Industrial Technology Research Institute

Ping Ping Tsai

Yingjeng James Li

Chia-Jung Lu

Chun-Yuan Lee

A porous poly(2-acryl-amido-2-methyl-propane sulphonic acid)-based humidity sensing element is disclosed which provides improved range of humidity measurement and response time with little or no hysteresis. It includes: (a) a non-conductive substrate which has a pair of electrodes formed thereon; (b) a porous poly(2-acryl-amido-2-methyl-propane sulphonic acid) film formed on said electrodes. The porous poly(2-acryl-amido-2-methyl-propane sulphonic acid) film is formed by first forming a non-porous poly(2-acryl-amido-2-methyl-propane sulphonic acid) film on the electrodes, then subjecting the non-porous poly(2-acryl-amido-2-methyl-propane sulphonic acid) film to a heat treatment at temperatures between about 170&deg; C. and 240&deg; C. such that a porous structure is formed in said poly(2-acryl-amido-2-methyl-propane sulphonic acid) film. The poly(2-acryl-amido-2-methyl-propane sulphonic acid) can be modified by incorporating a cation, such as hydrogen, lithium, potassium, sodium, ammonium, primary, secondary, and tertiary amine ions, and tetra-alkyl ammonium ions.

Polymer-based humidity sensing elements

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.degree. 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.sub.2 O).sub.x WO.sub.3.zH.sub.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.

Solid state humidity sensor

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.degree. 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.sub.2 O).sub.x WO.sub.3.zH.sub.2 O, in which M is a cation, x is about 0.5, and z, which is the amount of crystalline water contained in said crystal, is typically less than 2.

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Hsinchu, Taiwan

Ping Ping Tsai