A sensitive and highly linear capacitive thin film sensor for trace moisture measurement in gases

This paper presents the experimental work on the sensitivity enhancement of porous aluminium oxide based capacitive humidity sensor for trace moisture measurement. The pore morphology of nanostructured Al2O3 sensing film has been tuned by adding the different amount of polyethylene glycol (PEG) in the sol solution. X-ray diffraction (XRD), Field Emission Scanning Electron Microscopy (FESEM) and Bruner-Emmet-Teller (BET) were performed for pore morphology analysis of thin films prepared by sol-gel technique. Three parallel plate capacitive sensors with identical geometries but different pore morphologies have been fabricated on Fluorine doped Tin Oxide (FTO) substrate and experimented to analyze the effects of PEG addition. The electrical characterization of the sensors has been performed to determine sensitivity, hysteresis, response and recovery time using Agilent 4294A impedance analyzer with frequency range of 1-1000 kHz. It has been observed that the addition of suitable amount of PEG improves the electrical characteristics of the sensor significantly in the range of 10-210 ppm moisture. Response characteristics of the sensors are highly linear (R2 = 0.995) and the sensitivity is almost twice in comparison to a sensor without PEG addition.