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Microlens has been widely employed in various consumer products including optical storage. Microlens fabricated by the thermal reflow process has been used in various optical industries. This paper aims to investigate the influence of interfacial tension and gravity on the profile of microlens fabricated by the thermal reflow process. Theoretical analysis on the interaction between interfacial tension and gravity of liquid droplet is first investigated. The result showed that the sag ratio, i.e., the height/diameter ratio, of the liquid droplet is affected by the Bond number ( ), defined as the ratio of gravity to interfacial tension. The sag ratio is not sensitive with respect to when is small. However the sag ratio decreases as increases when is over the critical number. That means the profile of the microlens is strongly affected by the gravity in this condition. Two experiments are then designed and conducted to compare with the theoretical analysis. The first experiment to measure the profile of droplets of water and the photoresist AZ4620 showed that the sag ratio decreases when the volume of droplet increases, which cause the Bond number increases at the same time. The other experiment to fabricate microlens array using AZ4620 photoresist with different aperture diameters are then conducted. The result showed that the sag ratio of the photoresist reduces from 0.095 to 0.065 when increases from 0.0048 to 0.192. The experimental results showed consistent to that by theoretical analysis.
Date of Publication: March 2011