Low Cost Interdigital BST Varactors for Tunable Microwave Applications

In this paper, a simple and inexpensive technique for the fabrication of barium strontium titanate (BST) varactors is presented. BST films were deposited using RF magnetron sputtering on platinum coated silicon substrates. The advantages of silicon include low cost and ease of integration with existing fabrication processes. The microstructural properties of the BST layer were examined with scanning electron microscopy (SEM), X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS) techniques. Gold top layer electrodes were deposited using DC sputtering and patterned with a conventional photolithographic process. The S-parameters of the varactor were measured from 40 MHz to 20 GHz on a vector network analyser. From this data, the capacitance, tunability and Q-factor of the device were extracted. The BST-based varactors show potential for integration into electronically tunable microwave circuits.