JPS62119524A - Liquid crystal display device - Google Patents

Abstract

PURPOSE:To eliminate noise from a drain bus line by connecting a light shielding metallic film of each thin film transistor TR to a circuit of gate bus line which is preceding in the scanning order. CONSTITUTION:Gate bus lines 5 are scanned in the order from (a) to (c); and when taking notice of an optional gate bus line, the potential of the adjacent gate bus line preceding this gate bus line in the scanning order is kept at the earth potential until a TFT on the noticed gate bus line is selected next after it is selected, that is, duing about 100% of the period when a written signal should be held. Since the adjacent gate bus line 5 and a light shielding film 2 are close with respect to position and they can be easily connected, they are connected. Thus, the noise component from a drain bus line 6 which is transmitted to a display electrode 10 of a liquid crystal element 4 through the light shielding film 2 and the capacitive coupling between source and drain electrodes 9 and 8 is eliminated.

Description

[Detailed Description of the Invention] [Summary] In an active matrix type liquid crystal display device, noise can be reduced by circuit-connecting the light-shielding metal film of a thin film transistor that constitutes a unit pixel to the gate bus line immediately preceding in the scanning order. A display device that achieves clear gradation display.

[Industrial application field]

The present invention relates to an active matrix liquid crystal display device that achieves low noise.

Active matrix display devices are used together with simple matrix display devices as terminals of information processing devices, and liquid crystals are used as the display medium.

Comparing the characteristics of the two, the active matrix type allows a large number of pixels to be driven independently, and can theoretically provide a large display capacity.

Furthermore, when the same type of liquid crystal is used, the contrast is high and the viewing angle is wide.

However, since each pixel is provided with a thin film transistor or transistor, the cost tends to be high, and there is also a restriction that all thin film transistors must be of good quality [Prior art] FIG. This figure shows an equivalent circuit of an active matrix type liquid crystal display device, which is the same as the conventional one except for the connection position of a light-shielding metal film 2 provided in a thin film transistor (hereinafter abbreviated as TPT) 1.

That is, TPT 1 is provided for each pixel 3,
Its source electrode is circuit-connected to the liquid crystal element 4.

In other words, gate bus line 5 and drain bus line 6
are formed on the same glass substrate so as to intersect with each other at right angles, and bus lines 1 to 5 are connected to pixel 3.
The drain bus line 6 is circuit-connected to the drain electrode 8 of the TFT 1.

Further, the source electrode 9 of the TFT 1 is circuit-connected to the display electrode of the liquid crystal element 4, and the transparent electrodes of the liquid crystal element 4, which are provided on another glass substrate facing the display electrode and sandwiching the liquid crystal, are commonly grounded. ing.

As a driving method for such a display device, a large number of gate bus lines 5 provided on the panel are driven with a pulse width of 30 to 60 μs.
While line addressing is being performed sequentially using short pulses of ec, a signal pulse is applied from the drain bus line 6, which is provided in large numbers, and a display signal synchronized with the address pulse is applied to each liquid crystal element 4. Therefore, a liquid crystal display is performed.

In other words, when the TFT is turned on, the liquid crystal element 4
Charging is performed between the display electrode and the transparent electrode, and the resulting potential difference turns the liquid crystal element 4 into an ON state, and T
Even after FT1 becomes active, the charged charge is maintained as it is, so the liquid crystal element 4 continues to be in the ON state, and the next time the line is addressed again and TNT1 is turned ON, the refresh is activated. I'm here.

Now, the amorphous silicon (St) layer that constitutes the I-conductor of TFT 1 exhibits photoconductivity, and the OF
Even in the F state, when exposed to light, a small current flows between the train and the source, so 1゛! A light-shielding metal film (hereinafter simply referred to as a light-shielding film) is placed between the main electrode and the source electrode through an insulating layer.
is provided, thereby maintaining the TPT characteristics.

Conventionally, methods for connecting this light shielding film include: (1) setting it in a floating state, (2) setting it at the gate potential of its own TPT, and (2) setting it at ground potential.

However, when method (2) is used, there is a problem in that noise from the drain lot line 6 is added to the display electrode of the liquid crystal element 4 due to the capacitance caused by the overlamp between the drain/source electrode and the light shielding film. When method (2) is used, there is a problem in that noise is added from the gate bus line 5 to the display electrode due to capacitive coupling between the gate bus line 5 and the source electrode; In addition to the drain bus lines 6, it is necessary to form ground bus lines on the glass substrate in front of each other, which not only complicates the structure but also reduces the driving area ratio (display electrode area/pixel area). Yes, it is not practical.

For the above reasons, conventional active matrix type display devices are insufficient in noise removal, and twisted nematic (j18 +\i'+ T N ) crystals are used to
In order to display 6 gradations, the drive voltage should be set to 0. Although it is necessary to slice each IV, there is a problem that a good display cannot be obtained due to large noise, and a solution to this problem has been desired.

