Enhancement of Epitaxial LaNiO3 Electrode on the Ferroelectric Property of La-doped BiFeO3/SrTiO3 Artificial Superlattice Structure by Rf Sputtering

Improvement of ferroelectric property by LaNiO3 (LNO) electrode on superlattice films was shown in this study. High quality asymmetric multiferroic 5 at% La-doped BiFeO3 (BFO) and paraelectric SrTiO3 (STO) superlattice structure was deposited on LNO electrode by rf magnetron sputtering system. High crystalline quality of the La-doped BFO/STO artificial superlattice structure on LNO electrode have been confirmed by clear main feature and satellite features around (002) STO substrate Bragg peak shown in (002) radial scan spectrum. The results of in-pane crystal truncation rod (CTR) spectrum and the rocking curve indicated that superlattice films with high crystal quality behaved in-plane strain closed to fully strained state on both LNO and Nb-doped STO electrode. The epitaxial relation between the La-doped BFO and STO layers in the superlattice was examined through a (103) azimuthal scan and (103) Lscan. The results show a four-fold symmetry and slight distorted of γ angle of the BFO unit cell, confirming the pseudocubic structure of the La-doped BiFeO3 structure. The measurement of hysteresis loops showed that La-doped BFO superlattice structure on LNO electrode behaved lower, but stable and saturated ferroelectric properties than that of films with Nb-doped STO substrate in our previous study. The measurement of resistivity and leakage current density of superlattice films demonstrated that resistivity of electrode is the main factor to determine the leakage properties of films. The superlattice films behaved larger piezoelectric coefficient (d33) on LNO electrode than films on Nb-doped STO substrate, which indicated the enhancement of intrinsic ferroelectric properties in La-doped BFO/STO superlattice films.