Electrode Metal Dependence of Leakage Current Characteristics of Epitaxial BaTiO3 Films on p- and n-Type Electrodes

BaTiO3 (BTO) films are grown on the bottom electrodes of Nb-doped SrTiO3 (STON) and La2CuO4. The current through the BTO films exhibits diode properties having a reproducible hysteresis at a forward bias with polarity determined by the bottom electrode. In BTO/La2CuO4 the current intensity is almost independent of metal top-electrode materials, which is explicable by regarding BTO/La2CuO4 as a pn junction [p: hole carrier, n: electron carrier]. The current through BTO/STON is limited by the work functions of the metal and BTO, suggesting that it is suppressed by an electrode metal with a high work function, e.g., Pt, in an n-type ferroelectric such as BTO. In a p-type ferroelectric such as PLZT, it is suppressed by an electrode metal with a low work function. The relaxation current, the large leakage current in epitaxial ferroelectric films, and the effect of the ferroelectric carrier type on fatigue are discussed.