Deuterium in the gate dielectric of CMOS devices

Most of the electronic integrated circuits used today are Complementary MOS (CMOS) circuits, which consist mainly of Metal-Oxide-Semiconductor Field-Effect Transistors (MOSFETs). In the last forty years there has been a tremendous reduction of the MOSFET dimensions.\ud This reduction will continue, enabling even faster and more complex integrated circuits. But, there are a number of hurdles on the road. One of these hurdles is the thickness reduction of an essential electrically isolating layer inside the MOSFET, the so-called gate dielectric. This gate dielectric is becoming so thin, it starts to leak electrical current under operating conditions. This increases the power consumption and can lead to a non-functional transistor. Reliability is also of concern, because the gate dielectric deteriorates under device operation, leading to even larger leakage currents.\u

Reducible oxides as ultrathin epitaxial films

This chapter reviews and discusses recent work on two-dimensional films of reducible oxides supported on metal substrates. In general, peculiar chemical and structural phases, different from the bulk ones, can be stabilized depending on the oxygen chemical potential, on kinetic processes and on the specific substrate used. A peculiarity of reducible oxides is that the observed phases can often be reversibly transformed one into the other by applying reducing and oxidizing treatments

Stable and efficient photoelectrodes for solar fuels production

[eng] The excessive consumption of non-renewable energy sources such as fossil fuels has lead the world to a global climate change, urging for new energy consumption habits together with developing cost- effective alternative renewable technologies. Photoelectrochemical (PEC) water splitting allows for direct conversion of solar light and water into hydrogen and oxygen, storing energy into chemical bonds, solving the storage problem of photovoltaic technology. It has demonstrated to produce pure hydrogen and oxygen in significant efficiencies, although this technology is not ready for market implementation due to lack of efficient, stable and scalable photoelectrodes. In this work, we undertake a journey from improving the efficiency of stable metal-oxide-based photoanodes to stabilizing efficient photovoltaic materials by the introduction of protective, transparent, conductive and catalytic layers. Efforts have focused on using cost-effective and scalable materials and techniques. Metal oxide candidate TiO2 is reported stable in alkaline electrolytes and at anodic potentials, but they present low photon to current conversion efficiencies. This is due to excessively large band gap, absorbing small part of the visible spectra, and small electron and hole mobility. Its efficiency is increased both by microstructuring the substrate and nanostructuring the thin film into nanorods, and by modifying the electronic structure with a reductive H2 treatment, enhancing potential drop inside the nanorods. The strategy is shifted into stabilizing highly efficient short band gap semiconductor materials used by the photovoltaic industry. Silicon based photocathodes are protected from acidic electrolyte corrosion by TiO2 overlayers grown by atomic layer deposition (ALD). Temperature is found to play a key role for both efficient film conductivity and stability, being this caused by polycrystalline films formation. ALD enabled high thickness control and pinhole-free layers, together with lower crystallization temperatures than other techniques. Copper-indium-gallium-selenide (CIGS) solar cells fabricated on flexible stainless steel substrates are also protected from corrosion by TiO2 ALD protective layers. The transparent conductive oxide (TCO) already used in solar cells is found necessary for efficient p-n junction formation and charge transport to the hydrogen evolution reaction. Copper-zinc-tin- sulfide/selenide (CZTS/Se) solar cells, where scarce indium and gallium are substituted by tin and zinc, are implemented for PEC devices with TiO2 overlayers too. By modifying the S/Se ratio, band gap can be tuned, an especially interesting characteristic to design tandem PEC devices. ALD deposited protective layers are also studied in anodic polarizations and alkaline electrolytes. By varying the deposition temperature of TiO2, completely amorphous, mixed amorphous and crystalline and fully crystalline films are deposited, and a clear conductivity increase is observed correlated to crystallization. Preferential conductivity paths are observed inside crystalline grains, proposed to be related to crystalline defects and grain boundaries. Few hundred hours stability tests reveals significant photocurrent decrease, with no observed dissolution of the Si photoabsorber. This is attributed to oxidative potentials and electrolyte hydroxides diminishing the n-type semiconductor behavior of TiO2 and forming a barrier to charge injection into the oxygen evolution reaction. UV superimposed illumination partially recovered conductivity. NiO films are ALD-deposited on Si photoanodes and conductivity is found to decrease when temperature is increased from 100 to 300 ºC, simultaneous to a change in preferential crystal growth direction. Higher stoichiometric film, being formed when increasing temperature, decreases Ni2+ vacancies, responsible of the p-type semiconductor behavior. Impressive 1000 hours stability measurements are obtained. Although, this is only attained under periodic cyclic voltammetries, avoiding partial deactivation of the photoanodes. This is attributed to chemical modifications at the surface in such highly oxidative conditions

