A comparative study on the electrical conduction mechanisms of (Ba0.5Sr0.5)TiO3 thin films on Pt and IrO2 electrodes

Abstract

Electrical conduction mechanisms for ${\mathrm{Pt/(Ba}}_{\mathrm{0.5}}{\mathrm{Sr}}_{\mathrm{0.5}}{\mathrm{)TiO}}_{\mathrm{3}}$ (BST)/Pt, ${\mathrm{IrO}}_{\mathrm{2}}{\mathrm{/BST/IrO}}_{\mathrm{2}},$ and ${\mathrm{Pt/BST/IrO}}_{\mathrm{2}}$ capacitors were studied. The Pt/BST/Pt capacitor shows a Schottky emission behavior with interface potential barrier heights of about 1.5–1.6 eV. The barrier height is largely determined by the surface electron trap states of the BST. The ${\mathrm{IrO}}_{\mathrm{2}}\mathrm{/BST}$ interface shows an ohmic contact nature due to the elimination of the surface trap states as the result of the formation of strong chemical bonds between the ${\mathrm{IrO}}_{\mathrm{2}}$ and BST which results in the Poole–Frenkel emission conduction mechanism. ${\mathrm{Pt/BST/IrO}}_{\mathrm{2}}$ capacitor shows Schottky emission behavior and a positive temperature coefficient of resistivity (PTCR) effect depending on the bias polarity. The electron trap states at the Pt/BST interface and the positive space charges within the carrier depletion layer result in the PTCR effect.