Low temperature bonding of ceramics by sol-gel processing

Silicon, sapphire and polycrystalline wafers have been bonded using a sol-gel process involving spin-coating solutions containing partially hydrolysed silicon or modified aluminium alkoxides. The two coated-substrates were assembled and the resulting sandwich was fired at temperatures ranging from 60 to 600degreesC. The sol-gel coatings were characterised using ellipsometry and AFM, while the corresponding bonded specimens were investigated using cross-sectional TEM. Their mechanical properties were characterised using both micro-indentation and tensile testing. Bond strengths of 0.8 MPa were achieved at 60degreesC between silicon wafers using a methacrylate/alumina hybrid system. The strength was increased to 1.3 MPa by using a nano-particulate sol, produced by hydrolysis of Al((OC4H9)-C-s)(3) modified with ethylacetoacetate, and firing at 600degreesC. However, significantly lower bond strengths were achieved with sapphire and polycrystalline alumina substrates (0.4 and 0.1 MPa, respectively). The effect of precursor chemistry on the bonds produced is discussed.