JPH05333376A - Liquid crystal display device and driving method therefor - Google Patents

Abstract

PURPOSE:To provide a liquid crystal panel, which does not lower the opening ratio of picture element electrodes and can easily discover the defect of switching elements by adding a storage capacitor, concerning the liquid crystal panel provided with the plural switching elements at picture elements. CONSTITUTION:On an active matrix substrate, plural drain bus lines 4 and plural gate bus lines 1 cross on a glass substrate, and this active matrix substrate is provided with plural TFT (thin film transistors) 2-1 and 2-2 near the intersection, plural picture element electrodes 7-1 and 7-2 corresponding to the TFT, switching element 8 to connect the plural picture element electrodes, and electrode 9 for storage capacitor. On this active matrix board, the electrode 9 for storage capacity is spread over the plural picture element electrodes 7-1 and 7-2, and the electrode 9 for storage capacity is arranged so as to be also used as the switching control electrode of the switching element 8.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an active matrix liquid crystal display panel used for information terminals.

Generally, an active type liquid crystal display device has several hundreds of thousands of switching elements, and it is very difficult to manufacture all of them without defects in the current process technology. Therefore, a so-called redundant configuration in which a plurality of switching elements are provided for each display pixel is widely adopted.

[0003]

2. Description of the Related Art FIG. 12 shows one pixel of a conventional active matrix liquid crystal panel. This is because when a selection voltage is applied to the gate electrode 3 of the TFT 2 by the selection voltage sent from the gate bus line 1, the signal voltage sent from the drain bus line 4 is passed through the drain electrode 5 and the source electrode 6. It is applied to the pixel electrode 7 to be displayed. However, at this time, if the TFT fails, for example, if the gate electrode 3 does not operate even if a selection voltage is applied, a contact failure between the source electrode 6 and the pixel electrode 7, an increase in channel resistance, etc. occur, the signal voltage is applied to the pixel electrode. However, there was a problem in that no display voltage was applied to the display defect.

Therefore, in Japanese Patent Laid-Open No. 60-97322, one pixel is divided into a plurality of 7 _-1 , 7 _-2 as shown in FIG. 13, and each pixel is connected to a separate TFT 2 _-1 , 2 _-2. In addition, even if there is a pixel defect due to a TFT failure, a redundant configuration is proposed in which display is performed in the remaining pixels and no display defect occurs. However, since this method is pseudo-defect-free, there is no problem in displaying a moving image on a TV or the like, but in the case of displaying a still image on an information terminal or the like, if a defect occurs in a divided pixel, a character or a picture is missing and becomes difficult to see. Not suitable for.

Therefore, recently, as shown in FIG. 14, when a switching element 8 is provided between each pixel electrode 7 _-1 , 7 _-2 obtained by dividing one pixel into a plurality of pixels and the TFT of the division element is broken, A method has been proposed in which the TFT is separated by a laser or the like and the switching element 8 drives an external circuit to supply a signal voltage from another divided pixel.

[0006]

In the system shown in FIG. 13, the aperture ratio of the pixel electrode is remarkably reduced when a storage capacitor for holding the voltage of the liquid crystal voltage is added to this pixel structure, and the panel is There is a problem that it leads to a decrease in brightness. Further, in the method of FIG. 14, in the case of a defect due to a short circuit of the TFT, this TFT can be separated by a laser and repaired, but there is a problem that it is difficult to detect this defect.

The present invention is a liquid crystal panel having a plurality of switching elements in one pixel, in which the aperture ratio of the pixel electrode does not decrease even if a storage capacitor is added, and a liquid crystal panel in which a defect of the switching element can be easily found. Try to realize.

[0008]

In the liquid crystal display device of the present invention, a plurality of drain bus lines 4 for supplying a signal voltage and a plurality of gate bus lines 1 for supplying a scanning voltage are orthogonal to each other on a glass substrate. , Multiple TFTs near the intersection
(Thin film transistor) 2 _-1 , 2 _-2 , a plurality of pixel electrodes 7 _-1 , 7 _-2 corresponding to the TFT, a switching element 8 connecting the plurality of pixel electrodes, and a storage capacitor electrode 9 are provided. In an active matrix liquid crystal panel including the provided active matrix substrate, the counter substrate in which the counter electrode and the liquid crystal alignment film are provided on the glass substrate, and the liquid crystal sandwiched between the counter substrate and the active matrix substrate, the same The storage capacitor electrode 9 is provided between the plurality of pixel electrodes 7 _-1 , 7 _-2 to which a signal voltage or different signal voltages are supplied, and the storage capacitor electrode 9 is switched by the switching element 8. It is characterized in that it is arranged so as to also serve as a control electrode.

