Niobate-tantalate thin films microwave varactors

We present comparative characteristics of microwave variable capacitors (varactors) fabricated on Na0.5K0.5NbO3 (NKN), AgTa0.5Nb0.5O3 (ATN) and Ba0.5Sr0.5TiO3 (BST) ferroelectric films sintered by pulsed laser deposition technique. Two port 2 μm finger gap coplanar waveguide interdigital capacitive (CPWIDC) structures were defined on ferroelectric films surface by a standard lift off technique. Results of the microwave on-wafer tests performed in frequency range 1 to 40 GHz have been examined with a de-embedding technique to extract device characteristics from the measured S-parameters. The frequency dispersion of capacitance was 37%, 4.3%, and 17%; the voltage tunability (200 kV/cm) 22%, 4.7%, and 22% at 20 GHz; loss tangent ∼0.23, 0.068, and 0.137 at 20 GHz for NKN/Nd:YAlO3, ATN/Al2O3, and BST/Al2O3 films capacitors.