| Description |
This 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. |
