Coulomb glass origin of defect-induced dielectric loss in thin-film oxides

The dielectric loss in amorphous, thin-him oxide insulators produces a real part of the ac conductivity sigma'(omega) that scales as omega (s) with s similar to1. Conventional models explain this frequency dependence by hoppi ng or tunneling of charge between neighboring defect sites. These models fa il at low temperatures since they predict that sigma' should vanish at T=0. We observe that the ac conductivity of Ta2O5, ZnO, and SiO2 has a nonzero extrapolated value at T=0. We propose that this behavior is consistent with the predictions of a Coulomb glass, an insulator with a random distributio n of charged defects. (C) 2001 American Institute of Physics.