Densification, crystallization, and electrical properties of lead zirconate titanate glass-ceramics

Piezoelectric glass-ceramics in the lead zirconate titanato-lead silicate system were developed. SiO(2) was required for glass formability, and excess PbO allowed low temperature processing. The amounts of those constituents were limited by the optimization of the piezoelectric properties. Only a small region of compositions in this system yielded the desired combination of glass formability, crystallization and densification behavior, and resulting piezoelectric properties. Selected compositions were melted and roller quenched to form glass ribbon, then milled into glass powder. Pressed glass powder densified to closed porosity at 850 degrees C with piezoelectric d(33 ) and g(33) coefficients of 26 pC/N and 33x10(-3 ) Vm/N. The low temperature sintering behavior of these ferroelectric glass-ceramics provides the possibility of incorporating a piezoelectric material as a sensor or actuator in thick film circuits or low-fire multilayer packages.     

Genetic analysis of Shigella sonnei form I antigen: identification of a novel IS630 as an essential element for the form I antigen expression

The form I coding region of Shigella sonnei was cloned and shown to have an operon-like rfb organization. It was found that the 11.0 kb HindIII-XbaI fragment of pHH201 encoding the form I antigen contains 10 contiguous open reading frames (ORF), ORF1 to ORF10. Deletions from either end of pHH201, within ORF1 or ORF10, eliminated form I expression. ORF1 and ORF2 share significant nucleic and amino acids homologies to two ORF's of the Salmonella typhi Vi antigen genes. ORF5 in pHH201 is identical to IS630. pHH2064, derived from pHH201, lacks the IS630 element and can stably express the form I antigen inE. coli HB101. However, pHH2064 is structurally unstable in a S. sonnei form II host. This indicates that the presence of the IS630 gene within the S. sonnei rfb operon may be necessary for the stability of form I expression in S. sonnei. This finding is substantiated by the observation that all virulent S. sonnei isolates examined in this study retained the IS630 element within their rfb operon.     

Microwave InxGa1?xAsyP1?y/InP f.e.t

Microwave performance of InxGa1?xAsyP1?y quaternary alloy metal-semiconductor field effect transistors (m.e.s.f.e.t.s) is reported. Liquid-phase epitaxy (l.p.e.) using a step cooling technique has been employed to grow submicrometre quaternary layers having room-temperature bandgaps of 0.9, 1.0, 1.05, 1.15 and 1.2eV. F.E.T.s having gate dimensions of 1×200 ?m and a channel length of 5 ?m have been fabricated using 1.15 and 1.2 eV quaternary alloys. A maximum d.c. transconductance of about 10 mS and a maximum available gain of about 7 dB at 10 GHz have been obtained.     

Hot-electron effects on AlGaAs/InGaAs/GaAs PHEMTs under accelerated DC stresses

The behavior of Schottky gate characteristics before and after hot-electron stress has been a relatively neglected topic. Thus, this paper discussed the effects of hot-electron accelerated stress on the DC characteristics of AlGaAs/InGaAs/GaAs PHEMTs as they relate to Schottky gate characteristics. It also presents studies of reverse Schottky gate characteristics before and after hot-electron stresses, as related to two major mechanisms: (1) the widening of the depletion region under the gate; and (2) the impact of the carriers trapped under the gate. The former induces a larger Schottky barrier height with a smaller reverse leakage current density than the latter, while the latter induces the opposite. Two hot-electron conditions are used to investigate the impact of the hot-electron stress on the gate leakage current. The gate leakage current decreases after a hot-electron stress, due the effect of hot-electron stress on the Schottky diode characteristics. Moreover, improvement in the noise performance is expected, due to the decrease in the gate leakage current. Both pre- and post-stress noise measurements have been done to demonstrate this.     

