Development of a microelectromechanical system pressure sensor for rehabilitation engineering applications

Based on computer finite-element analysis ANSYS 5.3 and microelectromechanical systems (MEMS) technologies, a micropressure sensor was designed and fabricated. The sensor can be used to measure the distribution of normal stress between soft tissues on an above-knee amputee's skin and the contacting surface of a rehabilitation device. A square membrane with dimensions 2400 µm × 2400 µm × 80 µm is formed by backside photolithography and wet etching of an n-type ?100? monolithic silicon wafer. On the middle of the membrane edge, an X-shaped silicon wafer was implanted with boron ions and then enhanced by diffusion to form a piezoresistive strain gauge. In the design process, a finite-element method is used to analyse the effects of pressure sensitivity and its temperature coefficients. The developed micropressure sensors, which have smaller weight and volume than a conventional machine type, perform well and fit our design specifications.     

Globalization and heterogenization: Cultural and civilizational clustering in telecommunicative space (1989–1999)

The globalization of telecommunicative ties between nations is studied from a heterogenization perspective. A theoretical model inspired by Appadurai’s “disjuncture hypothesis,” which stipulates that global flows of communication are multidimensional and reinforce regional/local identities, is tested empirically on an international voice traffic dataset. Spatial-statistical measures (global and local versions of Moran’s I) indicate that countries that share the same linguistic (English, Spanish, or French) or civilizational (Catholic, Protestant, and Buddhist–Hindu) background are more likely to be each other’s “telecommunicative neighbors” and that this tendency has increased over time (1989–1999).     

Current gain dependence on subcollector and etch-stop doping inInGaP/GaAs HBTs

The DC current gain dependence of InGaP/GaAs heterojunction bipolar transistors (HBTs) on subcollector and etch-stop doping is examined. Samples of InGaP/GaAs HBTs having various combinations of subcollector doping and etch-stop doping are grown, and large area 60 μm×60 (μ) HBTs are then fabricated for DC characterization. It is found that the DC current gain has a strong dependence on the doping concentration in the subcollector and the subcollector etch-stop. Maximum gain is achieved when the subcollector is doped at 6~7×10 ¹⁸ cm^-3 while the subcollector etch-stop is doped either above 6×10¹⁸ cm^-3 (current gain/sheet resistance ratio, β/R_b=0.435 at I_c=1 mA) or below 3.5×10¹⁷ cm^-3 (β/R_b=0.426~0.438 at I_c=1 mA). The data show that it is not necessary to heavily dope the subcollector etch-stop to reduce the conduction barrier and to obtain high current gain. The high current gain obtained with the low InGaP etch-stop doping concentration is attributed to the reduction of the effective energy barrier thickness due to band bending at the heterojunction between the InGaP etch-stop and the GaAs subcollector. These results show that the β/R_b of InGaP/GaAs HBTs can improve as much as 69% with the optimized doping concentration in subcollector and subcollector etch-stop     

Maximum contrast beamformer for electromagnetic mapping of brain activity

Beamforming technique can be applied to map the neuronal activities from magnetoencephalographic/electroencephalographic (MEG/EEG) recordings. One of the major difficulties of the scalar-type MEG/EEG beamformer is the determination of accurate dipole orientation, which is essential to an effective spatial filter. This paper presents a new beamforming technique which exploits a maximum contrast criterion to maximize the ratio of the neuronal activity estimated in a specified active state to the activity estimated in a control state. This criterion leads to a closed-form solution of the dipole orientation. Experiments with simulation, phantom, and finger-lifting data clearly demonstrate the effectiveness, efficiency, and accuracy of the proposed method.     

Titanium nitride electrodes for micro-gap discharge

Titanium and titanium nitride (TiN) were used as thin film electrodes for a micro-gap discharge device. The titanium electrodes were fabricated by sputter deposition of pure titanium accompanied with a lift-off process. The TiN electrodes were prepared by nitriding the titanium electrodes with nitrogen plasma. Gas discharges between the electrodes at various argon pressures were characterized and their breakdown voltages were compared. Both the titanium and TiN electrodes have a minimum breakdown voltage about 220 V at a pressure spacing product (P·d) of 0.8 mbar·cm. The nitrided electrodes were more durable than the as-deposited titanium electrodes upon a DC discharge for 5 s or 200 cycles of electrostatic discharge.     

