High-k gadolinium scandate on Si obtained by high pressure sputtering from metal targets and in-situ plasma oxidation

This article studies the physical and electrical behavior of Gd2-xScxO3 layers grown by high pressure sputtering from metallic Gd and Sc targets. The aim is to obtain a high permittivity dielectric for microelectronic applications. The films were obtained by the deposition of a metallic nanolaminate of Gd and Sc alternating layers, which is afterwards in-situ oxidized by plasma. The oxide films obtained were close to stoichiometry, amorphous and with minimal interfacial regrowth. By fabricating metal-insulator-semiconductor capacitors we found that a moderate temperature annealing is needed to enhance permittivity, which reaches a high value of 32 while keeping moderate leakage. Finally, the feasibility of interface scavenging in this material with Ti gate electrodes is also demonstrated.Comment: 36 pages, 13 figure

Scavenging effect on plasma oxidized Gd2_2O3_3 grown by high pressure sputtering on Si and InP substrates

In this work, we analyze the scavenging effect of titanium gates on metal insulator semiconductor capacitors composed of gadolinium oxide as dielectric material deposited on Si and InP substrates. The Gd$_2$O$_3$ film was grown by high pressure sputtering from a metallic target followed by an in situ plasma oxidation. The thickness of the Ti film was varied between 2.5 and 17 nm and was capped with a Pt layer. For the devices grown on Si, a layer of 5 nm of Ti decreases the capacitance equivalent thickness from 2.3 to 1.9 nm without compromising the leakage current (1e-4 A cm$^{-2}$ at Vgate equal to 1 V). Thinner Ti has little impact on device performance, while 17 nm of Ti produces excessive scavenging. For InP capacitors, the scavenging effect is also observed with a decrease in the capacitance equivalent thickness from 2.5 to 1.9 nm (or an increase in the accumulation capacitance after the annealing from 1.4 to 1.7-1.8 uF cm$^{-2}$). The leakage current density remains under 1e-2 A cm$^{-2}$ at Vgate equal to 1.5 V. For these devices, a severe flatband voltage shift with frequency is observed. This can be explained by a very high interface trap state density (in the order of 1e13-1e14 eV$^{-1}$ cm$^{-2}$).Comment: 29 pages, 12 figure

High Pressure Sputtering For Kigh-k Dielectric Deposition. Is It Worth Trying?

Our research group studies the deposition of high permittivity dielectrics by a non-standard method: high-pressure sputtering. The dielectrics studied here are gadolinium scandate deposited from dielectric targets, and gadolinium oxide deposited from a metallic target, with an in situ plasma oxidation. The stoichiometric gadolinium scandate presents a slight permittivity boost after annealing, but with gadolinium-rich scandate (grown with an annealing of a nanolaminate) the dielectric shows a high effective permittivity of 21 and no noticeable SiO2 layer at the interface with Si. On the other hand, the stacks fabricated with the metallic Gd target have a SiO2 interface less than 0.7 nm thick that can be further reduced by scavenging with Ti gates. In fact, this scavenging effect is also demonstrated for the first time with indium phosphide substrates, obtaining a low capacitance equivalent thickness of only 2.1 nm.Comment: 25 pages, 9 figure

Herramienta de evaluación de la calidad de los Materiales Educativos Digitales: perfiles de aplicación del profesor y del alumno

Este documento contiene dos adaptaciones de la herramienta de evaluación de la calidad de materiales educativos digitales (MED) del estándar UNE 71362 al profesor y al alumno que no son especialistas en Tecnologías ni en Accesibilidad con el fin de facilitar o mejorar la creación y selección de MED. Estos perfiles de aplicación no garantizan el cumplimiento del 100% de los criterios de calidad, por lo que no pueden ser usados como herramienta para certificar la calidad de los MED. Sin embargo, sí pueden ser usados para asegurar/comprobar con más facilidad determinados aspectos de la calidad

Simulación numérica de terremotos en medios porosos: influencia del acoplamiento poroelástico en la ruptura dinámica y caracterización de la incertidumbre asociada

