G. Soncini

A Foveated Retina-Like Sensor Using CCD Technology

A CCD imager whose sampling structure is loosely modeled after the biological visual system is described. Its architecture and advantages over conventional cameras for pattern recognition are discussed. The sensor has embedded in its structure a logarithmic transformation that makes it size and rotation invariant. Simulations on real images using the actual sensor geometry have been performed to study the sensor performance for 2D pattern recognition and object tracking.

On phosphorus diffusion in silicon under oxidizing atmospheres

Phosphorus diffusion in silicon has been carried out in both inert (nitrogen) and oxidizing (90% nitrogen plus 10% oxygen, dry oxygen, steam) atmospheres, over a wide temperature range (1000–1200°C) and for doping concentrations usually encountered in the silicon planar technology. The experimental data, interpreted on the basis of the Kato and Nishi theoretical model taking into account the redistribution phenomena at the moving oxide-silicon interface, show that the phosphorous diffusion coefficient is strongly influenced by the nature of the ambient atmosphere in which the diffusion is carried out. Two different values for the activation energy of the diffusion process, Ei = 3·5 eV for the inert and E0 = 2·5 eV for the oxidizing conditions, have been found. These values seem to confirm the phosphorous diffusion mechanism based on E-centers for the inert case, while for the oxidizing case a different diffusion mechanism should be considered.

A retinal CCD Sensor for fast 2D shape recognition and tracking

Abstract A human-retina-like image sensor has been developed for applications in robotics. The CCD imager has a circular pixel organization and the resolution is a decreasing function of the radius. Detailed software modeling resulted in an imager design consisting of four main parts: a circular CCD, a radial CCD, a coupler and an output structure. In order to avoid a blind spot in the center, a central fovea with a rectangular interline transfer imager is included. This paper outlines in detail the design concepts and reports on the electrical performance and functionality of the first prototypes.

Oxidation-rate dependence of phosphorus diffusivity in silicon

Abstract The diffusion of phosphorus in silicon at 1100°C in inert and three different oxidizing atmospheres has been investigated by using the standard two stages technique, and the results interpreted using the Kato and Nishi theoretical model. A linear relationship has been obtained between the silicon oxidation rate and the induced enhancement of phosphorus diffusivity, in agreement with the hypothesis of - excess interstitials generated at the inward moving oxide-silicon interface. This enhancement has been demonstrated to be practically independent of the distance from the silicon surface. Finally a dual phosphorus diffusion mechanism has been suggested, with a dominant interstitialcy component in oxidizing atmospheres and with a dominant vacancy (E-centre) component in inert atmospheres.

Bipolar Schottky logic device failure modes due to contact metallurgical degradation

Abstract Failure modes of bipolar Schottky logic devices due to metallurgical degradation of PtSi/Ti-W/Al contacts were studied. Both to the purpose prepared wafers and commercial 74LSOO TTL Low-Power Schottky devices were used. Metallurgical failures are primarily due to Al diffusion through the Ti-W barrier layer. As a consequence, thermal treatments induce electrical failures which begin with a loss of fan-out followed by longer rise and fall switching times. Finally complete device failure is observed when the output stays always at the high logic level. Emitter-base leakages and short-circuits, due to Si dissolution in the overlaying metal system, can explain the observed electrical degradations which are markedly delayed by a thin oxygen layer present at the Al/Ti-W interface.

VLSI reliability: Contributions from a three year national research program

The continuous trend to further I.C. miniaturization implies increased local electric field strength and power dissipation density, and a perverse scaling, behaviour of metal interconnections and contacts. This will result in new failure mechanisms while old ones, non under control, may become a threat again. This work reports on the most relevant results, related to VLSI reliability, obtained by the seven University Research Teams involved in a three years Research Program sponsored by the Italian Ministero Pubblica Istruzione. In particular new methods to investigate electromigration and to localize latch-up phenomena have been successfully developed. Also test and diagnosis techniques to analyze faults in digital I.C. with emphasis on ECL and custom VLSI have been studied, and electromagnetic interference effects, in operational amplifiers have been modelled and simulated.

Anisotropic boron diffusion in silicon under oxidizing atmospheres

Abstract The anisotropy of boron diffusion into silicon under oxidizing atmospheres has been experimentally analysed, and the results interpreted by using a modified form of the Kato and Nishi theoretical model. Explanations based on redistribution phenomena and on dislocations induced at the oxide-silicon interface are critically discussed.