A importância da pesquisa em eletrônica orgânica, se comparada à microeletrônica convencional baseada principalmente em silício, surge pela presença de inúmeros semicondutores e técnicas de deposição de baixo custo e em grande superfície. Os Transistores de Filmes Finos Orgânicos (OTFTs, do inglês Organic Thin-Film Transistors) são a unidade fundamental em circuitos eletrônicos e, geralmente, apresentam a estrutura de um transistor de efeito de campo. Podem ser fabricados sobre substratos plásticos e oferecem grande número de aplicações como: mostradores, etiquetas de identificação por rádio frequência e eletrônica têxtil. Além disso, há demanda por componentes eletrônicos portáteis e baratos, principalmente como sensores em diagnósticos médicos e veterinários in-situ. A geometria de OTFT mais utilizada em sensores na atualidade é a bottom gate sobre substratos de silício altamente dopado e com óxido de porta inorgânico. Polímeros como poli(3-hexiltiofeno) (P3HT) vêm sendo amplamente utilizados pela comunidade científica, atestando o potencial comercial deste semicondutor em sensores. Neste contexto, esta tese apresenta o desenvolvimento de transistores à base de P3HT como sensores na detecção de analitos em fase vapor. O estudo é composto por uma etapa inicial de caracterização da mobilidade dos portadores de carga por técnicas de transiente de corrente, seguida pela otimização do desempenho de parâmetros elétricos do transistor através de alterações no processamento dos filmes dielétrico e semicondutor. Enfim, conclui-se a investigação através do entendimento dos fatores ligados à degradação do OTFT após exposição à atmosfera e sob estresse elétrico, além do detalhamento da sensibilidade e especificidade do sensor. Sensores de P3HT oferecem enorme potencial de detecção de amônia, cetonas e compostos organoclorados. Outros semicondutores poliméricos são provavelmente necessários para maior especificidade em relação a vapor dágua e álcoois. / Research on organic electronics, compared to conventional silicon-based microelectronics, is necessary as it offers plenty of semiconductors and low-cost deposition techniques that can be performed over wide surfaces. Organic Thin-Film Transistors (OTFTs) are the fundamental unity in electronic circuits and, usually, display the metal insulator semiconductor field-effect transistor (MISFET) structure. OTFTs can be processed over cheap plastic substrates and integrate a high number of applications as: flexible displays, radio frequency identification tags, textile electronics and sensors (e.g. chemical and biological compounds). Nowadays, consumers demand portable and low-cost electronic devices, mainly as sensors for in-situ medical and veterinarian diagnosis. The most widely used OTFT structure in sensing is the bottom-gate/bottom-contact FET over highly-doped silicon substrates and inorganic dielectrics. Polymers as poly(3-hexylthiophene) (P3HT) have found increasing acceptance by the scientific community, attesting their potential as semiconductors for commercial applications. In this context, the thesis lies in the development of organic transistors based in P3HT polymer for the detection of vapor-phase compounds. This study begins with transistor performance optimization through changes in dielectric and semiconductor processing. Thin-film thickness and P3HT cast solution drying time are the main studied parameters. It involves also the understanding of device performance degradation when exposed to atmosphere and under bias stress, before finally mapping sensitivity and specificity against gaseous analytes. P3HT-based sensors are potentially interesting for ammonia, ketones and organochlorides detection. Other polymeric semiconductors may be necessary to increase specificity against water steam and alcohol analytes.

