Fabrication and characterization of gridded Pt/SiO2/Si MOS structure for hydrogen and hydrogen sulphide sensing

A gridded gate Pt/SiO2/Si MOS capacitor has been fabricated for detection of Hydrogen (H-2) and Hydrogen Sulphide (H2S) gases. The MOS device was fabricated on P-type Si <100> (1-6 Omega cm) wafer with thermal oxide layer of thickness about 100 angstrom, whereas, Platinum (Pt) gate of similar to 350 angstrom was deposited by thermal evaporation technique. The C-V (capacitance vs voltage) and G-V (conductance vs voltage) measurements have been performed for the evaluation of gas sensing behavior of fabricated MOS capacitor structure in H-2 (250-4000 ppm) and H2S (1000-6000 ppm) gases at both room and 120 C temperatures, in a closed chamber in air atmosphere. It has been observed that the value of capacitance decreases with increase in gas concentration. The fabricated MOS capacitor sensor has shown better sensitivity towards H-2 (88.6%) at room temperature (similar to 25 degrees C) as compared to (similar to 45%) at 120 degrees C. Scanning electron microscopy (SEM) and Atomic force microscopy (AFM) studies have revealed the porous nature of the deposited metal film. The side wall diffusion, spillover of Hydrogen into oxide layer, increase in fixed oxide charge density, increase in surface area caused by gridded structure, the formation of dipole layer and change in interface state density on gas exposure, may be the mechanisms of gas sensing for improved sensitivity of the fabricated MOS device. (C) 2014 Elsevier B.V. All rights reserved.