CN1688920A - High speed and wide viewing angle liquid crystal displays - Google Patents

Abstract

Novel structural configurations of a TFT-LCD (Thin Film Transistor Liquid Crystal Display) which results in both fast response to input data and provides wide-viewing-angles. The structure of the device is comprised of one pixel electrode layer and two common electrode layers. The structure of the invention can be used with liquid crystal display television (LCD-TV) monitors that require both fast-response as well as wide-viewing-angle. In addition, other liquid crystal technologies which require high speed response would benefit from the TFT-LCD of the present invention.

Description

High Speed, Wide Viewing Angle LCD Display

This application claims priority to US Provisional Application No. 60/405,999, filed 26,2002.

field of invention

The present invention relates to displays, and more particularly to methods and apparatus for preparing TFT-LCDs (Thin Film Transistor Liquid Crystal Displays) that respond quickly to high input data rates and provide viewers with a wide viewing angle.

Background and Prior Art

The slow response time and narrow viewing angle of ordinary TFT-LCD are two limiting factors for its potential wide and endless applications.

FIG. 1 shows the structure of a general TFT-LCD. A liquid crystal (LC) layer 10 is sandwiched between a top glass substrate 11 and a bottom glass substrate 12, and a thin transparent electrode (indium tin oxide (ITO)) is coated on each substrate to apply an electric field to switch the liquid crystal. Usually, the electrode 13 of the top substrate 11 is a common electrode with a constant voltage (such as 0 volts), where 0 volts refers to a low voltage. The common electrode extends continuously to all pixels in the entire display, so it is called a common electrode. On the other hand, the electrode 14 on the base substrate 12 is called a pixel electrode because the transistor assigned to each pixel controls it. The voltage applied to LC10 is varied across this electrode. When the pixel electric > 0, Fig. 1 also shows the electric field distribution E. Obviously, for this device, there is only one electric field, the vertical electric field, which is used to switch on the device by switching the liquid crystal molecules, which is a fast process. But when the device is turned off, the pixel voltage is either eliminated or reduced, causing the molecules to gradually relax back to their low state. Generating only one electric field results in extremely slow relaxation, which slows the turn-off time, which is the main limiting factor for many potential applications of liquid crystals today.

Various related prior art references are discussed below. These documents relate to three key concepts used by the present invention: cross-field effects, fringe-field switching and multi-domain techniques.

The concept of cross-field effect first appeared in D.J. Channin's paper in 1975 (Applied Physics Letters', Vol.26, No.11, p.603 (1975)), and then appeared in D.J. Channin and D.E.Carlson's paper (Applied Physics Letters', Vol.28, No.6(1976)).

Six years later, Akihiko Sugimura et al published a paper in Proceedings of 14th Conference on Solid State Devices, Tokyo (1982), and Akihiko Sugimura and Takao Kawamura in Japanese Journal of AppliedPhysics, Vol.24, No.8 in 1985 , another paper was published on p.905 (1985). Liquid crystal displays using cross-field effects have various disadvantages, such as high voltage requirements, low contrast, more complex structures, uneven emission, and more complicated driving. The driver refers to the electronic circuit used to provide (ie drive) the required voltage (data, etc.) to the TFT-LCD. Some drives are more complex. Such as requiring different types of voltages at different time intervals. In the cross-field effect, additional electrodes are often required to control two types of electric fields (vertical and lateral), so the driving is more complicated, so the cross-field effect concept has not been used in TFT-LCD because it requires a much higher operating voltage , the structure and drive are more complex, and the contrast is lower. However, the present invention overcomes many of the above problems by utilizing a different electrode design, enabling the cross-field effect to be used in TFT-LCDs. In addition, the present invention also provides inherently wide viewing angle characteristics by utilizing the cross-field effect, which is another extremely important requirement for TFT-LCD televisions (TVs).

