BSocial: Deciphering Social Behaviors within Mixed Microbial Populations

BSocial Analysis: http://m4m.ugr.es/BSocial.htmlEcosystem functionality depends on interactions among populations, of the same or different taxa, and these are not just the sum of pairwise interactions. Thus, know-how of the social interactions occurring in mixed-populations are of high interest, however they are commonly unknown due to the limitations posed in tagging each population. The limitations include costs/time in tediously fluorescent tagging, and the number of different fluorescent tags. Tag-free strategies exist, such as high-throughput sequencing, but ultimately both strategies require the use of expensive machinery. Our work appoints social behaviors on individual strains in mixed-populations, offering a web-tool (BSocial http://m4m.ugr.es/BSocial.html) for analyzing the community framework. Our quick and cheap approach includes the periodic monitoring of optical density (OD) from a full combinatorial testing of individual strains, where number of generations and growth rate are determined. The BSocial analyses then enable us to determine how the addition/absence of a particular species affects the net productivity of a microbial community and use this to select productive combinations, i.e., designate their social effect on a general community. Positive, neutral, or negative assignations are applied to describe the social behavior within the community by comparing fitness effects of the community against the individual strain. The usefulness of this tool for selection of optimal inoculum in biofilm-based methyl tert-butyl ether (MTBE) bioremediation was demonstrated. The studied model uses seven bacterial strains with diverse MTBE degradation/growth capacities. Full combinatorial testing of seven individual strains (triplicate tests of 127 combinations) were implemented, along with MTBE degradation as the desired function. Sole observation of highest species fitness did not render the best functional outcome, and only when strains with positive and neutral social assignations were mixed (Rhodococcus ruber EE6, Agrobacterium sp. MS2 and Paenibacillus etheri SH7), was this obtained. Furthermore, the use of positive and neutral strains in all its combinations had a significant higher degradation mean (x1.75) than exclusive negative strain combinations. Thus, social microbial processes benefit bioremediation more than negative social microbial combinations. The BSocial webtool is a great contributor to the study of social interactions in bioremediation processes, and may be used in other natural or synthetic habitat studies.JP was funded by Junta de Andalucía through the “Programa Proyectos de Excelencia” (Project reference P10-RNM-6153). The work was funded by CEIBioTic through their “II Convocatoria de Proyectos I+D+I” (project reference CEI2013-MP-31), the Spanish Ministry of Science and Technology (project reference TIN2012-38805), and the Consejeria de Innovacion, Investigacion y Ciencia, Junta de Andalucia (project reference TIC-02788)

Nouveaux concepts de transistors de puissance à haute mobilité électronique (HEMT) en Nitrure de Gallium (GaN).

