Applications of semiconductor gas sensors

Applicability of Semiconductor Gas Sensors Research into the applications of this type of sensor has mainly been concerned with measuring carbon monoxide concentration in flue gases. Tests show that sensors follow the concentration of carbon monoxide in the flue gas. Improvement in sensor performance has resulted with the introduction of a catalytic additive (palladium or... 

The application of semiconductor gas sensors (mainly the Sn02 sensor) is ever expanding into various fields, domestic and industrial, as shown in Figure 3. Examples are the CO selective sensor and combustion monitor sensor, which are applicable to micro wave ovens or ventilation fans, kerosene or gas stoves, hot water supply systems, and so on. 

Ishibashi, N. and Kaneyasu, K. (2009), Development and application of semiconductor gas sensor using MEMS technology , presented at 3rd GOSPEL Workshop Gas Sensors Based on Semiconducting Metal Oxide - New Directions,Tnbmgen, Germany, November 30-December 1,2009. 

In 1967 both Shaver [24] and Loh [25] described effects achievable with oxide semiconductors modified by the addition of noble metals (e.g.. Pt, Pd, Ir, Rh), and since that time the sensitivity and selectivity of semiconductor sensing devices has been significantly enhanced. Intense efforts in this direction, coupled with the further addition of metal oxides [26]-[28], resulted in widespread application of semiconductor gas sensors beginning in the 1970s. 

Thus, the major conclusions of tiie early studies by Volkenshtein and his colleagues applicable to the theory of the method of semiconductor gas sensors are the following a) chemisorption of particles on a semiconductor surface can be accompanied by a charge transfer between adsorption-induced surface levels and volume bands of adsorbent and b) only a certain fraction of absorbed particles is charged, the fraction being dependent on adsorbate and adsorbent. 

The experimental studies of the surface properties of monocrystals of oxides of various metals recently conducted at well-controlled conditions [32, 210] enable one to proceed with detailed analysis of separate effects of various factors on characteristics of semiconductor gas sensors. In this direction numerous interesting results have been obtained regarding the fact of various electrophysical characteristics of monocrystalline adsorbents on the value of adsorption-related response. Among these characteristics there are crystallographic orientation of facets [211], availability of structural defects, the disorder in stoichiometry [32], application of metal additives, etc. These results are very useful while manufacturing sensors for specific gases with required characteristics. 

More recently inks specifically developed for sensor applications have become available, for example Sn02 pastes incorporating Pt, Pd, and Sb dopants for the construction of semiconductor gas sensors. For biosensor applications, thick-film technology based on polymer films is extremely important, and special grades of polymer pastes (carbon, Ag, and Ag/AgCl) are becoming available... 

Yajima T, Kdde K, Takai H, Fukatu N, Iwahara H (1995) Application of hydrogen sensor using proton conductive ceramics as a solid electrolyte to aluminum casting industries. Solid State Ionics 79 333-337 Yamazoe N (1991) New approaches for improving semiconductor gas sensors. Sens Actuators B 5 7-19 Yamazoe N, Miura N (1992) Some basic aspects of semiconductor gas sensors. In Yamauchi S (ed) Chemical sensors technology, vol 4. Kodansha/Elsevier, Tokyo/Amsterdam, pp 20-41 Yamazoe N, Kurokawa Y, Seiyama T (1983) Effects of additives on semiconductor gas sensors. Sens Actuators 4 283-289... 

FIS, MICS, CityTech, AppliedSensor, UST, Microsens and Paragon [44-48]. In addition, since they were used in the automotive applications (indoor air quality control), one can say that they became relevant for mass-market applications [23], Examples of semiconductor gas sensors are shown in Figure 22.3 where commercial available sensors are present together with actual research prototypes. 

From the above-given condensed review of the EEP detection methods one can infer that none of these methods can independently satisfy all the requirements specified for the study of heterogeneous processes involving the EEP participation. To our opinion, the application of semiconductor sensors for detection of EEPs can be provided by a combination of required qualities. The sensors are highly sensitive, miniature, can be operated within wide ranges of gas temperatures and pressures, and are made of simple devices. At the same time, a series of problems arise connected with the preliminary preparation of sensors and improving their selectivity. These and other questions of general nature will be considered in the section that follows. 

For many conducting polymers including polyaniline, polypyrrole, and polythiophene, a rich chemistry of structural modifications has been developed making them potentially attractive materials for sensor applications [45,77-81]. Since, conjugated polymers respond to vapors at room temperature and can be deposited on a wide variety of substrates, they could be used in applications that prove to be difficult for traditional semiconductor gas sensors which often require high-temperature operation. 

Shimizu, Y. and Egashira, M. Sensitization of odor semiconductor gas sensors by employing a heterolayer structure. In Sensors Update Sensor Technology — Applications — Markets, Baltes, H., Gopel, W., and Hesse, J., Eds. VCH Weinheim, 1999, Vol. 6, pp. 211-229. 

Nakata, S., Hashimoto, T., and Okunishi, H. Evaluation of the responses of a semiconductor gas sensor to gaseous mixtures under the application of temperature modulation. Analyst 2002,127, 1642-1648. 

Particularly attractive for numerous bioanalytical applications are colloidal metal (e.g., gold) and semiconductor quantum dot nanoparticles. The conductivity and catalytic properties of such systems have been employed for developing electrochemical gas sensors, electrochemical sensors based on molecular- or polymer-functionalized nanoparticle sensing interfaces, and for the construction of different biosensors including enzyme-based electrodes, immunosensors, and DNA sensors. Advances in the application of molecular and biomolecular functionalized metal, semiconductor, and magnetic particles for electroanalytical and bio-electroanalytical applications have been reviewed by Katz et al. [142]. 

The use of catalysts and promotors of various reactions applied as a fine dispersion phase to the surface of semiconductor adsorbent became most popular in providing a required selectivity of sensors with respect to a given gas. As it has been established in experiments (see for instance [8] and the reference list therein), apart from obtaining required selectivity application of such additives results in increase of sensitivity of the sensor with respect to a given gas. However, as of today there is no clarity with regard to understanding the mechanism of effect of cata-l)rtic additives on the sensor effect nor in optimization of the choice of catalysts applied. 

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