A glass reflowed microlens array on a Si substrate with rectangular through-holes

A thermally reflowed glass microlens array was fabricated on a Si substrate. Glass lenses are more durable and scratch-resistant than plastic lenses made by the same, simple thermal reflow process. The microlens was designed using the ray tracing technique and optimized by controlling the nominal diameter and height of glass cylinders. The glass cylinders were formed by wet etching a glass plate in a HF (49%) solution and reflowed to form a semi-spherical lens shape at 850??C (glass transition temperature Tg = 820??C) for 20?min in a furnace. Then, the Si substrate was etched in a TMAH (5%) solution to make rectangular through-holes underneath the microlens array for high optical transmission. The profile of the fabricated microlens was measured with a confocal microscope, and its optical characteristics (lens size, beam radius and focal length) were evaluated with a 633?nm laser diode beam. The experimental beam waist (minimum beam radius) at the focal point of 1000??m was 8??m, which was in good agreement with a calculated value. The results show that the microlens array can be used in a broad wavelength range from UV to the IR region.