JPH0469622A - Active matrix type liquid crystal display device - Google Patents

Abstract

PURPOSE:To prevent the deterioration in liquid crystal by providing shielding electrodes for electrically shielding gate lines and maintaining the shielding electrodes at the same potential as the potential of transparent electrodes. CONSTITUTION:The shielding electrodes 105 exist between the gate lines 102 and the transparent electrodes 206 of a counter substrate on the gate lines and since the shielding electrodes are at the same potential as the potential of the transparent electrodes 206, on electric fields are applied at all to the liquid crystal 210 existing therebetween and the deterioration by a DC voltage does not arise. Namely, the shielding electrodes 105 are so formed as to shield the voltage change on the gate lines 12 against the transparent electrodes 206 and, therefore, the influence of the gate lines 102 to the electrodes 206 is obviated. The shielding electrodes 105 are used commonly as light shielding films (black matrix). The opening rate of picture elements is thereby improved.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to an active matrix liquid crystal display device using thin film transistors as switching elements.

[Conventional technology]

An active matrix liquid crystal display device consists of an active matrix substrate in which thin film transistors and thin film diodes are formed in a matrix, transparent electrodes, color filters,
It has a structure in which liquid crystal is sandwiched between a counter substrate on which a black matrix or the like is formed. In a typical configuration, a polarizing plate is provided on the outside of these two substrates, a backlight is provided on one side as a light source, and the light switched by the liquid crystal is viewed as a color image through a color filter provided on one substrate. be. In addition, on the side of the substrate where color filters and transparent electrodes are attached, in order to prevent excess light leakage, light leaking from between each color filter and between the wiring and pixel electrodes of the active matrix substrate is placed. A light shielding flux (flux) risk is provided.

FIG. 3 shows an equivalent circuit of a basic active matrix substrate. In FIG. 3, ]01 is a signal line, 10
2 is a gate I-line, 104 is a thin film transistor, 705 is an equivalent capacitance representing a liquid crystal, and 212 is a counter electrode. The signal input operation to the liquid crystal is performed as follows. Signal line 1
01, an image signal is held for each horizontal line by an external circuit. At this time, when a gate pulse is applied to one of the gate lines 102, the thin film transistor 104 connected to that gate line 102 is turned on and the image signal is written to the liquid crystal, and then the image signal is written in the liquid crystal by turning it off. is retained on the liquid crystal. Thereafter, this process is repeated until one screen of images is displayed.

[Problems to be Solved by the Invention] The problem with the conventional active matrix liquid crystal display device described above is that a direct current voltage is applied to the liquid crystal on the line, causing deterioration of the liquid crystal. This deterioration is visually observed as image burn-in, stains, and unevenness. As is well known, the twisted nematic liquid crystal used in this type of display device is subject to severe deterioration due to direct current voltage, so it must be driven with alternating current. Therefore, a signal whose polarity is inverted is applied to the signal line every frame or line. (Actually, an intermediate potential of the signal potential is applied to the counter electrode to create a pseudo alternating current.) Therefore,
An alternating current voltage is applied to the signal line and the pixel electrode. However, a DC voltage is applied to the liquid crystal on the gate line as described below.

FIG. 4 shows the pulse waveform applied to one gate line and the potential of the counter electrode. In the figure, V+ indicates the positive potential of the gate I pulse, - indicates the negative potential of the gate pulse, and Vc indicates the potential of the counter electrode. 1 on the gate line as shown in the figure.
A positive pulse is applied every frame to write a signal to the pixels connected to the gate line, and the potential is normally set to be slightly negative during other periods. This is to minimize leakage current during non-writing. As an actual example, 15V is applied to V+, and -5V is applied to V-. Assuming that the signal voltage is 0 to 1-0 and 5 V is applied to the counter electrode potential VC, a DC voltage of 10 V is always applied between the gate line and the counter electrode during non-writing. Although this voltage is not directly applied between the picture electrodes because there is a black matrix, an insulating film, etc. in addition to the liquid crystal, it is thought that at least a DC voltage of several volts is applied to the liquid crystal. Therefore, the deterioration of the liquid crystal progresses in this area, and this gradually spreads to the entire area, deteriorating the image quality.

[Means to solve the problem]

The active matrix liquid crystal display device of the present invention comprises an active matrix substrate in which thin film transistors connected to pixel electrodes as switching elements are arranged in an array and connected in a matrix by gate lines and signal lines, and a counter substrate having a transparent electrode. In an active matrix type liquid crystal display device comprising a liquid crystal sandwiched between the active matrix substrate side, at least the upper part of the gate line is insulated from the gate line, and at least the transparent electrode on the opposite substrate side is insulated from the gate line. A shield electrode for electrically shielding the cable is provided, and the shield electrode is made to have the same potential as the transparent electrode.

