Good sensitivity and high stability of humidity sensor using micro-arc oxidation alumina film

Humidity sensor based on thin micro-arc oxidation alumina (MOA) film was fabricated by a transient self-feedback control (TSFC) technique for the first time. The MOA film consisted of a polycrystalline nature of α and γ-Al2O3 phases, while high surface/volume ratio led to remarkable adsorption of the MOA film. Moreover, the humidity performance of the MOA sensor indicated good sensitivity of 8045.55 at 98% RH. Fast response and recovery times of the MOA sensor were 90 s and 30 s, respectively, at 20 °C and 1000 Hz. Exposing the MOA sensor to different humidities for longer durations indicated an excellent stability due to the α-Al2O3 phase in the MOA film. The mechanism in the sensor, to humidity, was explained by using equivalent circuits of (RC) and (C(RZ)). In the low RH range, the process was mainly dominated by the migration of protons through the adsorbed water molecule layer on the surface of the MOA film; while, in the high RH range, the process was due to the faster diffusion of protons in the single or multiple layers that were formed on the materials surface.

► Micro-arc oxidation alumina (MOA) film is used as humidity sensor.
► MOA film is prepared by transient self-feedback control (TSFC) mode.
► MOA film with high surface/volume ratio consists of α- Al2O3 and γ-Al2O3 phases.
► MOA sensor shows good sensitivity, fast response and excellent stability.