Suk Pil Kim

Auger spectroscopy and properties of Ir(Pt)/PZT(PZT/PT)/Ir nanosized thin-film structures

Studies of the elemental distribution profiles through the thickness of thin-film ferroelectric capacitor structures using Auger spectroscopy made it possible to establish the relation between the elemental and phase composition of the structures, on the one hand, and their electrophysical properties, on the other. Special features were observed in the behavior of the lead titanate underlayer both in the as-fabricated and aged structures. It is shown that the variation in the characteristics of the capacitor structures during aging is caused by diffusion of the elements at the interfaces and in the PZT film against a background of a significant increase in the oxygen concentration. As a result, interface-modifying oxide layers form and the trap density on the upper and lower interfaces decreases in all samples.

Linear astigmatism of confocal off-axis reflective imaging systems and its elimination

Linear astigmatism of a confocal off-axis reflective imaging system when the object plane is tilted and located at a finite distance from the imaging system is derived. We show that linear astigmatism can be eliminated by proper configuration of the parent mirror axes in confocal off-axis two-mirror systems. The tilt angle of the image plane is also derived. The developed theory is verified by ray-tracing analysis of an example system.

Preparation of Pb(ZrxTi1 - x)O3 Films on Trench Structure for High-Density Ferroelectric Random Access Memory

The growth characteristics of Pb(ZrxTi1 - x)O3 thin films on three-dimensional (3D) electrodes were investigated for the application to high-density ferroelectric random access memory (FeRAM) devices. PZT films have been grown on Ir coated trench structures having aspect ratio of 1.2 by liquid delivery-metal organic chemical vapor deposition (LD-MOCVD). Atomic layer deposited (ALD) Ir electrode showed good step coverage and electrical properties. MOCVD PZT films showed step coverage of 90% at the deposition temperature of 500°C, while it is decreased to 63% at 550°C. Compositional non-uniformity of PZT along the sidewall was greatly affected by the types of the metal organic sources.

Comparison of Retention Characteristics of Pb(Zr,Ti)O3 (PZT) Capacitors Fabricated with Noble Metal Electrodes and Their Oxide Electrodes

We compared retention characteristics of Pb(Zr,Ti)O3 (PZT) capacitors with either noble metal electrodes or their oxide compounds. Very thin PZT films with thickness below 100 nm were deposited by metal-organic chemical vapor deposition (MOCVD) on Ir bottom electrodes, and Pt, Ir, IrO2 were covered as top electrodes thereon. The capacitors with IrO2 top electrodes had the better opposite-state retention performance than those with Pt, Ir top electrodes. Inserting IrO2 top electrode affected the alleviation of the size effect more in the aged capacitors than in the virgin capacitors. In addition, we also discuss problems of using IrO2 as a bottom electrode in our PZT capacitors.

INVESTIGATION OF Sr-Ru-O/Ru MULTILAYER-ELECTRODES PREPARED BY MOCVD

ABSTRACT We proposed tailored metal organic chemical vapor deposition (MOCVD)-SrRuO3/Ru electrode for 3D ferroelectric capacitors to prevent the Ru diffusion to Pb(Zr,Ti)O3 [PZT] together with the formation of coherent interfaces with PZT due to the same perovskite structure. The effects of the Sr/(Sr+Ru) ratio on the crystallinity, surface roughness and the electrical properties of PZT films prepared on Sr-Ru-O/Ru bottom electrodes were investigated together with those of Sr-Ru-O layers prepared on Ru. PZT films prepared on Sr-Ru-O layers with the Sr/(Sr+Ru) ratio (x) of x = 0.50 showed the lower leakage current density and the larger remanent polarization than those with x = 0.30 and 0.60.

TRIAL FOR MAKING THREE DIMENSIONAL PZT CAPACITOR FOR HIGH DENSITY FERROELECTRIC RANDOM ACCESS MEMORY

ABSTRACT Three dimensional capacitors of Pb(Zr,Ti)O3 [PZT] together with the Ru electrodes were tried to deposit by metal organic chemical vapor deposition for realizing high density ferroelectric random access memory (FeRAM). Good conformability was obtained for both of CVD-Ru and PZT layers on the trenched substrates by optimizing the deposition conditions. In addition, PZT films deposited on Ru bottom electrode showed the good compositional conformability. Finally we demonstrated the Ru/PZT/Ru three dimensional capacitor. These data accelerate the development of three dimensional PZT capacitors.

Enhancement of Ferroelectric Properties of Pb(Zr,Ti)O3 Films Grown by Metal-Organic Chemical Vapor Deposition on Noble-Alloy Bottom Electrodes

Pb(Zr,Ti)O3 (PZT) films grown on Ir electrodes by a metal-organic chemical vapor deposition (MOCVD) have suffered from high leakage and rough surface. We sputtered Pt and Ir simultaneously onto Ti/SiO2/Si substrates and formed Ir-Pt alloy bottom electrodes with various compositions. With an optimal composition of Ir and Pt, PZT films grown by MOCVD on this substrate showed smoother surface and suppressed leakage via the bottom interface. At the specific composition of Ir and Pt, two different phases seemed to be acquired. They constituted the electrodes and affected the PZT grain nucleation independently so that the grains with different origins grew and restrained the vicinal grains, and finally soothed the faceted-grain-formation. No fatigue was observed even in PZT on Ir-Pt alloy with much Pt content.

A method of determining the charge trapped at the interfaces of a metal/ferroelectric/metal thin-film structure

A method is developed for determining the trap density at the metal/ferroelectric interfaces in a completely depleted ferroelectric film with two Schottky barriers. The method is based on the recharging of traps induced by an external pulsed bias. The ranges of the bias fields and of the parameters of the metal/ferro-electric/metal structure for which analytical solution of the Poisson equation is possible are found. Using this method and measurements of the transient current, the density of the charge trapped at the upper and lower interfaces of Pt(Ir)/PZT/Ir(Ti/SiO2/Si) capacitors is determined. The interface charge as estimated from the trap density proved to be much smaller than the residual polarization of the PZT film. The observed correlation between the symmetry of the interface trap charges and the symmetry of the hysteresis loops and switching currents indicates the reliability of the estimation of the trap density determined using the proposed method.