[Problem that the invention seeks to solve]

As described above, in an active matrix liquid crystal display device, it is necessary to further reduce noise in order to display good gradation, but the challenge is to find a practical solution.

[Means for solving problems]

The above problem arises when a plurality of gate bus lines and drain bus lines are patterned in a matrix, and a thin film transistor of a unit pixel and a display electrode 1 are patterned in a rectangular area surrounded by the two bus lines. In an active matrix display device in which a liquid crystal is sandwiched between a first substrate and a second glass substrate on which transparent electrodes are formed, the light-shielding metal film of each transistor is placed one next in scanning order. This problem can be solved by using a liquid crystal display device that is characterized by having a circuit connected to each network bus line.

[Effect]

In the present invention, in FIG. 1, the scanning order of the gate hash line 5 is assumed to be a, b, c, and scanning is performed from the bottom to the top, and when focusing on an arbitrary gate hash line, the scanning order is higher than this. The potential of the gate lotus line adjacent to the previous one is approximately 100% of the time from when TFT 1 on the data 1 to lotus line is selected until immediately before the next selection, that is, approximately 100% of the time that the written signal is to be held. The gate bus lines 5 and 5 are held at ground potential, and the adjacent gate bus lines 5
The light shielding film 2 and the light shielding film 2 are located close to each other and can be easily connected. Therefore, by connecting the two, the drain lotus that is transmitted to the display electrode of the liquid crystal element 4 through the coupling between the light shielding film 2 and the source/drain electrode can be reduced. This makes it possible to remove noise components from the line 6.

That is, the capacitance between the light shielding film 2 and the drain electrode 8 is Cd, the capacitance between the light shielding film 2 and the source electrode 9 is Cs, and the series capacitance between the two is Cds, and the display of the liquid crystal element 4 is as follows. The capacitance between the electrode and the transparent electrode is C
Let Lc be C of the pulse voltage Vd applied to the drain bus line 6.
ds/(CLc + Cd5) pups) noise is 1'l
Although it is applied randomly when lT1 is not selected, it can be removed by connecting the light shielding film 2 to the previous game/i bus line 5 in the scanning order and aligning it with the ground potential.

〔Example〕

A concrete implementation method of the present invention is as follows.

FIG. 2 shows a unit pixel 3, and it is assumed that the line address of the gate bus line 5 is performed in the order of 5a→5b.

After gate electrodes 7 made of chromium (Cr) are branched from gate bus lines 5a and 5b and patterned on a glass substrate, a silicon nitride (Si2H4) insulating layer,
An amorphous Si semiconductor layer and a Si02 layer were sequentially formed using plasma chemical vapor deposition (P-CVD), and TF was formed using a conventional method.
After forming the connection window 11.T1 on the gate bus line 5a that is one line before the display electrode 10 in the scanning order. An insulating film made of polyimide or the like is formed to a thickness of about 1 μm on the front surface of the substrate except for the connection window 12 above the drain electrode 8.

Next, aluminum (AI) was vacuum-deposited to a thickness of about 1 μm, and then patterned by photolithography to form a drain lot line 6, a light-shielding film 2. When forming the source/display electrode connection portion 13, the light shielding film 2 may be extended to the gate bus line 5a, and the circuit may be connected through the connection window 11.

- On the other hand, the drain electrode 8 and the drain bus line 6 are connected through the connection window 12.

Now, in order to display 16 gray levels using a normal TN liquid crystal, 0. Although it is necessary to slice the IV7-drive voltage, implementation of the present invention has been able to reduce the noise voltage to almost zero.

〔Effect of the invention〕

According to the present invention, the light-shielding film can be held at a pseudo-ground potential without complicating the pattern formation process, so noise from the drain bus line can be removed, thereby enabling good gradation display. becomes.

[Brief explanation of drawings]

FIG. 1 is an equivalent circuit of a liquid crystal display device embodying the present invention, and FIG. 2 is a plan view of a Qj-order pixel embodying the present invention. In the figure, 1 is TPT, 2 is a light shielding film, 3 is a pixel, 4 is a liquid crystal element, 5 is a gate bus line, 6 is a drain bus line, 7 is a gate electrode, 8 is a drain electrode, 9 is a source electrode, 10 is a source electrode Display electrodes, 11.12 are connection windows.

Claims (1)

[Claims] A first substrate on which a plurality of gate bus lines and drain bus lines are patterned in a matrix, and a thin film transistor of a unit pixel and a display electrode are patterned on a rectangular area surrounded by the two bus lines; In an active matrix display device in which a liquid crystal is sandwiched between a second glass substrate on which electrodes are formed, the light-shielding metal film of each thin film transistor is circuit-connected to each gate bus line immediately preceding in the scanning order. A liquid crystal display device characterized by: