Patent Application
20060274253
The present invention relates to a technique to reduce the partial voltage exerted from an external static charge source on the liquid crystal layer in liquid crystal displays (LCDs) to mitigate the damaging effect of the charges on the liquid crystals (LCs) such that the capability of the LCD to withstand high-voltage electrostatic charges will be enhanced.
For conventional LCD products exposed in an environment of high-voltage electrostatic charges, instantaneous injection of the charges would either cause burnout of the ITO circuits or make the LC cells (the pixels) malfunctioning. A guarding element or structure against electrostatic discharging (ESD) is necessary and usually found in designing the entire module. However, this approach usually results in the penalty of larger size for the modules or related parts, and hence a higher cost for products.
Several approaches have been proposed to diminish the damages from the electrostatic charges in LCD products. In U.S. Patent Publication No. 20020088629A1 entitled “Grounding device for a portable radio terminal”, a device which is connected with the RF part provides a ground path to the coupled upper board and lower board in the display module. Through the flexible print circuit (FPC) connecting the RF module and the LCD module, the electrostatic charges trapped in the LCD can be conducted to the ground and the damages caused by ESD can then be eliminated.
It is well known that the alignment of liquid crystal molecules is strongly affected by the applied electric field. By changing the consistence of the alignment scheme between the LCs and the polarization layers, the brightness/intensity of a pixel can be modulated through the exerted electric field. Since the LC molecules are affected by the electric field, the display quality will be deteriorated if there are trapped charges in the LC cells. This is still a serious issue not totally solved by conventional discharging approaches.
Efforts in finding new compositions for the LCs were also devoted by researchers. ROC Patent Publication No. 434310 entitled “Liquid crystal composition” disclosed a nematic liquid crystal including 1 to 10000 ppm of lariat ethers and some other similar compositions to achieve a resistivity about 1×1011 Ω-cm to release the internal electrostatic charges in the LC layer.
The aforesaid references have tried to overcome the electrostatic charge problems by a special grounding device or uncommon materials. Both will result in a much higher cost in fabrication. In short, their disadvantages can be summarized as below:
1. Special shielding lines or discharging lines are added while the LCD adopts the scheme of guarding rings. These special lines will make the design of the interconnection layout more complicated. Even with a conductive layer coated on the entire outer surface of the board will also increase the fabrication cost.
2. In investigating new conductive structures against the electrostatic discharging effect will inevitably include some special materials in the LCs and a few conductive materials doped in the polyimide layers. This makes the structure more complicated, and also increases the manufacturing cost.
To solve the aforesaid disadvantages, the primary object of the present invention is to make spacers conductive in the liquid crystal layer of a LCD in which the spacers originally provides a function of anchoring the upper and lower board and now also forms a conductive path to reduce the unwanted voltage built between the upper and lower sides of the liquid crystal layer. The capability of the modified LCD to withstand the static charge will be promoted.
Since the slightly leaky liquid crystals and the conductive spacers provide two equivalent resistors in parallel with each other, another object of the invention is to decrease the partial voltage exerted on the liquid crystal layer from the external high-voltage static charges by the smaller resistance formed by the liquid crystals and the spacers. The damage in the liquid crystal layer from the external static charge source is thereby reduced. The display quality and its reliability of the LCD panel can also be pertained.
This invention includes an upper board and a lower board that couple to each other. There forms a space between them. A liquid crystal layer is sandwiched between the upper and the lower boards. There are also a plurality of spacers to anchor the space between the upper and the lower boards. These spacers are not electrically connected to one another.
By means of the above construction set forth, the liquid crystals and the spacers in the liquid crystal layer play as two resistors that are coupled in parallel. The partial voltage found in the liquid crystal layer will be smaller so that the damaging effect of the external electrostatic charge source on the liquid crystals in the liquid crystal layer will be reduced. Therefore the display quality of the display panel may be pertained as desired and the capability of the LCD to withstand the electrostatic charge is enhanced.
The foregoing, as well as additional objects, features and advantages of the invention will be more readily apparent from the following detailed description, which proceeds with reference to the accompanying drawings.
Please refer to
There is a liquid crystal layer 13 sandwiched between the upper board 11 and the lower board 12 and a plurality of spacers 131 located in the space between the upper board 11 and the lower board 12. The spacers 131 are conductive and are used to anchor the space between the upper board 11 and the lower board 12. Namely, the height of the spacers 131 is the height of the space between the upper board 11 and the lower board 12.
The spacers 131 are conductive (referring to
The conductive spacers 131 are sprayed within an area surrounded by sealing framing resin on the board. In the later processes, liquid crystals are injected and the boards are compressed and sealed to form the liquid crystal layer 13 embedded with the conductive spacers 131. In the conventional techniques, the conductive materials are located in the sealing framing resin of the LCD to form conductive path between the upper and lower glass board as shown in
In order to prevent possible shorts between the electrodes of pixels, the spacers should be placed where the operation of the pixels will not be interfered. Referring to
The electrically conductive polymer composite composition may also be selected from thermoplastic polymers such as polyphenylene ethers, polyamides, polysiloxanes, polyesters, polyidmides, polyetherimides (PEI), polysulfides (PSU), polysulfones (PSF), polyether sulfones (PES), olefin polymers, polyurethanes, and polycarbonates; or thermosetting polymers such as polyepoxides, phenolic resins, polybisimaleimides, natural rubbers, synthetic rubbers, silicone gums and thermosetting polyurethanes; or photosensitive resins formed by mixtures of unsaturated functional groups and photosensitive multifunctional group single elements. Electrically conductive fillers are added to the aforesaid thermoplastic polymers, thermosetting polymers or photosensitive resins.
The electrically conductive filler may be selected from carbon blacks, carbon fibers, carbon filaments, carbon nanotubes, carbon fibers coated with metal, graphites coated with metal, glass fibers coated with metal, metal particles, stainless steel filaments, metal foils and metal powders; or conductive polymers such as polyanilines (PANI), polypyrroles (PPy), poly-para-phenylenes (PPP), polythiophenes (PT), or metal oxide powders such as indium tin oxides (ITO) or indium zinc oxides (IZO). Selection of the material and the proportion thereof may take into account of material characteristics and the partial voltage to be found in the liquid crystal layer 13.
The photosensitive spacers may also be formed in a desired pattern by exposing and developing techniques according to requirements, and be distributed on selected locations on the necessary films of the surface of the lower board 12 as shown in
The partial voltage principle of the parallel resistor circuit adopted in the invention is as follow:
Vi=Vs×Ri/Rs (where Vs is total voltage, Ri is the resistor i, Rs is total resistance, Vi is the partial voltage of the resistor i). When the resistance Ri is greater, the partial voltage found in the resistor also proportionally increases.
The upper and lower layers of the LCD can be seen as a plurality of equivalent resistors coupled in parallel (referring to
Use condition, materials and content proportion of the spacers 131 and 131′ may be adjusted according to the resistance of the liquid crystal layer to reduce the partial voltage as desired to withstand the static charge. The effect of bearing the static charge also may be altered according to special requirements such as the types, physical characteristics, adding proportion of the conductive substance, and the like.
While the preferred embodiments of the present invention have been set forth for the purpose of disclosure, modifications of the disclosed embodiments of the invention as well as other embodiments thereof may occur to those skilled in the art. Accordingly, the appended claims are intended to cover all embodiments which do not depart from the spirit and scope of the invention.
