Effect of oxide additives on the low-temperature sintering of dielectrics (Zn,Mg)TiO3

The effect of oxide additives on the low-temperature sintering and dielectric properties of microwave dielectrics (Zn,Mg)TiO₃ have been investigated. The study showed that a small amount of V₂O₅ accelerated the densification rate of (Zn,Mg)TiO₃ dielectrics as compared with the other oxide additives. In addition to lower sintering temperature of zinc titanate dielectrics, the addition of V₂O₅ decreased the decomposition temperature of (Zn,Mg)TiO₃. Additionally, the increased amount of magnesium raised both the sintering temperature and the decomposition temperature of (Zn,Mg)TiO₃. Relative permittivity of (Zn,Mg)TiO₃ dielectrics decreased accompanied with increase of Q × f as the amount of magnesium content increased. The temperature coefficient of resonant frequency of (Zn,Mg)TiO₃ shifted to more negative values as the amount of magnesium increased.     

GaAs PIN electro-optic travelling-wave modulator at 1.3 ?m

A GaAs PIN travelling-wave modulator operated at 1.3 ?m has been fabricated from material grown by organometallic vapour phase epitaxy (OMVPE) on an n+ (100) GaAs substrate. The device has a constant V? of 8 V from DC to 10 GHz and an optical extinction ratio of 13 dB. The optical insertion loss of the device is 3.5 dB, and the 3 dB frequency bandwidth is measured to be 4.1 GHz, which is limited by the microwave slowing induced by the n+ substrate.     

Titanium nitride diffusion barrier for copper metallization on gallium arsenide

The diffusion properties of Cu, Cu/titanium nitride (TiN) and Cu/TiN/Ti metallization on GaAs, including as-deposited film and others annealed at 350-550 °C, were investigated and compared. Data obtained from X-ray diffractometry, resistivity measurements, scanning electron microscopy, energy dispersive spectrometer and Auger electron spectroscopy indicated that in the as-deposited Cu/GaAs structure, copper diffused into GaAs substrate, and a diffusion barrier was required to block the fast diffusion. For the Cu/TiN/GaAs structure, the columnar grain structure of TiN films provided paths for diffusion at higher temperatures above 450 °C. The Cu/TiN/Ti films on GaAs substrate were very stable up to 550 °C without any interfacial interaction. These results show that a TiN/Ti composite film forms a good diffusion barrier for copper metallization with GaAs.     

Effect of Ru addition on the properties of Al-doped ZnO thin films prepared by radio frequency magnetron sputtering on polyethylene terephthalate substrate

The addition of ruthenium in aluminum-doped zinc oxide transparent conducting thin films was deposited on polyethylene terephthalate at 20 °C by radio frequency magnetron sputtering technique. The structure and electrical properties of the films were investigated with respect to variation of Ru concentration. The XRD and FESEM results show that the film with 0.5 wt% Ru doping has the best crystallinity and larger pyramid-like grains, therefore the resistivity reached to a lowest value of 9.1 × 10⁻⁴ Ωcm. The low carrier mobilities of the films (3–7.2 cm² V⁻¹ s⁻¹), however, were limited by ionized impurity scattering and grain boundary scattering mechanisms since the carrier concentrations were ranged from 2.2 × 10²⁰ to 9.5 × 10²⁰ cm⁻³. The transmittance in the visible is greater than 80% with the optical band gap in the order of 3.352–3.391 eV.     

Impact of cholesterol reduction on peripheral arterial disease in the Program on the Surgical Control of the Hyperlipidemias (POSCH)

BACKGROUND: Few lipid/atherosclerosis intervention trials have assessed the impact of cholesterol reduction on peripheral arterial disease. The 838 patients evaluated in the Program on the Surgical Control of the Hyperlipidemias (POSCH) trial represent more than the total number of patients in the seven previously reported studies. METHODS: Peripheral arterial disease in POSCH was assessed by progression of clinical disease, serial changes in the systolic blood pressure ankle/brachial index (ABI), and changes on sequential peripheral arteriograms. RESULTS: At the time of formal closure of the POSCH trial on July 19, 1990, claudication or limb-threatening ischemia was exhibited in 72 of 417 control group (CG) patients and in 54 of 421 intervention group (IG) patients (IG relative risk [RR] 0.702, 95% confidence interval [CI] 0.169 to 1.000, p = 0.049). With additional follow-up evaluation to September 30, 1994, clinical peripheral arterial disease was evident in 91 CG patients and 64 IG patients (RR 0.656, 95% CI 0.200 to 0.903, p = 0.009). At the 5-year follow-up evaluation, an ABI of less than 0.95 was present in 41 of 120 CG patients and in 24 of 126 IG patients, all of whom had an ABI of 0.95 or greater at baseline (RR in the IG of 0.557, 95% CI 0.360 to 0.863, p < 0.01). No appreciable differences were noted in the progression or regression of arteriographic peripheral arterial disease between the two groups. CONCLUSIONS: Effective cholesterol reduction in POSCH led to statistically significant differences between the control and the intervention groups in the development of clinically evident peripheral arterial disease and in the ABI values, but not in the peripheral arteriograms. Additional studies need to assess the correlation between peripheral arterial changes and coronary arterial changes and clinical atherosclerosis events. Intervention trials that study peripheral arterial disease have intrinsic value in the evaluation of the impact of risk factor modification on progression of atherosclerotic peripheral arterial disease.     

Alpha 2-antiplasmin causes thrombi to resist fibrinolysis induced by tissue plasminogen activator in experimental pulmonary embolism

BACKGROUND: In patients with pulmonary embolism, thrombi resist fibrinolysis induced by plasminogen activators. Because the molecular basis of this thrombus resistance is poorly understood, we used a potent inhibitor to examine the potential role of alpha 2-antiplasmin (alpha 2AP) in experimental pulmonary embolism. METHODS AND RESULTS: Lysis of experimental pulmonary emboli was measured 4 hours after embolization in anesthetized ferrets. All animals received heparin (100 U/kg). Five experimental groups were studied: (1) no recombinant tissue plasminogen activator (rTPA); (2) rTPA at 1 mg/kg; (3) rTPA at 2 mg/kg; (4) rTPA at 1 mg/kg plus a control monoclonal antibody (MAb); and (5) rTPA at 1 mg/kg plus an alpha 2AP inhibitor (MAb 77A3). In comparison with ferrets receiving no rTPA (15.6 +/- 10.5% lysis, mean +/- SD), rTPA-treated groups showed significantly greater lysis (P < .01). Animals treated with rTPA and alpha 2AP inhibitor (56.2 +/- 4.7% lysis) showed significantly greater lysis than all other treatment groups, including ferrets treated with the same dose of rTPA alone (38.5 +/- 6.3%, P < .01), with twice the rTPA dose alone (45.0 +/- 6.5%, P < .05), or with a control MAb (35.2 +/- 4.6%, P < .01). The combination of rTPA treatment and alpha 2AP inhibition caused no consumption of fibrinogen. CONCLUSIONS: Inhibition of alpha 2AP significantly amplified the lysis of experimental pulmonary emboli by rTPA without increasing fibrinogen consumption. These results suggest that alpha 2AP may play an important role in thrombus resistance in patients with venous thromboembolism.     

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.