A K-Band Distributed Analog Phase Shifter Using Etched Ba_0.6Sr_0.4TiO₃ Thin Films

Abstract

This work presents the design, fabrication and microwave performance of distributed analog phase shifter (DAPS) fabricated on etched Ba 0.6 Sr 0.4 TiO 3 (BST) thin films for K-band applications. Single phase Ba 0.6 Sr 0.4 TiO 3 thin films for interdigitated capacitors (IDC) were deposited by the pulsed laser deposition (PLD) on (001) MgO substrates. The DAPS design consists of periodically loading high impedance coplanar waveguide (CPW) with tunable BST IDC, and the phase shift of the loaded line can be controlled by varying the applied bias voltage to the BST thin films. BST thin films except IDC areas were etched, which means that BST layers locally exist beneath IDC and are removed from the CPW by photolithography and RF-ion milling, to reduce the insertion loss of DAPS and to eliminate the alteration of unloaded CPW properties according to an applied dc bias voltage. The DAPS can be accurately and easily modeled using a combination of full-wave electromagnetic and microwave circuit analysis. Experimental results are shown to agree very well with the simulated ones at the frequencies of interest. The fabricated DAPS showed that the return loss was better than -13 dB through the whole K-band frequency range. The measured differential phase shift based on BST thin films was 179° and the insertion loss is -5.6 dB–-2.1 dB with increasing the bias voltage from 0 to 200 V at 20 GHz.