Tunable patterned ferroelectric parallel-plate varactors for matching network

The columnar textured Ba0.5Sr0.5TiO3 (BST) thin film was well grown on the Pt(1 1 1)/Si substrate by pulsed laser deposition. A tunable impedance matching network based on the parallel-plate capacitor with Au/BST/Pt structure was fabricated and tested. The BST thin films in the varactors were patterned only on the selected area of substrate in order to reduce loss and eliminate undesired modes. The dielectric properties of BST film with parallel-plate structure were investigated and compared systematically in the wide frequency range from 1 kHz to 1.6 GHz. The tunability of BST varactor reached up to 25.1% at 100 kHz and 21.8% at 0.9 GHz under 10 V dc bias, respectively. Compared with the impedance matching network based on coplanar interdigital capacitors using 100 V dc voltages, the performance of tunable impedance matching showed a significant improvement only at the low biased voltage of 10 V.