S. Ziolkowski Wroclaw Univ. of Technology (Poland) Ines Frese Institute of Microtechnology Mainz GmbH (Germany) Henryk T. Kasprzak Technical Univ. of Wroclaw (Poland) Stefan Kufner Institut fuer Mikrotechnik Mainz Gmb (Germany)
Contactless embossing of microlenses (CEM) is a well-known fabrication method for refractive microlenses. By applying pressure and heat, a thermoplastic material expands into circular holes of a hot embossing tool. Compared to normal hot embossing, the holes for forming the latter microlenses are so deep that the lens surface is never in contact with the embossing tool itself. Surface tension caused by the applied pressure to the outside lens region is the basic mechanism that forms spherical microlenses. Recently published results describe the f-number of such lenses to be always larger than two for microlenses with diameters below 300 μm. In our approach we newly adapted temperature parameters and additionally applied vacuum during the hot embossing process, which yielded microlenses in, e.g., polymethyl methacrylate (PMMA) with f-numbers as small as 1.2 even for large diameters around 1.5 mm.