Low-temperature fabrication of amorphous BaTiO3thin-film bypass capacitors

Amorphous BaTiO₃ thin-film capacitors suitable for integration into a multichip module packaging process were fabricated. The multilayer capacitor structure consisted of an adhesion layer (TiO _xN_y or Ti), a bottom electrode (Cu), a dielectric (amorphous BaTiO₃), and a top electrode (Cu). A 3000-Å amorphous BaTiO₃ film was deposited onto the electrode by the reactive partially ionized beam (RPIB) technique at near room temperature. After a 300°C postdeposition anneal, the capacitors had the following properties: ε_r=17-18 and tanδ<0.01 up to 600 MHz, J_leak=0.06-0.5 μA/cm² at 0.5 MV/cm, and breakdown field E_max=3.3 MV/cm     

Effect of neutron and gamma irradiation on the low-frequency noise in GaAs m.e.s.f.e.t.s

Low-frequency noise in GaAs m.e.s.f.e.t.s has been measured from 2 kHz to 1.5 MHz as a function of fast neutron fluence and gamma dose. From 5 × 1013 to 8 × 1014 n/cm2, the noise increases appreciably, with the noise enhancement from 2 to 10 kHz attributed to generation-recombination noise in the gate depletion layer and from 500 kHz to 1.5 MHz to channel trapping effects. There was comparably little change with gamma irradiation up to doses above 107 rad (Si).     

Accelerated kinetics study of neohesperidine DC hydrolysis under conditions relevant to high-temperature-processed dairy products

 The degradation of neohesperidine DC in solution as a function of temperature (70–100 °C) and pH (6–7) was studied in order to estimate losses during thermal processing of non-fermented milk-based products. First order rate constants were observed in all the conditions tested. An increase in the pH from 6 to 7 produced an increase in rate constants by a factor of 5. These data were used to predict losses that would occur during conditions prevailing during the manufacture of non-fermented dairy products. Results indicate that neohesperidine DC would withstand these heat treatments without significant degradation. Received: 19 December 1995/Revised version: 14 June 1996     

Interface state density in Au-nGaAs Schottky diodes

A method for determining the surface state density in Schottky diodes taking into account both I–V and C–V data while considering the presence of a deep donor level is presented. The model assumes that the barrier height is controlled by the energy distribution of surface states in equilibrium with the metal and the applied potential and does not include, explicitly, an interfacial layer. The model was applied to extract interface state densities of Au-nGaAs guarded Schottky diodes fabricated from bulk and VPE (100) GaAs with carrier conentrations between 3 × 10¹⁵ and 8 × 10¹⁶ cm^?3. These diodes exhibited ideality (n) factors of approximately 1.02 and room temperature saturation current densities ～10^?8 A/cm². This model is in substantial agreement with forward bias measurements over the 77–360°K temperature range investigated, in that a temperature-independent energy distribution of interface states was obtained. In reverse bias the interface state model is most valid with the higher carrier concentration material and at high temperature and low bias voltage. Typical interface state densities from 0.07 eV above the zero bias Fermi level to 0.01 eV below the Fermi level were 2 × 10¹³ cm^?2 eV^?1. The validity of the model under reverse bias is restricted by a non-thermionic reverse current, thought to be enhance field emission from traps.     

Extension of Gummel's charge control relation

Gummel's charge control relation for bipolar transistors is extended to be valid for the base region of thyristors and pin rectifiers. The modified relationship is derived under the assumption of one dimensional current flow and includes the effects of recombination and majority carrier flow in the base region.     

OMVPE growth of CdTe on InSb substrates

In this paper we report on the growth and electrical characteristics of CdTe on InSb substrates, grown by OMVPE. The growth was carried out over a range of temperatures from 350 to 440° C, and a range of dimethylcadmium (DMCd) and diethyltelluride (DETe) pressures from 0.5 − 7 × 10⁻⁴ atm and 2 − 10 × 10⁻⁴ atm, respectively. The sublinear growth characteristic observed has been explained by means of the Langmuir Hinshelwood model. This provides an insight into the mechanism by which this material is grown. The effect of temperature and the reactant partial pressure on the growth rate and electrical characteristics have been explained in light of the observed results. The photoluminescence properties of these layers are indicative of their suitability for device applications, and are superior to those of CdTe layers grown on bulk CdTe. It has been shown that growth of high quality layers can be achieved over a wide range of partial pressure ratios of DMCd and DETe.     

