Tunable microwave devices using BST (barium strontium titanate) and base metal electrodes.

摘要

Microwave devices such as filters, phase shifters, and antennas form an integral part of modern communication systems. Currently there is a huge research interest in utilizing ferroelectric thin films for microwave devices since they have high tunability, low loss, and good power handling capability at GHz frequencies.; Barium strontium titanate, (BST), is a potential candidate for integration into microwave devices. Planar interdigitated capacitor Ba0.6Sr 0.4TiO3 thin films with Cu top electrodes were fabricated on polycrystalline alumina substrates using a single step photolithographic technique. RF magnetron sputtering and thermally evaporation was used for fabrication of BST and Cu thin films respectively. The dielectric tunability of the BST IDCs was 40% (E = 12 V/mum). A dielectric Q ∼ 100 (1 MHz) and a device Q ∼ 30 (26 GHz) is obtained. Low leakage current characteristics (J = 1.0 x 10-6 A/cm 2 for E = 10 V/mum) was observed.; A 3rd order bandpass filter was fabricated and characterized. The center frequency of the filter was 1.85 GHz (0 V) and it tuned to 2.05 GHz (125 V). The insertion loss was 4.5 dB (0 V) and 3.5 dB (125 V). The return loss was better than 9 dB. The filter also exhibited low power consumption (6 muW) and low intermodulation distortion (IP3 = 38 dBm).; A X--band (8-12 GHz) phase shifter showed a figure of merit of 17°/dB for an applied bias of 130 V at 10 GHz. The return loss was better than 19 dB. The insertion loss (1.1 dB at 10 GHz) is among the best reported to date for a X--band phase shifter.; In this work we report the fabrication, characterization, and process optimization for microwave devices using low cost materials, simple and inexpensive processing routes entirely compatible with large volume manufacturing. This thesis represents the first comprehensive demonstration of ferroelectric thin film integrated microwave devices using ceramic substrates and base metallization at room temperature.