An Electrically Tunable Barium Strontium Titanate Phase Shifter

It is well known that a slot-line fabricated on a dielectric substrate supports the propagation of electromagnetic waves. In order to realize electrical tuning of the slot-line characteristics, nonlinear dielectrics such as barium strontium titanate (BST) could be used as substrates. A prototype BST phase shifter was fabricated and characterized at 47 GHz. The design is based on a multi-slot line patterned on an alumina substrate and a BST film of thickness 0.6 $\mu $m and dielectric permittivity of 1500. The electrode topology on the BSTO film includes three inner copper electrodes of thickness 3 $\mu $m. The width of the inner electrodes is equal to 50 $\mu $m, and the gap between them is also 50 $\mu $m. A part of the outer electrodes had a funnel-shape configuration in order to provide necessary coupling with input/output circuits. Measurements of the phase shift at 47 GHz revealed a differential phase shift of 270 deg. for a bias voltage of 500 V. The total signal attenuation was about 7 dB. -Work supported by a grant from the Delphi Automotive Corporation.