Rozprawy doktorskie na temat „Titanium Dioxide Dielectric”

In this thesis, we focused on understanding the synthesis of titanium dioxide (TiO2) films and nitrogen doped TiO2 films using an atmospheric pressure Dielectric Barrier Discharge (DBD). The first part of the work was dedicated to the deposition of TiO2 films by cold plasma DBD with titanium tetraisopropoxide as precursor in a single-step process at room temperature. The deposition rate was about 70 nm·min-1. The photocatalytic degradation rate for the degradation of methylene blue (MB) under ultra violet (UV) irradiation of the TiO2 film after annealing was close to a reference anatase TiO2 spin coated film. Moreover, the TiO2 films showed a good photocatalytic stability. The second part of the study focused on the optimization and the understanding of the effect of the plasma parameters (gas flow rate and power) on the morphology of the TiO2 films and on the investigation of the deposition mechanisms. The morphology of the film changed from granular to compact film by either increasing the total flow rate or decreasing the plasma power. In other words, adapting the energy density in the plasma allowed the control of the morphology of the TiO2 films. To our knowledge, it was the first time that the energy density parameters of the plasma were used to control the morphology of TiO2 films. The photocatalytic degradation rate for the degradation of MB under UV irradiation of the annealed TiO2 film turned out to be about 2 and 15 times higher than the one of the commercial TiO2 film and the as-deposited TiO2 films, respectively. In order to extend the light utilization to the visible light range, TiO2 films were doped with nitrogen using a room temperature argon/ammonia plasma discharge. XPS and SIMS results confirmed that the nitrogen has been incorporated in the TiO2 lattice mostly in Ti-N state. This was further confirmed by Raman spectroscopy and XRD. The plasma properties and the doping mechanism were studied by Optical Emission Spectroscopy. It is suggested that the NH radicals played a key role in the doping of TiO2. The concentration of nitrogen in the N-TiO2 coatings could be tuned by adapting the ratio of NH3 in the plasma or the plasma power. The band gap of our N-TiO2 coatings is lower than the one of undoped TiO2 coating. The photocatalytic degradation rate for N-TiO2 coating was more than 4 times higher than the one of the undoped TiO2 coating.
Doctorat en Sciences
info:eu-repo/semantics/nonPublished

Defects have gained increasing attention for their capability in tailoring the properties and/or exploring new functionalities in oxide materials. For instance, the colossal permittivity (CP, >103) was successfully achieved by introducing the acceptor/donor co-doping in rutile TiO2. The resultant dielectric properties can be either affected by the defect-induced polarisation or totally dominated by the defects. The defect configurations and its related dielectric properties vary with the different properties of dopant ions, e.g. ionic size, electronegativity, valence state, and so on. More interestingly, the different dopant ions affect their nearby environment differently in structurally strong correlated solid-state system, which may lead to special defect complexes. The research on the dielectric properties of defect-engineered rutile TiO2 is still at early stage and more work need to be done in this field for comprehensive understanding the defect chemistry and dielectric polarization behaviours. This dissertation, therefore, aims to use defect engineering to control the dielectric behaviour of rutile TiO2. Stimulated by the excellent CP behaviour achieved in In+Nb co-doped rutile TiO2, investigation was carried out on the CP behaviour of Ga and Nb co-doped rutile TiO2 i.e. Ga0.5xNb0.5xTi1-xO2 (x = 0.1%, 0.5%, 5%, 10%), where Ga3+ is from the same group as In3+ but with a much smaller ionic radius. Colossal permittivity up to 104 ~ 105 with an acceptably low dielectric loss (tan δ = 0.05 ~ 0.1) over broad frequency/temperature ranges is obtained at x = 0.5% after systematic synthesis optimizations. Systematic structural, defect and dielectric characterizations suggest that the CP in this system is not dominated by the EPDD. Instead, multiple polarisation mechanisms including defect dipoles, polaron-like electron hopping/transport and a surface barrier layer capacitor effect together make contributions to the CP behaviour observed in this new material. This work provides a comprehensive guide for the design of new CP materials by considering the choice of the acceptor dopant. CP materials have many important applications in electronics but their development has generally been obscured due to the difficulty in achieving a relatively low dielectric loss. A new ionic co-doping material system, i.e. In+Ta