Jan Szeponik

Room-Temperature Hydrogen Sensitivity of a MIS-Structure Based on the

An LaF3 layer was shown to improve the characteristics of field-effect gas sensors for room-temperature hydrogen monitoring. The Pt/LaF3 interface leads to a Nernst-type response and a detection limit of 10-ppm hydrogen in atmospheric air. The response time was shown to be about 110 s and was independent of hydrogen concentration. A method for the stabilization of a long-term behavior of the sensor was successfully demonstrated. The mechanism of the sensors response to hydrogen was shown to be different from that of the metal/insulator/semiconductor (MIS)-type sensors

hboxPt/LaF_3

A silicon based semiconductor sensor structure Pd/LaF3/Si3N4/SiO2/Si was prepared using thin layer technology. The sensor can be used for hydrogen detection at room temperature. Therefore, the power consumption is reduced by a factor 10 compared to the best low power consumption hydrogen sensors. In contrast to other sensors it can be used for measurements at very low and high hydrogen partial pressure. The limit of detection was determined to be 0.5 ppm. Measurements at high concentrations near to and above the Lower Explosion Level (LEL) of 4 % hydrogen in air are demonstrated. A method to achieve long lifetime of the sensor was developed.

Interface

Abstract Impedance spectroscopy has been performed with EICS ( e lectrolyte/ i on c onductor/ s emiconductor) sensor structures using the fluoride-sensitive Si/LaF 3 system. LaF 3 bulk and interface properties have been determined. The blocked interface between the silicon substrate and the lanthanum fluoride thin film governs the electrical impedance behavior of the whole sensor structure in the high frequency range. This is important for capacitance-voltage measurements because the C - V curve depends in size and steepness on the quality of the Si/LaF 3 interface. Contamination free Si surfaces have been obtained using the MBE process. Epitaxial LaF 3 films of good quality were fabricated but they failed in fluoride-ion sensitivity.