Non traduit / The introduction of nanometer technologies, has allowed the semiconductor industry to create nanoscale devices in combination with gigascale complexity. However, new technologies bring with them new challenges. In the era of large systems embedded in a single System-On-Chip and fabricated in continuously shrinking technologies, it is important to test and ensure fault-free operation of the whole system. The cost involved in semiconductor test has been steadily growing and testing techniques for integrated circuits are today facing many exciting and complex challenges. Although important advances have been made, existing test solutions are still unable to exhaustively cover all types of defects in advanced technology nodes. Consequently, innovative solutions are required to cope with new failure mechanisms under the constraints of higher density and complexity, cost and time to market pressure, product quality level and usage of low cost test equipment.The work of this thesis is focused on the development of silicon test and characterization methodologies that aid in the accurate detection and resolution of issues that may arise due to variability, manufacturing defects, wear-out or interference. A wide spectrum of these challenges has been addressed from a test perspective to ensure that the availability of effective test solutions does not become a bottleneck in the path towards further scaling. Additionally the advances and innovations introduced in the myriad domains of electronic design, reliability management, manufacturing process improvements etc. that call for the development of advanced, modular and agile test methodologies have been effectively covered within the scope of this work.This thesis presents the significant contributions made for enabling resolution of state of the art industrial test challenges via the design and implementation of novel test strategies (targeting the 28nm FDSOI technology node) for:•Detection & diagnosis of timing faults in standard cells.•Analysis of Setup and Hold margins within silicon.•Verification & reliability analysis of innovative test structures.•Analysis of on-chip self heating.•Enabling characterization and performance evaluation of high speed digital IPs.

The motivation to study this non-classical CMOS device is necessary to face with the ITRS constraints. In the ITRS roadmap, the gate length of devices are being scaled down rapidly but this rapid scaling is not in pace with the relatively slow scaling of the gate equivalent oxide thickness which leads to a degradation in the performance of the transistor. One of the solutions to this problem is the use of non-classical devices, such as the Gate-All-Around (GAA) MOSFET. Owing to the flexibility of SOI technology, these novel devices can be adapted to this technology bringing along with it the benefit of SOI technology. One of the main advantage of building this GAA device on SOI technology is that it offers the possibility whereby the second gate is easily built into the back of the device. GAA devices are also interesting because they do not need to scale down the thickness of the gate oxide rapidly but still able to maintain a suitable thickness to avoid problems such as current leakage through the thin gate oxide by tunnelling. The objective of this research can be divided into three parts; the first is to study the feasibility of the various fabrication process for this GAA device, the second to analyse the electrical characteristics of these fabricated GAA devices from DC characteristics up to 110 GHz and the third one is the use of commercial numerical simulation softwares (IE3D, Silvaco) in order to describe the physics of these novel devices. In this study, these different structures shows advantages and disadvantages when used in either analog or RF applications. The graded-channel structure has shown that it is advantageous when used in high performance analog circuits. The advantages of this structure is further enhanced when it is combined with the double-gate structure, forming a double-gate graded channel SOI MOSFET. Optimizing in terms of doping level along the channel of the graded-channel is important to yield good electrical results. In order for these devices to be successful commercially, it is important that they are compatible with the fabrication technology and trends available today and in the near future. To confirm that these devices can be adapted into today's and tomorrow's technology, we have shown that these they are easily adaptable in the current technology. Multiple-gate devices are a new group of devices which have been identified by ITRS as potential devices to meet the demands in the future. In this study, we have shown that these multiple-gate devices do indeed show improved short-channel effects and improved analog and RF characteristics when compared to the single-gate devices in existence. One of the main contributors to these improvements is due to what is known as the “volume inversion”.