Optimising the Structure of Metal-Insulator-Metal Diodes for Rectenna Applications

The work in this thesis investigates the design and fabrication of metal-insulator-metal (MIM) diodes using an ultrathin organic insulator. The organic insulating layer was found to be compact, highly conformal, and uniform, effectively overcoming the main design challenge in MIM diodes. The fabricated diodes have strong nonlinear current-voltage characteristics with a zero-bias curvature coefficient and a voltage responsivity among the best values reported in the available literature. The fabrication process is simple and carried out at low temperature, which is cost effective, and can potentially be ported to large-area roll-to-roll manufacturing. An encapsulation method to prevent MIM junctions’ degradation has also been developed. Following the successful production of these MIM devices on a rigid substrate, with the fabrication only requiring low-temperature processing, the diodes were successfully fabricated on a flexible substrate with results similar to those fabricated on a rigid substrate. The flexible substrate diodes show no significant degradation in performance when stressed in a one-off bending experiment, although extreme mechanical stress testing does produce some loss in quality. Also, an elegant method for matching the impedance of an antenna to that of a MIM diode was successfully developed, for optimal external conversion efficiency where the diodes are used in a rectenna device. The responsivity of the impedance-matched rectenna is approaching an order of magnitude higher than that of a control device without a matching network. The fabrication, electrical characterisation and physical analysis of both the MIM diodes and rectennas are discussed in detail in this thesis

Investigation of Gate Dielectric Materials and Dielectric/Silicon Interfaces for Metal Oxide Semiconductor Devices

The progress of the silicon-based complementary-metal-oxide-semiconductor (CMOS) technology is mainly contributed to the scaling of the individual component. After decades of development, the scaling trend is approaching to its limitation, and there is urgent needs for the innovations of the materials and structures of the MOS devices, in order to postpone the end of the scaling. Atomic layer deposition (ALD) provides precise control of the deposited thin film at the atomic scale, and has wide application not only in the MOS technology, but also in other nanostructures. In this dissertation, I study rapid thermal processing (RTP) treatment of thermally grown SiO2, ALD growth of SiO2, and ALD growth of high-k HfO2 dielectric materials for gate oxides of MOS devices. Using a lateral heating treatment of SiO2, the gate leakage current of SiO2 based MOS capacitors was reduced by 4 order of magnitude, and the underlying mechanism was studied. Ultrathin SiO2 films were grown by ALD, and the electrical properties of the films and the SiO2/Si interface were extensively studied. High quality HfO2 films were grown using ALD on a chemical oxide. The dependence of interfacial quality on the thickness of the chemical oxide was studied. Finally I studied growth of HfO2 on two innovative interfacial layers, an interfacial layer grown by in-situ ALD ozone/water cycle exposure and an interfacial layer of etched thermal and RTP SiO2. The effectiveness of growth of high-quality HfO2 using the two interfacial layers are comparable to that of the chemical oxide. The interfacial properties are studied in details using XPS and ellipsometry

Design and Assembly of Nanostructured Complex Metal Oxide Materials for the Construction of Batteries and Thermoelectric Devices