AlGaN/GaN HEMTs are very promising candidates for high frequency applications with high power and low noise. While switching applications strongly demand normally-off operation, conventional HEMTs attain a channel populated with electrons at zero gate voltage making them normally-on. For the sake of achieving normally-off HEMTs, several structures have been proposed such as recessed gate structures, fluorine ion treatment, pn junction gate structures, thin AlGaN barrier and Gate Injection transistor. The effectiveness of the agent used to obtain normally-off, whether it is recessing the gate, introducing a cap layer or implanting fluorine, increases as the agent comes closer to the AlGaN/GaN interface. Unfortunately, when introducing a cap layer or recessing the gate, coming closer to the interface means decreasing the barrier thickness, which strongly affects the density of the 2DEG. In the case of fluorine implantation, getting closer will increase the probability of fluorine ions getting into the channel and hence degrade the mobility of the 2DEG. In this work we propose two new concepts to achieve normally-off operation. We suggest the introduction of negative fluorine ions on one hand or a p-GaN region on the other hand, below the channel, under the AlGaN/GaN interface and away from high current density regions. After calibrating the simulator using experimental results from a normally-on HEMT device, we have shown that our proposed structures are more effective: the concentration required to achieve normally-off operation is lower than in the other existing solutions and the confinement of the two dimensional electron gas below the gate is better. The proposed ideas were also applied to Metal Insulator Semiconductor HEMT (MIS-HEMT) and Gate Injection Transistor (GIT), giving rise to a normally-off HEMT with high controllable threshold voltage.Les transistors à haute mobilité électronique (HEMTs) en AlGaN/GaN sont des candidats très prometteurs pour les applications haute fréquence, forte puissance et faible bruit. Alors que les applications de puissance exigent des interrupteurs normally-off, les HEMTs conventionnels sont, eux, normally-on, leur canal (gaz bidimensionnel d’électrons 2DEG) étant peuplé d’électrons pour une tension de grille nulle. Plusieurs structures de HEMTs ont été récemment proposées afin de satisfaire à la fonctionnalité normally-off : les plus notables sont celles à grille enterrée (“recessed gate”), à traitement aux ions fluor, à grille de jonction pn, à fine barrière d’AlGaN et à injection de grille (“Gate Injection Transistor”). L’efficacité de l’ « agent » utilisé pour obtenir la fonctionnalité “normally-off”, que ce soit une grille enterrée, une couche barrière ou du fluor implanté, augmente lorsque cet agent se rapproche de l’interface AlGaN/GaN. Malheureusement, introduire une couche barrière ou enterrer une grille proche de cette interface implique une diminution de la hauteur de barrière, ce qui affecte fortement la densité du gaz 2DEG. Dans le cas d’une implantation de fluor, se rapprocher de l’interface augmente la probabilité que des ions de fluor pénètrent dans le canal et dégradent ainsi la mobilité du 2DEG. Dans ce travail nous proposons deux nouveaux concepts pour réaliser la fonctionnalité normally-off. Nous suggérons l’introduction d’ions fluor négatifs d’une part ou d’une région P-GaN d’autre part, sous le canal et sous l'interface AlGaN/GaN, loin des régions à forte densité de courant. Après étalonnage du simulateur, à partir de résultats expérimentaux d’un dispositif HEMT conventionnel normally-on, nous avons montré que les structures proposées étaient plus efficaces : la concentration requise pour réaliser la fonctionnalité normally-off est plus faible que dans les solutions existantes et le confinement du gaz 2D d’électrons sous la grille est meilleur. Les idées proposées ont été aussi appliquées au Métal-Isolant-Semiconducteur HEMT (MIS-HEMT) et au Gate Injection Transistor (GIT), mettant en évidence la possibilité d’obtenir des HEMTs normally-off avec des tensions de seuil élevées

Localized buried P-doped region for E-mode GaN MISHEMTs

International audienceA new design for an enhancement mode Gallium Nitride based high electron mobility transistor is proposed along with a novel fabrication technique. Normally-off operation is achieved through the introduction of a localized p-region below the AlGaN/GaN interface underneath the gate electrode. Since achieving high hole concentration through ion implantation is experimentally challenging, the effect of a localized buried p-region was replicated through the growth of an epitaxial p-layer in which N-wells will be later introduced. Simulation results conducted under ATLAS, a TCAD simulation tool from Silvaco, demonstrated a successful shift of the threshold voltage to positive values. The physics behind this shift is explained through the band diagram. A sensitivity analysis is conducted showing the effect of device parameters on the threshold voltage and the current density

A solution for channel electron migration in normally-off MIS-HEMT with buried fluorine ions

International audienceHigh electron mobility transistors based on Gallium Nitride are promising devices for high frequency and high-power applications. While switching applications demand normally-off operation, conventional HEMTs possess a channel populated with electrons at zero gate voltage making them normally-on. By implanting fluorine below the channel, normally-off operation can be achieved. However, at high gate voltages, a drop in the transconductance is obtained due to electron migration from the AlGaN/GaN interface to the insulator/AlGaN interface. In this work, to recover the drop in the transconductance and hence increase the current density, an AlN interlayer is introduced between the AlGaN and GaN layers to block electron migratio

Localized buried P-doped region for E-mode GaN MISHEMTs

International audienceA new design for an enhancement mode Gallium Nitride based high electron mobility transistor is proposed along with a novel fabrication technique. Normally-off operation is achieved through the introduction of a localized p-region below the AlGaN/GaN interface underneath the gate electrode. Since achieving high hole concentration through ion implantation is experimentally challenging, the effect of a localized buried p-region was replicated through the growth of an epitaxial p-layer in which N-wells will be later introduced. Simulation results conducted under ATLAS, a TCAD simulation tool from Silvaco, demonstrated a successful shift of the threshold voltage to positive values. The physics behind this shift is explained through the band diagram. A sensitivity analysis is conducted showing the effect of device parameters on the threshold voltage and the current density

