JPH05119346A - Liquid crystal display device - Google Patents

Abstract

PURPOSE:To provide a liquid crystal display device where short driving is executed during the ON-period of a gate signal by providing an auxiliary switching element and executing charging till common potential by means of the gate signal of a preceding stage gate line. CONSTITUTION:The device is constituted in such a way that drain lines DL and gate lines GL which are arrayed in the shape of a matrix and a picture element electrode which is arrayed in the shape of the matrix between the both lines are provided, the auxiliary switching element 2 whose gate is connected with the preceding stage gate line GL is provided, the picture element electrode 20 is charged till common potential by the preceding stage gate signal and charging is executed till picture element electrode potential VP by the present stage gate signal.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a liquid crystal display device, and more particularly to a liquid crystal display device which can be driven with a short ON period of a gate signal.

[0002]

2. Description of the Related Art An active matrix type liquid crystal display device using a thin film transistor (TFT) is used as a display for a portable television, a video monitor and a liquid crystal projector. As a detailed explanation of this technical trend, there is "Flat Panel Display 1991" issued by Nikkei BP. Although liquid crystal display devices having various structures are described therein, an active matrix liquid crystal display device using a TFT will be described here.

This active matrix liquid crystal display device has a structure as shown in FIG. 4, for example. First there is a transparent insulating substrate, for example a glass substrate (11). On the glass substrate (11), a gate (12) and an auxiliary capacitance electrode (13), which are constituent elements of the TFT, are formed on, for example, Mo-.
It is made of Ta alloy or the like. Furthermore, SiNx is formed on the entire surface.
A film (14) made of is laminated. Then, on the SiNx film (14) corresponding to the gate (12), a non-doped amorphous silicon film (15) and N ^+.
Type amorphous silicon films (16) are laminated, and a semiconductor protective film (17) is provided between the two layers of amorphous silicon films (15) and (16). Then, on the N ⁺ type amorphous silicon film (16),
Source electrode (18) and drain electrode (1
9) is provided as a laminated body of Mo and Al, for example.
Furthermore, the SiN corresponding to the auxiliary capacitance electrode (13)
On the x film (14), the pixel electrode (2
0) is provided and is electrically connected to the source electrode (18). Further, for protection of the entire surface, a SiN _x film (21) is passivated and an alignment film (2
2) is attached.

Another glass substrate (23) is provided so as to face the glass substrate (11).
3) A counter electrode (25) is provided on it. A light-shielding film (24) is provided in a portion facing the TFT, a common counter electrode (25) is formed on the entire surface, and an alignment film (26) is attached thereon. And this pair of glass substrates (11) (23)
Liquid crystal (27) is injected between them to form a liquid crystal display device.

As shown in FIG. 5, each pixel of the liquid crystal display device is arranged in a matrix by connecting the drain and gate of the TFT to the drain line DL and the gate line GL arranged in a matrix. The shaded liquid crystal capacitance C _L is formed between the pixel electrode (20) and the counter electrode (25), and the non-slanted auxiliary capacitance C _A is formed between the pixel electrode (20) and the auxiliary capacitance electrode (13). There is.

[0006]

In such a liquid crystal display device, since a large number of pixels are connected to one gate line GL for display, if the ON period of the gate signal supplied from the gate line GL is short, Due to the resistance component of the gate line GL, the gate signal of a sufficient ON period is not transmitted to the TFT of the pixel at the end of the gate line GL due to a signal delay, which causes a problem that the liquid crystal cannot be sufficiently charged. ..
As a result, for example, when the pixel is black on the input side of the gate line GL in the case of normally white, the same black signal is grayed at the end.

As the number of pixels increases, the gate line G
Since L also increases, the number of gate lines GL (scanning lines) also increases, and the ON period of one gate line GL also becomes short. For example, when the gate line GL is 240 lines, the ON period is 63 μsec, and when it is 480 lines, it is ON.
The period is 32 μsec. To this end, the gate line G
The liquid crystal at the end of L cannot obtain sufficient charging time.

[0008]

SUMMARY OF THE INVENTION The present invention has been made in view of these problems, and the auxiliary switching element turns on by precharging the liquid crystal of the main stage with the gate signal of the gate line GL of the previous stage. A liquid crystal display device with a short period is realized.

[0009]

According to the present invention, the auxiliary switching element performs the primary charging to the common potential by the gate signal of the preceding gate line GL, and then the switching element of the present stage performs the first charging until the predetermined field signal by the gate signal. Since the secondary charging is performed, the ON period of the gate signal of each gate line GL can be shortened to the period during which the secondary charging can be performed.

