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Porous silicon layer coupled with thermoelectric cooler: a humidity sensor

2000; Elsevier BV; Volume: 79; Issue: 3 Linguagem: Inglês

10.1016/s0924-4247(99)00285-x

1873-3069

A. Foucaran, B. Sorli, M. Garcia, F. Pascal‐Delannoy, Alain Giani, A. Boyer,

Thermal properties of materials

In this work, an original humidity sensor is described. It is based on the study of the capacitance variation of a porous silicon layer (PSL) during water condensation induced by a commercial small-size thermoelectric cooler (TEC). The measurement principle is to detect the weak increase of capacitance created when water condensation occurs in a PSL stuck on a TEC. This important variation of capacitance is related to the high difference between the dielectric constant of PS (εr<12) and water (εr≅80). The dielectric constant of PS ranges from these of silicon oxide (εr=3.9) to these of silicon (εr=12) [H. Mathieu, Physique des semiconducteurs et des composants électroniques, Masson, 1987, p. 36]. Experimental measurements are performed in a climatic chamber for several values of relative humidity from 10% to 95% and for a TEC current equal to 0.43 A for the cooling part of the process. The analysis of the PS capacitance leads to information over the condensation formation during the TEC cooling. A quick increase of the capacitance appears after a delay time, τ, of 0.5–2 s from the start of the TEC cooling. The higher the humidity level, the faster the capacitance increase. It is possible to draw the capacitance reached after 1 s, from the start of the TEC cooling as a function of the relative humidity level.