JPH05224235A - Active matrix type liquid crystal display device - Google Patents

Abstract

PURPOSE:To obtain high picture quality which is free from a brightness irregularity, a flicker, etc., by dividing a counter electrode into plural parts and adjusting respective voltages so that liquid crystal is driven, part by part, with AC voltages having no DC component. CONSTITUTION:In the respective divided areas A-F, plural gate lines 1 and plural drain lines 2 are formed crossing each other at right angles and TFTs 3 are formed at their intersection parts. Picture element electrodes are connected to the respective TFTs 3 and the picture element electrodes and counter electrodes form picture element capacitances via the liquid crystal. The voltages of the respective counter electrodes divided into the counter electrode 16 in the area F can individually be controlled from, for example, the counter electrode in the area A. Consequently, feedthrough voltages generated by the TFTs 3 in the respective areas are different and even if the center values of picture element voltages are different as a result, the counter electrode voltages are individually set to eliminate the application of a DC voltage component on the liquid crystal, thereby making a display without any brightness irregularity nor flicker.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION The present invention particularly relates to an active matrix type liquid crystal display device using a thin film field effect transistor.

[0002]

2. Description of the Related Art An active matrix type liquid crystal display device (hereinafter abbreviated as AM-LCD) has recently attracted attention as a space-saving display which has a high image quality comparable to that of a CRT and is thin and lightweight. Conventional A
FIG. 5 shows the circuit configuration of the display section of the M-LCD, and FIG. 6 shows the drive voltage of the liquid crystal. In the AM-LCD, as shown in FIG. 5, a plurality of parallel gate lines 1 and a plurality of parallel drain lines 2 are formed orthogonally to each other on a translucent insulating substrate (not shown). A thin film field effect transistor 3 is formed near each intersection of the gate line and the drain line, a pixel electrode (not shown) is connected to each thin film field effect transistor 3, and the thin film field effect transistor 3 is connected to the translucent insulating substrate. A counter electrode 10 is formed by a counter substrate (not shown) arranged to face each other, liquid crystal is filled between the translucent insulating substrate and the counter substrate, and a pixel capacitance is formed between the pixel electrode and the counter electrode 10 via the liquid crystal. 6 is a structure for forming 6. In FIG. 5, 9 is
Thin film field effect transistor (hereinafter abbreviated as TFT) 3
Is a capacitance component between the gate and the source (hereinafter abbreviated as CGS). Due to the influence of this capacitance, the pixel voltage of FIG. 4 changes by ΔV from the drain voltage after the writing is completed. The value of this ΔV is

[0003]

It takes a value indicated by. Here, CLC is the pixel capacitance value, and VG _ON and VG _OFF are the on-voltage and off-voltage values input to the gates, respectively. Therefore, in order to give a signal to the pixel so that the direct current voltage component is not applied to the liquid crystal,
It is necessary to set the counter electrode voltage with a shift of ΔV from the center value of the drain voltage in advance.

[0005]

The size of the AM-LCD is becoming larger, and it is practically used for personal computers for diagonals of 10 inches or more, for EDTVs, HDTVs, and engineering workstations (hereinafter abbreviated as EWS). In this case, a diagonal size of 20 inches or more is required. When manufacturing these AM-LCDs, a pattern is generally formed by using a technique such as photolithography. But,
In the large AM-LCD as described above, since the exposure area is large, it is not possible to expose all the patterns at once with one mask. For example, a method of dividing the pattern into a plurality of ranges and exposing the pattern is used. To create a pattern.

With such a manufacturing method, it is impossible to equalize the amount of superposition of all the patterns in the screen, and the amount of superposition is deviated at the boundary of the exposure seam. Furthermore, even in the exposure range of one mask, it is impossible to obtain a uniform overlapping amount due to distortion of the optical system. This causes the CGS value of the TFT to be different in each part of the screen, and the value of ΔV in FIG. 4 also becomes different depending on the place on the screen. Therefore, even if the voltage of the counter electrode is set so that there is no direct current component in the liquid crystal drive voltage in some parts of the screen, the direct current component remains in the drive voltage in other parts, which causes uneven brightness, flicker, and This has been a cause of problems such as display deterioration such as image sticking and shortening of the life of the liquid crystal.

[0007]

According to the active matrix type liquid crystal display device of the present invention, on the translucent insulating substrate,
A plurality of parallel gate lines and a plurality of parallel drain lines are formed so as to be orthogonal to each other, thin film field effect transistors are formed near respective intersections of the gate lines and the drain lines, and each of the thin films is formed. In an active matrix liquid crystal display device having a structure in which a pixel electrode is connected to each field effect transistor and a pixel capacitance is formed by the pixel electrode and a counter electrode via liquid crystal, the counter electrode is divided into a number of tails, It is characterized in that different voltages can be supplied to the respective counter electrodes.

[0008]

According to the present invention, the counter electrode is divided at a portion where the amount of misalignment of the pattern overlapping on the TFT substrate changes, for example, like a seam of the pattern at the time of photolithography, and the voltage of each counter electrode is divided. Allows for separate control. As a result, even if the voltage ΔV shown in FIG. 4 is different at the boundary of the pattern and the holding voltage at both ends of the liquid crystal is accordingly different for each part of the screen, the liquid crystal is individually applied to all parts of the screen for each part. It can be driven by an ideal AC voltage with almost no offset voltage applied.

[0009]

EXAMPLE FIG. 1 shows an example of using an AM-LCD having a counter electrode divided into two parts, and FIG. 2 shows the driving voltage of the liquid crystal of the present invention. In FIG. 1, 1 is a gate line for supplying a signal for turning on / off the TFT 3, 2 is a drain line for supplying a voltage to a pixel electrode, 3 is a TFT serving as a switch for supplying electric charge to a pixel capacitance, and 4 is a TFT. Counter electrode on the left side of the screen, 5 is a counter electrode on the right side of the screen, 6 is a pixel capacitance composed of a pixel electrode and a counter electrode via liquid crystal, 7 is a gate-source capacitance CGS1 on the left side of the screen, 8 is a gate on the right side of the screen The inter-source capacitance CGS2 is shown.

