| dc.description.abstract |
<p>With the advent of the internet-of-things (IoT) and a more connected digital ecosystem,
new electronic sensors and systems are needed. Printing has been identified as a means
of fabricating low-cost electronics on non-rigid, large-area substrates. Printed
electronics have been demonstrated to have the required electrical and mechanical
properties to facilitate new and unique flexible electronic sensors for the IoT. One
printable material that has demonstrated significant promise, specifically when compared
to more traditional printed semiconductors, is solution-processed carbon nanotubes
(CNTs). While some work has been done to facilitate the fabrication of CNT thin-film
transistors (TFTs), little work has been done to assess the viability and potential
of CNT-TFTs and other CNT thin films for real-world sensing applications. </p><p>The
work contained in this dissertation describes the use of aerosol jet printing to fabricate
CNT-TFTs, and the resulting study of their capability for various sensing applications.
Aerosol jet printing allows for printing all the materials necessary for a fully-functional
CNT-TFT, including the semiconducting thin film, conducting contacts and gate, and
insulating gate dielectric. Using this system, flexible and fully printed CNT-TFTs
were developed and characterized. Fully printed transistors were fabricated with
field-effect mobilities as a high as 16 cm2/(Vs). The transistors were also resilient
to substantial bending/strain, showing no measurable performance degradation after
1000 bending cycles at a radius of curvature of 1 mm. </p><p>The printed CNT-TFTs
were evaluated for several sensing applications, including environmental pressure
sensing and point-of-care biological sensing. The biological sensors, which were electronically
transduced immunoassays, consisted of an antifouling polymer brush layer to enhance
the CNT-TFT sensitivity and printed antibodies for detection of target analytes.
Unparalleled sensitivity in unfiltered biological milieus was realized with these
printed biosensors, detecting protein concentrations as low as 10 pg/ml in whole blood.
In addition to demonstrating an electronically transduced TFT-based biosensor, work
was done to develop a stable platform with high yield that will provide the means
for a deeper understanding of the biosensing mechanisms of transistor-based sensors.
As part of this biosensor platform development, novel solution-gated CNT-TFTs were
demonstrated, with stable operation in ionic solutions for periods as long as 5 hours.
</p><p>Another important electronic sensing technique is capacitive-based sensing.
Using aerosol jet printed carbon nanotubes, a capacitive sensor has been developed
and demonstrated for measuring insulating material thickness. The sensors rely on
the fringing field between two adjacent electrodes interacting with the material out-of-plane,
and that interaction being perturbed differently based on the thickness of the overlaid
material. This sensor was also demonstrated in a one-dimensional array, which can
be used to map tire tread thickness from the outside of the tire.</p><p>Overall, this
dissertation explores the use of printed carbon nanotubes for diverse sensing applications.
While this work provides real-world demonstrations that have potential impact for
the IoT, there are also substantial scientific advancements made. Namely, insight
into biosensing mechanisms, operation of solution-gated nanomaterial-based transistors,
and demonstration of porosity and thickness effects on printed capacitive sensor electrodes.</p>
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