Fabrication of Glass Microlens Array Using Contactless Hot Embossing

Contactless hot embossing or so called partial-filling hot embossing process is one promising replication-based methods for fabrication of high quality microlens array (MLA) with different sag height. By applying heat, holding time, and pressure, the glass material squeezes into the mold holes to form lens shape without contacting the bottom of the mold; thus, adhesion between substrate and mold can be minimized and at the same time increased the mold durability. Herein, by using simple and inexpensive home-built setup, fabrication of glass microlens array (MLA) using contactless hot embossing process is proposed. Mild steel plate with an array of through holes fabricated via electrical discharge machining (EDM) was used as the mold. The morphology of the imprinted glass MLA was confirmed via the 3D measuring laser microscope. As a result, very high aspect ratio and smooth spherical glass MLA array with different sag height were successfully fabricated. The maximum MLA sag height could reach up to 250 µm, which is extremely difficult to obtain using any other conventional fabrication approach. However, it was observed that with nominal MLA diameter of 500 µm as used in this study, the MLA height should not exceed 300 µm, which in turn deteriorated and damaged the formation of the MLA. This approach allows rapid fabrication of high aspect ratio MLA with the advantages of simple mold fabrication process and smooth surface roughness.