Low temperature bonding of ceramics by sol-gel processing

Abstract

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 coatedsubstrates were assembled and the resulting sandwich was fired at temperatures ranging from 60 to 600° C. 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 60°C 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(OsC4H9)3 modified with ethylacetoacetate, and firing at 600°C. 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.