Investigation of electroless cobalt-phosphorous layer and its diffusion barrier properties of Pb-Sn solder

The capability of a cobalt-phosphorous [Co(P)] layer, which was grown via the electroless plating process, to serve as the diffusion barrier of lead-tin (PbSn) solder was investigated in this work. The Auger electron spectroscopy (AES) and energy dispersive spectrometry (EDX) indicated that the phosphorous contents in Co(P) films decrease with increasing film thickness and that the average contents are no less than 8.7 at.% for the specimens prepared in this work. X-ray diffraction in conjunction with composition analyses revealed that the electroless Co(P) layer was a mixture of amorphous and nanocrystalline structures; however, the AES depth profile and subsequent analyses indicated that the first-formed Co(P) layer should be amorphous because it contains as much as 18 at.% P. This implied a good barrier capability for electroless Co(P) because, as revealed by EDX line scan, the Sn and Cu atoms could not penetrate the Co(P) layer after the PbSn/Cu/Co(P)/Cu/Ti/Si sample was subjected to annealing at 250°C in a forming gas ambient for 24 h. The fact that Sn and Cu underlayers could not penetrate the Co layer after such a liquid-state annealing step was evidence that the Co(P) layer may simultaneously serve as a diffusion-barrier interlayer dielectric and as an under-bump metallization for flip-chip copper (Cu) ICs.     

New nonlinear algorithms for estimating and suppressing narrowbandinterference in DS spread spectrum systems

It has been shown that the narrowband (NB) interference suppression capability of a direct-sequence (DS) spread spectrum system can be enhanced considerably by processing the received signal via a prediction error filter. The conventional approach to this problem makes use of a linear filter. However, the binary DS signal, that acts as noise in the prediction process, is highly non-Gaussian. Thus, linear filtering is not optimal. Vijayan and Poor (1990) first proposed using a nonlinear approximate conditional mean (ACM) filter of the Masreliez (1975) type and obtained significant results. This paper proposes a number of new nonlinear algorithms. Our work consists of three parts. (1) We develop a decision-directed Kalman (DDK) filter, that has the same performance as the ACM filter but a simpler structure. (2) Using the nonlinear function in the ACM and the DDK filters, we develop other nonlinear least mean square (LMS) filters with improved performance. (3) We further use the nonlinear functions to develop nonlinear recursive least squares (RLS) filters that can be used independently as predictors or as interference identifiers so that the ACM or the DDK filter can be applied. Simulations show that our nonlinear algorithms outperform conventional ones     

On the relation between V-BLAST and the GDFE

This letter shows that the receiver processing of the Vertical Bell Labs Layered Space-Time (V-BLAST) architecture may he viewed as a generalized decision feedback equalizer (GDFE) as applied to a multiple-input-multiple-output (MIMO) channel. It is proven that, depending on the criterion chosen to reduce the interference, the receiver operations of the V-BLAST system are fundamentally equivalent to either a zero-forcing (ZF) or a minimum-mean-square-error (MMSE) GDFE     

Ferroelectric neuron integrated circuits using SrBi2Ta2O9-gate FET's and CMOS Schmitt-triggeroscillators

A pulse frequency modulation (PFM) type ferroelectric neuron circuit composed of a metal-ferroelectric-semiconductor field effect transistor (MFSFET) and a CMOS Schmitt-trigger oscillator was fabricated on an SOI structure, in which SrBi₂Ta₂O₉ (SBT) was used as a ferroelectric gate material of the FET. It was found that the fabricated MFSFET showed a relatively good I_D-V_G (drain current versus gate voltage) characteristic with a hysteresis loop due to the ferroelectricity of the SBT film and that it acted as a synapse device with adaptive-learning function. It was also found that the output pulse height of the circuit was as high as the power supply voltage and that output pulse frequency was changed as the number of applied input pulses increased     

Fabrication and performances of a double-layer organicelectroluminescent device using a novel starburst molecule,1,3,5-tris[N-(4-diphenylaminophenyl)phenylamino]benzene, as ahole-transport material and tris(8-quinolinolato)aluminum as an emittingmaterial

