SrxBa(1−x)TiO3 thin films for active microwave device applications

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Abstract
Thin (0.3–50 μm) films of SrxBa(1−x)TiO3 (SBT) with x=0.35 − 0.8 have been deposited by pulsed laser deposition onto single crystals of MgO, LaAlO3 and thin films of YBa2Cu3O7−δ. The SBT films were characterized morphologically, structurally and electrically at frequencies ≤ 13 GHz. On MgO, smooth, oriented single phase films were obtained at substrate temperatures ≥ 825°C. Films as thick as 10 μm were exclusively (100) oriented. At thicknesses approaching 50 μm SBT films were phase pure but polycrystalline. The dielectric constant of SBT films, as determined from patterned structures using microstrip geometries, was ∼20% of that observed in bulk SBT (εmax(film)=1100 for x=0.5 at 200 K). The temperature dependence of the dielectric constant was broad in comparison to the sharply peaked behavior of the bulk material. The ferroelectric thin film properties described, while significantly different from bulk material, are very encouraging for use in active devices at microwave frequencies.

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