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Sensors based on carbon nanotube field-effect transistors and molecular recognition approachesCid Salavert, Cristina Carlota 23 January 2009 (has links)
La unión de las propiedades de los CNT con los principios de reconocimiento molecular se presenta como una base adecuada para el desarrollo de sensores altamente específicos. El objetivo de la presente tesis ha sido desarrollar sensores químicos, del tipo transistores de efecto campo (CNTFET), basados en interacciones receptor-analito, mediante el empleo de los nanotubos de pared sencilla (SWCNT), que actúan como transductores de la señal analítica.Las principales etapas de la parte experimental han sido: Crecimiento de SWCNT con la técnica de deposición química en fase vapor. Integración de los SWCNTs en sistemas CNTFET. Empleo del CNTFET como base del sensor en distintos campos utilizando modelos de reconocimiento molecular. Dependiendo del tipo de funcionalización de los SWCNTs se pueden obtener sensores para proteínas, iones, etc. Como resultado, se han desarrollado y estudiado sensores basados en CNTFETs para la detección distintos analitos de interés, como son la Inmunoglobulina G Humana, los iones potasio y el dióxido de azufre. / The general objective of this thesis is to develop chemical sensors whose sensing capacities are based on the principle of molecular recognition and where the transduction is carried out by single-walled carbon nanotubes (SWCNT).The sensing device used is the carbon nanotube field-effect transistor (CNTFET). The new structure of the CNTFET allows nanotubes to be integrated at the surface of the devices, thus exploiting SWCNTs' sensitivity to changes in their environment. The functionalization of SWCNTs with several types of molecular receptors such as antibodies, ion selective membranes, and synthetic receptors, achieve a high selectivity towards the analyte of interest. This thesis shows that CNTFETs can be used for the successful selective detection of different types of target analytes. These can be biomolecules such as antigens, small compounds such as cations or gas-phase compounds such as SO2.
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Effects of the Dielectric Environment on the Electrical Properties of GrapheneAnicic, Rastko January 2013 (has links)
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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A floating-gate low dropout voltage regulatorLow, Aichen 05 1900 (has links)
No description available.
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Scaling limits and opportunities of double-gate MOSFETSChen, Qiang 05 1900 (has links)
No description available.
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A large-signal model for the RF power MOSFETBordelon, John H. 05 1900 (has links)
No description available.
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Limitations of high speed sigma-delta A/D converter in GaAs technologyAsibal, Romeo Lim 08 1900 (has links)
No description available.
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Cryogenic on-wafer microwave load-pull power measurements and device performance analysisGebara, Edward 05 1900 (has links)
No description available.
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TUNNELING STUDY OF SUPERCONDUCTIVITY IN MAGNESIUM DIBORIDEBadr, Mohamed Hosiny 01 January 2003 (has links)
Although the pairing mechanism in MgB2 is thought to be phonon mediated, there are still many experimental results that lack appropriate explanation. For example, there is no consensus about the magnitude of the energy gap, its temperature dependence, and whether it has only one-gap or not. Many techniques have been used to investigate this, like Raman spectroscopy, farinfrared transmission, specific heat, high-resolution photoemission and tunneling. Most tunneling data on MgB2 are obtained from mechanical junctions. Measurements of energy gap by these junctions have many disadvantages like the instability to temperature and field changes. On the other hand, sandwich-like planar junctions offer a stable and reliable measurement for temperature dependence of the energy gap, where any variation in the tunneling spectra can be interpreted as a direct result from the sample under study. To the best of our knowledge, we report the first energy gap temperature- and magnetic field-dependence of MgB2/Pb planar junctions. Study of the temperature-dependence shows that the small gap value (reported by many groups and explained as a result of surface degradation) is a real bulk property of MgB2. Moreover, our data is in favor of the two-gap model rather than the onegap, multi-gap, or single anisotropic gap models. The study of magnetic field effect on the junctions gave an estimation of the upper critical field of about 5.6 T. The dependence of energy gap on the field has been studied as well. Our junctions show stability against temperature changes, but "collapsed" when the magnetic field (applied normal to the junction barrier) is higher than 3.2 T. The irreversible structural change switched the tunnling mechanism from quisiparticle tunneling into Josephson tunneling. Josephson I-V curves at different temperatures have been studied and the characteristic voltages are calculated. The estimated MgB2 energy gap from supercurrent tunneling in weak link junctions agrees very well with that from quasiparticle tunneling. Reported properties on polycrystalline, single crystal and thin film MgB2 samples are widely varied, depending on the details of preparation procedure. MgB2 single crystals are synthesized mainly by heat treatment at high temperature and pressure. Single crystals prepared by this way have the disadvantages of Mg deficiency and shape irregularity. On the other hand, improving the coupling of grain boundaries in polycrystalline MgB2 (has the lowest normal state resistivity in comparison to many other practical superconductors) will be of practical interest. Consequently, we have been motivated to look for a new heat treatment to prepare high quality polycrystalline and single crystal MgB2 in the same process. The importance of our new method is its simplicity in preparing single crystals (neither high pressure cells nor very high sintering temperatures are required to prepare single crystals) and the quality of the obtained single crystal and polycrystalline MgB2. This method gives high quality and dense polycrystalline MgB2 with very low normal state resistivity (σ(40 ) = 0.28 cm). Single crystals have an average diagonal of 50 m and 10 m thickness with a unique shape that resembles the hexagonal crystal structure. Furthermore, preparing both forms in same process gives a great opportunity to study inconsistencies in their properties. On the other hand, magnesium diboride thin films have also been prepared by magnetron sputtering under new preparation conditions. The prepared thin films have a transition temperature of about 35.2 K and they are promising in fabricating tunnel junctions.
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Distributed-channel bipolar device : experimentation, analytical modeling and applicationsJiang, Fenglai January 1994 (has links)
Thesis (Ph. D.)--University of Hawaii at Manoa, 1994. / Includes bibliographical references (leaves 593-597). / Microfiche. / 2 v. (xliii, 597 leaves), bound ill. 29 cm
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Hot carrier degradation of sub-micron n-channel MOSFETs subject to static stressAminzadeh, Payman G. 18 June 1993 (has links)
Hot carrier effects in sub-micron lightly doped drain (LDD) n-channel
MOSFETs under static (DC) stress are studied in order to establish the degradation
mechanisms of such devices. Degradation is monitored as a function of time at various
gate voltages. Under accelerated aging conditions (i.e. large drain voltages) the gate
voltage for maximum degradation is found to be different than the gate voltage for
which the substrate current is maximum; this is in contrast to the results of previous
workers who found degradation and substrate current to be strongly correlated.
However, under normal operating conditions, degradation and substrate current are
found to be correlated. Furthermore, through the use of charge pumping
measurements it is shown that two primary mechanisms are accountable for the
degradation of these devices at small and large gate voltages. First, at large gate
voltages there is an increase in the degradation which is predominantly due to electron
injection and trapping in the oxide. An alternating static injection experiment shows
that this type of electron trapping degradation is recoverable. Second, at small gate
voltages degradation is mainly related to interface state generation near the drain LDD
region. Floating gate measurements demonstrate that electron and hole injection occurs
at large and small gate voltages, respectively. It is also shown that maximum interface
state creation occurs when electron and hole injection happens simultaneously. / Graduation date: 1994
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