Plasmonic antennas and zero mode waveguides to enhance single molecule fluorescence detection and fluorescence correlation spectroscopy towards physiological concentrations

Single-molecule approaches to biology offer a powerful new vision to elucidate the mechanisms that underpin the functioning of living cells. However, conventional optical single molecule spectroscopy techniques such as F\"orster fluorescence resonance energy transfer (FRET) or fluorescence correlation spectroscopy (FCS) are limited by diffraction to the nanomolar concentration range, far below the physiological micromolar concentration range where most biological reaction occur. To breach the diffraction limit, zero mode waveguides and plasmonic antennas exploit the surface plasmon resonances to confine and enhance light down to the nanometre scale. The ability of plasmonics to achieve extreme light concentration unlocks an enormous potential to enhance fluorescence detection, FRET and FCS. Single molecule spectroscopy techniques greatly benefit from zero mode waveguides and plasmonic antennas to enter a new dimension of molecular concentration reaching physiological conditions. The application of nano-optics to biological problems with FRET and FCS is an emerging and exciting field, and is promising to reveal new insights on biological functions and dynamics.Comment: WIREs Nanomed Nanobiotechnol 201

Impact of parameter variations on circuits and microarchitecture

Parameter variations, which are increasing along with advances in process technologies, affect both timing and power. Variability must be considered at both the circuit and microarchitectural design levels to keep pace with performance scaling and to keep power consumption within reasonable limits. This article presents an overview of the main sources of variability and surveys variation-tolerant circuit and microarchitectural approaches.Peer ReviewedPostprint (published version

IR detection and energy harvesting using antenna coupled MIM tunnel diodes

The infrared (IR) spectrum lies between the microwave and optical frequency ranges, which are well suited for communication and energy harvesting purposes, respectively. The long wavelength IR (LWIR) spectrum, corresponding to wavelengths from 8um to 15um, includes the thermal radiation emitted by objects at room temperature and the Earth's terrestrial radiation. Therefore, LWIR detectors are very appealing for thermal imaging purposes. Thermal detectors developed so far either demand cryogenic operation for fast detection, or they rely on the accumulation of thermal energy in their mass and subsequent measurable changes in material properties. Therefore, they are relatively slow. Quantum detectors allow for tunable and instantaneous detection but are expensive and require complex processes for fabrication. Bolometer detectors are simple and cheap but do not allow for tunability or for rapid detection. Harvesting the LWIR radiation energy sourced by the Earth's heating/cooling cycle is very important for the development of mobile energy resources. While speed is not as significant an issue here, conversion efficiency is an eminent problem for cheap, large area energy transduction. This dissertation addresses the development of tunable, fast, and low cost wave detectors that can operate at room temperature and, when produced in large array format, can harvest Earth's terrestrial radiation energy. This dissertation demonstrates the design, fabrication and testing of Antenna Coupled Metal-Insulator-Metal (ACMIM) tunnel diodes optimized for 10um wavelength radiation detection. ACMIM tunnel diodes operate as electromagnetic wave detectors: the incident radiation is coupled by an antenna and converted into a 30 terahertz signal that is rectified by a fast tunneling MIM diode. For efficient IR radiation coupling, the antenna geometry and its critical dimensions are studied using a commercial finite-element based multi-physics simulation tool, and the half-wave dipole-like bow-tie antennas are fabricated using simulation-optimized geometries. The major challenge of this work is designing and fabricating MIM diodes and coupled antennas with internal capacitances and resistances small enough to allow response in the desired frequency range (~30 THz) and yet capable of efficiently coupling to the incident radiation. It is crucial to keep the RC time constant of the tunnel junction small to achieve the requisite cut-off frequency and adequate rectification efficiency. Moreover, a low junction resistance is necessary to load the coupled AC power across the MIM junction. For energy harvesting applications, the device has to operate without an external bias, which requires asymmetry at the zero bias operation point. To address these requirements, the MIM tunnel junction is established so that one electrode has a field enhancing sharp tip (cathode) and the other is a rectangular patch. This asymmetric geometry not only offers asymmetric current-voltage behavior at the zero bias point, but also it decouples the junction resistance and capacitance by concentrating the charge transport in a small volume around the tip. Various fabrication methods are developed in order to create small junction area (= low parasitic capacitance), low junction resistance (= effective power coupling through antenna), asymmetry (= zero bias operation), high fabrication yield and low cost ACMIM tunnel diodes. High resolution fabrication needs are accomplished by electron beam lithography and nano-accuracy in the junction area is achieved by employing dose modifying proximity effect correction and critical alignment methods. Our Ni/NiOx/Ni ACMIM diodes with an optimized insulation layer created with O2 plasma oxidation are the most successful devices presented to date. A novel fabrication technique called "strain assisted self lift-off process" is used to achieve small junction area devices without relying on lithographic resolution. This technique eliminates the rival parasitic capacitance issue of today's ACMIM tunnel diodes and does not rely on extreme-high resolution lithography technologies

