Roles of target composition on the dielectric property of RF sputtered Bi_2O_3-ZnO-Nb_2O_5 pyrochlore thin film

摘要

Bi_2O_3-ZnO-Nb_2O_5 (BZN) thin films were well formed on a Pt/TiO_2/SiO_2/Si substrate by RF magnetron sputtering. Process induced nonstoichiometric of BZN yielded two typical crystalline structures i.e. cubic and monoclinic. Due to the low sputtering yield of Bi, BZN cubic phase, could be obtained not only from the sputtering of corresponding target (Bi_(1.5)Zn_(0.5))(Zn_(0.5)Nb_(1.5)) O_7 but also from the target which has Bi-enriched monoclinic composition (Bi_2(Zn_(0.33)Nb_(0.66))_2O_7). Even film which was deposited from monoclinic BZN has better tunability. It was observed that BZN cubic films were continuously deposited until target composition increased up to (Bi:Zn:Nb = 4:1:2) from stoichiometry (Bi:Zn:Nb = 3:1:2) and that tunability maximized with a dielectric constant of 184, loss tangent of 0.008, and maximum tunability of 42% at 1.1MV/cm from 3.2:1:2 composition. In the mid nonstoichiometric range, only Bi_5Nb_3O_(15) secondary orthorhombic phases were observed along with cubic phase which showed synergetic effects on BZN cubic films.