Realization of humidity sensors based on a screen-printed anionic clay

Anionic clays, also referred as lamellar-double hydroxides (LDHs) are well known to display a high ionic conductivity for a large variety of interlamellar anionic species. In previous works, it was shown that the conductivity was mainly protonic and closely related to the hydration state of the compound. Such phases can therefore be used as humidity sensors providing that a reliable device could be formed. A Zn0.67Al0.33(OH)2Cl0.33 · nH2O compound is studied. The forming of this material by the screen printing technique is optimized in order to obtain adherent thick layers with regular levelling and a good resolution on alumina substrates. Two devices are studied, one working on A.C. with a two electrodes geometry and the other on D.C. with a four electrodes geometry. The results about sensitivity, stability and response time measurements carried out on each device are compared and discussed.