Much of today’s high performance computing engines and hand-held mobile devices are products of aggressive CMOS scaling. Technology scaling in semiconductor industry is mainly driven by corresponding improvements in optical lithography technology. Photolithography, the art used to create patterns on the wafer is the heart of the semiconductor manufacturing process. Lately, improvements in optical technology have been difficult and slow. The transition to deep ultra-violet (DUV) light source (193nm) required changes in lens materials, mask blanks, light source and photoresist. It took more than ten years to develop a stable chemically amplified resist (CAR) for DUV. Consequently, as the industry moves towards manufacturing end-of-the-roadmap CMOS devices, lithography is still based on 193nm light source to print critical dimensions of conman, 32nm and likely 22nm. Sub-wavelength lithography creates a number of printability issues. The printed patterns are highly sensitive to topographic changes due to metal planarization, overlay errors, focus and dose variations, random particle defects to name a few. Design for Manufacturability (DFM) methodologies came into being to help analyze and mitigate manufacturing impacts on the design. Although techniques such as Resolution Enhancement Techniques (RET) which involve optical proximity correction (OPC), phase shift masking (PSM), off-axis illumination (OAI) have been used to greatly improve the printability and better the manufacturing process window, they have not been able to perfectly compensate for these lithographic deficiencies. DFM methods were primarily devised to predict and correct systematic patterning problems that arise during manufacturing. Apart from systematic errors, random manufacturing variations may occur during photolithography. This is where a statistical approach to modeling of error behavior and its impact on different design parameters may prove to be effective. For example, by incorporating statistical analysis to parameter variation, an effective, non-conservative design can be obtained. IC manufacturing yield is the foremost measure that determines the profitability of a given semiconductor manufacturing process. Early prediction of yield detractors is an important step in the design process. Such predictions are based on models that mimic the behavior of the underlying manufacturing process. Success of yield prediction is based on quality of models. The models must capture all physical phenomena and yet be efficient for computation. In this work, we present a lithography-based yield model that is computationally practical for use in the design process. The work also provides a methodology to perform statistical lithography rules check to identify hot spots in the design that can contribute to yield loss. Yield recovery methods aimed at minimally modifying the design ultimately produce more printable masks. Apart from IC manufacturing yield, ICs today are vulnerable to various reliability failures including electromigration (EM), negative bias temperature instability (NBTI), hot carrier injection (HCI) and electro-static discharge (ESD). Though such reliability issues have been examined since the beginning of CMOS, manufacturability impacts have created a renewed interest in analyzing them. This dissertation work introduces the concept of Design for reliable manufacturability (DFRM) to consider the effect of linewidth changes, gate oxide thickness variations and other manufacturing artifacts. A novel Litho-aware EM calibration and analysis has bee shown in this work. Results indicate that there is a significant difference in EM estimation when litho-predicted layouts are considered during analysis. DFM has always looked at linewidth and material thickness variation as detractors to the design. However, the increase in such variations with technology scaling is inevitable. Part of this dissertation aims at utilizing these fluctuations to improve manufacturing test quality. Test structures sprinkled all over the wafer encounter varying process fluctuations. This can be harnessed to predict the current lithographic process corner which will later be used to choose the test pattern set that results in maximum fault coverage. In summary, the objective of this dissertation is to consider the impact of subwavelength lithography on printability and the overall impact on circuit reliability and manufacturing test development.

<p>Laboratory results on some of the optical properties of Deuteporfin, a relatively new photosensitizing drug that has been in clinical trials in China since around 2009, is discussed. The drug was characterized on the basis of one photon absorption and fluorescence emission for providing data for proper drug applications and dosimetry. In addition, the effects of photobleaching were investigated to characterize decay kinetics. The results of this research on this photosensitizer were also compared against HMME Hematoporphyrin monomethyl ether (HMME) (Hemoporfin^&reg;) key characterization data which includes Q-band absorption to compare peak wavelengths and fluorescence intensity to show that Deuteporfin has similar absorption profile to HMME while it has superior fluorescence characteristics. The findings help to support the manufacturer&rsquo;s claim that Deuteporfin can be an effective photosensitizer for tumor treatment. </p>