Las rupturas sísmicas en medios poroelásticos implican un conjunto de fenómenos complejos derivados de inestabilidades de fricción stick-slip y de los acoplamientos termohidromecánicos. En esta tesis, propongo un modelo de elementos finitos totalmente implícito, con un paso de tiempo adaptativo y monolíticamente acoplado para simular secuencias dinámicas de terremotos en medios poroviscoelásticos. Considero un material viscoelástico de Kelvin-Voigt y caracterizo el impacto de los efectos inerciales en los terremotos inducidos por inyección. En esta tesis, presento, por primera vez, simulaciones dinámicas de rupturas en fallas rate-and-state en medios poroelásticos. Mis simulaciones resuelven el ciclo sísmico completo incluyendo las fases intersísmica de nucleación espontánea del terremoto y de ruptura dinámica. Comparo las simulaciones dinámicas con las cuasi-dinámicas, en las que se desprecian los efectos inerciales y la singularidad del deslizamiento se resuelve mediante una aproximación de amortiguacin por radiación. La disipación viscosa modela el proceso físico de atenuación de las ondas sísmicas: a medida que aumenta el amortiguamiento viscoso, el tamaño del parche y el deslizamiento máximo de la falla se reducen, con lo que disminuye la magnitud esperada del terremoto. Desde un punto de vista computacional, la viscoelasticidad ayuda a evitar oscilaciones espurias de alta frecuencia durante la propagación de las ondas. Al incluir los efectos inerciales, el modelo dinámico tiene en cuenta las fluctuaciones transitorias en las presiones y en las tensiones del sólido durante la ruptura, que se desprecian en el enfoque cuasi-dinámico. La comprensión de estas perturbaciones transitorias puede arrojar luz sobre el papel de la presión de poro en el mecanismo del dynamic triggering. El enfoque dinámico poroviscoelástico es un buen compromiso entre el modelo sin viscosidad, totalmente dinámico, y el cuasi-dinámico. Una pequeña cantidad de amortiguación viscosa permite realizar cálculos más eficientes, preservando al mismo tiempo las características más relevantes de las rupturas dinámicas, en particular las velocidades de deslizamiento, el deslizamiento acumulado y el momento sísmico liberado. Además, la intensidad y daño potencial de los terremotos están relacionados con la velocidad de propagación de la ruptura a lo largo de las fallas de la corteza terrestre. La mayoría de los terremotos son sub-Rayleigh, con rupturas más lentas que las ondas de Rayleigh superficiales. En los terremotos supershear, la ruptura es más rápida que las ondas de corte, lo que da lugar a fuertes concentraciones de tensiones y a mayores intensidades en comparación con los más comunes sub- Rayleigh. A pesar de los importantes avances teóricos y experimentales de las dos últimas décadas, el control geológico y geomecánico de las transiciones de velocidad de ruptura sigue siendo poco conocido. En esta tesis, propongo que los fluidos de los poros desempeñan un papel importante en la explicación de la velocidad de ruptura de los terremotos: la presión de los poros puede aumentar bruscamente en el frente de compresión durante la propagación de la ruptura, promoviendo el fallo por cortante por delante del frente de ruptura y acelerando su propagación hacia el rango de las rupturas supershear. Caracterizo la transición de la ruptura sub-Rayleigh a la supershear en rocas saturadas, y muestro que el mecanismo de debilitamiento poroelástico propuesto puede ser un factor de control para las rupturas sísmicas intersónicas. Además, comprender el riesgo asociado a los terremotos antropogénicos es esencial para el desarrollo y la gestión de los procesos de ingeniería y las infraestructuras hidráulicas que pueden alterar las presiones y tensiones de los poros en profundidad. La posibilidad de que se produzcan terremotos provocados por el embalse, las mareas oceánicas y los fenómenos hidrológicos en la superficie de la Tierra (hidrosismicidad) ha sido objeto de un amplio debate. La relación entre la sismicidad inducida y los fenómenos hidrológicos se basa actualmente en correlaciones estadísticas mas que en mecanismos físicos. En este manuscrito, exploro las condiciones geomecánicas que podrían permitir que pequeños cambios de presión de poros debidos a la gestión de los yacimientos y a los cambios del nivel del mar se propaguen a profundidades compatibles con el desencadenamiento de terremotos en fallas sometidas a tensiones críticas (varios kilómetros). Considero una zona de falla dañada que está incrustada en una matriz de roca poroelástica, y realizo simulaciones hidromecánicas totalmente acopladas de la difusión de la presión y la deformación de la roca. Caracterizo las propiedades hidráulicas y geomecánicas de las zonas de falla que podrían permitir que pequeños cambios