Characteristic of sputtered La$_{0.5}$Sr$_{0.5}CoO_3$ oxide electrode thin film for FRAM and ferroelectric ceramics

Abstract

This study has two parts. First part is for upgrading of electrode material and deposition method in the mass production of the nonvolatile memory(FRAM). There are several deposition methods(sputtering, PLD, CVD). However, for large size deposition(larger than 3-inch wafer), the sputtering method is more suitable. In previously reported studies, almost LSCO thin film electrodes were deposited by PLD(Pulsed Laser Deposition) just for study. To improve the experimental method of LSCO thin film electrode for application, this study has been undergone. Also, it is very important to get a lower resistivity than 500μΩcm for the application. To get a lower resistivity thin film, the stoichiometry of LSCO thin film is main key. So, in this study, I have tried to make a good stoichiometry $La_{0.5}Sr_{0.5}CoO_3(LSCO)$ electrode with a LSCO sputtering target having an excess Co or Sr. Also, it is very important to reduce the current density of capacitor because it has a large consumption of power. However, previously reported LSCO electrode capacitor has a high current density $(~10^{-3}A/cm^2 at 250kV/cm)$. One aspect of this study is to reduce the current density by upgrading the experimental process. For the MEMS(micro electromechanical systems) application, a good buffer layer is need. Because general dielectric buffer layer has a low contact between the ferroelectric layer and electrode, a good lattice match buffer layer should be needed to increase the contact. This LSCO thin film, it is well matched as buffer layer. So, I tried to deposited LSCO with 5nm thickness on $Pt(111)/TiO_2/SiO_2/Si(100)$ and studied for the possibility as buffer layer. Having this purpose in the LSCO thin film study, I have improved the good stoichiometric LSCO thin film electrode having a 300μΩcm on $SiO_2/Si(100)$ substrate using the rf sputtering method with 3inch sputtering target. In case of MgO substrate, I got a LSCO thin film having a near 100μΩcm. Also, using a 3inch sputt...