1,721,853 research outputs found
An analysis of the compositional techniques in John Chowning's Stria
No full textThis article describes an analytic study of the process used by John Chowning for the composition of Stria. This article is intended to complete the description of the compositional process given in a previous work (Meneghini 2003), largely restated by Bossis in a subsequent paper (Bossis 2005). Stria was composed in 1977 and was fully generated by means of computer algorithms (Chowning 1977c) and the corresponding input files (Chowning 1977a,b): all the parameters of the sounds generated in Stria are determined and calculated by these algorithms on the basis of specific mathematical rules and of numerical parameters chosen by Mr. Chowning as input for the programs. For this reason, an accurate analysis of these algorithms is-fundamental for a complete comprehension of the compositional process. This analysis has three degrees of interest: at first, it enables a study of the composer's intentions regarding the piece's characteristics. Secondly, it complements the comprehension of Stria obtainable from listening with analytic data on the properties of the sounds. Finally, it provides information on the characteristics of the piece that can be used for the re-writing of the algorithms and for the analysis and re-synthesis of the piece (Baudouin 2007; Dahan 2007). The work described in this article began in 2002, and it started with the study of the programming language SAIL) used for the generation of the algorithms (Smith 1976; see also www.xidak.com/mainsail/ documentation_set_1630_html/docset.html), which was necessary for the understanding of the programs. The algorithms (Chowning 1977c) have been then carefully analyzed, line by line, to achieve a complete understanding on how the parameters of each sound generated in Stria are determined. Personal communication with the composer was indispensible for the interpretation of some of the procedures used, and for the understanding of Mr. Chowning's intentions related to programming choices. © 2007 Massachusetts Institute of Technology
Analysis of the physical processes that limit the reliability of GaN-based optoelectronic devices
Full text linkThis thesis reports the results of an extensive analysis of the reliability of GaN-based Light-Emitting Diodes (LEDs) and Laser Diodes (LDs). The analysis has been carried out in close cooperation with the manufacturers of the devices: for this reason, we have worked on state-of-the-art LEDs, lasers and R&D samples, providing a feedback to the manufacturer on the weaknesses of adopted technology. By means of specific experiments on suitable test structures, we have been able to separately analyze (i) the degradation of the LEDs active region, (ii) the role of passivation layer in limiting LEDs reliability, (iii) the degradation of the ohmic contacts of the devices, (iv) the degradation of the properties of LEDs package and resins and (v) the degradation of violet laser diodes and its dependence on driving conditions
Reliability issues in GaN-Based optoelectronic devices: from material to package
No full textGallium Nitride optoelectronic devices are expected to significantly penetrate the market, due to
their intrinsically high efficiency and to their long expected lifetime. However, over the last few
years, several authors have demonstrated that the lifetime of LEDs and lasers based on GaN can be
shorter than expected: this is due to the existence of a number of physical mechanisms that can
determine the degradation of the devices, when they are submitted to high current or high
temperature stress conditions. With this presentation we give a complete description of the physical
processes that limit the reliability of optoelectronic devices on Gallium Nitride. Based on a number
of case studies, we describe in detail (i) the degradation of the active region of the devices due to
the generation of point and extended defects; (ii) the electro-optical degradation of high power
Light-Emitting Diodes related to the worsening of the properties of the ohmic contacts; (iii) the
degradation of the facets of high power laser diodes; (iv) the degradation mechanisms of high power
white LEDs due to the worsening of the optical properties of the package. The presented results
provide important information on the weaknesses of state-of-the-art optoelectronic devices,
including high power white LEDs, Blu-Ray laser diodes, and Deep-Ultraviolet Light-Emitting
Diodes. Furthermore, presentation will provide hints for the design of procedures for reliability
evaluation, based on the execution of accelerated stress tests, and on the combined electrical, optical
and thermal characterization of LEDs and lasers. Results are compared with literature data
throughout the presentation
Recent advancements in the reliability of GaN-based LEDs
No full textWith this paper we give an overview on the
physical mechanisms that limit the reliability of
GaN-based LEDs. In particular, we describe
recent data concerning (i) the degradation of
the active layer of LEDs, due to the increase in
non-radiative recombination; (ii) the degradation
of the chromatic properties of white LEDs,
submitted to high current/temperature stress;
(iii) the degradation of LEDs submitted to reverse-
bias stress tests; (iv) the catastrophic
failure of advanced LED structures, related to
Electrostatic Discharge (ESD) events. The
presented results provide important information
on the weaknesses of LED technology and on
the design of procedures for reliability evaluation
State of the art in the reliability of GaN-based LED
No full textWith this paper we give an overview on the physical
mechanisms that limit the reliability of GaN-based LEDs. In
particular, we describe recent data concerning (i) the degradation
of the active layer of LEDs, due to the increase in non-radiative
recombination; (ii) the degradation of the chromatic properties of
white LEDs, submitted to high current/temperature stress; (iii) the
degradation of LEDs submitted to reverse-bias stress tests; (iv) the
catastrophic failure of advanced LED structures, related to
Electrostatic Discharge (ESD) events. The presented results
provide important information on the weaknesses of LED
technology and on the design of procedures for reliability evaluation
Reliability of GaN-based optoelectronic devices: state of the art and perspectives
No full textWith this work we review the failure modes and mechanisms of GaN-based optoelectronic devices. A number of reliability tests are presented and specific degradation mechanisms of state-of-the-art optoelectronic devices are analyzed. In particular, we describe recent results concerning (i) the degradation of the active layer of LEDs and lasers, due to the increase in non-radiative recombination; (ii) the degradation of LEDs submitted to reverse-bias stress tests; (iii) the catastrophic failure of advanced LED structures, related to Electrostatic Discharge (ESD) events; (iv) the degradation of the ohmic contacts of GaN-based LEDs; (v) the degradation of the optical properties of the package/phosphors system of white LEDs. The presented results provide important information on the weaknesses of LED technology and on the design of procedures for reliability evaluation. Results are compared with literature data throughout the presentation
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