A importância da pesquisa em eletrônica orgânica, se comparada à microeletrônica convencional baseada principalmente em silício, surge pela presença de inúmeros semicondutores e técnicas de deposição de baixo custo e em grande superfície. Os Transistores de Filmes Finos Orgânicos (OTFTs, do inglês Organic Thin-Film Transistors) são a unidade fundamental em circuitos eletrônicos e, geralmente, apresentam a estrutura de um transistor de efeito de campo. Podem ser fabricados sobre substratos plásticos e oferecem grande número de aplicações como: mostradores, etiquetas de identificação por rádio frequência e eletrônica têxtil. Além disso, há demanda por componentes eletrônicos portáteis e baratos, principalmente como sensores em diagnósticos médicos e veterinários in-situ. A geometria de OTFT mais utilizada em sensores na atualidade é a bottom gate sobre substratos de silício altamente dopado e com óxido de porta inorgânico. Polímeros como poli(3-hexiltiofeno) (P3HT) vêm sendo amplamente utilizados pela comunidade científica, atestando o potencial comercial deste semicondutor em sensores. Neste contexto, esta tese apresenta o desenvolvimento de transistores à base de P3HT como sensores na detecção de analitos em fase vapor. O estudo é composto por uma etapa inicial de caracterização da mobilidade dos portadores de carga por técnicas de transiente de corrente, seguida pela otimização do desempenho de parâmetros elétricos do transistor através de alterações no processamento dos filmes dielétrico e semicondutor. Enfim, conclui-se a investigação através do entendimento dos fatores ligados à degradação do OTFT após exposição à atmosfera e sob estresse elétrico, além do detalhamento da sensibilidade e especificidade do sensor. Sensores de P3HT oferecem enorme potencial de detecção de amônia, cetonas e compostos organoclorados. Outros semicondutores poliméricos são provavelmente necessários para maior especificidade em relação a vapor dágua e álcoois. / Research on organic electronics, compared to conventional silicon-based microelectronics, is necessary as it offers plenty of semiconductors and low-cost deposition techniques that can be performed over wide surfaces. Organic Thin-Film Transistors (OTFTs) are the fundamental unity in electronic circuits and, usually, display the metal insulator semiconductor field-effect transistor (MISFET) structure. OTFTs can be processed over cheap plastic substrates and integrate a high number of applications as: flexible displays, radio frequency identification tags, textile electronics and sensors (e.g. chemical and biological compounds). Nowadays, consumers demand portable and low-cost electronic devices, mainly as sensors for in-situ medical and veterinarian diagnosis. The most widely used OTFT structure in sensing is the bottom-gate/bottom-contact FET over highly-doped silicon substrates and inorganic dielectrics. Polymers as poly(3-hexylthiophene) (P3HT) have found increasing acceptance by the scientific community, attesting their potential as semiconductors for commercial applications. In this context, the thesis lies in the development of organic transistors based in P3HT polymer for the detection of vapor-phase compounds. This study begins with transistor performance optimization through changes in dielectric and semiconductor processing. Thin-film thickness and P3HT cast solution drying time are the main studied parameters. It involves also the understanding of device performance degradation when exposed to atmosphere and under bias stress, before finally mapping sensitivity and specificity against gaseous analytes. P3HT-based sensors are potentially interesting for ammonia, ketones and organochlorides detection. Other polymeric semiconductors may be necessary to increase specificity against water steam and alcohol analytes.

In this dissertation, the electrical characteristics of generally used hydrogenated amorphous silicon (a-Si:H) TFTs in LCD and newly risen amorphous indium-gallium-zinc oxide (a-IGZO) TFTs were studied. For modern mobile display and large-size flat panel display application, the traditional thin-film transistor-liquid crystal display (TFT-LCD) technology confronts with a lot of challenges and problems. In general, flexible displays must exhibit some bending ability; however, bending applies mechanical strain to electronic circuits and affects device characteristics. Therefore, the electrical characteristics of a-Si:H TFTs fabricated on stainless steel foil substrates with uniaxial bending were investigated at different temperatures. Experimental results showed that the on-state current and threshold voltage degraded under outward bending. This is because outward bending will induce the increase of band tail states, affecting the transport mechanism at different temperatures. In addition, for practical operation, the electrical characteristics of a-Si:H TFTs under flat and bending situations after AC/DC stress at different temperatures were studied. It was found that high temperature and mechanical bending played important roles under AC stress. The dependence between the accumulated sum of bias rising and falling time and the threshold voltage shifts under AC stress was also observed. Because a-Si:H is a photosensitive material, the high intensity backlight illumination will degrade the performance of a-Si:H TFTs. Thus, the photo-leakage current of a-Si:H TFTs under illumination was investigated at different temperatures. Experimental results showed that a-Si:H TFTs exhibited a pool performance at lower temperatures. The indirect recombination rate and the parasitic resistance (Rp) are responsible for the different photo-leakage-current trends of a-Si:H TFTs under varied temperature operations. To investigate the photo-leakage current, the a-Si:H TFTs were exposed to ultraviolet (UV) light irradiation. It was found that the photo current of a-Si:H TFTs was reduced after UV light irradiation. The detail mechanisms on reducing/increasing photo-leakage current by UV light irradiation were discussed. Recently, the oxide-based semiconductor TFT, especially a-IGZO TFT, is considered as one of promising candidates for active matrix flat-panel display. However, the a-IGZO TFT exists significant electrical instability issue and manufacturing problems. As a consequence, we investigated the effect of hydrogen incorporation on a-IGZO TFTs to reduce interface states between active layer and insulator. Experimental results showed that the electrical characteristics of hydrogen-incorporated a-IGZO TFTs were improved. The threshold voltage shift (£GVth) in hysteresis loop is suppressed from 4 V to 2 V due to the hydrogen-induced passivation of the interface trap states. Finally, we reported the effect of ambient environment on a-IGZO TFT instability. As a-IGZO TFTs were stored in atmosphere environment for 40 days, the transfer characteristics accompanying strange hump were observed during bias-stress. The hump phenomenon is attributed to the absorption of H2O molecule. Additionally, the sufficient electric field is also necessary to cause this anomalous transfer characteristic.

