Preparation Of Polymer Woodpile Structure For Photonic Crystals

The woodpile structure has the advantage of a wide range of parameter adjusting. It can produce wide band gaps in a wide parameter range where it can generates complete band gaps, so it becomes one focus in photonic crystals study in recent years. In this paper, a new method of fabricating multilayer polymer woodpile structure was presented. Through the design of the mould and the systemic studies of preparation conditions, including prepolymer filtration and preparation, mold choice, surface treatment, prepolymer filling, mold release, hot embossing, the multilayer polymer woodpile structure was fabricated successfully. Comparing this method with soft lithography, it has the advantage of high efficiency, big area, low cost and no residual polymer layer.Initiator dosage and polymerizing temperature were studied as function of fabricating polystyrene prepolymer and polymethyl methacrylate prepolymer to choose the appropriate prepolymer, Base on the facts of viscosity change in the polymerizing process, a better parameter condition of fabricating prepolymer was confirmed.To achieve selective release of polymer layer from the mold, the Si mold treatment technologies of hydrophile, hydrophobicity and oxygenation were studied. H2SO4/H2O2 system was used to acquire the hydrophilic Si mold. Hydrophobic mold which was treated by CF3CH2CH2SiCl3 gas was fabricated to reduce interfacial free energy. SiOX film was formed on the surface of the mold through oxidation for 3 hours at 800℃.The method (μTM and MIMIC) and technology were studied systemically, by which prepolymer was filled into microchannels of the mold. A new mould was designed to increase filling area and avoid residual polymer layer. Finally, large area two-layer polymer mirostructure was fabricated, which has not residual polymer layer by adding air pressure or vacuumizing. A better mold match was found and achieved selective release of polymer layer from the mold through studying different mold matches of different interfacial free energy.Temperature, pressure and time were studied as function of fabricating mutilayer three-dimensional woodpile structure across layer-by-layer stacking method. A better hot embossing technology condition was defined. Finally four-layer polymer woodpile structure was fabricated successfully.The effect of high parameter (c/a) and width parameter (w/a) to band gaps were studied, which were calculated by RSoft-Bandsolve. It provides theory instruction for fabricating specifically band gaps photonic crystals structure by this means.