<p> Even though image sensor performance has improved tremendously over the years, there are two key areas where sensor performance leaves room for improvement. Firstly, small pixel performance is limited by low full well, low dynamic range and high crosstalk, which greatly impact the sensor performance. Also, low light color image sensors, which use color filter arrays, have low sensitivity due to the selective light rejection by the color filters. The quanta image sensor (QIS) concept was proposed to mitigate the full well and dynamic range issues in small pixel image sensors. In this concept, spatial and temporal oversampling is used to address the full well and dynamic range issues. The QIS concept however does not address the issue of crosstalk. In this dissertation, the high spatial and temporal oversampling of the QIS concept is leveraged to enhance small pixel performance in two ways. Firstly, the oversampling allows polarization sensitive QIS jots to be incorporated to obtain polarization information. Secondly, the oversampling in the QIS concept allows the design of alternative color filter array patterns for mitigating the impact of crosstalk on color reproduction in small pixels. Finally, the problem of performing color imaging in low light conditions is tackled with a proposed stacked pixel concept. This concept which enables color sampling without the use of absorption color filters, improves low light sensitivity. Simulations are performed to demonstrate the advantage of this proposed pixel structure over sensors employing color filter arrays such as the Bayer pattern. A color correction algorithm for improvement of color reproduction in low light is also developed and demonstrates improved performance.</p>

<p> This dissertation explores three related embodiments of light&ndash;matter interactions at the micro&ndash; and nano&ndash;scales, and is focused towards tangible device applications. The first topic provides a fundamentally different transistor or electronic switch mechanism, which is termed a light&ndash;effect transistor (LET). The LET, unlike exotic techniques, provides a practical and viable approach using existing fabrication processes. Electronic devices at the nanoscale operate within the ballistic regime, where the dominate source of energy loss comes from impurity scattering. As a LET does not require extrinsic doping, it circumvents this issue. Electron&ndash;phonon coupling, however, is the second largest source, and it is a pertinent and important parameter affecting electronic conductivity and energy efficiency, such as in LETs. The third topic is laser writing, or the use of a laser to perform post&ndash;growth modifications, to achieve specific optical and electrical characteristics. </p><p> A LET offers electronic&ndash;optical hybridization at the component level, which can continue Moore&rsquo;s law to the quantum region without requiring a FET&rsquo;s fabrication complexity, e.g., physical gate and doping, by employing optical gating and photoconductivity. Multiple independent gates are therefore readily utilized to achieve unique functionalities without increasing chip space. LET device characteristics and novel digital and analog applications, such as optical logic gates and optical amplification, are explored. Prototype cadmium selenide (CdSe) nanowire&ndash;based LETs show output and transfer characteristics resembling advanced FETs, e.g., on/off ratios up to ~1.0x10⁶ with a source-drain voltage of ~1.43 V, gate-power of ~260 nW, and a subthreshold swing of ~0.3 nW/decade (excluding losses). The LET platform offers new electronic&ndash;optical integration strategies and high speed and low energy electronic and optical computing approaches.</p><p> Electron&ndash;phonon coupling is typically studied as an intrinsic property, which is particularly important for electronic transport properties at the nanoscale, where controversy and even contradictory experimental and theoretical findings still persist. Zinc telluride (ZnTe) has important uses in optical or laser refrigeration, and the existing studies do not consider extrinsic effects, such as laser&ndash;forming tellurium&ndash;based species. Nanostructures, with their large surface&ndash;to&ndash;volume ratios, are more susceptible to extrinsic perturbations that ultimately effect coupling. In this dissertation, ZnTe is studied in bulk, thin film, and nanowire forms with primary focus on the latter. Raman spectroscopy under near resonant excitation is used to extract electron&ndash;phonon coupling strengths, which is obtained through the ratio of the first and second order Raman peaks, <i>R</i> = <p style="font-variant: small-caps"> I2LO/I1LO</p> (and is proportional to the Huang&ndash;Rhys factor). Laser&ndash;formation of tellurium&ndash;based species on ZnTe nanowires dynamically altered the ratio R from ~6-7 to 2.4 after laser processing, while tuning the (532 nm) laser power from a few microwatts to 150 microwatts (with constant optical exposure time) did not significantly impact the EPC strength. Other explored effects include size dependence, chemical effects (methanol exposure), and interface effects (e.g., at a gold&ndash;nanowire junction). The findings suggest that the previously reported size dependence in ZnTe was extrinsic in nature. Tunable coupling strengths also suggest the possibility of novel electronic and optoelectronic devices.</p><p> The electrical characteristic of CdSe nanowire M-S-M devices are shown to be tunable with laser illumination. As with any semiconductor material, sufficiently low optical powers produce stable and reproducible electrical properties, while higher optical powers and exposure times can induce laser modifications of the material. Drastic modification of electrical characteristics were observed, such as from converting an ohmic response (linear slope change) to rectified characteristics, and modification of both forward and reverse currents. Results suggest the potential to laser write wavelength&ndash;specific electronic functions that could be used in applications requiring wavelength discrimination, such as with night vision products. Using a combination of laser modification and device fabrication processes provides the ability to offer a menu of electrical behaviors using the same materials and fabrication processes.</p>

