Direct evaluation method to measure permittivity and conductivity of thin layers via wave approach in the THz region

The direct evaluation method for measuring the permittivity and conductivity of thin layers was proposed via the wave approach in the terahertz (THz) region. The terahertz time-domain spectroscopy (THz-TDS) was employed for performing experiments with thin dielectric layers. The proposed method takes advantage of the wave prediction for propagated THz waves in the thin layer. The transient and spectral responses of the THz waves propagated in the thin layer were predicted directly through the proposed wave approach. The numerical procedures utilizing the predicted waves were presented to derive the complex wavenumber in the THz region, which is composed of the permittivity and conductivity. The derived properties were verified by comparing with the measured behaviors in time and frequency domains. The proposed numerical procedures allow us to measure precisely the complex dielectric property of the thin layer without any pre-estimation for layer inner conditions.