A novel sol–gel thin film porous alumina based capacitive sensor for measuring trace moisture in the range of 2.5–25 ppm

Present work deals with the development of a low cost moisture sensor for measuring moisture in the range of 2.5–25 ppm using nanoporous thin film of alumina (γ-Al2O3). Thin film of γ-Al2O3 prepared by low cost and simple sol–gel method offers very high surface to volume ratio with distribution of micro pores for moisture detection. Pore morphologies of the film have been studied by FESEM, AFM, XRD and BET methods. To form a capacitive sensor, the porous film of 3–6 μm thickness was dip-coated in between two parallel gold electrodes. The characteristic of the sensors have been examined by Agilent 4294 A impedance analyzer for the frequency range of 1–20 kHz. The characteristics of the sensor can be used for making trace moisture sensor for commercial applications. The capacitance change with moisture is almost linear with 1.05% nonlinearity and 0.33% hysteresis.