An Improvement in C–V Characteristics of Metal-Ferroelectric-Insulator-Semiconductor Structure for Ferroelectric Gate FET Memory Using a Silicon Nitride Buffer Layer

Metal-ferroelectric-insulator-semiconductor (MFIS) structures using silicon nitride (SiNx) and silicon oxynitride (SiON) layers as an insulating barrier against interdiffusion have been proposed and investigated. SrBi2Ta2O9 (SBT) films are deposited as ferroelectric layers by pulsed laser deposition (PLD) method on SiNx/SiO2/Si and SiON/Si substrates at low temperatures. An Al/SBT/SiNx/SiO2/Si (MFNOS) structure exhibits a larger memory window and a smaller shift in C–V curve than those of the Al/SBT/SiO2/Si structure. Moreover, strong barrier effect of SiNx layer is demonstrated by both Rutherford back scattering spectroscopy (RBS) analysis and comparison of two Al/SiNx/SiO2/Si structures with and without depositing SBT film. An Al/SBT/SiON/Si (MF(ON)S) structure also shows good C–V characteristics with no degradation in the curve gradient. In addition, the C–V curve shows no change when the sweep rate of the bias voltage is increased from 0.2 V/s to 40 kV/s, which indicates that the hysteresis originates not from ion drift but from high-speed ferroelectric polarization.