This work is aimed at developing a high sensitivity salinity (conductivity) sensor for marine applications. The principle of sensing involves the use of parallel plate capacitors, which minimizes the proximity effects associated with inductive measurement techniques. The barrier properties of two different materials, AZ5214 and Honeywell's ACCUFLO T3027, were investigated for use as the insulation layer for the sensor. Impedance analysis performed on the two coatings using Agilent's 4924A Precision Impedance Analyzer served to prove that ACCUFLO was a better dielectric material for this application when compared to AZ5214.Two separate detection circuits have been proposed for the salinity sensor. In the Twin-T filter method, a variation in capacitance tends to shift the resonant frequency of a Twin-T oscillator, comprising the sensor. Simulations of the oscillator circuit were performed using Pspice. Experiments were performed on calibrated ocean water samples of 34.996 psu and a shift of 410 Hz/psu was obtained. To avoid the problems associated with the frequency drift in the oscillator, an alternate detection scheme is proposed which employs frequency-to-voltage converters. The sensitivity of this detection scheme was observed to be 10 mV/psu.

Dielectrics have been an integral part of the electron devices and will likely resume playing a significant role in the future of nanoelectronics. An important step in assessing graphene potential as an alternative channel material for future electron devices is to benchmark its transport characteristics when integrated with dielectrics. Using back-gated and dual gated graphene field-effect transistors with top high-k metal-oxide dielectric, we study the dielectric thickness dependence of the carrier mobility. We show the carrier mobility decreases after deposition of metal-oxide dielectrics by atomic layer deposition (ALD) thanks to the Coulomb scattering by charged point defects in the dielectric. We investigate a novel method for the ALD of metal-oxide dielectrics on graphene, using an ultrathin nucleation layer that enables the realization of graphene field-effect transistors with aggressively scaled gate dielectric thickness. We show the nucleation layer significantly affects the quality of the subsequently deposited dielectric. In addition, we study transport characteristics of double layer systems. We demonstrate heterostructures consisting of two rotationally aligned bilayer graphene with an ultra-thin hexagonal boron nitride dielectric in between fabricated using advanced layer-by-layer transfer as well as layer pickup techniques. We show that double bilayer graphene devices possess negative differential resistance and resonant tunneling in their interlayer current-voltage characteristics in a wide range of temperatures. We show the resonant tunneling occurs either when the charge neutrality points of the two bilayer graphene are energetically aligned or when the lower conduction sub-band of one layer is aligned with the upper conduction sub-band of the opposite layer. Finally, we study the Raman spectra and the magneto-transport characteristics of A-B stacked and rotationally misaligned bilayer graphene deposited by chemical-vapor-deposition (CVD) on Cu. We show that the quantum Hall states (QHSs) sequence of the CVD grown A-B stacked bilayer graphene is consistent with that of natural bilayer graphene, while the sequence of the QHSs in the CVD grown rotationally misaligned bilayer graphene is a superposition of monolayer graphene QHSs. From the magnetotransport measurements in rotationally misaligned CVD-grown bilayer we determine the layer densities and the interlayer capacitance. / text

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M. Tech. Chemical Engineering. / Aims of this study is to determine the relationship between the temperature of the coal coke (and other mixtures) and the measured microwave impedance in the waveguide feeding the applicator.

Step and Flash Imprint Lithography (S-FIL) is a high resolution, next-generation lithography technique that uses an ambient temperature and low pressure process to replicate high resolution images in a UV-curable liquid material. Application of the S-FIL process in conjunction with multi-level imprint templates and new imprint materials enables one S-FIL step to reproduce the same structures that require two photolithography steps, thereby greatly reducing the number of patterning steps required for the copper, dual damascene process used to fabricate interconnect wirings in modern integrated circuits. Two approaches were explored for the implementation of S-FIL in the dual damascene process: sacrificial imprint materials and imprintable dielectric materials. Sacrificial imprint materials function as a pattern recording medium during S-FIL and a three-dimensional etch mask during the dielectric substrate etch, enabling the simultaneous patterning of both the via and metal structures in the dielectric substrate. Development of sacrificial imprint materials and the associated imprint and etch processes are described. Application of S-FIL and the sacrificial imprint material in a commercial copper dual damascene process successfully produced functional copper interconnect structures, demonstrating the feasibility of integrating multi-level S-FIL in the copper dual damascene process. Imprintable dielectric materials are designed to combine the multi-level patterning capability of S-FIL with novel dielectric precursor materials, enabling the simultaneous deposition and patterning of the interlayer dielectric material. Several candidate imprintable dielectric materials were evaluated: sol-gel, polyhedral oligomeric silsesquioxane (POSS) epoxide, POSS acrylate, POSS azide, and POSS thiol. POSS thiol shows the most promise as functional imprintable dielectric material, although additional work in the POSS thiol formulation and viscous dispense process are needed to produce functional interconnect structures. Integration of S-FIL with imprintable dielectric materials would enable further streamlining of the dual damascene fabrication process. The fabrication of electronic devices on flexible substrates represents an opportunity for the development of macroelectronics such as flexible displays and large area devices. Traditional optical lithography encounters alignment and overlay limitations when applied on flexible substrates. A thermally activated, dual-tone photoresist system and its associated etch process were developed to enable the simultaneous patterning of two device layers on a flexible substrate. / text

