Ag(Ta, Nb)O 3 thin-film low-loss variable interdigital capacitors

Epitaxial silver tantalate-niobate Ag(Ta, Nb)O3 (ATN) films have been grown on LaAlO3(001) MgO(001), and Al2O3(011_2) single crystals by pulsed ablation of stoichiometric AgTa0.38Nb0.62O3 ceramic target. Rutherford backscattering spectroscopy has revealed Ag0.9Ta0.42Nb0.58O3−δ composition of fabricated films. Micrometer size interdigital capacitor structures have been defined photolithographically on the top surface of ATN films. ATN/LaAlO3 thin-film capacitors exhibit superior overall performance: loss tangent as low as 0.0033 @1 MHz, dielectric permittivity 224 @1 kHz, weak frequency dispersion of 5.8% in 1 kHz to 1 MHz range, tunability as high as 16.8%, factor K=tunability/tan δ higher than 48, and leakage current as low as 230 nA/cm2 @100 kV/cm. ATN films on MgO show the lowest loss factor of 0.0025 @1 MHz and the weakest frequency dispersion of 2.5×10−8 Hz−1.