Further, in the method for driving the liquid crystal display device of the present invention, when the plurality of TFTs 2 _-1 , 2 _-2 are normally switching, the storage capacitor electrode 9 is used.
Is applied with a voltage for turning off the switching element 8 between the plurality of pixel electrodes, and the storage capacitor electrode 9 is applied to the storage capacitor electrode 9 only when the switching operation of any of the plurality of TFTs 2 _-1 , 2 _-2 fails. A voltage for turning on the switching element 8 between the plurality of pixel electrodes is applied.

Further, in the liquid crystal display device of the present invention,
In an active matrix type liquid crystal display device having a plurality of switching elements per display pixel, a plurality of divided pixels 7 _-1 , 7 _-2 and a corresponding switching element 2 _-1 , 2 _-2 are provided for each display pixel. , Divided pixels 7 _-1 , 7 _-2
An optical switch 30 is provided between them. Also,
In addition, an a-Si optical switch is used as the optical switch 30, and the resistance value of this switch is 30 when the light is irradiated.
It is characterized in that the resistance value which can drive the adjacent divided pixels via the switch is set to a resistance value which is not affected by the potential of the adjacent pixel via the switch 30 in the dark.

Further, in the liquid crystal display device of the present invention,
It is characterized in that it has a gate bus line 51 corresponding to the switching elements 2 _-1 , 2 _-2 of the divided pixels, and an optical switch 50 is provided between the waveform supply end of the gate bus line 51 and the display section. In addition to the above, the optical switch 50
The a-Si optical switch is used as the resistance value, and the resistance value is set to a resistance value such that the waveform reaching the pixel portion during light irradiation is not blunt, and a resistance value where the waveform reaching the pixel portion is rounded in the dark. By adopting this configuration, in a liquid crystal display device having a plurality of switching elements in one pixel,
It is possible to obtain a liquid crystal display device in which the aperture ratio of a pixel electrode does not decrease even if a storage capacitor is added, and a liquid crystal display device in which a defect of a switching element can be easily found.

[0012]

In the liquid crystal display device of the present invention, the storage capacitor electrode is provided so as to straddle the divided pixels, and the storage capacitor electrode also serves as the switching control electrode of the switching element provided between the divided pixels, whereby the aperture ratio is improved. It is possible to prevent the deterioration, and to realize a panel with no defects and high contrast.

Further, since the optical switch is provided between the divided pixels, the divided pixels are connected via the optical switch during light irradiation (a normal liquid crystal display device has a backlight and uses the light). Even if one of the TFTs has an open defect, writing can be performed from the other TFT, so that no pixel defect occurs. However, if even one of the TFTs has a short defect, the entire display image is a pixel defect (black defect).
Becomes Here, by some means, the light that enters the optical switch
For example, if a light-shielding mask is used for light shielding, the connection by the optical switch between the divided pixels is lost, so that the defective pixel can be identified and the defective TFT can be separated by the laser. After that, in the normal display, the optical switch is irradiated with light, so it is possible to write from another TFT.
It does not result in a pixel defect.

[0014]

1 is a diagram showing a first embodiment of the present invention. In this embodiment, as shown in the figure, a gate bus line 1 for supplying a scanning voltage, a drain bus line 4 for supplying a signal voltage provided so as to be orthogonal to the gate bus line, and the drain bus line. 4 and the gate bus line 1 of intersection TFT 2 _-1 provided near, 2 _-2 and, dividing the pixel electrode 7 _-1 connected to each TFT, and 7 _-2, the divided pixel electrode 7 _-1, 7 _- One pixel is formed by the switching element 8 connecting the _two and the storage capacitor electrode 9 provided across the divided pixel electrodes 7 _-1 , 7 _-2 , and the storage capacitor electrode 9 is formed.
Is formed so as to also serve as a switching control electrode of the switching element 8.

