Electron Transport Mechanisms in Thin Insulating Films

Abstract

Tests have been performed on a number of Ta-${\mathrm{Ta}}_2$ ${\mathrm{O}}_5$-Au diodes of various thicknesses over a range of temperatures to determine the mechanism of current flow. The mechanism proposed for the current flow is field ionization of trap-type states at low temperatures and thermal ionization of these states at high temperatures and thermal ionization of these states at high temperature. High-temperature voltage-current data and low-temperature comparisons between forward and reverse characteristics agree well with the bulk-limited hypothesis and are in striking disagreement with barrier mechanisms. A discontinuity in the oxide properties is noted at a thickness of approximately 500 Å. High-temperature measurements at applied voltages less than the difference in the metal work functions yield an Ohmic characteristic with an activation energy of approximately 0.1 eV, consistent with an impurity conduction process but not with a barrier process.