Bi-Shiou Chiou

Catalytic and Gas Sensing Characteristics in Pd‐Doped SnO2

A tin oxide based ceramic doped with ThO{sub 2}, MgO, and PdCl{sub 2} is developed to detect the CO gas. The sensitivity of gas sensing is measured with respect to the relative resistance change in the ceramic matrix upon the introduction of the CO gas. Intermediate operating temperature is required for the gas sensing and high sensitivity is observed at 300{degrees}C. Metallic Pd is present in the sensing matrix after mixing in ethyl, while PdO shows up after sintering at 800{degrees}C. The presence of PdO enhances the CO gas sensitivity and the response rate. However, PdO tends to be transformed to Pd in the sensing process, which leads to the deterioration in the sensitivity. A post-oxidation treatment at 600{degrees}C proves to be effective in retaining PdO and high sensitivity without degradation can be obtained. A model in the gas sensing process is proposed.

Dielectric tunability of barium strontium titanate/silicone-rubber composite

The dielectric tunability, which is defined as the percentage change of the permittivity under DC biasing, is over 30% for polycrystalline barium strontium titanate (BST) under a field of at around the Curie peak. Various volume fractions (18%, 40%, 52%, and 64%) of BST powder are mixed with silicone rubber to obtain a multi-phase dielectric composite. The effective permittivity of the composite follows the Maxwell-Garnett relation with a shape parameter of about 14 for volume fractions below 52%. The dielectric tunabilities at for the samples made with 52% and 64% powder are about 0.7% and 7.4%, respectively. The results are compared to the dielectric tunabilities obtained on the basis of series, parallel, and logarithmic models. It is suggested that the dielectric tunability is enhanced when a sample with a more continuous BST powder phase is obtained. An increase of the permittivity with a small DC field applied to the composite is attributed to the effect of polarization of the interface between the BST and silicone-rubber phases.

The effect of substrate surface roughness on the wettability of Sn-Bi solders

The effect of substrate surface roughness on the wettability of Sn-Bi solders is investigated by the eutectic Sn-Bi alloy on Cu/Al2O3 substrates at 190 °C. To engineer the surface with different roughnesses, the Cu-side of the substrates is polished with sandpaper with abrasive number 100, 240, 400, 600, 800, 1200, and 1 μm alumina powder, respectively. Both dynamic and static contact angles of the solder drops are studied by the real-time image in a dynamic contact angle analyzer system (FTA200). During dynamic wetting, the wetting velocity of the solder drop decreases for the rougher surface. However, the time to reach the static contact angle seems to be identical with different substrate surface roughness. The wetting tip of the solder cap exhibits a waveform on the rough surface, indicating that the liquid drop tends to flow along the valley. As the solder drops reach a static state, the static contact angle increases with the substrate surface roughness. This demonstrates that the wettability of solders degrades as the substrates become rough.

Antireflective coating for ITO films deposited on glass substrate

The refractive index n of radio-frequency (r.f.) magnetron sputtered indium tin oxide (ITO) films varies with sputtering parameters, such as sputtering power and oxygen percentage in the sputtering ambient. In this study, the feasibility to fabricate multilayer antireflective (AR) coating with a single ITO target by controlling the sputtering conditions is explored. Reduction in the reflectance can be achieved by using a one-quarter-wavelength inner layer ITO with a refractive index n = 1.87 and a one-quarter-wavelength outer layer ITO with n = 2.17. Hence, a single ITO target suffices in the preparation of multilayer AR coating. This simplifies the deposition processes and equipment for the fabrication of AR coating. Surface corrugation, another approach to the reduction of reflectance, is also discussed.

Thermal cycling test in Sn-Bi and Sn-Bi-Cu solder joints

The eutectic SnBi solder alloy is a candidate for Pb-free replacement of the conventional eutectic SnPb solders. This study presents series of results on the binary eutectic SnBi and ternary SnBi-1 wt % Cu a solder joints. Compositional analysis and wettability of the as-fabricated solder alloys are reported. In addition, microstructure, adhesion strength, fracture surface and contact resistance of the solder joints are also evaluated. The results of the wetting balance show that the addition of 1 wt % Cu has little effect on the contact angle of the eutectic SnBi solder alloy with various metallization layers. The adhesion strength of solder joints degrades abruptly after 2000 thermal cycles. In addition, thermal cycling would result in cracking in the solder joints, which is due to the mismatch in thermal expansion coefficients. Portions of the thermal fatigue cracks nucleate at the edge of the solder fillet, and then propagate along the solder/conductor interface. Some cracks are, however, through the Al2O3 substrate. The contact resistance of the solder/Cu joint does not increase after thermal cycling since the resistivity of Cu6Sn5 is lower than that of the solder. The solder joints of 42Sn-58Bi/Cu, SnBi-1Cu/Cu, 42Sn-58Bi/PtAg, and SnBi-1Cu/PtAg assemblies maintain their integrity after 2000 thermal cycles since the increase in contact resistance is rather small (ΔR<0.5 mΩ).

