Dielectric dispersion and polarization effects in thin transition metal oxide films : B. Lalevic, N. Annamalai, B. Leung, G. Taylor and W. Slusark, Jr.Vacuum27, (4) 249

Abstract

Dielectric properties of thin polycrystalline and amorphous films of NiO, NiO(Li), CoO, CoO(Li), Nb2O5 and TiO2 in the thickness range 0.14–15 ωm were studied as a function of frequency, temperature, applied voltage and dopant concentration in the frequency range 3–108 Hz. These films were prepared either by anodization or thermal oxidation and in some cases by reactive sputtering. Experimental data for the real ϵ1 and imaginary ϵ2 parts of the dielectric constant, ac conductivity σ(ω) and loss tangent tan δ indicate the existence of several dispersion mechanisms. Cole-Cole plots and the modified Debye relations were used to derive the values for relaxation times at low frequencies. The frequency dependence of σ(ω) in the frequency region 103–106 Hz where σ(ω)αωn indicates that the dispersion mechanism is due to charge carriers hopping between sites with either correlated or non-correlated potentials. The observed quadratic dependence of σ(ω) on frequency in the frequency region 106–108 Hz is attributed to a Debye type loss resulting from thermally activated hopping. Polarization effects at lower frequencies <103Hz indicate the existence of Schottky barriers at the metal-insulator interfaces in agreement with Simmons theory of MIM structures.