Fabrication of microlens arrays using a CO(2)-assisted embossing technique

This paper reports a method to fabricate microlens arrays with a low processing temperature and a low pressure. The method is based on embossing a softened polymeric substrate over a mold with micro-hole arrays. Due to the effect of capillary and surface tension, microlens arrays can be formed. The embossing medium is CO2 gas, which supplies a uniform pressing pressure so that large-area microlens arrays can be fabricated. CO(2) gas also acts as a solvent to plasticize the polymer substrates. With the special dissolving ability and isotropic pressing capacity of CO2 gas, microlens arrays can be fabricated at a low temperature (lower than T(g)) and free of thermal-induced residual stress. Such a combined mechanism of dissolving and embossing with CO2 gas makes the fabrication of microlens arrays direct with complex processes, and is more compatible for optical usage. In the study, it is also found that the sag height of microlens changes when different CO2 dissolving pressure and time are used. This makes it easy to fabricate microlens arrays of different geometries without using different molds. The quality, uniformity and optical property of the fabricated microlens arrays have been verified with measurements of the dimensions, surface smoothness, focal length, transmittance and light intensity through the fabricated microlens arrays.