Bulk- or interface-limited electrical conductions in IrO2(Ba,Sr)TiO3/IrO2 thin film capacitors

The electrical conduction behavior of sputter-grown (Ba,Sr)TiO3 thin films having IrO2 electrodes were studied under the assumption of a fully accumulated film having a negative space charge density of 1 x 10(19) cm(-3) at 25 degreesC. The negative space charge decreased the actual field strength in the film and resulted in a decreasing leakage current with increasing, film thickness at a given applied field. The current conduction in a very low field, roughly less than 150 KV/cm. showed a linear current density-voltage (J-V) behavior at 25 degreesC. From that field to about 420 KV/cm, the bulk-limited Poole-Frenkel mechanism controlled the overall conduction property at room temperature. Under high field strength, from 420 KV/cm to 1 MV/cm, the interface-limited thermionic field emission mechanism was dominant. The dielectric constant obtained from Poole-Frenkel fitting was approximately 300 +/- 50 at 25 degreesC, which was in qualitative agreement with th value obtained from low-frequency capacitance measurements. The detailed mechanisms of the linear and nonlinear field-dependent emission conductions were discussed with reference to the direction of band bending, not to the carrier concentration.