New MFIS structure of sol gel-(Bi,La)4Ti3O 12 with silicon nitride buffer layer

Pt/Bi_3.25La_0.75Ti₃O₁₂ /Bi₂SiO₅/Si₃N₄/Si MFIS (Metal/Ferroelectric/Insulator/Semiconductor) structures were prepared by sol-gel method. Bi_3.25La_0.75Ti₃O₁₂ and Bi ₂SiO₅ films were deposited at 800°C. The Si ₃N₄ was made by exposing N₂ radicals to a Si substrate from a radical gun in a vacuum chamber at temperatures from 800°C. The MIS diode with this Si₃N₄ showed no hysteresis after any thermal treatment. 200 nm-thick Bi_3.25La_0.75Ti₃O₁₂ and 10 nm-thick Bi₂SiO₅ buffer films were formed by sol-gel method on a 1.8 nm thick Si₃N₄ layer. The capacitance-vs-voltage (C-V) characteristic of the MFIS diode showed 1.4 V memory window for the +/-5V voltage scan. The memory window width agreed well with the polarization characteristics (remanent polarization Pr=0.9 μ C/cm² and coercive field Ec=40 kV/cm) of a Bi_3.25La_0.75Ti₃O₁₂ film, which were measured using a Pt/c-axis-oriented 100 mn-thick Bi_3.25 La_0.75Ti₃O₁₂/Pt capacitor. Moreover, two capacitance values at zero-bias were kept constant for over 24 h, which indicates the retention characteristic of the diode is excellent