Distributed phase shifters using (Ba,Sr)TiO3 thin films on sapphire and glass substrates

In this paper, we present distributed phase shifter results employing voltage tunable (Ba,Sr)TiO3 (BST) thin film capacitors deposited by RF magnetron sputtering. Both parallel-plate and interdigital structures are investigated for different application requirements. The parallel-plate capacitor based circuit on glass (Vycor) substrate has a continuous 0-180? phase shift at 30 GHz with an insertion loss of 4dB and return loss better than 12 dB. A similar K-band phase shifter on a sapphire substrate was also demonstrated with a 0-270? differential phase shift and an insertion loss of 6.1dB at 20 GHz. The circuit using interdigital BST capacitors on sapphire substrate shows a continuous 0-360? phase shift at 8.2 GHz with an insertion loss of only 4.9 dB. These results show the feasibility of using BST thin film technology in microwave and millimeter wave phase shifter applications.