Design of chemoresistive silicon sensors for application in gas monitoring
Pike, Andrew Charles (1996) Design of chemoresistive silicon sensors for application in gas monitoring. PhD thesis, University of Warwick.
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Official URL: http://webcat.warwick.ac.uk/record=b1352685~S1
The growing concerns over our exposure to hazardous substances have been
addressed by stringent legislation to ensure air quality. A wide variety of applications
have therefore arisen which require the reliable detection of hazardous gases. Hence,
the motivation behind the research presented in this thesis was the aim of developing a
portable gas monitor to detect nitrogen dioxide, carbon monoxide and volatile organic
compounds (e.g. benzene, toluene). The need to improve gas sensor technology for
suitability to this demanding application has been identified. Thus, the objectives
were to develop a number of ultra-low power devices consisting of an array of
chemoresistive gas sensors for incorporation into an intelligent sensor system. The
operation of these sensors relies on the measurement of a change in resistance of a
gas-sensitive material when exposed to specific gases.
Silicon technology has been employed in order to obtain reproducible,
miniaturised sensors with a low unit cost. Furthermore, chemoresistors employing
metal oxide semiconductor (MOS), metal-substituted phthalocyanine (XPc) and
conducting polymer (CP) materials have been used because of their sensitivity to the
gases of interest.
Common problems associated with these materials are poor specificity to a target
gas and poor stability. However, the approach to minimising these problems was to
design arrays of cross-sensitive chemoresistors for use in a microprocessor-based
intelligent sensor system. The microprocessor applies a pattern recognition algorithm
to the sensor outputs to extract the required information. This thesis describes the
design, fabrication and characterisation of these sensor arrays.
MOS and XPc materials have shown an optimum performance at elevated
temperatures. Micromachining techniques have therefore been employed to integrate
resistance heaters in a micro-hotplate structure, which can allow temperatures of
600°C to be attained in —15 ms with a typical power consumption of —150
mW/sensor. A pulsed mode of operation should provide average power consumptions
of less than 1 mW. A low power consumption is critical for a portable batterypowered
instrument. The design, modelling and characterisation of the micro-hotplate
structures have also been described.
The design and development of a novel automated gas sensor test system was
also fundamental to this research, in order to accurately characterise sensor responses
and to validate theoretical models.
The research objectives have been fulfilled in that a number of sensor array
devices have been produced, which are suitable for a portable intelligent instrument.
The different designs and materials are compatible for integration into a hybrid sensor.
The advancements achieved in sensor technology provide a foundation for future
research into the production of a portable intelligent sensor system.
|Item Type:||Thesis or Dissertation (PhD)|
|Subjects:||T Technology > TP Chemical technology|
|Library of Congress Subject Headings (LCSH):||Gas detectors -- Design and construction|
|Official Date:||June 1996|
|Institution:||University of Warwick|
|Theses Department:||School of Engineering|
|Sponsors:||Great Britain. Health and Safety Executive (HSE) ; Engineering and Physical Sciences Research Council (EPSRC)|
|Extent:||xvi, 269 leaves|
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