Low temperature bonding for microfabrication of chemical analysis devices

A low temperature bonding process was developed for the fabrication of microchip devices for liquid and heterogeneous phase chemical analysis, Photolithographically etched microchannels on glass substrates were closed by bonding a glass cover plate using a spin-on sodium silicate layer as an adhesive. Good channel sealing was achieved by curing at 90 degrees C for 1 h or room temperature overnight. The fluidic performance of the device was evaluated by monitoring the electroosmotic flow on the chip. The results compared well with those obtained from devices made by high temperature direct bonding of the substrate and cover plate. The dielectric and mechanical strength for bonds, created using the low and high temperature methods, were compared. A dielectric strength of 400 kV cm(-1) was obtained for the sodium silicate bonding and 1100 kV cm(-1) for the high temperature bonding. Mechanical strength measurements gave a surface energy value of approximate to 2.7 J m(-2) for sodium silicate bonding, compared to 6.5 J m(-2) for direct bonding. The mechanical strength of glass bonds obtained with sodium silicate at low temperature was comparable to that reported for the sodium silicate bonding of silicon wafers at >200 degrees C or by conventional direct bonding of oxidized silicon at 1400 degrees C. The low temperature bonding performance is adequate for microfabricated fluidic devices that employ electrokinetic transport phenomena. The reduced temperature of the bonding process will allow chemical surface modification prior to bonding. (C) 1997 Elsevier Science S.A. All rights reserved.