A double-layer organic electroluminescent (EL) device was fabricated using a novel starburst molecule, 1,3,5-tris[N-(4-diphenylaminophenyl)phenylamino]benzene (p-DPA-TDAB), as a hole transport material and tris(8-quinolinolato) aluminum (Alq₃ ) as an emitting material, and its performance characteristics were investigated. It was found that p-DPA-TDAB, which forms a stable amorphous glass with a glass-transition temperature of 108°C, functions as a good hole-transport material and that the EL device is thermally stable, operating at a temperature of 120°C     

Psychology and Common Sense

This article examines the nature of the relationship between psychology and common sense. It is postulated that common sense may be categorized in three ways: (a) as a set of shared fundamental assumptions, (b) as a set of maxims or shared beliefs, and (c) as a shared way of thinking. It is further argued that psychology has and should have a different relationship with each area. The role that conceptual analysis and other research techniques can play in investigating commonsense cognitive schemata is discussed. It is concluded that common sense is a valuable but inherently dangerous resource available to psychologists.     

Loop-shaping techniques applied to the least-mean-squares algorithm

The least-mean-squares (LMS) algorithm is analysed as a feedback control system. It is shown that despite the fact that LMS is a time-variant system that in fact it behaves much as a linear time-invariant (LTI) closed-loop control system. Therefore, it is possible to treat the LMS algorithm as a control system in the classical sense and define properties such as bandwidth to determine how fast a response (and hence convergence) is maximally possible. Similarly, the steady-state error response to a deterministic noise-free input can also be calculated. Moreover, it is then shown that classical control-based loop-shaping techniques can be used to improve the performance of the algorithm.     

Double-stream electron cyclotron maser

A new mechanism for stimulated radiation combining the cyclotron instability with the plasma double-stream instability is presented. It can be regarded as a new type of electron cyclotron resonance maser (ECRM) (Hirshfield 1979, Liu 1979) as well as a two-stream free-electron laser (FEL) (Piestrup 1981, Bekefi and Jacobs 1982) in a broader sense. One can say that this device combines ECRM and the two-stream FEL into one. The linear theory of the double-stream ECRM is given. Numerical calculations show that it offers the attractive advantages of high gain and broadband as compared with the conventional ECRM.     

Inherent limitations in data-aided time synchronization ofcontinuous phase-modulation signals over time-selective fading channels

Time synchronization of continuous phase modulation (CPM) signals over time selective, Rayleigh fading channels is considered. The Cramer-Rao lower bound (CRLB) for this problem is studied for data-aided (DA) synchronization (i.e., known symbol sequence transmission) over a time-selective Rayleigh fading (i.e., Gaussian multiplicative noise) channel. Exact expressions for the bound are derived as well as simplified, approximate forms that enable derivation of a number of properties that describe the bound's dependence on key parameters such as signal-to-noise ratio (SNR), channel correlation, sampling rate, sequence length, and sequence choice. Comparison with the well-known slow fading (i.e., constant) channel bound is emphasized. Further simplifications are obtained for the special case of minimum phase keying (MSK), wherein it is shown how the bound may be used as a sequence design tool to optimize synchronization performance     

Vector-valued time-frequency representations

Cohen's (1989) class of time frequency distributions (TFDs), which includes the spectrogram (SP), Wigner distribution (WD), and reduced interference distributions (RIDs) has become widely known as a useful signal analysis tool. It has been shown that every real-valued TFD can be written as a weighted sum of SPs. The “SP decomposition” has been used to construct fast approximations to desirable TFDs using the SP building block, for which there exist accessible and efficient hardware and software implementations. We introduce a class of linear, vector-valued time-frequency representations (TFRs) that are easily related to associated bilinear TFDs through the SP decomposition. We solve a least-squares signal synthesis problem on modified vector-valued TFRs that are associated with nonnegative TFDs as a weighted sum of least-squares short-time Fourier transform (STFT) signal synthesis schemes. We extend the solution to vector-valued TFRs associated with high-resolution TFDs in order to define a high-resolution alternative to STFT signal synthesis, as demonstrated by desirable properties and examples. The resulting signal synthesis methods can be realized as a weighted sum of STFT synthesis schemes, for which there exist accessible and efficient hardware and software implementations     

ESD phenomena in GMR heads in the manufacturing process of HDD and GMR heads

It is well known that giant magnetoresistive (GMR) heads used for hard disk drives (HDD) are very sensitive to electrostatic discharge (ESD). In this paper, we describe a method of categorizing ESD damage modes from a standpoint of magnetic influences on the heads as observed by quasi-static test (QST) characteristics as well as electromagnetic characteristics like off-track profiles. In addition, we report an example of GMR stack interlayer diffusion which is one type of hard ESD damage. We also present an example of ESD damage that happened in an actual production process and its preventive measures as guidelines.     

