Fabrication and characterization of Sr0.8Bi2.2Ta2O9 /Al2O3 gate stack for ferroelectric field effect transistors

Abstract

We analyze and report the structural, electrical and ferroelectric properties of Sr0.8Bi2.2Ta2O9/Al2O3/silicon gate stack for ferroelectric field effect transistors (FETs). RF sputtering and plasma-enhanced atomic layer deposition (PEALD) have been used for the deposition of Sr0.8Bi2.2Ta2O9 (SBT) and Al2O3 film, respectively. Different deposition and process parameters of the SBT and Al2O3 films were optimized by obtaining the structural properties of the deposited film, and electrical properties of metal/ferroelectric/silicon (MFeS), metal/insulator/silicon (MIS), and metal/ferroelectric/metal (MFeM) structures. X-ray diffraction analysis reveals the polycrystalline perovskite structure of the SBT film having a dominant intensity peak along direction at different annealing temperatures. Crystalline film morphology with a maximum grain size of 45 nm was confirmed at the annealing temperature of 500 °C by the field emission scanning electron microscopy. Ellipsometric analysis of the SBT film reveals the maximum refractive index of 3.46 at the annealing temperature of 500 °C. Introduction of a 10 nm buffer layer between ferroelectric and silicon substrate shows the improved memory window of 6.07 V in metal/ferroelectric/insulator/silicon (MFeIS) structure as compared to the 3.07 V in the MFeS structure. MFeI(10 nm)S structure also shows improved leakage current characteristics as compared to MFeS structures and endurance greater than 1013 read/write cycles with the data retention time of higher than 10 years.