Fabrication of M3+-Substituted and M3+/V5+-Cosubstituted Bismuth Titanate Thin Films [M=lanthanoid] by Chemical Solution Deposition Technique

Abstract

Lanthanoid (M3+=La3+, Pr3+, Nd3+ and Sm3+)-substituted and lanthanoid/vanadium (V5+)-cosubstituted bismuth titanate thin films were fabricated on (111)Pt/Ti/SiO2/(100)Si substrates by a chemical solution deposition (CSD) technique. All the films consisted of a polycrystalline structure with random crystal orientation. Pr3+, Nd3+ and Sm3+-substituted BIT films [BPT, BNT and BST] had larger remanent polarization (Pr) values than that of conventional La3+-substituted BIT film [BLT]; furthermore, the Pr value of the BNT film was higher than those of the BPT and BST films. On the other hand, no significant difference in the coercive field (Ec) value was found among those films. Pr and Ec values of the BNT film with y=0.50 in (Bi4.00-y, Ndy)Ti3.00O12 were measured to be 32 µC/cm2 and 126 kV/cm, respectively. V5+-substitution varied the Pr value of the lanthanoid-substituted BIT films without changing the in Ec value. The Pr value of the BNT film with y=0.50 was improved up to 37 µC/cm2 by V5+-substitution of x=0.02 in (Bi4.00-y, Ndy)1-(x/12)(Ti3.00-x, Vx)O12 [BNTV]. Ferroelectric properties of the Pb-free polycrystalline BNT and BNTV films are comparable to those of conventional Pb-based ferroelectric films such as lead zirconate titanate [PZT] films.