Jai-Hyun Kim

Brillouin Scattering Study on Polycrystalline Relaxor Ferroelectrics

Brillouin spectra of Pb(Yb1/2Nb1/2)O3(PYN)-based relaxor ferroelectric ceramics were measured using a conventional tandem Fabry-Perot interferometer. The measured spectra were composed of a strong elastic peak and a broad doublet with a sharp cutoff at the high-frequency side. The broad doublet was attributed to the distributed Brillouin shift of the longitudinal acoustic mode owing to the scattering events at all scattering angles from 0° to 180° which is due to multiple reflections and refractions. From the sharp high-frequency cutoff of this band, which corresponds to the largest Brillouin shift of the backward scattering geometry, the average longitudinal sound velocities were estimated to be 4.22–4.33 km/s for PYN-based relaxor ceramics. The present results imply that Brillouin spectroscopy can be used to derive elastic properties of not only single crystals but also ceramic samples in the gigahertz range, which will be very important for high-frequency applications.

Phase Transition Behavior of Sc-Substituted Pb(Yb 1/2 Nb 1/2 )O 3 Ceramics

The crystal structure and the dielectric properties of (1 m x )Pb(Yb 1/2 Nb 1/2 )O 3 m x Pb(Sc 1/2 Nb 1/2 )O 3 (PYN 1 m x PSN x ) (0 h x h 0.50) solid solution have been studied. According to the XRD study, the room temperature crystal structure of PYN 1 m x PSN x becomes pseudocubic from the PYNs orthothombic with increasing x . Also the diffraction line intensities ascribed respectively to the AFE lattice modulation and the B-site ordering become gradually weaker and they disappear altogether for x > 0.30. In the PYN-rich composition range (0 h x h 0.30), the paraelectric(PE)-antiferroelectric(AFE) phase transition occurs sharply and is independent of the applied frequency. However, on further increasing Sc concentration (0.30 < x h 0.50), the dielectric constant vs. temperature curve becomes gradually broader and begins to display the frequency-dependent relaxor behavior.

Robust Two-Dimensional Stack Capacitor Technologies for 64 Mbit One-Transistor–One-Capacitor Ferroelectric Random Access Memory

It is very important to develop capacitor module technologies such as robust Pb(ZrxTi1-x)O3 (PZT) film technology at nm scaled PZT thickness and damage minimized ferroelectric capacitor etching technology are crucial for the success of high density one-transistor–one-capacitor (1T1C) ferroelectric random access memory (FRAM). We resolved this issue from the change of the capacitor etching system and optimization of the PZT/SrRuO3 (SRO) deposition process. As a result, we realized a highly reliable sensing window for 64 Mbit 1T1C FRAM that were realized by novel technologies such as robust MOCVD PZT deposition technologies, optimized SRO electrode and damage minimized ferroelectric capacitor etching technologies.

Structural and Dielectric Behavior or Ba-Substituted Pb(Yb 1/2 Nb 1/2 )O 3 Ceramics

The crystal structure and the dielectric properties of the antiferroelectric solid solution of (1 m x )Pb(Yb 1/2 Nb 1/2 )O 3 m x Ba(Yb 1/2 Nb 1/2 )O 3 (Pb 1 m x Ba x YN) (0 h x h 0.30) have been studied. The crystal structure is shown to become pseudocubic from the PYNs orthorhombic structure on solutionizing for x >0.5 while the transition shows a normal first-order paraelectric(PE) - antiferroelectric(AFE) behavior increasing x < 0.14. The transition temperature gradually decreases with the increasing Ba 2+ concentration. In the composition range 0.16 x 0.30, a typical relaxor behavior is displayed.

X-Ray and Dielectric Studies of Sc-Substituted Pb(Yb 1/2 Nb 1/2 )O 3 Ceramics

The crystal structure and the dielectric properties of (1 m x )Pb(Yb 1/2 Nb 1/2 )O 3 m x Pb(Sc 1/2 Nb 1/2 )O 3 (PYN 1 m x PSN x ) (0 h x h 0.50) solid solution have been studied. According to our XRD study, the room temperatures crystal structure of PYN 1 m x PSN x becomes pseudocubic from the PYNs orthothombic with increasing x . Also the diffraction line intensities ascribed respectively to the AFE lattice modulation and the B-site ordering become gradually weaker and they disappear altogether for x > 0.30. In the PYN-rich composition range (0 h x h 0.30), the paraelectric(PE)-antiferroelectric(AFE) phase transition occurs sharply and is independent of the applied frequency. However, on further increasing Sc concentration (0.30 < x h 0.50), the dielectric constant vs . temperature curve becomes gradually broader and begins to display a frequency-dependent relaxor behavior.