<p> The non-resonant heating of gases by laser irradiation and plasma formation has been under investigation since the development of 100 megawatt peak power, Q-switched, nanosecond pulse duration lasers and the commensurate discovery of laser air sparks. More recently, advances in mode-locking and chirped pulse amplification have led to commercially available 100 gigawatt peak power, femtosecond pulse duration lasers with a rapidly increasing number of applications including remote sensing, laser spectroscopy, aerodynamic flow control, and molecular tagging velocimetry and thermometry diagnostics. This work investigates local energy deposition and gas heating produced by focused, non-resonant, nanosecond and femtosecond laser pulses in the context of flow control and laser diagnostic applications. </p><p> Three types of pulse configurations were examined: single nanosecond pulses, single femtosecond pulses and a dual pulse approach whereby a femtosecond pre-ionizing pulse is followed by a nanosecond pulse. For each pulse configuration, optical and laser diagnostic techniques were applied in order to qualitatively and quantitatively measure the plasmadynamic and hydrodynamic processes accompanying laser energy deposition. Time resolved imaging of optical emission from the plasma and excited species was used to qualitatively examine the morphology and decay of the excited gas. Additionally, Thomson scattering and Rayleigh scattering diagnostics were applied towards measurements of electron temperature, electron density, gas temperature and gas density. </p><p> Gas heating by nanosecond and dual pulse laser plasmas was found to be considerably more intense than femtosecond plasmas, irrespective of pressure, while the dual pulse approach provided substantially more controllability than nanosecond pulses alone. In comparison, measurements of femtosecond laser heating showed a strong and nonlinearly dependence on focusing strength. With comparable pulse energy, measurements of maximum temperature rise ranged from 50K to 2000K for 500mm and 175mm focal length lenses, respectively. Experiments with various lens and pulse energy combinations indicated an important connection between gas heating and the phenomena of intensity clamping and self-guiding. The long-term behavior of the heated region varied considerably among pulse configurations. However, in each case, the formation of a toroidal vortex could be suppressed or enhanced depending on the variables of pressure, focusing and pulse energy.</p>

Thesis (Ph.D.)--Drexel University, 2007. / Includes abstract. Includes bibliographical references (leaves 152-171).

