Berlin 2018 – scientific programme

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DS: Fachverband Dünne Schichten

DS 6: Thin Film Applications

DS 6.4: Talk

Monday, March 12, 2018, 15:45–16:00, H 0111

Effect of cation stoichiometry on electric properties of thin-film varactors with Ba_xSr_1−xTiO₃ tunable dielectric and highly conducting SrMoO₃ electrodes — •Lukas Zeinar¹, Patrick Salg¹, Aldin Radetinac¹, Dominik Walk², Philipp Komissinskiy¹, Holger Maune², Rolf Jacoby², and Lambert Alff¹ — ¹Materials Science, TU Darmstadt, Germany — ²Microwave Engineering and Photonics, TU Darmstadt, Germany

We present Au/Pt/Ba_xSr_1−xTiO₃/SrMoO₃ varactor heterostructures utilizing single crystalline Ba_xSr_1−xTiO₃ films grown epitaxially by pulsed laser deposition on a highly conducting thin*film oxide SrMoO₃ bottom electrodes with a room-temperature resistivity of 30 µΩcm. The stoichiometry of the dielectric Ba_xSr_1−xTiO₃ was tuned to achieve the desirable high tunability and low losses of the varactors at room temperature. Influence of the cation stoichiometry of the Ba_xSr_1−xTiO₃ films on their Curie temperature and room-temperature dielectric permittivity was investigated. The changes of the Ba_xSr_1−xTiO₃ out-of-plane lattice parameter by 2 % and the corresponding changes of the Ba-Sr and (Ba,Sr)-Ti cation ratios by 6 and 11 %, respectively, were observed by varying the laser energy fluence in the range between 0.3 and 1.4 J/cm². Tunability and leakage current of the varactors were investigated by a vector network analyzer at frequencies between 300 MHz and 10 GHz. Fine tuning of the Ba_xSr_1−xTiO₃ cation stoichiometry allows high relative tunability of the varactors up to 80 % and reduction of the varactor leakage current by up to three orders of magnitude down to 10 nA.