Ferroelectric Sr₂(Nb, Ta)₂O₇ Thin Films Prepared by Chemical Solution Deposition

Abstract

Ferroelectric Sr 2 (Nb, Ta) 2 O 7 (SNTO) thin films were prepared by chemical solution deposition process, i.e. the modified sol-gel method. The stock solutions were spin-coated onto either Pt/Ti/SiO 2 /Si(100) or Pt/TiO 2 /SiO 2 /Si(100) substrate. After multiple coating/baking steps, dried thin film stacks were annealed for crystallization at 850–1000°C in oxygen. X-ray diffraction (XRD) and scanning electron microscope (SEM) analyses revealed that the crystallization temperature by modified sol-gel process can be lowered to 850°C if Pt/TiO 2 /SiO 2 /Si(100) substrate was used, while temperature higher than 950°C is required for Pt/Ti/SiO 2 /Si(100) substrate. Leakage current and relative permittivity ( ε r ) values were measured in the range of about 10 -9 –10 -7 A/cm 2 , and 30–45, respectively, depending on the composition, heat-treatment and substrate type. Polarization hysteresis loops were not saturated regardless of composition and annealing temperature. Remanent polarization (2 P r ) and coercive field ( E c ) values for typical SNTO(30/70) film were approximately 1.9 µC/cm 2 , and 17 kV/cm, respectively, when ±5 V pulse was applied.