co-doped TiO2 with nominal compositions In0.5xTa0.5xTi1-xO2 (x = 0.5%, 5%, and 10%), was also systematically investigated. This system manifests high dielectric permittivity and low dielectric loss based on the electron-pinned defect-dipole. The dielectric loss can be reduced down to e.g. 0.002 at 1k Hz, giving high performance, less temperature-independent dielectric property i.e. εr >104 meanwhile tan δ <0.02 in a broad temperature range of 50-400 K. Density functional theory computation coupled with the defect analysis uncover electron-pinned defect-dipoles (EPDDs), in the formation of highly stable triangle-diamond and/or triangle-linear dopant defect clusters with well-defined relative positions for Ti reduction, are also presented in the host material for the CP observed. Such a high-performance dielectric property would thus help for practical applications and discovery of promising new materials of this type. Furthermore, synthesis of bivalent acceptor and pentavalent donor co-doped rutile TiO2 was carried out to further understand the EPDDs. A new EPDD in rutile TiO2 was made by co-doping Mg and Ta with nominal composition Mgx/3Ta2x/3Ti1-xO2 (x = 0.5%, and 5%), which was characterized to exhibit colossal permittivity (>7000) as well as ultralow dielectric loss (e.g. 0.002 at 1 kHz) over a broad frequency/temperature range after optimized process conditions at x = 0.5%. Both experimental and theoretical evidences indicate such a colossal permittivity and low dielectric loss originate from the intragrain polarisation that links to the electron pinned defect clusters with a specific configuration, which differs from the defect cluster previously reported in tri-/pent-valent ion co-doped rutile TiO2. This work not only extends the research on colossal permittivity to bi-/penta-valent ion co-doped rutile TiO2, but also for the first time shows a likely defect cluster model existed in this system. These results further benefit the development of colossal permittivity materials and advance the defect chemistry in solids. With the success in synthesizing heavily Al+Ta co-substituted rutile TiO2 structure with nominal composition Al0.5xTa0.5xTi1-xO2 (x up to 50%), the dielectric properties of this type materials were systematically investigated. Structural characterizations and Raman spectra suggest that the materials maintain rutile TiO2 phase even for x up to 50% and there is signature of disorder. Defect analysis and dielectric characterisations suggest the significantly low ratio of Ti3+/Ta5+ as well as magnitude of permittivity (800~3000) in this new system, both of which are much smaller than that of the systems previously described or reported. Interestingly and surprisingly, the permittivity increases as x increases up to 20% and decreases after over 20% followed by exponential decrease of relaxation frequency as well as significant increase of the thermal activation temperature for defect dipole relaxation (e.g. the thermal activation energy increases from 33.4 meV to 131.4 meV when x increases from 5% up to 50%). The system present a typical dipole-glass character especially when x increases over 20%. This dissertation also reports for the first time, by using defect engineering, the linear polarisation behaviour of binary oxide, e.g. rutile TiO2 can be changed to a nonlinear one at room temperature. With slightly doping acceptor Mg into rutile TiO2, a combination of electrical measurements and theoretical calculations suggest that Mg-oxygen vacancy defect dipole can facilitate certain neighboring Ti4+ with large move-off-center ability, offering the doped rutile TiO2 an unexpected role as a new family of room temperature nonlinear dielectrics. More importantly, a poling induced internal electric field abnormally varies with the direction of poling electric field can be observable, which is quite different from that observed in ferroelectrics and relaxor ferroelectrics. Despite its potential novel applications in electronic and energy related areas, this research provides a newly/fundamentally important picture about the role of defects and its interaction with crystal environment.

Magister Scientiae - MSc
In this research project, nanostructured composites based on Tin dioxide (SnO2) and Titanium dioxide (TiO2) with poly-4-styrene sulfonic acid (PSSA) doped polyaniline (PANI) conducting polymer has been investigated based on their structural, electrical and electrochemical properties. The synthesis of conducting polymers and their metal oxide or composites have been carried out chemically or electrochemically according to methods modified from the literature. Layer-by-layer construction of nano-Metal Oxide/PSSA doped polyaniline composites were successfully constructed by electroanalytical methods on the surface of a glassy carbon working electrode (GCE).
