L'influence de l'anthropisation sur la répartition géographique du condor des Andes (Vultur gryphus L.) dans le Parc National Torres del Paine en Patagonie chilienne

Mémoire numérisé par la Division de la gestion de documents et des archives de l'Université de Montréal

Material insights of HfO2-based integrated 1-transistor-1-resistor resistive random access memory devices processed by batch atomic layer deposition

With the continuous scaling of resistive random access memory (RRAM) devices, in-depth understanding of the physical mechanism and the material issues, particularly by directly studying integrated cells, become more and more important to further improve the device performances. In this work, HfO2-based integrated 1-transistor-1-resistor (1T1R) RRAM devices were processed in a standard 0.25 μm complementary-metal-oxide-semiconductor (CMOS) process line, using a batch atomic layer deposition (ALD) tool, which is particularly designed for mass production. We demonstrate a systematic study on TiN/Ti/HfO2/TiN/Si RRAM devices to correlate key material factors (nano-crystallites and carbon impurities) with the filament type resistive switching (RS) behaviours. The augmentation of the nano-crystallites density in the film increases the forming voltage of devices and its variation. Carbon residues in HfO2 films turn out to be an even more significant factor strongly impacting the RS behaviour. A relatively higher deposition temperature of 300 °C dramatically reduces the residual carbon concentration, thus leading to enhanced RS performances of devices, including lower power consumption, better endurance and higher reliability. Such thorough understanding on physical mechanism of RS and the correlation between material and device performances will facilitate the realization of high density and reliable embedded RRAM devices with low power consumption

Residual Metallic Contamination of Transferred Chemical Vapor Deposited Graphene

Integration of graphene with Si microelectronics is very appealing by offering potentially a broad range of new functionalities. New materials to be integrated with Si platform must conform to stringent purity standards. Here, we investigate graphene layers grown on copper foils by chemical vapor deposition and transferred to silicon wafers by wet etch and electrochemical delamination methods with respect to residual sub-monolayer metallic contaminations. Regardless of the transfer method and associated cleaning scheme, time-of-flight secondary ion mass spectrometry and total reflection x-ray fluorescence measurements indicate that the graphene sheets are contaminated with residual metals (copper, iron) with a concentration exceeding 10$^{13}$ atoms/cm$^{2}$. These metal impurities appear to be partly mobile upon thermal treatment as shown by depth profiling and reduction of the minority charge carrier diffusion length in the silicon substrate. As residual metallic impurities can significantly alter electronic and electrochemical properties of graphene and can severely impede the process of integration with silicon microelectronics these results reveal that further progress in synthesis, handling, and cleaning of graphene is required on the way to its advanced electronic and optoelectronic applications.Comment: 26 pages, including supporting informatio

The oxidation of the (100) surface of the intermetallic alloys Ni₃Al and CoAl and the growth of Co on the clean and oxidized N3Al(100) surface

The aim of this work was the preparation and characterization of thin Al-oxide films an the (100) surface of the intermetallic compounds Ni$_{3}$Al and COAT, as well as the study of Co growth an the clean and oxidized Ni$_{3}$Al(100) surface. The films were characterized by Auger electron spectroscopy (AES), Low Energy Electron Diffraction (LEED), Electron Energy Loss Spectroscopy (EELS) and Scanning Tunneling Microscopy (STM). \textbf{The clean Ni_{3}Al(100) surface} The LEED pattern of clean Ni$_{3}$Al(100) Shows a (1 x 1) structure. STM images of the Ni$_{3}$Al(100) surface display flat and large terraces (500 - 1000 A) separated by steps with a step height of 3.5 $\mathring{A}$ which corresponds to the lattice constant of Ni$_{3}$Al and represents a double atomic step. This suggests that different terraces have always the Same termination. \textbf{Co/Ni_{3}Al(100)} At low coverage (0 .1 ML) and 300 K, the cobalt deposited an the Ni$_{3}$Al(100) surface shows a two-dimensional growth mode. For deposition of 0.3 ML the nucleation takes also place in the second layer. After deposition of 3.5 ML Co, the surface consists of Co islands with a mean diameter of $\sim$ 90$\mathring{A}$. Annealing at 700 K leads to the growth of large terraces of fcc-Co which are arranged with the (100) plane parallel to the (100) surface of the Substrate. Co is stable an Ni$_{3}$Al(100) up to 750 K when it starts to diffuse into the substrate. At 1100 K, Co is disappeared completely from the surface via diffusion into the Substrate. \textbf{Al_{2}$O$_{3}$/Ni$_{3}Al(100)} At room temperature oxygen adsorption an Ni$_{3}$Al(100) leads to the formation of a thin amorphous Al-oxide (a-Al$_{2}$O$_{3}$) layer ($\sim$ 5$\mathring{A}$). Oxidation at 1100 K leads to formation of a well ordered $\gamma'$-Al$_{2}$O$_{3}$ film with a thickness of $\sim$ 10$\mathring{A}$. The STM images of the completely oxide-covered surface exhibit hexagonal superstructures with lattice constants of 18, 24 and 54 $\mathring{A}$. The band gap of Al$_{2}$O$_{3}$ formed an Ni$_{3}$Al(100) amounts for the amorphous film to $\sim$ 3.2 and to $\sim$ 4.3 eV for the well ordered Al$_{2}$O$_{3}$ film, respectively and both are strongly diminished with respect to the bulk values. \textbf{Co/Al_{2}$O$_{3}$/Ni$_{3}Al(100)} Co deposited at room temperature an a Al$_{2}$O$_{3}$ film, which was grown an Ni$_{3}$Al(100) at 1100 K, Shows a three dimensional (Volmer-Weber) growth mode. After a nominal deposition of 30 $\mathring{A}$ the 3D cobalt clusters have a mean diameter of 70 $\mathring{A}$ and a roughness of $\sim$ 10 $\mathring{A}$. Annealing at 700 and 900 K leads to a coalescence of the Co clusters, and to a gradually diffusion of Co through the oxide into the substrate. After annealing at 1000 K the entire surface of alumina is Co free. \textbf{Al_{2}$O$_{3}/CoAl(100)} Oxygen adsorption at 300 K leads to the formation of an amorphous Al$_{2}$O$_{3}$ film an CoAl(100). Annealing at temperatures between 800 - 1000 K induces a phase transformation from a-Al$_{2}$O$_{3}$ into the $\theta$-Al$_{2}$O$_{3}$ phase, which exhibits a (2x1) structure with respect to the substrate. After annealing at temperatures > 1200 K a transition to $\alpha$-Al$_{2}$O$_{3}$ occurs, while above 1300 K the decomposition and removal of the oxide film from the surface is observed

