Yong Jun Park

Fabrication of 3D trench PZT capacitors for 256Mbit FRAM device application

We fabricated trench PbZrxTi1-xO3 (PZT) capacitors that can be used in 256Mbit 1T-1C FRAM devices. The capacitor has 0.25mum diameter and 0.4mum depth. Three layers, Ir(20nm)/PZT(60nm)/Ir(20nm), were deposited in SiO2 trench holes by ALD and MOCVD. Both columnar and granular grains were formed on the sidewalls of the trench capacitors, and their relative portion had strong size dependence. The trench capacitors with more columnar PZT grains showed good switching behavior under 2.1V external bias and 19 to 24 muC/cm2 remnant polarization

Wafer-scale arrays of epitaxial ferroelectric nanodiscs and nanorings

Wafer-scale arrays of well-ordered Pb(Zr(0.2)Ti(0.8))O3 nanodiscs and nanorings were fabricated on the entire area (10 mm x 10 mm) of the SrRuO3 bottom electrode on an SrTiO3 single-crystal substrate using the laser interference lithography (LIL) process combined with pulsed laser deposition. The shape and size of the nanostructures were controlled by the amount of PZT deposited through the patterned holes and the temperature of the post-crystallization steps. X-ray diffraction and transmission electron microscopy confirmed that (001)-oriented PZT nanostructures were grown epitaxially on the SrRuO3(001) bottom electrode layer covering the (001)-oriented single-crystal substrate. The domain structures of PZT nano-islands were characterized by reciprocal space mapping using synchrotron x-ray radiation. Ferroelectric properties of each PZT nanostructure were characterized by scanning force microscopy in the piezoresponse mode.

Correlation between glaze-colors and structural properties of the HIZEN celadons produced in the Edo period of Japan, by means of X-ray diffraction (І)

HIZEN celadons produced at Arita and Imari areas in Japan from 1630s to 1790s (Edo period) have been investigated by means of X-ray fluorescence analysis, and X-ray diffraction and X-ray absorption spectra using synchrotron radiation. It is found that, in the HIZEN celadons, the color brightness of the celadon glazes depends on the structural property of the raw basic ceramics taken at Imaizumi (Arita) and Ohkwachi (Imari), where the former is mainly Quartz-SiO2, and the later is Sanidine ((K,Na)Si3O8). It is confirmed that CaCO3 of natural wood ash added artificially into the raw celadon ceramics makes a glassy glaze on the surface of the basic body of the HIZEN celadons. Transition-metal ions (Cr, Cu, Zn) of very small amount are detected in the celadon glazes, in addition to Fe and Mn of small amount. It is considered that Cu and Cr are related to the color brightness of green-brown and blue-green in the HIZEN celadon glazes, respectively.

Domain structures and piezoelectric properties of Pb(Zr0.2Ti0.8)O3 nanocapacitors

Epitaxial ferroelectric Pb(Zr0.2Ti0.8)O3 (PZT) nanoislands and nanocapacitors were fabricated by stencil mask-assisted pulsed laser deposition. By x-ray diffraction reciprocal space mapping it was observed that PZT nanoislands contain mainly c-domains and residual fractions of tilted and nontilted a-domains, while extended thin films contain only c-domains and tilted a-domains. The presence of nontilted a-domains manifests clearly that the misfit strain is significantly reduced in PZT nanoislands, compared to the thin film. Some of the a-domains turned out to be switchable under an external electric field due to the strain relaxation in the PZT nanocapacitors. The piezoresponse of PZT nanocapacitors was higher than that of continuous thin-film capacitors.

Incommensurate cooperative tilting modes of MnF6 octahedra relatedto the structural phasetransitions in BaMnF4

Abstract The structural phase transitions of the layer compound BaMnF4 were studied by high-resolution X-ray diffraction using synchrotron radiation. The intensities and profiles of two kinds of superlattice reflections having incommensurate reduced wave vectors q 1= (∼ ± 1/5,0,0) p and q 2 =(∼ ± 2/5,1/2,1/2)p, respectively, were measured as a function of temperature from 25 K to 280 K. These temperature dependencies show that incommensurate structural phase transitions of second order occur at 234 K and 244 K. These structural phase transitions are interpreted as successive condensations of a folding-screen-like incommensurate plane-distortion mode and a commensurate anti-ferro-distortive tilting mode of the MnF6 octahedra around the primitive a0 - and b0 -axes, when cooled down. It is also found that there is another structural phase transition at about 45 K related to a precursor structural distortion for the antiferromagnetic transition occurring at about 26 K.

