Sense amplifiers are important circuit components of a dynamic random access memory (DRAM), which forms the main memory of digital computers. The ability of the sense amplifier to detect and amplify voltage signals to correctly interpret data in DRAM cells cannot be understated. The sense amplifier plays a significant role in the overall speed of the DRAM. Sense amplifiers require matched transistors for optimal performance. Hence, the effects of mismatch through process variations must be minimized. This thesis presents a research which leads to optimal nanoscale CMOS sense amplifiers by incorporating the effects of process variation early in the design process. The effects of process variation on the performance of a standard voltage sense amplifier, which is used in conventional DRAMs, is studied. Parametric analysis is performed through circuit simulations to investigate which parameters have the most impact on the performance of the sense amplifier. The figures-of-merit (FoMs) used to characterize the circuit are the precharge time, power dissipation, sense delay and sense margin. Statistical analysis is also performed to study the impact of process variations on each FoM. By analyzing the results from the statistical study, a method is presented to select parameter values that minimize the effects of process variation. A design flow algorithm incorporating dual oxide and dual threshold voltage based techniques is used to optimize the FoMs for the sense amplifier. Experimental results prove that the proposed approach improves precharge time by 83.9%, sense delay by 80.2% sense margin by 61.9%, and power dissipation by 13.1%.

Transmembrane protein ion channels can regulate intercellular transport in response to external stimulus, playing a vital role in diverse physiological functions. Replicating such stimulus-responsive behaviors in the artificial counterparts, e.g. solid-state nanopores, is of great interest in a variety of cross-disciplinary studies and applications, yet has remained challenging due to complicated structures of naturally occurring protein channels and anomalous transport phenomena of the nanoscale fluid. Current stimulus-responsive solid-state nanopores are achieved by employing functional materials and/or geometrical/surface charge asymmetry but suffer from low sensitivity, slow response, and limited reversibility. To tackle the existing challenges, this thesis investigates electromechanical coupled transport phenomena in a new type of stimulus-responsive nanopores, i.e., nanoparticle-blocked nanopores, and their potential applications in gating and sensing. The first part of this thesis describes a bio-inspired liposome-enabled nanopore gating strategy inspired by the ''ball-and-chain'' inactivation mechanism in voltage-gated protein ion channels. By manipulating the position of the liposome nanoparticles around the nanopore, we demonstrate an electromechanically gated nanopore with rapid, reversible, and complete gating response, which allows unprecedented spatial and temporal control of ion/chemical transport across the nanopore. In the second part of the thesis, we report an ultra-mechanosensitive ion transport across the single nanopore blocked by the rigid nanoparticles. The observed pressure-suppressed ion conduction partially mimics the behavior of stretch-inactivated ion channels and is rationalized with mechanical-induced particle motion. Finally, in the third part of the thesis, we further utilize the mechanosensitive ion conduction in nanoparticle-blocked nanopores to develop a nanopore-based platform for mechanical characterization of single nanoparticles. This new platform overcomes the limitations of current characterization techniques and provides an alternative nano-mechanical characterization approach in an efficient and cost-effective manner. We expect this work to provide a convenient platform to achieve natural stimulus-responsive functionalities as well as to develop emerging applications in drug delivery, biosensing, single-molecule manipulation, and ionic-based computation and storage. / 2024-01-25T00:00:00Z

Biological force microscopy (BFM) was developed to quantitatively measure pico- to nano-Newton forces (10-9 to 10-12 N) as a function of the nanoscale distance (nanometers) between living bacteria and mineral surfaces, in aqueous solution. Native cells were linked to a force-sensing probe, which was used in a force microscope to measure attractive and repulsive forces as a mineral surface approached, made contact with, and subsequently withdrew from a bacterium on the probe. The resulting data were used to interpret the interactive dynamics operative between bacteria and mineral surfaces under environmentally relevant conditions. BFM was used to study bacterial adhesion to mineral surfaces. In the case of Escherichia coli interactions with goethite, graphite, and muscovite, attractive and repulsive forces were detected at ranges up to 400 nanometers, the magnitude and sign depending on the ionic strength of the intervening solution and the mineral surface charge and hydrophobicity. Adhesion forces, up to several nanoNewtons in magnitude and exhibiting various fibrillation dynamics, were also measured and reflect the complex interactions of structural and chemical functionalities on the bacteria and mineral surfaces. In the study of Burkholderia cepecia interactions with mica, it was found that the physiological condition of the cell affected the observed adhesion forces. Cells grown under oligotrophic conditions exhibited an increased affinity for the mineral surface as opposed to cells grown under eutropic conditions. BFM was also used to characterize the transfer of electrons from biomolecules on Shewanella oneidensis to Fe(III) in the structure of goethite. Force measurements with picoNewton resolution were made in aqueous solution under aerobic and anaerobic conditions. Energy values (in attoJoules) derived from these measurements show that the affinity between S. oneidensis and goethite rapidly increases by two to five times under anaerobic conditions where electron transfer from bacterium to mineral is expected. Specific signatures in the force curves, analyzed with the worm-like chain model of protein unfolding, suggest that the bacterium recognizes the mineral surface such that a 150 kDa putative, iron reductase is quickly mobilized within the outer membrane of S. oneidensis and specifically interacts with the goethite surface to facilitate the electron transfer process. / Ph. D.

