Reliability and performance scaling of very high speed SiGe HBTs

We discuss the SiGe HBT structural changes required for very high performance. The increase in collector concentration, affecting current density and avalanche current, appears to be the most fundamental concern for reliability. In device design, a narrow emitter and reduced poly–single-crystal interfacial oxide are important elements in minimizing device parameter shifts. From the application point of view, avalanche hot-carriers appear to present new constraints, which may be managed through limiting voltage (to 1.5×–2× BV_CEO), or through circuit designs robust to base current parameter shifts.     

3.9 ps SiGe HBT ECL ring oscillator and transistor design for minimum gate delay

We show empirical results that demonstrate the effect of high performance SiGe HBT design parameters on the minimum gate delay of an ECL ring oscillator. SiGe HBT devices with a high f/sub MAX/ (338 GHz) and a low f/sub T/ (180 GHz) achieve a minimum delay of 3.9 ps, which to our knowledge is the lowest reported delay for a silicon based logic gate. Compared to the extracted (extrapolated) f/sub T/ and f/sub MAX/, a simple figure of merit proportional to /spl radic/f/sub T//R/sub B/C/sub CB/ with R/sub B/ and C/sub CB/ extracted from S-parameter measurement is best correlated to the minimum gate delay.     

Water removal from porous media by gas injection: experiments and simulation

The flow of a saturated gas through a porous medium, partially occupied by a liquid phase, causes evaporation due to gas expansion. This process, referred to as flow-through drying, is important in a wide variety of natural and industrial applications, such as natural gas production, convective drying of paper, catalysts, fuel cells and membranes. X-ray imaging experiments were performed to study the flow-through drying of water-saturated porous media during gas injection. The results show that the liquid saturation profile and the rate of drying are dependent on the viscous pressure drop, the state of saturation of the gas and the capillary characteristics of the porous medium. During the injection of a completely saturated gas, drying occurs only due to gas expansion. Capillary-driven flow from regions of high saturation to regions of low saturation lead to more uniform saturation profiles. During the injection of a dry gas, a drying front develops at the inlet and propagates through the porous medium. The experimental results are compared with numerical results from a continuum model. A good agreement is found for the case of sandstone. The comparison is less satisfactory for the experiments with limestone.     

Synthesis of Functionalized Silsesquioxane Nanomaterials by Rhodium-Catalyzed Carbene Insertion into Si−H Bonds

We report carbene insertion into Si?H bonds of polyhedral oligomeric silsesquioxanes (POSS) for the synthesis of highly functionalized siloxane nanomaterials. Dirhodium(II) carboxylates catalyze insertion of aryl-diazoacetates as carbene precursors to afford POSS structures containing both ester and aryl groups as orthogonal functional handles for further derivatization of POSS materials. Four diverse and structurally varied silsesquioxane core scaffolds with one, three, or eight Si?H bonds were evaluated with diazo reactants to produce a total of 20 new POSS compounds. Novel diazo compounds containing a fluorinated octyl group and boron-dipyrromethene (BODIPY) chromophore demonstrate the use of highly functionalized substrates. Transformations of aryl(ester)-functionalized POSS compounds derived from this method are demonstrated, including ester hydrolysis and Suzuki–Miyaura cross-coupling.     

Localized shear discontinuities near the tip of a mode I crack

In this paper we study the deformation and stress fields near the tip of a crack under plane strain mode I conditions. A fully nonlinear theory of finite deformations is used and the material, which is assumed to be homogeneous, isotropic, incompressible and elastic, is characterized by its stress-strain behavior in simple shear. For the class of materials considered the governing system of differential equations may lose ellipticity at sufficiently severe strains. The analysis is based on a direct asymptotic calculation. The results involve two curves, issuing from each crack-tip, across which the deformation gradient, the effective shear and the stresses are discontinuous.     