Further, in the above configuration, the shield electrode may also be configured to serve as a black matrix that blocks excess light, and furthermore, the shield electrode may be provided on the signal line or above the signal line, and the shield electrode may be provided on the signal line. It is also possible to have a configuration in which a window having a size not exceeding the size of the signal line is provided at the position.

[Operation] According to the present invention, there is a shield electrode on the gate line between the transparent electrode of the counter substrate and the shield electrode has the same potential as the transparent electrode, so that no electric field is applied to the liquid crystal existing between the shield electrode and the transparent electrode. No deterioration due to DC voltage occurs. That is, since this shield electrode is formed to shield the transparent electrode from voltage changes on the gate line, the influence of the gate line does not affect the transparent electrode.

Further, since this shield electrode also serves as a light shielding film (black matrix), the aperture ratio of the pixel is improved. This is because, with current technology, the exposure machines used in the semiconductor process for forming thin film transistors are more than an order of magnitude more accurate than the bonding of liquid crystal substrates, and the margin can be set smaller.

Furthermore, the window formed above the signal line according to claim 3 can reduce the capacitance formed between the signal line and the shield electrode, and can reduce the capacitance between the shield of the gate line and the signal line and the gate without impairing the operation speed. Can be used to shade lines.

〔Example〕

Next, the present invention will be explained with reference to the drawings.

(Embodiment 1) FIG. 1 is a plan view of an embodiment of the present invention, and FIG. 2 is a sectional view thereof. 1 and 2, 101 is a signal line, 102 is a gate line made of aluminum, 103 is a pixel electrode, 104 is a thin film transistor, 105 is a shield electrode and black matrix made of chromium, 201, 2
14 is a glass substrate, 202 is an active layer of a thin film transistor made of polycrystalline silicon, 203 is a gate insulating film made of silicon dioxide, 204 is a gate electrode made of doped polycrystalline silicon, 206 is a transparent electrode made of indium tin oxide, 207 209 and 211 are alignment treatment films made of polyimide, 210 is a liquid crystal, 212 is a transparent counter electrode made of indium tin oxide, and 213 is a color filter.

As can be seen from FIGS. 1 and 2, the gate line 102 and the gate electrode 204 serve as the shield electrode and black matrix 1.
It is completely covered by 05. Further, this shield electrode/black matrix 105 is kept at the same potential as the transparent electrode of the counter substrate, that is, the counter electrode 212, and especially the second
As is clear from the figure, no DC voltage component is applied to the liquid crystal 210 located above the gate line 102.

In this example, as stated in claim 2, the electrode that shields the gate line 102 from the transparent electrode (counter electrode 212) of the counter substrate also serves as a part of the black matrix. 105).

Since this black matrix is formed on the active matrix substrate, it has the advantage that it can be formed more accurately than when alignment is performed on the opposing substrate. However, gate line 10
2, it is necessary to provide a striped black matrix on the opposing substrate to shield the signal line 101 from light.

(Embodiment 2) FIG. 5 shows another embodiment of the active matrix liquid crystal display device of the present invention. In FIG. 5, 505 is a shield electrode and black matrix, and the signal line 10
1. The gate line 1021, pixel electrode 103, and thin film transistor 104 are the same as those shown in FIG.

In this embodiment, a shield electrode is also provided above the signal line 101. As described above, a pseudo AC voltage is applied to the signal line 101, but a slight DC bias may be applied in anticipation of signal potential changes such as so-called field-through occurring in the thin film transistor 104. Therefore, this example shows a case where the DC voltage generated on the signal line 101 is also cut. This is also shown as an example (claim 2) in which it is also used as a black matrix at the same time.

(Embodiment 3) FIG. 6 shows an embodiment of claim 3 of the present invention. In FIG. 6, 605 is a shield electrode and flux matrix, and 606 is a seal 1 above the believing wire 101.
~A window opened in the electrode/black matrix 605 is shown. Shin η line 101. Gate line 102, pixel electrode 103
and a thin film transistor 104ζj similar to that shown in FIG.

The difference between Example 3 and Example 2 is the window provided in the shield electrode. The effect of this window will be explained using the equivalent circuit of the active multi-mode liquid crystal display device (claims 2 and 3) of the present invention shown in FIG.

In FIG. 7, 1.01 is a signal line, 102 is a goo wire, 104 is a thin Ml transistor, 212 is a counter electrode, 7
05 is the equivalent capacitance indicating the liquid crystal, 706 is the capacitance formed between the shield electrode and flux matrix 505, 605 and the signal line 101, and 707 is the shield electrode and black matrix I.
This is the capacitance created between the gate line 102 and the gate line 102.

As shown in FIG. 7, in the active matrix liquid crystal display device of the present invention, by providing a shield electrode, a counter electrode 212, a gate line], 02, and a signal line 1 are connected.
01, a capacity such as 706.707 is generated. Since these capacitances cause delays in signals and gate pulses, it is desirable to make them as small as possible. This delay may limit the number of pixels, the resistance value of the wiring, the driving ability of the drive circuit, etc. If this restriction occurs for the signal line 101, by employing this window 606, the area of the overlapping portion can be reduced, the capacitance can be reduced, and the delay can be reduced. If there is no need to shield the signal line 01, there is no need for the seal 1 to electrode on the signal line 101'-, so there is no need for a shield electrode that generates capacitance as long as it does not impair the light shielding effect.

