TFT LCD Wide Viewing Angle Technologies


LCD has a genetic disadvantage compared to other display technologies: Narrow Viewing Angles.  For the last 40 years, scientists and engineers put a lot of effort to improve LCD viewing angles and made great progress. Although LCD viewing angle still has the limitation, it has been accepted by most applications.  We will briefly introduce different LCD technologies and the improvement of LCD viewing angle.

TFT LCD Structure

Orient Display: Gray Scale Inversion for TN Type TFT LCD

Fig. 1 TFT LCD Structure

TN (Twisted Nematic) Type TFT LCD

TN LCD has been discussed before (review Twisted Nematic LCDs), we will not get in depth here.

    • PROs: Low Cost
    • CONs:
      • Overall viewing angles will be smallest for TN LCD.
      • One of the four viewing directions will have a narrow viewing angle. The location of this weak angle can be controlled in the “rubbing process” of the TFT glass at the early stage of the TFT glass fab.
      • Gray scale inversion will occur in the direction opposite the weak viewing angle.
      • Normal White (NW) mode: dead pixel = a bright spot.
      • Slower response time, lower contrast, lower aperture ratio.
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Orient Display: Gray Scale Inversion for TN Type TFT LCD

Fig. 2 Gray Scale Inversion for TN Type TFT LCD

From the Fig. 2, we see that the 6 o’clock viewing direction has gray scale inversion and the angle is not usable.  But viewing angle testing equipment can’t identify gray scale inversion. Normally gray scale inversion viewing angle has the biggest viewing angle which confused a lot of users. For this reason, we indicate the angle with gray scale inversion in Orient Display specification.

TN TFT operates in “Normal White” (NW) mode.  This means the background color is “light” when the pixel is in the OFF state. 

There are several ways to resolve the gray scale inversion issue.

  • O-Film TFT LCD

O-Film is an optical film that is applied to the TN TFT LCD and redirects light, providing all round viewing angles to any TN TFT LCD to which it is applied. It is easy to apply and relatively low cost.

Orient Display: Normal TN TFT vs O-Film Applied TFT

Fig. 3 Normal TN TFT vs O-Film Applied TFT

1. Viewing angle for Normal TFT
Item   Symbol Contrast Min Typ. Max. Unit
Viewing angle Horizontal ΘR CR≧10 65 Deg.
ΘL 65
Vertical ΦT 55
ΦB 55
2. Viewing angle for O-Film TFT
Item   Symbol Contrast Min Typ. Max. Unit
Viewing angle

(Gray Scale inversion Direction)

Horizontal ΘR CR≧10 75 Deg.
ΘL 75
Vertical ΦT 75
ΦB 75

Orient Display: Viewing Angle Definition

Fig. 4 Viewing Angle Definition

  • MVA (Multi-domain Vertical Alignment) TFT LCD

In the basic VA mode, the molecules can tilt towards to any directions because of the lacking of in-place easy axis, therefore the umbilics defects appear, which is not desired in the display application because it not only produces transmission fluctuation but also slows down the response time.

In order to obtain a symmetric viewing angle, the pixel is divided into domains, where the LC molecules will have pre-determined tilt directions. The multi-domain is obtained by introducing protrusions on both substrates. This is the Multi-Domain VA mode (MVA).

In the off state, the LC molecules are perpendicularly aligned, hence no transmission after crossed polarizers, this is the black state. In the on state, the LC molecules tilt in a direction controlled by the protrusions, a phase retardation is present to the incoming light, and transmission is not zero after the exist polarizer; at high field, the LC molecules in the mid-layer are all parallel to the substrate surface, a higher transmission is obtained.

Orient Display: MVA (Multi-Domain Vertical Alignment) TFT LCD

Fig. 5 MVA (Multi-Domain Vertical Alignment) TFT LCD

Orient Display: MVA (Multi-Domain Vertical Alignment) TFT LCD Structure

Fig. 6 MVA (Multi-Domain Vertical Alignment) TFT LCD Structure

The MVA was first introduced by Fujitsu, and now adopted by a few manufactures. It can give very good viewing angles because of the symmetric LC domains. The MVA mode eliminates the need for a rubbing process, which makes manufacturing simpler and the MVA-TFTs more stable.

    • PROs:
      • Wide viewing in all directions (80 / 80 / 80 / 80)
      • High contrast (1,000:1)
      • Normal Black (NB) mode: dead pixel = black spot
      • Better performance over wide temperature range
    • CONs:
      • Higher manufacturing cost than TN LCD or O-Film LCD
      • Color differential with changing viewing angle
      • Slight gray scale inversion
  • IPS (In Plane Switching) TFT LCD

IPS (in-plane switching) is a screen technology for liquid-crystal displays (LCDs). It was designed to solve the main limitations of the twisted nematic field effect (TN) matrix LCDs which were prevalent in the late 1980s. These limitations included strong viewing angle dependence and low-quality color reproduction. In-plane switching involves arranging and switching the orientation of the molecules of the liquid crystal (LC) layer between the glass substrates. This is done, essentially, parallel to these glass plates.

Orient Display: Warranty

Fig. 7 IPS (In Plane Switching) TFT LCD Structure

Instead of moving up and down in a vertical direction, the rod shaped LC molecules twist in the same plane between on and off. IPS LCD is widely used in different applications now.

    • PROs:
      • Wide viewing in all directions (80 / 80 / 80 / 80)
      • Consistent, accurate color in all directions
      • Normal Black (NB) mode: dead pixel = black spot
      • High contrast and fast response time
    • CONs:
      • Highest manufacturing cost
      • TFT panel draws 15% more power
      • Needs brighter backlight due to lower aperture ratio

IPS LCD is widely used in different applications now. It is becoming less cost effective. Orient Display provides wide selection of IPS TFT LCD. Because this technology will be the mainstream in LCD market.

  • TN vs O-Film vs MVA vs IPS TFT LCD

Orient Display: TN vs O-Film vs MVA vs IPS TFT LCD

Fig. 8 TN vs O-Film vs MVA vs IPS TFT LCD

  • AFFS (Advanced Fringe Field Switching) TFT LCD

This is an LCD technology derived from the IPS by Boe-Hydis of Korea. Known as fringe field switching (FFS) until 2003, Advanced Fringe Field Switching is a technology similar to IPS, offering superior performance and color gamut with high luminosity. Color shift and deviation caused by light leakage is corrected by optimizing the white gamut, which also enhances white/grey reproduction. AFFS is developed by Hydis Technologies Co., Ltd, Korea (formally Hyundai Electronics, LCD Task Force).

In 2004, Hydis Technologies Co., Ltd licensed its AFFS patent to Japan’s Hitachi Displays. Hitachi is using AFFS to manufacture high end panels in their product line. In 2006, Hydis also licensed its AFFS to Sanyo Epson Imaging Devices Corporation.

Hydis introduced AFFS+ which improved outdoor readability in 2007.

Now AFFS TFT LCD is mainly used for mobile phone panels.

Fig. 9 AFFS vs IPS TFT LCD

AFFS operates opposite to IPS.  It provides high transmittance and requires lower voltages to reduce power consumption.

Orient Display: AFFS TFT LCD Single Pixel

Fig. 10 AFFS TFT LCD Single Pixel

AFFS design & layout maximizes the active area of the individual pixel.  This increased aperture ratio allows more transmittance, reducing the power required by the backlight.

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