Next, the manufacturing method of this embodiment will be described with reference to FIGS. FIG. 2 is a diagram for explaining a method of manufacturing a TFT. First, a Ti or Cr material is laminated on the entire surface of a transparent glass substrate 10 having a thickness of 1.1 mm by sputtering,
The gate bus line and the gate electrode 3 are patterned. Next, a gate insulating film (SiO ₂ , SiN) 11 and a semiconductor layer 12 made of an a-Si material are continuously laminated thereon by a plasma CVD method and patterned by a transistor pattern. Further, n ⁺ type a-Si material 13 and Ti or Al
The source electrode 6, the drain electrode 5 and the drain bus line made of a material are formed.

FIG. 3 shows electrodes for storage capacitors and switching elements.
It is a diagram for explaining the manufacturing method of the child, (a) is a plane
FIG. 2B is a sectional view taken along line bb of FIG. Book
The manufacturing method is as follows. First, Ti or Cr material is placed on the transparent substrate 10.
Laminated over the entire surface by sputtering, and gate bus line and storage
The capacitor electrode / gate electrode 9 is patterned. Next
From above the gate insulation film (SiO₂, SiN) 14 and a-Si materials
The semiconductor layer 15 formed by
Laminate and pattern with a transistor pattern.
Then n⁺a-Si material 16 and Ti or Al material
Source (drain) electrode 6 and drain (source) electrode 5
Form. Furthermore, the divided pixel electrode 7_-1, 7 _-2Each
Part of the source electrode 6 or the drain electrode 5 overlaps
To form.

This switching element is connected to the defective TFT
The pixel electrode on the exposed side is defined as the source electrode.
ing. The size of the switching element is TFT2._-1or
Is 2 _-2The same as With this configuration, as shown in Fig. 3 (a)
Divided pixel electrode 7_-1, 7_-2A certain condition can be provided between
Applying voltage to the bus line for storage capacitor
Electrode 7_-1, 7_-2You can connect between them. Accumulate here
The capacitance of the capacitance electrode is preferably about three times the pixel capacitance, for example.
More preferably, the storage capacitor electrode 9 and the divided pixel electrode at this time
7_-1, 7_-2The overlapping area with is, for example, 2.5 × 10^-9m²
The degree is appropriate. In addition, it also functions as an electrode for storage capacitance and switching.
The element 8 is not in the same pixel 7 as in FIG.
It may be built in between the previous pixels.

FIG. 5 is a diagram showing the present embodiment including peripheral circuits. For example, the storage capacitor electrode 9 is drawn out to the left side of the panel 20, a voltage for turning off the switching element, for example, -10V is applied by the analog switch circuit 21 or the like, and the switching element is turned on only for the gate line with the TFT failure. The circuit configuration is such that a voltage to be applied, for example, 10 V can be arbitrarily applied. Gate bus line 1 is panel 2
It is drawn to the right of 0, and a scan pulse is generated by the shift register circuit 22 and the like. In addition, the data bus line (=
The drain bus line 4 is, for example, an odd line on the panel 2
On the upper side of 0, the even line is pulled out to the lower side, and the shift register 23 and the latch circuit 24 generate a signal voltage.

In this way, even if there is a failure in the TFT, the defect T is caused by operating the switching element 8.
The split pixels connected to the FT can be activated to leave a defect free state. In addition, since the storage capacitor electrode can be provided without lowering the aperture ratio, an active matrix liquid crystal panel with high contrast and high brightness can be realized.

FIG. 6 is a diagram showing a second embodiment of the present invention. In this embodiment, one pixel is divided into four divided pixel electrodes 7 ₋₁ to
7 _-4 , two switching elements 8 and 8'connect two divided pixel electrodes. This embodiment has the same effect as the previous embodiment.

FIG. 7 is a diagram showing a third embodiment of the present invention. In this embodiment, a gate bus line 1 and a drain bus line 4 provided orthogonal to the gate bus line 1,
The TFT 2 _-1 , 2 _-2 provided near the intersection of the gate bus line 1 and the drain bus line and the divided pixel electrodes 7 _-1 , 7 _-2 obtained by dividing one pixel 7 are formed. An optical switch 30 is provided, which is connected to the TFT _{2 -1} and the TFT _{2 -2} , respectively, and is connected between the divided pixel electrodes 7 _-1 and 7 _-2 .

