Spin-coating of polyimide-silica hybrid optical thin films

Organic-inorganic hybrid materials have shown potential optoelectronic applications. However, the spin-coating of hybrid thin films has rarely been reported. In this study, spin-coating on three trialkoxy-capped poly(amic acid)-silica solutions for applications of optical thin film are presented, including poly(3,3',4,4'-biphenyltetracarboxylic dianhydride-co-4,4'-oxydianiline) (BPDA-ODA) amic acid/silica, poly(pyromellitic dianhydride-co-4,4'-oxydianiline) (PMDA-ODA) amic acid/silica, and poly(4,4'-hexafluoroisopropylidenediphthalic anhydride-co-4,4'-oxydianiline) (6FDA-ODA) amic acid/silica. The studied solutions showed the behavior of a Newtonian fluid. It was found that the film thickness of the studied hybrid film had the dependence of a minus exponent on spin speed. The exponents were in the range -0.57 to -0.84 and decreased with increasing silica content. The solvent composition of the hybrid precursor solution was used to explain the results. As the silica content in the hybrid precursor solution increased, the fraction of the low-evaporation-rate solvent, n-methyl pyrrolidone (NMP) or dimethylacetamide (DMAC), decreased while that of the high-evaporation-rate solvent, methanol, increased. This resulted in the reduction of the absolute exponent value with increasing spin speed. The results suggest that the thickness of the hybrid thin film could be controlled by spin speed and solution composition. (C) 2003 The Electrochemical Society.