Design and detection method of three-electrode humidity sensor based on micro-arc MgO

In order to solve the problems of low sensitivity and low detection accuracy of semiconductor humidity sensor, magnesium oxide (MgO) humidity sensor was prepared by micro-arc oxidation (MAO) technology in this work. The micro-arc MgO film has a large number of abnormal pore structure (about 4-5 um), and the thickness of the film is 33.8 um, which has good continuity. A pair of asymmetric interdigital electrodes was sputtered on the surface of the micro-arc MgO film as the first electrode and the second electrode, and the metal matrix with dots is polished on the back of the micro-arc MgO film to directly serve as the third electrode. Humidity sensing results show that the average output of 12 electrodes, 13 electrodes and 23 electrodes with impedance as the response signal in the relative humidity (RH) range (11.3-97.3%) can reach (91, 35, 49) respectively. The fitting formulas of relative humidity and impedance were obtained by fitting the maximum and minimum values of three pairs of electrodes in different humidity ranges (11.3% RH-97.3% RH). Then, the humidity sensor impedance data collected under different humidity ranges are substituted into the fitting formula to obtain the corresponding humidity ranges and the intersections are taken to contract each other. The experimental results show that the measurement accuracy of the micro-arc MgO humidity sensor has been significantly improved, the highest measurement accuracy can reach +/- %1.1RH, and the average measurement accuracy under different humidity ranges can reach +/- %1.4RH. Therefore, the three-electrode design balances the relationship between measurement accuracy and structural complexity, indicating that it is possible to design different electrode structures and increase the number of electrode pairs to further improve the humidity measurement accuracy of the sensing material.