Characterisation and process optimisation of photosensitive acrylates for photonics applications

摘要

In this paper, we present our recent progress on the characterisation and process optimisation of photoresist-like fluorinated acrylate and Cyclomer acrylate copolymers. Different acrylate formulations from cyclized acrylic copolymers (Cyclomer) have been exploited and compared with fluorinated acrylate, ORMOCER from available sources. Refractive indices of the Cyclomer acrylate at transverse electric (TE) mode is 1.56 while refractive index of fluorinated acrylate at TE is 1.52 at room temperature. Both acrylates show negative thcrmooptic (TO) effect with temperature. The thermooptic coefficient, dn/dT of the polymers are as high as the order of 10~(-4), which is comparable to those of available optical polymers. Higher values of dn/dT are shown by the Cyclomer acrylate compared to that of the fluorinated acrylate. Thermal stability determination were measured using Thermal Gravimetric Analysis and decomposition were evaluated at 5 and 10% decomposition. It was found that Cyclomer is more stable than ORMOCER. From glass transition and specific heat capacity values obtained using Differential Scanning Calorimeter, fluorinated acrylate has more specific heat capacity than Cyclomer. Characterisation of pre baked and UV cured polymer samples had been analysed using FTIR. The time and intensity of UV curing were optimised to obtain waveguide channel of width between 40 and 10 μm for Cyclomer. For fluorinated acrylate, only the UV curing time parameter had been optimised. The development techniques of these acrylates are also different; the Cyclomer used the aqueous based developers while fluorinated acrylate used hydrocarbon solvent. Microstructural channel waveguide had also been analysed via scanning electron microscope (SEM), which shows the channel waveguide structures.