Review of porous anodic aluminium oxide (AAO) applications for sensors, MEMS and biomedical devices

Anodising of aluminium is one of the simplest metal surface finishing processes, and results in a porous anodic aluminium oxide (AAO) which is integral with the parent metal. Pore size, interpore spacing and thickness of the porous oxide film can be controlled by careful selection of the anodising electrolyte (type and concentration), and the operating parameters (voltage, temperature, time) employed. A self-ordered nanoporous AAO can be obtained without the need for expensive or complex processes required for traditional materials employed in microelectronics and MEMS applications (e.g. photolithography in the production of porous silicon). Planar and curved AAO surfaces can be manufactured. The simple and low-cost process for the production of AAO has enabled this material to gain inroads in the manufacture of various sensors and MEMS devices. This review paper discusses the anodising process and the resulting AAO structures tailored for MEMS, sensors, biomedical and nanotechnology fabrication.