Self-Centering Effect of a Thickness-Gradient Dielectric of an Electrowetting Liquid Lens

The experimental verification of the electrical centering effect of a thickness-gradient dielectric in an electrowetting micro liquid lens is presented. This device features an efficient centering scheme and easy fabrication. Two types of liquid lenses with a thickness-gradient and uniform-thickness dielectric layer are fabricated and experimentally compared. Repeatability tests for the off-centering error of the fabricated lenses are carried out for the same tuning range of focal length. The acquired maximum off-centering error for a thickness-gradient dielectric layer is 20 $\mu{\rm m}$ (equivalent to a tilt angle of 0.05 $^{\circ}$ ), whereas the lens with a uniform-thickness dielectric layer is 162 $\mu{\rm m}$ . Off-centering is considerably improved, even compared to the mechanical centering method using a conical geometry (50 $\mu{\rm m}$ ). Moreover, the thickness-gradient dielectric layer could be easily fabricated using a photoresist reflow process, which reduces the required processing steps, making it suitable for mass production.