Development of Spin Coated Mesoporous Oxide Films for MEMS Structures

Abstract

Mesoporous materials offer several unique properties when incorporated in microelectromechanical systems (MEMS) including low density, thermal insulation and the ability to carry out rapid etching. This paper describes the development of two mesoporous thin film materials for MEMS structures, an organically modified silicate and crystalline TiO₂. The morphologies of the mesoporous thin films are similar in that they have approximately 50% volume porosity, an average pore diameter of ∼5 nm, and a narrow pore size distribution. However, the chemistries of the two materials are very different as are their properties for MEMS applications. The organically modified silicate film is designed to have controlled hydrophobicity. CH₃ groups which are present in the sol precursor are retained in the final material despite the 400^∘C calcination temperature used for producing the porous mesostructure. Contact angles as high as 80 degrees have been achieved. The mesoporous TiO₂ is designed to have resistance to HF etching. Heat treatments of the mesoporous material are carefully controlled enabling the TiO₂ pore walls to crystallize without collapsing the pore network structure. A combination of anatase and rutile phases are produced in the solid phase and exhibit excellent resistance to HF.