Detection of Xyelene (C8H10) by Pd-gate MOS Sensor

The sensors capable of detecting the toxic as well as explosive gases such as Xyelene which is known to be having very serious effects on the respiratory systems are need to be developed. The promise of small integrated sensors with high sensitivity has motivated the numerous researchers [1-4] to develop and study the gas sensors based on Pd gate MOS structure. These sensors have been found to be sensitive for hydrogen and the detection mechanism could be attributed to change in metal work function on exposure to hydrogen. [5,6]. The model for mechanism of hydrogen sensitivity of Pd MOS device has been proposed by Lundstrom et al. [7]. Exposure of hydrogen gas on the sensor causes the hydrogen molecule to dissociate into atomic hydrogen on Pd surface, and then these atoms diffuse through the Pd film and get adsorbed at Pd/insulator interface. The adsorbed and dissolved hydrogen atoms give rise to the formation of dipole layer at the Pd/ insulator interface and work function of the Pd is decreased which can be measured in terms of change in flat band voltage of the MOS capacitor [7]. It is possible to detect the hydrocarbons or other hydrogen containing gases by these sensors provided they can be dehydrogenated on the Pd surface, so that hydrogen atoms can diffuse and are adsorbed on Pd/ insulator interface and give rise to change in the flat band voltage of the device. This paper presents the result of, analysis of C-V and G-V responses of Pd gate MOS capacitors, exposed to various Concentration (500 ppm – 1. 6 %) of Xyelene vapors, in air at several temperatures. It is found that Pd gate becomes more sensitive to Xyelene, in air at operating temperature 70˚C.