Pixel oil motion in Electrowetting Displays: a study of stability and reproducibility

Problem Definition:

Samsung’s electrowetting displays are known to combine high reflectivity with energy efficiency and millisecond switching times enabling video speed. Displays can be operated in reflective, transmissive and transflective mode and offer the possibility to show full color images, which demonstrates the versatility of the technology. The principle of an electrowetting display is based on an optical switch operating between a light absorbing state and a light transmissive state.
The electrowetting system consists of a two liquids: a light absorbing non-polar liquid (herein referred to as oil) and a transparent polar liquid (hereinafter “electrolyte”). When the system is idle (“off-state”) the oil covers the pixel area and absorbs either the ambient light or the light from a backlight. In the “on-state”, when an electrical field is applied, the wetting properties of the hydrophobic layer change and consequently cause the oil’s surface to break and contract to leave a significant fraction of the pixel area open for light transmission. The electro optical properties of pixel switching are affected strongly by the position where the oil surface breaks and the location where the oil collects. This position can be influenced significantly by the pixel architecture and the material properties, both before and after operation.

Objectives:

The objective of the project is to investigate the electro-optical behavior of the electrowetting pixel in terms of reproducibility of the oil motion and the stability of the operation during lifetime. Contribution from different critical parameters (variations in pixel layout, materials and processes) will need to be assessed in order to determine their contribution to the final performance of an electrowetting display. The experimental part of the project also encompasses the validation of numerical simulation models, such as computational fluid-dynamics and electro-hydrodynamics models. To obtain detailed experimental data optical techniques, such as high speed camera image processing and spectrometry, are available to determine the correlation between experiment and simulations. Furthermore depending on the first results of the study there is the possibility to improve the current characterization methods and tools with the support of Samsung engineers.

Keywords:

electrowetting, reflective displays, samsung, simulation and experimental

Location:

Samsung in Eindhoven (formerly Liquavista)