6 February 2008 A fabrication technique for microlens array with high fill-factor and small radius of curvature
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Abstract
In this paper, we report a technique for microlens array (MLA) fabrication based on lithography and thermal reflow process. The boundary of MLA was defined by a thin photoresist (PR) layer. Then, the second thick PR cylinders were patterned inside the micro-holes from the first PR layer. MLA was formed after reflowing the second think PR cylinders. In the previous processes, the gaps between the thick PR cylinders were large due to the diffraction effect. To increase the fill-factor, some residual PR between the cylinders makes the PR flow outward. But the PR cylinders merge together easily due to inexact reflow time and temperature distribution. It results in small radius of curvature and low uniformity. In our work, the first thin PR became a limiting wall so that no cylinders merge together even at over reflow time. Therefore, both the uniformity and the radius of curvature can be well controlled. Besides, the gap is small and the fill-factor is very high due to the diffraction effect is not significant at first thin PR layer. The results show that the gaps are only 2 um and the radius of curvature is approximately 24 um for MLA with 50 um in pitch and hexagonal arrangement.
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Hsin-Ta Hsieh, Hsin-Ta Hsieh, Guo-Dung John Su, Guo-Dung John Su, } "A fabrication technique for microlens array with high fill-factor and small radius of curvature", Proc. SPIE 6883, Advanced Fabrication Technologies for Micro/Nano Optics and Photonics, 68830Z (6 February 2008); doi: 10.1117/12.760927; https://doi.org/10.1117/12.760927
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