Horii Hideki

Depletion layer thickness and Schottky type carrier injection at the interface between Pt electrodes and (Ba, Sr)TiO3 thin films

The electrical conduction properties of rf sputter-deposited (Ba, Sr)TiO3 (BST) films on Pt and IrO2 electrodes and metalorganic chemical vapor deposited (MOCVD) BST films on a Pt electrode were investigated and a new energy band model that satisfactorily explains the observed leakage current characteristics and film thickness dependent dielectric properties is proposed. The BST and Pt junction constituted a blocking contact with interface potential barrier heights of 1.6–1.7 eV and 1.2 eV for the sputtered and MOCVD films, respectively. Schottky emission behavior was observed at measurement temperatures higher than 120 °C and tunneling related conduction behavior appeared below that temperature for a film thickness of 40 nm. A partial depletion model with a very thin (about 1 nm) layer devoid of space charge at the interface with the Pt electrode is proposed to explain the V1/2 dependent variation of ln(Jo) as well as the decreasing dielectric constant with decreasing film thickness.

A positive temperature coefficient of resistivity effect from a paraelectric Pt/(Ba0.5,Sr0.5)TiO3/IrO2 thin-film capacitor

A (Ba0.5,Sr0.5)TiO3 (BST) thin film was deposited on IrO2 thin-film electrode by a rf magnetron sputtering method. Top Pt electrode was deposited on the BST film to make a planar structured capacitor. The BST thin film showed paraelectric behavior at room temperature. A positive temperature coefficient of resistivity (PTCR) effect was observed when the conduction electrons were injected from the IrO2 electrode to BST, while Schottky emission behavior was observed when they were injected from the Pt electrode to BST. The electrical double layer formed at the Pt/BST interface results in the PTCR effect. A model that can explain the asymmetrical conduction behavior with respect to the bias polarity is suggested based on the energy band configurations at the interfaces with the electrodes.