Layout regularity metric as a fast indicator of process variations

Integrated circuits design faces increasing challenge as we scale down due to the increase of the effect of sensitivity to process variations. Systematic variations induced by different steps in the lithography process affect both parametric and functional yields of the designs. These variations are known, themselves, to be affected by layout topologies. Design for Manufacturability (DFM) aims at defining techniques that mitigate variations and improve yield. Layout regularity is one of the trending techniques suggested by DFM to mitigate process variations effect. There are several solutions to create regular designs, like restricted design rules and regular fabrics. These regular solutions raised the need for a regularity metric. Metrics in literature are insufficient for different reasons; either because they are qualitative or computationally intensive. Furthermore, there is no study relating either lithography or electrical variations to layout regularity. In this work, layout regularity is studied in details and a new geometrical-based layout regularity metric is derived. This metric is verified against lithographic simulations and shows good correlation. Calculation of the metric takes only few minutes on 1mm x 1mm design, which is considered fast compared to the time taken by simulations. This makes it a good candidate for pre-processing the layout data and selecting certain areas of interest for lithographic simulations for faster throughput. The layout regularity metric is also compared against a model that measures electrical variations due to systematic lithographic variations. The validity of using the regularity metric to flag circuits that have high variability using the developed electrical variations model is shown. The regularity metric results compared to the electrical variability model results show matching percentage that can reach 80%, which means that this metric can be used as a fast indicator of designs more susceptible to lithography and hence electrical variations

Nanoshape imprint lithography : fabrication and modeling

Complex nanoshaped structures have been shown to enable emerging nanoscale applications in energy, electronics, photonics and medicine. Such nanoshaped fabrication at high throughput is well beyond the capabilities of advanced optical lithography. Even the highest resolution electron beam lithography processes (Gaussian beam tools with non-chemically amplified resists) can achieve only ~10nm resolution, but at very low throughputs. In this work, fabrication of precise diamond-like nanoshapes with ~3nm radius corners is demonstrated using nanoimprint lithography. An exemplary shaped silicon nanowire ultracapacitor device was fabricated with these nanoshaped structures, wherein the half pitch was 100nm. The device significantly exceeded standard nanowire capacitor performance (by 90%) due to relative increase in surface area per unit projected area, enabled by the nanoshape. In the process of further scaling these nanoshaped structures to 10nm half pitch and below, a new “shape retention” resolution limit is observed due to polymer relaxation in imprint resists, which cannot be predicted with a linear elastic continuum model. An all-atom molecular dynamics model of the nanoshape structure is developed to study this shape retention phenomenon and accurately predict the polymer relaxation. The atomistic framework has been used as a modeling and design tool to extend the capability of imprint lithography to sub 10nm nanoshapes. This framework can propose process refinements that maximize shape retention, and design template assist features (design for nanoshape retention) to achieve targeted nanoshapes.Mechanical Engineerin

Numerical Optical Centroid Measurements

Optical imaging methods are typically restricted to a resolution of order of the probing light wavelength $\lambda_p$ by the Rayleigh diffraction limit. This limit can be circumvented by making use of multiphoton detection of correlated $N$-photon states, having an effective wavelength $\lambda_p/N$. But the required $N$-photon detection usually renders these schemes impractical. To overcome this limitation, recently, so-called optical centroid measurements (OCM) have been proposed which replace the multi-photon detectors by an array of single-photon detectors. Complementary to the existing approximate analytical results, we explore the approach using numerical experiments by sampling and analyzing detection events from the initial state wave function. This allows us to quantitatively study the approach also beyond the constraints set by the approximate analytical treatment, to compare different detection strategies, and to analyze other classes of input states.Comment: 15 pages, 18 figure