A gas sensor based on a p crystalline silicon resistor with a sensing porous silicon layer is presented. The fabrication process, which involves standard lithography and an electrochemical step, is described with a particular emphasis devoted to the photoresist masking properties against the HF/ethanol electrochemical etching solution. Preliminary measurements of the I-V characteristic in N2 atmosphere and in presence of a 15,000 ppm isopropanol concentration are presented and discussed. A new characteristic of this device, in which the gas sensitivity can be tuned by a reverse voltage applied to a pn junction, is described. Both this feature and the resistance variations in presence of a polar gas are tentatively explained in terms of space charge layers modulation.
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