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 earner, 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.