Made available in DSpace on 2014-06-11T19:27:12Z (GMT). No. of bitstreams: 0 Previous issue date: 2010-12-21Bitstream added on 2014-06-13T20:08:18Z : No. of bitstreams: 1 gasparotto_g_me_araiq.pdf: 3559380 bytes, checksum: fb3a7ae9b231ef8abae43cc0439f427f (MD5) / Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq) / Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES) / O presente trabalho consiste no estudo da viabilidade para a obtenção de cerâmicas densas de SnO2 com baixa resistividades, dopados com Zn2+, Nb5+ e Al3+. Os pós cerâmicos foram preparados pelo método químico (método Pechini) e por de mistura de óxidos, usando a sinterização em forno microondas. Fez-se a caracterização do pó por difratometria de raios X (DRX), medidas de área superficial (BET) e termogravimetria e termogravimetria diferencial (TG/DTA). Depois de conformar os pós, fez-se a caracterização microestrutral e elétrica dos compactos. A baixa densificação do material é justificada pela presença de microestruturas em formas de agulhas, constituída pelo agente densificante. Os menores resultados de resistividade à temperatura ambiente foram obtidos para as composições SZ100N e S200ZNA, obtidos pelo método Pechini, cujos valores são, respectivamente, 12,4 e 11,3 Ω.cm. Quando aumentou a temperatura de 50º a 400ºC, os menores resultados de resistividade foram obtidos pelo material preparado por mistura de óxidos com valor próximo a 5 Ω.cm / The present work is to study the viability to obtain high densification of SnO2 with low resistivity doped Zn2+, Nb5+ and Al3+. The ceramic powders were prepared by chemical method (Pechini method) and by solid state reaction, using the microwave sintering. There was the characterization by powder X-ray diffraction (XRD), surface area measurements (BET) and thermogravimetry and differential thermogravimetry (TG/DTA). After conforming the powder, it was the characterization of electrical and microestrutral compact. The low densification of the material is justified by the presence of microstructures in forms of needles constituted of the densifying agent. The lowest specific resistivity at room temperature were obtained for the compositions and S200ZNA SZ100N, obtained by Pechini method, whose values are respectively 12.4 and 11.3 Ω.cm. When the temperature increased from 50 º to 400 º C, the lowest resistivity results were obtained for material prepared by mixing oxides with a value next 5 Ω.cm

Submitted by Roberto de Aguiar Ramos Junior null (robeerto.aguiar.ramos@gmail.com) on 2018-04-03T14:25:40Z No. of bitstreams: 1 dissertaçao_final.pdf: 2202514 bytes, checksum: b29c60407d282d9848bdfc887c1a97c8 (MD5) / Approved for entry into archive by Lucilene Cordeiro da Silva Messias null (lubiblio@bauru.unesp.br) on 2018-04-04T19:31:40Z (GMT) No. of bitstreams: 1 ramosjunior_ra_me_bauru.pdf: 2202514 bytes, checksum: b29c60407d282d9848bdfc887c1a97c8 (MD5) / Made available in DSpace on 2018-04-04T19:31:40Z (GMT). No. of bitstreams: 1 ramosjunior_ra_me_bauru.pdf: 2202514 bytes, checksum: b29c60407d282d9848bdfc887c1a97c8 (MD5) Previous issue date: 2018-02-08 / Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES) / Este trabalho traz o estudo das propriedades óticas, elétricas e morfológicas do material TiO2 de forma individual e acoplado com SnO2 dopado com 4at%Sb, formando uma heteroestrutura. Tanto TiO2 quanto a heteroestrutura foram trabalhados na forma de filmes finos depositados pelo método sol-gel-dip-coating, e, no caso do TiO2 também foi relevante sua análise em forma de pós prensados (pastilhas). No que diz respeito ao SnO2:4%Sb, este trabalho traz uma revisão literária de suas principais propriedades, buscando apresentar um panorama geral, pois com isto pode-se entender melhor os fenômenos que ocorrem na heteroestrutura. Os resultados das pastilhas de TiO2 indicam uma transição parcial de fase anatase/rutilo para tratamentos térmicos entre 500ºC e 1000ºC, confirmadas pela fotoluminescência, que apresentou bandas relacionadas a fase anatase ou rutilo, dependendo do processamento utilizado. Filmes de TiO2 mostraram boa foto sensibilidade, com a corrente elétrica respondendo imediatamente à excitação independente da energia, além de um rápido decaimento com relação ao valor excitado. Fora isto, medidas de decaimento da corrente foto induzida, realizadas em atmosfera de O2, indicaram que o decaimento se torna ainda mais rápido na presença do gás, estando associado ao aprisionamento de portadores de carga pelas moléculas adsorvidas na amostra, além da recombinação dos pares elétron-buraco. Com relação à heteroestrutura, quando a condução ocorre preferencialmente no TiO2, a