1,721,077 research outputs found
On the short and long term degradation of GaInP/GaAs heterojunction bipolar transistors
No full textThis work deals with the short and long term effects of a current stress performed at room temperature on Carbon doped GaInP/GaAs heterojunction bipolar transistors, The investigation has been carried out by means of DC characterizations and low frequency noise (LFN) measurements in the 250 Hz-100 kHz frequency range. During the stress the devices were biased in the forward active region, a collector-emitter voltage of 7.7 V and a collector current density of 2.2 x 10(4) A/cm(2) were imposed. The effect of the stress on the DC and LFN characteristics were compared and discussed in terms of two recombination mechanisms, The discussion points out that both extrinsic and intrinsic recombination processes have to be taken into account in order to justify the short and long term effects of the electrical stress. (C) 1999 Elsevier Science Ltd. All rights reserved
Evaluation of the hot carrier/ionizing radiation induced effects on the RF characteristics of low-complexity SiGe heterojunction bipolar transistors by numerical simulation
No full textThe hot carriers (HC)/ionizing radiation (IR) effects on the DC and RF characteristics of Si/SiGe HBTs have been investigated by numerical simulations. Once reproduced the typical DC degradation modes, the changes in the scattering (S) parameters were investigated up to 30 GHz. The degradation is caused by the increase of the Shockley-Hall-Read (SHR) surface recombination located around the emitter perimeter. Simulations were carried out by keeping the base or the collector current as they were before introducing the degradation mechanism. When the base current is kept constant, the most relevant effect is a reduction of \ S-21\ while the other S-parameters exhibit only minor changes. On the other hand, no remarkable hot carrier/ionizing radiation effects on the RF characteristics were observed when the collector current was kept constant. (C) 2000 Elsevier Science Ltd. All rights reserved
Hydrogen induced degradation in GaInP/GaAs HBTs revealed by low frequency noise measurements
No full textOne of today’s challenges to enable the improved electrical performances and reliability of microelectronic devices consists in controlling impurities contamination : hydrogen appears to be present in most (if not all) the processes steps of the devices making (ambient atmosphere, or associated with AsH3 -VPE or AsCl3 -VPE for example in GaAs based devices, ...). Hydrogen induced reliability has already been investigated for many technologies Si or GaAs based ((C)MOS, FET, HEMT, PHEMT as well as HBT devices). These effects of hydrogen on electrical behavior and on long term reliability are very difficult to understand because of the different nature and ionic association of hydrogen (H, H+, H-, H2, or associated with impurities (Ge-H, Be-H, C-H, ...). Most of these studies make use of IR, SIMS, Hall measurements : in this paper, we use low frequency noise measurements, associated with static as well as dynamic characterization to identify the degradation process in GaInP/GaAs Heterojunction Bipolar Devices (HBT provided by Thomson LCR). Firstable, we will present the influence of passivation (SiN and GaInP ledge) on the reliability associated with Hydrogen : low frequency noise measurements will be performed in the range of 250Hz to 100 kHz. The noise spectra evolutions (current and voltage noise sources at the input of the device, and their correlation) will allow us to identify the activation process responsible of the static and dynamic rise and fall of the HBT’s current gain. C-H complexes have been proved to be the process responsible of this degradation. Additive reliability tests have been performed on two sets of devices (featuring different emitter length) under two distinct stocking conditions (temperature and biasing of the devices) leading to different junctions temperatures : low frequency and high frequency noise measurements, associated with static and dynamic S parameters measurements will lead to the same conclusions about the hydrogen chemical reaction. C-H complexes breaking, and diffusion of H towards the extrinsic surface of the device have been observed. Sealed devices have proved to get the same degradation signature than on wafer devices : Hydrogen is assumed to be present in high concentration levels in the device layers, and reacts under thermal and electrical stress. This study will also present the emitter orientation effects on the reliability, i.e. of the piezoelectric contribution both to electrical performances and reliability level of the device
Influence of surface recombination on the burn-in effect in microwave GaInP/GaAs HBT's
No full textIn this paper, we report on the early increase of the de current gain (burn-in effect) due to the electrical stress of carbon doped GaInP/GaAs heterojunction bipolar transistors (HBT's). Devices featuring different passivation layers, base doping, and emitter widths were investigated. The obtained data demonstrate that the burn-in effect is due to a reduction of the surface recombination located at the extrinsic base surface, around the emitter perimeter. It is concluded that the recombination centers are related to defects at the passivation/semiconductor interface and that, during the stress, they are passivated by hydrogen atoms released from C-H complexes
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Investigation of the burn-in effect in microwave GaInP/GaAs HBTs by means of numerical simulations
No full textThe GaInP/GaAs HBTs demonstrate outstadning long-term reliability performance. Nevrtheless they still suffer from a short-term DC current gain instability, known as the Burn-in effect. Even if the effect is usually attributed to Hydrogen contamination passivating the Carbon atoms employed as base dopant, the underlying physical mechanism is still unclear.The present work addresses the Burn-in effect by means of numerical simulations performed with the device simulation software BLAZE by Silvaco. The rsults give support to the hypothesis that the Burn-in effect is a surface related phenomenon. The simulations reveal that a fixed surface charge located near the edge of the emitter mesa should be introduced. The work points out also that simultaneous variations of both this charge and of the surface recombination velocity should be taken into account. This simulation approach could be a useful tool, in order to develop a chemical/physical model of the Burn-in effect
Hot Carrier Effects in Si/SiGe HBT's
No full textLife tests were performed at room temperature on Si-SiGe HBTs by reverse biasing the base-emitter junction under open collector conditions. The effects on the DC, the low-frequency noise, and the microwave characteristics were investigated both by the analysis of experimental data and by simulations and analytical models. The stress-induced surface damage close to the emitter perimeter was identified to be the degradation mechanism mainly responsible for the variations observed, in all the investigated parameter
Transimpedance amplifier based full low frequency noise characterization set-up for Si/SiGe HBTs
No full textAn experimental setup, based on current/voltage conversion through transimpedance amplifiers (TAs), has been implemented for the direct full low-frequency noise (LFN) characterization of Si/SiGe heterojunction bipolar transistors (HBTs) in terms of base and collector short-circuit current noise sources. This setup performs a full characterization, as it measures simultaneously the two noise current sources and their correlation, thanks to an original technique based on the specific properties of a specially designed buffer amplifier using a low-noise common-base bipolar transistor (CB BJT). By means of translation formulae, the obtained measurements are compared with those carried out with a multi-impedance technique. They show a good agreement both for the noise sources spectral densities and for their correlation. The TA-based setup provides enhanced capabilities in terms of measurement speed and remote control potentialities
Variations on the Author
Full text link“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
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