Sun-Oo Kim

Anisotropic tuning behavior in epitaxial Ba0.5Sr0.5TiO3 thin films

The tuning properties of epitaxial Ba0.5Sr0.5TiO3 (BST) thin films were investigated by a scanning microwave microscope (SMM) and an LCR meter. Although the BST films on LaAlO3 and MgO substrates showed similar tuning behavior when measured by the LCR meter at 1 MHz, remarkably different tuning properties were observed in the planar capacitors measured by SMM. The BST films on LaAlO3 substrates were hardly tuned when measured by SMM, while the BST films on MgO showed significant tuning behavior between the electrodes. We attribute these different tuning properties to the anisotropic tuning caused by the strain in BST films. This will enable the design of much improved tunable devices while minimizing the loss associated with the dielectric.

Fabrication of n‐metal–oxide semiconductor field effect transistor with Ta2O5 gate oxide prepared by plasma enhanced metalorganic chemical vapor deposition

n‐metal–oxide semiconductor field effect transistors (MOSFETs) were fabricated with plasma enhanced metalorganic chemical vapor deposited Ta2O5 gate oxide on Czochralski grown Si wafers using localized oxidation of silicon isolation technology by the conventional Si‐based process. The Ta2O5 gate oxide n‐MOSFETs showed excellent electrical characteristics such as subthreshold swing of 68–74 mV/dec, transconductance of 4 μS/μm for 4 μm gate length, and carrier mobility of 400 cm2/V s at the saturation region. The large Cox of the gate oxide with the high dielectric constant, er=20–25, allowed the higher drain current of the device. During the whole process of n‐MOSFET fabrication, the cross sectional transmission electron microscopy analysis of the Ta2O5/Si interface showed SiO2 interfacial oxide formation of about 35 A thick. The Ta2O5 gate oxide n‐MOSFET showed good performance compared to the high‐temperature silicon oxide gate devices and thus has great potential for applications in the electronic devices.

Host cell proteins binding to the encapsidation signal epsilon in hepatitis B virus RNA.

Summary. The highly conserved encapsidation signal (ɛ) of hepatitis B viral (HBV) pregenomic RNA has been reported as an essential component for encapsidation and protein priming of HBV polymerase. Here, we report that two HBV ɛ RNA-binding host proteins (80 and 43 kDa) and a copurifying protein (100 kDa) were purified and characterized by the combined methods of UV cross-linking analysis with the ɛ RNA and column chromatography. Amino-terminal micro-sequencing showed that 80- and 43-kDa proteins were identified as the heterodimeric nuclear factor of activated T cells (NF90/NF45) and 100 kDa as a molecular chaperone, the GRP94. The heterodimeric factor interacted preferentially with the upper-bulge region of HBV ɛ RNA helping the HBV polymerase bind the lower-bulge region. Using in vitro protein priming analysis, the initial oligonucleotide of the protein-priming product was deduced as 5′-GAAC-3′, which is the complementary sequence of both regions of DR1 and ɛ in the pregenomic RNA. Previously, we also proposed that the GRP94 was associated with HBV polymerase in the human liver cell HepG2. These results suggest that the heterodimeric factor plays an important role in the priming activity of HBV polymerase.

The effect of substrate temperature on the composition and growth of tantalum oxide thin films deposited by plasma-enhanced chemical vapour deposition

Tantalum oxide (Ta2O5) thin films were deposited on silicon substrates by plasma-enhanced chemical vapour deposition using tantalum ethylate (Ta(C2H5O)5) and nitrous oxide (N2O). The growth rate of the tantalum oxide thin films showed Arrhenius behaviour and the apparent activation energy was 3.75 kcal mol−1. The composition of tantalum oxide, determined from Rutherford backscattering spectroscopy and X-ray photoelectron spectroscopy analyses, showed a dependence on the substrate temperature. The refractive index of the tantalum oxide thin films measured by ellipsometry showed a strong relation to the composition of thin films, However, the growth rate and composition of the thin films were somewhat independent of the r.f. input power. The deposition behaviour of tantalum oxide films was regarded as the competitive reaction between the tantalum-containing species and oxidant species on the silicon substrate surface. The structure of the deposited films was amorphous, but it changed to a polycrystalline structure after annealing at 900°C in a N2 ambient. The electrical properties of the deposited films were also characterized by capacitance-voltage and current-voltage characteristics.

The effects of substrate and annealing ambient on the electrical properties of Ta2O5 thin films prepared by plasma enhanced chemical vapor deposition

Abstract Ta 2 O 5 thin films were deposited onto p-Si, n + -Si, RTN (rapid thermal nitridation) nitride and HSG (hemispherical grain) Si substrates by plasma enhanced chemical vapor depostion (PECVD). The physical and electrical properties were characterized after annealing in the temperature range 600–900°C in N 2 or O 2 ambient. Fourier transform IR analysis revealed that an interfacial oxide which affected the electrical properties of Ta 2 O 5 thin film was formed at the Ta 2 O 5 -Si interface during annealing above 800°C. The electrical properties of the Ta 2 O 5 thin film were strongly dependent on annealing conditions. The Ta 2 O 5 thin films showed 1.5 times higher capacitance, but higher leakage current owing to the edge effect, on the enlarged surface area of HSG Si than on the flat p-Si or n + -poly Si. RTN treatment of Ta 2 O 5 thin films on the Si substrate reduced the leakage current without loss of the high dielectric constant.