Phase transition behaviors of (1–x)Pb(Yb1/2Nb1/2)O3–xBa(Yb1/2Nb1/2)O3 ceramics

The phase transition behaviors of (1-x)Pb(Yb1/2Nb1/2)O3-xBa(Yb1/2Nb1/2)O-3 (PBYN) solid solution system (0 less than or equal tox less than or equal to0.30) have been investigated by X-ray diffraction, permittivity and E-P hysteresis loop measurements. In the solid solution, for x less than or equal to0.10, the transition shows a normal first-order paraelectric (PE)-antiferroelectric (AFE) behavior and its AFE crystal structure is orthorhombic. The transition temperature gradually decreases with the increasing Ba2+ concentration. On the composition range 0.16 less than or equal tox less than or equal to0.30, a typical relaxor behavior is displayed. The low temperature crystal structure is pseudocubic in this composition range

A study of the dielectric properties and diffuse phase transition of the (1-x)Pb(Yb/sub 1/2/Nb/sub 1/2/)O/sub 3/-xPbZrO/sub 3/ binary system

The dielectric properties and the behavior of the phase transition in the (1-x) Pb(Yb/sub 1/2/Nb/sub 1/2/)O/sub 3/-xPbZrO/sub 3/ (0/spl les/x/spl les/0.6) ceramic system have been investigated. For 0/spl les/x/spl les/0.3, the phase transition is relatively sharp and the dielectric constant approximately follows the Curie-Weiss law above the transition temperature. Beyond x=0.4, the temperature dependence of dielectric constant becomes broadened and the transition temperature shifts toward the high temperature with an increase in the measuring frequency.

Hydrogen and Stress-Induced De-lamination in an IrO2 Layer of Ferroelectric Random Access Memories

During the device lifetime tests such as high temperature operational life (HTOL) and high temperature storage (HTS) tests, a physical de-lamination of the IrO2 layer in vertical conjunction to pulsed plate-line, so-called here additional top electrode (ATE), ATE has appeared and localized in specific cell arrays. This failure stems either from the reduction of IrO2 by the penetrated hydrogen at the interface between ATE Ir to top electrode (TE) Ir or from lack of dummy cells applied, or both. In the back end of line (BEOL), several heat treatments were introduced and then the reduction was reduced. It is essential to consider a deliberated anneal procedure in the BEOL integration. This is because otherwise case may provoke a contact failure in pulsed plate-line node of cell arrays. Also, we simulate stress distribution in cell arrays depending on how many dummy cells have been taken into account. The fluctuation of the stress projected on the IrO2 layer should be controlled uniformly by adding a certain number dummy cells.

Phase Transition Study on Degenerate Modes of Pb(Yb1/2Nb1/2)O3 and Pb(Yb1/2Ta1/2)O3

Pb(Yb1/2Nb1/2)O3 [PYN] and Pb(Yb1/2Ta1/2)O3 [PYT] are highly ordered enough to be a prototype for spectroscopic studies of complex lead-based perovskite compounds Pb(B′, B″)O3 system. We find out changes in the numbers of vibrational mode at each phase by Raman scattering. PYN based antiferroelectrics have the modes with the triple degeneracy. It may originate from antiparallel arrangements of cations and the accompanied octahedral tilting. PYT systems display an additional degeneracy as lowering a temperature. These results implicate Raman spectroscopy is more efficient than other methods for characterizing phases of PYN and PYT.

X-Ray and Dielectric Studies of Fe and Nb-Substituted Pb(Mg 1/2 W 1/2 )O 3 Ceramics

The crystal structure and dielectric properties of (1-x)Pb(Mg 1/2 W 1/2 )O 3 -xPb(Fe 1/2 Nb 1/2 )O 3 (PMW 1-x PFN x ) (0≤ x ≤ 0.3) solid solution have been studied by X-Ray diffraction and dielectric property measurements. On increasing PFN substitutions up to x = 0.14, the crystal structure changes from the cubic to the orthothombic at a sharp phase transition of the paraelectric(PE)-antiferroelectric(AFE) type that is independent of applied frequency. However, on further increasing PFN substitution(0.16 ≤ x ≤ 0.30), the dielectric constant curve as a function of temperature becomes gradually broader and the apparent transition becomes frequency-dependent while the crystal structure changes to the pseudocubic.