<p> In the past few decades, imaging technology has made great strides. From high resolution sensors for photography to 3D scanners in autonomous driving, imaging has become one of the key drivers of the modern society. However, there are still many scenarios where the traditional methods of imaging are woefully inadequate. Examples include high-resolution non-visible light imaging, 3D scanning in the presence of strong ambient light, and imaging through scattering media. In these scenarios, the two classical solutions of single-shot imaging using 2D sensors and point scanning using photodiodes have severe shortcomings in terms of cost, measurement rate and robustness to non-idealities in the imaging process. </p><p> The goal of this dissertation is the design of computational imagers that work under traditionally difficult conditions by providing the robustness and economy of point scanning systems along with the speed and resolution of conventional cameras. In order to achieve this goal, we use line sensors or 1D sensors and make three contributions in this dissertation. The first contribution is the design of a line sensor based compressive camera (LiSens) which uses a line sensor and a spatial light modulator for 2D imaging. It can provide a measurement rate that is equal to that of a 2D sensor but with only a fraction of the number of pixels. The second contribution is the design of a dual structured light (DualSL) system which uses a 1D sensor and a 2D projector to achieve 3D scanning with same resolution and performance as traditional structured light system. The third contribution is the design of programmable triangulation light curtains (TriLC) for proximity detection by rotating a 1D sensor and a 1D light source in synchrony. This device detects the presence of objects that intersect a programmable virtual shell around itself. The shape of this virtual shell can be changed during operation and the device can perform under strong sunlight as well as in foggy and smoky environments. We believe that the camera architectures proposed in this dissertation can be used in a wide range of applications, such as autonomous driving cars, field robotics, and underwater exploration.</p><p>

<p> The search for robust, low-noise modelocked comb sources has attracted significant attention during the last two decades. Passively modelocked fiber lasers are among the most attractive comb sources. The most important design problems for a passively modelocked laser include: (1) finding a region in the laser&rsquo;s adjustable parameter space where it operates stably, (2) optimizing the pulse profile within that region, and (3) lowering the noise level. Adjustable parameters will typically include the cavity length, the pump power, and the amplifier gain, which may be a function of the pump power, the pump wavelength, and both the material and geometry of the gain medium. </p><p> There are two basic computational approaches for modeling passively modelocked laser systems: the evolutionary approach and the dynamical approach. In the evolutionary approach, which replicates the physical behavior of the laser, one launches light into the simulated laser and follows it for many round trips in the laser. If one obtains a stationary or periodically-stationary modelocked pulse, the laser is deemed stable and, if no such pulse is found, the laser is deemed unstable. The effect of noise can be studied by using a random number generator to add computational noise. In the dynamical approach, one first obtains a single modelocked pulse solution either analytically or by using the evolutionary approach. Next, one finds the pulse parameters as the laser parameters vary by solving a root-finding algorithm. One then linearizes the evolution equations about the steady-state solution and determines the eigenvalues of the linearized equation, which we refer to as the equation&rsquo;s dynamical spectrum. If any eigenvalue has a positive real part, then the modelocked pulse is unstable. The effect of noise can be determined by calculating the noise that enters each of the modes in the dynamical spectrum, whose amplitudes are described by either a Langevin process or a random walk process. </p><p> The evolutionary approach is intuitive and straightforward to program, and it is widely used. However, it is computationally time-consuming to determine the stable operating regions and can give ambiguous results near a stability boundary. When evaluating the noise levels, Monte Carlo simulations, which are based upon the evolutionary approach, are often prohibitively expensive computationally. By comparison, the dynamical approach is more difficult to program, but it is computationally rapid, yields unambiguous results for the stability, and avoids computationally expensive Monte Carlo simulations. The two approaches are complementary to each other. However, the dynamical approach can be a powerful tool for system design and optimization and has historically been undertilized. </p><p> In this dissertation, we discuss the dynamical approach that we have developed for design and optimization of passively modelocked laser systems. This approach provides deep insights into the instability mechanisms of the laser that impact or limit modelocking, and makes it possible to rapidly and unambiguously map out the regions of stable operation in a large parameter space. For a given system setup, we can calculate the noise level in the laser cavity within minutes on a desktop computer. </p><p> Compared to Monte Carlo simulations, we will show that the dynamical approach improves the computational efficiency by more than three orders of magnitude. We will apply the dynamical approach to a laser with a fast saturable absorber and to a laser with a slow saturable absorber. We apply our model of a laser with a slow saturable absorber to a fiber comb laser with a semiconductor absorbing mirror (SESAM) that was developed at National Institute of Standards and Technology (NIST), Boulder, CO. We optimize its parameters and show that it is possible to increase its output power and bandwidth while lowering the pump power that is needed.</p><p>

