Characterization of Dielectric Properties of Metal Films in Terahertz Frequency Range

Dielectric constants of materials are a key parameter for device design. We report on the results of terahertz time-domain ellipsometry (THz-TDE) for thick and thin metal films and found that the difference between the experimental and fitting results based on the Drude model becomes significant with increasing the thickness of the metal films. It was found that the conductivity of the metal film decreases with decreasing the film thickness due to the size effect. We discuss a possible origin of the error and demonstrate that THz-TDE is capable of dielectric constant evaluation for thin metal films.