Nanoscale Field Emission Devices for High-Temperature and High-Frequency Operation

Citation

De Rose, Lucía Belén (2023) Nanoscale Field Emission Devices for High-Temperature and High-Frequency Operation. Dissertation (Ph.D.), California Institute of Technology. doi:10.7907/8qa5-kn97. https://resolver.caltech.edu/CaltechTHESIS:03312023-192646665

Abstract

Field emission—the quantum-mechanical tunneling of electrons from the surface of a material into vacuum by means of a strong electric field—has been studied for over a century. However, the usage of devices based on this mechanism has been limited to a handful of niche applications such as high-power RF systems and field emission displays. The preference for solid-state devices relies on their low cost, long lifetimes, reduced power consumption, ease of integrability, and simple and scalable fabrication. Nonetheless, with the advent of modern fabrication techniques, it has been possible to build field emission devices with nanoscale dimensions that offer several advantages over traditional semiconductor devices. The use of vacuum allows ballistic transport with no lattice scattering. As device capacitance can be engineered by tuning the geometry, these devices are appealing for high-frequency operation. Vacuum is also inherently immune to harsh operating conditions such as high temperature and radiation, which is desirable for aerospace, nuclear, and military applications. In addition, even though field emission requires substantial electric fields, by exploiting the nanoscale gaps that can be easily fabricated with state-of-the-art lithographic capabilities, we can expect operating voltages comparable to CMOS. Thus, vacuum emission devices have the potential to greatly improve upon the limitations of current technologies.

In this work, we experimentally demonstrate various design paradigms to develop nanoscale field emission devices for high-temperature environments and high-frequency operation. First, we propose suspended lateral two- and four-terminal devices. By removing the underlying solid substrate, we aim to increase the resistance of the leakage current pathways that emerge at elevated temperatures. Tungsten is the chosen electrode material due to its low work function and ability to withstand high temperatures. Our next architecture consists of a multi-tip two-terminal array, which exclusively relies on the inherent fast response of field emission. Due to the strong non-linearity in the emission characteristic, frequency mixing is measured. Lastly, we combine field emission with plasmonics to conceive devices that can be modulated both electrically and optically at telecommunication wavelength. By taking advantage of the strong confinement and significant optical field enhancement of surface plasmon polaritons, we seek to minimize the applied voltages required for field emission as well as the necessary laser powers for photoemission towards the development of high-speed, low-power, nanoscale optoelectronic systems.

Thesis Files