As a condition of the optical switch 30, it is possible to write to the adjacent divided pixel electrodes 7 _-1 , 7 _-2 via the optical switch 30 during light irradiation (during normal display). The two points are that writing can be performed without being affected by the divided pixels in which the adjacent TFTs are short-circuited during darkness (during defect inspection). When this is calculated by simulation, the resistance value is 10 ⁷ Ω or less, and 10 ¹⁰ Ω is
If it becomes the above, the conditions applied to the present invention can be satisfied.

As an example of this optical switch, a-Si having photoconductivity is used. The photoconductivity of a-Si is 10 ³ Ωcm during light irradiation and 10 ⁸ Ωcm during darkness, as shown in FIG. 8 (reference document: Terukodo, amorphous solar cell p107). Therefore, the film thickness of a-Si is 0.3 μm and the overlap is 5 μm.
With the m port, the resistance value of the sandwich cell is 10 ⁵ when light is irradiated, and 10 ¹⁰ Ω when dark, and the conditions can be satisfied. As the sandwich structure, as shown in FIG. 9, a-Si is formed between the metal film 40 connected to one of the divided pixel electrodes 7 _-1 and the other of the divided pixel electrodes 7 _-2.
The film 41 may be sandwiched, or the a-Si film 41 may be sandwiched between the divided pixel electrodes 7 _-1 , 7 _-2 and the metal film 40 as shown in FIG.

In this embodiment having such a structure, the divided pixel electrodes 7 _-1 , 7 _-2 are connected through the optical switch 30 during light irradiation, and even if one of the TFTs has an open defect. However, since the other TFT can perform writing, no pixel defect will occur. If even one of the TFTs has a short defect, the entire display pixel becomes a pixel defect (black defect). Here, if the light entering the optical switch 30 is shielded by some means, for example, a light shielding mask, the connection by the optical switch between the divided pixels is lost, and the defect of the divided pixels can be determined. After that, if the defective TFT is cut by a laser, the optical switch 30 is turned on in the normal display, and writing can be performed from other TFTs without causing a pixel defect. By controlling the light entering the optical switch 30 in this manner, the defective pixel can be detected.

Further, as shown in FIG. 11 as a modified example, when there are a plurality of scan bus lines 51, this optical switch 50 is provided between the voltage supply end and the pixel region. For example, the optical switches corresponding to the upper line and the optical switches corresponding to the lower line are arranged in different rows. As a result, they can be driven separately, and defective short-circuited TFTs can be detected. The optical switch at this time is a
-Si film thickness is 0.3 μm, size is 100 μm x 30
If it is set to μm, it is calculated by the same calculation as above, and it is 10 ³
Ω, 10 ⁹ Ω in the dark, and can be used as an optical switch.

[0026]

According to the present invention, a redundant structure of a pixel division system can be adopted, and defects of divided pixels can be repaired, so that a defect-free active matrix liquid crystal panel can be realized. Further, since the storage capacitor electrode can be provided without lowering the aperture ratio, an active matrix liquid crystal display device with high contrast and high brightness can be realized. Further, by providing an optical switch between the divided pixel electrodes, it is possible to realize a liquid crystal display device in which a short circuit defect of the TFT can be easily found.

[Brief description of drawings]

FIG. 1 is a diagram showing a first embodiment of the present invention.

FIG. 2 is a drawing for explaining the manufacturing method of the TFT in the embodiment of the present invention.

FIG. 3 is a diagram for explaining a method of manufacturing the storage capacitor electrode and the switching element according to the embodiment of the present invention.
Is a plan view and (b) is a sectional view taken along line bb of FIG.

FIG. 4 is a diagram showing a modification of the first embodiment of the present invention.

FIG. 5 is a diagram showing a peripheral circuit according to an embodiment of the present invention.

FIG. 6 is a diagram showing a second embodiment of the present invention.

FIG. 7 is a diagram showing a third embodiment of the present invention.

FIG. 8 is a diagram showing the photoconductivity of a-Si.

FIG. 9 is a diagram showing an example of an optical switch, (a) is a plan view,
(b) is a sectional view taken along line bb of (a).

