Parametric study of microlens array fabricated on polymer substrate through hot embossing with a micro-EDM mould and its optical characterisation

Abstract

ABSTRACTThe surface topography of embossed micro-patterns relies on hot embossing (HE) parameters and micro-patterns over the mould. Traditionally, moulds were made using photolithography (X-ray/UV/E-beam) followed by wet etching or reactive ion etching. This technique is costlier, time-consuming, and expensive. To resolve these issues, researchers are shifting to micromachining to make HE moulds. In this investigation, a mould fabricated by μ-electric discharge machining (μ-EDM) was employed in an in-house developed HE set-up. In this work, embossing temperature (Te), embossing pressure (Pe), embossing time (te), and deembossing temperature (Tde) were used as operational factors and their influence on micro (μ)-lens surface profile was evaluated. Te, Pe, and te increases the sag height (hsag) of μ-lens array. As hsag increases, radius-of-curvature (R) and focal length (f) of the embossed μ-lens array decrease, which enables the production of μ-lenses with different diameters by modifying HE parameters. The maximum percentile change in hsag is 292.49% with Te. The maximum percentile drop in calculated R and f values were observed in case of Tde, i.e. 70.89% followed by Pe (54.18%) and te (49.52%). Hemispherical shaped μ-lens array was obtained at Te of 140°C, Pe of 50 kg/cm2, te of 20 min, and Tde of 40°C.