Performance analysis of DS/SSMA unslotted ALOHA system withvariable length data traffic

We analyze the throughput of a direct-sequence spread spectrum multiple access (DS/SSMA) unslotted ALOHA system with variable length data traffic. The system is analyzed for two cases: (1) systems without a channel load sensing protocol (CLSP) and (2) systems with a CLSP. The bit-error probability and the throughput are obtained as a function of the signal-to-noise ratio (SNR) during message transmission, considering the number of overlapped messages and the amount of time overlap. We assume that the generation of data messages is Poisson distributed and that the messages are divided into packets before transmission. The system is modeled as a Markov chain under the assumption that the number of packets in a message is geometrically distributed with a constant packet length. The throughput variance of the DS/SSMA unslotted ALOHA system with variable length data traffic is obtained as the Reed-Solomon code rate varies. Results show that a significant throughput improvement can be obtained by using an error-correcting code     

Abelian codes over Galois rings closed under certain permutations

We study n-length Abelian codes over Galois rings with characteristic p/sup a/, where n and p are relatively prime, having the additional structure of being closed under the following two permutations: (i) permutation effected by multiplying the coordinates with a unit in the appropriate mixed-radix representation of the coordinate positions and (ii) shifting the coordinates by t positions. A code is t-quasi-cyclic (t-QC) if t is an integer such that cyclic shift of a codeword by t positions gives another codeword. We call the Abelian codes closed under the first permutation as unit-invariant Abelian codes and those closed under the second as quasi-cyclic Abelian (QCA) codes. Using a generalized discrete Fourier transform (GDFT) defined over an appropriate extension of the Galois ring, we show that unit-invariant Abelian and QCA codes can be easily characterized in the transform domain. For t=1, QCA codes coincide with those that are cyclic as well as Abelian. The number of such codes for a specified size and length is obtained and we also show that the dual of an unit-invariant t-QCA code is also an unit-invariant t-QCA code. Unit-invariant Abelian (hence unit-invariant cyclic) and t-QCA codes over Galois field F/sub p//sup l/ and over the integer residue rings are obtainable as special cases.     

TE- and TM-coupling coefficients in multiquantum well distributed feedback lasers

Transverse-electric (TE)- and transverse-magnetic (TM)-coupling coefficients for typical 1.55- mu m InGaAs/InP buried-heterostructure (BH) multiquantum-well (MQW) distributed-feedback (DFB) lasers are calculated as a function of waveguide and grating parameters using coupled-mode theory. It is shown that the TE- and TM-coupling coefficients become maximum at a certain number of wells; that number is smaller for TE modes than for TM modes, and increases as the BH stripe width decreases. The difference between the TE- and TM-coupling coefficients decreases as the number of wells increases. There exists a value of the thickness of the grating layer which maximizes the coupling coefficient.<>     

A New Planar InGaAs&#8211;InAlAs Avalanche Photodiode

We discuss a new simple InGaAs–InAlAs avalanche photodiode (APD) with a planar buried multiplication region. Some of the advantages compared to standard APDs are as follows: 1) The thickness of the avalanche and the charge control regions are accurately controlled by molecular beam epitaxy growth in contrast to the standard diffusion process; 2) InAlAs is the multiplication material (avalanching faster electrons) instead of InP (avalanching slower holes); 3) InAlAs avalanche gain has a lower noise figure than that for InP; 4) a guard ring is not required; 5) fabrication is as simple as that for a p-i-n detector; 6)the APD has high wafer uniformity, and high reproducibility; 7)the InAlAs breakdown voltage is lower than InP, and its variation with temperature is three times lower than that for InP; 8) excellent aging and reliability including Telcordia GR-468 qualification for die and modules; 9) high gain-bandwidth product as high as 150 GHz; and 10) high long-range (LR-2) bit-error-rate$10^-12$receiver sensitivity of$-$29.0 dBm at 10 Gb/s,$-$28.1 at 10.7Gb/s, and$-$27.1 dBm at 12.5 Gb/s.     

