Solid State Phenomena Vols. 124-126

Abstract: We have studied thermo-electrical properties for Ni-based germanosilicide to understand the influence of temperature on the evolution of sheet resistance and micro-structures of contacts on heavily-doped SiGe grown by reduced pressure chemical vapor deposition. After the deposition of Ni, Ni/Ti, Ni/Pt films on Si0.83Ge0.17 epi layer and subsequently annealing for silicide reaction, we analyzed sheet resistance, surface roughness and reaction interfaces using four point probe method, scanning probe micrograph and transmission electron microscope. Bi-layer metal structures of Ni/Ti and Ni/Pt were investigated to study feasible use for suppressing inappropriate reaction at interface. It is found that bi-layer structure with thin Pt interlayer presented promising properties for germanosilicide of n+-Si0.83Ge0.17 with low sheet resistance, smooth surface morphology and high temperature stability up to 800 oC.

Abstract: On nontextured substrates, YBCO superconducting thick films were fabricated using a simple screen-printing method, from Cu-free powders (Y2O3 and BaCO3). However, the films have poor superconducting properties, such as the critical current density, Jc value due to the random orientation of the films. In this work, we investigate the influence of substrate texture on superconducting properties of the film. The films screen-printed on the nontextured and textured Cu substrates were heat-treated by 2-step procedure in air (980 °C 10 sec + 930 °C 90 sec) followed by oxygen annealing at 450 °C for 1 hr. We speculate that Cu ions diffusion from the textured Cu substrates is still faster than Cu ions diffusion from the nontextured Cu substrates that CuO formed excessively in the film deteriorates superconducting properties of the YBCO film.

Abstract: The nano-CeO2 was synthesized by two-step solid-phase reaction. The image of TEM showed that nano-CeO2 with an average size of about 70 nm. The series of polyaniline/nano-CeO2 composites with different PANi: CeO2 ratios were prepared by in-situ polymerization in the presence of hydrochloric acid (HCl) as dopant by adding nano-CeO2 into the polymerization reaction mixture of aniline. The composites obtained were characterized by FT-IR and UV-vis spectroscopy analysis. The FT-IR spectra of nanocomposites indicate different blue-shifts, attributed to C–N stretching mode for benzenoid unit. The UV-vis spectra of nanocomposites display einstein-shifts compared with PANi at 620nm. The conductivity properties of the composites are also changed compare to the pure PANi. These results suggest that the interactions between the polymer matrix and nanoparticles take place in polyaniline/nano- CeO2 composites.

Abstract: The etching in SiO2 is a crucial step in fabricating thin film transistor. For large area etching, high density plasma which independently controls ion energy and ion flux is preferable than conventional RIE etcher for its high etching capability. In an attempt to understand how the bias power of N-slot ICP affects the etching rate and uniformity, we study the correlation among bias power, inductive power, etching rate and uniformity. The results show that the etching rate is proportional to the bias power up to 800 W which has the best uniformity. Beyond that power, the etching rate enters the different slope and the uniformity become worse. This phenomenon might be attributed to the combined effects of resist etching and polymer film growth. For N-slot ICP system, high etching rate and good uniformity can be obtained only when the bias power is in the moderate range.

Abstract: Using a thermally-crosslinkable organosiloxane-based organic-inorganic hybrid material, solution-processable gate dielectric layer for organic thin-film transistors (OTFTs) have been fabricated. The hybrid dielectric was synthesized by the sol-gel process. The surface of the prepared dielectric was modified by self-assembled monolayers (SAMs) treatment using wet chemical method. Prior to surface modification, the chemical inertness of prepared dielectric was investigated by immersing into various solvents such as toluene, acetone, isopropyl alcohol, and DI-water. The existence of SAMs on the surface of dielectric was confirmed by measuring current density-electric field characteristics and it was observed that surface morphology of SAMs-treated hybrid dielectric was very smooth.

Abstract: Flexible piezoelectric polymer materials for smart apparel and wearable computer applications are of great interest. Among known ferroelectric and piezoelectric polymers, polyvinylidene fluoride (PVDF) exhibit β-phase under poling and is known to give highest piezo-, pyro-, and ferroelectric properties. Previous reports suggests that, during corona poling of the PVDF film, a high surface electric potential is generated resulting in a high internal electric field within the polymer film causing the polarization of the dipoles along the direction of the applied electric field. The resultant phase change from α- to β-phase and the dipole switching generates displacement of charges or piezoelectricity. And also mechanical variation would change dipole density of PVDF film. In this report, we measured human heartbeat signal from an DAQ interfaced with a custommade voltage-amplifier with specific frequency filtering function using the corona-poled PVDF film of various sizes and thickness as a piezoelectric sensor and analyzed it. We employed elastic textile band to sensor system for comfortable fit on wrist or ankle. And then, we found the feasibility of applying flexible PVDF film sensor to smart apparel application which can sense heartbeat rate, blood pressure, respiration rate, accidental external impact on human body, etc.

Abstract: In this paper, the surface crystalline morphology and piezoelectricity of P(VDF/TrFE)(72/28) copolymer ultrathin films were studied using different scanning probe microscopy (SPM) techniques. Atomic force microscopy (AFM) was used to study the changes in their crystalline morphology with varying temperature conditions. From electric force microscopy (EFM) studies, the change in dipole moment vectors along the applied field direction and the resultant change in amplitude image for '1 or 0' state were monitored and used to 'write/erase and read' the data on the memory bit. These results indicate the possibility of using SPM-based high density data storage with these copolymer ultrathin films.

Abstract: The dishing phenomena of soft materials in chemical mechanical polishing (CMP) process were problematic in delineating inlaid metal patterns. The inlaid copper structures were fabricated on Si wafer where SiO2 was thermally grown. Seed layer was deposited by thermal evaporate method followed by copper electrodeposition. Copper was electrodeposited with IBM paddle type electroplating machine to obtain uniform thickness of coating. The dishing amounts were measured at various current density and current type. The dishing amounts with pattern density and line width were also measured. The losses of copper were not sensitively dependent on current density however those were dependent on current type. The dishing amount of copper was decreased at high pattern density especially over 50% and increased with line width. Surface topology and grain size of coating were investigated with surface profilometer and FESEM.

Abstract: MWO4 (M = Ca, Sr, Ba and Pb) was solvothermally prepared using metallic nitrates and sodium tungstate in 25/5 volume ratios of glycerol/water (SGL) and propylene glycol/water (SPG) at 160 oC for 6 h. XRD revealed the presence of MWO4 single phase with tetragonal scheelite structure. The strong W-O stretching band of WO4 tetrahedrons was detected at 705-875 cm-1. The product images show nano-sized particles in basic SGL and SPG solvents and flower-like particles in SPG solvent with pH of 6.7. Central peaks of the luminescent spectra are 445, 446, 443 and 440 nm, respectively.