The major sources of power dissipation in a nanometer CMOS circuit are capacitive switching, short-circuit current, static leakage and gate oxide tunneling. However, with the aggressive scaling of technology the gate oxide direct tunneling current (gate leakage) is emerging as a prominent component of power dissipation. For sub-65 nm CMOS technology where the gate oxide (SiO2) thickness is very low, the direct tunneling current is the major form of tunneling. There are two contribution parts in this thesis: analytical modeling of behavioral level components for direct tunneling current and propagation delay, and the reduction of tunneling current during behavioral synthesis. Gate oxides of multiple thicknesses are useful in reducing the gate leakage dissipation. Analytical models from first principles to calculate the tunneling current and the propagation delay of behavioral level components is presented, which are backed by BSIM4/5 models and SPICE simulations. These components are characterized for 45 nm technology and an algorithm is provided for scheduling of datapath operations such that the overall tunneling current dissipation of a datapath circuit under design is minimal. It is observed that the oxide thickness that is being considered is very low it may not remain constant during the course of fabrication. Hence the algorithm takes process variation into consideration. Extensive experiments are conducted for various behavioral level benchmarks under various constraints and observed significant reductions, as high as 75.3% (with an average of 64.3%).

Thesis (Ph. D. (Physics)) -- University of Limpopo, 2016. / Single and double doped nanometric powders of Single and double doped nanometric powders of titanium dioxide (TiO2) were synthesised by the sol-gel process using titanium isopropoxide (TTIP) as the precursor. For comparison, an undoped sample was also prepared. The metal dopants, Ag and Cu, were used at doping levels of 5% molar weight. The samples were dried at 100°C in air and post annealing was done at 300°C, 600°C, 900°C and 1100°C. Structural characterisation of the samples was carried out by X-ray Diffraction (XRD), Raman Spectroscopy, Scanning Electron Microscopy (SEM) and Energy dispersive X-ray Spectrometry (EDS) techniques. Most samples annealed at the 300°C temperature (and lower) revealed the predominantly-anatase phase, while those annealed at 900°C and above were rutile-only. The double-doped powder that was annealed at 300°C was found to be constituted by anatase and brookite phases (with the dopants incorporated into the TiO2 matrix), and the one annealed at 600°C was a mixture of brookite and rutile. The results suggest that multiple doping of titania may favour a two-phase structure at lower temperatures than singly-doped powders. The co-existence of brookite with anatase is believed to be responsible for the enhancement of anatase to rutile transformation in the double-doped sample. UV-visible (UV-vis) and Photoluminescence (PL) measurements were also carried out to study the optical properties of the TiO2 nanoparticles. This revealed the active PL band at around 440 nm. By narrowing the band gap, the double-doped powders that exhibited the brookite phase, again showed improved visible light photo absorption over the other samples, with a significant shift of the absorption edge to shorter wavelengths. Further, PL spectra revealed a change in PL intensity with phase change, as well as the presence of exciton energy levels at the base of the conduction band. The changes in the electrical conductivities of representative anatase and rutile TiO2 nanopowders upon exposure to water-vapour, ammonia (NH3) and hydrogen (H2) were also investigated. Sensing measurements for water-vapour was done at room temperature for various humidity levels ranging from 5.4% RH to 88.4% RH. The detection of NH3 and H2 gases were carried out at temperatures extending from room temperature to 350°C and over concentration ranges of 25 sccm to 500 sccm and 15 v sccm to 200 sccm respectively. The gas-sensing results show that the sol-gel fabricated TiO2 nanoparticles (particularly in anatase form), has excellent fast and stable dynamic responses to humidity, NH3 and H2. They feature good sensitivities, even at a low operating temperatures. However, acceptor behaviour, for which there was a conductivity switch from n-type to p-type, was recorded for the Ag-doped rutile powders at operating temperatures of 300ºC and 350ºC. Overall, the double-doped sample annealed at 300ºC was deemed the most promising candidate for gassensing. (TiO2) were synthesised by the sol-gel process using titanium isopropoxide (TTIP) as the precursor. For comparison, an undoped sample was also prepared. The metal dopants, Ag and Cu, were used at doping levels of 5% molar weight. The samples were dried at 100°C in air and post annealing was done at 300°C, 600°C, 900°C and 1100°C. Structural characterisation of the samples was carried out by X-ray Diffraction (XRD), Raman Spectroscopy, Scanning Electron Microscopy (SEM) and Energy dispersive X-ray Spectrometry (EDS) techniques. Most samples annealed at the 300°C temperature (and lower) revealed the predominantly-anatase phase, while those annealed at 900°C and above were rutile-only. The double-doped powder that was annealed at 300°C was found to be constituted by anatase and brookite phases (with the dopants incorporated into the TiO2 matrix), and the one annealed at 600°C was a mixture of brookite and rutile. The results suggest that multiple doping of titania may favour a two-phase structure at lower temperatures than singly-doped powders. The co-existence of brookite with anatase is believed to be responsible for the enhancement of anatase to rutile transformation in the double-doped sample. UV-visible (UV-vis) and Photoluminescence (PL) measurements were also carried out to study the optical properties of the TiO2 nanoparticles. This revealed the active PL band at around 440 nm. By narrowing the band gap, the double-doped powders that exhibited the brookite phase, again showed improved visible light photo absorption over the other samples, with a significant shift of the absorption edge to shorter wavelengths. Further, PL spectra revealed a change in PL intensity with phase change, as well as the presence of exciton energy levels at the base of the conduction band. The changes in the electrical conductivities of representative anatase and rutile TiO2 nanopowders upon exposure to water-vapour, ammonia (NH3) and hydrogen (H2) were also investigated. Sensing measurements for water-vapour was done at room temperature for various humidity levels ranging from 5.4% RH to 88.4% RH. The detection of NH3 and H2 gases were carried out at temperatures extending from room temperature to 350°C and over concentration ranges of 25 sccm to 500 sccm and 15 v sccm to 200 sccm respectively. The gas-sensing results show that the sol-gel fabricated TiO2 nanoparticles (particularly in anatase form), has excellent fast and stable dynamic responses to humidity, NH3 and H2. They feature good sensitivities, even at a low operating temperatures. However, acceptor behaviour, for which there was a conductivity switch from n-type to p-type, was recorded for the Ag-doped rutile powders at operating temperatures of 300ºC and 350ºC. Overall, the double-doped sample annealed at 300ºC was deemed the most promising candidate for gassensing.

