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La thèse de Giovanni BETTI BENEVENTI portes sur la caractérisation électrique et la modélisationphysique de dispositifs de mémoire non-volatile à changement de phase. Cette thèse a été effectuée dans le cadre d’une cotutelle avec l’Università degli Studi di Modena e Reggio Emilia (Italie).Le manuscrit en anglais comporte quatre chapitres précédés d’une introduction et terminés par uneconclusion générale.Le premier chapitre présent un résumé concernant l’état de l’art des mémoires a changement de phase. Le deuxième chapitre est consacré aux résultats de caractérisation matériau et électrique obtenus sur déposition blanket et dispositifs de mémoire à changement de phase (PCM) basées sur le nouveau matériau GeTe dopé carbone (GeTeC).Le chapitre trois s’intéresse à l’implémentation et à la caractérisation expérimentale d’un setup demesure de bruit a basse fréquence sur dispositifs électroniques a deux terminaux développé auxlaboratoires de l’Università degli Studi di Modena e Reggio Emilia en Italie.Enfin, dans le dernier chapitre est présentée une analyse rigoureuse de l’effet d’auto-chauffage Joulesur la caractéristique I-V des mémoires a changement de phase intégrant le matériau dans la phase polycristalline. / Within this Ph.D. thesis work new topics in the field of Non-Volatile Memories technologies have been investigated, with special emphasis on the study of novel materials to be integrated in Phase-Change Memory (PCM) devices, namely:(a) Investigation of new phase-change materialsWe have fabricated PCM devices integrating a novel chalcogenide material: Carbon-doped GeTe (or simply, GeTeC). We have shown that C doping leads to very good data retention performances: PCM cells integrating GeTeC10% can guarantee a 10 years fail temperature of about 127°C, compared to the 85°C of GST. Furthermore, C doping reduces also fail time dispersion. Then our analysis has pointed out the reduction of both RESET current and power for increasing carbon content. In particular, GeTeC10% PCM devices yield about a 30% of RESET current reduction in comparison to GST and GeTe ones, corresponding to about 50% of RESET energy decrease.Then, resistance window and programming time of GeTeC devices are comparable to those of GST.(b) Advanced electrical characterization techniquesWe have implemented, characterized and modeled a measurement setup for low-frequency noise characterization on two-terminal semiconductor devices.(c) Modeling for comprehension of physical phenomenaWe have studied the impact of Self-induced Joule-Heating (SJH) effect on the I-V characteristics of fcc polycrystalline-GST-based PCM cells in the memory readout region. The investigation has been carried out by means of electrical characterization and electro-thermal simulations.

The main goal of this Master’s thesis is to describe relationship between low frequency noise spectral characteristics of Cadmium-Telluride radiation detectors depending on applied voltage and detectors reaction to illumination of various wavelengths. Also, the reaction and influence of higher operating temperatures were investigated. The noise measurements shown that the dominant noise type at low frequencies is the 1/f noise. Several samples with different resistivity were tested. By comparing results, we are able to estimate the quality of detectors and their sensibility to illumination and higher operating temperatures. We have found that all the studied CdTe detectors are sensitive to one particular wavelength of 548nm. Resulting data were processed by EasyPlot program that provided graphical representation of spectral noise characteristics. All measured characteristics of tested samples are compared and it’s estimated the similarity between the samples.

This letter presents a scalable technique to reduce the power of the analog input stage in neural recording front-ends in Globalfoundries 22 -nm FDSOI. The back-gate voltages are adapted to reduce the threshold voltage and thus allow supply voltage reduction. This adaption increases PVT stability of subthreshold circuits. A comparison to a conventional delta–sigma ADC is drawn and the minimum power point is measured, resulting in 0.7 - μW /channel at 7.2 - μV input-referred noise. Additionally, the transition to smaller technologies promises low-power consumption in the digital domain, by allowing smaller supply voltage and higher integration density.

