Ferroelectric thin films on ferrites for tunable microwave device applications

Wideband tunable microwave transmission lines are being developed using pulsed-laser-deposited ferroelectric thin films on liquid-phase-epitaxially grown ferrite thick films. The ferroelectric-ferrite combination makes it possible to independently tune both the inductance per unit length and capacitance per unit length of the integrated structure, and thus, overcome the deleterious effects of modifying the capacitance per unit length on the impedance match of the transmission line. Initial microwave measurements have indicated that both magnetic and electric tuning mechanisms are functional and that the phase velocity can be tuned equally well by either magnetic or electric field. An equivalent differential phase shift can be achieved with a magnetic bias on the order of 320 Oersteds as has been achieved with an electric bias of 21 kV/cm. The effects are additive to first order, allowing for maximum observed total differential phase shift of over 40 degrees at 11.6 GHz.