Work-Function-Type Gas Sensors

Sensing Layers in Work-Function-Type Gas Sensors 

Classical work-function-type gas sensors are specific devices based on the Kelvin method. The Kelvin method ( vibrating capacitor/condenser method, capacitive probe method ), using a so-called Kelvin probe (KP) or Kelvin oscillator, is an established tool for measuring the work function of a sample or, more precisely, the contact potential between the sample and a reference. 

A major advantage of this method is that it is a noncontact and nondestructive way of measuring. Additionally, it is not expected to influence the electrical or chemical structure of the material. The technique is very simple, but fast, accurate, and versatile it can, in principle, be used in many environments. However, experience has shown that for practical sensor applications Kelvin probes are not suitable due to the necessary instrumentation and the limits to miniaturization. Most probes are rather macroscopic with a reference electrode the size of a few millimeters or centimeters. In addition, this method of measurement is complicated in comparison with other methods used in gas sensing and requires specific conditions and equipment. As a result, these devices are not available on the sensor 

Korotcenkov, Handbook of Gas Sensor Materials Properties, Advantages and Shortcomings for Applications Volume 1 Conventional Approaches, Integrated Analyticeil Systems, 

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Sensing Layers in Work-Function-Type Gas Sensors. 377... 

Other inorganic materials were also studied by KP. Studies on gas sensitivity are reported for carbonates, especially BaCOj, being sensitive to CO and NO even at ambient temperature (Ostrick et al. 1999, 2000a, 2003), TiN (Ostrick et al. 2000b) as ammonia sensitive layers, and LaFj as oxygen (Cho et al. 1991 Choi et al. 1993) and ozone (Doll et al. 1996) sensing layers. The sensitivity of barium carbonate to CO in work-function-type gas sensors is due to the formation of bicarbonate... 

Oprea A, Simon E, Fleischer M, Frerichs H-P, Wilbertz C, Lehmann M, Weimar U (2005) Flip-chip suspended gate field effect transistors for ammonia detection. Sens Actuators B 111 582-586 Ostrick B, Mlihlsteff J, Fleischer M, Meixner H, DoU T, Kohl C-D (1999) Adsorbed water as key to room temperature gas sensitive reactions in work function type sensors the carbonate-carbon dioxide system. Sens Actuators B 57 115-119 Ostrick B, Fleischer M, Meixner H, Kohl C-D (2000a) Investigation of the reaction mechanisms, in work function type gas sensors at room temperature by studies of the cross sensitivity to oxygen and water the carbonate-carbon dioxide system. Sens Actuators B 68 197-202... 

Stegmeier S, Fleischer M, Hauptmann P (2010) Thermally activated platinum as VOC sensing material for work function type gas sensors. Sens Actuators B 144 418-424... 

Exploration to make FET type and oxygen concentration cell type gas sensors more flexible in operating temperature FET-based on silicon cannot function at temperatures higher than ca.l80°C, whereas the cell using zirconia cannot function at temperatures lower than ca. 550°C neither is able to work in the most important temperature range for gas sensing. Exploration for new semiconductors and new solid electrolytes is desired to eliminate these limitations. 

Ostrick, B., MUhlsteff, J., Fleischer, M., Meixner, H., Doll, T. and Kohl, C. (1999), Adsorbed water as key to room temperature gas-sensitive reactions in work function type sensors the carbonate-carbon dioxide system Sensors and Actuators B Chemical, 57,1-3,115-19. 

Electrical sensors, operating due to a surface interaction with target gas, cover a large group of gas sensors polymer, metal, metal oxide, or saniconductor conductometric sensors capacitance sensors and work-function-type and Schottky barrier-, MOS-, and FET-based sensors (Korotcenkov 2011). 

Ostrick B, Pohle R, Fleischer M, Meixner H (2000b) TiN in work function type sensors a stable ammonia sensitive material for room temperature operation with low humidity cross sensitivity. Sens Actuators B 68 234-239 Ostrick B, Fleischer M, Meixner H (2003) The influences of interfaces and interlayers on the gas sensitivity in work function type sensors. Sens Actuators B 95 271-274... 

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