Thesis (Ph. D.)--Rutgers University, 2008. / "Graduate Program in Electrical and Computer Engineering." Includes bibliographical references (p. 80-83).

Thesis (Ph. D.)--Chemistry and Biochemistry, Georgia Institute of Technology, 2006. / Mohan Srinivasarao, Committee Member ; David Collard, Committee Member ; Uwe Bunz, Committee Member ; Art Janata, Committee Member ; Marcus Weck, Committee Member ; Laren Tolbert, Committee Chair.

Thesis (M.Phil.)--Hong Kong University of Science and Technology, 2005. / Includes bibliographical references. Also available in electronic version.

Thesis (Ph.D.)--Hong Kong University of Science and Technology, 2007. / Vita. Includes bibliographical references (leaves 134-143). Also available in electronic version.

The conversion gain of GaAs MESFET mixers is known to be dependent on the impedances seen by the applied signals and the resulting mixing products at all ports of the device. For an accurate representation, all these loading conditions should be considered; however, the design of gate and drain networks then becomes rather difficult. As a result, no sufficiently accurate and yet usable design procedures exist for MESFET mixers; instead, a few simple rules involving short- and open-circuit terminations have been given by various authors. Unfortunately, these rules are often inappropriate, particularly in upconverter applications. In this thesis, the conversion efficiency dependence on the drain loading at the local oscillator frequency has been studied for a gate upconverter; the local oscillator signal is by far the most dominant in terms of its influence on mixer performance. It has been found that the conversion gain can significantly deteriorate for a narrow range of load values. In addition, the local oscillator drain termination resulting in highest gain has been found to be generally different from the short-circuit recommended in the literature. Based on these findings, a novel FET upconverter design procedure has been developed that incorporates the local oscillator loading phenomenon in the FET equivalent circuit by means of a load dependent mixing transconductance. It allows the optimization of the drain network for an acceptable match at the selected sideband and desired local oscillator rejection while avoiding impedance values in the local oscillator frequency range which would otherwise cause severe degradation in conversion gain. / Applied Science, Faculty of / Electrical and Computer Engineering, Department of / Graduate

Depuis sa découverte en 2004, le graphène n’a cessé de capter l’intérêt de la communauté scientifique grâce à ses innombrables propriétés et à la diversité de ses applications potentielles. Néanmoins, son implémentation à l’échelle industrielle exige encore beaucoup de contraintes et notamment concernant la stabilité de ses performances.L’objectif de cette thèse est de développer un procédé de fabrication de dispositifs intégrant une couche de graphène faiblement dopée et présentant des caractéristiques électriques stables. Le graphène, étant un matériau extrêmement sensible à l’environnement, il s’est avéré primordial de le protéger afin d’avoir un bon contrôle sur ses propriétés. Pour ce faire, plusieurs approches technologiques ont été abordées et analysées à l’aide d’une étude statistique des caractéristiques de plus de 500 transistors. Le procédé optimal intègre une couche de « protection » du graphène réalisée après son transfert et la passivation des dispositifs fabriqués avec une couche d’oxyde. Grâce à cette méthode, 75% des transistors fabriqués sont fonctionnels, présentent une faible hystérèse et sont stables dans le temps, ce qui constitue des critères indispensables pour l’intégration du graphène dans des composants discrets en particulier pour l’optoélectronique.Par la suite, le procédé technologique développé a été adapté à la fabrication de lignes coplanaires à base de graphène pour la photodétection hyperfréquence. Des valeurs de photo-courant, proches de celles de la littérature (0.15 mA/W), ont été mesurées avec un laser 1.55 µm modulé à des fréquences allant jusqu’à 40 GHz. Cette technologie est maintenant évaluée pour la fabrication de mixeurs optoélectroniques haute fréquence. / Since its discovery in 2004, graphene has attracted the attention of the scientific community due to its unique properties as well as the diversity of its potential applications. Nevertheless, its implementation at industrial scale still requires many challenges including its performance stability.The objective of my PhD is to develop a technological process for the fabrication of devices integrating low-doped graphene and exhibiting stable electrical characteristics. As graphene is extremely sensitive to the environment, it is crucial to protect its surface to accurately control its properties. To do this, several technological approaches have been analyzed using the statistical characteristics of more than 500 transistors. The optimal process integrates a “protection” layer after graphene transfer and the passivation of the fabricated devices with an oxide layer. 75% of the passivated transistors were functional, with low hysteresis and time-stable performances. These criteria are essential for the integration of graphene in discrete components, in particular for optoelectronic devices.Subsequently, the technological process developed was adapted for the fabrication of graphene based coplanar waveguides for high frequency photodetection. We report on a measured photocurrent of 0.15 mA/W with a 1.55 µm laser modulated up to 40 GHz. This technology is currently studied for the fabrication of high frequency optoelectronic mixers

It is proposed to represent a nonlinear two-port device by a scattering parameter (S-parameter) model containing a single nonlinearity. Furthermore, it is proposed that the nonlinearity be modeled as a memoryless nonlinear function. A bipolar junction transistor (BJT) operating in the active region is suggested as one application of this modeling approach. The validity of the model is demonstrated by the comparison of measured and model-predicted data for a microwave BJT. The proposed nonlinear model is represented by a linear three-port flowgraph having one of its ports terminated in a real-valued, nonlinear reflection. The model parameters are determined from measurements of device-under-test (DUT) transmission and reflection at various input drive levels. As an illustration of its utility, the model is applied to the design of an oscillator. The measured results of a constructed oscillator are provided. A presentation of a new form of calibration for microwave measurement systems precedes the nonlinear modeling discussion. The new calibration technique combines the transmission line approach to calibration with a load-pull process common to nonlinear device measurements. A two-port, one-way measurement process obviates the need for DUT reversal. The calibrated measurement of input reflection, transmission, and load reflection is discussed. In addition, the procedure for determining the small-signal S parameters of the DUT is given. / Master of Science

The punch-through space-charge-limited load (PTSCLL) may be an alternate VLSI design as a high resistance load device. A surface and geometrical study on the PTSCLL device is presented. From this research, it is found out that the dynamic resistance value increases as the surface bias to a negatively voltage. Also, the resistance increases as the channel length and substrate doping increase. But the resistance value decreases as the channel width, junction depth, and overlap oxide thickness increase. Incorporate these design considerations, it can maximize the resistance value of the PTSCLL.

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No description available.