e-Paper

Display Week 2013 Review:  e-Paper

Display Week 2013 Review:  e-Paper

A new product line from E Ink Corp. topped the surprises at this year’s show.

by Jason C. Heikenfeld

MANY OF US expect Display Week to provide one of the best annual measures of the momentum and status of advances in display technology, and Display Week 2013 lived up to that expectation yet again as a “can’t miss event.”  The first measure of interest in reflective displays came at the e-Paper seminar I gave on the day before the symposium and exhibit.  The presentation was unfortunately the very last seminar of the day, in a large room, and it was therefore pleasing to see a sizable attendance for the second year in a row.  Clearly, there is strong industry desire to understand what is available in e-Paper today and what the future holds.  Many of us working in this area continue to field a barrage of inquiries for “zero-power,” sunlight-legible, super-lightweight, or flexible displays, all of which e-Paper is uniquely positioned to satisfy.  Our response tends to be: “We are working on it, stay tuned!”  So the demand for the next generation of e-Paper products remains robust, and the remaining question is what progress is being made to satisfy that demand.

E Ink Corp. remains the dominant player in the field, surrounded by a diverse set of technologies and small companies vying to grab its market share through improved performance or to enable new applications unmet by E Ink Corp’s electrophoretic imaging film.  Unlike in recent years at the show, it was not the insurgent technologies or companies that caused the greatest excitement in Vancouver; it was E Ink Corp. itself.  The big news occurred on Tuesday in the form of a new product line from E Ink Corp. that was not incremental and not an R&D demo that would never turn into a product.

The press release read: “E Ink Corp. Launches Spectra, the World’s First True Three-Pigment Electronic-Paper Display.” This is significant for two reasons.  First, it shows a major investment and advance toward capturing market share in the electronic-shelf label and signage market.  The market right now is dominated by simple and dim reflective liquid-crystal displays (LCDs), with at best poor color that is relegated to only sub-sections of the display.  Now, with E Ink Corp.’s Spectra, any part of the display can provide a deep black, a brighter and more paper-like white, or a red color to highlight sales or promotions (Fig. 1).

 

Fig. 1:  E Ink Corp.’s Spectra, a new commercial product, adds a third color – red.  At left is a schematic showing how the new product works.  In the middle are examples of three-color labels that could be used as shelf labels in stores, and at right is a shot of a Spectra display alongside the author’s paper business card (conveniently in red, black, and white) for comparison.

 

The second reason for excitement steps us back to last year’s breakthrough reported by Fuji-Xerox on full-color electrophoretic displays based on cyan/magenta/yellow switchable particles.  Many of us wondered whether more than two particles (black and white) could ever be commercialized.  The answer is now yes, and it should be interesting to see just how far this type of technology can continue to advance for signage.  Don’t expect it to lead to color eReaders anytime soon, though, because each time you add another colored particle, the switching speed slows dramatically.  The Spectra demos shown provided only 1-bit gray scale.  Nonetheless, it is great to see a significantly new and visibly compelling product from E Ink Corp.  Credit should be given also to the researchers formerly at SiPix Corp. (which was acquired by AUO and then by E Ink Corp.) who originally developed the technology that underpins this new E Ink Corp. product.

The fluid in E Ink has a level of “stickiness” to it, such that it takes a bit of a threshold of electric field to get colored particles moving such that more weakly charged particles will move more slowly.  The displays first switch between black and white colors, as normal, and in the process move the red particles to the back where they are invisible.  Then, a weaker second electric field is applied to move the red particles to the front in select regions, and, voila, now you have color without the losses of side-by-side color-filter systems such as RGBW (red, green, blue, and white).  Simply put, the demonstrated units at the E Ink Corp. booth looked great.  How long then until additional colored particles can be added?  Despite Fuji-Xerox’s 2012 demonstration of full-color single pixels, the general suspicion is that full-color operation is still fairly far away from commercialization.

Other players showing e-Paper in the exhibit hall included Sharp, Opalux, and Qualcomm, each displaying familiar looking e-Paper demonstrators.  The Qualcomm booth had two smartphones with the company’s “next generation” mirasol technology.  These displays looked really, really good and completely superior to the performance of the commercially available Kobo eReader that uses mirasol.  If e-Paper modules like this can be manufactured economically, it would be tough for any other technology to compete with its visual performance in bright ambient light.  However, the prototypes were, in fact, static images, meant to convey the expected performance of a “multiposition” mirror that uses optical interference to generate any pure color within a single subpixel (except white, which still significantly limits the maximum possible white state).  These static-image prototypes are just thin-film interference stacks, and I recall seeing similarly beautiful static images shown a decade ago by Iridigm (acquired by Qualcomm in 2004).  Given the manufacturing challenges Qualcomm had faced for just the two-position mirrors, multi-position mirrors are likely to raise even more difficult challenges (Fig. 2).

 

Fig. 2:  Wouldn’t it be great if e-Paper displays looked like this?  This “static” non-switchable demonstrator from Qualcomm shows the excellent potential performance of a multi-position mirror, next to a white business card for brightness comparison.

