Ferroelectric field-effect memory device using Bi4Ti3O12 film

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.