Another new e-paper technology has appeared on the horizon. It has all the properties people are looking for in e-paper, including bi-stable operation for low power and high reflectivity, possibility of flexible substrates and up to 85% reflectivity according to the developers. But there is more, including video rate operation and full color with high reflectivity.

Matt Brennesholtz
Insight Media Analyst

The start-up developing this electro-fluidic technology is Gamma Dynamics, (Cincinnati, OH; www.gammadynamics.net) a spin-out of the University of Cincinnati. It is working with strategic partners, Sun Chemical, Polymer Vision and, of course, the U. of Cincinnati. John Rudolph, who was VP of business development at US Precision Lens in the 1980’s when USPL dominated the CRT projection lens business, is President and Dr. Jason Heikenfeld, head of the UC Novel Devices Laboratory, is Principal Scientist.

Electrofluidic displays place an aqueous pigment dispersion inside a tiny reservoir within each pixel. The reservoir covers <5-10% of the viewable pixel area and when the fluid is in the reservoir, the back of the display is visible, which would normally be a diffuse, white reflector. Voltage is used to electromechanically pull the pigment out of the reservoir and spread it as a film directly behind the viewing substrate. Looking through the pigment at the white backplane is very similar to looking through the pigments on printed paper at the white paper underneath. This similarity to paper allows Gamma Dynamics to achieve paper-like performance.

When voltage is removed, surface tension causes the pigment dispersion to rapidly recoil into the reservoir. Response time of the system is on the order of 1mS, plenty fast enough for full-motion video. In the black and white version or the sub-pixelated color version of this technology, the pigment is a black carbon dispersion.

Gamma Dynamics can achieve full color operation in two ways. The first is the normal red/green/blue/white sub-pixelization process with black pigments and red, green and blue color filters, plus the white sub-pixel. With this method, the color saturation can be good but the maximum reflectivity is on the order of 40%. An alternative approach is to use a 3 layer structure with the subtractive-color pigments magenta, cyan and yellow. When all three pigments are drawn out of their respective reservoirs, all light is absorbed and the system produces black. When all three pigments are in their reservoirs, light passes through all three layers, reflects off of the white backplane and returns to the viewer. According to Gamma Dynamics this allows 75% reflectivity in the white state.

A two layer version based on a sub-pixel configuration where each sub-pixel has both color filters and two different colored pigments can also produce full-color operation. This system is likely to have a maximum reflectivity of about 60%, according to Heikenfeld. It would be significantly less expensive to manufacture than the 3 layer version but would have better reflectivity than the sub-pixelated version.

This technology was originally developed by the Novel Devices Laboratory at the U. of Cincinnati. (http://www.ece.uc.edu/devices/index.html) Several videos of prototype systems in operation are posted on the website here.

Insight Media had a brief chance to talk to Rudolph and Heikenfeld while they were driving to Dayton to give a presentation on the technology to the local chapter of SID. They clarified one point for me: the current version of this technology is not in fact bi-stable and requires a holding voltage to maintain the image. Different versions of the design have true bistability but those are not the current focus of the company. They promised to e-mail me additional information and have a longer phone discussion in time for an expanded version of this article to appear in the May issue Mobile Display Report.