[0010]

Embodiments of the present invention will be described below with reference to FIGS. FIG. 1 is an equivalent circuit diagram of the liquid crystal display device of the present invention. A large number of gate lines GL are arranged in the horizontal axis direction, and a large number of drain lines DL are arranged so as to be orthogonal to the gate lines GL. Therefore, the gate line G
The L and the drain line DL are insulated and arranged in a matrix or a lattice, and one pixel is formed in a square space formed therebetween. A switching element (1), an auxiliary switching element (2) and a pixel electrode (20) are formed in one pixel.

The switching element (1) is formed of a TFT, the drain is connected to the drain line DL, the gate is connected to the gate line GL, and the source is connected to the pixel electrode (2).
0). The shaded liquid crystal capacitance C _L is formed between the pixel electrode (20) and the counter electrode (25), and the non-slanted auxiliary capacitance C _A is formed between the pixel electrode (20) and the auxiliary capacitance electrode (13). There is.

In the auxiliary switching element (2), which is a feature of the present invention, the drain is connected to the auxiliary capacitance electrode (13), the gate is connected to the preceding gate line GL, and
Is connected to the pixel electrode (20). The auxiliary capacitance electrode (13) is connected to the counter electrode (25) and both have a common potential COM (ground potential in this embodiment) indicated by a white circle.

Such a liquid crystal display device operates as shown in FIG. When the auxiliary switching element (2) is turned on by the gate signal V _G1 at the previous stage shown by the dotted line, the primary charging starts in the liquid crystal capacitance C _L and the auxiliary capacitance C _A connected in parallel,
It is charged to the common potential COM (ground potential). Then, the switching element (2) is turned on by the gate signal V _G2 of the main stage, the second charge is started in the liquid crystal capacitance C _L and the auxiliary capacitance C _A, and the common potential is charged to the positive pixel electrode potential V _P. It Since the liquid crystal display device is driven by an alternating current, the positive pixel electrode potential V _P charged in the liquid crystal capacitance C _L and the auxiliary capacitance C _A by the next gate signal V _G1 reaches the common potential COM (ground potential). is discharged, it is discharged to the pixel electrode potential -V _P inverted by the gate signal V _G2 of the main stage.

Since the gate signal is formed by shifting the phase by the number of gate lines GL in one field signal, two-stage charging / discharging is alternately performed by the gate signals of the preceding stage and the present stage. Next, the structure of the pixel will be specifically described with reference to FIG. Since the cross-sectional structure is the same as the conventional one shown in FIG. 4, the planar structure will be described here using the reference numerals of FIG.

A large number of hatched gate lines GL (3) are provided on the glass substrate in parallel with the horizontal axis direction, and auxiliary capacitance electrodes (13) are provided in parallel along the gate lines GL (3). There is. The gate line GL (3) and the auxiliary capacitance electrode (13) are formed by vapor deposition of Mo-Ta alloy or the like,
The surface is covered with an anodic oxide film (28). The entire surface is covered with an insulating film (14) made of SiN _x . Amorphous silicon film (15) is formed on this insulating film (14).
And an N ⁺ type amorphous silicon film (16) are laminated. The auxiliary switching element (2), which is a feature of the present invention, is provided between the preceding gate line GL (3) and the auxiliary capacitance electrode (13) of the main stage, and the switching element (1) is the gate line GL of the main stage. Immediately above (3), both are formed near the drain line DL (4). That is, both amorphous silicon films (15) and (16) are etched to leave an amorphous silicon film (15) forming a channel region, and a semiconductor protective film (17) is provided on the channel region, and N ⁺ A source amorphous silicon film (16) is separated on the semiconductor protective film (17) to form a source region (5) and a drain region (6). On the source region (5) and the drain region (6), a source electrode (18) and a drain electrode (19) having a laminated structure of M _O and Al are formed. Insulating film (14)
A pixel electrode (20) made of ITO is provided on the remaining portion of the pixel and is connected to the source region (5) by the source electrode (18). The drain line DL (4) is formed at the same time when the drain electrode (19) is formed, and is arranged so as to be orthogonal to the gate line GL (3).
The gate line GL (3) is a switching element (1).
And a gate of the auxiliary switching element (2) of the next stage are formed so as to project vertically and extend under the respective channel regions. Furthermore, auxiliary capacitance electrode (13)
Is also connected to the drain of the auxiliary switching element (2). Furthermore, the auxiliary capacitance electrode (13) is the counter electrode (2
5) is connected.