Transition metal doped cadmium manganese telluride: A new material for tunable mid-infrared lasing

Relatively new materials for mid-infrared tunable lasing using chromium-doped Cd_1-xMn_xTe and cobalt-doped Cd_1-xMn_xTe have been developed. Previously, ZnS and ZnSe were used as host materials for chromium to produce mid-infrared (MIR) lasing. Compared to these materials, large diameter CdMnTe is easier to grow (using the Bridgman technique) and can be made more homogeneous. Moreover, the ternary nature of Cd_1-xMn_xTe offers the unique opportunity to optimize the optical properties of the material through variation of chemical composition and lattice parameter. Using Cd_0.55Mn_0.45Te:Cr, we have demonstrated room temperature lasing from 2.1 to 3.0 m, and we have demonstrated quasi-continuous wave (cw) lasing. To our knowledge, the observed tuning range (∼840 nm) of Cr²⁺:Cd_0.55Mn_0.45Te is the largest ever reported from a transition metal ion laser. Furthermore, this is the first time that a room temperature quasi-cw laser operating at 3 m has been demonstrated using this type of material. Also, preliminary work on Cd_0.55Mn_0.45Te:Co indicates its potential for tunable mid-infrared lasing around 3600 nm at cryogenic temperatures. Results from inductively coupled plasma mass spectrometry (ICP-MS), which determine the concentration of dopant that has been incorporated in to the host lattice, will be reported, as will the materials characterization and lasing results. The processing issues for optimizing the laser performance in these material systems will also be discussed.     

Two-step rapid thermal annealing (TS-RTA) to suppress out-diffusionof dopants without degrading short channel effect of transistor

We examined the effects of source/drain annealing condition on the gate sheet resistance and short channel effect. We found that two-step rapid thermal annealing (TS-RTA) technology, where 700°C, 3 min pre-annealing in O₂ is introduced before 1000°C anneal in N₂, suppressed dopant out-diffusion without degrading short channel effect of transistor     

Non-linear free surface flows and an application of the Orlanski boundary condition

The focus of this paper is the analysis of spatially two-dimensional non-linear free surface problems. The critical aspects of the problem concern the treatment of the non-linear free surface, the body boundary condition for large motions and the imposition of suitable radiation conditions. To address such complexities, time domain simulation was chosen as the method of analysis. With the use of a finite domain for simulation, a major concern is with the radiation condition to be applied at the open or truncation boundary. For the two-dimensional problem at hand, no theoretical radiation conditions are known to exist. An extension of the Orlanski open boundary condition, based on phase velocity determination at the free surface, is proposed. Three categories of problems were analysed using numerical simulation-namely, freely moving steep waves, waves over a submerged body and forced body motion. Simulation results have been compared with linear theory and experiments.     

On generalized Clifford groups II

The earlier study of the irreducible representations of the generalized Clifford groups G^m_n in the case where m is a prime number, is now extended to the case where m is any integer. The analysis of class structure and hence the construction of the irreducible representations of G^m_n for a non-prime integer m is found to be more complicated. This investigation also requires the properties of the generalized Clifford algebras C^m_n(I) which are studied in Section 2 of the paper. The case of infinite generalized Clifford group, i.e. G^∞_n involving the infinite- order root of unity as well as the physical relevance of the generalized Clifford groups are briefly dealt with.     

A Mössbauer study of the substituted hexagonal ferrites BaSrxCa1−xFe4O8 (0 ⩽ x ⩽ 1)

Ferrites of the formula BaCa_1?xSr_xFe₄O₈ (0 ? x ? 1) gave rise to magnetically split Mössbauer spectra indicative of antiferromagnetic ordering at room temperature. These spectra were analysed to yield the isomer-shift, quadrupole splitting, internal magnetic field and its orientation. The unit cell dimensions were obtained from X-ray powder patterns and were used in obtaining estimates of the electric field gradient (e.f.g.). The calculated and observed e.f.g. values indicate increasing symmetry as x → 1. A temperature dependence study of BaCaFe₄O₈ gave a Neel temperature T_N = 670 K and H_eff(O) = 485 kOe.