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Kadmium telurid je velmi důležitý materiál jak základního, tak i aplikovaného výzkumu. Je to dáno zejména jeho výhodnými elektronickými, optickými a strukturními vlastnostmi, které ho předurčují pro náročné technické aplikace. Dnes se hlavně používá pro jeho vysoké rozlišení k detekci a X-záření. Hlavní výhodou detektorů na bázi CdTe je, že nepotřebují chlazení a mohou spolehlivě fungovat i při pokojové teplotě. To způsobuje efektivnější interakce fotonů než je tomu u Si nebo jiných polovodičových materiálů. Obsahem této práce byla analýza a interpretace výsledků získaných studiem šumových a transportních charakteristik CdTe vzorků. Měření ukázaly že odpor homogenní části CdTe krystalů mírně klesá při připojení elektrického pole na vzorku. Při změně teploty navíc dochází k odlišné reakci u CdTe typu p a n. Právě těmto efektům je v práci věnována pozornost. Pomocí šumové spektroskopie bylo zjištěno, že při nízkých frekvencích je u vzorků dominantní šum typu 1/f, zatímco při vyšších frekvencích je sledován generačně-rekombinační šum a tepelný šum. Všechny měřené vzorky vykazovaly mnohem vyšší hodnotu šumu na nízkých frekvencích než udává Hoogeova rovnice. Byly nalezeny a popsány zdroje nadbytečného šumu.

Les HEMT à base de nitrure de gallium sont des composants très prometteurs en termes de performances en puissance et de fréquence de travail. L'enjeu est donc de développer des technologies performantes et fiables, afin d'intégrer ces transistors aux systèmes hyperfréquences, notamment dans le domaine des télécommunications, et en milieu durci. Les travaux ont été focalisés sur l'étude de la localisation des sources de bruit en excès aux basses fréquences, et de leur évolution suite aux phases de tests de vieillissement accéléré. Les caractérisations électriques ont été réalisées sur des structures fabriquées sur quatre plaques, dont trois sont basées sur une hétérostructure AlGaN/GaN, et la quatrième sur l'hétérostructure AlInN/AlN/GaN. Les résultats obtenus ont permis de valider une méthode de modélisation des sources de bruit en 1/f, localisées dans les zones d'accès aux contacts ohmiques et dans le canal. Des tests de vieillissement accéléré sous contraintes électriques ont permis de détecter des dégradations des performances statiques et du niveau de bruit en excès. Les effets combinés de piégeage et des effets thermiques expliquent ces dégradations, la température s'en étant révélée un facteur d'accélération. / The HEMT based on GaN materials are very promising, speaking of performance in power and frequency. The challenge is to develop efficient and reliable GaN based technologies, to intagrate these transistors to power microwave circuits, especially in the telecommunications field and on harsh environment. The work was focused on the study of the location of low frequency noise sources, and their evolution after accelerated life tests. The electrical characterizations were performed on structures made on four different wafers, three based on the AlGaN/GaN heterostructure, and the fourth based on the AlInN/AlN/GaN heterostructure. Thanks to the achieved results, a method for modeling 1/f noise sources, located in the channel and in the ohmic contacts access areas, has been validated. Life tests under electrical stress have been performed to detect DC and excess noise degradation. These degradations are explained by combined effects of trapping and thermal phenomena, with the temperature as an acceleration factor of degradation.

The master’s thesis deals with the noise diagnostic in the solar cells. Describes the main kinds of noises. The samples were quality and reliability screened using noise reliability indicators. The samples were surveyed by measuring the I-V characteristics, the noise spectral density as a function of forward voltage and frequency. It was calculated the noise spectral density as a function of forward current.

The main object of this work is noise spectroscopy of CdTe radiation detectors (-rays and X–rays) and CdTe samples. The study of stochastic phenomenon and tracing redundant low-frequency noise in semiconductor materials require long-term measurements in time domain and evaluate suitable power spectral densities (PSD) with logarithmic divided frequency axes. We have used the means of time-frequency analysis derived from the discrete wavelet transform (DWT) and we have designed the effective algorithm for PSD estimation, which is comparable with an original analog method. CdTe single crystal with Au contacts we can imagine as a series connection of two Schottky diodes with a resistor between them. The bulk resistance at constant temperature and other constant parameters changes due to the carrier concentration changing only. The p-type CdTe sample shows metal behavior with every temperature changes. Semiconductor properties of the sample begin to dominate just after some period of time. This behavior is caused by the hole mobility changing. The voltage noise spectral density of 1/f noise depends on the quantity of free carriers in the sample. All the studied samples have very high value of low frequency noise, much higher than it should have been according to Hooge’s formula. The excess value of low frequency noise is caused by the low carrier concentration within the depleted region.

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