Seung Ho Hong et al published the paper "Hybrid Aligned Fringing Field" in Japanese Journal of Applied Physics (Vol.40, p.L272 (2001)) and in Japanese Journal.Applied Physics, Vol.41, pp.4571-4576 (2001 ) published a prior art study on fringe field switching (FFS). The present invention employs a structure very similar to the fringe field switching FFS mode structure described by Seung HoHong et al., which uses an improved efficiency in-plane switching method to produce a wide viewing angle. By adopting this structure in the present invention, the required voltage for generating lateral or fringe fields is reduced, since the gap between electrodes is small for fringe field generation, thereby making it possible to lower the operating voltage. Thus, the operating voltage is reduced. Furthermore, the FFS structure can form a very uniform vertical field without a dead zone, which is defined as the gap between electrodes without an electric field. In the present invention, the gap between the electrodes also has an electric field generated by the substrate electrode structure, which includes a gapped electrode layer, called a discontinuous electrode, separated from the continuous electrode layer by an electrically insulating layer, but discontinuous. The segments of electrodes are all connected to the same transistor within the pixel. The base substrate electrode structure is similar to that of a common FFS structure.

However, there are at least three major differences between the present invention and the conventional FFS structure. First, the present invention has two common electrodes, while the common FFS structure has only one low-voltage common electrode. The last reported FFS mode also uses two common electrodes, but in this case both common electrodes are low voltage, such as 0 volts. In contrast, in the present invention, one common electrode is high voltage and the other common electrode is low voltage. Second, unlike the liquid crystal (LC) mode, common FFS uses parallel alignment with in-plane switching, while the recently reported FFS mode with two common electrodes uses hybrid-aligned nematic (HAN). The present invention can use any liquid crystal mode, and the generation mechanism of the wide viewing angle is also different from that of the original technology of FFS. Third, all FFS structures of the prior art have slow response times because they do not use cross-field effects, and the off-off process relies on the natural relaxation of the LC molecules and is slow.

In addition, the original technical documents relate to the multi-domain technology LCD, and the present invention adopts the formation mechanism of wide viewing angle called multi-domain, but the present invention is significantly different from all the prior technologies using this technology, because the present invention uses the FFS structure to generate fringe fields, while other prior art literature mainly uses protrusions to generate multiple domains. See the paper "MVA, Multi-Domain Verticai Alignment" by A. Takeda et al., SID'98, p.1077 (1998). K. H. Kim et al. in SID'98, p. 1085 (1998) discuss an interdigitated structure for generating fringing fields to form multiple domains. In addition, compared with the vertical alignment (VA) mode mainly used in the prior art, the present invention can use a variety of different liquid crystal modes.

Therefore, there is a need to improve today's thin film transistor liquid crystal display (TFT-LCD) technology. It is desirable that the cross field effect structure has low operating voltage, high contrast, simple driving and easy fabrication. For common structures applying FFS or multi-domain LCDs, faster response is desired.

The present invention provides a significant improvement in the production and performance of TFT-LCDs to which different LC modes can be applied, which result in different light efficiencies, response times and viewing angles. The choice of LC mode depends on the type of application.

Contents of the invention

A first object of the present invention is to provide a TFT-LCD (Thin Film Transistor Liquid Crystal Display) structure and method with fast response for high input data rate applications.

The second object of the present invention is to provide the structure and method of applying a TFT-LCD (Thin Film Transistor Liquid Crystal Display) with two common electrodes (one is a low voltage such as 0 volts, and one is a high voltage such as 5 volts) and a pixel electrode , thus generating vertical and non-vertical electric fields to switch liquid crystals at high speed.

A third object of the present invention is to provide a structure and method for making the cross-field effect require less voltage than common cross-field devices and thus be applicable to TFT-LCD (Thin Film Transistor Liquid Crystal Display).

A fourth object of the present invention is to provide a structure and a method for making the cross-field effect allow a simple driving method for TFT-LCD (Thin Film Transistor Liquid Crystal Display).

The fifth object of the present invention is to provide a structure and method for making the cross-field effect TFT-LCD (Thin Film Transistor Liquid Crystal Display) have high contrast performance and simple manufacturing process.

A sixth object of the present invention is to provide a structure and method for applying a TFT-LCD (Thin Film Transistor Liquid Crystal Display) having a wide viewing angle for viewers.

Other objects and advantages of this invention will become apparent from the following detailed description of a presently preferred embodiment shown schematically in the accompanying drawings.