In this dissertation, we investigates the electrical stress induced degradation in low-temperature polycrystalline-silicon thin film transistors (LTPS TFTs) applied for system-on-panel (SOP), including the electrical degradations of device for switch operation in active matrix flat-panel displays, driving circuit and nonvolatile memory. Finally, we also present the reliability of LTPS TFTs applied for flexible displays. In first part, electrical degradation of conventional and pattered metal-shielding LTPS TFTs under darkened and illuminated dynamic AC stresses are investigated. Experimental results reveal that competitive mechanisms are generated in conventional LTPS TFTs during illuminated stress, namely, carrier increase and electric field weakening. This phenomenon is verified by stressing the patterned source/drain open metal-shielding LTPS TFTs, which determines that the electric field weakening dominates; conversely, the carrier increase is dominated the electrical degradation in channel open metal-shielding device under illuminated stress. In addition, an improvement in anomalous on-current and subthreshold swing (S.S.) in n-channel LTPS TFTs after positive gate bias stress are studied. These improved electric properties are due to the hole trapping at SiO2 above the lightly doped drain regions, which causes a strong electric field at the gate corners. The effect of the hole trapping is to reduce the effective channel length and the S.S.. Besides, the stress-related electric field was also simulated by TCAD software to verify the mechanism above. Secondly, a mechanism of anomalous capacitance in p-channel LTPS TFTs was investigated. In general, the effective capacitance of the LTPS TFTs was only dependent with the overlap area between gate and source/drain under the off-state. However, the experimental results reveal that the off-state capacitance was increased with decreasing measurement frequency and/or with increasing measurement temperature. Besides, by fitting the curve of drain current versus electric field under off-state region, it was verified that the TAGIDL is consisted of the Pool-Frenkel emission and Thermal-Field emission. In addition, the charge density calculated from the Cch-Vg measurement also the same dependence with electric field. This result demonstrates that the anomalous capacitance is mainly due to the trap-assisted-gate-induced-drain-leakage (TAGIDL). In order to suppress the anomalous capacitance, a band-to-band hot electron (BTBHE) stress was utilized to reduce the vertical electric field between the gate and the drain. In third part, in order to realize the reliability in p-channel TFTs under illuminated environment operation, the degradation of negative bias temperature instability (NBTI) with illumination effect is investigated. The generations of interface state density (Nit) are identical under various illuminated intensity DC NBTI stresses. Nevertheless, the degradation of the grain boundary trap (Ntrap) under illumination was more significant than for the darkened environment, with degradation increasing as illumination intensity increases. This phenomenon is mainly caused by the extra number of holes generated during the illuminated NBTI stress. The increased Ntrap degradation leads to an increase in the darkened environment leakage current. This indicates that more traps are generated in the drain junction region that from carrier tunneling via the trap, resulting in leakage current. Conversely, an increase of Ntrap degradation results in a decrease in the photoleakage current. This indicates that the number of recombination centers increases in poly-Si bulk, affecting photosensitivity in LTPS TFTs. Besides, the transient effect assisted NBTI degradation in p-channel LTPS TFTs under dynamic stress is also presented, in which the degradation of the Ntrap becomes more significant as rise time decreases to 1 £gs. Because the surface inversion layer cannot form during the short rise time, transient bulk voltage will cause excess holes to diffuse into the poly-Si bulk. Therefore, the significant Ntrap increase is assisted by this transient effect. Fourthly, we study the electric properties of n- and p-channel LTPS TFTs under the mechanical tensile strain. The improved on-current for tensile strained n-channel TFTs is originated form an increase in energy difference between 2- and 4-fold valleys, reducing the inter-valley