Thermoelectric devices and lithium-ion batteries are among the fastest growing energy technologies. Thermoelectric devices generate energy from waste heat, whereas lithium-ion batteries store energy for use in commercial applications. Two different topics are bound with a common thread in this thesis - nanotechnology! In fact, nanostructuring is a more preferred term for the approach I have taken herein. Another commonality between these two topics is the material system I have used to prove my hypotheses - complex metal oxides. Complex metal oxides can be used for both energy generation and storage as they are stable at high temperatures, are benign and inexpensive, and are chemically stable. . Nevertheless, complex metal oxide-based materials have drawbacks when they are used in thermoelectric devices. Since they have high thermal conductivities and low power factors, they have lower thermoelectric figures of merit (ZT). This affects their performance as thermoelectric materials. Nanostructuring can solve this critical problem as thermal conductivity, electrical conductivity and Seebeck coefficient become quasi-independent of each other under these conditions. However, oxide-based materials have proven to be greatly recalcitrant to forming nanostructures when traditional synthetic methods such as solid-state reactions have been employed. Solid-state reactions usually proceed at extremely high temperatures that are not particularly conducive to forming nanostructures. The first part of this thesis presents novel solution-based synthetic methods that were developed in order to produce novel nanostructured complex metal oxides. Typical structures include nanowires. The second part of this thesis extends this methodology to study the effect of nanostructuring on the thermal conductivity of strontium titanate (SrTiO3), a promising high temperature thermoelectric material. Ultrathin nanowires of SrTiO3 were synthesized using a novel hydrothermal reaction. These ultrathin nanowires were compressed into a `nanostructured\u27 bulk pellet through spark plasma sintering. The thermal conductivity measured on the nanostructured bulk pellet showed a drastic decrease compared to bulk SrTiO3. Through theoretical modeling it was realized that drastic decrease in thermal conductivity was due to scattering of phonons, which contribute to the lattice thermal conductivity, at the interface of the nanowires. Another aspect of the thermoelectric research presented herein includes the development of a new phase of misfit layered oxide, calcium cobalt oxide (Ca9Co12O28), for high temperature applications. This phase had hardly been researched in literature because of its high thermal conductivity, thus limiting its use in thermoelectric devices. Through a unique single source precursor-based technique, porous nanowire structures of Ca9Co12O28 were prepared at much lower temperatures than conventional solid-state techniques. Significantly improved ZT were observed in our nanowire system up to 700K due to reduced thermal conductivity and enhanced Seebeck coefficient. The synthetic approach was also applied to prepare different nanostructures (porous nanowires and nanoparticles) of lithium cobalt oxide (LiCoO2) by tuning individual reaction parameters. The importance of reaction temperature and the role of nanostructures on the final electrochemical performance of LiCoO2 was also deduced. Saliently, the nanostructured electrodes so prepared can withstand high cycling rates and achieve capacities that are close to the theoretical capacity of LiCoO2 at 0.1C

Recent Advances in Metal, Ceramic, and Metal-Ceramic Composite Films/Coatings

This reprint gathers works on various coating materials and technologies aimed at the improvement of materials’ properties, such as corrosion resistance or biocompatibility. Systematic studies demonstrate how the structure and morphology of coatings can change the mechanical, chemical and various functional properties of materials. The reprint contributes to the better understanding of various phenomena induced by metal, ceramic or composite coatings in core materials and, thus, it can help in the more rational design of the selected material’s properties in future studies by the application of coatings