[Effects of the Invention] (Effects on Claim 1) Currently, it is difficult to quantitatively express the deterioration of liquid crystals. This is because burnouts and unevenness may appear due to differences in the abrasive quality of the liquid crystal or alignment film, differences in formation conditions, etc.
This is because the image quality of various motes appears to be degraded, such as when the shading is wide. Using the Aku-Eve matrix type liquid crystal display device that we created and the conventional device, we displayed still images of Shibai'↑ for 20 hours and whether or not there was an afterimage when switching to another screen 1) Mari-image ζ As a result of 1 and 7, I made a qualitative judgment as to whether the head was bad or not by looking at the image.The results of 1 and 7 are that the conventional model leaves a clear afterimage, but the present invention has an afterimage. I can't see it.lr. From these two points, the shield electrode is clearly effective. It was so powerful.

(Effects listed in claim 2) By serving as a shield electrode or a black matrix, the aperture ratio can be increased to 1. t, 1::
.

For example, in the case of a high-definition display device with a pixel width of 90 microns, the alignment accuracy of the conventional opposing substrate is +/-5.
Therefore, considering this margin, the aperture ratio was 540% (less than 1J). Since the alignment accuracy is less than 1 mta, we have achieved an aperture ratio of just under 00%.As a result, we have been able to increase the brightness of the screen by as much as 50%3. Depending on L7 and lr, the smaller the pixel, the greater the effect.

(Claim 3G, Effects for 2) Forming a window in the shield electrode/black matrix 1 The saw effect becomes larger as the screen becomes larger and as the number of pixels increases. This is because as the size increases, both wiring resistance and capacitance increase7, and as the number of pixels increases, the overlap between the signal line and gate line increases. The capacitance will not increase (1').

For example, if the screen size is 10 inches diagonally and the number of pixels is 64 horizontally. OX 3” 1920, vertical 480
The case of a display device for a personal computer will be described. In this case, the gate line is longer, and the number of intersecting lines is four times greater. However, in this example (jge・−1・
The line is made of aluminum wiring, whereas the trust line uses polycrystalline silicon wiring at the part where it intersects with the gate line to connect the ζ aluminum wiring, so the resistance value is more than 2 digits. ” - large, and as a result, the delay for J3 on the +3 line is nearly an order of magnitude larger.

In addition, the black mask I in front of the shield electrode, which is a feature of the present invention,
- When applying RISK, the gate pulse could be transmitted at a sufficient speed, but the signal could only be transmitted up to 70% within 1 inch due to the delay at the pixel farthest from the drive circuit. However, if the window of claim 3 is not applied to this, a margin of 1.5 times is expected for the signal writing time, and 100%
able to transmit signals.

[Brief explanation of the drawing]

11 and 2 are respectively a plan view and a sectional view of an embodiment of the present invention, FIG. 3 is a diagram showing an equivalent circuit of an active matrix I/RIX substrate, and FIG. 4 is a diagram showing a gate pulse and a counter electrode potential. 5 and 6 are plan views showing other embodiments of the present invention, and FIG. 7 is a diagram showing an equivalent circuit of the active matrix liquid crystal display device of the present invention. 101... Signal line, 102... Gate line, 103...
... Pixel electrode, 104 ... Thin film transistor, 105
゜505.605...Shield electrode and black matrix, 201,214...Glass substrate, 202...
Active layer of thin film transistor, 203... Gate insulating film, 204... Gate I electrode, 206... Transparent electrode,
207... Interlayer insulating film, 209, 211... Alignment treatment film, 210... Liquid crystal, 212... Counter electrode, 21
3...Color filter, 606...Window.

Claims (1)

[Claims] 1. An active matrix substrate in which thin film transistors connected to pixel electrodes as switching elements are arranged in an array and connected in a matrix with gate lines and signal lines, and a counter substrate having a transparent electrode is sandwiched between the active matrix substrate and the opposite substrate having a transparent electrode. In the active matrix type liquid crystal display device, the active matrix liquid crystal display device includes at least the gate line on the side of the active matrix substrate, which is insulated from the gate line, and electrically connects at least the gate line from the transparent electrode on the opposite substrate side. An active matrix type liquid crystal display device, characterized in that a shield electrode is provided for shielding, and the shield electrode is made to have the same potential as the transparent electrode. 2. The active matrix liquid crystal display device according to claim 1, wherein the shield electrode also serves as a black matrix that blocks excess light. 3. Claim 2, wherein the shield electrode is also provided above the signal line, and has a window at a position corresponding to the signal line, the size of which does not exceed the size of the signal line.
The active matrix liquid crystal display device described above.