Ag(Ta,Nb)O3 thin-film interdigital capacitors for microwave applications

Epitaxial silver tantalate-niobate Ag(Ta,Nb)O3 (ATN) films have been grown on LaAlO3(0 0 1) single crystals by pulsed laser ablation of stoichiometric AgTa0.38Nb0.62O3 ceramic target. Extensive X-ray diffraction analysis reveals epitaxial relationship between the ATN film and LaAlO3(0 0 1) substrate. 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 at 1 MHz, dielectric permittivity 224 at 1 kHz, weak frequency dispersion of 5.8% in 1 kHz to 1 MHz range. Dielectric permittivity and loss tangent were also measured at the microwave range. Conformal mapping techniques were employed to extract dielectric properties of ATN film on substrate at the microwave frequency range. Theoretical properties of conformal mapping techniques for interdigital capacitors and CPW microstrip lines were discussed.