boundaries.

Effect of atmosphere on the PTCR characteristics of porous Ba(Ti,Sb)O3 ceramics produced by adding corn-starch

Porous Ba(Ti,Sb)O3 ceramics were fabricated by adding corn-starch at 20 wt %. The effect of atmosphere on the PTCR characteristics of the porous Ba(Ti,Sb)O3 ceramics and the role of oxygen on the grain boundaries in the PTCR characteristics of the Ba(Ti,Sb)O3 ceramics were investigated. In air, O2, N2, and H2 atmospheres, the electrical resistivity of Ba(Ti,Sb)O3 ceramics below 150 °C was independent of atmosphere, while it was strongly dependent on atmosphere above 200 °C. The low electrical resistivity in reducing atmospheres was due to a decrease in potential barrier height, which originated from an increase in the number of electrons owing to the desorption of chemisorbed oxygen atoms at the grain boundaries. In a N2 atmosphere, the electrical resistivity of Ba(Ti,Sb)O3 ceramics during the cooling cycle was lower than that during the heating cycle, and then the electrical resistivity of the porous Ba(Ti,Sb)O3 ceramics during subsequent heating and cooling cycles was increased again by exposure to an O2 atmosphere.

Effect of measuring atmosphere on the electrical properties of nanoporous (Ba,Sr)(Ti,Sb)O 3 ceramics

Nanoporous (Ba,Sr)(Ti,Sb)O 3 ceramics were fabricated by the addition of partially oxidized Ti powder of 4 wt.%, corn- and potato-starch of 20 wt.% into the (Ba,Sr)(Ti,Sb)O 3 powder, respectively. The effect of measuring atmosphere on the electrical properties of the porous (Ba,Sr)(Ti,Sb)O 3 ceramics and the role of oxygen on the grain boundaries in the PTCR characteristics of the (Ba,Sr)(Ti,Sb)O 3 ceramics were investigated. The electrical resistivity of the porous (Ba,Sr)(Ti,Sb)O 3 ceramics was measured in the air, O 2, N 2 and H 2 atmospheres during heating and cooling cycles. It was found that the PTCR characteristics and room-temperature resistivity of the porous (Ba,Sr)(Ti,Sb)O 3 ceramics decreased in reducing atmosphere mainly because of the decrease in potential barrier height, whereas it increased in oxidizing atmosphere mainly because of the increase in potential barrier height.

Effect of atmosphere on the PTCR characteristics of porous (Ba,Sr)TiO 3 ceramics

Porous and fine-grained (Ba,Sr)TiO 3 ceramics were fabricated by adding partially oxidized Ti powders. During heating and cooling, the electrical resistance was measured in air, O 2, N 2, and H 2 atmospheres and in H 2 followed by air atmosphere. The effect of atmosphere on the PTCR characteristics and the role of oxygen on the grain-boundaries in the PTCR characteristics were investigated. The porous (Ba,Sr)TiO 3 ceramics showed a large PTCR effect, which was strongly sensitive to atmosphere. This effect was increased in oxidizing atmosphere mainly because of an increase in potential barrier height whereas decreased in reducing atmosphere mainly because of a decrease in potential barrier height.