Microcantilevers with nanowells as moisture sensors

An anodic aluminum oxide (AAO) layer with hexagonally ordered nanowells was fabricated on an aluminum specimen with two-step anodization, and then AAO cantilevers were fabricated with photolithography and electrochemical etching. Each resulting AAO cantilever has a larger surface area and a lower modulus than that of a plain cantilever with the same dimensions due to the presence of the nanowells. We measured the variations in the resonance frequency and deflection of the cantilevers when exposed to moisture and found that the sensitivity in both mass and stress measurements of the porous AAO cantilever is superior to that of the nonporous cantilever. The changes in the deflection and resonance frequency of the AAO cantilever were found to be reproducible and proportional to moisture concentration.