Expression of stable hepatitis B viral polymerase associated with GRP94 in E. coli.

Summary. We here presented evidence that a 94-kDa glucose-regulated protein (GRP94) was associated with hepatitis B viral (HBV) polymerase in the human liver cell HepG2 and this association could be applied even in Escherichia coli. We investigated the role of GRP94 in the expression and stabilization of HBV polymerase in Escherichia coli by coexpression of the two proteins. The affinity column-purified glutathione S-transferase-tagged HBV polymerase (GST-P, 130 kDa) showed a proper molecular size and reverse transcriptase activity on several exogenous templates and was sensitive to specific inhibitors. The GST-P was associated with the maltose-binding protein-tagged GRP94 (MBP-GRP94, 130 kDa) using analyses by an affinity chromatography, native gel electrophoresis and glycerol gradient centrifugation. However, nondenaturing and partially denaturing activity gel analyses showed two active bands of ∼260 kDa and ∼130 kDa, respectively. Furthermore, in the presence of the encapsidation signal RNA template (HBV ɛ RNA), the ∼260-kDa active band was gradually converted to ∼130 kDa, which implies that HBV polymerase was dissociated from the chaperone GRP94 and bound preferentially to the HBV ɛ RNA. These results suggested that the chaperone GRP94 was necessary for the stabilization and production of HBV polymerase as an active form.

Formation of low pressure chemically vapour deposited W thin film on silicon dioxide for gate electrode application

Abstract We have investigated the feasibility that low pressure chemically vapour deposited W can be used as a gate electrode material of metal-oxide-semiconductor (MOS) field effect transistors. We improved adhesion of the W film to SiO2 by using a pulsing injection of source gas. The pulsing injection of the reactant gas enhancesthe desorption of byproduct gases from the surface of the growing film and thus more W nuclei formed on SiO2. Tungsten thin films were deposited on the SiO2/Si with a deposition rate of 1000–2000 A min-1. The deposition was carried out at various temperatures of 300–750 °C and various SiH4:WF6 ratios of 0.6–1.5. The higher adhesion strength and resistivity of W thin films were achieved at the higher SiH4:WF6 ratio and higher deposition temperature. X-ray diffraction analysis showed that the crystal structure of all W films, deposited at various temperatures, was α-W in spite of either high reactant gas ratio or high temperature. Since W thin films had good adhesion to SiO2, MOS structure capacitors were fabricated with a W electrode via wet chemical processes and their electrical properties were also characterized. The extreme value distribution function of dielectric breakdown strength indicates that the thin SiO2 layer was significantly degraded by the diffused F ions. However, the stacked gate dielectric of SiO2 and Si3N4 layers instead of the single SiO2 layer was not degraded by the W gate electrode, since the Si3N4 layer protected SiO2 from chemical attack or restricted the F diffusion during deposition of the W gate electrode.

Comparison of ultrathin SiO2 films grown by thermal oxidation in an N2O ambient with those in a 33% O2/N2 ambient

An N2O ambient allowed the oxidation rate to be substantially low while forming an oxynitride layer at the early stage of oxidation, and also provided nitrogen atoms to the oxide film during further oxidation. Both the formation of an oxynitride layer in the interface of SiO2 and Si substrate and a nitrogen incorporation in the grown oxide film were determined by wet chemical etching and x‐ray photoelectron spectroscopy analysis of the grown oxide film. The electrical properties of the N2O oxide films were determined and compared with those of the oxide films grown in a pure or 33% O2/N2 ambient. The superiority in electrical properties appeared to be caused by the formation of the oxynitride layer in the interface of SiO2 and Si substrate.

Electrical properties of the p+-gate electrode of an a-Si/poly-Si double layer

Abstract The single and mixed p + -gate electrodes of a-Si and poly-Si layers were fabricated and analyzed by cross-sectional transmission electron microscopy, Raman, X-ray diffraction, secondary ion mass spectrometry and electrical measurements. The as-deposited a-Si layer, which transformed to a large grain polycrystalline structure during annealing, showed lower resistivity and less gate electrode-induced strain than the single poly-Si layer. The interface in the mixed layer of a-Si and poly-Si layers showed a discontinuity of grains of upper and lower layers. The mixed electrode layers on 80 A thick N 2 O oxide were implanted with BF 2 + at 30 keV and annealed at 900 °C to fabricate p + -gate MIS capacitors. The high frequency and quasi-static C - V measurements of the MIS capacitors showed the formation of a shallow p + -n junction in the Si substrate of MIS capacitors, caused by B and F atoms penetrating into the Si substrate through the ultrathin N 2 O gate oxide during annealing. However, the mixed layer including the a-Si layer partially restricted B penetration into the Si substrate during furnace annealing, and thus MIS capacitors with the mixed layer had better electrical properties, such as time dependent dielectric breakdown and charge trapping, than those with the single poly-Si electrode structure. This might be due to less B penetration into the oxide layer and relaxation of residual stress in gate electrodes owing to phase transformation of a-Si to poly-Si.