Organic dyes are examined in photoelectrochemical systems wherein they engage in thermal (rather than photoexcited) electron donation into metal oxide semiconductors. These studies are intended to elucidate fundamental parameters of electron transfer in photoelectrochemical cells. Development of novel methods for the structure/property tuning of electroactive dyes and the preparation of nanostructured semiconductors have also been discovered in the course of the presented work. Acceptor sensitized polymer oxide solar cell devices were assembled and the impact of the acceptor dyes were studied. The optoelectronic tuning of boron-chelated azadipyrromethene dyes has been explored by the substitution of carbon substituents in place of fluoride atoms at boron. Stability of singlet exited state and level of reduction potential of these series of aza-BODIPY coumpounds were studied in order to employ them as electron-accepting sensitizers in solid state dye sensitized solar cells.

Thesis: M.S., Massachusetts Institute of Technology, Department of Electrical Engineering and Computer Science, 1979 / Includes bibliographical references. / by Leslie Louis Szepesi, Jr. / M.S. / M.S. Massachusetts Institute of Technology, Department of Electrical Engineering and Computer Science

Library characterization and 'Static Timing Analysis' (STA) are widely used in the design of modern CMOS integrated circuits to confirm that critical timing constraints are met. While many commercial tools are available to do timing validation using library characterization and static timing analysis, their operation depends on calculations relative to a global synchronous clock. This thesis applies timing validation to circuits from which the global synchronous clock is absent, making application of commercial tools difficult. Previous work at the University of Southern California (USC) showed how to overcome the incompatibility of commercial STA tools for asynchronous circuits. This thesis shows how to overcome the incompatibility of library characterization with respect to asynchronous circuits, and ties the results into the STA solution of USC. The particular family of circuits considered in this thesis is called GasP. GasP circuits are light in area and light in power. They have demonstrated operation at about twice the throughput one would expect from conventional clocked circuits. This makes GasP circuits excellent candidates for modern many-core, concurrent network-on-chip and system-on-chip architectures. In part, GasP circuits achieve their performance advantages by using a `single-track' signaling protocol. Two GasP modules communicate with each other over a single wire. One module drives the wire up and a second module at the other end of the wire drives the wire down. This conflicts with the common assumption that wires are driven only from one end. As a result, special circuitry is needed to characterize a GasP library module. This thesis shows how to break a GasP module and its timing constraints into manageable pieces and how to simulate and collect the data relevant for characterization and static timing analysis. When combined with software tools for identifying the critical timing constraints, the results of this work will provide confidence in the correct operation of GasP circuits.