scattering and further improving the carrier mobility. On the contrary, the hole mobility decreases in p-channel, suggesting the split between the light hole and heavy hole energy bands and an increase in hole population on the heavy hole energy band of poly-Si when the uniaxial tensile strain is parallel to the channel direction. In addition, the Nit and Ntrap degradations induced by NBTI for tensile strained LTPS TFTs are more pronounced than in the unstrained. Extracted density-of-states (DOS) and conduction activation energy (EA) both show increases due to the strained Si-Si bonds, which implies that strained Si-Si bonds are able to react with dissociated H during the NBTI stress. Therefore, the NBTI degradation is more significant after tensile strain than in an unstrained condition. Finally, the SONOS-TFT applied to nonvolatile memory is prepared and studied. In the gate disturb stress, a parasitic capacitance and resistance in off-state region are identified as electrons trapped in the gate-insulator (GI) near the defined gate region. Meanwhile, these trapping electrons induced depletions in source/drain also degraded the I-V characteristic when the gate bias is larger than the threshold voltage. However, these degradations slightly recover when the trapped electrons are removed after negative bias stress. The electric field in the undefined gate region is also verified by TCAD simulation software.

Amorphous oxide semiconductors (AOSs) are of great current interest for thin-film transistor (TFT) channel layer applications. In particular, indium gallium zinc oxide (IGZO) is under intense development for commercial applications because of its demonstrated high performance at low processing temperatures. The objective of the research presented in this thesis is to provide detailed assessments of device stability, temperature dependence, and related phenomena for IGZO-based TFTs processed at temperatures between 200 °C and 300 °C. TFTs tested exhibit an almost rigid shift in log₁₀(I[subscript D]) – V[subscript GS] transfer curves in which the turn-on voltage, V[subscript ON], moves to a more positive gate voltage with increasing stress time during constant-voltage bias-stress testing of IGZO TFTs. TFT stability is improved as the post-deposition annealing temperature increases over the temperature range of 200 – 300 ºC. The turn-on voltage shift induced by constant-voltage bias-stressing is at least partially reversible; V[subscript ON] tends to recover towards its initial value of V[subscript ON] if the TFT is left unbiased in the dark for a prolonged period of time and better recovery is observed for a longer recovery period. V[subscript ON] for a TFT can be set equal to zero after bias-stress testing if the TFT electrodes are grounded and the TFT is maintained in the dark for a prolonged period of time. Attempts to accelerate the recovery process by application of a negative gate bias at elevated temperature (i.e., 100 ºC) were unsuccessful, resulting in severely degraded subthreshold swing. An almost rigid log₁₀(I[subscript D]) – V[subscript GS] transfer curve shift to a lower (more negative) V[subscript ON] with increasing temperature is observed in the range of –50 °C to +50 °C, except for a TFT with an initial V[subscript ON] equal to zero, in which case the log₁₀(ID) – V[subscript GS] transfer curve is temperature-independent. A more detailed temperature-dependence assessment, however, indicates that the log₁₀(I[subscript D]) – V[subscript GS] transfer curve shift is not exactly rigid since the mobility is found to increase slightly with increasing temperature. A noticeable anomaly is observed in certain log₁₀(I[subscript D]) – VGS transfer curves, especially when obtained at elevated temperature (e.g., 30 and 50 ºC), in which I[subscript D] decreases precipitously near zero volts in the positive gate voltage sweep. This anomaly is attributed to a gate-voltage-step-involved detrapping and subsequent retrapping of electrons in the accumulation channel and/or channel/gate insulator interface. In fact, all IGZO TFT stability and temperature-dependence trends are attributed to channel interface and/or channel bulk trapping/detrapping. / Graduation date: 2009

