Research on design and fabrication of electrowetting-based varifocal liquid lens array

Abstract

Electrowetting is a phenomenon that can control the surface tension of liquid when a voltage is applied. This thesis introduces the fabrication method and characteristics of liquid lens array operated by the electrowetting phenomenon. The lens array chamber is fabricated by the three different methods: mold, lithography, and dry etching. IZO deposited by sputter is used as an electrode. For the dielectric layers between the two electrodes, parylene C and tantalum oxide are deposited. Parylene C known as a good moisture barrier is used to prevent water penetration and tantalum oxide(ε=23-25) with its high dielectric constant is used to minimize the increase of operating voltage.Dielectric materials are arranged as the sandwich structure where parylene C is divided into two layers and tantalum oxide is inserted between the parylene C layers. This sandwich layer prevents pinhole effect further. Hydrophobic surface which enables the range of contact angle from 60 to 160 degree is coated to maximize the effect of electrowetting, making wide band of dioptric power.Liquid injection into each lens chamber is proceeded by two different ways. First way is using self water-oil dosing that requires cosolvent and diffusion effect, while the second way is micro-syringe way using hydrophobic surface properties. After distilled water and dodecane oil the two immiscible liquids are injected into each lens of the lens array, it is sealed by IZO coated glass inside the water bath. The underwater sealing is performed using UV adhesive that does not dissolve inside water. The fabricated 23x23 lens array has 1mm diameter size with 1.6mm interval distance between adjacent lenses. Several lens characteristics including diopter, capacitance, uniformity, operating voltage, and operating temperature are measured and evaluated. The diopter of the lens is obtained by measuring focal distance when the lens is in convex state. The measured diopter is from -124 to 120.2 when voltage changes ...