Characterization of highly preferred PZT thin films on LSCO and LNCO electrodes prepared in low temperature

Abstract

Lead Zirconate titanate(PZT) is a ferroelectric material which has perovskite structure. The PZT film is one of the promising materials applicable to capacitors in memory devices, such as ferroelectric non-volatile memory(FRAM), because of its high remanent polarization and P-E hysteresis properties. There has been much research on integrated PZT thin film memories for the past several years. In particular the fatigue properties of PZT thin films, which is a critical problem in applications for FRAM devices, has been extensively studied. To date, many approaches to overcome the switching fatigue problem have been proposed. To overcome the switching fatigue problem, we used conducting oxide electrodes, i.e., LSCO and LNCO. In this research, the possibility of the low temperature growth of ferroelectric capacitor was studied using DC reactive sputtering method. LNCO electrode was proposed as a new candidate for conducting oxide electrodes. $La_{0.5}Sr_{0.5}CoO_3$(LSCO) and $LaNi_{0.6}Co_{0.4}O_3$(LNCO) thin films were deposited on Pt/Ti/$SiO_2$/Si and $SiO_2$/Si substrates by DC reactive sputtering at 450℃ and annealed at temperatures ranging from 550℃ to 750℃ for 30 min in $O_2$ ambient to improve the crystallinity of films and to reduce their resistivity. PZT thin films with 150nm thickness were then deposited on the LSCO and LNCO electrodes using DC reactive sputtering at the substrate temperature of 500℃ and 550℃. PZT films grown on LSCO and LNCO showed highly (001) preferred orientation and had uniform matrix of densely packed round grains. The leakage current density remained on the order of $10^{-7}~10^{-9}A/㎠$ at the applied voltage below 5V. PZT thin films on LSCO/Pt showed a remanent polarization(2Pr) of about 46~52㎛/㎠, and a coercive voltage of about 1 V. PZT capacitor grown on LNCO/Pt electrodes showed a lower coercive voltage(＜0.6V) and a smaller remanent polarization(2Pr) of about 28.8~32μC/㎠ and excellent Ⅰ-Ⅴ characteristics($10^{-8}A/㎠$) compare...