New termination architecture for 1700 V diamond schottky diode

International audienceNew field plate architecture is applied to pseudo vertical diamond Schottky diode. Using several field plate architectures, a TCAD simulation is realized in order to reduce the electric field in the dielectric while maintaining high breakdown voltage. Firstly and after simple variations in the field plate architecture, the breakdown voltage was improved from 1632 V to 2141 V at 700 K. Concerning Emax in the dielectric, we obtained a decreasing of maximum electric field from 57 to 18 MV/cm

Un interrupteur GaN HEMT normally-off grâce à des ions fluor implantés sous l'interface AlGaN/GaN

National audienceAlGaN/GaN HEMTs are very promising candidates for high frequency applications with high power and low noise. Unfortunately, while switching applications strongly demand normally-off operation, conventional HEMTs are normally-on. For the sake of achieving normally-off HEMTs, several structures have been proposed. One of the major normally-off HEMTs uses fluorine implantation in the AlGaN layer. We suggest in this work the implantation of fluorine ions under the AlGaN/GaN interface only below the gate electrode rather than implanting in the AlGaN layer. Simulation results show that the proposed method is capable of achieving normally-off operation and more effective when it comes to the fluorine concentration required to obtain the desired threshold voltage. Neither the vertical breakdown voltage, nor the off-state current are affected by this approach.Les HEMTs en AlGaN/GaN sont des candidats prometteurs pour les applications forte puissance, haute fréquence et faible bruit. Grâce au champ électrique critique élevé du GaN et à la haute mobilité électronique dans le gaz bidimensionnel (2DEG) du HEMT, ce composant peut afficher des tenues en tension et des fréquences de commutation élevées ainsi que des résistances à l'état passant faibles, dépassant ainsi les limites des composants conventionnels en silicium. Alors que les applications de commutation de puissance nécessitent très souvent des composants normally-off, les HEMTs conventionnels ont un fonctionnement normally-on. C'est pourquoi plusieurs structures de HEMTs normally-off ont été proposées récemment dans la littérature, l'une d'entre elles utilisant l'implantation de fluor dans la couche d'AlGaN. Dans ce travail, nous suggérons d'implanter les ions fluor non pas dans l'AlGaN mais dans la couche de GaN, sous l'interface AlGaN/GaN et seulement sous l'électrode de grille. Les résultats de simulations montrent que la méthode proposée permet d'obtenir un fonctionnement normally-off. En outre, cette méthode semble être plus efficace, notamment en terme de concentration du fluor implanté, qui est le paramètre d'ajustement permettant d'obtenir la tension de seuil souhaitée

Enhancement mode HEMT using fluorine implantation below the channel

International audienceGallium nitride based high electron mobility transistors (HEMT) are powerful candidates for high frequency and high power applications. While switching applications demand normally-off operation, these devices are normally-on. Recent normally-off HEMTs were demonstrated by implanting fluorine above the channel, in the barrier layer. During implantation, fluorine ions penetrate into the channel and cause mobility degradation. In this paper, we propose and simulate an alternative approach in which fluorine ions are implanted below the channel of the HEMT rather than above it. The simulation tool ATLAS is calibrated using experimental data from a real HEMT device. Simulation results have shown that implanting fluorine ions below the channel is capable of achieving normally-off operation. When compared to the implantation in the barrier layer, the proposed approach offers better confinement for the two dimensional electron gas (2DEG) below the gate, eliminates the scattering of fluorine ions with channel electrons and is more efficient when it comes to the fluorine concentration required to achieve a desired threshold voltage. This technique neither affects the breakdown voltage nor the off-state current

P-doped region below the AlGaN/GaN interface for normally-off HEMT

International audienceDevelopment of a new design for enhancement-mode AlGaN/GaN HEMT is presented. The normally-off operation was achieved by burying a p-GaN region below the AlGaN/GaN interface only below the gate. Simulation results show that the proposed technique is capable of shifting the threshold voltage to positive values, making the HEMT normally-off. To address the advantages and drawbacks of the proposed structure a comparison with the normally-off Gate injection transistor (GIT) was performed. The proposed structure seems to be more effective when it comes to the p-doping concentration required to achieve normally-off operation and offers superior confinement for the two dimensional electron gas. On the other hand, the low forward gate voltage limits the increase of the threshold voltage