Fabrication and electrical properties of Pt/(Bi,La) ₄Ti ₃O ₁₂/HfO ₂/Si structures

HfO ₂ and (Bi,La) ₄Ti ₃O ₁₂ were chosen as the respective buffer layer and ferroelectric film in forming MFIS (metal-ferroelectric-insulator-semiconductor) diodes on Si(100) substrates. HfO ₂ films were prepared by an MBD (molecular beam deposition) method, and they were subjected to ex-situ O ₂ annealing in a rapid thermal annealing (RTA) furnace at 800°C for 1 min. In order to obtain optimal properties, especially the electrical leakage current characteristic, three kinds of HfO ₂ films were prepared, which were deposited at room temperature, at 300°C substrate temperature, and with chemical oxidation. On the HfO ₂/Si structures, Bi _3.45La _0.75Ti ₃O ₁₂ films ranging from 300 nm to 400 nm in thickness were deposited by a sol-gel technique and they were crystallized in O ₂ atmosphere at 750°C. The memory window width in the C-V (capacitance-voltage) curve of the BLT/HfO ₂/Si diode was about 1.0 V for a voltage sweep of ±6 V. It was also found that the retention time of this diode was longer than 8 hours.