Low-voltage ferroelectric phase shifters from L- to C-band and their applications

This paper describes the design, fabrication and test results of a family of integrated low-voltage ferroelectric phase shifters ranging in frequency of operation from 0.7 GHz to 6 GHz. All devices use a common material system of barium strontium titanate (Ba_xSr_1-x TiO₃ or BST) thin-films on a sapphire (Al₂O ₃) substrate. Thick copper (Cu) metallization is used to allow integration of ferroelectric varactors with high-Q inductors and other passive microwave elements. Novel bias structures have also been developed to reduce the voltages required to tune the materials to less than 20V. The flip-chip mounted devices measure less than 0.080 in. times 0.080 in.. Data for an all-pass network BST phase shifter shows that more than 100deg of differential phase shift may be obtained over a 30% fractional bandwidth. To demonstrate the utility of BST phase shifters, a two-element phased array antenna was designed and tested in conjunction with a wireless local area network (WLAN). Field tests showed that the data throughput of the WLAN was significantly improved in the presence of strong interference by use of the BST phased array antenna