Dielectric constant measurement of thin films using goniometric terahertz time-domain spectroscopy

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 to terahertz. An ultrafast optoelectronic system, including an emitter and a detector unit, is constructed with a theta-2theta goniometer. A silicon wafer was analyzed as the reference substrate material. A sharp pi phase-shift of the reflected EM wave was observed at the Brewster angle of 73.5degrees 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.