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Asic gas sensors based on ratiometric principles
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Khawaja, Jaleed Ejaz (2009) Asic gas sensors based on ratiometric principles. PhD thesis, University of Warwick.
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Official URL: http://webcat.warwick.ac.uk/record=b2282594~S9
Abstract
The wide-scale usage of VOCs in industrial processes requires monitoring the
concentrations of these vapours to keep a safe operating environment. Most combustible
hydrocarbons can be ignited as a gas-air mixture in the range of 0.5% to 15% by
volume. This has led to the development of several portable air quality monitoring
instruments. However, the high costs and lack of durability of these instruments has
remained an issue to be addressed. This PhD thesis reports on the development and
characterization of a novel low cost smart gas sensor technology adaptable for use in a
portable instrument. The smart gas sensor devices have been developed to target four
different VOCs in air.
The smart gas sensor device combines a smart ASIC (SRL 194 designed at
SRL, Warwick University) fabricated in standard 0.7 μm CMOS technology and two
alkyl-dithiol based self-assembled gold nanoparticle chemoresistive sensors (fabricated
at Sony Deutschland GmbH) in a ratiometric array to offer a robust system which can
address the common mode variations found in polymer based gas sensor systems. The
ratiometric ASIC sensor array architecture allows for the reduction of the baseline
value’s dependence on environmental variations and the elimination of baseline drift
due to long term application of DC voltage.
Three ratiometric array arrangements - mono-type uni-variate with only one
chemosensor per device, mono-type bi-variate with two chemosensors of the same film
material per device and duo-type with a polar and a non-polar chemosensor per device
and their variations were characterized in an automated FIA test station against
exposure to methanol, ethanol, propan-1-ol, and toluene at 30°C and 0-5% rh. It was
determined that the devices’ response output to VOC analytes was entirely dependent
on the variation of the resistance ratio of the chemoresistive sensors in the ratiometric
sensor array. The effects of variations of the temperature and rh on the smart sensor
output were calibrated. The mono-type devices gave a high magnitude response to the
vapours whereas the duo-type arrangement offered a high degree of discrimination
between the test analytes with little post-processing steps.
Three different alkyl-dithiol chemoresistive sensor films on gold electrodes
were successfully used as the VOC vapour sensitive elements in each arrangement. The
effects of using a silicone sealant gel as a partitioning layer were characterized and it
was observed that at vapour concentrations less than 3000 ppm the silicone
encapsulated chemosensor devices reported a larger response to the VOC analytes as
compared to those without the silicone. The test devices reported promising response
repeatability and reproducibility with excellent return to baseline properties, a negligible
hysteresis and an error margin of under 10%. Ideal operating temperature was
determined to be 40°C at which rh variations were found to be minimal. The test
devices were found to be robust with little variation in the quality of the device output
over the course of 18 months.
The novel research demonstrated that it is possible to get high level of
diversification between analytes from a low cost and robust gas sensor system for
monitoring VOCs. The work carried out here has opened the opportunity to develop
highly integrated programmable hand-held gas sensor and e-nose systems for
environmental monitoring use in health and safety applications.
Item Type: | Thesis (PhD) | ||||
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Subjects: | T Technology > TP Chemical technology | ||||
Library of Congress Subject Headings (LCSH): | Volatile organic compounds, Chemical detectors, Gas detectors | ||||
Official Date: | April 2009 | ||||
Dates: |
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Institution: | University of Warwick | ||||
Theses Department: | School of Engineering | ||||
Thesis Type: | PhD | ||||
Publication Status: | Unpublished | ||||
Supervisor(s)/Advisor: | Gardner, J. W. (Julian W.), 1958- | ||||
Description: | This is an abridged version for electronic use; lacks Appendix C, Eurosensors XX Conference Paper (Khawaja, J.E., Cole, M. and Gardner, J.W. (2006). Gold nanoparticle CMOS sensor of VOC detection. Eurosensors XX Conference, Göteborg, Sweden, 17-20 September, 2006.) |
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Format of File: | |||||
Extent: | 224 leaves : ill., charts | ||||
Language: | eng |
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