BCxNy films were characterized as a potential pore sealing layer for low κ dielectrics. The changes in chemical bonding were studied as a function of growth temperature to aid in understanding the variation in electrical performance of these films. Thermal chemical vapor deposition of BCxNy using dimethylamine borane and ethylene were deposited on porous methylsilsesquioxane substrates at 335 °C and 1 Torr. BCxNy was able to seal the porous interface with a thickness of 3.9 nm for both blanket and patterned substrates. BCxNy films deposited over a temperature range of 300-400 °C with dimethylamine borane and either ethylene or ammonia coreactant gas were characterized. Films deposited with ethylene became more concentrated in B at the expense of C with increasing temperature. These films favored C-B intermixing over C-C and B-B bonding at higher temperature. H was detected in the form of B-H and C-H bonds. Films deposited with ammonia became concentrated in N at the expense of B, and favored B-N viii bonding at higher temperatures. H was found in the films as B-H, C-H, and N-H bonds. The amount of H in the films decreased with increasing growth temperature for both ethylene and ammonia coreacted films. The valence band offset of C-rich films increased from 0.17 ± 0.22 eV to 0.32 ± 0.22 eV when deposited at 300°C and 400 °C. For the Nrich films, the valence band offset shifted from 0.26 ± 0.28 at 300 °C to -0.15 ± 0.24 eV at the same deposition conditions. High temperature annealing from 400-800 °C in forming gas caused all BCxNy films to decrease in thickness up to 30%. At the same time, the index of refraction increased, and likely, the dielectric constant. X-ray photoelectron spectroscopy revealed little change in the constituent bonding, suggesting that volatile –H containing species were removed during the annealing process. / text

Η ευρεία χρήση των διηλεκτρικών υγρών για μόνωση σε υψηλές τάσεις και ψύξη εξοπλισμού ισχύος οφείλεται στην μεγάλη τους διηλεκτρική αντοχή και θερμική αγωγιμότητα, σε σχέση με τα αέρια μονωτικά υλικά. Η ικανότητα τους να προσαρμόζονται σε πολύπλοκες γεωμετρίες σημαίνει ότι συχνά είναι πιο πρακτικά σε σχέση με τα στερεά μονωτικά, ενώ ταυτόχρονα μπορούν να παρέχουν προστασία σε αυτά αν χρησιμοποιηθούν συνδυαστικά. Αυτή η εργασία εστιάζει στον σχηματισμό καναλιών ιονισμού, γνωστά ως electrical streamers. Αυτά είναι αγώγιμα κανάλια χαμηλής πυκνότητας που σχηματίζονται σε περιοχές του λαδιού που καταπονούνται από ηλεκτρικά πεδία της τάξης των 1x103 kV/cm, ή ισχυρότερα. Μόλις δημιουργηθεί ένα τέτοιο κανάλι, έχει την τάση να επιμηκύνεται, αυξάνοντας από το σημείο δημιουργίας του προς ένα γειωμένο σημείο. Η έκταση της ανάπτυξης του streamer εξαρτάται από την φύση της ηλεκτρικής διέγερσης που το προκάλεσε. Αν η διέγερση συνεχίζει να υφίσταται, μπορεί να έχει σαν αποτέλεσμα το κανάλι να γεφυρώσει το διάκενο μεταξύ του σημείου από το οποίο προέρχεται και του γειωμένου σημείου. Όταν συμβεί αυτό, έχουμε τον σχηματισμό ηλεκτρικού τόξου και άρα συμβαίνει ηλεκτρική εκκένωση. Επομένως, σε αυτήν την εργασία αναπτύσσεται ένα μοντέλο που βασίζεται σε αυτόν τον μηχανισμό, και περιλαμβάνει εξισώσεις για τρεις διαφορετικούς ελεύθερους φορείς φορτίου, οι οποίοι είναι τα θετικά ιόντα, τα αρνητικά ιόντα, και τα ηλεκτρόνια. Χρησιμοποιείται η διάταξη ακίδα-πλάκα, η οποία εισάγεται στο COMSOL Multiphysics, το οποίο είναι ένα πακέτο λογισμικού που χρησιμοποιεί την μέθοδο των πεπερασμένων στοιχείων. Δοκιμάζονται διαφορετικές κυματομορφές τάσης, και εξάγονται χρήσιμα συμπεράσματα για τα χαρακτηριστικά των streamer, όπως διαστάσεις, μορφή και ταχύτητα διάδοσης. / The widespread use of dielectric liquids for high voltage insulation and power apparatus cooling is due to their greater electrical breakdown strength and thermal conductivity, compared to gaseous insulators. Their ability to conform to complex geometries means that they are often of more practical use than solid insulators, while at the same time they can provide protection to them if used in combination. This work focuses on the formation of ionization channels, known as electrical streamers. These are low-density conductive structures that form in regions of oil that are over-stressed by electric fields on the order of 1x103 kV/cm or greater. Once a streamer forms it tends to elongate, growing from the point of initiation towards a grounding point. The extent of a streamer's development depends upon the nature of the electrical excitation which caused it. Sustained over-excitation can result in a streamer bridging the oil gap between its point of origin and ground. When this happens an arc will form and electrical breakdown will occur. Therefore, in this thesis, a model is developed, which is based on that mechanism, and includes equations for three different charge carriers, which are positive ions, negative ions and electrons. The geometry needle-plane is used, which is imported into COMSOL Multiphysics, which a finite element simulation suite. Various voltage excitations are being studied and useful conclusions are drawn concerning the characteristic of streamers, such as dimensions, size and propagation velocity.

This thesis provides the study of graphene’s electrostatic interaction with the substrate surrounding it. Mathematical models based on current experimental configurations of graphene field-effect transistors (FET) are developed and analyzed. The conductivity and mobility of charge carriers in graphene are examined in the presence of impurities trapped in the substrate near graphene. The impurities encompass a wide range of possible structures and parameters, including different types of impurities, their distance from graphene, and the spatial correlation between them. Furthermore, we extend our models to analyze the influence of impurities on the fluctuations of the electrostatic potential and the charge carrier density in the plane of graphene. The results of our mathematical models are compared with current experimental results in the literature.

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