Electron Quantum Tunneling Sensors

Quantum tunneling sensors are typically ultra-sensitive devices which have been specifically designed to convert a stimulus into an electronic signal using the wondrous principles of quantum mechanical tunneling. In the early 1990s, William Kaiser developed one of the first micromachined quantum tunneling sensors as part of his work with the Nasa Jet Propulsion Laboratory. Since then, there have been scattered attempts at utilizing this phenomenon for the development of a variety of physical and chemical sensors. Although these devices demonstrate unique characteristics such as high sensitivity, the principle of quantum tunneling often acts as a double-edged sword and is responsible for certain drawbacks of this sensor family. In this review, we briefly explain the underlying working principles of quantum tunneling and how they are used to design miniaturized quantum tunneling sensors. We then proceed to describe an overview of the various attempts at developing such sensors. Next, we discuss their current need and recent resurgence. Finally, we describe various advantages and shortcomings of these sensors and end this review with an insight into the potential of this technology and prospects.Comment: arXiv admin note: substantial text overlap with arXiv:2006.1279

Parametrically Amplified Low-Power MEMS Capacitive Humidity Sensor

We present the design, fabrication, and response of a polymer-based Laterally Amplified Chemo-Mechanical (LACM) humidity sensor based on mechanical leveraging and parametric amplification. The device consists of a sense cantilever asymmetrically patterned with a polymer and flanked by two stationary electrodes on the sides. When exposed to a humidity change, the polymer swells after absorbing the analyte and causes the central cantilever to bend laterally towards one side, causing a change in the measured capacitance. The device features an intrinsic gain due to parametric amplification resulting in an enhanced signal-to-noise ratio (SNR). 11-fold magnification in sensor response was observed via voltage biasing of the side electrodes without the use of conventional electronic amplifiers. The sensor showed a repeatable and recoverable capacitance change of 11% when exposed to a change in relative humidity from 25-85%. The dynamic characterization of the device also revealed a response time ~1s and demonstrated a competitive response with respect to a commercially available reference chip

Doctor of Philosophy

dissertationThis dissertation presents a new class of batch-fabricated, low-power and highly sensitive chemiresistive sensors. We first present the design, fabrication, and characterization of batch-fabricated sidewall etched vertical nanogap tunneling-junctions for bio-sensing. The device consists of two vertically stacked gold electrodes separated by a partially etched sacrificial spacer-layer of α-Si and SiO2. A ~10 nm wide air-gap is formed along the sidewall by a controlled dry etch of the spacer, whose thickness is varied from ~4.0 - 9.0 nm. Using these devices, we demonstrate the electrical detection of certain organic molecules from measurements of tunneling characteristics of target-mediated molecular junctions formed across nanogaps. When the exposed gold surface in the nanogap device is functionalized with a self-assembled monolayer (SAM) of thiol linker-molecules and then exposed to a target, the SAM layer electrostatically captures the target gas molecules, thereby forming an electrically conductive molecular bridge across the nanogap and reducing junction resistance. We then present the design, fabrication and response of a humidity sensor based on electrical tunneling through temperature-stabilized nanometer gaps. The sensor consists of two stacked metal electrodes separated by ~2.5 nm of a vertical air gap. Upper and lower electrodes rest on separate 1.5 μm thick polyimide patches. When exposed to a humidity change, the patch under the bottom electrode swells but the patch under the top electrode does not, and the air gap thus decreases leading to iv increase in the tunneling current across the junction. Finally, we present an electrostatic MEMS switch which is triggered by a very low input voltage in the range of ~50mV. This consists of an electrically conductive torsional see-saw paddle with four balanced electrodes. It is symmetrically biased by applying the same voltage at its inner electrodes leading to bistable behavior at flat or collapsed equilibrium positions. The use of elevated symmetric bias softens the springs such that the paddle collapses when a few milliVolts are applied to one of its outer electrodes thus causing the device to snap in and result in switch closure. Using the "spring softening" principle, we also present an application of a new kind of high sensitivity chemo-mechanical sensors

Nanostructures for Biosensing, with a Brief Overview on Cancer Detection, IoT, and the Role of Machine Learning in Smart Biosensors

Biosensors are essential tools which have been traditionally used to monitor environmental pollution and detect the presence of toxic elements and biohazardous bacteria or virus in organic matter and biomolecules for clinical diagnostics. In the last couple of decades, the scientific community has witnessed their widespread application in the fields of military, health care, industrial process control, environmental monitoring, food-quality control, and microbiology. Biosensor technology has greatly evolved from in vitro studies based on the biosensing ability of organic beings to the highly sophisticated world of nanofabrication-enabled miniaturized biosensors. The incorporation of nanotechnology in the vast field of biosensing has led to the development of novel sensors and sensing mechanisms, as well as an increase in the sensitivity and performance of the existing biosensors. Additionally, the nanoscale dimension further assists the development of sensors for rapid and simple detection in vivo as well as the ability to probe single biomolecules and obtain critical information for their detection and analysis. However, the major drawbacks of this include, but are not limited to, potential toxicities associated with the unavoidable release of nanoparticles into the environment, miniaturization-induced unreliability, lack of automation, and difficulty of integrating the nanostructured-based biosensors, as well as unreliable transduction signals from these devices. Although the field of biosensors is vast, we intend to explore various nanotechnology-enabled biosensors as part of this review article and provide a brief description of their fundamental working principles and potential applications. The article aims to provide the reader a holistic overview of different nanostructures which have been used for biosensing purposes along with some specific applications in the field of cancer detection and the Internet of things (IoT), as well as a brief overview of machine-learning-based biosensing

Voltage_Actuation_MP4.mp4

This video shows the tunable imaging through the VLCF lenses under varying external voltages