amostra apresenta resultados muito similares às dos filmes de TiO2, tendo uma rápida resposta à excitação com fonte de luz acima do bandgap do TiO2 e um rápido retorno para seu estado de equilíbrio, no escuro. Entretanto, em atmosfera gasosa, o decaimento se torna muito mais rápido, o que também está associado ao aprisionamento de portadores pelas moléculas adsorvidas de gás. Porém, o aumento na taxa com que isto acontece, está relacionado à formação da heteroestrutura e às compensações de carga na interface, que podem ocorrer quando a excitação utiliza comprimento de onda adequado. A configuração lado a lado da heteroestrutura mostrou emissão Poole – Frenkel para tensões maiores que 40V, e quando irradiada com luz que simula o espectro solar apresentou uma região de resistência negativa para algumas potências de excitação que pode estar ligada ao aprisionamento de elétrons na interface. Desta forma, este trabalho visa trazer uma contribuição importante à compreensão do mecanismo de transporte elétrico dos materiais estudados. Por fim, pode-se dizer que os materiais aqui estudados podem ser aplicados como sensores de gás ou dispositivos retificadores/amplificadores desde que seja escolhida a melhor configuração para a aplicação desejada. / This work presents a study of the optical, electrical and morphological characterization of TiO2 thin films, deposited individually or coupled with SnO2 doped with 4at%Sb, forming a heterostructure. Both sort of samples, TiO2 and the heterostructure were studied in thin film form, deposited by sol-gel-dip-coating, and, in the case of TiO2, it was relevant the analysis of samples also in the form of pellets form (pressed powders). With regards to SnO2:4%Sb, this work brings a literary revision of its principal properties, trying to present a general overview, for the better understanding of the phenomena that occur in the heterostructure. The results of TiO2 pellets indicates a partial anatase/rutile phase transition to thermal annealing between 500 and 1000ºC, confirmed by the photoluminescence that presented bands related to anatase or rutile, depending the utilized processing. TiO2 films showed fair photo-sensibility, with immediate response on the electric current to light excitation, independent on the utilized energy, along with fast decay in relation to the excited value. Moreover, photo-induced current decay measurements, performed in O2 atmosphere, indicated that the decay becomes faster in gas presence, being associated to charge carriers trapping by the adsorbed molecules on sample, besides the electron-hole recombination. Concerning the heterostructure, when the conduction occurs preferentially in TiO2 layer, the sample shows very similar results to the TiO2 films, with a fast response to light excitation above the TiO2 bandgap and fast return to the equilibrium state, in dark. However, in gas atmosphere, the decay becomes much faster, which is also associated to the carriers trapping by the gas adsorbed molecules. Nevertheless, the rate increase in this phenomenon is related to the heterostructure formation and the charge compensations at the interface, which may occur when appropriate wavelength is used for excitation. The side by side heterostructure sample showed a Poole – Frenkel emission to bias higher than 40V, and presented a negative resistance region to some irradiation power when illuminated with solar light that can be associated to electrons trapping at the interface. In summary, this work aims to bring a contribution related to the electric transport mechanism of the studied materials. The materials investigated here may be applied in gas sensors or rectifiers/amplifiers devices, according the sample configuration. / CAPES: 1578735

Silicon Carbide is a wide bandgap semiconductor with excellent physical and opto-electrical properties. Among these excellent properties are its radiation hardness, high temperature operation and high electric field breakdown. SiC can therefore be used in the fabrication of electronic devices capable of operating in harsh environments, e.g. radiation detectors. Like any other semiconductor, the success of SiC in device fabrication depends on elimination of defects that are detrimental to desired devices or controlled introduction of desired energy levels. The first step in so doing is understanding the defects that are either found in as grown material, introduced during device fabrication or introduced during device operation. In this study nickel ohmic and Schottky contacts were resistively fabricated on n-type 4H-SiC with a net doping density of 4 × 1014 cm-3. Current-Voltage (I-V), Capacitance-Voltage (C-V), Deep Level Transient Spectroscopy (DLTS) and Laplace-DLTS measurement techniques were used to electrically characterize the fabricated Schottky diodes. The diodes were then irradiated with low energy electrons, alpha particles and protons. The characterization measurements were repeated after irradiation to evaluate the effect of irradiation on the electrical properties of SiC. It was observed from I-V measurements that electron, alpha particle and proton irradiations do not significantly affect the rectification of Ni/SiC Schottky contacts. C-V measurements indicated that the free carrier removal rate is higher for alpha particle irradiation as compared to electron irradiation. The irradiated diodes were annealed in argon ambient and significant recovery in the free carrier concentration was observed below 600 °C. The free carrier concentration of proton irradiated Schottky contacts, which was decreased to below detection levels was also partly recovered after heat treatment of up to 400 °C. DLTS and Laplace-DLTS measurements revealed the presence of four defect levels in as-grown 4H-SiC. These defects have been labelled E0.10, E0.12, E0.17 and E0.69 where the subscripts indicate the activation energies of the respective defects. Electron, alpha particle and proton irradiations were observed to induce three more defect levels with activation energies of 0.42 eV, 0.62 eV and 0.76 eV. Additionally, these irradiations were also observed to enhance the concentration of level E0.69. All the radiation induced defects were annealed out at temperatures below 600 °C. In proton irradiated diodes, another defect with activation energy of 0.31 eV was observed after annealing the irradiated diodes at 625 °C. / Dissertation (MSc)--University of Pretoria, 2014. / lk2014 / Physics / MSc / Unrestricted

No description available.

A film which is optically transparent and electrically conductive is difficult to come by but can be realized in ways such as doping an oxidized film or by oxidizing a metallic film resulting in what is known as a transparent conducting oxide (TCO). TCO's have many important uses in electronics, especially as the top contact in to solar cells where efficient transmission of light and low electrical resistivity allow for higher efficiency solar cells and as the gate contact in AlGaN/GaN HFET's allowing for optical characterization of the subsurface transistor properties. Because these devices rely heavily on the characteristics of its material interfaces, a detailed analysis should be done to investigate the electrical effects of implementing a TCO. In this work, the electrical characterization of ruthenium dioxide (RuO₂) Schottky contacts to gallium nitride (GaN) formed by evaporating ruthenium with a subsequent open-air annealing is presented. The results gathered from the current-voltage-temperature and the capacitance-voltage relationships were compared to ruthenium (Ru) on GaN and platinum (Pt) on GaN. Additionally, the measurement and analysis procedure was qualified on a similar structure of nickel on GaAs due to its well-behave nature and presence in the literature. The results indicate that an inhomogeneous Gaussian distribution of barrier heights exists at the RuO₂/GaN interface with an increase of 83meV in the mean barrier height when compared to Ru/GaN. / Master of Science

As the current requirements of power devices are moving towards high frequency, high efficiency and high-power density, Silicon-based devices are reaching its limits which are instigating the need to move towards new materials. Gallium Nitride (GaN) has the potential to meet the growing demands due to the wide band-gap nature which leads to various enhanced material properties like, higher operational temperature, smaller dimensions, faster operation and efficient performance. The metal contacts on semiconductors are essential as the interface properties affect the semiconductor performance and device operation. The low resistance ohmic contacts for n-GaN have been well established while most p-GaN devices have still high contact resistivity. Significant work has not been found that focuses on software-based modeling of the device to analyze the contact resistance and implement methods to reduce the contact resistivity. Understanding the interface physics in n-GaN devices using simulations can help in understanding the contacts on p-GaN and eventually reduce its metal contact resistivity. In this work, modeling of the metal-semiconductor interface along with the effect of a heavily doped layer under the metal contact is presented. The extent of reduction in contact resistivity due to