<p> For decades, traditional remote sensing retrieval methods that rely solely on the spectral intensity of the water-leaving light have provided indicators of aquatic ecosystem health. With the increasing demand for new water quality indicators and improved accuracy of existing ones, the limits of traditional remote sensing approaches are becoming apparent. Use of the additional information intrinsic to the polarization state of light is therefore receiving more attention. One of the major challenges inherent in any above-surface determination of the water-leaving radiance, scalar or vector, is the removal of extraneous light which has not interacted with the water body and is therefore not useful for remote sensing of the water itself. Due in-part to the lack of a proven alternative, existing polarimeter installations have thus far assumed that such light was reflected by a flat sea surface, which can lead to large inaccuracies in the water-leaving polarization signal. This dissertation rigorously determines the full Mueller matrices for both surface-reflected skylight and upwardly transmitted light by a wind-driven ocean surface. A Monte Carlo code models the surface in 3D and performs polarized ray-tracing, while a vector radiative transfer (VRT) simulation generates polarized light distributions from which the initial Stokes vector for each ray is inferred. Matrices are computed for the observable range of surface wind speeds, viewing and solar geometries, and atmospheric aerosol loads. Radiometer field-of-view effects are also assessed. Validation of the results is achieved using comprehensive VRT simulations of the atmosphere-ocean system based on several oceanographic research cruises and specially designed polarimeters developed by the City College of New York: one submerged beneath the surface and one mounted on a research vessel. When available, additional comparisons are made at 9 km altitude with the NASA Research Scanning Polarimeter (RSP). Excellent agreement is achieved between all instrumentation, demonstrating the accuracy of the modeling approach and validating the computed Mueller matrices. Further, the results are used to demonstrate the feasibility for polarimetric retrieval of the total attenuation coefficient for Case II waters, a feat which is not possible using scalar remote sensing methods.</p><p>

<p> <b>Part 1: High-Sensitivity Amplifiers for Detecting Fluorescence </b></p><p> Monitoring electrical activity and Ca<i>_i</i>²⁺ transients in biological tissues and individual cells increasingly utilizes optical sensors based on voltage-dependent and Ca<i>_i</i>²⁺-dependent fluorescent dyes. However, achieving satisfactory signal-to-noise ratios (SNR) often requires increased illumination intensities and/or dye concentrations, which results in photo-toxicity, photo-bleaching and other adverse effects limiting the utility of optical recordings. The most challenging are the recordings from individual cardiac myocytes and neurons. Here we demonstrate that by optimizing a conventional transimpedance topology one can achieve a 10-20 fold increase of sensitivity with photodiode-based recording systems (dependent on application). We provide a detailed comparative analysis of the dynamic and noise characteristics of different transimpedance amplifier topologies as well as the example(s) of their practical implementation.</p><p> <b>Part 2: Light-Scattering Models for Interpretation of Fluorescence Data</b></p><p> Current interest in understanding light transport in cardiac tissue has been motivated in part by increased use of voltage-sensitive and Ca<i>_i</i>²⁺-sensitive fluorescent probes to map electrical impulse propagation and Ca<i>_i</i>²⁺-transients in the heart. The fluorescent signals are recorded using such probes represent contributions from different layers of myocardial tissue and are greatly affected by light scattering. The interpretation of these signals thus requires deconvolution which would not be possible without detailed models of light transport in the respective tissue. Which involves the experimental measurements of the absorption, scattering, and anisotropy coefficients, <i>&mu;_a, &mu;_s,</i> and <i>g</i> respectively.</p><p> The aim of the second part of our thesis was to derive a new method for deriving these parameters from high spatial resolution measurements of forward-directed flux (FDF). To this end, we carried out high spatial resolution measurements of forward-directed flux (FDF) in intact and homogenized cardiac tissue, as well as in intralipid-based tissue phantoms. We demonstrated that in the vicinity of the illuminated surface, the FDF consistently manifested a fast decaying exponent with a space constant comparable to the decay rate of ballistic photons. Using a Monte Carlo model we obtained a simple empirical formula linking the rate of the fast exponent to the scattering coefficient, the anisotropy parameter <i> g,</i> and the numerical aperture of the probe. The estimates of scattering coefficient based on this formula were validated in tissue phantoms. The advantages of the new method are its simplicity and low-cost.</p><p>