Photosynthetic oxidation of MnS and FeS by Chlorobium spp

The ability of two species of green phototrophic sulfur bacteria (Chlorobium limicola and Chlorobium phaeobacteroides) to photosynthetically oxidize several metal sulfides (MnS, FeS, NiS, CuS, ZnS, CdS and PbS) by has been tested in laboratory batch cultures. Both species only oxidized MnS and FeS, which are the ones having higher solubilities (pKs = 13.5 and 18.1, respectively). The specific oxidation rates were directly related to the solubility of the metal sulfide involved. C. limicola oxidized MnS and FeS at specific rates of 11.8 and 0.9 mumol S2-h-1 mg protein-1, respectively. Specific oxidation rates of C. phaeobacteroides for MnS and FeS were 7.1 and 1.8 mumol S2-h-1 mg protein-1, respectively. The oxidation of both metal sulfides resulted in the release of the free-soluble metal ions in the culture media, but no toxic effect of these cations on the photosynthetic activity of the cells was observed. The anaerobic photosynthetical oxidation of MnS and FeS by Chlorobium reveals an adaptation of this bacterial species to sulfide-poor environments, and introduces a new process in the Mn, Fe, and S biogeochemical cycles to be considered.     

Degradation of GaAs MESFETs in Radiation Environments

The effects of gamma and neutron irradiation on lownoise, GaAs MESFETs are reviewed, with emphasis on microwave amplifier characterisitics. With gamma irradiation, the amplifier noise figure degrades above 107 rads (Si), without change in signal parameters. With neutron irradiation, amplifier gain and noise figure degrade above 1014 n/cm2. With gamma irradiation, unidentified levels are apparently introduced that respond at microwave frequencies. With neutron irradiation, changes are caused principally by carrier compensation in the graded region between the channel and substrate. Device characterization procedures, experimental results, and degradation mechanisms are discussed.     

Leakage current enhancement in impatt oscillators by photoexcitation

A technique for investigating the r?le of dynamic or effective leakage current in the r.f. performance of an impatt diode is described. The technique involves the design of a device structure and microwave cavity which permits the leakage current to be varied externally by photogeneration of carriers, and is compatible with c.w. operation. Typical results for flat-profile single-drift X-band silicon are a 10% reduction in power and a 10 MHz increase in frequency at a photo/bias-current ration of 0.005.     

ChIP-Seq-Based Approach in Mouse Enteric Precursor Cells Reveals New Potential Genes with a Role in Enteric Nervous System Development and Hirschsprung Disease

Hirschsprung disease (HSCR) is a neurocristopathy characterized by intestinal aganglionosis which is attributed to a failure in neural crest cell (NCC) development during the embryonic stage. The colonization of the intestine by NCCs is a process finely controlled by a wide and complex gene regulatory system. Several genes have been associated with HSCR, but many aspects still remain poorly understood. The present study is focused on deciphering the PAX6 interaction network during enteric nervous system (ENS) formation. A combined experimental and computational approach was performed to identify PAX6 direct targets, as well as gene networks shared among such targets as potential susceptibility factors for HSCR. As a result, genes related to PAX6 either directly (RABGGTB and BRD3) or indirectly (TGFB1, HRAS, and GRB2) were identified as putative genes associated with HSCR. Interestingly, GRB2 is involved in the RET/GDNF/GFRA1 signaling pathway, one of the main pathways implicated in the disease. Our findings represent a new contribution to advance in the knowledge of the genetic basis of HSCR. The investigation of the role of these genes could help to elucidate their implication in HSCR onset.