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[Patterned Vertical Alignment (PVA) mode]

The PVA mode was originally developed by Samsung in 1996. It is characterized by multi-domain structures with fringe-field effect. The electrodes are designed in a zigzag/cheveron pattern, as show in the figure 1.

Figure 1. The working principle of Patterned Vertical Alignment (PVA) mode.

In the off state, the LC molecules are oriented perpendicularly to the substrate, as result, there is no phase retardation and an excellent black state is obtained. In the on state, the LC molecules will align perpendicular to the electric field because of Δε < 0, consequently a multi-domain structure of LC director configuration is obtained, which gives excellent viewing angle. A PVA on-pixel texture under polarized microscope is shown in figure 2, a retardation plate is inserted to distinguish the director tilt direction. In the yellowish area, the director tilts 45 degrees upper left, and in the greenish area, the director tilts 45 degrees upper right.

Figure 2. On-pixels of PVA under polarized microscope. Retardation film is inserted.

Compared with IPS, PVA has higher peak contrast ratio because of the good black state, however IPS usually has a better off axis contrast ratio, figure 3 shows a comparison between PVA and S-IPS.

Figure 3. Viewing angle performance comparison between PVA and IPS LCD.

Recent development of PVA mode has increased the domain numbers from 4 to 8, so-called S-PVA, which further increased the viewing angle performance. With Samsung's Dynamic Capacitance Compensation (DCC) driving scheme, the response time can be improved from 50ms to 8ms. Figure 4 shows the driving scheme of the DCC II.

Figure 4. Samsung's Dynamic Capacitance Compensation (DCC) driving scheme.

The first low amplitude pulse is to establish the pretilt angle, and the overshoot speeds up the switching. A comparison with conventional driving scheme is shown in animation 1.

Animation 1. DCC II driving scheme compared with conventional driving scheme. (Right-click to replay the flash).

Now, S-PVA is widely used in large size flat panel LCD, PC monitors, TV. Samsung used S-PVA to build the world largest 82-inch TFT-LCD in March 2005 (press release).

Further Readings and References:

K.H. Kim, and J. H. Souk et. al, Proceeding of Asia Display 98, 383 (1998).

K.H. Kim, "Advance of PVA Technology for Multi-media Applications", SID Digest, 40.4 1208 (2003)


Last update: April, 2006
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