Brief introduction to the drawings

FIG. 1 shows the structure of a common prior art TFT-LCD having one common electrode.

FIG. 2 shows a preferred embodiment of a novel TFT-LCD structure with two common electrodes and a pixel electrode layer.

FIG. 3 shows the TFT-LCD structure of FIG. 2, which generates a uniform vertical field when the pixel voltage is 0 volts (dark state).

FIG. 4 shows the TFT-LCD structure of FIG. 2, and a new electric field distribution diagram is generated when the pixel voltage is 5 volts (bright state).

Figure 5 shows a second preferred embodiment of the novel TFT-LCD structure.

Fig. 6 shows the TFT-LCD of Fig. 5, with power applied to different electrode layers.

Fig. 7 shows a third embodiment using a resistive film with two common electrodes.

FIG. 8 shows a fourth embodiment using a dielectric layer with the new structure of FIG. 2 .

Figure 9 shows the non-perpendicular electric field distribution generated by the new structure.

Description of the preferred embodiment

Before describing in detail the disclosed embodiments of the invention, it is to be understood that the invention is not limited in application to the details of the specific construction shown, for other embodiments are capable of other embodiments of the invention. Also, the terminology used herein is for the purpose of description and not of limitation.

Note that the present invention includes a first substrate, a second substrate, a liquid crystal between the first and second substrates, a device for generating an electric field between electrode layers in the vicinity of the first and second substrates. The unique feature of the present invention lies in the arrangement of the electrode layers, which will now be described in detail.

The common electrode can be high voltage or low voltage, connected or intermittent, and the applied voltage does not depend on the input data during TFT-LCD operation. The pixel electrodes can be continuous or discontinuous, and the applied voltage depends on the input data. One common electrode is installed in the upper substrate, that is, the first substrate, and the second common electrode is installed in the lower substrate, that is, the second substrate; in addition, the third electrode layer in the lower substrate can be designed to be intermittent, collectively referred to as One layer, using one label in all figures.

Obviously, the combination of two common electrodes with different voltages and one pixel electrode will constitute a TFT-LCD with fast response and wide viewing angle when a varying voltage is applied to the pixel electrode. When the on and off modes of the device are driven by an electric field, a fast response is achieved; using the electric field, the LC molecules can align and relax extremely rapidly.

Fig. 2 shows the novel design of the TFT-LCD structure of the present invention, and its major feature is that instead of using a common electrode, there are two common electrodes 21, 23, one for low voltage such as 0 volts, and the other for high voltage Such as 5 volts. The first common electrode layer 21 in the top substrate 22 has a constant high voltage of 5 volts, while the second common electrode layer 23 in the bottom substrate 24 has a low voltage of 0 volts. The common electrode 23 is separated from the pixel electrode 25 by a passivation layer 26 (electrical insulation layer). When a low voltage of 0 volts is applied to the pixel electrode 25, a uniform vertical field 30 as shown in FIG. 3 is generated. This uniform vertical field generated at a pixel voltage of 0 volts typically results in a dark state with extremely fast switching because it is driven by an electric field. This is similar to the fast switching caused by the vertical field generated by common TFT-LCD devices.

In Figure 4, the pixel is in the bright state when the voltage is 5 volts. Applying 5 volts to the pixel electrode 25 rapidly creates a new electric field profile 40 due to the fringing fields shown in FIG. 4 . As previously mentioned, the voltage of the common electrode 21 in the top substrate is 5 volts, while the voltage of the common electrode layer 23 in the bottom substrate is 0 volts, and the voltage of the pixel electrode 25 is 5 volts, thus forming a different light emission The new liquid crystal alignment state, usually bright state. The switching speed of this new state is also fast because it is driven by an electric field. Therefore, the new structure of this TFT-LCD design results in fast turn-on and turn-off because both are electric field driven.

Example 1 - A common electrode with low voltage

The voltage of the common electrode 21 in FIG. 2 is 5 volts; in order to reduce the vertical electric field strength and enhance the lateral field, the voltage can be set lower. As the transverse field becomes stronger, more molecules are switched into the bright state, thus contributing to higher light efficiency. However, this prolongs the corresponding light-dark state response time due to the formation of a weaker vertical field. For the common electrode 23 on the base substrate 24, the residual voltage reading is V=0 volts; for the pixel electrode 25, V=0˜5 volts. The common electrode 23 is electrically insulated from the pixel electrode 25 by the passivation layer 26 .

