Structural features and phase transition temperature of BaxSr1-xTiO3 films grown on various substrates

Ferroelectric BaxSr1−xTiO3 (BSTO) films were grown on various substrates (α-Al2O3, LaAlO3, MgO and polycrystalline alumina) by RF sputtering of a BSTO target with Ba/Sr ratio x in the range from 0.50 to 0.65. The results of comprehensive structural diagnostics of the films are correlated with the temperature Tm corresponding to the maximum capacitance of a planar BSTO varactor, measured at a frequency of 1 MHz. BSTO films of the same cationic composition, grown on various single-crystal substrates, have markedly different Tm correlated with the structural ordering of ferroelectric films. Highly oriented BaSrTiO3 films approximately 300 nm thick, grown on MgO and LaAlO3 substrates, are characterized by low tan δ ≤ 8 × 10−4 and Tm = 140− 230 K. However, textured and polycrystalline BSTO films of the same composition, grown on sapphire and alumina substrates, are less strained, having tan δ ≤ 10−3, and Tm ≥250 K.