different doping and thickness of n++ layer is presented with simulations. These results have been verified by the growth of device based on simulation results and reduction in contact resistivity has been observed. The effect of different TLM pattern along with different annealing conditions is presented in the work. / Master of Science / Technology has become part and parcel of the life of humans which is slowing gearing towards Automation, Internet of Things (IoT). The hardware for this is being provided by semiconductor silicon for a very long time. However, the demand is moving towards smaller size and better performance. Silicon material has reached its limitations in terms of dimension scaling and performance enhancement. A quest for new material has led to Gallium Nitride (GaN) which has the potential to provide enhanced properties like higher operational temperature, smaller dimensions, faster operation and efficient performance. Metal contact on the semiconductor is essential as these contacts provide the external connection. The contact characteristic of the metal-semiconductor interface is evaluated by contact resistance. It is expected that contact has linear IV characteristics (ohmic contact) and low contact resistance to avoid perturbing the semiconductor performance in devices. There are metals which can provide ohmic contacts for n-GaN but they offer low contact resistance only on annealing. These contact characteristics are studied by simulating the metal-semiconductor interface by replicating the thermionic and tunneling effects at the junction by physics-based device modeling. It is essential to reduce the contact resistivity for better interface properties which can be provided by a heavily doped (n⁺⁺) layer under the metal layer. The effect of various doping and thickness of n⁺⁺ layer is presented in this research work. Devices were grown based on simulation results and the extent of reduction in contact resistivity due to the n⁺⁺ layer is documented in this research. This reduction in contact resistivity can aid in a significant reduction in power dissipation in the devices which could lead to efficient device operation.

Cette thèse s’intéresse à une technique de caractérisation particulièrement bien adaptée à l’étude de couches diélectriques ultra-minces sur semiconducteurs. La génération de seconde harmonique (SHG) est une méthode très prometteuse, basée sur l’optique non-linéaire. Un laser est focalisé sur l'échantillon à caractériser et le signal à deux fois la fréquence fondamentale est mesuré. Pour les matériaux centrosymétriques comme c-Si, SiO2 et Al2O3, le signal SHG est dû aux défauts et au champ électrique Edc d’interface (induit par les charges préexistantes Qox et/ou piégées au niveau des pièges d’interface Dit). La SHG donne ainsi accès à la qualité des interfaces entre diélectriques/semiconducteurs. Néanmoins, le signal SHG dépend aussi des phénomènes de propagation optique dans les structures multicouches. Pour cette raison, nous avons développé un programme de simulation qui prend en compte les phénomènes optiques et les champs électriques statiques aux interfaces. Nous avons utilisé la SHG pour analyser la qualité de passivation de structures Al2O3/Si préparées avec des procédés différents et nous avons montré une corrélation entre SHG et mesure de durée de vie des porteurs de charges. Les valeurs de Qox et Dit ont été extraites par des mesures de capacité-tension et elles ont permis de calculer le champ Edc. La simulation optique, avec les valeurs extraites de Edc a permis de reproduire les données expérimentales de SHG dans ces structures. La SHG a été utilisée également pour la caractérisation des substrats Silicium-sur-Isolant (SOI). Pour les structures SOI épaisses, la simulation et les résultats expérimentaux ont montré que la réponse SHG est dominée par les interférences optiques (faible impact de Edc). Pour les structures SOI ultraminces, les interfaces sont couplées électriquement et des valeurs de Edc sont nécessaires pour reproduire les données expérimentales par simulation. Cela implique que pour les SOI ultraminces, la SHG pourrait donner accès aux champs électriques au niveau des interfaces d’une manière non-destructive. / This PhD work was developed in the context of research for novel characterization methods for ultra-thin dielectric films on semiconductors and their interfacial quality. Second harmonic generation (SHG) is a very promising non-invasive technique based on nonlinear optics. A laser emitting at the fundamental frequency is incident upon the sample which responds through its 2nd order polarization, generating a signal