Wet-etching of precipitation-based thin film microstructures for micro-solid oxide fuel cells

In micro-solid oxide fuel cells (mu-SOFCs) ceramic thin films are integrated as free-standing membranes on micromachinable substrates such as silicon or Foturan (R) glass ceramic wafers. The processing of mu-SOFCs involves unavoidable dry- or wet-chemical etching for opening the substrate below the free-standing fuel cell membranes. In the first part of this paper current dry- and wet-chemical etchants for structuring of ceria-based electrolyte materials are reviewed, and compared to the etch-rates of common mu-SOFCs substrates. Wet-chemical etchants such as hydrofluoric acid are of high interest in mu-SOFC processing since they allow for homogeneous etching of ceria-based electrolyte thin films contrary to common dry-etching methods. In addition, HF acid is the only choice for substrate etching of mu-SOFC based on Foturan (R) glass ceramic wafers. Etching of Ce(0.8)Gd(0.2)O(1.9-x) spray pyrolysis electrolyte thin films with 10% HF:H(2)O is investigated. The etch-resistance and microstructures of these films show a strong dependency on post deposition annealing, i.e. degree of crystallinity, and damage for low acid exposure times. Their ability to act as a potential etch-resistance for mu-SOFC membranes is broadly discussed. Guidance for thermal annealing and etching of Ce(0.8)Gd(0.2)O(1.9-x) thin films for the fabrication of Foturan (R)-based mu-SOFCs is given. (C) 2009 Elsevier B.V. All rights reserved.