With the quick development and expansion of the liquid crystal display (LCD) market, high transmittance, fast response, high contrast ratio and wide view angle are usually required to get the higher quality liquid crystal display (LCD) devices. The higher quality attributes are critically required in large size monitors and television (TV) applications. Vertical alignment (VA) LCDs in normally black mode can provide a sufficiently dark off-state, so it is relatively easy to fabricate a LCD with high-contrast ratio. On the other hand, special techniques are needed to enhance the transmittance and improve the view angle. At present, multi-domain vertical alignment (MVA), patterned vertical alignment (PVA) and advanced-super-view (ASV) are the typical modes for getting the high quality display in VA LCDs on the market today.
The rapid evolution of flat screen and wall mounted display monitors has increased the demand for easy to fabricate devices and structures that provide high transmittance, fast response, high contrast ratio and wide view angles. The present invention presents another viable, inexpensive alternative.
Fujitsu Ltd. invented a super high quality MVA LCD as shown in FIG. 1. It was published in SID Technical Digest, vol. 29, p. 1077 (1998), SID Technical Digest, vol. 30, p. 206 (1999), Fujitsu Science Technical Journal, vol. 35, p. 221 (1999), and a typical MVA LCD is disclosed in U.S. Pat. No. 6,424,398 B1 to Taniguchi (2002). The chevron-patterned protrusions are created on the upper and lower substrates to form a multi-domain LCD cells in multiple independent directions. The devices provide a high contrast ratio higher than 300:1, view angle wider than 160 degrees, and a fast response of 25 ms while it has a limited transmittance of 3.4% to a 15″ MVA LCD. In addition, since the horizontal gap between the upper and the lower protrusions must be less than 30 μm in order to obtain fast response time, the pixel alignment needs high precision. Thus, the design specification and preparation process are not easy and the aperture ratio is limited.
Patterned vertical alignment (PVA) was developed by Samsung Electronics Corp. as disclosed in U.S. Pat. No. 6,285,431 B2 to Lyu et al. in 2001, U.S. Pat. No. 6,570,638 to Song in 2003, and first published in Journal of Information Display, vol. 1, p. 3 (2000). In the PVA mode, a fringe field at the patterned indium tin oxide (ITO) drives the LC materials into different directions to form the multi-domains in the on-state as shown in FIG. 2. Instead of bulky protrusions in MVA, PVA uses thin patterned-ITO with slits, which results in a perfect vertically aligned LC cell structure with easy process control. The shapes of the slits are usually rectangular, tilted or zig-zag in series. The devices provide a high contrast ratio higher than 500:1, view angle at 160 degrees, a fast response of 25 ms and a high transmittance at 69% as that of a twisted nematic (TN) cell.
Advanced-super-view (ASV) was developed by Sharp Corp. as described in SID Technical Digest, vol. 32, p. 1090 (2001), and IDW Technical Digest, p. 203 (2002). In the ASV mode, LCs are vertically aligned in the off-state. When the electric filed is applied, LCs tilt towards the center of the sub-pixel electrodes as shown in FIG. 3. The LCs in an ASV LCD mode would face all directions, so the image looks the same no matter what the view angle is and a wide view angle can be guaranteed. Therefore, the wide view angle of 170 degrees, high contrast ratio of 500:1 and a fast response time of 16 milliseconds (ms) can be obtained in the advanced-super-view (ASV) mode using the special flashing backlight system. Since there are improper disclination lines existing in the on-state, the light transmittance is limited at 50% as that of a TN cell when no chiral dopant is added to the LC materials.
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