Complex permittivity of thin films at millimeter and THz frequencies

The measurement of complex dielectric permittivity of thin films are very difficult at millimeter and THz frequencies because the phase shift is not large enough to determine the real part of dielectric permittivity. To overcome this difficulty, dispersive Fourier transform spectroscopy is improved for the first time to have the mirror movement of 0.5 micrometer step size to characterize the permittivity of ultra low-loss thin films.