Reliable sandwich-like multilayer dielectric structure for tunable lens application design

Abstract

Tunable lens is one of the most popular application of electrowetting-on-dielectric (EWOD) technology. Nowadays, the electrowetting-based tunable lens has successfully manufactured and commercialized by several companies. To be able to compete with the already developed electrowetting tunable lens, several parameters such as low operational voltage and dioptric power range should be improved. Theoretically, a low operating voltage can be obtained by using a very thin and/or high dielectric constant materials. However, thin dielectric layer is known to be vulnerable to dielectric failure and pinholes problem. A multilayer dielectric structure is commonly used to increase the breakdown voltage and delay the dielectric failure. In this thesis, a modification of conventional multilayer dielectric structure for EWOD called sandwich-like multilayer dielectric is introduced. In conventional multilayer, two dielectric materials are simply stacked together forming a two layer structure while in sandwich-like multilayer, those two materials are assembled to form a three layer structure. One dielectric material will be deposited two times, as the first and third layer respectively. Those layers are called the sandwich layer while the other material placed in between the sandwich layer is called the middle layer. The performance of both multilayer structures was compared. Both were composed from the same dielectric materials and designed to have an identical thickness and total capacitance. Dodecane oil (n = 1.421) and DI water with 0.1% SDS (n = 1.33) were used as the conducting liquid and the insulating medium respectively. Although both structures were operated at a low voltage, sandwich-like multilayer structure gave a lower contact angle saturation, higher breakdown voltage and a mild electrolysis compared to the conventional structure. To further enhance the breakdown voltage, three dielectric materials, Parylene C, Aluminum Oxide (Al2O3) and Tantalum Oxide (TaOx),...