Robert Andrew Hayes

Screen-printing fabrication of electrowetting displays based on poly(imide siloxane) and polyimide

Abstract We report a screen-printing fabrication process for large area electrowetting display (EWD) devices using polyimide-based materials. The poly(imide siloxane) was selected as hydrophobic insulator layer, and relatively hydrophilic polyimide as grids material. EWD devices that use poly(imide siloxane) as hydrophobic insulator fabricated with conventional methods showed good and reversible electrowetting performance on both single droplet level and device level, which showed its potential application in EWDs. The compatibility of polyimide-based materials (hydrophobic poly(imide siloxane) and hydrophilic polyimide) guarantee the good adhesion between two layers and the capability of printable fabrication. To this end, the hydrophilic grids have been successfully built on hydrophobic layer by screen-printing directly. The resulting EWD devices showed good switch performance and relatively high yield. Compared to conventional method, the polyimide-based materials and method offer the advantages of simple, cheap and fast fabrication, and are especially suitable for large area display fabrication.

Microfluidics for electronic paper-like displays

Displays are ubiquitous in modern life, and there is a growing need to develop active, full color, video-rate reflective displays that perform well in high-light conditions. The core of display technology is to generate or manipulate light in the visible wavelength. Colored fluids or fluids with particles can be used to tune the light intensity (greyscale) or wavelength (colors) of reflective displays by different actuation methods. Microfluidic technology plays an increasing role in fluidic manipulation in microscale devices used in display areas. In this article, we will review microfluidic technologies based on different actuation methods used for display applications: pressure-driven flow, electrophoresis, electroosmosis, electrowetting, magnetic-driven flow, and cell-actuation principles.

Interfacial electrofluidics in confined systems.

Electrofluidics is a versatile principle that can be used for high speed actuation of liquid interfaces. In most of the applications, the fundamental mechanism of electro-capillary instability plays a crucial role, yet it’s potential richness in confined fluidic layers has not been well addressed. Electrofluidic displays which are comprised of thin pixelated colored films in a range of architectures are excellent systems for studying such phenomena. In this study we show theoretically and experimentally that confinement leads to the generation of a cascade of voltage dependent modes as a result of the electro-capillary instability. In the course of reconciling theory with our experimental data we have observed a number of previously unreported phenomena such as a significant induction time (several milliseconds) prior to film rupture as well as a rupture location not corresponding to the minimum electric field strength in the case of the standard convex water/oil interface used in working devices. These findings are broadly applicable to a wide range of switchable electrofluidic applications and devices having confined liquid films.

Novel Driving Methods for Manipulating Oil Motion in Electrofluidic Display Pixels

By applying driving voltage schemes with different rising gradient and the same final voltage in an electrofluidic display device (EFD), several kinds of oil patterns have been generated. The results show that, in the initial stage of oil film splitting and contraction, driving voltage has a crucial influence on the microfluidic behavior and oil distribution in each pixel. Oil patterns significantly affect the pixel aperture and, ultimately, the reflectivity of the display panel. The oil pattern with fewer oil droplets has a higher aperture ratio and higher reflectivity. The observation that oil patterns can be controlled by varying driving schemes offers a new way of manipulating oil motion in EFD pixels.

A novel driver for active matrix electrowetting displays

Abstract Electrowetting display (EWD) is a reflective display technology in which fluidic pixels can response and switch quickly by electronic control, showing the capability for video-speed reflective display applications. In this paper, a new driver system is proposed and realized for video playing function of active matrix electrowetting display (AM-EWD). The hardware system is designed based on Field-Programmable-Gate-Array (FPGA) and the existing electrophoretic display (EPD) driving integrated chips (IC). A driving logic circuit and FPGA software is introduced for providing the EWD system with driving and timing control. And a set of specific driving waveforms, which is loaded to a lookup table of the FPGA in advance, is designed to display grayscale on EWDs. 4-level gray scale videos have been successfully performed by applying the driving waveforms. To our knowledge, such work has not been reported before.

Simplified dynamical model for optical response of electrofluidic displays

Abstract In this work we analyze the switching behavior of an electro-fluidic pixel in separate stages. For ‘on’ switching we consider the motion leading to oil film rupture (initiation stage), fast oil-dewetting and a slower droplet rearrangement stage. For ‘off’ switching we consider fast oil wetting and surface reforming to the flat (dark) state. A dynamic model derived from an overall energy balance analysis has been employed to describe the optical response inside an electrofluidic display (EFD) pixel for the oil dewetting and wetting stages. By comparison with the experimental electro–optic response data, the accuracy and shortcomings of this model can be illuminated. The optical response asymmetry between on and off-switching and optical response delay during the on-switching process are well described and explained. In addition, the liquid film reforming dynamics and electrohydrodynamic instability analysis are used to estimate the oil film rupture and film reforming times very well. This study provides a straightforward approach to describe the complicated electrofluidic switching dynamics inside an EFD pixel, which may guide the further optimization of EFD device design and driving schemes.

Influence of fluoropolymer surface wettability on electrowetting display performance

Abstract Amorphous fluoropolymer (FP), as a material for both insulating and hydrophobic coating, plays an essential role in electrowetting displays (EWD). In this work, three FPs based on Teflon AF1600, Hyflon AD60 and Cytop 809A were studied according to their influence on the EWD performance. Both water/air and oil/water contact angles were utilized to compare the surface wettability of these three FPs. Reversible and fast optical switch could be achieved in the EWD devices fabricated using all three FPs; however, the less hydrophobicity of the Cytop 809A surface would lead to a slower Off-switching speed or even incomplete close of the micro-pixels. The “reflow” temperature for restoring the hydrophobicity of fluoropolymer surface should be high enough to achieve a sufficient surface recovery, and at the same time avoid inducing failures like film dislocation and breakdown. The optimal “reflow” temperature has been investigated and evaluated based on the EWD performance. This work would help us deeply understand the surface wettability effect on fluidic behavior in micro-pixels driven by electrowetting, and related optical phenomena in EWDs as well.

A Reflective Display Technology Based on Electrofluidics

In this paper we describe the design, driving and electro-optical behavior of an electrofluidic, or electrowetting, display panel. Electrofluidic displays involve the movement of a colored oil water interface as a result of polarizing the interface between water and a hydrophobic surface under the influence of external electric field. The proposed direct-segment drive approach successfully drives the display panel based on electrofluidic. The electro-optical behavior of electrofluidic display samples are measured and analyzed. The ton and toff of the pixel is 16 ms and 8 ms, respectively, which demonstrates that electrofluidic display panels have the capability to show video content.