Dielectric permittivity measurements of thin films at microwave and terahertz frequencies

The measurement of complex dielectric permittivity of thin films are very difficult at microwave, millimeter and THz frequencies because the phase shift is not large enough to evaluate the real part of dielectric permittivity. It is now necessary to determine the dielectric permittivity values of such films directly because of the growing use of thin films in integrated circuitry. Two different types of instrumentation were utilized and new techniques were developed so that the dielectric permittivity values can be determined accurately at microwave as well as at millimeter wave and terahertz frequencies. The Agilent 8510C vector network analyzer was employed together with a specially designed slotted cavity for the X-band microwave measurements of thin films. A step size of 500 nano meter for the mirror movement was implemented for the dispersive Fourier transform spectroscopy (DFTS) technique to provide higher resolution phase reproduction leading to the determination of the real part of dielectric permittivity values for thin films as a continuous function of frequency from about 60 GHz to 1,000 GHz. Data for one mil (25 μm) thin Teflon, Mylar and black polyester are shown.