Hydrogen Sensor Made of Porous Silicon and Covered by TiO$_{2-{\rm x}}$ or ZnO$\langle$Al$\rangle$ Thin Film

Abstract

Hydrogen sensor working at room and 40degC temperatures made of porous silicon covered by the TiO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2-x</sub> or ZnO(Al) thin film was realized. Porous silicon layer was formed by electrochemical anodization on a p- and n-type Si surface. Thereafter, n-type TiO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2-x</sub> and ZnO(Al) thin films were deposited onto the porous silicon surface by electron-beam evaporation and magnetron sputtering, respectively. Platinum catalytic layer and Au electric contacts were for further measurements deposited onto obtained structures by ion-beam sputtering. The sensitivity of manufactured structures to 1000-5000 ppm of hydrogen, propane-butane mixture, and humidity was studied. Sensitivity of obtained structures was determined as ratio of the resistivity of structures in the presence of investigated gas to that in air. Results of sensitivity measurements showed that it is possible to realize a hydrogen nanosensor, resistivity of which can be decreased up to 2.5 times at room temperature and four times at 40degC for the Pt/TiO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2-x</sub> /PS structure, as well as two times for the Pt/ZnO(Al)/PS structure at 40degC at 5000 ppm hydrogen concentration, respectively. Both structures have the recovery and response time of approximately 20 s and rather high durability and selectivity to hydrogen gas.