Randomized Network of Single Walled Carbon Nanotubes Thin Film Transistor: Fabrication, Simulation and Application as Biosensor
Abstract
Nanoelectronic devices based on nanomaterials, such as carbon
nanotubes (CNTs) have attracted remarkable attention as a promising
building block for future nanoelectronic circuits due to their
exceptional electrical, mechanical and chemical characteristics. The
electrical characteristics of CNTs, such as high mobility, quasiballistic
conductance and resistance against electromigration, allow to
surpass the properties of current Si based complementary metal oxide
semiconductor (CMOS) devices. In particular, the large surface area
and nanoscale structure makes SWCNTs promising candidates for
chemical and biological sensing applications as well. Current research
covers broad scientific fields, such as study of materials properties at
nanoscale, development, fabrication and simulation of nanoscale
structures, for electronics and biomedical applications. However, there
is ample space for advancements in both theoretical studies and
practical applications for CNT-based systems.
This thesis addresses the design and manufacture of thin film
transistor (TFT) based on randomized network of single walled carbon
nanotubes (SWCNTs) that exploit the unique properties of such
materials to create a label-free biosensor for detection of variety
biomolecules, particularly proteins. In addition, in order to analyze the
electric transport of SWCNTs network in the TFT channel a numerical
3-dimensional (3D) model for the thin film layer is developed.
The SWCNTs-TFTs are fabricated by using microfabrication to
obtain a micro-interdigitated electrode (μ-IDE) as drain-source
electrode. The sizes vary between 2 to 50 μm. Thin-film transistors
(TFTs) are fabricated by using SWCNTs thin film as the
semiconducting layer and SiO2 thin film as the dielectric layer. The
high purity semiconducting network of SWCNTs layer is deposited
with an effective technique that combines the silanization of the
substrate with vacuum filtration process from dispersed SWCNTs in
surfactant solution. . The adopted technique provides a low-cost, fast,
simple, and versatile approach to fabricate high-performance
SWCNTs-TFTs at room temperature. The morphological arrangement
of SWCNTs forming the active layer in the channel of the transistor is
checked with scanning electron microscopic (SEM). The TFTs
obtained exhibit p-type transistor characteristics and operate in
2
accumulation mode. The results are interpreted by considering the
percolation theory. The exponent a of the power law describing the
conductivity can be linked to the structural complexity of the SWCNT
network. In particular an exponent = 1.7 was found experimentally,
showing that the obtained thin film is relatively dense and near
percolation. In addition, the experimental data have been compared
with the results of the 3D model simulating the charge transport in the
SWCNT structures formed in the TFT channel. The simulation results
lead to an exponent = 1.8 that is in good agreement with the
experimental data. The proposed model seems to be able to reliably
reproduce the transport characteristics of the fabricated devices and
could be an effective tool to improve the SWCNTs-TFTs structure.
Moreover, the fabricated SWCNTs-TFT devices provide a suitable
platform for high-performance biosensors in label-free protein
detection. The sensing mechanism is demonstrated on a proof of
principle level for the interaction of biotin and streptavidin on the
SWCNTs surface. It is used as a research model for biosensor
application. The SWCNTs thin-film biosensor has high sensitivity and
it is capable of detecting streptavidin at concentration of 100 pM. [edited by author]