The Biprimary Color System for E-Paper: Doubling Color Performance Compared to RGBW Sayantika Mukherjee and Jason Heikenfeld Novel Devices Laboratory, University of Cincinnati, Cincinnati, 45221, USA Nathan Smith, Mark Goulding, Claire Topping and Sarah Norman Merck Chemicals Ltd. University Parkway, Southampton, UK. Qin Liu and Laura Kramer Hewlett Packard, Corvallis, Oregon, USA Abstract: We demonstrate the “biprimary” color system with dual particle electrophoretic dispersions and a 3- electrode system. Preliminary contrast ratios reach 10:1. Furthermore an electrokinetic cell is demonstrated confirming basic functionality for EKD panels. A theoretical pixel simulation confirms biprimary doubles the color performance compared to RGBW pixels. Introduction Reflective displays or electronic paper aims to mimick the same ability of print on paper, due to sunlight legibility, low-power, light weight and improved compatibility with roll-to-roll manufacturability 1 . However, out of all the technologies that exist for reflective e-paper, none has been able to provide bright colors without compromising performance such as switching speed or pixel resolution, which is the case for multilayer subtractive CMY technologies 2,3 . Fast switching and high resolution technologies tend to use the RGBW system which provides saturated color at only 25% of the display area 4 . Hence, there is a need for a new single-layer color system, which acheives color performance similar to subtractive CMY color without such significant compromises in other performance metrics. We demonstrate here the biprimary color system, which utilizes both the RGB and CMY colors by grouping two complimentary colors, one from each, such that they are inside the same pixel. As demonstrated in Figure 1, the pixel is divided into three subpixels and each subpixel is dual-colored with one from the RGB additive primaries and its complementary color in the CMY subtractive primaries. Theoretically a high brightness white (W) state can be achieved by clearing up the pigments and the black (K) state can be achieved by fully mixing them. The experimental demonstration utilizes electrophoretic switching and two-particle complementary dispersions developed by Merck 5 . Here we demonstrate the dual particle complementary Green/Magenta (G/M) dispersion 5 in a simple interdigitated three electrode architecture, by using controlled motion of the pigment particles. All the four states of KWGM could be achieved with an initial contrast ratio of 10:1. The same ink is also demonstrated in a faster, two-electrode electrokinetic layout. The potential of the other two biprimary pairs (R/C and B/Y) is similar, and can be extrapolated from this work. Figure 1: Diagrammatic representations of RGBW and biprimary color systems, along with examples for display of the colors W, G, and M. Calculations of theoretical reflection (%R) and color-fraction (CF) are shown in (b, d). Design and Operation The dual particle ink dispersions are generic dyed polymeric microparticles formulated and synthesized by Merck Chemicals (known as EMD in North America). They can synthesize dispersions by altering particle size, charge, and surface functionality by using suitable dyes to formulate combinations of two colored particles including RGBCMY. They serve as a “ready to use” color electrophoretic inks. The typical range of particles is from 60-1000 nm, we have used the G/M dispersion with the green particles being negatively charged and the magenta being positively charged. We have fabricated both 3 and 4 interdigitated electrode architectured devices to test the G/M dispersion. The 3-electrode system has been used in Late-News Paper 59.4L / S. Mukherjee SID 2014 DIGEST • 869 ISSN 0097-966X/14/4502-0869-$1.00 © 2014 SID