South Africa

The general concepts of hybrid and nanocomposite were used not only to classify but also to drive the synthesis optimizing the materials for the different applications. The common denominator of each material was the titanium dioxide as photoreactive material, chapters 3 and 4, and dielectric material in chapter 5. Because both the morphology and the crystal phase of the titanium dioxide play a crucial role on the material performances the used TiO2 was always synthesized ex situ by hydrothermal synthesis allowing to control the morphological characteristics. In the chapter 3 and 4 anatase phase was used for its photocatalytic ability in presence of oxygen and water while in the chapter 5 the rutile phase was used because its highest dielectric constant compare anatase. In chapter 3 a polyacrilate composite material prepared by mechanical mixing of nanocrystalline titania with acrylate oligomers shows that, without titania surface functionalisation, the oxide forms micrometric aggregates reducing the exposed surface of the TiO2. Despite the filler aggregation the material preserves its photocatalytic properties. As drawback of the photocatalytic activity in phenol photomineralisation (use to simulate pollutants in water) some photooxidative degradation phenomena involve the organic matrix. Hence the necessity to have a stable material was the driving force to create a new material containing titania as photoactive material while embedded into an inorganic matrix. In the chapter 4 this porous and UV transparent inorganic-inorganic nanocomposite material is described. In order to obtain the desired porosity of the final material the silica sol-gel solution was mixed with PEG obtaining a class I hybrid material. During the silica formation PEG segregates in warm-like polymeric phase that, once the material is calcinated, leaves the voids conferring the desired macroporosity to the material. The photoactive oxide, previously functionalized on the surface with organic molecules, migrates in the polymeric phase during silica precursors hydrolysis and condensation. After calcination the titania nanocrystallites decorate the wall of the channels leaved by the organic species remotion. The molecules functionalizing the catalyst surface induce the TiO2 migration into the PEG phase because of their more affinity with polymer instead with silica. The exposed titania is then able to freely react with pollutants while the silica matrix provides the UV transparency and macroporosity for the photocatalytic reactions. The abatement efficiency of the material is comparable with slurry TiO2. The material is not affected by the photocatalyst leaching demonstrating that it is suitable for an industrial application. The nanocomposite material was tested for NOx degradation too using P25 commercial titania instead of home made one demonstrating the generality of the preparation method. The abatement efficiency of the NOx was comparable with the DENOX technology currently used for industrial applications. In chapter 5 the same reaction technique used to functionalize the nanoparticles in the chapter 4 was used to functionalize rutile titania nanoparticles with a RAFT reagent. After the styrene “polymerization from” reaction polystyrene chains were obtained. The brush like conformation of the chains justifies the high polymer surface density. The functionalized nanoparticles (class II material) are mixed in different concentrations with commercial polystyrene. The different concentration materials present good dispersion because of the high compatibilization properties of the surface functionalisation. At high concentrations the material shows a percolative behavior ascribed to the formation of chestnut like aggregates which increase the relative dielectric constant. Despite the charges percolation trough the material the polymeric surface layer acts as an insulating layer which contributes to mitigate the charge mobility and consequently the conductivity of the material. The low conductivity of the material allows to obtain low tanδ values. The low tanδ values in a large range of frequencies allows to candidate the material for radio frequency (RF) applications where very low dissipation factor is desired to avoid signal losses. In conclusion the present work, despite it covers three different materials, demonstrates how it is possible to create and optimize a material modifying the surface of the nanoparticles in order to confer them peculiar properties which drive the final material morphology. The final material morphology is then able to combine the properties both of the active material and of the matrix giving a new optimized material for a specific application.

Nesse trabalho foram fabricados filmes finos de TiO2 por RF magnetron sputtering reativo sobre substrato de silício (1 0 0). A pressão parcial do oxigênio na câmara foi variada de 5 a 100% em relação ao argônio. Após a deposição os filmes foram submetidos a tratamento térmico em atmosfera de oxigênio. A estequiometria dos filmes e o perfil de profundidade foram obtidos por RBS. A estrutura cristalina foi obtida por XRD. As propriedades ópticas foram obtidas por interferometria e reflectância e as elétricas por meio das curvas C-V. Os valores de espessura dos filmes sem tratamento térmico aumentaram aproximadamente 41% com o aumento do oxigênio na câmara de deposição. Essa variação está ligada ao aumento da eficiência do sputtering do alvo. Os índices de refração dos filmes sem tratamento térmico se mantiveram dentro de um intervalo de aproximadamente 2,3 a 2,4. A diminuição do band gap com o tratamento térmico é consequência da mudança de fase cristalográfica de anatase para rutila. A estequiometria TiOx dos filmes antes do tratamento térmico apresentaram valores de x entre 2,0 e 2,4. A espessura em TFU dos filmes aumentou com o percentual de oxigênio na câmara. As amostras que receberam tratamento térmico apresentaram difusão de titânio na interface do substrato e incorporação de oxigênio no filme. Os valores da constante dielétrica aumentaram com o percentual de oxigênio na câmara, em contraposição com o efeito do tratamento térmico que diminuiu o valor. Todos os resultados observados são coerentes do ponto de vista da mudança de fase anatase rutila e aumento do percentual de oxigênio na câmara.
