18.3: Implementation of a New Wide Viewing Angle Mode for TFT‐LCDs

Abstract

Compare to the conventional twisted nematic (TN) mode TFT-LCD fabrication process, so far suggested method [1][2][3][4][5][6] for the wide viewing angle modes require extra mask-counts. Patterning of the color filter common electrode to achieve the multi-domain vertical alignment (VA) mode costs additional process step. In addition, to avoid improper disclinations, strict alignment margin is necessary. Enhanced vertical alignment (EVA) mode has been developed where the multi-domain cell is formed by the interaction between fringe fields of the pixel electrodes and protrusions on the TFTarray panel. Compared to the TN-mode, since the common electrode is not patterned, EVA mode does not require any additional mask-count. Using the combinations of multi-layer overlap patterns with gate metal, gate dielectrics, passivation nitride, and source/drain metal, protrusions can be formed during the normal TFT-array fabrication process. Viewing angle of the EVA mode can even surpass other wide viewing modes.

High-transmittance Multi-domain Vertical Alignment Liquid Crystal Device with Protrusion Structure

“…To overcome this problem, several methods to realize a multi-domain structure have been proposed. The patterned electrodes and the protrusion structure make it possible to develop a multi-domain VA mode [5][6][7]. Although a multi-domain VA mode offers better viewing angle characteristics than a single-domain VA mode, the transmittance of a multi-domain structure decreases because of the presence of disclination lines at the domain boundaries.…”

Electrode structure for high transmittance and aperture ratio in TFT-LCD

“…TN mode, however, has shortcomings such as a narrow and non-uniform viewing angle characteristic. To resolve the drawbacks of TN mode, a variety of novel concepts such as in-plane switching (IPS), fringe field switching (FFS), patterned vertical alignment (PVA), multidomain vertical alignment (MVA) modes were proposed [2][3][4][5]. Although these modes exhibit better viewing angle characteristic than the conventional TN mode, their cell structures were designed in such a way that more than two domains are formed for a wider viewing angle.…”

Liquid crystal VAN tilt bias by surface relief patterning

“…The layers allowed the production of multiple domains by controlled oblique fields. Kwag et al introduced the "Enhanced Vertical Alignment" (EVA) mode [8]. Of these methods, that proposed by Kwag et al is perhaps of particular interest for projection LCOS applications.…”

“…The presence of the features modifies the electric field lines around the underlying pixel electrodes. The angle between electric field lines and LC director have a strong effect on the direction in which the director will reorient [ 7,8,9]. This is especially important in the dip case where the shape of the electric field can oppose and override the effect of the surface feature anchoring.…”

“…Hence, a small electrode gap is desirable beneath a rectangular dip feature. Conversely, a large electrode gap is desirable beneath a bump feature to produce a deep through in the equipotentials, encouraging tilt bias away from the feature comparable to the effect seen in electrode gaps in Kwag's paper [8].…”