Potentialities and basic principles of controlling the plastic relaxation of GeSi/Si and Ge/Si films with stepwise variation in the composition

GeSi/Si heterostructures consisting of a plastically relaxed layer that includes various fractions of Ge and which is grown on Si (001) span the values of the lattice parameter from equal to that in silicon to equal to that in germanium. The corresponding substrates are conventionally referred to as artificial. A number of methods exist for growing high-quality GeSi layers with as large as 100% of Ge on Si (001) substrates through an intermediate GeSi layer with a varying composition. However, it is desirable in a number of cases to have ultrathin (<1 μm) GeSi and Ge layers directly on the Si (001) substrate for practical applications. The results of new methods such as the use of a buffer Si layer grown at a comparatively low temperature (300–400°C) in plastic relaxation of the GeSi/Si(001) heterostructures and also the use of surfactants (antimony and hydrogen) are analyzed. The examples of artificial introduction of centers for origination of misfit dislocations as an alternative to their introduction from the rough surface are considered. It can be concluded that, in order to expand the range of potentialities of growing perfect plastically relaxed GeSi (001) films, it is necessary to (i) make it possible to form in a controlled manner the centers for origination of the misfit dislocations and (ii) retard or completely suppress the transition of the growth mechanism from two-to three-dimensional in order to prevent the formation of additional misfit dislocations from the surface of the stressed film and, correspondingly, additional threading dislocations.     

Trends in local wireless networks

Pahlavan (1985) published an article entitled "Wireless office information networks". That article examined spread spectrum, standard radio and infrared (IR) technologies for intra-office wireless networking. In May of that year the FCC released the ISM (industrial, scientific, and medical) bands for spread spectrum local communications. Although ISM bands are not restricted to any specific application, wireless local area networks (LANs) were one of the most prominent applications that were envisioned by the rule makers in the FCC. Since 1985, many small start-up companies, as well as small groups in larger companies, have started to develop wireless LANs. The present paper provides a sequel to Pahlavan by providing an overview of the past and present of the wireless LAN industry, as well as a perspective of the future directions that encompass a vision for a ubiquitous local wireless computing environment that leads to a fusion of communications and computation     

Link-level connection control schemes in a high-speed satellitedata network: a performance comparison

The author makes a performance comparison between a connection-oriented (CO) logical link control (LLC) protocol and a connectionless (CL) LLC protocol in a high-speed satellite packet network with the time-division-multiple-access (TDMA)-reservation multiple-access protocol. In particular, the way that the channel transmission rate affects the performance of the two LLC protocols is examined. The most suitable LLC protocol for any given system environment is determined. The comparison indicates that the CL-LLC protocol has more advantages over the CO-LLC protocol as the channel transmission rate increases and that the suitable region for the CL-LLC protocol becomes wider as the receiver-buffer capacity increases and as the network load decreases     

Dynamic representation-based tracker for long-term pedestrian tracking with occlusion

This paper presents a dynamic representation-based tracker (DRT) to handle occlusions in the long-term pedestrian tracking of a single target. In our DRT, an adaptive representation network (ARN) is first constructed to extract multiple features, including classical features such as appearance and pose as well as some vector-format deep features. These features are then stacked to form a dynamic representation so as to convert the target tracking into a matching problem between the target features and candidate features, where the Euclidean distance (ED) and locality-constrained linear coding (LLC) are used as measurements in the decision-making. Next, the target state is determined through a voting procedure according to the feature matching error. Finally, a pose supervised module (PSM) and an IOU filtering module (IFM) are applied, respectively, to refine the target state and to filter out some invalid candidate targets that have been detected. Experimental results on public benchmark datasets show that our DRT is quite robust to complex environments with long-term pedestrian occlusions, and outperforms several existing state-of-the-arts trackers as it produces the best performance on both the pedestrian tracking dataset with occlusion (PTDO) and the pedestrian tracking dataset with occlusion plus (PTDO Plus).     

Decorrelation of Wavelet Coefficients for Long-Range Dependent Processes

We consider a discrete-time stationary long-range dependent process (X_k)_kisinZ such that its spectral density equals phi(|lambda|)^-2d, where phi is a smooth function such that phi(0)=phi'(0)=0 and phi(lambda)gesclambda for lambdaisin[0,pi]. Then for any wavelet psi with N vanishing moments, the lag k within-level covariance of wavelet coefficients decays as O(k^2d-2N-1) when krarrinfin. The result applies to fractionally integrated autoregressive moving average (ARMA) processes as well as to fractional Gaussian noise