Electrodes semiconductor gas sensors

Golovanov, V., J. L. Solis, V. [.antto, and S. Leppavnori. Different Thick-Film Methods in Prinr-mg ot one-Electrode. Semiconductor Gas Sensors. Sensors Actuators B34 (1996), pp. 410-416. Lantto, V., and V. Golovanov. A Comparison of Conductance Behaviour between SnO> and CdS Gas-Sensitive Films, Sensors Actuators B24-25 (1995), pp. 614-618. 

On the other hand, electrodes with different geometry were applied to the semiconductor gas sensors. Korotcenkov reviewed practical aspects in the design of one-electrode semiconductor gas sensors. Figure 3.8 shows standard two-electrode and one-electrode sensors schematically in planar view. The schematic electrical circuits of these sensors are also shown in Fig. 3.8, where i pt is a coil resistance of Ft spiral, i Meo is the inter-turn resistance of metal-oxide ceramics and Rs is a total resistance of the sensor. The physical configuration of ceramics type and thin film type one-electrode semiconductor gas sensors are shown in Figs 3.9 and 3.10. ... 

Planar constructions of (a) standard (two-electrode), and (b) one-electrode semiconductor gas sensors. 

Schematic view of ceramics type, one-electrode, semiconductor gas sensor. 

Korotcenkov, G., Practical aspects in design of one-electrode semiconductor gas sensors Status report Sensor Actuat. B, 2007,121,664-78. 

Table 12.2 Surface filters employed in one-electrode semiconductor gas sensors to improve sensor selectivity...

FfCURE 13.54 Semiconductor gas sensors (o) tubular, (b) thick film, (e) bulk-type one-electrode sensor where a thin Pt wire spiral is embedded Inside a sintered oxide semiconductor button. ... 

Zeolite membranes and films have been employed to modify the surface of conventional chemical electrodes, or to conform different types of zeolite-based physical sensors [49]. In quartz crystal microbalances, zeolites are used to sense ethanol, NO, SO2 and water. Cantilever-based sensors can also be fabricated with zeolites as humidity sensors. The modification of the dielectric constant of zeolites by gas adsorption is also used in zeolite-coated interdigitaled capacitors for sensing n-butane, NH3, NO and CO. Finally, zeolite films can be used as barriers (for ethanol, alkanes,...) for increasing the selectivity of both semiconductor gas sensors (e.g. to CO, NO2, H2) and optical chemical sensors. 

Takao Y., Miyazaki K., Shimizu Y., and Egashira M., High ammonia sensitive semiconductor gas sensors with douhle-layer structure and interface electrodes, J. Electrochem. Soc., 141, 1028-1033, 1994. 

Electrode materials and electrode-oxide interfaces in semiconductor gas sensors... 

Electrodes of semiconductor gas sensors have a function of conductor to an external circuit as a contact material. Contact resistance that is formed in the electrode-oxide semiconductors may in some cases have significant contribution on the response of the sensors. Electrode materials are also utilized as catalyst activators in the sensor operation. In special cases, for electrode materials to operate at high temperature in automotive and aerospace industries, they have to endure at temperature up to 600°C. Therefore, the electrode materials of semiconductor gas sensors are responsible for their sensitivity and selectivity to specific gases. 

The resistance of a tin oxide gas sensor consists of bulk resistance, surface resistance and contact resistance. The reduction of contact resistance is useful for improving the properties of oxide semiconductor gas sensors. An ohmic contact between the electrode and sensing material can reduce the contact resistance. Zhou et al. compared conventional tin dioxide-gold electrode structures with devices in which an n+ layer was introduced between the sensor and electrode. The use of the metal-n+-n contact not only improved the sensitivity of the sensor to alcohol, but also the sensor selectivity to other gases did not change with the addition of an n+ layer. 

The physical understanding of the electrode-oxide semiconductor interfaces are described in this section. Interfaces of this type occur in oxide semiconductor gas sensors and metal-insulator-semiconductors (MIS) devices. When a metal is contacted with oxide, the potential barrier arises from the separation of changes of the metal-oxide interface as well as the metal-semiconductor contacts. 

Vilanova, X., Llobet, E., Brezmes, X, Calderer, X and Correig, X., Numerical simulation of the electrode geometry and position effects on semiconductor gas sensor response . Sensors Actual. B, 1998,48,425-31. 

Williams DE (1999) Semiconducting oxides as gas-sensitive resistors. Sens Actuators B 57 1-16 Wu N, Zhao M, Zheng JG, Jiang C, Myers B, Le S, Chyu M, Mao SX (2005) Porous CuO-ZnO nanocomposite for sensing electrode of high-temperature CO solid-state electrochemictil sensor. Nanotechnology 16(12) 2878-2881 Yamazoe N, Kurokawa Y, Seiyama T (1983) Effects of additives on semiconductor gas sensors. Sens Actuators 4 283-289... 

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]. 

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