Electrical Behavior and Technology Optimization of Si/SiGeC HBTs on Thin-Film SOI

A growing interest has been focused on silicon on insulator (SOI) technologies over the past years. Yet, few studies were carried out regarding the integration of vertical SiGe heterojunction bipolar transistors (HBTs) using such substrates. This paper deals both with the integration of a SiGeC HBT on thin-film CMOS-compatible SOI, and a comprehensive study of its electrical behavior based on physical simulation and electrical characterization. Various aspects of the optimization of device performances are described, considering process or layout improvements.     

H/D Exchange on Silica-Grafted Tantalum(V) Imido Amido [(≡SiO)<Subscript>2</Subscript>Ta<Superscript>(V)</Superscript>(NH)(NH<Subscript>2</Subscript>)] Synthesized from Either Ammonia or Dinitrogen: IR and DFT Evidence for Heterolytic Splitting of D<Subscript>2</Subscript>

The silica-grafted Ta^(V) imido amido complex [(≡SiO)₂Ta(NH)(NH₂)], 2, obtained from the reaction of either ammonia or dinitrogen plus hydrogen with the silica-grafted hydrides [(≡SiO)₂Ta^(III)H], 1a, and [(≡SiO)₂Ta^(V)H₃], 1b, undergoes H/D exchange with D₂. In situ IR spectroscopy shows that the fully labelled compound [(≡SiO)₂Ta(ND)(ND₂)], 2-d, can be obtained by moderate heating (60 °C, 3 h) under D₂ atmosphere (550 torr, 300 eq. with respect to Ta), and that the exchange is reversible. The observed stretching and bending frequencies of 2-d are in agreement with the expected isotopic shift upon H/D replacement with respect to literature values reported for 2 and have been corroborated by the independent synthesis of 2-d by reaction of deuterated 1a and 1b with N₂ and D₂. Density functional theory (DFT) calculations, performed using a periodic or a cluster model, explored the structures and energetics of all minima involved in the reaction with H₂ and showed that among the explored pathways the energetically preferred mechanisms for H₂ reaction with [{(μ-O)[(HO)₂SiO]₂}Ta^(V)(NH)(NH₂)], 2q, is the heterolytic cleavage of either the imido Ta=N or the amido Ta-N bonds, to yield respectively [{(μ-O)[(HO)₂SiO]₂}TaH(NH₂)₂], 3q (ΔE = −9.5 kcal mol⁻¹ and ΔG_298K = +2.6 kcal mol⁻¹ with respect to 2q) and [{(μ-O)[(HO)₂SiO]₂}Ta(NH)(NH₃)], 4q (ΔE = −6.0 kcal mol⁻¹ and ΔG_298K = +7.9 kcal mol⁻¹ with respect to 2q). All activation barriers are moderate (between 17.7 and 30.2 kcal mol⁻¹) in agreement with the observed mild heating conditions necessary for the reaction to occur.     

Kinetics and Mechanism of the Water–Gas Shift Reaction Over Platinum Supported Catalysts

A dual-site reaction mechanism is proposed for Pt based water–gas shift catalysts. The sorption equilibrium parameters are evaluated in detail to validate their physical significance. The values of the van ‘t Hoff parameters for CO and H₂ correspond to those for chemisorption on platinum. The sorption parameters of H₂O and CO₂ on the supports have been quantitatively determined from temperature-programmed desorption experiments and have been compared to the values obtained from the kinetic study. Finally the proposed model is able to explain the different activities between the two catalysts.     

A compact model for SiGe HBT on thin-film SOI

Heterojunction bipolar transistor (HBT) fabrication on thin-film silicon-on-insulator (SOI) has been recently demonstrated. Due to the space volume constraint (thin film) for the device fabrication, the HBT structure is different from bulk HBT. In fact, compared to a bulk device, the buried layer has been suppressed and a lateral collector contact configuration is introduced. This device features a vertical expansion followed by a lateral expansion of the base-collector space charge region. This nonconventional charge behavior induces a kink in the base-collector junction capacitance characteristics, and as a consequence a modified Early effect. Furthermore, the low current transit time is modified compared to a bulk HBT. In this paper, all these effects are analyzed and a compact model for SOI-HBT is proposed. The model is validated on real SOI-HBTs with different collector doping levels.     

Screening of bifunctional water-gas shift catalysts

A large number of different formulations have been recently proposed in the literature as new catalysts for the water-gas shift (WGS) reaction. These formulations typically consist of a metal deposited on a reducible support. As these catalysts have been synthesized and tested by different groups in different operating conditions, a true comparison of their activities is not really possible. The aim of this study is to screen these samples under identical conditions using a model reformate as reaction mixture. A commercial parallel reactor has been used for this task. Comparison of the data obtained for the Pt catalysts from the parallel reactor with those obtained from a single fixed bed reactor showed deviations of 20–30% in the kinetic parameters. Rh and Ru based catalysts produced significant amounts of methane. Pt/CeO₂/Al₂O₃ and Pt/TiO₂ were found to be the most active catalysts for the high temperature water-gas shift while gold and copper catalysts showed promising results for low temperature applications, but they require testing at lower CO partial pressures.     

Relating chemical and biological diversity space: a tunable system for efficient gene transfection

Polyethyleneimine (PEI), a well-established nonviral transfection reagent, was combinatorially modified with varying proportions of methyl, benzyl, and n-dodecyl groups to create a library of 435 derivatized polymers. Screening of this library for transfection, DNA binding, and toxicity allows systematic correlation of the biological properties of our polymers to their derivatizations. Combinations of derivatizations bring about a 100-fold variation in transfection efficiency between library members. The best PEI derivatives exhibit increases in transfection efficiency of more than 80-fold over unmodified PEI (up to 28+/-7 % of cells transfected) and rival commercial reagents such as Lipofectamine 2000 (21+/-10 %) and JetPEI (32+/-5.0 %). In addition, we can identify compounds that are specifically tuned for efficient transfection in CHO-K1 over Ishikawa cells and vice versa, demonstrating that the approach can lead to cell-type selectivity of at least one order of magnitude. This work demonstrates that multivalent derivatization of a polymeric framework can create functional diversity substantially greater than the structural diversity of the derivatization building blocks and suggests an approach to a better understanding of the molecular underpinnings of transfection as well as their exploitation.     

H2-induced promotion of CO oxidation over unsupported gold

The kinetics and mechanism of the preferential oxidation of carbon monoxide in the presence of hydrogen (PrOx) over an unsupported gold powder (mean particle size 20 nm and free of silver) have been investigated using flow fixed bed catalytic testing and diffuse reflectance infrared Fourier transform spectroscopy coupled to mass spectrometry (operando DRIFTS or DRIFTS-MS). It is shown that the presence of H₂ has a favourable effect on the oxidation of CO, either by strongly accelerating the reaction or by preventing the catalyst deactivation, depending on the conditions used. Variation of the hydrogen partial pressure has allowed us to determine partial reaction orders for both CO oxidation and H₂ oxidation under PrOx conditions. An infrared band at 2113 cm⁻¹, corresponding to on-top CO adsorption on metallic gold, has been observed below 150 °C. In addition, adsorbed hydroxyl groups gradually develop simultaneously to gas-phase water in the course of the reaction at increasing temperatures. The promotional effect of hydrogen is ascribed to highly oxidative H_xO_y intermediates formed from the interaction between H₂ and O₂ on the gold surface.