Graduation Semester and Year

2013

Language

English

Document Type

Dissertation

Degree Name

Doctor of Philosophy in Electrical Engineering

Department

Electrical Engineering

First Advisor

Zeynep Celik-Butler

Abstract

Nanoimprint lighography (NIL) is emerging as a viable contender for fabrication of large-scale arrays of 5-500 nm features. The work presented in this dissertation aims to leverage the advantages of NIL for realization of novel Nano Electro Mechanical Systems (NEMS). The first application is a nanoporous membrane blood oxygenator system. A fabrication process for realization of thin nanoporous membranes using thermal nanoimprint lithography is presented. Suspended silicon nitried membranes were fabricated by Lowe-Pressure Chemical Vapor Deposition (LPCVD) in conjunction with a potassium hydroxide-based bulk michromachining process. Nanoscale features were imprinted into a commercially available thermoplastic polymer resist using a prefabricated silicon mold. The pattern was reversed and transferred to a thin aluminum oxide layer by means of a novel two stage lift-off technique. The pattern aluminum oxide was used as an etch mask in a CHF3/He based reactive ion etch process to transfer the pattern to silicon nitride. Highly directional etch profiles with near vertical sidewalls and excellent Si3N4/Al2O3 etch selectivity was observed. One-micrometer-thick porous membranes with varying dimensions of 250x250 um2 to 450x450 um2 and pore diameter of 400 nm have been engineered and evaluated. Results indicate that the membranes have consistent nanopore dimensions and precisely define porosity, which makes them ideal as gas exchange interfaces in blood oxygenation systems as well as other applications such as dialysis. Additionally, bulk - micromachined microfluidic channels have been developed for uniform, laminar blood flow with minimal cell trauma. NIL has been used for ordered growith of crystalline nanostructures for sensing and energy harvesting. Highly ordered arrays of crystalline ZnO nanorods have been fabricated using a polymer template patterned by thermal nanoimprint lithography, in conjuction iwth a low temperature hydrothermal growth process. Zinc Oxide nanorods were characterized to determine their piezoelectric response to an applied force. An atomic force microscope operating in the force spectroscopymode was used to apply forces in the nN range. In contrast to previously published reports using lateral tip motion (C-AFM), the action of the tip in our experiment was perpendicular to the plane of the nanorods, allowing a more defined tip-nanorod interaction. Voltage pulses of a positive polarity with amplitude ranging from hundreds of uV to few mV were observed. The tip - nanorod interaction was modeled using commercial soid modeling software and was simulated using finite element analysis. Comparison of the results yielded useful observations for design of piezoelectric energy harvesters/sensors suing ZnO nanorods. A nanoelectromechanical (NEMS) piezoelectric energy harvester suing crystalline ZnO nanowires developed. The device converst ambient vibrations into usable electrical energy for low power sensor applications. This is accomplished by mechanical excitation of an ordered ZnO nanorod array using a suspended buld micromachined proof mass. The device is capable of generating up to 14.2 mV single polarity voltage under an input vibration of amplitude 1 g (9.8 m/s2) at a frequency of 1.10 KHz. Finally, large area arrays of ordered ZnO piezoelectric nanorods are developed on flexible substrates towards self-powered sensing skin for robots. The sensor array is designed to measure tactile pressure in the 10 kPa - 200 kPa range with 1 mm spatial resolution. A voltage signal in the range of few mV is observed in response to applied pressure. This work represents the first demonstration of perfectly oredered, vertically aligned, crystalline ZnO nanorod arrays, fabricated in polyimides to ensure conformity to non-planar surfaces such as a robot's. The sensors are self-packaged using a flexible substrate and a superstate. in addition to the novelty of the sensor structure itself, the work includes an innovative low-temperature hydrothermal ZnO growth process compatible with the temperature restrictions imposed by the polyimide substrate/superstrate.

Disciplines

Electrical and Computer Engineering | Engineering

Comments

Degree granted by The University of Texas at Arlington

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