Fabrication and Characterization of Pt/(Bi, La)4Ti3O12/Si3N4/Si Metal Ferroelectric Insulator Semiconductor Structure for FET-Type Ferroelectric Memory Applications

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Abstract
For field effect transistor (FET)-type ferroelectric memories, c-axis oriented (Bi, La)4Ti3O12 films with small remanent polarization Pr of 4 µC/cm2 were investigated. Bi3.25La0.75Ti3O12 films were prepared by the sol-gel method on amorphous Si3N4 layers formed on Si substrates using atomic nitrogen radicals. It was found that the films formed using stoichiometric sol-gel solution did not crystallize even after annealing at 800°C in O2 ambient. Therefore, 2.5 to 7.5% excess-Bi solutions were used and such parameters as pre annealing and crystallization temperatures, film thickness and crystallization ambient were optimized. As a result, the well c-axis-oriented Bi3.25La0.75Ti3O12 films with good crystallinity and good surface morphology were obtained at temperatures higher than 600°C. It was also found in a Pt/100 nm-Bi3.25La0.75Ti3O12/3 nm-Si3N4/Si (metal/ferroelectric/insulator/semiconductor) structure that C–V characteristics showed a hysteresis loop with a memory window of about 1 V and both high and low capacitance values kept at zero bias voltage did not change for more than 3 h.