CO2 Gas-Assisted Micro Hot Embossing Process for arge-Area Replication of Microstructures

In traditional micro hot embossing, substrates are pressed by hot plates, but the pressure distribution is not uniform; Si-wafers and glasses are not proper mold material because of the non-uniform pressure distribution. Furthermore, repeated heating cycle of the conventional hot embossing was not only time wasted but also energy consumed.his thesis is devoted to the development of an effective fabrication process for the replication of large-area microstructures with uniform pressure at room temperature. This process integrates the plasticizing capacity of carbon dioxide (CO2) and the uniform embossing pressure of gas to perform the large area imprinting. In this study, highly compressed CO2 is employed not only as the plasticing agent to soften the substrate but also the pressing medium. Gas-assisted pressurizing has been proven to provide a uniform pressure distribution over a large-area substrate. As a result, CO2-assisted embossing can be performed under lower temperatures and with lower pressure, and enhances the replication quality by reducing the residual stress in the substrates. he experimental results show that the microstructures can be successfully replicated onto the whole large area (330 mm ? 196 mm) substrate with high replication uniformity. Even using brittle Si-wafer, the shapes and conformations were complete.he process has been used to replicate microstructure of V grooves for brightness enhancement films (BEF), microlens array, Fresnel lens, pyramid array and rainbow hologram structures onto PMMA substrate. The size is 330mm by 190mm. The potential of mass fabrication of large-area polymer plate/film with microstructures using CO2-assisted process has been demonstrated.