10A and 10B are views showing another example of the optical switch, FIG. 10A is a plan view, and FIG. 10B is a sectional view taken along line bb of FIG. 10A.

FIG. 11 is a diagram showing a modification of the third embodiment of the present invention.

FIG. 12: 1 of conventional active matrix liquid crystal panel
It is a figure which shows one pixel.

FIG. 13 is a diagram showing one pixel of an active matrix liquid crystal panel obtained by dividing one pixel into a plurality of pixels.

FIG. 14 is a diagram showing one pixel of an active matrix liquid crystal panel in which a switching element is provided between divided pixels.

[Explanation of symbols]

DESCRIPTION OF _SYMBOLS 1 ... Gate bus line 2 _{-1 to} 2 _-4 ... TFT 3 ... Gate electrode 4 ... Drain bus line 5 ... Drain electrode 6 ... Source electrode 7 _{-1 to} 7 _-4 ... Divided pixel electrode 8, 8 '... Switching element 9 Storage electrode 10 Transparent glass substrate 11 Gate insulating film 12 a-Si semiconductor layer 13 n ⁺ a-Si 20 Liquid crystal panel 21 Analog switch 22, 23 Shift register 24 Latch circuit 30, 50 … Optical switch

Front page continuation (72) Inventor Keizo Morita 1015 Kamiodanaka, Nakahara-ku, Kawasaki-shi, Kanagawa Fujitsu Limited

Claims (6)

[Claims] 1. A plurality of drain bus lines (4) for supplying a signal voltage and a plurality of gate bus lines (1) for supplying a scanning voltage are orthogonal to each other on a glass substrate, and a plurality of TFTs (thin film transistors) are provided in the vicinity of their intersections. ) (2 _-1 , 2 _-2 ), a plurality of pixel electrodes (7 _-1 , 7 _-2 ) corresponding to the TFT, and a switching element (8) connecting the plurality of pixel electrodes
An active matrix substrate provided with a storage capacitor electrode (9), a counter substrate provided with a counter electrode and a liquid crystal alignment film on a glass substrate, and a liquid crystal sandwiched between the counter substrate and the active matrix substrate. In the active matrix liquid crystal panel, the storage capacitor electrode (9) is provided between the plurality of pixel electrodes (7 _-1 , 7 _-2 ) to which the same signal voltage or different signal voltages are supplied, The liquid crystal display device is characterized in that the storage capacitor electrode (9) is arranged so as to also serve as a switching control electrode of the switching element (8). 2. The liquid crystal display device according to claim 1,
When the plurality of TFTs ( _2-1 , _2-2 ) are performing normal switching operation, the switching element (8) between the plurality of pixel electrodes is turned off in the storage capacitor electrode (9). A switching element (8) between the plurality of pixel electrodes is provided on the storage capacitor electrode (9) only when a voltage is applied and the switching operation of the plurality of TFTs (2 _-1 , 2 _-2 ) fails. A method for driving a liquid crystal display device, characterized in that a voltage for turning on is applied. 3. An active matrix liquid crystal display device having a plurality of switching elements per display pixel, wherein a plurality of divided pixels ( _7-1 , _7-2 ) per display pixel,
A liquid crystal display device having switching elements (2 _-1 , 2 _-2 ) corresponding thereto and an optical switch (30) between divided pixels (7 _-1 , 7 _-2 ). 4. The a-Si as the optical switch (30)
An optical switch is used, and its resistance value is influenced by the resistance value that can be driven by adjacent divided pixels via this switch (30) during light irradiation, and is influenced by the potential of the adjacent pixel via this switch (30) during darkness. The liquid crystal display device according to claim 3, wherein the liquid crystal display device has a resistance value that does not exist. 5. A switching element (2 _-1 , 2) of divided pixels
_-2 ), which has a gate bus line (51) corresponding to ( ₂ ), and an optical switch (50) is provided between the waveform supply end of the gate bus line (51) and the display section. 6. The a-Si as the optical switch (50)
6. The liquid crystal according to claim 5, wherein an optical switch is used, and its resistance value is set to a resistance value which does not make the waveform reaching the pixel portion dull during light irradiation, and is set to be a resistance value where the waveform reaching the pixel portion is rounded in the dark. Display device.