Microwave characterization of ferroelectric thin-film materials

Computer-aided-design models are developed and used for the characterization of ferroelectric materials at microwave frequencies, which aim at measuring the dielectric properties of BST-0.5 thin films on alumina substrates. Complex dielectric constant, voltage tunability, and K-factor are determined for the ferroelectric materials with a series of BST/alumina coplanar waveguides (CPWs) and interdigital capacitors (IDCs) of different BST film thicknesses. Propagation constants are extracted through measurements for CPWs using a multiline thru-reflect-line calibration technique from 1 to 16 GHz. IDC capacitance is measured at different bias points ranging from 0 to 35 V over the frequency range of 1-10 GHz. Conformal mapping models are deployed to interrelate circuit measurements with the BST film intrinsic properties. Dielectric constants of approximately 500-700 and loss tangents of approximately 0.07 are typically obtained at low frequencies for the BST films investigated in this study. BST voltage tunability is typically 15% at 35 V and 6 GHz.