Dielectric properties of disordered insulators

We have measured the dielectric permittivity in the frequency range 10−4 Hz to 107 Hz for electron beam evaporated Co Al2O3 films and reactively sputtered silicon oxynitride films. The results for Co Al2O3 show two power laws in frequency, which can be interpreted as being due to fractal structures and processes. Results for SiOxNy films, on the other hand, show a crossover between dc conductivity and a power-law behaviour of the permittivity that is not accounted for by current theories.