In this work thin films of TiO2 were produced by reactive RF magnetron sputtering on silicon substrate (1 0 0). The oxygen partial pressure in the chamber was varied from 5 to 100% in relation to argon. After deposition the films were submitted to thermal treatment under an oxygen atmosphere. The stoichiometry of the films and the depth profile were obtained by RBS. The crystal structure was obtained by XRD. Its optical properties were obtained by interferometry and reflectance and the electrical were obtained by means of the C-V curves. The thickness values of films without heat treatment increased approximately 41% with the increase of oxygen in the deposition chamber. This variation is linked to the increased sputtering efficiency of the target. The refractive indexes of films without heat treatment remained within a range of about 2.3 to 2.4. The decrease of the band gap with the heat treatment is a consequence of the change of crystallographic phase from anatase to rutile. The TiOx stoichiometry of the films before the heat treatment showed values of x between 2.0 and 2.4. The TFU thickness of the films increased with the percentage of oxygen in the chamber. The samples that received heat treatment shows diffusion of titanium at the interface of the substrate and incorporation of oxygen in the film. The values of the dielectric constant increased with the percentage of oxygen in the chamber, as opposed to the effect of the thermal treatment that decreased the value. All the results observed are consistent from the point of view of the anatase - rutile phase transition and the increase in the oxygen percentage in the chamber.

This diploma thesis is focused on the analysis of basic problematics of dielectrics and nanocomposites. It describes the fabrication of experimental samples of nanocomposites from sealing epoxy resin and nanoparticles of titanium dioxide with various weight filling. Further, the thesis deals with measuring and evaluation of dielectric properties of the samples. It examines the influence of weight filling, temperature and frequency of the electric field on volume resistivity, relative permitivity and loss factor.

The surge of interest in multifunctional materials over the past 15 years has been driven by their fascinating physical properties and huge potential for technological applications such as sensors, microwave devices, energy harvesting, photovoltaic technologies, solid-state refrigeration, and data storage recording technologies. Among the others, magnetoelectric multiferroic composites are a special class of advanced solid-state compounds with coupled ferromagnetic and ferroelectric ferroic orders which allow to perform more than one task by combining electronic, magnetic and mechanical properties into a single device component. The production and characterization of lead zirconate titanate (PZT)- cobalt ferrite composites was the main topic of the thesis. During the PhD activity different ceramic processing and characterization technologies were studied and involved in order to optimize the produced materials as a function of the final microstructural and functional properties. The synthesis of cobalt ferrite (CF) and niobium-doped lead zirconate titanate (PZTN) powders by solid state reaction method and sol-gel technique, to control the particle size distributions and their microstructural and functional properties through calcination and milling treatments has been addressed first, followed by the mixing of the PZT and CF powders to produce particulate composites. The dispersion of PZT and CF in a liquid media, to produce layered composites by depositing the particles by electrophoretic deposition was an objective of the work as well. Key issues such as the lead loss during the sintering of PZTN-CF composites and the reaction between CF and titania have been addressed and have resulted in improvements in the sintering and characterization techniques leading to the production of fully dense PZTN-CF dual-particulate composites. In particular, the optimized sintering parameters have configured a new paradigm of ceramic sintering, which has been called quite-fast sintering, in respect to the traditional one, and the study of the PbO loss has led to propose an equation to calculate the PbO loss through XRD analysis. Further important achieved results were: the production of nanocobalt ferrite particles by multi-step milling, the correlation between the spin-canting angle with the microstrain and the average crystallite size of nanocobalt ferrite particles, the understanding of the CF growth mechanisms, the extension of the Globus model from small ferromagnetic grains “having no defect inside” to multiparallel-twinned overgrown ones, the understanding of heating rate effect on the interface nucleation onset of the anatase-to-rutile transformation and the anatase particle size, and the reaction products between CF and rutile at 1200 °C at the variation of CF/rutile ratio.

