Na_0.5K_0.5NbO₃ Film Microwave Varactors

Abstract

Na_0.5K_0.5NbO₃ (NKN) and Pb(Zr_0.53Ti_0.47)O₃ (PZT) films have been grown by rf-magnetron sputtering and pulsed laser deposition techniques, correspondingly, on sapphire (Al₂O₃-0112, r-cut), quartz (Y+36°-cut) and YAlO₃ + 1% Nd (Nd:YAlO₃-001) single crystal substrates with Interdigital Capacitor (IDC) of Coplanar Waveguide (CPW) structure. Photolithography and metal lift-off technique was used for processing of the tunable microwave capacitor. Microwave network analyzer with G-S-G Picoprobe and probe station performed microwave measurement with external DC bias. NKN film interdigital capacitors on Nd:YAlO₃ show superior performance in the microwave range from 1 to 40 GHz. Within this range, the voltage tunability (40 V, 200 kV/cm) was about 29%, loss tangent ∼ 0.13, K-factor from 152% @10 GHz to 46% @40 GHz, voltage independent C _p was about 230 fF, tan δ _p changes from 0.14 @10 GHz to 0.36 @40 GHz, real and imaginary part of interconnect impedance increases with frequency from 0.13 Ω @10 GHz to 0.50 Ω @40 GHz and from 1.9 Ω @10 GHz to 5.9 Ω @40 GHz respectively.

Keywords:

• rf-magnetron sputtering
• pulsed laser deposition
• thin ferroelectric NKN films
• coplanar waveguide
• interdigital capacitor
• network analysis

ACKNOWLEDGEMENTS

This research was funded by the Swedish Foundation for Strategic Research (SSF).