Steady-state and non-steady-state current flow in thin-film Al-CeF3-Al samples

An experimental study of steady-state and non-steady-state current-voltage characteristics of thin-film Al-Ce${\mathrm{F}}_2$-Al samples is presented. At high temperatures where steady-state conditions prevail, the $I-V$ characteristics are observed to be independent of the insulator thickness, and to obey the relationship ${log}_{10}I\propto V^{\frac{1}{4}}$. At low temperatures, where non-steady-state conditions prevail, the $I-V$ characteristics are no longer uniquely determined, but rather depend on the voltage $V_d$ applied during cooling. Furthermore, negative currents are observed to flow in the system when $V<\mathrm{}{V}_d$, and positive currents for $V>\mathrm{}{V}_d$; no current flows in the system when $V\approx V_d$. In all cases it is found that the conduction process is bulk limited, and the $I-V$ characteristic is characterized by ${log}_{10}I\propto V^{\frac{1}{2}}$. The results are interpreted in terms of Schottky barriers existing at the metal-insulator interfaces. Excellent correlation is obtained between the steady-state and the non-steady-state theory and experiment. The trap parameters used in generating the theoretical characteristics are consistent with those obtained from previous thermal and isothermal dielectric relaxation current studies. In view of these studies it is concluded that steady-state uniform-field concepts cannot be generally applied to the analysis of the experimental data on metal-insulator-metal systems, and that any previous analysis of data that has involved such concepts should be viewed with caution.