In this research project, nanostructured composites based on Tin dioxide (SnO2) and Titanium dioxide (TiO2) with poly-4-styrene sulfonic acid (PSSA) doped polyaniline (PANI) conducting polymer has been investigated based on their structural, electrical and electrochemical properties. The synthesis of conducting polymers and their metal oxide or composites have been carried out chemically or electrochemically according to methods modified from the literature. Layer-by-layer construction of nano-Metal Oxide/PSSA doped polyaniline composites were successfully constructed by electroanalytical methods on the surface of a glassy carbon working electrode (GCE).

The field of advanced solution processed spin-coated electronics has rapidly expanded over the last few decades towards the development of low-cost, large area and low power consumer electronics for the design of system-on-panel, system-on-glass, and system-on-chip circuits. They have diverse applications such as wearable and textile integrated devices, seamless and twistable systems, soft skin systems, as well as roll-to-roll light-weight, transparent, conformable, stretchable, and even biodegradable systems. So far, all demonstration of solution processed electronics use thin lm transistors (TFT) without any memory. However, memory is an essential electronic component of all systems and it is important to realize floating gate ash memory devices using similar spin-coated solution processing compatible technique. The first demonstration of floating memory by Kahng and Size in 1967 on transparent glass substrates utilized floating metal gate charge storage layers deposited by high temperature vacuum technology. Since then, there has been intensive research on floating gate technology. However, the high temperature and high vacuum technology is incompatible with large area, flexible and low cost electronics due to the process integration issue. Hence the alternative challenge was taken up on developing solution processed spin-coated memory devices for sol-gel electronics. In this thesis we first introduce different solution processed dielectrics and oxide semi-conductors, thin lm deposition, and behavior at different processing temperatures. Further, we also demonstrate how the band structure of the dielectric, particularly the electron a finity, changes with annealing temperature. Then we propose and demonstrate a new high speed measurement technique for two terminal capacitive devices. In particular, we show that the entire capacitance-voltage curve can be measured in 2.5 s. The measurement is useful for characterization of two terminal capacitive memory devices in terms speed, endurance and retention. This achievement is followed by its application to newly developed fully solution processed, nanoparticle based, robust two terminal memory devices. The link between device performance and its structural and processing parameters such as annealing temperature, thickness of memory layer, supporting dielectric layer and substrate materials, is highlighted. In addition, a detailed analysis and comparison of performance of solution processed memory with regard to state-of-the art processing techniques as well as the selection of materials is presented. This work was extended to achieve the worlds first three terminal fully solution processed inorganic material-based robust ash memory devices with different kinds of solution processed charge trapping layers. We also discuss the advantage of this technology over previously reported sophisticated ultra high vacuum technology based three terminal ash memory devices. Afterwards, we report the discovery of deep level intrinsic traps in solution processed aluminium oxide phosphate. It is also shown that the traps are tunable with the processing temperature. Using XPS and UPS characterization techniques, the origin of these traps is linked with the molecular structure. Utilizing this trap behavior we have fabricated the worlds first fully solution processed ash memory device without tunneling and blocking layers at below 200 C. This discovery may be a breakthrough for large area, solution processed, and flexible electronics applications. Finally, conclusions are drawn on the performance of the memory stack with respect to other processing techniques, along with an outlook for this field and predictions for the future of this technology.

