Spacer, LCD

LCD spacer has two kinds of usage. Spacer particles used in a display portion is called cell spacer or sinply spacer . Another use pf spacer particle is for an epoxy-sealant which encloses liquid crystals in a LCD cell as shown in Figure 8-1. 

The basic modes of construction of the various commercial types LCD described in detail in Chapter 3 share many common elements. They consist of a very thin layer of a nematic liquid crystal mixture enclosed between two transparent parallel glass substrates held apart by solid spacers and glued together around the edges, see Figure 2.11 for a schematic representation of the optical elements, some or all of which can be combined to construct an LCD. The cell gap (d ss 2-10 pm) should be as uniform as possible in order to minimise variations in the optics of the display. Thick cells are turbid, due to... 

In principle, this mode of operation creates the possibility of producing high-information-content displays due to the short frame times associated with bistable displays, since they are basically a memory effect and only new information must be changed. Unfortunately, metastable twist states of intermediate twist, which degrade the optical performance of the device, form around dust particles in cells with a cell gap below a certain value (d < 20 m). Therefore, since the response time is proportional to d, very long response times are observed ( 1 s) for LCDs with a cell gap above this critical value. These optically disruptive metastable twist states also form at the interface with spacers used to generate a uniform cell gap. 

Figure 4.7 Set-up of a typical active matrix LCD Exploded" view of twelve pixels (left) and cross-section of three sub-pixels in the basic colors (right) (PI = polyimide, TFT = thin film transistor). The spacers are used to adjust the cell gap to typically 5-6 pm.

One traditional low-pretilt OCB LCD using PI without POSS dopant (0p 2°) and one high-pretilt OCB LCD using PI with 0.05 wt% POSS dopant (dp 65°) were fabricated for comparison. As shown in Fig. 5, the pretilt angle of an OCB LC cell in the PI alignment layers is in the opposite direction. The cell gap maintained by ball spacers was kept around 5.1 pm in this work. The cells were capillary filled with the positive dielectric anisotropic LC molecules E7. 

The LCD panel is constructed by two glass substrates with deposited indium-tin oxide (ITO) electrode film. The space between the two glass substrate, that is, the cell is filled with liquid crystals. Spacer particles are used to maintain the cell gap between two glass substrates as shown in Figure 8-1. The high uniformity ofthe thickness ofthe Uquid crystal layer is very important in order to raise the display characteristic of the LCD. 

At present, most of the cell spacer used for LCD are the resin spacer or the silica spacer. Among them, the resin spacer is more popular than the silica spacer. The reason for this is... 

Figure 8-4. Example of silica spacers dispersed in the sealant of a LCD cell...

Since the market of PDA (Personal Digital Assistance), a cellular phone and LCD television will be expanded globally in near future, the quantity of production of LCD panel increases, and it is thought that the amount of consumption of silica particle will be increase greatly. However, inexpensive silica spacer with the accuracy maintained is required, and the development of a new process of manufacture with a new raw material is thought to be necessary. 

Koyanagi T. Recent application examples of silica powder. The properties of silica spacer used for LCD. Ceramics (Japan) 1998 33(1) 25-29... 

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