Superior positive relative humidity sensing properties of porous nanostructured Al:ZnO thin films deposited by jet-atomizer spray pyrolysis technique
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A highly responsive resistive type humidity sensor is fabricated from porous aluminium-doped ZnO (Al:ZnO, AZO) thin films deposited by using jet-atomizer spray pyrolysis technique. The deposited thin films are calcined at various temperatures, ranging from 450 to 650 °C, to improve the crystallinity, electrical and optical properties. Electrical resistivity of the films is measured by Van der Pauw technique. Lowest resistivity of 13 Ω·cm is obtained for 3 at.% AZO samples calcined at 500 °C. Humidity sensing properties like responsivity, sensitivity, repeatability, response time and recovery time of the AZO samples are investigated at room temperature in the range of 10–90% of relative humidity (RH). Among all the samples, 5 at.% AZO thin films show the highest responsivity of 733% at 90% RH. In contrast to other ZnO based sensors, it is found that the resistance of the AZO sensors, prepared in our method, increases with the increase of relative humidity. A sensing mechanism of the AZO and ZnO thin films is proposed to explain the water adsorption technique and the cause of increase in resistance of the sensors during water adsorption.
Authors would like to say thanks to Department of Science and Technology (DST), INDIA for their financial support to this research.
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