| abstract |
A method for forming a solid state humidity sensor is disclosed which comprises the steps of: (a) dissolving a tungstate salt into an aqueous solution; (b) adjusting the pH of the aqueous tungstate salt solution to below 8.5; (c) forming one or a pair of electrodes on an insulating substrate; (d) placing the substrate into the pH-adjusted aqueous tungstate salt solution and heating the aqueous solution containing the substrate at temperatures above 70° C. to thereby form a pyrochlore-type crystalline tungsten trioxide film over the electrode or pair of electrodes; and (e) forming another electrode over the pyrochlore-type crystalline tungsten trioxide film if only one electrode is formed during step (c). Alternatively, the pyrochlore-type crystalline tungsten trioxide film can be formed over or between the electrodes by heating the pH-adjusted aqueous tungstate salt solution to cause a precipitation of pyrochlore-type crystalline tungsten trioxide, then screen-printing the pyrochlore-type crystalline tungsten trioxide powder on one or both of the electrodes to thereby form a humidity sensing element. The pyrochlore-type crystalline tungsten trioxide is represented by the general formula of (M 2 O) x WO 3 .zH 2 O, in which M is a cation, x is about 0.5, and z, which is the amount of crystalline water contained in the crystal, is typically less than 2. |