Transport phenomena at the nanoscale can differ from that at the continuum because the large surface area to volume ratio significantly influences material properties. While the modeling of many such transport processes have been reported in the literature, a few examples exist that integrate molecular approaches into the more typical macroscale perspective. This thesis extends the understanding of nanoscale transport governed by charge, mass and energy transfer, comparing these phenomena with the corresponding continuum behavior where applicable. For instance, molecular simulations enable us to predict the solvation structure around ions and describe the diffusion of water in salt solutions. In another case, we find that in the absence of interfacial effects, the stagnation flow produced by two opposing nanojets can be suitably described using continuum relations. We also examine heat conduction within solids of nanometer dimensions due to both the ballistic propagation of lattice vibrations in small confined dimensions and a diffusive behavior that is observed at larger length scales. Our simulations determine the length dependence of thermal conductivity for these cases as well as effects of isotope substitution in a material. We find that a temperature discontinuity at interfaces between dissimilar materials arises due to interfacial thermal resistance. We successfully incorporate these interfacial nanoscale effects into a continuum model through a modified heat conduction approach and also by a multiscale computational scheme. Finally, our efforts at integrating research with education are described through our initiative for developing and implementing a nanotechnology module for freshmen, which forms the first step of a spiral curriculum. / Ph. D.

An understanding of the fluid coupled dynamics of micro and nanotechnology has the potential to yield significant advances yet many open and interesting questions remain. As an important example we consider the coupling of two closely spaced cantilevers immersed in a viscous fluid subject to an external driving. While one cantilever is driven to oscillate, the adjacent cantilever is passive. This system is modeled as two simple harmonic oscillators in an array whose motion is coupled through the fluid. Using simplified geometries and the unsteady Stokes equations, an analytical expression is developed that describes the dynamics of the passive cantilever. Full numerical simulations of the fluid-solid interactions that include the precise geometries of interest are performed. The analytical expressions are compared with the numerical simulations to develop insight into the fluid-coupled dynamics over a range of experimentally relevant parameters including the cantilever separation and frequency based Reynolds number. In addition, a shaker-based actuation device is investigated in order to demonstrate its feasibility for use with micro and nanoscale systems. / Master of Science

When we stretch and contract a rubber band a hundred times, we expect the rubber band to fail. Yet our heart stretches and contracts the same amount every two minutes, and does not fail. Why is that? What causes the significantly higher elasticity of certain molecules and the rigidity of others? Equally importantly, can we use this information to design materials for precise mechanical tasks? It is the aim of this dissertation to illuminate key aspects of the answer to these questions, while detailing the work that remains to be done. In this dissertation, particular emphasis is placed on the nanoscale properties of elastomeric proteins. By better understanding the fundamental characteristics of these proteins at the nanoscale, we can better design synthetic rubbers to provide the same desired mechanical properties. / Ph. D.

Molecular Dynamics (MD) simulations of nano-scale flows typically utilize fixed lattice crystal interactions between the fluid and stationary wall molecules. This approach cannot properly model thermal interactions at the wall-fluid interface. In order to properly simulate the flow and heat transfer in nano-scale channels, an interactive thermal wall model is developed. Using this model, the Fourier’s law of heat conduction is verified in a 3.24 nm height channel, where linear temperature profiles with constant thermal conductivity is obtained. The thermal conductivity is verified using the predictions of Green-Kubo theory. MD simulations at different wall wettability ( εωf /ε ) and crystal bonding stiffness values (K) have shown temperature jumps at the liquid/solid interface, corresponding to the well known Kapitza resistance. Using systematic studies, the thermal resistance length at the interface is characterized as a function of the surface wettability, thermal oscillation frequency, wall temperature and thermal gradient. An empirical model for the thermal resistance length, which could be used as the jump-coefficient of a Navier boundary condition, is developed. Temperature distributions in the nano-channels are predicted using analytical solution of the continuum heat conduction equation subjected to the new temperature jump condition, and validated using the MD results. Momentum and heat transfer in shear driven nanochannel flows are also investigated. Work done by the viscous stresses heats the fluid, which is dissipated through the channel walls, maintained at isothermal conditions. Spatial variations in the fluid density, kinematic viscosity, shear- and energy dissipation rates are presented. The energy dissipation rate is almost a constant for εωf /ε < 0.6, which results in parabolic temperature profiles in the domain with temperature jumps due to the Kapitza resistance at the liquid/solid interfaces. Using the energy dissipation rates predicted by MD simulations and the continuum energy equation subjected to the temperature jump boundary conditions developed in this study, the analytical solutions are obtained for the temperature profiles, which agree well with the MD results.

