Dielectric Permittivity and Loss Tangent of Barium Titanate for mmW Applications

Barium titanate (BTO) is employed in various applications for high-speed electronics due to its high dielectric permittivity, ferroelectricity, and electro-optic properties. Although the dielectric properties of BTO are studied at lower frequencies, there is a need for dielectric characterization of BTO in millimeter wave spectrum to enable next-generation electronic devices. In this work, we present a method for characterizing the permittivity and loss tangent of BTO using a multilayer coplanar waveguide (CPW) fixture. The CPW is patterned on a thin BTO layer that can be grown on conventional substrates, such as Silicon, Sapphire, or Quartz. Using the measured S-parameters of the 2-port CPW structures fabricated on different substrates, the effects of the fixtures can be removed in two steps. Initially, for calibrated S-parameter measurements, a Thru-Reflect-Line (TRL) calibration is applied. We extract the effective permittivity of the multilayered CPW by applying the Nicolson-Ross-Weir algorithm (W. B. Weir, “Automatic measurement of complex dielectric constant and permeability at microwave frequencies,” Proc. IEEE, vol. 62, no. 1, pp. 33–36, Jan. 1974, A. Nicolson and G. Ross, “Measurement of the intrinsic properties of materials by time-domain techniques,” IEEE Trans. Instrum. Meas., vol. IM-19, no. 4, pp. 377–382, Nov. 1970) on the calibrated S-parameters of the CPW. With known BTO thickness, a quasi-TEM analysis is used to calculate the BTO's intrinsic permittivity from the measured effective propagation constant of the multilayer CPW. Secondly, the measurements from different substrate fixtures are used to improve the loss tangent characterization for the first time. As such, we demonstrate a new and effective method of characterizing the complex relative permittivity of the thin BTO films in millimeter wave range. The proposed approach can also be applied to characterize other thin film material used in nanofabrication as well as electronic packaging.