 

Also in the exhibit was the Japan Display, Inc. (JDI), reflective-display prototype, which I was able to see up close for the first time.  The color looks excellent for a reflective LCD (Fig. 3).  It employs a gain reflector.  I was very skeptical of gain reflectors until recently, when through some of my own company’s (Gamma Dynamics) developments I saw that, if properly implemented, gain reflectors can look diffuse over a wide viewing cone and in diffuse or off-axis lighting.  This is the case, however, only if the reflector is properly engineered and has adequate amplitude.  Gain reflectors, when they work best, leverage the fact that for a personal device such as an eReader, you can orient the panel toward yourself.  This allows the reflector to then do at least one of two things: (1) reduce light loss due to total-internal reflection (TIR) at the front glass and (2) amplify the light falling within the typical viewing cone of the user.

 

Fig. 3:  At left, the JDI color reflective LCD appears next to a business card for color reference.  The middle image shows the LCD with directional lighting at the booth, and the image at right appears with the author’s portfolio blocking the light so the panel receives off-angle light only.

 

In the case of the color reflective LCD from JDI, the designers chose to use a highly directional (and conventional) gain reflector that does not make efficient use of off-axis (diffuse) illumination.  This was evident if you blocked the directional light source above the demo and permitted only diffusion illumination.  So this embodiment would require a bright ambient light source located just behind your head or shoulders to make a compelling eReader or tablet display.  However, such displays could be valuable in a fixed orientation and lighting environment, which, for example, signage or electronic shelf labels can provide.  Also to its credit, in its proceedings paper, JDI does show diagrams and openly communicates the lighting and measurement orientations used in its characterization of performance.

The e-Paper symposium talks were all on Tuesday this year, with a few other related papers and posters scattered throughout the remainder of the week.  In the first talk of the day, Seiko-Epson reported on a binary (1-bit, only black/white) eReader based on E Ink that allowed fast scrolling, page turning, and pen input.  I tried the pen input at the author-interview session and it was nearly flawless with seemingly immediate response.  The talk showed how high resolution (300 ppi) can help spatially dither gray-scale images with fast 1-bit E-Ink switching.  Most importantly, the talk provided human-perception tests that show that simple black/white operation might be better for dedicated reading and office documents – applications for which the faster page turning, scrolling, and pen-input might bring real value to the user.  It has been known for some time that E Ink can provide fast switching if you are willing to give up some or all gray scale, and, for video demos, sacrifice display contrast.

During the second e-Paper session, my Ph.D. student Matthew Hagedon delivered an invited talk on “Progress in Electrofluidic Imaging Film.”  The data presented supports an argument that this is the only known technology with a roadmap that can provide high resolution, video speed, and SNAP (newsprint) quality color.  Unfortunately, as I am intimately aware, the technology development is early stage, only about 18 months old, and active-matrix-driven modules are just now in development.  One promising demonstration for the electrofluidic imaging film, though, was basic proof of concept for passive-matrix addressing.  Passive-matrix addressing is highly desirable for applications such as signage and electronic shelf labels, where low cost is critical.  Passive-matrix addressing is something that E Ink currently cannot provide.

In the second e-Paper session, IRX Innovations (Henzen et al.) presented some much more sophisticated active-matrix-driven electro-osmotic display technology (Fig. 4).  This approach is unique in terms of particle movement, but not enough information was presented to provide a deep understanding of the underlying physics.  The early prototype results were modest (3:1 contrast, slow switching of several seconds) but the team from IRX maintains that the upside potential includes a maximum white state near 70% in stacked CMY (cyan, magenta, yellow) operation and near-video speeds.  The electro-osmotic approach is novel in many ways and will be worth following closely as IRX continues to develop the technology.

 

Fig. 4:  Alex Henzen of IRX Innovations displays active-matrix magenta and yellow modules built on electro-osmotic technology.

 

Another talk of note was given by Norihisa Kobayashi from Chiba University.  Prof. Kobayashi was part of the early electro-chromic material development that led to Ricoh’s recent demonstration of a strikingly beautiful color active-matrix electrochromic display.  This year, he presented a single electrochromic cell that could switch between a clear state, a black state, and also a mirror reflector state.  Although this is early-stage work, and the maximum number of switching cycles is unknown, I can imagine many interesting applications ranging from switchable mirrors, to privacy windows, to light- and thermal-management technology.

The last note of interest came not at Display Week 2013, but right before the conference, with the revelation that Amazon had just purchased Liquavista from Samsung.  The history of this company began with Philips, from which it was spun off in 2006.  Then it was purchased by Samsung, then Amazon.  Time will tell what this all means.  It has been clear for some time, especially with its investment in Lab 126, that Amazon takes the hardware side of displays quite seriously.  The speculation is, of course, that this could lead to a next-generation color-video reflective eReader or tablet product from Amazon.

With Display Week 2013 now behind us, progress clearly continues on all fronts.  Without doubt, e-Paper is a real and growing segment of the display industry.  What is less clear is how much longer it will take to satisfy consumer and corporate demands for the next generation of e-Paper technology.  OLEDs and LCDs will continue to battle it out in coming years, but neither will supplant many of the e-Paper applications.  With the huge shift to LCD tablets already enacted, e-Paper is left to control much of its future destiny and that will depend on its ability to provide bright whites, more saturated color, and access to broader media content such as seamless web browsing and at least crude animation/video.  Looking forward to 2014!  •

 


Jason C. Heikenfeld is a Professor in the Department of Electrical Engineering and Computing Systems at  the University of Cincinnati.  He can be reached at (513) 556-4763; heikenjc@ucmail.uc.edu..