Ce travail de thèse a pour sujet l'étude de transistors en couches minces (TFTs) à base d'Indium Gallium Zinc Oxide (IGZO). Nous nous sommes intéressés au procédé de réalisation des TFTs, et à la caractérisation des couches d'IGZO afin d'obtenir les caractéristiques au plus près de l'état de l'art. Nous avons également étudié le processus de passivation, paramètre identifié comme critique pour stabiliser les TFT et atteindre de bonnes performances.Dans un premier temps, nous avons mis au point les conditions du dépôt de la couche active, et de la réalisation des TFTs. Les analyses morphologiques et structurales ont montré l'absence de cristallites de couche, ainsi qu'une surface peu rugueuse. La densité des porteurs de charge de la couche IGZO diminue lorsque le débit d'oxygène, variable durant son dépôt, augmente. La couche active déposée à 200°C et à 4 sccm d'oxygène présente une densité de porteurs de charge de l'ordre de 1E17 cm-3, valeur adaptée au fonctionnement des TFTs.Dans un second temps, nous avons évalué l'influence d'un recuit sur les caractéristiques des TFTs. Nous avons mis en évidence que le recuit sous oxygène conduit à des TFTs opérationnels, tandis que celui sous azote ou en absence de recuit induisent une suppression de l'effet de champ. Nos études ont également montré qu'une température de recuit de 300°C est favorable aux performances des transistors. Les premiers TFTs présentent des mobilités entre 5 et 15 cm2/Vs, des rapports ION/IOFF de l'ordre de 1E7, et des pentes sous le seuil d'environ 0.3 V/décade. Les tensions de seuil (VT), quant à elles, demeurent faibles donc restent à améliorer.Pour finir, nous avons étudié l'impact d'une couche de passivation sur les TFTs, en raison de la dégradation des caractéristiques de ces derniers dans l'atmosphère ambiante. Les couches de SiO2 (déposée par PECVD) et d'Al2O3 (déposée par ALD) ont été étudiées. Nous avons mis en évidence que ces passivations peuvent dégrader les TFTs au lieu de les protéger. VT tend à se décaler dans le sens négatif lorsque l'on augmente l'épaisseur de la couche d'Al2O3 ou le débit de Silane durant le dépôt du SiO2. Une des raisons principales de ce phénomène est la présence de l'hydrogène généré lors de la passivation. Nous avons évalué les solutions pour éviter la dégradation lors du dépôt et assurer une bonne protection du TFT. / This thesis aims to study thin-film transistors (TFTs) based on Indium Gallium Zinc Oxide (IGZO) in the framework of applications in active matrix flat panel LCD and OLED display. The TFT fabrication process and the characterization of IGZO deposited film are two key studies in this thesis in order to obtain TFT electrical characteristics close to the state-of-the-art. We have also studied the passivation which is identified as crucial for stabilizing the TFT and achieving good performance.The deposition of the active layer and the fabrication process of TFT are firstly studied. Smooth surface of deposited films is demonstrated by AFM and the absence of the crystalline peak of the material is shown by X-ray diffraction. The density of charge carriers decreases with the increase of oxygen flow rate. The active layer deposited at 200°C and at 4 sccm of oxygen flow has a carrier density in the order of 1E17 cm-3 which is suitable for TFT operation. This condition is chosen to fabricate IGZO-based TFT in this thesis.In a second step, we have evaluated the influence of annealing condition on TFTs' electrical characteristics. Annealing in oxygen leads to operational TFTs while doing the same under nitrogen or the absence of annealing suppresses field-effect behavior. Our studies have also shown that annealing temperature of 300°C is suitable to obtain good performance of the transistors. From this study, we have obtained TFTs with high mobility (between 5 and 15 cm2/Vs), high ION/IOFF ratios (about 1E7), and reasonable sub threshold slope (about 0.3 V/decade). The threshold voltage (VT) however remains low (between -4 and -2 V) and needs to be improved.Finally, we have investigated the impact of a passivation layer on the performance of IGZO TFTs. SiO2 film (deposited by PECVD) and Al2O3 film (formed by ALD) were studied. We have observed that such passivation can degrade the TFTs rather than protecting them. Concretely, VT shifts in negative direction when increasing the Al2O3 layer thickness or the silane flow during SiO2 deposition. Principal reason for this shift is the presence of hydrogen which is generated during passivation. We have evaluated some solutions to reduce the degradation during deposition and ensure a good protection of the TFTs.

