Development of highly reliable BiFeO3/HfO2/Silicon gate stacks for ferroelectric non-volatile memories in IoT applications

Abstract

We have investigated the structural, electrical, and ferroelectric properties of metal–ferroelectric-high-k-silicon capacitors with BiFeO3 ferroelectric films deposited on the HfO2/Si substrate. BiFeO3, HfO2 films, and their stack were deposited on the silicon substrate using RF magnetron sputtering and plasma-enhanced atomic layer deposition (PEALD). Film crystal orientation, refractive index, and absorption constant parameters were extracted from X-ray diffraction and ellipsometric analysis. Electrical characterization of metal/ferroelectric/metal (MFM), metal/ferroelectric/silicon (MFS), metal/dielectric/silicon (MIS), and metal/ferroelectric/insulator/silicon (MFIS) capacitor structures provide memory window, leakage current density, hysteresis, fatigue, and data retention time. The metal/ferroelectric/silicon structure exhibits clockwise capacitance–voltage characteristics with the memory window of 5.04 V for the bias voltage of ± 10 V. The electrical and ferroelectric characteristics of MFIS structures were studied for different thicknesses of HfO2 layer, which shows that the introduction of high-k dielectric film between ferroelectric and silicon improves the interface quality. The memory window of the MFIS structure was found to significantly increase to 9.65 V with the introduction of a 10 nm HfO2 layer between the ferroelectric layer and the silicon substrate. Two-order reduction in the leakage current density was also observed in the MF(200 nm)I(10 nm)S structure as compared to the MF(200 nm)S structure. The fabricated MF(200 nm)I(10 nm)S gate stack shows fatigue resistance for read/write operations greater than 1012 cycles and data retention time for greater than 104 s. To the best of author’s knowledge, this is the first investigation to integrate pure BiFeO3 on PEALD-HfO2 dielectric for the gate stack of ferroelectric field effect transistors.