Porous silicon in low moisture content dry gas by impedance spectroscopy

The present work is aimed to develop porous silicon (PS)‐based sensor to measure very low humidity concentration with possible industrial applications. This work is in continuation of our previous results reported (Islam et al., Sens. Lett. 6 , 746 (2008)) that the PS layer with pore morphology above 10 nm shows good response above 50 ppmV. To obtain improved sensitivity in the lower range below 50 ppmv, the porous structure with pore dimensions below 10 nm is fabricated by controlling the anodization parameters using precision Solatron Electrochemical Cell (1280C). The sensor based on capacitive principle has porous top metal electrode having pores above 1 µm formed on the porous layer by screen printing technique. The mesh structure increases the area of the electrodes and allows the moisture molecules penetrating through the mesh thus improving both sensitivity and ohmic nature of the contacts. The electrical properties were evaluated by impedance spectroscopy for different contents of water vapour in N 2 gas with Agilent 4294A Impedance Analyzer.