Fabrication of Ion-Cosubstituted Bismuth Titanate Thin Films by Chemical Solution Deposition Method

Abstract

Ferroelectric properties of ion-cosubstituted BIT thin films, (Bi4.00 − yLny)4-δ (Ti3.00-xXx)3O12 (BLnTX), with various lanthanoid (Ln: e.g., La3+, Nd3+, Pr3+, Sm3+) and higher-valent ions (X: e.g., V5+, Nb5+, Ta5+, W6+) were investigated to determine the optimum condition of the ion-cosubstitution. Ion-substituted BIT films were fabricated on (111)Pt/Ti/SiO2/(100)Si substrates using a chemical solution deposition (CSD) technique. In the case of Bi-site substitution, Pr3+, Nd3+ and Sm3+-substituted BIT films (BPT, BNT and BST) had larger remanent polarization (P r ) values than that of conventional La3+-substituted BIT film (BLT). Especially, P r and E c values of (Bi3.50Nd0.50)Ti3.00O12 film were measured to be 32 μC/cm2 and 126 kV/ cm, respectively. On the other hand, Ti-site substitution by higher-valent cations degraded the large leakage current density of the BIT film from ∼10−6 down to ∼10−7 A/cm2. V-substituted (Bi3.50Nd0.50)Ti3.00O12 films, i.e., Nd3+/V5+-cosubstituted BIT films (BNTV), had larger P r values than that of non-substituted (Bi3.50Nd0.50)Ti3.00O12 film. (Bi3.49Nd0.50)(Ti2.97V0.03)O12 film possessed P r and E c values of 37 μC/cm2 and 119 kV/cm respectively, which were comparable with those of conventional Pb-based ferroelectric thin films like lead zirconate titanate, Pb(Zr,Ti)O3.