Tunneling Through Thin Insulating Layers

The resistance of thin aluminum-oxide films has been measured as a function of the voltage across the film and of the film thickness as calculated from its capacitance. All films showed ohmic behavior at low voltages, and exponential rise of current at higher voltages, in qualitative agreement with R. Holm's theoretical calculations for tunneling through thin vacuum layers. However, the resistance was several orders of magnitude lower than either the bulk value for Al2O3 or the calculated value for tunneling through vacuum. By making use of an effective mass in the oxide equal to about19 of the electron mass, the calculated values for tunneling can be brought into line with the experimental results.