Comparison of the Electrical Properties for Etched and As-Deposited BET Thin Films

Abstract

In recent years, some Bi-layered perovskite oxide such as SrBi 2Ta2O9(SBT) and Bi4-xILa xTi3O12(BLT) have been intensively studied for use in FRAMs because of its low leakage current, low coercive field, and fatigue-free with simple Pt electrode. The fatigue-free behavior of SBT and BLT thin film was due to the charge compensating effect of Bi2O 2 layersresulting in the reduction of space charge and from domain wall unpinning that happens at least as rapidly as domain pinning. However, SBT and BLT thin films have a disadvantage of low remanent polarization for the high-density integration of FRAMs. From the viewpoint of the general formula of Aurivillius compounds, radii of Europium ion (0.95 Å), similar to Bi ion (0.93 Å) in the Bi4Ti3O12 (BIT), occupies the A site in the perovskite unit BIT. The europium-substituted BIT(BET) thin films resulted in a large 2Pr, whose value (60.99μC/cm2) is much larger than that of Sm-modified BIT thin film (2Pr = BSmT: 49μC/cm2) and BLT thin film (2P r = 27μC/cm2) at an applied voltage of 10V. For this advantage, BET thin films have emerged as new ferroelectric materials. However, there is no report on etching BET thin films. BET thin films were prepared on Pt/Ti/SiO2/Si substrates by sol-gel processes. Pt top electrodes were deposited on BET thin films by using rf magnetron sputtering. We etched BET films with various gases Ar/CF4 plasmas. The maximum etch rate of the BET thin films was 78 nm/min for 90% Ar added CF4 gas. After the etching, the electrical properties are characterized in terms of hysteresis curves, leakage current, retention properties, and switching polarization. When the electrical properties of BET etched in 90% Ar added CF4 were compared, the value of remanent polarization in Ar added CF4 plasma is lower than that in as-deposited. The chemical states on the etched surface were investigated with x-ray photoelectron spectroscopy (XPS), Scanning electron microscopy (SEM) was used to investigate the surface morphology of BET thin films exposed in plasma and etching profile.