Replication of microlens arrays by gas-assisted hot embossing

This article reports an effective method for mass-production of 300 x 300 microlens arrays. A microlens array master is formed by imprint lithography and photo-resist reflow at room temperature. The electroforming is then applied to fabricating the Ni mold from the master, followed by the gas-assisted hot embossing to replicate the microlens arrays. The isotropic gas pressure on the plastic film against the Ni mold produces plastic microlens array of high quality and uniformity. The effects of processing parameters including the processing temperature, pressure, and time on the replication quality of microlens arrays were investigated. The experimental results show that the filling of molded microlens significantly increases as the processing temperature and pressure increase. Under the condition of 180 degrees C, 3.9 MPa for gas pressure, and 90 seconds processing time, the arrays of polycarbonate microlens of diameter 150 mu m and pitch 200 mu m have been successfully replicated. The deviation of replicated microlens from the mold is less than 0.25%. Compared with the conventional hot embossing process, the new replication method offers more uniform embossing pressure distribution. The great potential for replicating microlens array on large plastic films with high productivity and low cost was demonstrated.