Submitted by João Paulo Braga (jpbraga_ibilce@hotmail.com) on 2018-05-10T12:08:05Z No. of bitstreams: 1 dissertação.corrigida . Braga.JP...pdf: 4842769 bytes, checksum: 92b7f70c78131d4df05a4710783f132c (MD5) / Approved for entry into archive by Elza Mitiko Sato null (elzasato@ibilce.unesp.br) on 2018-05-10T17:11:35Z (GMT) No. of bitstreams: 1 braga_jp_me_sjrp_int.pdf: 4842769 bytes, checksum: 92b7f70c78131d4df05a4710783f132c (MD5) / Made available in DSpace on 2018-05-10T17:11:35Z (GMT). No. of bitstreams: 1 braga_jp_me_sjrp_int.pdf: 4842769 bytes, checksum: 92b7f70c78131d4df05a4710783f132c (MD5) Previous issue date: 2018-04-04 / Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq) / Neste trabalho, foram desenvolvidos e caracterizados transistores de filme fino (TFTs) de óxidos metálicos processados por solução, tendo como camada ativa filmes de óxido de zinco (ZnO), de óxido de zinco dopado com alumínio (AZO) e de óxido de índio e zinco (IZO). Os dispositivos foram construídos sobre substratos de silício dopado tipo p revestido com uma camada isolante de óxido de silício (Si/SiO2), em estruturas do tipo bottom-gate/top-contact, utilizando dois métodos distintos para a deposição da camada ativa: spray-pirólise e spin coating. Os transistores apresentaram excelentes propriedades elétricas, em especial os dispositivos à base de ZnO depositados via spray-pirólise. Esses dispositivos apresentaram valores de mobilidade dos portadores de carga (elétrons), superiores a 5 cm2V-1s-1 e da razão entre a corrente na acumulação e na depleção (IOn/IOff) superiores a 106, o que representa um desempenho bastante competitivo quando comparados com a literatura atual. A influência da exposição dos dispositivos ao oxigênio atmosférico nas propriedades elétricas dos transistores foi estudada através do monitoramento (pelo período de vários dias) do desempenho dos transistores quando caracterizados em atmosfera inerte (N2) ou no ar. Adicionalmente, os dispositivos apresentaram um proeminente efeito de fotoresposta persistente após a exposição à radiação ultravioleta na região do UVA em níveis de intensidade relativamente baixos (abaixo de 10-3 W.m-2), o que sugere uma potencial aplicação em sensores ou dosímetros de radiação UV. / In the present work, thin-film transistors (TFTs) based on solution-processed metal-oxides were developed and characterized, with the active layer comprising zinc oxide (ZnO), aluminum-doped zinc oxide (AZO) and indium zinc oxide (IZO). The devices were built on p-type doped silicon substrates with a thermally grown thin-layer of silicon dioxide (Si/SiO2), in a bottom-gate/top-contact structure, using two different active layer deposition methods: spray-pyrolysis and spin coating. The transistors presented excellent electrical properties, especially the ZnObased devices deposited by spray-pyrolysis, with charge carrier mobility superior to 5 cm2V-1s -1 and ratio between the accumulation current and the depletion current (Ion/Ioff) greater than 106 , which represents a very competitive performance compared to values from the current literature. The influence of the exposure to atmospheric oxygen on the transistor electrical properties was studied by monitoring (for several days) the TFT performance when characterized in inert atmosphere (N2) or in air. Additionally, the devices presented a prominent persistent photoresponse effect after the exposure to ultraviolet radiation in the UVA range at relatively low intensities (below 10-3 Wm-2), suggesting a potential application as UV-radiation sensors or dosimeters. / 134107/2016-0

Abstract This thesis presents a novel method for fabricating quantum dot light-emitting devices (QDLEDs) based on colloidal inorganic light-emitting nanoparticles incorporated into an organic semiconductor matrix. CdSe core/ZnS shell nanoparticles were inkjet-printed in air and sandwiched between organic hole and electron transport layers to produce efficient photon-emissive media. The light-emitting devices fabricated here were tested as individual devices and integrated into a display setting, thus endorsing the capability of this method as a manufacturing approach for full-colour high-definition displays. By choosing inkjet printing as a deposition method for quantum dots, several problems currently inevitable with alternative methods are addressed. First, inkjet printing promises simple patterning due to its drop-on-demand concept, thus overruling a need for complicated and laborious patterning methods. Secondly, manufacturing costs can be reduced significantly by introducing this prudent fabrication step for very expensive nanoparticles. Since there are no prior demonstrations of inkjet printing of electroluminescent quantum dot devices in the literature, this work dives into the basics of inkjet printing of low-viscosity, relatively highly volatile quantum dot inks: piezo driver requirements, jetting parameters, fluid dynamics in the cartridge and on the surface, nanoparticle assembly in a wet droplet and packing of dots on the surface are main concerns in the experimental part. Device performance is likewise discussed and plays an important role in this thesis. Several compositional QDLED structures are described. In addition, different pixel geometries are discussed. The last part of this dissertation deals with the principles of QDLED displays and their basic components: RGB pixels and organic thin-film transistor (OTFT) drivers. Work related to transistors is intertwined with QDLED work; ideas for surface treatments that enhance nanoparticle packing are carried over from self-assembled monolayer (SAM) studies in the OTFT field. Moreover, all the work done in this thesis project was consolidated by one method, atomic force microscopy (AFM), which is discussed throughout the entire thesis.

