A Comparative Study on the Moisture Response of Nanoporous γ-Alumina with Parallel Plate and Micro-Interdigital Electrodes

Abstract

Nanoporous γ-alumina thick films were prepared from its aqueous sol which in turn was prepared from an organometallic precursor. Ethylacetoacetate was added into the sol as a crack suppressing agent. The sensing behavior of the said film was measured in capacitive mode both in percentage relative humidity (%RH) level as well as parts per million by volume (ppmv) level moisture present in the gas phase. Two different electrode designs viz. parallel plate [parallel electrode configuration (PEC)] and micro-interdigital (inter-digital configuration) were employed for the sensing study. PEC shows superior sensing behavior over the interdigital electrode. The capacitance of the sensor with PE and ID configuration increase from ∼ 17 pF to ∼ 153 pF and ∼ 15 pF to ∼ 24 pF, respectively, as the moisture content increased from 2 ppm to 100 ppm. Further, the capacitance of the sensor with PE and ID configuration increased from ∼ 151 pF to ∼ 963 pF and ∼ 97 pF to ∼ 521 pF, respectively, as moisture content increased from 5% to 60%RH. Schematic and equivalent circuit diagrams for both electrode designs were invoked to explain the achieved superior sensitivity. In addition, the fabricated γ-alumina thick film based capacitive moisture sensor in parallel plate electrode geometry demonstrates low hysteresis (∼ 10 pF at 60%RH and ∼ 0.8 pF at 50 ppmv moisture content), appreciable repeatability over 15 cycles, prolonged stability for 12 months, robustness, drift-free measurement, impressive resolution, usability at high temperature, magnetic field, radiative and corrosive/toxic gas environment.