Properties of the GaAs oxide layer grown by the liquid-phase chemical-enhanced technique on the S-passivated GaAs surface

The properties of GaAs oxide layers prepared by liquid-phase chemical-enhanced oxidation of the (NH₄)₂S_x-passivated GaAs surface are investigated. The initial oxidation rate is suppressed and the refractive indices of oxide layers are lower after S passivation. In accordance with the depth profiles measured by secondary ion mass spectroscopy (SIMS), a model is proposed to illustrate the chemical composition of the oxide layer grown by liquid-phase chemical-enhanced oxidation after S passivation. Oxidation following different surface treatments was studied by analyzing their activation energies. In addition, we find that the leakage current and the breakdown electric field of oxide layers can be improved significantly with the passivation technique.     

Physical properties and flux effect of printed CdS thick films

Screen printed CdS films has been studied with various techniques. Although the thick films preserved the feature of powder crystals, i.e., lack of orientation, it is found that more amounts of (112) wurtzite phase might be good for the electrical property of CdS films. The flux CdCl₂, which was added to the CdS films, resulted in two trapping levels, 0.4 ev and 0.68 ev. The mechanism and the effect of flux on the CdS films are discussed. Besides, the effect of vacuum annealing is also described.     

Growth by liquid phase epitaxy and evaluation of submicron InxGa1−xAsyP1−y layers for microwave field effect transistors

The growth of In-Ga-As-P layers 0.2 μm thick that are lattice matched to (100)-oriented InP substrates is described. A step cooling technique was employed to obtain uniform In_xGa_1?xAs_yP_1?y layers with band gaps of 0.9, 1.04, 1.15 and 1.2eV. Excellent surface morphology and good (±15%) thickness uniformity were achieved primarily by preventing substrate degradation by means of loss of phosphorus or by removing the degraded surface during the saturation of the melt. Van der Pauw and capacitance-voltage measurements were employed to characterize the epitaxial films. The field effect transistors fabricated from 1.15 and 1.2eV material exhibited a maximum available gain of about 7 dB at 10 GHz.     

Effects of gate sidewall recess on Al<Subscript>0.2</Subscript>Ga<Subscript>0.8</Subscript>As/ In<Subscript>0.15</Subscript>Ga<Subscript>0.85</Subscript>As PHEMTs by citric-based selective etchant

In this report, an effective and simple method of selective gate sidewall recess is proposed to expose the low barrier channel at mesa sidewalls during device isolation for Al_0.2Ga_0.8As/ In_0.15Ga_0.85As PHEMTs (pseudomorphic high electron mobility transistors) by using a newly developed citric-acid-based etchant with high selectivity (> 250) for GaAs/Al_0.2Ga_0.8As or In_0.15Ga_0.85As/Al_0.2G_0.8 As interfaces. After sidewall recess, a revealed cavity will exist between the In_0.15Ga_0.85As layers and gate metals. Devices with 1 × 100μm² exhibit a very low gate leakage current of 2.4μA/mm even at V_GD = −10 V and high gate breakdown voltage over 25 V. As compared to that of no sidewall recess, nearly two orders of reduction in magnitude of gate leakage current and 100% improvement in gate breakdown voltage can be achieved.     

Urban Particle Capture in Bioretention Media. I: Laboratory and Field Studies

Bioretention is a novel stormwater best-management practice that uses a mixture of soil/sand/mulch as adsorptive filtration media that can capture both urban particulates and dissolved pollutants while promoting infiltration. This study conducted a series of laboratory column experiments and field observations, which showed that: (1) bioretention media stratification occurs with runoff percolation due to particulate deposition; (2) bioretention filter media are clogging limited, instead of breakthrough limited; and (3) both depth filtration and cake filtration significantly contribute to urban particle capture. Because of the fine size of bioretention media, incoming suspended solids cannot significantly penetrate below 5–10?cm of the media in the column tests and approximately 20?cm in the monitored field facility. Bioretention filters under intermittent flow conditions exhibited higher solids loading capacity (in kg/m2) before clogging than under continuous flow conditions. The clay components in incoming total suspended solids assume critical responsibility for bioretention media clogging. The media resistance due to solids deposition was estimated through Darcy’s law. The hydraulic conductivity of two media types decreased from 54±23 and 72±46?cm/h to less than 10?cm/h due to particle capture. Experimental results suggest that a 20-cm media depth is sufficient for bioretention design and maintenance procedures (media replacement) for runoff particle capture.     

住宅区小尺度室内外休憩空间的营造——以珠江三角洲小区为例

住宅区内的小尺度休憩空间 ,易于为居民把握并建立有效控制的空间 ,与居民日常活动有着密切的关系 .结合大量珠江三角洲商品住宅区的实例 ,着重探讨了住宅区室外、架空层、室内等三类小尺度公共休憩空间的设计和营造     

A compact bandpass filter with enhanced stopband characteristics by an asymmetric cross-shape defected ground structure

In this paper, we present an effective technique to enhance stopband bandwidth for a bandpass filter by using an asymmetric, cross-shape defected ground structure (CSDGS). A single CSDGS can provide a higher attenuation rate near passband and broader stopband bandwidth. Moreover, with the asymmetric CSDGS, two different resonant frequencies can be excited and controlled independently, resulting in synthesizing a passband. The synthesized bandpass filter can be modeled by parallel LC resonant circuits in connection with T-networks. The bandwidth and insertion loss of this bandpass filter at 4.2 GHz is 28.6% and -1.44 dB, respectively, and 20 dB rejection in the stopband is up to four times the central frequency. All the synthesized bandpass filters have been measured and are in good agreement with simulated results.     

Thermal resistance analysis and validation of flip chip PBGA packages

This work proposes a finite element numerical methodology to predict the thermal resistance of both flip chip-plastic ball grid array (FC-PBGA) with a bare die and FC-PBGA with a metal cap. The 3D finite element model was initially constructed to simulate the thermal resistance of FC-PBGA. A thermal resistance experiment was performed to verify the FEM results, following the construction of specimens of FC-PBGA with a bare die and with an aluminum cap, using six-layered substrate. The verified finite element model was employed to determine the thermal resistance of FC-PBGA with a copper cap using four-layered and six-layered substrates. Experimental results demonstrated that FC-PBGA with a metal cap improves thermal performance by 35% over with a bare die. FC-PBGA with a copper cap slightly improves thermal performance from 2% to 2.8% over that of FC-PBGA with an aluminum cap. The thermal resistance of FC-PBGA with a four-layered substrate is reduced by 4.0% to 5.9% from that of FC-PBGA with a six-layered substrate, since the four-layered substrate contains less metal. The finite element numerical results negligibly differ from the experimental results by 6% to 8.1%. A finite element numerical methodology is here proposed to predict the thermal resistance of FC-PBGA. The methodology is effective in researching and developing new products or improving existing packages.     

A novel compact ring dual-mode filter with adjustable second-passband for dual-band applications

In this letter, a novel compact ring dual-mode with adjustable second-passband for dual-band applications are presented. A ring resonator with two different geometric dimensions are derived and designed to have identical fundamental and the first higher-order resonant frequencies, and to establish appropriate couplings in the structure. Moreover, the proposed filter has smaller size as compared with the basic topology of stopband filters and stepped-impedance-resonator (SIR) filters. The measured filter performance is in good agreement with the simulated response.