( Ba , Sr ) TiO 3 (BST) thin films were deposited on high resistivity silicon substrates by in situ rf magnetron sputtering. A buffer layer was used to improve the cristallinity of the films, the composition was fixed to Ba/Sr=30/70. The relative permittivity and the losses were measured up to 60 GHz using coplanar strip lines. The dispersion of the permittivity and the losses has been determined with a home made numerical code based on finite elements: ELFI. We show that, with the measurements of the scattering parameters coupled with ELFI, it is possible to know the BST complex permittivity over a very broad frequency band. The BST films deposited by in situ (700 °C) present excellent properties between 1 to 60 GHz. The relative permittivity is in the order of 270 and the losses are very small 0.09 at 60 GHz. These structures BST/silicon high resistivity show good potentialities for devices microwaves applications which need future integration in a silicon environment.
400-nm-thick Ba0.3Sr0.7TiO3 thin films are deposited on high resistivity silicon by in situ radio frequency magnetron sputtering. Coplanar waveguides with 1 μm slot width are designed, with accurate knowledge frequency losses behavior, to determine ferroelectric thin-films properties up to 60 GHz. Permittivity, loss tangent, and tunability are extracted through measurements and home made finite element analysis. Tunability of 33% and 29%, with 30 V maximum applied voltage (electric field of 300 kV/cm), are measured at 5 GHz and 60 GHz, respectively, while the dielectric losses evolve from 0.5% to 5%. A brief highlight is proposed about tunable silicon integrated quarter wavelength transformer potentialities for impedance matching.
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