Origin of the enhanced electrical characteristics of BaTiO3-based thermistors by sputtered Al and Ni–Cu buffer electrode films

• Thin buffer electrodes of Al and Cu–Ni enhanced the PTCR performance.
• The maximum 75% improvement in the resistance jump was found in the Cu–Ni layer.
• The layer ensures the ohmic behavior with a lowered Schottky barrier potential.
• Promising electrode interfacial resistance is a key for the achievement.
• Correlative impedance analyses are provided to support the origin of enhancement.

Significant improvements in the characteristics of positive temperature coefficient of resistance for BaTiO3/Ag-based temperature sensors are reported by utilizing buffer electrode films of Al and Ni–Cu. The Ni–Cu buffer layer was more effective in reducing room temperature electrical resistance than the Al layer, which results in a significant increase in the resistance jump ratio. As a promising example, the use of a 541 nm thick Ni–Cu buffer film demonstrated a substantially increased log(Rmax/Rmin) value of 3.15, compared to 1.80 for only the Ag electrode without the buffer layer. Origin of the enhancement by Ni–Cu is attributed due to the improved ohmic behavior with a lowered Schottky barrier potential at the ceramic–electrode interfaces. The thicker layer is preferred regardless of the type of buffer layer since it demonstrates a lower interfacial electrical resistance as confirmed by the impedance analysis.

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