Introduction to Adaptive Lenses

Chapter 3

Electrowetting Lens

3.1 Introduction

When a small amount of conductive liquid (electrolyte), such as salt water, drips on an electrically insulating dielectric layer, the liquid can form a droplet on the layer surface with a contact angle. If the contact angle of the droplet can be modified by an external voltage, the change of the contact angle between the dielectric layer and the conductive liquid is defined as the electrowetting effect. The study of electrowetting has a long history. Probably Gabriel Lippmann was the first physicist to report such an effect by investigating the electrocapillary phenomenon of mercury in 1875 (1). Since then, electrowetting has aroused a lot of interest and has been studied extensively. In 1936, Froumkine used surface charge to vary the shape of water drops (2). In 1981, Beni and Hackwood first introduced the term “electrowetting” to describe a novel display using a dielectric liquid and a liquid electrolyte (3). A major challenge that limits the applications is electrolytic decomposition of water upon applying a certain voltage. In the early 1990s, Berge revolutionized the structure of electrowetting devices by using a thin insulating layer to separate the conductive liquid from the metallic electrode (4, 5). This approach successfully eliminated the electrolysis concern. These early device structures paved the foundation for today's advanced electrowetting on dielectric (EWOD) or electrowetting on insulator coated electrodes (EICE). ...