By Lori DeBoer
Technology that could alter the business of putting ink on paper was announced at the SID ’95 meeting in Orlando in May.
The electronic documument viewer prototype uses reflective cholesteric liquid crystals being developed in the ALCOMM Center. Using this newest generation of liquid crystal displays has several advantages. The high-contrast display is purely reflective, replicating paer-like viewing using available light—unlike other liquid crystal displays, which require backlighting. The display has a wide viewing angle, is sunlight readable, and has full color capability. Its screen requires power only to write an image, not to refresh it. These displays can also be made with plastic substrates, making them sturdy, lightweight, an economical to manufacture.
Using the dynamic drive technology featured in the April ALCOM Update, page-turn rates of less than a second are possible for even 300 dpi resolution displays of full-page size. Once the drive electronics can be produced cheaply, the display will become competitive as a commercial product.
The project is being conducted by researchers at Kent, the University Stuttgart in Germany, and Kent Display Systems in Kent, Ohio. The liquid crystal technology was developed by a research team lead by Bill Doane, LCI director. Other members were Deng-ke Yang, Phil Bos, and L.C. Chien, LCI senior research fellows, and John West, LCI associate director. The prototype itself was fabricated by Matthias Pfeifer, an LCI research associate, with the assistance of Rainer Bunz, a doctoral student under Professor Erst Luder at the University of Stuttgart, and Zvi Yaniv and Clive Catchpole, KDS. The project was supported by a $1.93 million, three-year grant from ARPA and the ministry of Science and Technology in Germany.
Work on the electronic newspaper prototype began in 193 in a cooperative effort with KDS and the University of Stuttgart, which has the facilities for making high-resolution, large-area displays. The ultimate goal of the project is to make a letter-size, 300 dpi, full-color reflective cholesteric display. In January 1994, the first effort yielded a full page-size, 100 dpi, green-on-black monochrome display without gray scale.
“The biggest problem to overcome was that the liquid crystals being used were polymer/liquid crystals mixtures, and it is difficult to fill large areas without the separation of the components,” said Pfeiffer. Any approach where the polymer is only on the surface of the liquid crystal cell proved more satisfactory. The team was able to make other colors because color technology has been developing simultaneously. A second-generation display prototype with yellow-on-back or white-on-black was developed in September/October 1994.
In May 1995, a third-generation prototype was presented to the public; it has a dual-scan display, which allows for even faster addressing. It uses tape-automated bonding (TAB) drive chips, a newer technology with higher density and more outputs per chip than standard integrated boards, said Pfeiffer. This prototype has a controller and microcomputer built in. A PCMCIA Flash Memory Card stores graphics data. The display system has select buttons to choose a page or invert the graphics data, whereas the two previous versions were static.
The first-and second-generation displays measured 896 x 1152 pixels, while the third-generation display measures 864 x 1120 pixels. The active area of all the displays is 8 ½ by 11 inches. The rows and columns of the first- and second-generation displays were alternately addressed from the right and left sides, and the tops and bottoms, respectively. Half the contacts on each side were combined in groups to increase the reliability of bonding. The columns of the third-generation display were split in the center. Each half of the columns is addressed from the top or bottom of the display, respectively. The electrode contacts are combined in high-density groups to allow for tape-automated bonding.
Pfeiffer said the team is now at work developing a viewer with a 3.87-million pixel display and a 200-dpi resolution. Plans for the electronic viewer include increasing the resolution, moving from glass to plastic substrates, and implementing color and gray scale.
Article originally published in the July 1995 issue of ALCOM Update, a newsletter for the NSF Science and Technology Center for Advanced Liquid Crystalline Optical Materials, a consortium off Kent, Case Western Reserve and Akron universities.
