Use of selective anodic bonding to create micropump chambers with virtually no dead volume

Membrane micropump chambers of 11 mm diam with virtually zero dead volume were realized using selective anodic bonding. The selective bonding was achieved with less than 1 nm thick metallic antibonding layers on the glass wafer. Experiments were carried out to come to a better understanding of the selective anodic bonding process. It was concluded that a conductive antibonding layer on the glass wafer prevents the formation of a bond, because in that case the electrostatic attraction between the Pyrex and silicon wafers will vanish upon contact. Chromium and Platinum were found to be suitable antibonding layers. Furthermore, it was found that during the anodic bonding process, the transport of oxygen ions from Pyrex toward the silicon-Pyrex interface results in the formation of SiO2, which forms the actual bond between both substrates. At positions of an intermediate antibonding layer the oxygen ions form oxygen gas. The Pyrex or silicon substrate may deform locally due to the buildup of oxygen gas pressure. This can be prevented by adding a gas outlet to the design. (C) 2001 The Electrochemical Society. All rights reserved.