The drain line DL (4) of this embodiment
Is sometimes referred to as a source line, but it is clear that it is within the scope of the present invention.

[0017]

According to the present invention, the auxiliary switching element (2) is provided to perform the primary charging to the common potential by the gate signal of the previous stage, and the second charge up to the pixel electrode potential V _P by the gate signal of this stage. Since the next charging is performed, the liquid crystal display device can be driven by the two-stage charging. As a result, there is an advantage that the ON period of the gate signal can be shortened to half as compared with the conventional driving.
Therefore, it is extremely effective for a large-sized liquid crystal display device having many gate lines GL.

In the present invention, the gate line GL (3) is used.
Of even resistance, because the charge and discharge of the second stage to drive the liquid crystal with two gate signals, without using a material expensive M _O like the electrode material of the gate line GL (3), such as Cr Can be changed to inexpensive materials. Further, in a large-sized panel, a clearer image can be obtained as the number of gate lines GL (3) is increased. However, when the driving method of the present invention is used, the line width of the gate lines GL (3) can be narrowed and a high-definition liquid crystal can be obtained. A display device can be realized.

[Brief description of drawings]

FIG. 1 is a circuit diagram illustrating an equivalent circuit diagram of a liquid crystal display device according to the present invention.

FIG. 2 is a waveform diagram illustrating the operation of the liquid crystal display device according to the present invention.

FIG. 3 is a plan view illustrating a pixel structure of a liquid crystal display device according to the present invention.

FIG. 4 is a cross-sectional view illustrating a conventional liquid crystal display device.

FIG. 5 is a circuit diagram illustrating an equivalent circuit diagram of a conventional liquid crystal display device.

[Explanation of symbols]

1 Switching Element 2 Auxiliary Switching Element 3 Gate Line GL 4 Drain Line DL 5 Source Region 6 Drain Region 11 Glass Substrate 12 Gate 13 Auxiliary Capacitance Electrode 14 Insulating Film 15 Amorphous Silicon Film 16 N ⁺ Type Amorphous Silicon Film 17 Semiconductor Protection Films 18 and 19 Source electrode and drain electrode 20 Pixel electrode 27 Liquid crystal

Claims (3)

[Claims] 1. A drain line and a gate line arranged in a matrix, a pixel electrode arranged in a matrix between both lines, a drain on the drain line, a gate on the gate line and a source on the pixel electrode. In a liquid crystal display device including a connected switching element and a liquid crystal material provided between the pixel electrode and a counter electrode, an auxiliary switching element connected to the pixel electrode and having a gate connected to a preceding gate line is provided, A liquid crystal display device, wherein the pixel signal is charged to a substantially common potential by the gate signal of the gate line of the preceding stage, and the pixel electrode is charged to a predetermined potential by the gate signal of the gate line of the present stage. 2. A drain line and a gate line arranged in a matrix, a pixel electrode arranged in a matrix between both lines, an auxiliary capacitance electrode extending under the pixel electrode, and the drain line. In a liquid crystal display device comprising a switching element having a drain connected to the gate line and a gate connected to the pixel electrode to the source, and a liquid crystal material provided between the pixel electrode and a counter electrode, the source is connected to the pixel electrode. An auxiliary switching element having a gate connected to the gate line of the previous stage and a drain connected to the auxiliary capacitance electrode is provided, and the pixel signal is charged to substantially the potential of the auxiliary capacitance electrode by the gate signal of the gate line of the previous stage. 2. The liquid crystal display device, wherein the pixel electrode is charged to a predetermined potential by the gate signal of the gate line. 3. A drain line and a gate line arranged in a matrix, a pixel electrode arranged in a matrix between both lines, an auxiliary capacitance electrode extending under the pixel electrode, and the drain line. In a liquid crystal display device comprising a switching element having a drain connected to the gate line and a gate connected to the pixel electrode to the source, and a liquid crystal material provided between the pixel electrode and a counter electrode, the source is connected to the pixel electrode. An auxiliary switching element having a gate connected to a preceding gate line and a drain connected to the auxiliary capacitance electrode is provided, the auxiliary capacitance electrode and the counter electrode are connected to each other, and the pixel electrode is supplied with a gate signal of the preceding gate line. Is characterized in that the pixel electrode is charged to a potential substantially opposite to that of the counter electrode, and the pixel electrode is charged to a predetermined potential by the gate signal of the gate line of the main stage. Liquid crystal display device.