Electrically and magnetically tunable phase shifters based on a barium strontium titanate-yttrium iron garnet layered structure

We report on the tuning of permittivity and permeability of a ferroelectric/ferromagnetic bilayer structure which can be used as a microwave phase shifter with two degrees of tuning freedom. The structure was prepared by the growth of a yttrium iron garnet (YIG) layer on a gadolinium gallium garnet substrate by liquid phase epitaxy, the growth of a barium strontium titanate (BST) layer on the YIG layer through pulsed laser deposition, and then the fabrication of a coplanar waveguide on the top of BST through e-beam evaporation and trilayer liftoff techniques. The phase shifters exhibit a differential phase shift of 38°/cm at 6 GHz through permittivity tuning under an applied electric field of ∼75 kV/cm and a static magnetic field of 1700 Oe. By tuning the permeability through the applied magnetic field we increase the differential phase shift to 52°/cm and simultaneously obtain a better match to the zero applied electric field condition, resulting in an improvement in the return loss from 22.4 to 24.9 dB....