Ausbau des Kompetenzzentrums Dünnschicht und Nanotechnologie für Photovoltaik Berlin, Teilvorhaben 6: Analytik

Derzeitiger Stand von Wissenschaft und Technik Die Photovoltaiklandschaft in Deutschland ist von der Wafer-Technologie dominiert. Im Bereich Dünnschicht-PV gibt es zahlreiche vielversprechende Entwicklungspotentiale, für die jedoch auch die geeigneten Depositions-, Analyse- und Simulationsverfahren zur Verfügung stehen müssen. Zielsetzung Ziel des Teilvorhabens war der Aufbau eines instituts- und standortübergreifenden Analysenetzwerks für Dünnschichtsolarzellen, um, durch die Kombination einer Vielzahl von in der Halbleiterindustrie etablierter Methoden mit neuentwickelten Messverfahren und begleitenden theoretischen Simulationen, neue Ansätze und Wege zur Wirkungsgradsteigerung von Silizium und CIS basierten Dünnschichtsolarzellen zu entwickeln. Ergebnis Die bisher nur in der Mikroelektronik genutzten Analysemöglichkeiten wurden hinsichtlich Probenpräparation und Messbedingungen auf die Untersuchung von Solarzellen angepasst. Dafür wurden spezielle Probenhalter, Eichproben Messkonzepte und Messrezepte angefertigt bzw. entwickelt. Anwendungsmöglichkeiten Die gewonnenen Erkenntnisse tragen zur Erweiterung der Kompetenzen auf dem Gebiet der Dünnschichtsolarzellenforschung im IHP bei und haben zur Entstehung einer permanenten Plattform für künftige Charakterisierungen auf diesem Anwendungsgebiet geführt.Current status of science and technology Photovoltaics industry in Germany is dominated by silicon wafer technology. However, there are various promising concepts for thin-film photovoltaics that require adequate techniques for deposition, analytics and simulation. Aim of the project The aim of this part of the project was to establish a network of analytical facilities for thin film based solar cell characterization. The existing analytical methods used for semiconductor technology have to be adapted to thin film based solar cell characterization in order to contribute to the improvement of solar cell efficiency. Results The analytical methods used in IHP for microelectronic devices were adapted to the characterization of thin film based solar cell by constructing characteristic sample holders, matching measurements recipes, developing new analytical concepts. Possible Applications The achieved know-how has led to the establishing of a competence platform for solar cell characterization based on thin films, which can be used in the future as a part of analytical facility network

Atomically Controlled Processing for Dopant Segregation in CVD Si and Ge Epitaxial Growth

International audienc

Impact of the precursor chemistry and process conditions on the cell-to-cell variability in 1T-1R based HfO2 RRAM devices

The Resistive RAM (RRAM) technology is currently in a level of maturity that calls for its integration into CMOS compatible memory arrays. This CMOS integration requires a perfect understanding of the cells performance and reliability in relation to the deposition processes used for their manufacturing. In this paper, the impact of the precursor chemistries and process conditions on the performance of HfO2 based memristive cells is studied. An extensive characterization of HfO2 based 1T1R cells, a comparison of the cell-to-cell variability, and reliability study is performed. The cells’ behaviors during forming, set, and reset operations are monitored in order to relate their features to conductive filament properties and process-induced variability of the switching parameters. The modeling of the high resistance state (HRS) is performed by applying the Quantum-Point Contact model to assess the link between the deposition condition and the precursor chemistry with the resulting physical cells characteristics

Accurate Graphene-Metal Junction Characterization

A reliable method is proposed for measuring specific contact resistivity (rho(C)) for graphenemetal contacts, which is based on a contact end resistance measurement. We investigate the proposed method with simulations and confirm that the sheet resistance under the metal contact (R-SK) plays an important role, as it influences the potential barrier at the graphene-metal junction. Two different complementary metal-oxide-semiconductor-compatible aluminum-based contacts are investigated to demonstrate the importance of the sheet resistance under the metal contact: the difference in RSK arises from the formation of insulating aluminum oxide (Al2O3) and aluminum carbide (Al4C3) interfacial layers, which depends on the graphene pretreatment and process conditions. Auger electron spectroscopy and X-ray photoelectron spectroscopy support electrical data. The method allows direct measurements of contact parameters with one contact pair and enables small test structures. It is further more reliable than the conventional transfer length method when the sheet resistance of the material under the contact is large. The proposed method is thus ideal for geometrically small contacts where it minimizes measurement errors and it can be applied in particular to study emerging devices and materials