Preparation and cathodoluminescence of ZnO phosphor

Zinc oxide phosphors (ZnO:Zn) were prepared with solid state sintering of ZnO powders with ZnS and screen printed onto ITO-coated glass substrates to form a thin layer. Structural characterization carried out by X-ray diffraction (XRD) analysis suggests that the Zn atoms originated from the decomposition of ZnS, and diffuse to occupy the oxygen vacancies in the host lattice. Both lattice parameters a and c decrease slightly with the increase of ZnS content and/or firing temperature. The cathodoluminescent (CL) peak band varies with ZnS content and ranges from 494 to 508 nm, which is close to the green band of ZnO phosphor. Various mechanisms have been proposed in literatures to explain the origin of the green emission band. Among them, the presence of oxygen vacancies and trace ZnS residue are possible causes for the green emission in this study. CL spectra and CIE color loci suggest that ZnO:Zn phosphor with 5 wt.% ZnS can be used as a green primary for color picture tubes.

Admittance spectroscopy and trapping phenomena of ZnO based varistors

Electrical properties of ZnO varistors are investigated through admittance spectroscopy. The observed ac admittance dispersion is caused by the existence of two deep bulk trap levels, which are 0.31 eV and 0.245 eV, respectively, below the conduction band. The 0.31 eV level is associated with the oxygen vacancy while the origin of the 0.245 eV level is not yet clear. An equivalent circuit model for ZnO varistors is proposed that is based on the existence of deep bulk traps.

Microstructure characteristics for anorthite composite glass with nucleating agents of TiO2 under non-isothermal crystallization

Abstract The anorthite-based composite glass doped with TiO2 and B2O3 was prepared by quenching of molten droplets. Phase development and crystals microstructure of glass were investigated under non-isothermal conditions. A glass transition temperature of 770°C and an exothermal peak around 870°C in the DTA trace was associated with anorthite crystallization (CaAl2Si2O8). For glass specimens under nucleation and crystallization heat-treatment, the final predominant phase was identified as anorthite. Anorthite crystals show preferential nucleation at specific sites with rutile TiO2 crystals precipitated from the glassy matrix and anorthite crystallization is governed by heterogeneous volume nucleation. The introduced TiO2 plays the role of nucleating agents to reduce the crystallization temperature lower than 900°C for anorthite-based glass–ceramics. Chemical compositions could be related to the crystal microstructures on different characteristic regions. It was observed that the sintering aid of B2O3 neither reacted with nor dissolved in the anorthite or rutile TiO2 crystals, and remained a glassy phase in the matrix. Occurrence of acicular precipitations was attributed to the orientation growth of TiO2 crystals. Anorthite crystals were observed to grow with the forms of feathery-spherical particles, having a tendency to coalescence into a huge domain.

Low Temperature Radio-Frequency-Sputtered ( Ba , Sr ) TiO3 Films on Pt/TiN/Ti/Si Substrates with Various Oxygen/Argon Mixing Ratios

(Ba,Sr)TiO 3 (BST) films were fabricated on Pt/TiN/Ti/Si substrates by low temperature radio frequency magnetron cosputtering at 300°C. Material and electrical properties of BST films sputtered at low temperatures are significantly affected by the O 2 /(Ar + O 2 ) mixing ratio (OMR). Plasma emission spectra indicate that the deposition rate declines at a higher OMR due to oxide formation on the target surface. The dielectric constant of the BST films can reach a maximum of 364 at 5% OMR. The ten-year lifetime of the time-dependent dielectric breakdown implies that the reliability of the capacitor can be enhanced at a higher OMR due to compensation of oxygen vacancies and smaller grain sizes. Current-voltage analysis indicates that the leakage current of the Pt/BST/Pt capacitor is limited by Schottky emission (SE)/Poole-Frenkel emission (PF) at a lower/higher applied field. The applied field boundary between SE and PF shifts toward higher field as OMR increases. Moreover, an energy band model was proposed and this leakage mechanism was discussed.

Corrosion behaviour of electroless nickel plating modified TiN coating

Abstract TiN films were prepared by reactive r.f. magnetron sputtering on low carbon steel substrates. An electroless Ni-P plating was introduced as the interlayer in the modification of the TiN coating. The corrosion behaviour of the TiN coating assembly was evaluated using the salt spray test and the polarization technique. For a thicker Ni-P interlayer (greater than 5 μm), no appreciable corrosion was observed up to hundreds of hours after salt spray testing. The polarization curve indicates a barrier-type passive film in the TiN/Ni 3 P/Fe coating assembly. The corrosion currents for TiN/Fe, Ni 3 P/Fe and TiN/Ni 3 P/Fe are 200, 40–70 and 6–7 μA cm -2 respectively. It appears that the electroless Ni-P interlayer modified TiN coating has better anticorrosion resistance than pure TiN coating on low carbon steel.