Example 2 - Higher bottom electrode voltage

In FIG. 2 , the voltage of the common electrode 21 is higher, and the voltage of the common electrode 23 is lower. In principle, these two electrodes can be interchanged, as shown in FIG. 5 . In Fig. 5, the voltage of the first common electrode 51 on the top substrate 52 is relatively low (0 volts), and the voltage of the second common electrode layer 53 in the bottom substrate 54 is relatively high (5 volts), and this alternative design will cause The vertical field is not uniform because the passivation layer 56 creates a slightly higher potential difference. In FIG. 5 , the pixel electrode 55 emits a high electric field, so a higher electric field is formed across the passivation layer 56 than when the top electrode 51 emits an electric field. Note that in describing the present invention, a "passivation layer" is generally referred to as an insulating layer. But in principle, the potential difference formed between the pixel electrode 55 and the second common electrode layer 53 can be reduced by changing the voltage of the second common electrode 53 or the voltage of the pixel electrode 55 to compensate for the voltage drop.

Example 3 - Interchanged Common and Pixel Electrodes

FIG. 6 shows the first common electrode layer 60 in the top substrate 61 at 5 volts. The bottom substrate 63 supports a pixel electrode layer 62 of 0-5 volts and a second common electrode layer 64 of 0 volts, and the pixel electrode layer 62 and the common electrode 64 are electrically insulated by a passivation layer 65 . Compared with the structure of FIG. 2 , the positions of the common electrode 64 and the pixel electrode 62 in this structure are exchanged. The choice of this structure depends on the capability of the manufacturing process and the optimized electrode width and gap.

Example 4 - Using Resistive Film

In order to extend the distance of the lateral field, a resistive film 70 can be used to connect the pixel electrode and the second common electrode in the bottom substrate, as shown in FIG. 7 . When the pixel voltage is high, the potential gradient formed at both ends of the resistive film between the pixel electrode 72 and the second common electrode 71, and the transverse field established therebetween switch the LC molecules during the bright state. The first common electrode 74 in the upper substrate has a high voltage of eg 5 volts, but this voltage can be reduced to eg 2 volts to increase the lateral field strength. On the other hand, when the voltage of the pixel electrode 72 is the same as the voltage in the common electrode 71, there is no potential difference between the two ends of the resistive film, and a uniform potential appears at both ends of the film due to the conduction electrons. FIG. 7 shows that a horizontal electric field is generated between the pixel electrode 72 and the second common electrode 71, resulting in a longer lateral fringe field and higher efficiency for the bright state.

Example 5 - Using Dielectric Layers

As shown in FIG. 8, when the common electrode layer 80 of the top substrate 81 is at 0 volts, using a dielectric layer 82 between the common electrode layer 80 and the LC layer 83 can increase the lateral field strength on the top of the LC unit cell, because the top 0 volts in the substrate is now farther from the bottom electric field. The dielectric layer 82 is adjacent to the common electrode layer 80, and its function is to maintain a small cell gap, which helps to make the lateral fringe field stronger, because the upper electrode is farther away in the pattern. A fringe field formed between the common electrode layer 84 and the pixel electrode layer 85 becomes stronger, thereby improving light efficiency.

Example 6 - Natural Wide Viewing Angle Construction

In FIG. 9 , the fringe field forms a multi-domain structure, which is symmetrical to the mid-plane of the gap 90 , 91 between the second common electrode layer 92 . This multi-domain configuration results in wide viewing angles in both left and right or up and down directions. Adopting a zigzag electrode structure known as multi-domain vertical alignment (MVA) enables wide viewing angles in all four directions. 9 shows that when the first common electrode layer 93 in the top substrate 94 is 5 volts, the second intermittent common electrode layer 92 in the lower substrate 95 is 0 volts, and the voltage of the pixel electrode 96 is 5 volts, due to the symmetrical Edge patterns naturally form multi-domain structures. Figure 9 has the same structure as Figure 4, but additionally shows how the fringe field enables different poses of the LC molecules to form a natural wide viewing angle.

