Influence of Structural Properties on RF and Microwave Characteristics of BaSrTiO3 Films on Various Substrates

Ferroelectric Ba_xSr_1-xTiO₃ (BSTO, x ≈ 0.6) films were grown on various substrates (SrTiO₃, LaAlO₃, MgO, α-Al₂O₃, alumina, and Y₃Fe₅O₁₂) using RF sputtering. The results of complex BSTO diagnostics using medium energy ion scattering (MEIS) were compared with dielectric characteristics at 1 MHz and 30 GHz. The BSTO films were different on the MEIS yield _s characterizing film structure and temperature T_m corresponded to maximal capacitance of BSTO varactor. Highly-oriented BSTO films of ∼ 500 nm thick grown on MgO and LaAlO₃ had T_m = (150-230 K), tunability K = □ (0)/□(E_max) ≈ 1,3 − 1,5□(E_max ≈ 10 V/m) and tan ≤ 10⁻³. The films grown on sapphire, alumina and YIG substrates had less ordered structure, lower strains, T_m = (250 - 260 K), K ≈ 1,6 - 2,2 and tan ≥ 10⁻³. The tan of the investigated BSTO films at f ≈ 30 GHz was higher by approximately one order of magnitude.