Anodic alumina membrane capacitive sensors for detection of vapors

Here we report membrane capacitive sensors based on anodic aluminum oxide (AAO) Au/AAO/Au structures fabricated by aluminum anodization, followed by gold electrodes sputtering on the countersides of porous ceramic membrane. Electrochemical impedance spectroscopy with AC amplitude 5–100 mV in the frequency range of 1–1000 Hz was utilized for sensor characterization in the presence of water and organic vapors in a full range of P/P0. The sensors illustrate ultimate sensitivity to ambient environment with exponential-scale capacitance relation to vapors content resulting in typical 4–6 orders of magnitude response signal change for 15–85% P/P0 range at a single AC frequency, and up to 7 orders of magnitude response range for 0–100% P/P0 pressure range with using two different AC frequencies. In case of water vapors, the sensitivity increases from ~0.5 nF/RH% at ~20 RH% to over ~1.0 μF/RH% at ~80 RH%. The sensors are capable for highly accurate sensing of gas humidity as well as any dissociative vapors with pKa