Measurement of the dielectric constant of thin films using goniometric time-domain spectroscopy

Abstract

Goniometric time-domain spectroscopy (GTDS), employing an ultrashort electromagnetic (EM) pulse technique has been developed for measuring the dielectric constant of thin films in a broad band of gigahertz (GHz) to terahertz (THz). An ultrafast optoelectronic system, including an emitter and a detector unit, is constructed with a θ-2θ goniometer. A silicon wafer was analyzed as the reference substrate material. A sharp π phase-shift of the reflected EM wave was observed at the Brewster angle of 73.5° for a bare silicon wafer. The phase shift for a film on the Si substrate is relatively smooth due to its two surfaces providing a complex reflectance. The dielectric constant of the film on Si, related with angular dependency of the phase shift, can be extracted by means of fitting the curve or measuring slope of the curve near the Brewster angle. The measured dielectric constants of FLARE, TiOx, and PZT film are reported.