Multidomain vertical alignment enhances LCDs

Dec. 1, 1997

Researchers at Fujitsu Ltd. (Kawasaki, Japan) have developed a method for enhancing the image quality and simplifying manufacture of large-sized liquid-crystal displays (LCDs). Applying the new technique to direct-view thin-film-transistor (TFT) LCD panels has allowed the researchers to make 15-in.-diagonal LCD screens with an image quality, viewing angle, and response time superior to any conventional TFT-LCD in the industry.

Paul Mortensen

Multidomain vertical-alignment LCDs exhibit wide viewing angles of more than 160°, both vertically and horizontally, compared to 45° and 80°, respectively, for a twisted-nematic display. The contrast ratio of 300:1 and a response time of 25 ms, which is almost equivalent to the specifications of a typical cathode-ray tube. The drawback, however, is that these panels require three times as much energy as traditional screens, which makes them unlikely to succeed at the low end of the market, although they will likely find application as high-end fixed computer monitors.

The new multidomain vertical-alignment (MVA) technology results from continuing research based on the company`s vertical-alignment technology developed last year. The technology introduced liquid crystals (LCs) with negative dielectric anisotropy, thereby increasing both response time and contrast compared to standard twisted-nematic LCDs. The MVA technology embodies the vertical-alignment achievements but with improved image quality and simplified manufacturing processes to realize volume production.

Display enhancements

The MVA technology improves viewing angles by allowing a "multidomain alignment," that is, the inclination of multidirectional LC molecules.

In the manufacturing process, the productivity and quality of MVA LCDs has been improved by eliminating the "rubbing" process normally required to align LC molecules in standard LCD manufacturing. A protrusion designed on the TFT substrates and on the color filter substrates automatically controls the alignment of the LC molecules, eliminating the need for the conventional rubbing process and the associated contamination problems (see figure).

For high contrast, MVA LCDs use a vertical-alignment layer and negative dielectric anisotropy LCs. Polarizers are adhered to the outside surface of both glass substrates at 90° to each other. This structure differs from a conventional twisted-nematic LCD in that the LC molecules are aligned vertically, rather than parallel, to the glass substrate when the applied voltage is off. This increases the ability of LC molecules to block light in the off-voltage state, resulting in a dark black level and the 300:1 contrast ratio.

Fujitsu began volume production of the 15-in. MVA LCDs in October 1997. Prototypes of the 15-in. XGA panel using MVA technology were shown at the Japan Electronics Show in Makuhari, Chiba, Japan (Oct. 1997). According to Fujitsu`s head of development for LCD screens, Shobu Orihara, although the MVAs use three times as much energy as conventional screens, the company expects to produce between 3000 and 5000 of them each month this year and to reach 10,000 each month next year.