We have investigated the noncovalent interactions in carbohydrate-aromatic interactions which are pivotal to the recognition of carbohydrates in proteins. We have employed quantum mechanical methods to study carbohydrate-aromatic complexes. Due to the importance of dispersion contribution to the interaction energy, we mainly use density functional theory augmented with an empirical correction for the dispersion interactions (DFT-D). We have validated this method with a limited number of high level ab initio calculations. We have also analysed the vibrational and NMR chemical shift characteristics using the DFT-D method. We have mainly studied the complexes involving β-glucose with 3-methylindole and p-hydroxytoluene, which are analogues of tryptophan and tyrosine, respectively. We find that the contribution for interaction energy mainly comes from CH/π and OH/π interactions. We find that the interaction energy of complexes involving CH/π and OH/π interactions is reflected in the associated blue and red shifts of vibrational spectrum. We also find that the interactions involving 3-methylindole are somewhat greater than those for p-hydroxytoluene. The C-H blueshifts are also in parallel with the predicted NMR proton shift. We have also tested different density functionals including both standard density functionals and newly developed M0x functionals and MP2 method for studying carbohydrate-aromatic complexes. The DFT-D method and M06 functionals of the M0x family are found to perform better, while B3LYP and BLYP functionals perform poorly. We find that the inclusion of a dispersion term to BLYP is found to perform better. The dispersion energy dominates over the interaction energy of carbohydrate-aromatic complexes. From the DFT-D calculations, we found that the complexes would be unstable without the contribution from dispersive energy. We have also studied the importance of noncovalent interactions in functionalization of nanotubes by nucleic acid bases and aromatic amino acids by using semi-empirical methods with dispersion term such asPM3-D and PM3-D*. We find that the both semi-empirical schemes give reasonable interaction energies with respect to DFT-D interaction energies. We have also used PM3-D method to study the adsorption of organic pollutants on graphene sheet and on nanotubes. We found that the semi-empirical schemes, which are faster and cheaper, are suitable to study these larger molecules involving noncovalent interactions and can be used as an alternative to DFT-D method. We have also studied the importance of dispersion interaction and the effect of steric hindrance in aggregation of functionalized anthracenes and pentacenes. We have also employed molecular dynamics simulation methods to study the aggregation of anthracene molecules in toluene solution.

<div>In this work, we investigate the trade-off between scalability and reliability for next generation logic-transistors i.e. Gate-All-Around (GAA)-FET, Multi-Bridge-Channel (MBC)-FET. First, we analyze the electronic properties (i.e. bandgap and</div><div>quantum conductance) of ultra-thin silicon (Si) channel i.e. nano-wire and nano-sheet based on first principle simulation. In addition, we study the influence of interface</div><div>states (or dangling bonds) at Si-SiO₂ interface. Second, we investigate the impact of bandgap change and interface states on GAA-FETs and MBC-FETs characteristics by</div><div>employing Non-equilibrium Green's Function based device simulation. In addition to that, we calculate the activation energy of Si-H bond dissociation at Si-SiO₂ interface for different Si nano-wire/sheet thickness and different oxide electric-field. Utilizing these thickness dependent activation energies for corresponding oxide electric-field, in conjunction with reaction-diffusion model, we compute the characteristics shift and analyze the negative bias temperature instability in GAA-FET and MBC-FET. Based on our analysis, we estimate the operational voltage of these transistors for a life-time of 10 years and the ON current of the device at iso-OFF-current condition. For example, for channel length of 5 nm and thickness < 5 nm the safe operating voltage needs to be < 0.55V. Furthermore, our analysis suggests that the benefit of Si thickness scaling can potentially be suppressed for obtaining a desired life-time of GAA-FET and MBC-FET.</div>