Microscopic mechanism of leakage currents in silica junctions

Combining the nonequilibrium Green's functions with the density-functional theory, we investigated the structural and electronic properties of silica junctions sandwiched between Al electrodes. The results show that the oxygen vacancies and tensile strain field play an important role in the electron transport properties of these two-probe systems. Sizable changes in leakage current across the barrier are found for the oxygen deficient system. It is found that Si dangling bonds formed by the introduction of oxygen vacancies are the main building blocks of the conduction channel in silica thin film. The midband gap states generated by the Si dangling bonds contribute to the leakage current. Detail analysis shows that four conduction channels are generated in silica junction after the presence of oxygen vacancies, resulting in a large enhancement of the electron transmission coefficient at the Fermi level. This leakage current mechanism provides useful information in the microelectronic designs.