Defense Date

2024

Document Type

Dissertation

Degree Name

Doctor of Philosophy

Department

Electrical & Computer Engineering

First Advisor

Vitaliy Avrutin

Abstract

Nanofabrication technology, especially nanopatterning, is a rapidly advancing field that has already resulted in creating novel devices and holds promise for producing even more with unmatched performance. These techniques also allow us to gain insight into physical phenomena at the micro- and nanoscale. The ultimate performance of nanofabricated devices and their compatibility with existing Si-based CMOS technology hinge upon the careful selection of materials and precise design, coordinated with meticulous pattern transfer. In this work, we applied nanopatterning techniques on silicon to create optical filters for the shortwave infrared (SWIR) region and nanoelectromechanical system (NEMS) relay-based logic gates. Additionally, these techniques were employed to investigate the factors constraining the operation and performance of NEMS devices. Single-crystal Si possesses mechanical robustness, chemical stability, and optical transparency in the SWIR and beyond. Its relatively high refractive index (~3.48) enables tight light confinement, enhancing light-matter interactions upon the creation of gratings in a thin Si film. Chemical compounds exhibit a spectral response composed of a series of narrow lines, which can serve as their fingerprint. Subwavelength gratings formed in Si-on-insulator, facilitating guided-mode resonance (GMR), can produce narrow linewidth transmission spectra valuable for spectral imaging of various chemical compounds which has wide range of applications including mineralogy, agriculture, object detection, food inspection, and surveillance to name a few. Conventional GMR transmission filter designs, based on a single ridge per period, necessitate multiple etching/fabrication steps for implementing an array of filters with different transmission bands on the same substrate. To address this problem, dual-period narrow linewidth GMR filters Page- 6 (based on two ridges per period) that offer more degrees of freedom for tuning the filter characteristics have been demonstrated. This design provides a two-prong benefit: it allows achieving (1) wider stop bands without changing the grating height and thus (2) requires a single nanopatterning step. A set of six dual-period transmission GMR filters with well-separated pass bands in the SWIR region (1200-1600 nm) were designed using COMSOL Multiphysics® simulation software and produced on the same silicon-on-quartz wafer in a single fabrication run. The 90 μm x 90 μm size filters exhibited passbands as narrow as 15 nm with peak-wavelength tunability over 200 nm, flat stopbands as wide as ~350 nm, and peak transmittance reaching 87%. Furthermore, it was shown experimentally that these transmission filters can be miniaturized to a size of 10 μm × 10 μm, while preserving transmittance of > 65% and linewidth of ~26 nm, which enables their integration into current focal plane arrays with a typical pixel size of 10 μm × 10 μm. NEMS relays is another area poised to benefit from advanced nanofabrication. Despite their vast range of potential applications, several failure mechanisms including stiction in the contact area, and arc-discharge leading to contact degradation and even contact welding limit their operational lifetime. In this thesis, a method for measuring stiction force is presented using in-plane electrostatically actuated Si NEMS cantilever relays with Pt contacts. The stiction force is determined using the actuation voltage hysteresis curves, the cantilever displacement information from COMSOL Multiphysics simulations, and force distribution obtained from an analytical model. It is shown that drain current and contact resistance strongly influence stiction, primarily due to metallic bonding forces which occur due to electron exchange between two metallic bodies. Consequently, the stiction force can be tuned by adjusting the current flow through the contact. In addition, stiction-related failures can be mitigated through design modifications such as increasing the cantilever width and using a flexible electrode (drain). To gain insight into the physics of arc Page- 7 discharge, nanostructures with precise control over the gap between electrodes with nanometer precision are produced, enabling experiments to quantify the electric arc discharge voltage in air for nanoscale gaps. Finally, implementation (fabrication and electrical operation) of NEMS-based logic gates, including complementary inverters, NOR/OR, and NAND/AND logic operations, are demonstrated.

Rights

© The Author

Is Part Of

VCU University Archives

Is Part Of

VCU Theses and Dissertations

Date of Submission

5-10-2024

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