Precise manipulation of heterogeneous droplets on an open droplet microfluidic platform could have numerous practical advantages in a broad range of applications, from proton exchange membrane (PEM) fuel cells and microreactors, to medical diagnostic platforms capable of assaying complex biological analytes. Toward the aim of developing electrically controllable micropost arrays for use in open droplet manipulation, custom-designed titanium dioxide (TiO2)- loaded poly(dimethylsiloxane) (PDMS) micropost arrays were developed in this work and indirectly mechanically actuated by applying an electric field. Initial experiments explored the bulk properties of TiO2-loaded PDMS films, with scanning electron microscopy (SEM) confirming a uniform TiO2 particle distribution in the PDMS, and tensile testing of bulk films showing an inverse relationship between TiO2 % (w/w) and Young’s Modulus with the Young’s Moduli quantified as 4.22 ± 0.51 MPa for unloaded PDMS, 2.27 ± 0.18 MPa for 10 % (w/w) TiO2, and 1.39 ± 0.20 MPa for 20 % (w/w) TiO2. Following bulk material evaluation, soft lithography methods were developed to fabricate TiO2- loaded PDMS micropost arrays. Mathematical predictions were applied to design microposts of varying shape, length, and gap spacing to yield super-hydrophobic surfaces actuatable by an electric field. Visual inspection and optical microscopy of the resulting arrays confirmed a non- collapsed micropost geometry. Overall, round microposts that were 100, 200, and 300 μm in length, 15 μm in diameter, and spaced 50 μm apart were produced largely free of defects, and used in contact angle measurements and micropost deflection experiments. Droplet contact angles measured on the arrays remained above 120° indicating the arrays successfully provided super- hydrophobic surfaces. Individual microposts deflected most notably above an electric field strength of 520 kV/m (12.5 kV nominal voltage). The ability to mechanically deflect customized microposts using an electric field demonstrated by this work is promising for translating this technology to precise droplet manipulation applications. Indirect actuation of droplets could enable the manipulation of liquids with varying electrical properties, which is a limitation of current micropumping technologies. Once optimized, electrically actuated micropost arrays could significantly contribute to the micro- handling of heterogeneous, highly ionic, and/or deionized fluids.
Thesis (Master, Chemical Engineering) -- Queen's University, 2013-03-03 17:25:49.785

The scaling down of Complementary Metal Oxide Semiconductor (CMOS) transistors requires replacement of conventional silicon dioxide layer with higher dielectric constant (K) material for gate dielectric. In order to reduce the gate leakage current, and also to maximize gate capacitance, ‘high K’ gate oxide materials such as Al2O3, ZrO2, HfO2, Ta2O5, TiO2, Er2O3, La2O3, Pr2O3, Gd2O3, Y2O3, CeO2 etc. and some of their silicates such as ZrxSi1–xOy, HfxSi1–xOy, AlxZr1–xO2 etc. are under investigation. A systematic consideration of the required properties of gate dielectrics indicates that the key guidelines for selecting an alternate gate dielectric are (a) permittivity, band gap and band alignment to silicon, (b) thermodynamic stability, (c) film morphology, (d) interface quality, (e) compatibility with the materials/process used in CMOS devices and (f) reliability. In this study titanium dioxide (TiO2) is chosen as an alternate to silicon dioxide (SiO2). This thesis work is aimed at the study of the influence of process parameters like deposition rate, substrate temperature and annealing temperature on the electrical properties like maximum capacitance, dielectric constant, fixed charge, interface trapped charge and leakage current. For making this analysis we have used p–type single crystal silicon (<100>) as substrates and employed direct current (DC) reactive magnetron sputtering method with Titanium metal as target and Oxygen as reactive gas. TiO2 thin films have been deposited with an expected thickness of 50 nm with different deposition rates starting from 0.8 nm/minute to 2 nm/minute with different substrate temperatures (ambient temperature to 500ºC). Some of the samples are annealed at 750ºC in oxygen atmosphere for 30 minutes. SENTECH make Spectroscopic Ellipsometer is used for analyzing the optical properties such as thickness, refractive index etc. The thicknesses of all the samples that are extracted from the Ellipsometry are varying from 35 ± 2 nm to 50 ± 5 nm. Agilent make 4284A model L−C−R meter along with KarlSUSS wafer probe station is used for the C − V measurements and Keithley make 6487 model Pico ammeter/Voltage source is used for the I−V measurements. MOS capacitors have been fabricated with Aluminium as top electrode to perform the bi directional Capacitance−Voltage and also Current−Voltage analysis. The X–ray diffraction studies on the samples deposited at 500ºC showed that the films are amorphous. Dielectric constant (K) and effective substrate doping concentration (Na), flat band voltage (VFB), hysteresis, magnitude of fixed charges (Qf) as well as interface states density (Dit') and Equivalent Oxide Thickness (EOT) are obtained from the