Date of Completion

12-12-2014

Embargo Period

12-12-2014

Major Advisor

Brian G. Willis

Associate Advisor

Ranjan Srivastava

Associate Advisor

Yu Lei

Associate Advisor

C. Barry Carter

Associate Advisor

Helena Silva

Field of Study

Chemical Engineering

Degree

Doctor of Philosophy

Open Access

Campus Access

Abstract

Nanogap electrodes are important elements in fabrication process of many nanoscale electronic devices. However, the conventional methods to make nanogap electrodes have not progressed beyond lab scale studies due to obstacles in process reliability, system integration and scale-up, and definitive process economics. In this work, we have introduced a novel methodology to develop nanogap electrodes through selective-area copper atomic layer deposition (ALD). To optimize this approach, the fundamentals of the ALD process have been investigated using a suite of in-situ and ex-situ characterization techniques. The sub-monolayer adsorption and desorption steps in ALD process has been resolved by in-situ real time spectroscopic ellisometry (RTSE), based on which a new mechanism of copper ALD on palladium has been proposed.

To realize the ultimate adoption of copper ALD in nanogap electrodes fabrication, one critical requirement is good selectivity on different materials. The selectivity of copper ALD process on palladium versus silicon dioxide has been investigated by in-situ quartz crystal microbalance (QCM), scanning electron microscope (SEM), energy-dispersive x-ray spectroscopy (EDX), and x-ray photoelectron spectroscopy (XPS). It has been found that the selectivity of copper ALD depends on deposition temperature and hydrogen partial pressure, based on which a selectivity window has been established. These fundamental studies eventually allows for a controlled and selective copper ALD process to be established for making nanogap electrodes.

Furthermore, this work has shed new insight on designing a tunnel-electrodes/nanopore device for next generation DNA sequencing technology. In such a device, nanopore acts as the channel for DNA translocation and nanogap electrodes act as the sensors to sequence DNA. We have developed an approach to fabricate the device using a combination of lithography techniques and the selective copper ALD. Electrodes with sub-10 nm have been accomplished. Electrical measurements of the fabricated device show tunneling current characteristics, which imply that sub-2 nm nanogap has been achieved. The nanogap electrodes device has been tested to be of negligible leakage current, and compatible with liquid phase environment, which is important for further DNA sequencing. Fabrication of nanogap electrodes by selective ALD would eventually enable widespread adoption of this technology in more nano-patterning productions.

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