Publication: The development of porcine biosensor using self limiting oxidation - atomic force microscope lithography
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Date
2023-08-01
Authors
Nurain Najihah Binti Alias
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Abstract
Silicon nanowires have been studied as biosensor due to excellent in detection
of biological molecules. Silicon nanowire biosensor has a huge amount of potential to
contribute to the field of biosensor for detecting deoxyribonucleic acid (DNA)
molecules due to its distinctive electrical and nanostructure morphological qualities.
In this research, silicon nanowires were fabricated using atomic force microscopy –
local anodic oxidation (AFM-LAO) via top-down approach. AFM-LAO lithography
is a non-destructive technique that provides precise and accurate patterning of
nanoscale features without damaging the underlying material. According to prior
research, the fabricated silicon sub-micron wires via AFM-LAO produced large range
of width. The width of silicon nanowires was scaled down by using self-limiting
oxidation (SLO) process to achieve the smallest possible width was studied. Firstly,
silicon nanowire device was fabricated on p-type silicon-on-insulator (SOI) wafer via
AFM-LAO and important parameters during AFM-LAO process was obtained. The
obtained results indicate that the oxide patterns fabricated using Au-coated cantilever
tip at 0.3 µm/s of writing speed and 9 V of applied voltage produce good structure of
oxide patterns. Therefore, the AFM-LAO optimized parameter was used to fabricated
oxide pattern for 5-wires, 10-wires, short-wires and long-wires devices. Then, the
oxide patterns undergo silicon wet etching using the mixture of tetramethylammonium
hydroxide (TMAH) with and without admixture of Triton X-100 and isopropyl alcohol
(IPA) to etch the silicon layer. The surface roughness and wetting behaviour of APTES
on etched SOI wafer was considered. The study found that the combination of the
ternary solution, TMAH + Triton X-100 + IPA produced the lowest surface roughness
which was 2.068 x 10-1 nm. It was also observed that, wetting behaviour of APTES on
lowest surface roughness etched SOI wafer produced the most hydrophilic effect on
the surface with 19.78 ° of contact angle. The hydrophilic behaviour of the SOI wafer
indicates the presence of a high density of OH groups on its surface, facilitating the
formation of hydrogen bonds with other molecules. This characteristic indirectly
contributes to the more effective detection of porcine DNA in the biosensor. The
silicon nanowires were then proceeded with the SLO process to reduce the width of
fabricated silicon nanowire. The temperature, soaking time, gas flow rate and number
of SLO cycles was investigated. The 1000 °C of temperature with three cycles of SLO
removed the most oxide layer after oxide etching. Therefore, 1000 °C of temperature
with three cycles of SLO was applied on fabrication of 5-wires, 10-wires, short-wires
and long-wires devices. Lastly, silicon nanowire devices were functionalized with 3-
aminopropyltriethoxysilane (APTES), glutaraldehyde and amine-terminated DNA to
detect porcine DNA. The current-voltage (I-V) characteristics of devices were
measured by using semiconductor parameter analysis (SPA) to investigate the device
performance based on number of wires and length of wires. For different number of
wires, device with 10-wires device obtained the highest sensitivity, 91.93 µAM-1 with
4.12 fM of LOD. While for different length of wires, short-wires device gained the
highest sensitivity, 90.80 µAM-1 with 4.44 fM of LOD