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<p>This Thesis details the design, fabrication and characterization of organic semiconductor field effect transistors with silicon oxide-nitride-oxide-semiconductor (SONOS) gates for use in spiking analog neural circuits. The results are divided into two main sections. First, the SONOS structures, parallel plate capacitors and field effect transistors, were designed, fabricated and characterized. Second, these results are used to model spiking analog neural circuits. The modeling is achieved using PSPICE based software.</p> <p>The initial design work begins with an analysis of the basic SONOS structure. The existence of the ultrathin layers of the SONOS structure is confirmed with the use of Transmission Electron Microscopy (TEM) and Energy Dispersive Spectroscopy (EDS) scans of device stacks. Parallel plate capacitors were fabricated prior to complete transistors due to the significantly less processing required. The structure and behaviour of these capacitors is similar to that of the transistor gates which allows for the optimization of the structures prior to the fabrication of the transistors. These capacitors were fabricated using the semiconductor materials of; crystalline silicon, amorphous silicon, Zinc Oxide, copper phthalocyanine (CuPc) and tris 8-hydroxyquinolinato aluminium (AlQ3). These devices are then subjected to standard capacitance voltage (C-V) analysis. The results of this analysis demonstrate that the inclusion of SONOS structures in the capacitors (and transistors) result in a hysteresis which is the result of charge accumulation in the nitride layer of the SONOS structure. This effect can be utilized as an imbedded memory. Standard control devices were fabricated and analysed and no significant hysteresis effect was observed. The hysteresis effect is only observed after the SONOS devices are subject to high voltages (approximately 14 volts) which allows tunneling through a thin oxide layer into traps in the silicon nitride layer. This analysis was conducted to confirm that the SONOS structure causes the memory effect, not the existence of interface states that can be charged and discharged.</p> <p>The next step was to design and fabricate amorphous semiconductor field effect transistors with and without the SONOS structure. First FETs without the SONOS gates were fabricated using amorphous semiconductor materials; Zinc Oxide, CuPc and AlQ3 and then the devices were characterized. This initial step confirmed the functionality of these basic devices and the ability to fabricate working control samples. Next, SONOS gate TFTs were fabricated using CuPc as the semiconductor material. The characterization of these devices confirmed the ability to shift the transfer characteristics of the devices through a read and write mechanism similar to that used to shift the C-V characteristics of the parallel plate capacitors. Split gate FETs were also produced to examine the feasibility of individual transistors with multiple gates.</p> <p>The results of these characterizations were used to model spiking analog neural circuits. This modeling was carried out in four parts. First, representative transfer and output characteristics were used to replicate analog spiking neural circuits. This was carried out using standard PSPICE software with the modification of the discrete TFT device characteristics to represent the amorphous CuPc organic transistors. The results were found to be comparable to circuits using crystalline silicon transistors. Second, the SONOS structures were modeled closely matching the characterized results for charge and voltage shift. Third, a simple Hebbian learning circuit was designed and modeled, demonstrating the potential for imbedded memories. Lastly, split gate devices were modeled using the device characterizations.</p> / Doctor of Philosophy (PhD)

A theoretical model describing photophysics of π-conjugated aggregates, such as molecular crystals and polymer thin films, is developed. A Holstein-like Hamiltonian expressed with a multi-particle basis set is used to evaluate absorption and photoluminescence (PL) spectra of neutral excitons as well as charge modulation spectra (CMS) and transient absorption spectra (TAS) of positively charges hole-type polarons. The results are used to develop a better theoretical understanding of the organic electronics being studied and their photophysics, and also to probe the morphology of poly(3-hexylthiophene) (P3HT) thin films, which are used in photovoltaic devices. / Chemistry

Electronic applications have expanded to encompass a variety of materials. In particular, allotropes of carbon interest researchers for their electronic applications. Knowledge of carbon allotropes and their applications has expanded significantly since the discovery of C60 Buckminsterfullerene in 1985, the discovery of multi- and single-walled carbon nanotubes in the early 1990s, and the isolation of graphene in 2004. Single-walled carbon nanotubes (SWNTs) have the potential to bring next-generation electronic devices to fruition. Such devices could be flexible, conformable, and inexpensive. SWNT-based electronics are promising for chemical and biological sensing applications, for example, where high carrier mobilities are unnecessary, and material conformity and inexpensive processing are significant advantages. Considerable progress has been made in separating semiconducting SWNTs from metallic SWNTs, enabling SWNT incorporation into semiconducting electronic technologies. Selective sorting of semiconducting SWNTs using π-conjugated polymers is an effective and efficient technique to enrich large quantities of ultra-pure semiconducting SWNTs. Following semiconducting enrichment, SWNTs can be incorporated into electronic devices. This thesis focuses on the enrichment of semiconducting SWNTs via conjugated polymer extraction and incorporating the resulting polymer-SWNT dispersions into thin-film transistors (TFTs). Novel copolymers were investigated for their capacity to selectively sort and disperse large-diameter sc-SWNTs synthesized using the plasma torch technique. Absorption and Raman spectroscopy were employed to monitor the efficacy of the conjugated polymer extraction procedure. Following enrichment, the polymer-SWNT dispersions were incorporated into TFTs. The interaction between the conjugated polymer and the SWNT and the conjugated polymer and dielectric was an essential component of TFT optimization. Furthermore, the procedure of sorting and dispersing sc-SWNTs is investigated for its effect on TFT performance and was another component of TFT optimization. TFTs were electrically characterized in terms of carrier mobility, threshold voltage, hysteresis, and current on/off ratio. The film morphology of the SWNT TFTs was also investigated. Atomic force microscopy and Raman mapping were used to provide insight into the nanometre and micrometre scale film morphology, respectively.

