Deep submicron CMOS based on silicon germanium technology

The advantages to be gained by using SiGe in CMOS technology are examined, Conventional MOSFETs are compared with SiGe heterojunction MOSFETs suitable for CMOS technology and having channel lengths between 0.5 and 0.1 μm. Two-dimensional computer simulation demonstrates that the improved mobility in the SiGe devices, due to higher bulk mobility and the elimination of Si/SiO₂ interface scattering by the inclusion of a capping layer, results in significant velocity overshoot close to the source-end of the channel. The cut-off frequency, f_t , is found to increase by around 50% for n-channel devices while more than doubling for p-channel devices for typical estimates of mobility. The results offer the prospect of a more balanced CMOS and improved circuit speed especially when using dynamic logic     

Compatibilizing PPE and PA6 with nitro-phthalimide derivatives

Compatibilization of poly(2,6-dimethyl (PPE) with 1,4 phenylene-ether) PA6 has been achieved in two steps: first, (PPE) was functionalized with N-methyl-4-nitro-phthalimide; then, functionalized PPE was allowed to react, by melt blending, with the amine end group of PA6, giving a trans-imidation product. The reaction path was followed by torque measurements in a Brabender apparatus and the products characterized by infrared (i.r.) and nuclear magnetic resonance (NMR) spectroscopy. The above PPE/PA6 blends, modified with a suitable rubbery component (Kraton G), showed a remarkable Izod impact strength value, compared to the uncompatibilized mixture (170 versus 30 Jm^–1). The maximum impact values were obtained with 1.65% functionalized PPE.     

Diffusion bonding of an aluminium-lithium alloy (AA8090) using aluminium-copper alloy interlayers

Diffusion bonds have been produced between sheets of an Al-Li-Cu-Mg-Zr alloy using aluminium-4% copper vapour deposited metallic interlayers. Microstructural changes occurred both in the parent alloy and in the bond interface after diffusion bonding cycles and post-bonding heat treatments were analysed. Different metallographic techniques (light microscopy, scanning and transmission electron microscopy) have been used. Diffusion bonding trials were carried out using the same alloy (AA8090), both in non-superplastic (T6) and superplastic conditions. Differences in their behaviours in relation to diffusion bonding were observed.     

Air bearing design, optimization, stability analysis andverification for sub-25 nm flying

Three sub-25 nm fly height sliders are presented for near contact recording. The designs are geared towards the goal of achieving 10 Gb/in ² areal density. The optimization procedure presented shows promise for facilitating achievement of this goal. The dynamic simulations show the stability of these designs when disturbed from their steady state conditions     

Millimeter-scale actuator with fiber-optic roller bearings

A technique combining semiconductor processing and fiber-optic technology has been developed to micromachine a 1-cm² silicon die that rolls on two wheels above a flat substrate. Each wheel consists of a glass capillary surrounding a fixed solid glass fiber axle. A 100-silicon die is anisotropically etched to create two variable width v-grooves. Each v-groove has a wide center section and two narrow ends, which is schematically illustrated as -==-. The capillary is free to rotate about the axle in the wide v-groove section while the axle is anodically bonded into the narrow v-groove ends. The gap between the die and the substrate is determined by the narrow v-groove width, fiber diameter, and capillary wall thickness. Several rolling die have been fabricated with 210-120 μm gaps. The coefficient of static friction (μ_S) has been investigated on several substrates as a function of the load on the die. Values for μ_S are compared to an unetched die with a silicon nitride coating. With loads ranging from 0-10 grams, the wheels reduce μ_S by more than 50% on borosilicate glass     

Recent developments in the extrusion of helical gears

With an improved die, a method for manufacturing gears by means of tube extrusion has been developed to a stage where, without noticeable wear of the die, 40,000 workpieces can be manufactured. The paper presents a numerical analysis of the stresses and deflection of the die, offering also a comparison between the modified and the conventional symmetric orifice. Based on the results obtained and using recent work on crack prediction for extrusion dies, the area most prone to rupture is determined. Moreover, a concept for the precorrection of the die is offered to improve the tooth quality of the gears.     

Properties of permease dimer, a fusion protein containing two lactose permease molecules from Escherichia coli

An engineered fusion protein containing two tandem lactose permease molecules (permease dimer) exhibits high transport activity and is used to test the phenomenon of negative dominance. Introduction of the mutation Glu-325-->Cys into either the first or the second half of the dimer results in a 50% decrease in activity, whereas introduction of the mutation into both halves of the dimer abolishes transport. Lactose transport by permease dimer is completely inactivated by N-ethylmaleimide; however, 40-45% activity is retained after N-ethylmaleimide treatment when either the first or the second half of the dimer is replaced with a mutant devoid of cysteine residues. The observations demonstrate that both halves of the fusion protein are equally active and suggest that each half may function independently. To test the possibility that oligomerization between dimers might account for the findings, a permease dimer was constructed that contains two different deletion mutants that complement functionally when expressed as untethered molecules. Because this construct does not catalyze lactose transport to any extent whatsoever, it is unlikely that the two halves of the dimer interact or that there is an oligomeric interaction between dimers. The approach is consistent with the contention that the functional unit of lactose permease is a monomer.