Relaxation characteristics of Ag(Ta,Nb)O3 thin film varactors

Silver tantalate niobate, which shows excellent microwave properties, was selected for this dielectric relaxation study. 4 mum gap Au(500nm)/ Cr(10nm)/Ag(Ta,Nb)O-3(0.4mum) interdigital capacitors (IDC) fabricated on LaAlO3 (LAO) and Al2O3 (sapphire) substrates were used as test structures. Frequency dispersion in the range 1 kHz to 1 MHz, loss tandelta, tunability and K-factor @ 100 kV/cm and 1 MHz were about 8.4%, 5.9%, 0.0033 and 17.8 and 3.5%, 3.8%, 0.0035 and 9.9 for IDCs on LAO and sapphire, respectively. Switching the voltage in stair-case mode results in slow and weak relaxation of the capacitance : at 50 kV/cm it was less than 0.05 % for 70 sec. Relaxation of leakage current follows power law: /I(t)/I-infinity -1/ = (t/12 s)(-0.98).