Characterization and Performance Analysis of BST-Based Ferroelectric Varactors in the Millimeter-Wave Domain

We present the realization and analysis of the microwave performances of interdigited varactors integrating thin ferroelectric layers of barium and strontium titanate (BaxSr1−xTiO3). Devices based on ferroelectric films of different compositions (x = 0.8 and x = 0.5) have been characterized in the millimeter-wave domain, from 200 MHz to 110 GHz. By applying different bias voltages, the tunability of the capacitance can reach up to 40% for the Ba0.8Sr0.2TiO3 composition, under relatively low applied electric fields of about 167 kV/cm. These promising characteristics allow the integration of the varactor devices in tunable antennas for a large frequency domain, from the microwaves to the millimeter waves range.