Interfacial Reactions of Sn, Sn-3.0Ag-0.5Cu, and Sn-9Zn Lead-Free Solders with Fe-42Ni Substrates

Interfacial reactions between Sn, Sn-3.0 wt.%Ag-0.5 wt.%Cu (SAC), and Sn-9 wt.%Zn (SZ) lead-free solders and Fe-42 wt.%Ni (alloy 42) substrates at 240°C, 255°C, and 270°C were investigated in this study. FeSn₂, (Fe,Ni, Cu)Sn₂, and (Ni,Fe)₅Zn₂₁ phases were formed, respectively, at the interface in the Sn/alloy 42, SAC/alloy 42, and SZ/alloy 42 couples. As the reaction time and temperature were increased, the layered intermetallic compound (IMC) assumed two distinct structures, i.e., a thicker layer and a pillar-shaped IMC, in all couples. The IMC thickness of these couples increased with the increase of reaction time and temperature. The IMC thickness was also proportional to the square root of the reaction time. The interfacial reaction mechanism of these couples was diffusion controlled.     

High performance AlyGa1−yAs-GaAs-lrxGa1−xAs quantum well lasers defined by silicon-oxygen impurity-induced layer disordering

In these experiments impurity-induced layer disordering (IILD) utilizing chemical reduction of SiO₂ by Al (from Al_0.8Ga_0.2As) is employed to generate Si and O to effect layer disordering. The SiO₂-Al_0.8Ga_0.2As reaction is studied with respect to annealing ambient. By controlling the extent of disordering via As₄ overpressure, closely spaced (∼1μm) Si-O IILD buried heterostructure lasers can be optically coupled or uncoupled. Direct observation of O incorporation into the buried layers is shown using secondary ion mass spectroscopy (SIMS). The thermal stability of separate-confinement Al_yGa_1−yAs-GaAs-In_xGa_1−xAs quantum well heterostructure (QWH) laser crystals is investigated using SIMS, transmission electron microscopy (TEM), and photoluminescence (PL) measurements. The data show that the thermal stability of a strained-layer In_0.1Ga_0.9As quantum well (QW) is strongly dependent upon: (1) the layer thickness and heterointerfaces of the Al_yGa_1−yAs-GaAs waveguide layers located directly above and below the QW, (2) the type of surface encapsulant employed, and (3) the annealing ambient. Narrow single-stripe (<2μm) lasers fabricated via Si-O diffusion and layer disordering exhibit low threshold currents (I_th ∼ 4 mA) and differential quantum efficiencies,η, of 22% per facet under continuous (cw) room-temperature operation.     

Structural Properties of Boron-Doped Germanium-Tin Alloys Grown by Molecular Beam Epitaxy

Boron-doped Ge_1?x Sn _x alloys with atomic fractions of tin up to x = 0.08 were grown on n-Ge(001) substrates using solid-source molecular beam epitaxy, in order to study their structural properties. The total boron concentration in the alloys was ~ 10¹⁸ cm^?3 as measured by secondary-ion mass spectroscopy, which also indicated low amounts of impurities such as carbon and oxygen. More than 90% of the Sn atoms occupied substitutional lattice sites in the alloy as determined by Rutherford backscattering spectrometry. High-resolution x-ray diffraction showed that the boron-doped Ge_1?x Sn _x alloys were single crystals that were completely strained with low defect densities and coherent interfaces for thickness up to 90 nm, and for Sn composition of 8%. The boron-doped Ge_1?x Sn _x /n-Ge formed p–n junctions with conventional rectifying characteristics, indicating that the boron produced electrically active acceptor states.     

Effective Number of Samples and Pseudo-Random Nonlinear Distortions in Digital OFDM Coded Signal

This paper concerns the theoretical modeling of OFDM coded signal’s degradation caused by pseudo-random nonlinear distortions introduced by an analog-to-digital or digital-to-analog converter. A new quantity, the effective number of samples, is defined and used for the derivation of accurate expressions for the autocorrelation function and the total power of the distortions. The derivation is based on a probabilistic model of the signal and its transition probability. It is shown that for digital (discrete and quantized) signals the effective number of samples replaces the total number of samples and is the proper quantity defining their properties.