bi directional C−V analysis. A maximum dielectric constant of 18 is achieved with annealed samples. The best value of fixed charge density we have achieved is 1.2 x1011 per cm2 corresponding to the deposition rate of 2.0 nm/minute and with 500ºC substrate temperature. The ranges of Qf values that we have obtained are varying from 1.2x 1011 − 1.0 x1012 per cm2. It was also found that, the samples deposited at higher substrate temperatures show lower Qf values than the samples deposited at lower temperatures. The same trend is observed in case of interface states density also. The range of Dit' values we have obtained are in the range of 1.0 x 1012 cm–2eV–1 to 9x1012 cm–2eV–1. The best value of Dit' we have obtained is 1.0x1012 cm–2 eV–1 for the sample deposited at 0.8 nm/minute deposition rate and with substrate temperature of 400ºC. From the flat band voltage values of different set of samples, it was found that the flat band voltage is decreasing and in turn trying to approach the analytical value for the films deposited at higher deposition rates. The minimum EOT that we have achieved is 11 nm that corresponds to the film, which is annealed at 750ºC in oxygen atmosphere. From the I−V analysis it was found that the leakage current density is increasing with increase in substrate temperature and the same trend is observed with annealed films also. The minimum leakage current density achieved is 1.72x10–6 A/cm2 at a gate bias of 1V (corresponding field of 0.3 MV/cm). From the time dependent dielectric breakdown analysis it was found that the leakage current is exhibiting a constant value during the entire voltage stress time of 23 minutes. From the I–V characteristics it was found that the leakage current is following the Schottky emission characteristics at lower electric fields (< 1MV/cm) and is following the Fowler–Nordheim tunneling mechanism at higher electric fields. Since our aim is to study the electrical properties of titanium dioxide thin films for the application as high K gate dielectric in microelectronic applications more emphasis is given on the electrical properties. The maximum dielectric constant we have achieved is in the comparable range of the values for this parameter. The leakage current density values obtained are higher than the required for the microelectronic devices, where as the interface state density values and fixed charge density values are in the same range of values that are reported with this particular oxide and more care has to be taken to minimize these parameters. The EOT values we have achieved are also falling into the range of values that it actually takes as it was reported in the literature.

The scaling down of Complementary Metal Oxide Semiconductor (CMOS) transistors requires replacement of conventional silicon dioxide layer with higher dielectric constant (K) material for gate dielectric. In order to reduce the gate leakage current, and also to maximize gate capacitance, ‘high K’ gate oxide materials such as Al2O3, ZrO2, HfO2, Ta2O5, TiO2, Er2O3, La2O3, Pr2O3, Gd2O3, Y2O3, CeO2 etc. and some of their silicates such as ZrxSi1–xOy, HfxSi1–xOy, AlxZr1–xO2 etc. are under investigation. A systematic consideration of the required properties of gate dielectrics indicates that the key guidelines for selecting an alternate gate dielectric are (a) permittivity, band gap and band alignment to silicon, (b) thermodynamic stability, (c) film morphology, (d) interface quality, (e) compatibility with the materials/process used in CMOS devices and (f) reliability. In this study titanium dioxide (TiO2) is chosen as an alternate to silicon dioxide (SiO2). This thesis work is aimed at the study of the influence of process parameters like deposition rate, substrate temperature and annealing temperature on the electrical properties like maximum capacitance, dielectric constant, fixed charge, interface trapped charge and leakage current. For making this analysis we have used p–type single crystal silicon (<100>) as substrates and employed direct current (DC) reactive magnetron sputtering method with Titanium metal as target and Oxygen as reactive gas. TiO2 thin films have been deposited with an expected thickness of 50 nm with different deposition rates starting from 0.8 nm/minute to 2 nm/minute with different substrate temperatures (ambient temperature to 500ºC). Some of the samples are annealed at 750ºC in oxygen atmosphere for 30 minutes. SENTECH make Spectroscopic Ellipsometer is used for analyzing the optical properties such as thickness, refractive index etc. The thicknesses of all the samples that are extracted from the Ellipsometry are varying from 35 ± 2 nm to 50 ± 5 nm. Agilent make 4284A model L−C−R meter along with KarlSUSS wafer probe station is used for the C − V measurements and Keithley make 6487 model Pico ammeter/Voltage source is used for the I−V measurements. MOS capacitors have been fabricated with Aluminium as top electrode to perform the bi directional Capacitance−Voltage and also Current−Voltage analysis. The X–ray diffraction studies on the samples deposited at 500ºC showed that the films are amorphous. Dielectric constant (K) and effective substrate doping concentration (Na), flat band voltage (VFB), hysteresis, magnitude