Characteristics of the ground-state lasing operation in V-groovequantum-wire lasers

Lasing from the ground subband transition, which has long been attempted in one-dimensional (1-D) structures, has been achieved for the first time with vertically stacked, AlGaAs-GaAs multiple quantum-wire (QWR) lasers, fabricated by flow-rate modulation epitaxy on V-groove substrates. Direct experimental evidence is provided by the consistency of the photon energies of the lasing and photoluminescence peaks, in the temperature range 4.5 K-300 K. It is further ensured by numerical calculation of the electronic subband energy states with the corresponding QWR structure. The lasers with cavity lengths of 350 μm, show fundamental transverse mode, typical threshold current of 5 mA, an internal quantum efficiency of 18.5%, ultrahigh characteristic temperature T₀~322 K above room temperature, and remarkably low wavelength-tuning rates of current (<0.012 nm/mA) and temperature (<0.19 nm/°C). Ultrafast lasing behaviors at the ground (n=1) and the second (n=2) transition of the QWR are also investigated in terms of the gain-switching method, using a characteristic of the wavelength shift from the n=1 to the n=2 subband with shortening the cavity length     

Vector-scalar-product circuit concept

A new circuit concept of vector-scalar-product and weighted-sum function implementation based on the translinear realisation of vector-space operation in the phase domain is introduced. The resulting nonlinear translinear circuit is a compact, power-efficient realisation of the weighted-sum function     

Influence of energy-transfer upconversion on the performance ofhigh-power diode-end-pumped CW lasers

The influence of energy-transfer upconversion (ETU) on the performance of diode-end-pumped lasers is studied by including ETU effects into the space-dependent rate equations. The dependence of ETU rates on the mode-to-pump size ratio and on the output mirror transmission is derived. Experiments for Nd:YAG and Nd:YVO₄ crystals are performed to validate the present model. It is found that the ETU process increases the sensitivity of the output power to the output mirror transmission but its influence on the output power is not significant for low output transmission     

A micromachined silicon depth probe for multichannel neural recording

A process of making a new type of silicon depth-probe microelectrode array is described using a combination of plasma and wet etch. The plasma etch, which is done using a low temperature oxide (LTO) mask, enables probe thickness to be controlled over a range from 5 to 90 mu. Bending tests show that the probe's mechanical strength depends largely on shank thickness. More force can be applied to thicker shanks while thinner shanks are more flexible. One can then choose a thickness and corresponding mechanical strength using the process developed. The entire probe shaping process is performed only at low temperature, and thus is consistent with the standard CMOS fabrication. Using the probe in recording from rat's somatosensory cortex, we obtained four channel simultaneous recordings which showed clear independence among channels with a signal-to-noise ratio performance comparable with that obtained using other devices.     

Separation of effects of statistical impurity number fluctuationsand position distribution on Vth fluctuations in scaled MOSFETs

We have investigated the effect of the statistical “position” distribution of dopant atoms on threshold voltage (V_th) fluctuations in scaled MOSFETs. The effects of impurity “number” fluctuations and impurity “position” distribution are successfully separated in two-dimensional simulation for fully-depleted (FD) SOI MOSFETs. It is found that the contribution by the position distribution is closely related to the charge sharing factor (CSF) and the effect of the impurity position distribution becomes dominant as CSF is degraded. Consequently, the contribution ratio of the impurity position distribution is kept almost constant when the device is properly scaled     

Asymptotic global confidence regions in parametric shape estimationproblems

We introduce confidence region techniques for analyzing and visualizing the performance of two-dimensional parametric shape estimators. Assuming an asymptotically normal and efficient estimator for a finite parameterization of the object boundary, Cramer-Rao bounds are used to define an asymptotic confidence region, centered around the true boundary. Computation of the probability that an entire boundary estimate lies within the confidence region is a challenging problem, because the estimate is a two-dimensional nonstationary random process. We derive lower bounds on this probability using level crossing statistics. The same bounds also apply to asymptotic confidence regions formed around the estimated boundaries, lower-bounding the probability that the entire true boundary lies within the confidence region. The results make it possible to generate asymptotic confidence regions for arbitrary prescribed probabilities. These asymptotic global confidence regions conveniently display the uncertainty in various geometric parameters such as shape, size, orientation, and position of the estimated object, and facilitate geometric inferences. Numerical simulations suggest that the new bounds are quite tight     

Osmium-metal coating device using hollow-cathode plasma CVD method

A novel osmium-metal coating device for SEM observation has been developed to prevent negative charge build-up on specimens by applying the hollow-cathode low voltage discharge plasma chemical vapour deposition (CVD) method. The CVD method using the hollow-cathode offers the following advantages. (i) The method can deposit osmium-metal at very low discharge voltage that is as low as half of that of the planar parallel electrode method. Therefore, the method avoids damage due to ion bombardment during the coating process. (ii) The method can minimize the quantity of the OsO4 gas by introducing directly into the hollow-cathode. This feature is important to prevent the air pollution caused by the purged gas. (iii) A large coating area is guaranteed because the Os ion is filled in the hollow-cathode where the specimen is holed. (iv) The lower discharge voltage can be used by mixing Ar, N2 or air with the OsO4 gas as the environmental gas in the chamber. (v) The hybrid coating is also available by lining the appropriate metal material such as platinum (Pt) on the surface of the inside of the hollow-cathode. The method uses the plasma CVD of Os metal as well as the ion-sputter deposition of the lined metal.     

Copper metallization for advanced IC: requirements and technological solutions

Due to the scaling down, the contribution of interconnects should become preponderant for the performance of IC. The use of low-k dielectrics and/or low resistivity metals in order to decrease the parasitic capacitance of interconnect is a technological requirement. Especially the use of copper, with mineral dielectric as IMD, instead of aluminium alloy is now commonly accepted. In this paper we compare the intrinsic performance of two damascene architectures. The planarization by metal CMP, which will determine the final metal thickness, may induce killer defects (shorts between lines) or degraded metal sheet resistance uniformity for multi-level metallization devices. The impact on electromigration of the damascene structure is presented: due to the reverse architecture, the grain sizes and orientations are found to be linewidth dependent. On the other hand, the life times extrapolated with different copper and barrier deposition processes vary on a large range: from similar to those obtained with aluminium for a full CVD metallization (barrier+copper) to more than one order of magnitude higher for a CVD barrier and a mixed CVD+PVD copper deposition.     

Anisotropic Properties of Bi2Sr2−xLa<Emphasis Type="Italic">x</Emphasis>Cu1O6+δ Thin-Films Grown on Vicinal SrTiO3 Substrates

Epitaxial Bi₂Sr_2?xLa _x Cu₁O_6+δ thin films were grown on vicinal substrates by magnetron sputtering. The growth mode and the superconductivity of the thin films were studied. The films were deposited on 5–7° misoriented (100) SrTiO₃ (STO). The surface of misoriented substrate is tilted to the 〈111〉 azimuth. The topographies of the Bi-2201 films show strip-like shapes. The transmission electron microscopy (TEM) study revealed that the films grew with very good in-plane alignments which were comparable to those of single crystals. Both of the temperature dependence of the a- and c-axis resistivities were studied under magnetic fields. The corresponding anisotropic activation energies and upper critical magnetic fields were investigated.