Crystallization Characteristics of LaNiO3 Layers and Their Effect on Pulsed Laser Deposited (Pb 1-xLax)(ZryTi 1-y)O 3 Thin Films

Abstract

Crystallization characteristics of LaNiO3 (LNO) thin films prepared by either rf magnetron sputtering or pulsed laser deposition (PLD), and their effect on the ferroelectric properties of subsequently pulsed-laser-deposited (Pb1-x Lax )(Zry Ti1-y )O3 (PLZT) films were examined. Post-annealing of the amorphous LNO layers, which were prepared by room-temperature sputtering, revealed that the LNO crystallized at temperatures higher than 450° C, and the annealed LNO layers were randomly oriented. However, a substrate temperature of only 250° C was required to form crystalline LNO films in a high-temperature sputtering process and the resultant films were preferentially (100) oriented with low electrical resistivity (ρ S=0.55 m Ω·cm). On the other hand, a substrate temperature of 400° C was required in situ to grow crystalline LNO phase by the PLD process and the obtained films were predominantly (110) oriented with a high resistivity (ρ S=6.38 m Ω·cm). The Pt used as an underlay markedly reduced the resistivity (ρ S=0.05 m Ω·cm) without changing the texture characteristics of LNO layers. It was also found that a reduction of gas pressure in the deposition chamber could enhance the (100)-oriented crystallization of LNO in both sputtering or PLD process. PLZT films subsequently deposited by PLD on the LNO layers required a substrate temperature ≥500° C to completely eliminate the pyrochlore phase. The structural characteristics of the PLZT films inherit that of the underlying LNO layer. Ferroelectric and dielectric properties of PLZT films were optimized when using the (100) LNO-Pt double-layers were used as bottom electrodes. The remanent polarization and coercive field obtained were P r=14.9 µ C/cm2 and E c=3.5 kV/cm, respectively, and the dielectric constant was 950 with a loss of tan δ<0.05 at 1 kHz.