A systematic study of the crystallization of terthiophene, chosen as a model compound, has been carried out using the thermal gradient technique. We have observed that nucleation and growth can be decoupled for organic semiconductors (OSC) crystallizing from the melt in a temperature gradient and that these conditions lead to the generation of highly textured thin films with uniaxial in-plane alignment. Furthermore, adequate gradient conditions allow the selective growth of a single polymorphic form of terthiophene. The last results obtained on terthiophene concern the orientation of the unit cell with the reciprocal vector c* normal to the substrate and the alignment of the [100] and [-100] directions parallel to the gradient direction. It is hypothesized that the geometry of the system and the temperature profile induce a preferential fast growth direction perpendicular to the gradient direction.<p>In order to validate these results, we embarked on an exploratory study of the crystallization of a set of organic semiconductors, carefully selected based on rational arguments, to evaluate the potential of the thermal gradient process as well as the required parameters for an OSC to perform adequately in this treatment. As in the case of terthiophene, nucleation and growth can be decoupled for the other organic semiconductors depending on their rate of growth. Furthermore, we have been able to reproduce on another polymorphic compound the selective growth of a single polymorphic form by applying adequate gradient conditions. We have also observed that compounds tend to orient preferentially along one of their major morphological planes parallel to the substrate, indicating a heterogeneous nucleation mechanism. A careful comparison between the different samples allowed us to confirm and complete our growth mechanism proposition. Based on the undercooling, maximal growth rate, primary and secondary nucleation rates of the compound, geometry of the system and adequate gradient parameters, a preferential alignment of the crystals along the thermal gradient direction can be achieved. Finally, we showed through this investigation and careful comparison that 2,7-didodecyl[1]benzothieno[3,2-b][1]benzothiophene possesses all the characteristics to be an excellent material candidate for the thermal gradient processing: low primary nucleation rate, moderate undercooling, high growth rate, platelet-like crystal growth morphology and liquid crystal phase allowing preorganization of the compound before crystallization and processing on single substrates without dewetting. Moreover, this compound is currently one of the best solution processable organic semiconductors.<p>We then investigated the directional crystallization of 2,7-dioctyl[1]benzothieno[3,2-b][1]benzothiophene directly from its liquid crystal phase as a function of thermal gradient parameters (magnitude of the gradient, sample velocity) and film thicknesses in thin film geometry (spin-coated films). Again, decoupling of the nucleation and growth has been observed for crystallization processed directly from the liquid crystal phase leading to the generation of highly textured films presenting uniaxial in-plane alignments of the crystallites. Moreover, secondary nucleation spots highlighted by POM in the alignment region give a clue to elucidate the alignment mechanism. The unit cell orients with the reciprocal vector c* normal to the substrate. Moreover, POM observation tends to indicate systematic thermal cracks orientations for higher rates of displacement (25 μm.s-1) as well as a reduction of the number of domains present in the sample, suggesting a preferential alignment of the crystallites at higher rates of displacement. All our results indicate that an optimum of the quality of the aligned film is reached for thermal gradient conditions of 120 °C - 90 °C - 25 μm.s-1. / Doctorat en Sciences de l'ingénieur / info:eu-repo/semantics/nonPublished

Printed and organic electronics have been intensely researched in the past few years, and their potential low-cost and sustainability benefits combined with their unique form properties makes them interesting from a product design perspective. However, there has been a lack of product design with printed and organic electronics, which has created a gap between research and market. The aim of this thesis is to find an application of printed and organic electronics in a previously unexplored application area. The thesis includes interviews and workshops with relevant actors, a SWOT analysis, and idea generation through brainstorming. It is found that printed and organic traceability tags (RFID/NFC) have the potential to facilitate circular business models in the fashion industry if they are developed to fulfil the identified requirements.  Three concepts of how traceability tags can facilitate rental fashion are developed. The main identified potential benefits for the rental companies are reduced logistics costs and the possibility of data collection. The potentially low cost of printed and organic traceability tags would also enable rental companies with smaller profit margins to implement a digital traceability solution which would help the survival of these companies and accelerate the shift towards circular fashion. These findings contribute with a new possible application of printed and organic electronics. In order to reach the identified benefits, more research on printed and organic traceability tags is needed, as well as a full product development process of the three concepts. To really know whether this and other identified applications of POE could be viable on the market there is a need for economic and performance analysis to determine whether their applications can be successful. Further the authors also see a need for life cycle analyses on all types of POE applications to determine their environmental impact.

This thesis focuses on understanding the chemistry involved in a variety of surface modification reactions, both on metal oxides and graphene. In this work, the rates of chemisorption of a prototypical phosphonic acid on ITO under several processing protocols are measured using XPS to determine the optimal procedure. UPS is used to track the dependence of the electronic structure of the system, specifically of the work function and position of the valence band maximum on coverage. Phosphonic acid monolayers with appropriate tail groups can also be used to initiate chemistry from surfaces, which has potential for building layers of organic-electronic devices, including organic solar cells and capacitors. The growth of non-conjugated polymers from BaTiO₃ nanoparticles using a facile ATRP technique is studied via solution-phase and solid-state techniques to determine its applicability to make matrix-free composites for hybrid dielectrics. In addition, the surface chemistry involved in Kumada Catalyst-Transfer to grow polythiophene derivatives from ITO is examined via XPS. Finally, the newly emerged alternative for replacement of ITO as transparent electrode, graphene, is n- and p-doped using redox-active, solution-processable metal-organics, which increased its conductivity and allowed the work function to be tuned over a range of 1.8 eV. The systems are characterized in a systematic study, and the results are promising for future applications of graphene.