On-wafer microwave characterization of ferroelectric thin film phase shifters

A phase shifter based on coplanar waveguide transmission lines has been used to characterize the microwave properties of Ba_0.5Sr_0.5TiO₃ thin films over a wideband frequency range (45 MHz-50 GHz). Films with tunability of ∼45% dielectric permittivity of ∼1000 and tan δ < 0.005 were obtained after optimization of the deposition processes. A phase shift of ∼220° at 40 GHz has been achieved along 5250 μm lines with a dc-bias voltage as small as 70 V (producing 2.8 kV cm^-1), with an insertion loss of 8 dB. Selected structural properties of the films were compared with the microwave properties.