Enhanced Ferroelectric Properties of Multilayer SBT-BTN Thin Films for NVRAM Applications

Abstract

Ferroelectric SrBi2Ta2O9-(Bi4Ti3)1-xNbxO12 (x = 0.02) (SBT-BTN) multilayer thin films with various stacking periodicity have been synthesized on Ir/Ti/SiO2/Si substrate by metal organic chemical vapor deposition technique (MOCVD). Tributylbismuth [Bi(C4H9)3], Strontium-bis[Tantal(pentanethoxy)(2-methoxyethoxid)] [Sr[Ta(OEt)5(OC2H4OMe)]2], Titanium Bis(isopropoxy)bis(1-methoxy-2-methyl-2-propoxide) [Ti(OiPr)2(mmp)2] and Niob-ethoxide [Nb(OC2H5)5] were selected as precursors. X-ray diffraction patterns show that the multilayer films annealed at 800˚C consist of fully formed perovskite phase with polycrystalline structure and plate-like grains with no crack. The remanent polarization (2∙Pr) and coercive field (Ec) are 16.2 μC/cm2 and 230 kV/cm, respectively, which is much higher, compared to pure SBT film (2∙Pr = 6.4 μC/cm2, Ec = 154 kV/cm). In the films prepared above 700˚C, postannealing increased the capacitor shorting rate; this was attributed to oxidizing of the top iridium layer. In this paper, the dependence of composition variation around stoichiometric on ferroelectric properties in SBT-BTN multilayer films is studied.