The detailed description, examples and simulation results of the present invention provide a tool for promoting the cognition and development of thin film transistor liquid crystal display technology. The novel features of the present invention include but are not limited to: application of cross-field effect in TFT-LCD; combination of cross-field effect and wide viewing angle to achieve fast response and wider viewing angle; double common electrode structure using high and low voltages; The structure produces cross-field effect; a multi-domain LCD is formed with a new structure.

While the invention has been described, disclosed, illustrated and illustrated in certain embodiments or modifications in which it is contemplated to practice, the scope of the invention is not and should not be limited thereby, and the contents herein are expressly reserved Other modifications or embodiments are proposed as they are within the breadth and scope of the appended claims.

Claims (18)

1. A thin film transistor liquid crystal display with fast response and wide viewing angle, characterized in that it comprises: a first substrate with a first common electrode layer; a second substrate having a pixel electrode layer and a second common electrode layer; a liquid crystal positioned between the first and second substrates; and The electric field generating device located between the first common electrode layer in the first substrate and the pixel electrode and the second common electrode layer in the second substrate enables the display to provide fast response to high input data rates and provide a wide viewing angle for viewers . 2. The display according to claim 1, wherein the electric field generating means has a second common electrode layer separated from the pixel electrode layer by an insulating layer in the second substrate. 3. The display according to claim 1, further comprising: means for providing a voltage source to the first common electrode layer. 4. The display according to claim 1, further comprising: means for providing a voltage source to the second common electrode layer. 5. The display of claim 1, further comprising: means for supplying a voltage source to the pixel electrode layer. 6. A display as claimed in Claims 3, 4 and 5, characterized in that the means for supplying a voltage source to one of the first and second common electrode layers results in an unequal voltage. 7. The display device according to claim 6, wherein the unequal voltage is higher in the first common electrode layer than in the second common electrode layer. 8. The display device according to claim 6, wherein the unequal voltage is higher in the second common electrode layer than in the first common electrode layer. 9. The display as claimed in claim 1, wherein the electric field generating means comprises: a resistive film positioned between the pixel electrode layer and the second common electrode layer portion. 10. The display according to claim 2, further comprising: a dielectric layer adjacent to the first common electrode layer. 11. A display as claimed in claim 1, characterized in that the generated electric field is non-vertical. 12. A display as claimed in claim 1, characterized in that the generated electric field is vertical. 13. A method for providing fast response and wide viewing angle to a thin film transistor liquid crystal display, characterized in that it comprises steps: providing a liquid crystal layer between the first and second substrates; and An electric field is generated between the substrates, wherein a voltage is applied to the first substrate with the first common electrode layer, the second substrate with the second common electrode layer and the pixel electrode layer, thus having a fast response to input data, and to the viewer Produces a wide viewing angle. 14. The method as claimed in claim 13, wherein the step of generating an electric field comprises the step of: applying a voltage approximately equal to the voltage of the second common electrode in the second substrate to the pixel electrode layer, thereby generating a uniform vertical electric field. 15. The method as claimed in claim 13, wherein the step of generating an electric field comprises the step of: applying a voltage not equal to the voltage of the second common electrode in the second substrate to the pixel electrode layer, thereby generating a non-vertical electric field. 16. The method of claim 15, wherein the step of generating a non-perpendicular electric field comprises the steps of: forming a resistance layer between the pixel electrode and the second common electrode; and A voltage not equal to the voltage of the second common electrode is applied to the pixel electrode, thereby generating a lateral electric field. 17. The method of claim 15, wherein the step of generating a non-perpendicular electric field comprises the steps of: forming a dielectric layer across one of the substrates; and A voltage is applied to the pixel electrodes, thereby generating a strong electric field that improves light efficiency. 18. The method according to claim 13, wherein applying a voltage to each electrode layer comprises the step of applying a unequal voltage between the first and second common electrodes, the pixel electrode voltage depends on the input data, and the first The voltage to the second common electrode does not depend on the input data.

Images