de presión y carga en la superficie del suelo (del orden de decenas o cientos de kPa) se propaguen con una atenuación relativamente pequeña hasta profundidades sismogénicas (hasta 10 km). Encuentro que la difusión de la presión a tales profundidades sólo es posible para zonas de falla altamente permeables y/o un fuerte acoplamiento poroelástico. ABSTRACT Earthquake ruptures in poroelastic media involve a suite of complex phenomena arising from stick-slip frictional instabilities and thermo-hydromechanical couplings. In this thesis, I propose a fully implicit, time-adaptive, and monolithically coupled finite element model to simulate dynamic earthquake sequences in poroviscoelastic media. I consider a Kelvin-Voigt viscoelastic material and characterize the impact of inertial effects on injection-induced earthquakes. In this thesis, I present, for the first time, dynamic simulations of ruptures in rate-and-state faults in poroelastic media. My simulations resolve the full earthquake cycle, including the interseismic, spontaneous earthquake nucleation, and dynamic rupture phases. I compare dynamic simulations with quasi-dynamic ones, in which inertial effects are neglected and the slip singularity is resolved through a radiation damping approximation. Viscous dissipation models the physical process of seismic wave attenuation: as viscous damping increases, the patch size and the maximum fault slip become smaller, hence decreasing the expected earthquake magnitude. From a computational perspective, viscoelasticity helps avoid spurious high-frequency oscillations during wave propagation. By including inertial effects, the dynamic model accounts for transient fluctuations of pressures and solid stresses during rupture, which are neglected in the quasi-dynamic approach. Understanding these transient perturbations may shed light on the role of pore pressure in the mechanism of dynamic earthquake triggering. The poroviscoelastic dynamic approach is a good compromise between the inviscid, fully dynamic model, and the quasi-dynamic one. A small amount of viscous damping allows us more efficient calculations, while preserving the most relevant features of dynamic ruptures, in particular slip velocities, accumulated slip, and seismic moment released. Moreover, the intensity and damage potential of earthquakes are linked to the speed at which rupture propagates along sliding crustal faults. Most earthquakes are sub-Rayleigh, with ruptures that are slower than the surface Rayleigh waves. In supershear earthquakes, rupture is faster than the shear waves, leading to sharp stress concentrations and larger intensities compared with the more common sub- Rayleigh ones. Despite significant theoretical and experimental advances over the past two decades, the geological and geomechanical control on rupture speed transitions remain poorly understood. In this thesis, I propose that pore fluids play an important role in explaining earthquake rupture speed: the pore pressure may increase sharply at the compressional front during rupture propagation, promoting shear failure ahead of the rupture front and accelerating its propagation into the supershear range. I characterize the transition from sub-Rayleigh to supershear rupture in fluidsaturated rock, and show that the proposed poroelastic weakening mechanism may be a controlling factor for intersonic earthquake ruptures. In addition, understanding the risk associated with anthropogenic earthquakes is essential in the development and management of engineering processes and hydraulic infrastructure that may alter pore pressures and stresses at depth. The possibility of earthquakes triggered by reservoir impoundment, ocean tides, and hydrological events at the Earth surface (hydro-seismicity) has been extensively debated. The link between induced seismicity and hydrological events is currently based on statistical correlations rather than on physical mechanisms. In this manuscript, I explore the geomechanical conditions that could allow for small pore pressure changes due to reservoir management and sea level changes to propagate to depths that are compatible with earthquake triggering at criticallystressed faults (several kilometers). I consider a damaged fault zone that is embedded in a poroelastic rock matrix, and conduct fully coupled hydromechanical simulations of pressure diffusion and rock deformation. I characterize the hydraulic and geomechanical properties of fault zones that could allow for small pressure and loading changes at the ground surface (in the order of tens or hundreds of kPa) to propagate with relatively small attenuation to seismogenic depths (up to 10 km). I find that pressure diffusion to such depths is only possible for highly permeable fault zones and/or strong poroelastic coupling