Pulsed laser deposition of Pb(Zr0.52Ti0.48)O3 thin film on cobalt ferrite nano-seed layered Pt(111)/Si substrate: effect of oxygen pressure

The effect of oxygen pressure during pulsed laser deposition of Pb(Zr0.52Ti0.48)O3 (PZT) thin films on CoFe2O4 nano-seed layered Pt(111)/Si substrate was investigated. The PZT film deposited at oxygen pressure lower than 25 mTorr is identified as both perovskite and pyrochlore phases and the films deposited at high oxygen pressure (50-100 mTorr) show the single-phase perovskite PZT that has a perfect (111)-orientation. In addition, the film deposited at PO2 of 50 mTorr has a uniform surface morphology, whereas the film deposited at PO2 of 100 mTorr has a non-uniform surface morphology and more incompacted columnar cross-section microstructure. The polarization of film deposited at 100 mTorr is higher than that deposited at 50 mTorr, but shift of the hysteresis loop along the electrical field axis in the film deposited at PO2 of 100 mTorr is larger than that of the film deposited at PO2 of 50 mTorr.

Characterization of 3D Trench PZT Capacitors for High Density FRAM Devices by Synchrotron X‐ray Micro‐diffraction

3D trench PbZrxTi1−xO3 (PZT) capacitors for 256 Mbit 1T‐1C FRAM devices were characterized by synchrotron X‐ray micro‐diffraction at Pohang Light Source. Three layes, Ir/PZT/Ir were deposited on SiO2 trench holes with different widths ranging from 180 nm to 810 nm and 400 nm in depth by ALD and MOCVD. Each hole is separated from neighboring holes by 200 nm. The cross sectional TEM analysis for the trenches revealed that the PZT layers were consisted of columnar grains at the trench entrance and changes to polycrystalline granular grains at the lower part of the trench. The transition from columnar to granular grains was dependent on the trench size. The smaller trenches were favorable to granular grain formation. High resolution synchrotron X‐ray diffraction analysis was performed to determine the crystal structure of each region. The beam was focused to about 500 μm and the diffraction patterns were obtained from a single trench. Only the peaks corresponding to ferroelectric tetragonal phases are observe...

Domain Structure in Ferroelectric PbTiO 3 Nano-islands

Evolution of complex ferroelastic domain structures of PbTiO3 nano-islands grown epitaxially on Pt(001)/MgO(001) single crystal substrate by chemical solution deposition has been investigated by two-dimensional reciprocal space mapping technique using synchrotron X-ray diffraction. With decreasing lateral size and thickness of the nano-islands, the proportion of c-domains increased continuously and fully c-domain dominant structure was emerged. At the same time, some of a-domains in the twinned a/c/a/c type structure turned into the a-domains with defective domain boundaries aligned normal to the substrate plane. The relative proportions of two types of a-domains were also dependent on the lateral size of nano-islands. The smaller islands favored the aligned a-domains with defective domain boundaries, which seem to be due to extensive relaxation of confining strain imposed by the substrate.

Characterization of Nanoscale Domain Structures in Epitaxial Ferroelectric PbTiO3 Capacitors by Reciprocal Space Mapping

In order to test a critical lateral dimension in two dimensional (2D) planar ferroelectric, epitaxial PbTiO3 discrete islands were fabricated by both lithography process and chemical solution deposition process with different lateral size. The evolution of 90° domain structures as a function of film thickness and lateral dimensions was characterized extensively by reciprocal space mapping using the Huber six‐circle diffractometer of the synchrotron x‐ray diffraction beam line at Pohang Light Source. This method is useful for considering a reciprocal lattice point that is tilted out of the growth plane and has many advantages for the investigation of imperfect heterostructures. As the pattern size decreases in micron scale, the substrate clamping effects is significantly reduced and thus the misfit strain in the films could be relaxed further. As the lateral size of patterns decreases to about 100 nm by e‐beam lithography, the quite different domain structures were observed especially in the strain distrib...