Fabrication of porous membranes for MEMS packaging by one-step anodization in sulfuric acid

A nonlithographic fabrication method that exploits the pore structure of anodic aluminum oxide to fabricate alumina porous membranes for microelectromechanical system (MEMS) packaging is proposed. This method allows wafer level packaging of MEMS devices at low temperature. We report on initial experiments indicating the feasibility of the technique. Patterned porous alumina films are formed by anodizing aluminum films on wafer substrates using sulfuric acid electrolytes. The etching of the barrier layer through the porous membrane by a plasma using a CF₄ + O₂ gas mixture, and the evidence of pore opening required for the release of a sacrificial MEMS layer are presented.status: publishe