dc.description.abstract |
<p>Carbon nanotubes (CNTs) have recently emerged as promising candidates for electron
field emission (FE) cathodes in integrated FE devices. These nanostructured carbon
materials possess exceptional properties and their synthesis can be thoroughly controlled.
Their integration into advanced electronic devices, including not only FE cathodes,
but sensors, energy storage devices, and circuit components, has seen rapid growth
in recent years. The results of the studies presented here demonstrate that the CNT
field emitter is an excellent candidate for next generation vacuum microelectronics
and related electron emission devices in several advanced applications.</p><p>
The work presented in this study addresses determining factors that currently confine
the performance and application of CNT-FE devices. Characterization studies and improvements
to the FE properties of CNTs, along with Micro-Electro-Mechanical Systems (MEMS) design
and fabrication, were utilized in achieving these goals. Important performance limiting
parameters, including emitter lifetime and failure from poor substrate adhesion, are
examined. The compatibility and integration of CNT emitters with the governing MEMS
substrate (i.e., polycrystalline silicon), and its impact on these performance limiting
parameters, are reported. CNT growth mechanisms and kinetics were investigated and
compared to silicon (100) to improve the design of CNT emitter integrated MEMS based
electronic devices, specifically in vacuum microelectronic device (VMD) applications.</p><p>
Improved growth allowed for design and development of novel cold-cathode FE devices
utilizing CNT field emitters. A chemical ionization (CI) source based on a CNT-FE
electron source was developed and evaluated in a commercial desktop mass spectrometer
for explosives trace detection. This work demonstrated the first reported use of a
CNT-based ion source capable of collecting CI mass spectra. The CNT-FE source demonstrated
low power requirements, pulsing capabilities, and average lifetimes of over 320 hours
when operated in constant emission mode under elevated pressures, without sacrificing
performance. Additionally, a novel packaged ion source for miniature mass spectrometer
applications using CNT emitters, a MEMS based Nier-type geometry, and a Low Temperature
Cofired Ceramic (LTCC) 3D scaffold with integrated ion optics were developed and characterized.
While previous research has shown other devices capable of collecting ion currents
on chip, this LTCC packaged MEMS micro-ion source demonstrated improvements in energy
and angular dispersion as well as the ability to direct the ions out of the packaged
source and towards a mass analyzer. Simulations and experimental design, fabrication,
and characterization were used to make these improvements.</p><p> Finally, novel
CNT-FE devices were developed to investigate their potential to perform as active
circuit elements in VMD circuits. Difficulty integrating devices at micron-scales
has hindered the use of vacuum electronic devices in integrated circuits, despite
the unique advantages they offer in select applications. Using a combination of particle
trajectory simulation and experimental characterization, device performance in an
integrated platform was investigated. Solutions to the difficulties in operating multiple
devices in close proximity and enhancing electron transmission (i.e., reducing grid
loss) are explored in detail. A systematic and iterative process was used to develop
isolation structures that reduced crosstalk between neighboring devices from 15% on
average, to nearly zero. Innovative geometries and a new operational mode reduced
grid loss by nearly threefold, thereby improving transmission of the emitted cathode
current to the anode from 25% in initial designs to 70% on average. These performance
enhancements are important enablers for larger scale integration and for the realization
of complex vacuum microelectronic circuits.</p>
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