Ferroelectric field-effect memory device using Bi4Ti3O12 film

Abstract

A ferroelectric field‐effect transistor has been investigated using a thin film of bismuth titanate (Bi₄Ti₃O₁₂) deposited on a Si substrate by rf sputtering. Achievement of the ferroelectric polycrystalline Bi₄Ti₃O₁₂ films without any cracks necessitates postdeposition heat treatment in air at temperatures ?550 °C for 30 min. The film, heat treated at 650 °C, has a remanent polarization of 4.0 μC/cm² and a coercive field of about 250 kV/cm at 1 kHz. A FET having a gate structure of Bi₄Ti₃O₁₂‐SiO₂‐Si was fabricated, where the SiO₂ served to prevent charge injection from Si into the ferroelectric film. (This process would degrade the retention of memorized states.) The FET can be switched by voltages of as low as 15 V applied to the gate. The on and off states are very stable at room temperature.