Growth Control and Study of Ultrathin Silver Films for Energy-Saving Coatings

Les couches minces fonctionnelles jouent un rôle prépondérant dans la plupart des secteurs industriels actuels. Ils peuvent aussi bien être une partie intégrante d’un dispositif (cellule solaire, diode électroluminescente, photodétecteur, Laser, capteur thermosolaire, cellule thermoélectrique et bien d’autres), ou bien y amener de nouvelles fonctionnalités (revêtements résistants à la corrosion, l’usure et l’érosion, revêtement antireflet). La montée rapide de cette science est à l’origine d’un développement tout aussi rapide des techniques de dépôt et de synthèse de couches minces. Aujourd’hui, la croissance d’une couche mince avec une précision au nanomètre peut être effectuée par un simple couchage à lame au sein d’un laboratoire de recherche aussi bien que par des techniques d’évaporation dans des chambres à vide industrielles à grande échelle. La facilité d’accès aux techniques de dépôt ainsi que l’envergure des applications scientifiques et technologiques font des couches minces une solution potentielle pour beaucoup d’enjeux technologiques et de sociétés. Certainement, un des plus grands enjeux actuels est le problème de la consommation énergétique à travers le monde et qui peut seulement qu’empirer si aucune solution convenable n’est adoptée. Une approche afin de contrer cette consommation énergétique est de modifier les vitrages architecturaux dans les bâtiments commerciaux et résidentiels en revêtant une fenêtre avec une couche réfléchissante la chaleur afin de réduire de façon drastique les charges de chauffages et de refroidissement. Le recouvrement des fenêtres par de fines couches optiques se fait par des chambres de dépôts montées en ligne, souvent jumelées avec la production du verre flotté. Bien que le maintien et l’installation de ces systèmes de dépôt est d’un grand intérêt et pose de nombreux défis, le travail de recherche présenté dans cette thèse se penche sur le mécanisme de croissance des couches minces d’argent déposé en phase vapeur par assistance plasma pour les filtres à basse émissivité. Le projet est mené en collaboration avec Guardian Industries dans le cadre des vitrages à économies d’énergie. Les couches minces d’argent possèdent des propriétés physiques changeantes dépendamment de leur mécanisme de croissance ainsi que de leur épaisseur. Elles ont tendance à croître en îlots en dessous d’une épaisseur critique et convergent vers une couche réfléchissante la radiation infrarouges. Cette épaisseur critique se nomme le seuil de percolation et dépend fortement de la couche sous-jacente.----------Abstract Functional thin films play a key role in almost all industries today. They can either form an integral part of a device (as heat-reflectors, solar cells, light-emitting diodes, photodetectors, lasers, thermal collectors, thermoelectric cells and many more) or bring additional coating functionalities (such as corrosion, wear and erosion resistance and antireflective coating). The rapid development of thin film science has led to the equally fast growth of thin film deposition techniques. The coating of a surface with precisions in the nanometers can be conducted by simple blade coating in a laboratory setting or large-scale vacuum chambers in heavy industrial environments. Moreover, the rapid rise of thin film science can also be attributed to progresses in characterization techniques. The accessibility of thin film deposition techniques and their wide-ranging scientific and technological applications make thin film science appear as an attractive answer to many industrial and societal challenges. Probably the greatest of these challenges is the energy consumption problem present in large parts of the world and which can only amplify in time if no suitable solutions are adopted. One approach to decrease this energy consumption is to alter glazing units in commercial and residential buildings by coating one side of the window pane with a heat-reflecting layer in order to drastically reduce heating and cooling loads. These glass panes are manufactured by large, in-line vacuum coaters that can be found on the glass production site. Even though the configuration and maintenance of such systems is of great interest and brings important challenges, the research work conducted throughout this thesis is focused in the growth mechanism of very thin silver films inside a low-emissivity stack deposited by plasma-assisted physical vapour deposition, with collaboration with Guardian Industries in the context of energy-saving glazing. Silver thin films have unique varying physical properties attributed to their distinct growth mechanism. They tend to progressively grow as light-absorbing agglomerated clusters below a certain thickness to infrared heat-reflective, continuous films. The main challenge in the context of silver film growth is the inability to obtain heat-reflecting properties below a certain thickness. This thickness is determined by the surface properties of the underlying layer, limiting the possible options available for silver film coating