Structural and electrical properties of metal-ferroelectric-insulator-semiconductor transistors using a Pt/Bi3.25Nd0.75Ti3O12/Y2O3/Si structure

The metal-ferroelectric-insulator-semiconductor (MFIS) capacitors were fabricated using the Pt/Bi3.25Nd0.75Ti3O12/Y2O3/Si(1 0 0) structure, yttrium sesquioxide (Y2O3) thin films as an insulating buffer layer with different thickness ranging from 10 to 40 nm were deposited on p-type Si(1 0 0) at room temperature by electron-beam evaporation method. Nd-modified bismuth titanate (Bi3.25Nd0.75Ti3O12:BNT) films were prepared as ferroelectric layers at a processing temperature of 750 °C by chemical solution deposition (CSD) method. The Y2O3 buffer layers show an amorphous structure, relatively high dielectric constant, and good electrical properties. The ferroelectric polarization-voltage (P-V) hysteresis was observed for Pt/BNT/Pt/Ti/SiO2/Si and Pt/BNT/Y2O3/Si(1 0 0) capacitors. The MFIS structure exhibits a larger clockwise C-V memory window of 2.63 V when the thickness of Y2O3 layer was 10 nm and a lower leakage current density of 7 × 10−9 A/cm2 at a positive applied voltage of 6 V. Capacitance-voltage (C-V) and leakage-current density (J-V) characteristics of Pt/BNT/Y2O3/Si(1 0 0) capacitor indicate that the introduction of the Y2O3 buffer layer prevents the interfacial diffusion between BNT thin film and the Si substrate effectively and improves the interface quality. Furthermore, the Pt/BNT/Y2O3/Si structures exhibit excellent retention characteristics, the high and low capacitance values biased in the hysteresis loop are clearly distinguishable for over 13.6 days. The experimental results show that the BNT-based MFIS structure is suitable for non-volatile ferroelectric memory field-effect-transistors (FETs) with large memory window.