of fixed charges (Qf) as well as interface states density (Dit') and Equivalent Oxide Thickness (EOT) are obtained from the bi directional C−V analysis. A maximum dielectric constant of 18 is achieved with annealed samples. The best value of fixed charge density we have achieved is 1.2 x1011 per cm2 corresponding to the deposition rate of 2.0 nm/minute and with 500ºC substrate temperature. The ranges of Qf values that we have obtained are varying from 1.2x 1011 − 1.0 x1012 per cm2. It was also found that, the samples deposited at higher substrate temperatures show lower Qf values than the samples deposited at lower temperatures. The same trend is observed in case of interface states density also. The range of Dit' values we have obtained are in the range of 1.0 x 1012 cm–2eV–1 to 9x1012 cm–2eV–1. The best value of Dit' we have obtained is 1.0x1012 cm–2 eV–1 for the sample deposited at 0.8 nm/minute deposition rate and with substrate temperature of 400ºC. From the flat band voltage values of different set of samples, it was found that the flat band voltage is decreasing and in turn trying to approach the analytical value for the films deposited at higher deposition rates. The minimum EOT that we have achieved is 11 nm that corresponds to the film, which is annealed at 750ºC in oxygen atmosphere. From the I−V analysis it was found that the leakage current density is increasing with increase in substrate temperature and the same trend is observed with annealed films also. The minimum leakage current density achieved is 1.72x10–6 A/cm2 at a gate bias of 1V (corresponding field of 0.3 MV/cm). From the time dependent dielectric breakdown analysis it was found that the leakage current is exhibiting a constant value during the entire voltage stress time of 23 minutes. From the I–V characteristics it was found that the leakage current is following the Schottky emission characteristics at lower electric fields (< 1MV/cm) and is following the Fowler–Nordheim tunneling mechanism at higher electric fields. Since our aim is to study the electrical properties of titanium dioxide thin films for the application as high K gate dielectric in microelectronic applications more emphasis is given on the electrical properties. The maximum dielectric constant we have achieved is in the comparable range of the values for this parameter. The leakage current density values obtained are higher than the required for the microelectronic devices, where as the interface state density values and fixed charge density values are in the same range of values that are reported with this particular oxide and more care has to be taken to minimize these parameters. The EOT values we have achieved are also falling into the range of values that it actually takes as it was reported in the literature.

The work carried out as a part of this thesis has been focussed on understanding different aspects of the chemical vapor deposition process namely, ALD / MOCVD. A large part of the thesis is aimed at solving the problem of a single-source precursor for the MOCVD process to obtain substituted metal oxide thin films. For a chemical vapor deposition technique, it is important to understand the requisite salient features of precursor for deposition of thin films. For this purpose, not only is the structural characterization of the chemical precursor is required but also an in-depth thermal analysis of the precursor to know its vapor pressure. Vapor pressure of a metalorganic complex is one of the important properties to evaluate the applicability of a metalorganic complex as a MOCV/ALD precursor. The thesis discusses a novel approach to use thermal analysis as a tool to gauge the viability of substituted metal “single source” precursor for MOCVD/ALD. The other half deals with material characterization of thin films grown by an ALD process using hydrogen and Ti(OiPr)2(tbob)2 as precursors. The films were further studied for their potential application as high-k dielectric in DRAM applications. The first chapter is an overview of topics that are relevant to the work carried out in this thesis. The chapter focuses on the description of techniques used for thin film deposition. A detailed review of CVD-type techniques (ALD/ MOCVD) is then given. Chapter1 reviews the various process parameters involved in ALD,i.e. film growth(specifically as a function of the reactant pulse length, the nature of the chemical reactant/precursor and that of the metal precursor, and purge length) and growth temperature. Following the discussion of ALD, CVD and its growth kinetics are also discussed. Chapter 1 then outlines a holistic understanding of precursors, followed the differences in requirement for using them in ALD and MOCVD. Further, an introduction to the titanium oxide (Stoichiometric titanium dioxide and various Magneli phases) system, its phase diagram, oxide properties and their applications is given. Chapter 1 concludes by delineating the scope of the work carried out which is presented in the thesis. The second chapter deals with the synthesis of a series of substituted metal “single source” precursors to be used for MOCVD of substituted metal oxides thin films. The precursor complexes were of the type AlxCr1-x (acac)3 where 0