at twice the fundamental frequency. For centrosymmetric materials such as c-Si, amorphous SiO2 or Al2O3, the SHG signal is mainly due to the defects and to the static electric field Edc present at the interface (due to pre-existing charges Qox and/or photo-injected charge trapping/detrapping at interface traps Dit). Thus, SHG measurement gives access to the quality of dielectric/semiconductor interfaces. Nevertheless, the SHG signal is also dependent on multilayer optical propagation phenomena. For this reason, we have developed a simulation program which accounts for the optical phenomena and the static electric fields at the interfaces. We have used SHG to monitor the passivation quality of Al2O3/Si structures prepared with different processes and showed a correlation between SHG and minority carrier lifetime measurements. Qox and Dit were extracted from capacitance-voltage measurements and helped calculating the Edc values. The optical simulation, fed with known Edc values reproduced the experimental SHG data in these structures. The SHG was also used for Silicon-on-Insulator (SOI) substrates characterization. In thick SOI structures, both simulations and experimental results show that the SHG response is mainly given by optical interferences (Edc has no impact). In ultrathin SOI, the interfaces are electrically coupled and Edc is needed as input in the simulation in order to reproduce the experimental SHG data. This implies that in ultrathin SOI, SHG can access the interface electric fields in a non-destructive way.

Today we face the formidable challenge of meeting the fuel needs of a growing population while minimizing the adverse impacts on our environment. Thus, we search for technologies that can provide us with renewable fuels while mitigating the emission of global pollutants. To this end, use of non-thermal plasma processes can offer novel methods for efficiently and effectively converting carbon dioxide and water vapor into synthesis gas for the production of renewable fuels. Particularly, non-thermal plasma technologies offer distinct advantages over conventional methods including lower operating temperatures, reduced need for catalysts and potentially lower manufacturing and operation costs. The non-thermal plasma reactors have been studied for ozone generation, material synthesis, decontamination, thruster for microsatellites, and biomedical applications. This dissertation focuses on producing synthesis gas using a non-thermal, microhollow cathode discharge (MHCD) plasma reactor. The prototype MHCD reactor consisted of a mica plate as a dielectric layer that was in between two aluminum electrodes with a through hole. First, electrical characterization of the reactor was performed in the self-pulsing regime, and the reactor was modeled with an equivalent circuit which consisted of a constant capacitance and a variable, negative differential resistance. The values of the resistor and capacitors were recovered from experimental data, and the introduced circuit model was validated with independent experiments. Experimental data showed that increasing the applied voltage increased the current, self-pulsing frequency and average power consumption of the reactor, while it decreased the peak voltage. Subsequently, carbon dioxide and water vapor balanced with argon as the carrier gas were fed through the hole, and parametric experiments were conducted to investigate the effects of applied voltage (from 2.5 to 4.5 kV), flow rate (from 10 to 800 mL/min), CO₂ mole fraction in influent (from 9.95% to 99.5%), dielectric thickness (from 150 to 450 [mu]m) and discharge hole diameter (from 200 to 515 [mu]m) on the composition of the products, electrical-to-chemical energy conversion efficiency, and CO₂-to-CO conversion yield. Within the investigated parameter ranges, the maximum H2/CO ratio was about 0.14 when H2O and CO₂ were dissociated in different reactors. Additionally, at an applied voltage of 4.5 kV, the maximum yields were about 28.4% for H2 at a residence time of 128 [mu]s and 17.3% for CO at a residence time of 354 [mu]s. Increasing residence time increased the conversion yield, but decreased the energy conversion efficiency. The maximum energy conversion efficiency of about 18.5% was achieved for 99.5% pure CO₂ at a residence time of 6 [mu]s and an applied voltage of 4.5 kV. At the same applied voltage, the maximum efficiency was about 14.8% for saturated CO₂ at a residence time of 12.8 [mu]s. The future work should focus on optimizing the conversion yield and efficiency as well as analyzing the temporal and spatial changes in the gas composition in the plasma reactor. / text