Fabrication of depletion-mode GaAs MOSFET with a selectiveoxidation process by using metal as the mask

The n-channel depletion-mode GaAs MOSFETs with a selective liquid phase chemical-enhanced oxidation method at low temperature by using metal as the mask (M-SLPCEO) are demonstrated. The proposed process can simplify one mask to fabricate GaAs MOSFET and grow reliable gate oxide films as well as side-wall passivation layers at the same time. The 1 μm gate-length MOSFET with a gate oxide thickness of 35 nm shows a transconductance of 90 mS/mm and a maximum drain current density larger than 350 mA/mm. In addition, a short-circuit current gain cutoff frequency f_T of 6.5 GHz and a maximum oscillation frequency f _max of 18.3 GHz have been achieved from the 1 μm×100 μm GaAs MOSFET     

Influence of an In2O3 buffer layer on the properties of ITO thin films

In the present study, an indium oxide (In₂O₃) thin film was deposited as a buffer layer between ITO (indium tin oxide) and PES (polyestersulfone) by RF (radio frequency) magnetron sputtering at room temperature, and X-ray diffraction (XRD) and field emission scanning electron microscopy (FESEM) were conducted to characterise the structural variation. The random texture of the ITO/In₂O₃ multilayered film favoured the (2 2 2) crystallographic plane rather than the (4 0 0) plane, which was favoured in single-layer ITO films. Transmission electron microscopy (TEM) observations further indicated that the buffer layer of In₂O₃ film was amorphous, while the ITO film was characterised by a columnar structure that was oriented perpendicular to the substrate surface. The electrical and optical properties of ITO/In₂O₃ multilayered films were enhanced due to the superior crystallinity and larger grain size of the material, as observed by XRD and FESEM. The multilayered film presented an electrical resistivity of 3.1 × 10⁻⁴ Ω cm, which is significantly better than that of a single-layer ITO film without an In₂O₃ buffer layer (4.7 × 10⁻⁴ Ω cm). In addition, optical transmission through the multilayered film increased by 2-4% due to the widening of the band gap by 0.2 eV, which was attributed to a Burstin-Moss shift.     

Low-loss GaAs/GaAlAs strip-loaded waveguides with high coupling efficiency to single-mode fibres

We report measurements of low-loss MOVPE-grown GaAlAs/GaAs strip-loaded waveguides with high coupling efficiency to single-mode fibres. A propagation loss of 2 dB/cm and a coupling efficiency of 70% has been achieved for a p+-i-n+-structure waveguide. A propagation loss of 0.7 dB/cm and a coupling efficiency of 61% has also been achieved for an n?-i-n?-structure waveguide.     

Enhanced polarisation self-switching in a vertical-cavitysurface-emitting laser by gain saturation of transverse modes

Enhanced polarisation self-switching is observed in a vertical-cavity surface-emitting laser by involving gain saturation due to transverse mode competition. Switching between orthogonal polarisations is triggered by a quarter-wave plate external cavity and does not change the total output power     

Real-time control of an immobilized-cell reactor for wastewater treatment using ORP.

The performance of an immobilized-cell reactor for simultaneous carbon nitrogen removal in synthetic wastewater with an intermittent aeration (IA) process under real-time control of oxygen supply was investigated. The oxidation-reduction potential (ORP) was monitored during operation. The ORP-time profile showed distinctive turning points. which directly correlated with the changes in the system chemistry and biological activity. The reactor was conducted by cyclic fixed-time aeration nonaeration operation at the beginning, followed by real-time control technology using ORP setpoint. A moving window along the slope of the ORP curve was employed to search for the nitrate breakpoint of the aeration cycle. Once the breakpoint was found, the reactor was aerated for a fixed period. The treatment process could effectively avoid the anoxic fermentation state under the real-time control. The cycle time was reduced around 30%. The duration of aeration period was found to be optimum at 3 h under the consideration of the removal efficiencies of COD and total nitrogen. The real-time control system not only exhibited a better nitrogen removal efficiency than the fixed-time control operation, but it also showed a stable effluent quality during the change of HRT from 3 to 8 h. Good operation stability was demonstrated even when a very high disturbance of the influent loading occurred.     

Current-dependent hot-electron stresses on InGaP-gated and AlGaAs-gated low noise PHEMTs

A newly proposed method, called the current-dependent hot-electron stress, is used to study InGaP-gated and AlGaAs-gated low noise PHEMT devices with different drain currents at high drain voltages. The impact ionization between gate and drain is the major mechanism affecting devices during hot-electron stressing, which are excited by the high gate-to-drain electric fields. However, the measure of the effects of the impact ionization related to the drain current during hot-electron stressing is less discussed in the published literatures. In this work, the designed hot-electron stressed conditions, which are related to the different drain currents, are used to demonstrate the influence of drain currents in hot-electron stresses and, furthermore, to estimate and compare InGaP-gated with AlGaAs-gated PHEMTs.