There is great need for the widespread use of indoor gas monitors as modern hermetically-sealed domestic buildings increasingly suffer from indoor air pollution. However, neither modern technologies of gas sensors nor analytical instruments are ideally suited to this purpose. The problems of gas sensors are poor selectivity and the fact that normally they can detect only one gas, and analytical instruments suffer from their large size and high price. Therefore, the aim of the project is "to develop a novel gas sensor with low cost, low power consumption, high reliability, which can detect multiple gases with excellent selectivity" for indoor gas monitoring. In the first part of the project, an SOI-CMOS micro-hotplate with a single crystal silicon (SCS) resistive heater was proposed, fabricated and characterised. The design obviates issues of traditional heater materials i.e. platinum is not CMOS compatible and polysilicon is not thermally stable due to its polycrystalline structure. The SCS micro-hotplate was found to have an ultra low power consumption of 11.6 mW to operate at 500°C, and an excellent reliability with less than 1% drift after 500 hour operation at 500°C. In the second part, a novel temperature modulation technique for a carbon black/polymer composite sensor was theoretically derived based upon linear solvation and Fickian diffusion. The processing technique comprises only two steps; summing the off and on transient conductance signals from a temperature-stepped sensor, and subtracting the steady-state signal. The technique was demonstrated by applying to a carbon black/polyvinylpyrrolidone composite sensor employing the novel micro-hotplate. Identification of water. methanol and ethanol vapours was successfully demonstrated using the peak time of the resultant curve. Furthermore, quantification of those vapours was found to be possible using the height of the peaks, which was linearly proportional to the concentration. In conclusion, a novel low-cost gas sensor has been realised that is capable of detecting more than one gas with a single sensing element and thermal modulation. This has the potential for commercial exploitation in the area of indoor air pollution monitoring.
| Identifer | oai:union.ndltd.org:bl.uk/oai:ethos.bl.uk:487908 |
| Date | January 2007 |
| Creators | Iwaki, Takao |
| Publisher | University of Warwick |
| Source Sets | Ethos UK |
| Detected Language | English |
| Type | Electronic Thesis or Dissertation |
| Source | http://wrap.warwick.ac.uk/89582/ |
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