It is widely recognized that device and interconnect fabrics at the nanoscale will be characterized by a higher density of permanent defects and increased susceptibility to transient faults. This appears to be intrinsic to nanoscale regimes and fundamentally limits the eventual benefits of the increased device density, i.e., the overheads associated with achieving fault-tolerance may counter the benefits of increased device density -- density-reliability tradeoff. At the same time, as devices scale down one can expect a higher proportion of area to be associated with interconnection, i.e., area is wire dominated. In this work we theoretically explore density-reliability tradeoffs in wire dominated integrated systems. We derive an area scaling model based on simple assumptions capturing the salient features of hierarchical design for high performance systems, along with first order assumptions on reliability, wire area, and wire length across hierarchical levels. We then evaluate overheads associated with using basic fault-tolerance techniques at different levels of the design hierarchy. This, albeit simplified model, allows us to tackle several interesting theoretical questions: (1) When does it make sense to use smaller less reliable devices? (2) At what scale of the design hierarchy should fault tolerance be applied in high performance integrated systems? In the second part of this thesis we explore perturbation-based computational models as a promising choice for implementing next generation ubiquitous information technology on unreliable nanotechnologies. We show the inherent robustness of such computational models to high defect densities and performance uncertainty which, when combined with low manufacturing precision requirements, makes them particularly suitable for emerging nanoelectronics. We propose a hybrid eNano-CMOS perturbation-based computing platform relying on a new style of configurability that exploits the computational model's unique form of unstructured redundancy. We consider the practicality and scalability of perturbation-based computational models by developing and assessing initial foundations for engineering such systems. Specifically, new design and decomposition principles exploiting task specific contextual and temporal scales are proposed and shown to substantially reduce complexity for several benchmark tasks. Our results provide strong evidence for the relevance and potential of this class of computational models when targeted at emerging unreliable nanoelectronics. / text

A computational analysis of a metamaterial window design is presented for the purpose of increasing the energy efficiency of buildings in seasonal or cold climates. Commercial low-emissivity windows use nanometer-scale Ag films to reflect infrared energy, while retaining most transmission of optical wavelengths for functionality. An opportunity exists to further increase efficiency through a variable emissivity implementation of Ag thin-film structures. 3-D finite-difference time-domain simulations predict non-linear absorption of near-infrared energy, providing the means to capture a substantial portion of solar energy during cold periods. The effect of various configuration parameters is quantified, with prediction of the net sustainability advantage. Metamaterial window glass technology can be realized as a modification to current, commercial low-emissivity windows through the application of nano-manufactured films, creating the opportunity for both new and after-market sustainable construction. / text

The establishment and maintenance of functional endothelial cells (ECs) on an engineered surface is central to tissue engineering. As the field advances, the role of cellular mechanisms, particularly the adhesive interaction between the surface of implantable devices and biological systems, becomes more relevant in both research and clinical practice. Knowledge of these interactions can address many fundamental biological questions and would provide key design parameters for medical implants. It has been shown that EC functionality and adhesivity, crucial for the re-endothelialization process, can be induced by nanotopographical modification. Therefore, the goal of this dissertation research was to develop an ensemble surface composing of nanoscale features for the enhancement of endothelial cell adhesion. Without adhesion, subsequent vital mechanism involved in cell alignment, elongation or spreading, proliferation, migration, and ECM proteins deposition will not occur.Experiments in support of this goal were broken down into three specific aims. The first aim was to characterize and develop a size-dependent self-assembly (SDSA) nanoarray of Octamer transcription factor 4 as a demonstration to the fabrication of nanoscale feature surface. This nanoparticle array platform was a pilot studied for the second aim, which was the development of an ensemble surface of nanoscale features for endothelial cell adhesion. The third aim was to evaluate and assess EC response to the ensemble surface.Hence, we developed an ensemble surface composed of nanoscale features and adhesive elements for EC adhesivity. By using shear stress as a detachment force, we demonstrated greater cell retention by the ensemble surface than uniform controls. Adhesive interactions and cellular migration through integrin expressions, which are critical to tissue development and wound healing process was also observed. Furthermore, cell viability was relatively sustainable, as indicated by the low expression of apoptotic signaling molecules. The findings presented within this dissertation research can be applicable to blood-contact medical implants and possess the potential for future clinical translation.