Influence of surfaces on the dielectric properties and leakage currents in paraelectric (pb0.72la0.28)tio3 thin films

In the voltage range of 0–30 V, dielectric and leakage current density (JL) behavior were studied in paraelectric (Pb,La)Ti03 or PLT thin films (0.1–0.36 μ.m) with bulk resistivity of 5.6x108 Ω -cm. With Pt electrodes, the properties were found to be contact dominated. With both top and bottom Pt electrodes, the interfacial capacitance (Ci) and the built-in voltage (Vbi) of the Schottky barrier were 380 pF and 1.3 V, respectively. A log-log plot of vs V exhibit slope of -1 and 9, respectively, in the range of V<10 and 10<V<30. In the former voltage regime, the spatial dependence of the space charge density and therefore the electric field, makes analysis and interpretation of JL behavior nontrivial. Note that a slope of ∼1 may be misconstrued as ohmic behavior. In the 10<V<30 voltage regime, the Schottky emission expression was modified to account for the interfacial space charge layer widening with voltage. A linear In Jl vs V1/4 plot coupled with a Schottky barrier potential of 1.5 V, indicated that Schottky emission process was operational at the interface. Due to a similar voltage dependence, however, Poole-Frenkel emission cannot be ruled out.