Sol-gel deposited LaZrO_x buffer layer for ferroelectric thin films

To investigate the possibility of LaZrO_x thin film as a buffer insulator for ferroelectric thin films, we fabricated (Bi,La)₄Ti ₃O₁₂ (BLT) ferroelectric films on a silicon substrate by using the LaZrO_x buffer insulator in forming the metal-ferroelectric- insulator-semiconductor (MFIS) structure. We prepared the LaZrO_x thin film and BLT films by using a sol-gel method. The films were characterized by X-ray diffraction (XRD) analysis, atomic force microscopy (AFM), capacitance-voltage (C-V) characteristics, and leakage current density-voltage (J-V) characteristics for both LaZrO_x/Si and BLT/LaZrO_x/Si structures. From C-V measurement results, equivalent oxide thickness (EOT) values of LaZrO_x thin films annealed at 700 °C and 800 °C were about 9 nm and 10 nm, respectively. Negligibly small hysteresis loops were observed for both LaZrO_x/Si structures. The leakage current density at an applied voltage of 5 V was lower than 1.0 × 10^-7 A/cm² for all samples. For the case of the BLT/LaZrO_x/Si structure, we obtained randomly oriented polycrystalline BLT films. From the C-V measurements, clockwise ferroelectric hysteresis loops were observed and the memory window width became larger as the bias voltage sweep increased from ±3 V to ±9 V. The memory window width was about 1.0 V for bias voltage sweep of ±7 V. The leakage current density was lower than 1.0 × 10^-6 A/cm₂ at 10 V.