Coulomb Glass Origin Defect-Induced Dielectric Loss in Thin Film Oxides

The dielectric loss in amorphous, thin film oxide insulators produces a real part of the ac conductivity with a frequency dependence sigma' (omega);omega sup s with s ~ 1. Conventional models explain this frequency dependence by hopping or tunneling of charge between neighboring sites where the density of barrier heights or tunneling lengths is uniform. These models fail at low temperatures where they predict that omega' should vanish at T=0. Instead, we observe that the ac conductivity of Ta sub 2 O sub (5) ZnO and SiO sub 2 has a non-zero extrapolated value at T=0. We propose that this behavior is consistent with the predictions of a Coulomb glass, an insulator with a random distribution of charged defects. We show that the observed defect concentration in Ta sub 2 O sub 5 films accounts for the low temperature ac conductivity using a Coulomb glass model.