Barium Strontium Titanate Capacitor Fabrication on Copper Printed Circuit Board

Procedures are described to fabricate barium strontium titanate (BST) gap capacitors within a microstrip resonator fabricated directly on a printed circuit board (PCB). This is the first time that an all-BST ceramic has been processed on epoxy-based PCBs at 175 °C. In order to accommodate the temperature limitations of the underlying PCB (<;200 °C), and to achieve the required dimensions, ~75-μm (3 mil) gap capacitors have been fabricated by hydrothermal processing of BST sol-gel composites. The performance of voltage-tunable microstrip resonators operating from 5 to 10 GHz showed a permittivity of 52 at 7.05 GHz and a voltage tunability consistent with that expected for thin-film BST devices. Measurements of these resonators are presented.