Inclined exposure and incomplete thermal reflow process for fabricating asymmetric microlens array

A novel fabrication method of tilted microlens array for light control films is developed to increase the efficiency of a liquid crystal display that can collect lateral light sources and improve the dazzling problem within the angle of view. Initially, the pattern allows UV exposure by placing a photoresist-coated substrate on an inclined fixture. An inclined photoresist column array is made with a round cross-section using the photolithography technique. During the incomplete thermal reflow processing, only the partial surface of photoresist column reaches the material glass transition temperature, which is transformed from a glassy state into a rubbery state. In order to minimize the structural surface energy and reduce the surface area, the surface of the inclined photoresist column forms the lens profile. With proper control of the thermal reflow temperature and time, the photoresist at the base will still maintain the original inclination and glassy state because it hasn´t reached the glass transition temperature. The experimental results show that the inclined exposure from different angles can precisely control the declination angle of the inclined photoresist column. It can then fabricate the asymmetrical microlens arrays with the tilted angle larger than 33° by using the upside-down substrate and incomplete thermal reflow method.