Electromigration-induced leakage current enhancement and its anisotropy in single crystal TiO2

Abstract

Time-dependent increases in electrical conductivity in dielectrics exposed to a direct-current voltage bias can be detrimental to device reliability and lifetime, while the same phenomenon may be exploited for resistive switching functionality. The applied electric field induces the electromigration of charged point defects, resulting in spatially inhomogeneous stoichiometry and modifications in the electrode electrostatics. Herein, we monitor the time-dependent changes in leakage current in rutile TiO2 with platinum electrodes. Current–voltage measurements before and after the extended electrical biasing demonstrate that changes in the electrostatics of the cathode Schottky barrier are responsible for the time-dependent increases in leakage current. We also find that electromigration is accelerated along the ⟨001⟩ relative to the ⟨010⟩ crystallographic direction in contrast to what would be predicted by high-temperature diffusion kinetics. We find the observed anisotropic behavior to be consistent with a change in the defect charge state of the titanium interstitials and dominant transport path at lower temperatures. A comparison of optical color front migration kinetics to the temporal evolution of leakage current further supports the interpretation that ionic electromigration near the cathode interface is responsible for the increased leakage current in the electrically degraded state.