Optimization of in situ plasma oxidation of metallic gadolinium thin films deposited by high pressure sputtering on silicon

Gadolinium oxide thin films were deposited on silicon by a two-step process: high pressure sputtering from a metallic gadolinium target followed by an in situ plasma oxidation. Several plasma conditions for metal deposition and oxidation were studied in order to minimize the growth of a SiOx layer at the interface between the high permittivity dielectric and the silicon substrate and to avoid substrate damage. Plasma emission was studied with glow discharge optical spectroscopy. The films were structurally characterized by Fourier transform infrared spectroscopy. Metal-insulator-semiconductor capacitors were fabricated with two different top metals (titanium and platinum) to analyze the influence of deposition conditions and the metal choice. Pt gated devices showed an interfacial SiOx regrowth after a forming gas annealing, while Ti gates scavenge the interface layer

The role of pore fluids in supershear earthquake ruptures

Abstract The intensity and damage potential of earthquakes are linked to the speed at which rupture propagates along sliding crustal faults. Most earthquakes are sub-Rayleigh, with ruptures that are slower than the surface Rayleigh waves. In supershear earthquakes, ruptures are faster than the shear waves, leading to sharp pressure concentrations and larger intensities compared with the more common sub-Rayleigh ones. Despite significant theoretical and experimental advances over the past two decades, the geological and geomechanical controls on rupture speed transitions remain poorly understood. Here we propose that pore fluids play an important role in explaining earthquake rupture speed: the pore pressure may increase sharply at the compressional front during rupture propagation, promoting shear failure ahead of the rupture front and accelerating its propagation into the supershear range. We characterize the transition from sub-Rayleigh to supershear rupture in fluid-saturated rock, and show that the proposed poroelastic weakening mechanism may be a controlling factor for intersonic earthquake ruptures

Electrical characterization of gadolinium oxide deposited by high pressure sputtering with in situ plasma oxidation

Está depositada la versión preprint del artículoIn this work, we characterized gadolinium oxide films deposited on silicon by high pressure sputtering with a two-step process: first, we sputtered metallic gadolinium in an argon atmosphere and then, we performed an in situ plasma oxidation of the metallic layer previously deposited. By means of high resolution transmission electron microscopy, we can detect the oxidation degree of the metallic film. Under optimized deposition conditions, fully oxidized Gd2O3 films are obtained. In addition, the capacitance and conductance as a function of gate voltage of Pt gated metal–insulator–semiconductor capacitors confirm stable dielectric behavior of the fully oxidized films. The devices show low gate leakage currents (∼10−5 A/cm2 at 1 V for 2.2 nm of equivalent oxide thickness), low interface trap density and an almost negligible hysteresis and frequency dispersion.Ministerio de Economía y Competitividad (España)Depto. de Estructura de la Materia, Física Térmica y ElectrónicaFac. de Ciencias FísicasTRUEpu

Optimization of scandium oxide growth by high pressure sputtering on silicon

Está depositada la versión preprint del artículoThis work demonstrates the viability of scandium oxide deposition on silicon by means of high pressure sputtering. Deposition pressure and radio frequency power are varied for optimization of the properties of the thin films and the ScOx/Si interface. The physical characterization was performed by ellipsometry, Fourier transform infrared spectroscopy, x-ray diffraction and transmission electron microscopy. Aluminum gate electrodes were evaporated for metal–insulator–semiconductor (MIS) fabrication. From the electrical characterization of the MIS devices, the density of interfacial defects is found to decrease with deposition pressure, showing a reduced plasma damage of the substrate surface for higher pressures. This is also supported by lower flatband voltage shifts in the capacitance versus voltage hysteresis curves. Sputtering at high pressures (above 100 Pa) reduces the interfacial SiOx formation, according to the infrared spectra. The growth rates decrease with deposition pressure, so a very accurate control of the layer thicknesses could be provided.Ministerio de Ciencia e Innovación (España)Universidad Complutense de MadridDepto. de Estructura de la Materia, Física Térmica y ElectrónicaFac. de Ciencias FísicasTRUEpu

Gadolinium scandate by high-pressure sputtering for future generations of high-κ dielectrics

Está depositada la versión preprint del artículoGd-rich gadolinium scandate (Gd2–xScxO3) was deposited by high-pressure sputtering on (1 0 0) silicon by alternating the deposition of <0.5 nm thick films of its binary components: Sc2O3 and Gd2O3. The formation of the ternary oxide was observed after the thermal treatments, with a high increase in the effective permittivity of the dielectric (up to 21). The silicon diffuses into the Gd2–xScxO3 films, which show an amorphous character. After the annealing no interfacial silicon oxide is present. CHF–VG curves indicated low hysteresis (55 mV) and a density of interfacial defects of 6 × 1011 eV–1 cm–2.Ministerio de Economía y Competitividad (España)Depto. de Estructura de la Materia, Física Térmica y ElectrónicaFac. de Ciencias FísicasTRUEpu