In the following embodiments, a case will be described in which the CGS capacitance values are different on the left and right with the center of the screen as the boundary. The capacitance values of CGS1 on the left side and CGS2 on the right side of the screen are C1 and C2, CLC of each pixel capacitance, ON voltage input to the gate line is VG _ON , and OFF voltage is VG _OFF.
At this time, if the field through voltages generated by the capacitance are ΔV1 and ΔV2, respectively, ΔV1 and ΔV2
Is

[0011]

[0012]

Takes the value indicated by The central values of the pixel voltage at this time are VC1 and VC2 in FIG. 2, respectively, and the central value of the drive voltage of the liquid crystal is ΔVC (= ΔVC1-ΔVC in FIG. 2).
Only 2) is different. Here, the voltage of the counter electrode 4 on the left side of the screen and the voltage of the counter electrode 5 on the right side of the screen are adjusted separately,
By adjusting to 1 and VC2, even if the center value of the drive voltage of the liquid crystal is different by ΔVC, it becomes possible to drive the liquid crystal with a voltage having no DC component in each part of the screen.

FIG. 3 shows a counter electrode according to the present invention.
FIG. 4 shows a state of the pixel voltage and the counter electrode voltage in each of the areas A to F divided into six areas, when the embodiment is applied to an AM-LCD divided into individual areas. In each of the divided regions A to F in FIG. 3, a plurality of gate lines 1 and a plurality of drain lines 2 are formed orthogonally to each other as shown in FIG. 1, and each intersection of the gate lines 1 and the drain lines 2 is formed. TF near each
T3 is formed, a pixel electrode is connected to each TFT 3, and the pixel capacitor 6 is formed by the pixel electrode and the counter electrode via the liquid crystal. In this embodiment, the counter electrode is divided into six from the counter electrode 11 in the area A to the counter electrode 16 in the area F, and the structure is such that each counter electrode voltage can be individually controlled. Therefore, even if the field through voltage generated in the TFT 3 in each region is different from ΔV3 to ΔV8 as shown in FIG. 4 and accordingly the center value of the pixel voltage is different from VC3 to VC8, the counter electrode By separately setting the voltages VC3 to VC8, it is possible to obtain a display in which no DC voltage component is applied to the liquid crystal as in the case of the first embodiment and luminance unevenness, flicker, burn-in, etc. do not occur.

In this embodiment, the case where the counter electrode is divided into left and right and the case where the counter electrode is divided into 6 are described. However, the shape and the number of divisions of the counter electrode of the AM-LCD to which the present invention is applied are not limited to this. It is possible to take any division shape and division number.

The present invention was applied to an AM-LCD, which is composed of 400 gate lines and 640 drain lines RGB each, and which is manufactured by exposing the display portion into two divided right and left portions. As a result, it has been possible to reduce the phenomenon such as uneven brightness, flicker, and burn-in of the display, which are conventionally visible, when the screen is divided into left and right. Further, since the offset voltage applied to the liquid crystal in each part in the image is reduced, the life of the liquid crystal is extended as compared with the case where the voltage of the counter electrode is one.

[0017]

As described above, according to the present invention,
It is said that the uneven brightness, flicker, image sticking, etc. in the image can be adjusted separately for each divided portion of the counter electrode, and as a result, a uniform display can be obtained without deterioration of the image quality due to the shift of the counter electrode voltage. effective. Further, it becomes possible to make the allowable range of the relative displacement of the pattern larger than that of the conventional method, so that the yield can be improved. Furthermore, since the DC voltage component applied to the liquid crystal is reduced, the life of the liquid crystal is extended.

[Brief description of drawings]

FIG. 1 is a diagram showing a first embodiment of a liquid crystal display according to the present invention.

FIG. 2 is a drive waveform diagram of liquid crystal pixels according to the first embodiment of the present invention.

FIG. 3 is a diagram showing a second embodiment of a liquid crystal display according to the present invention.

FIG. 4 is a drive waveform diagram of liquid crystal pixels according to a second embodiment of the present invention.

FIG. 5 is a diagram showing a liquid crystal display according to a conventional driving method.

FIG. 6 is a drive waveform diagram of a conventional liquid crystal pixel.

[Explanation of symbols]

 1 gate line 2 drain line 3 TFT 4 counter electrode on the left side of screen 5 counter electrode on the right side of screen 6 pixel capacitance 7 CGS1 8 CGS2 9 CGS 10 counter electrode 11 counter electrode in area A 12 counter electrode in area B 13 counter electrode in area C 14 counter electrode in region D 15 counter electrode in region E 16 counter electrode in region F

Claims (1)

[Claims] 1. A plurality of parallel gate lines and a plurality of parallel drain lines are formed on a translucent insulating substrate so as to be orthogonal to each other, and the gate lines and the drain lines are respectively provided in the vicinity of intersections thereof. A thin film field effect transistor is formed, a pixel electrode is connected to each of the thin film field effect transistors, and a counter electrode is formed on a counter substrate arranged facing the translucent insulating substrate. In an active matrix type liquid crystal display device having a structure in which a liquid crystal is filled between an optically insulating substrate and a counter substrate, and a pixel capacitance is formed between the pixel electrode and the counter electrode via the liquid crystal, the counter electrode has a plurality of electrodes. An active matrix type liquid crystal display device, characterized in that it is divided into parts and an independent voltage supply circuit is connected to each of the counter electrodes.