Dark current is an unwanted source of noise in images produced by digital imagers, the de facto standard of imaging. The two most common types of digital imager architectures, Charged-Coupled Devices (CCDs) and Complementary Metal-Oxide-Semiconductor (CMOS), are both prone to this noise source. To accurately reflect the information from light signals this noise must be removed. This practice is especially vital for scientific purposes such as in astronomical observations. Presented in this dissertation are characterizations of dark current sources that present complications to the traditional methods of correction. In particular, it is observed that pixels in both CCDs and CMOS image sensors produce dark current that is affected by the presence of pre-illuminating the sensor and that these same pixels produce a nonlinear dark current with respect to exposure time. These two characteristics are not conventionally accounted for as it is assumed that the dark current produced will be unaffected by charge accumulated from either illumination or the dark current itself. Additionally, a model reproducing these dark current characteristics is presented. The model incorporates a moving edge of the depletion region, where charge is accumulated, as well as fixed recombination-generation locations. Recombination-generation sites in the form of heavy metal impurities, or lattice defects, are commonly the source of dark current especially in the highest producing pixels, commonly called "hot pixels." The model predicts that pixels with recombination-generation sites near the edge of an empty depletion region will produce less dark current after accumulation of charge, accurately modeling the behavior observed from empirical sources. Finally, it is shown that activation energy calculations will produce inconsistent results for pixels with the presence of recombination-generation sites near the edge of a moving depletion region. Activation energies, an energy associated with the temperature dependence of dark current, are often calculated to characterize aspects of the dark current including types of impurities and sources of dark current. The model is shown to generate data, including changing activation energy values, that correspond with changing activation energy calculations in those pixels observed to be affected by pre-illumination and that produce inconsistent dark current over long exposure times. Rather than only being a complication to dark current correction, the presence of such pixels, and the model explaining their behavior, presents an opportunity to obtain information, such as the depth of these recombination-generation sites, which will aid in refining manufacturing processes for digital imagers.

No description available.

This study investigated the Class F and inverse Class F RF power amplifier operating at 5.8 GHz. The major challenging issue in design and implementation of CMOS power transistor is the breakdown voltage especially in sub-micron CMOS technologies. In order to eliminate this problem a Cascode topologies were implemented to reduce the Drain-toSource voltage (stress). A Cascode Class F & Inverse Class F RF power amplifier were designed, and optimized in order to improve efficiency and reliability using 0.18µm CMOS technology process. A 50% decrease in the stress has been achieved in the Cascode class-F and Inverse class F amplifiers. The sensitivity and temperature effect were investigated using BSIM-4 model. Such an amplifier was designed and optimized for a good sensitivity. A substrate bias circuit was implemented to achieve a good sensitivity. Recommendations were made for future advancements for modification and optimization of the class F and inverse class F circuit by the application of other stress reduction strategies, and improvement of the substrate bias circuit for a better sensitivity.

No description available.

Advancement in CMOS technology has become a driving force in the advancement of today's IC design arena. In the past few years, considerable research has been done on the CMOS devices and circuits. Constant efforts have been made to realize smaller and smaller devices by reducing the channel length of the transistors and scaling down various other device parameters. Consequently, various problems have arisen such as interconnect delay, signal integrity and signal coupling. The purpose of this thesis is to review and understand current problems in IC design and come up with various solutions to them. Efforts have been made to propose a model of interconnect which demonstrates the effects of parasitic components on the chip. Signal coupling effects have been demonstrated by simulating various RC and RLC models for interconnects. The impact of parasitic inductance on the performance of the chip is understood with the help of simulation results. The design of an eight bit shifter is realized using Clockless Asynchronous and Clocked Boolean design techniques. Both the chips are placed and routed using Silicon Ensemble, a high-tech CAD tool from Cadence Design Systems. Various optimization techniques have been applied to both the prototypes and a detailed comparison has been done considering factors such as area of the chip, total length of the interconnect, row utilization, chip congestion etc. Based on these results, it was found that Clocked Boolean Shifter was compact, compared to its Asynchronous counterpart design. However, Asynchronous Clockless architectures are well recommended where complex chip functionalities are intended to be integrated without much of the hassles of timing problems.