The research presented herein focuses on electrical assessment of oxide thin films as insulators. The current density-electric field (J-E) characteristics of four insulators of dramatically different electrical quality are assessed in terms of their operative electronic conduction mechanisms. Conduction in the two high-quality insulators is dominated by Ohmic conduction and Fowler-Nordheim tunneling, whereas conduction in the two low-quality insulators involves Ohmic conduction and space-charge limited current (SCLC). Ohmic conduction and SCLC are somewhat puzzling mechanisms for contributing to insulator leakage current since the existence of an Ohmic contact at the cathode is required. The conventional definition of an Ohmic contact makes it difficult to ascertain how an Ohmic contact could be formed to a wide bandgap insulator. This Ohmic contact dilemma is resolved by formulating an equivalent circuit appropriate for assessing the J-E characteristics of an insulator and then recognizing that an insulator Ohmic contact is obtained when the injection-limited current density from the cathode electrode is greater than that of the operative bulk-limited current density, i.e., Ohmic or SCLC for the four insulators under consideration.
Solution-processed insulator thin films typically exhibit large leakage currents. This poor electrical performance can be ascribed to (i) inadequate insulator band gap, (ii) residual water, and/or (iii) impurity incorporation within the film. Appropriately addressing these concerns, solution-processed Al2O3 thin films are realized with electrical performance approaching that of state-of-the-art Al2O3 thin films prepared by atomic layer deposition (ALD).