JPH11288000A - Liquid crystal display device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To improve the aperture rate by causing deterioration in writing characteristics of the liquid crystal display device. SOLUTION: This device has a liquid crystal layer having a liquid crystal composition held between a couple of substrates and also has a switching element 17 and reference electrodes 12A, 12B, and 12A formed on one substrate in the extending direction of a video signal line 10; and one of the reference electrodes (12B) serves as a reference signal line for supplying a reference signal to the reference electrodes 12A, 12B, and 12A and the reference electrode 12B serving as the reference signal line pass through an insulating film over a switching element TFT and connects two adjacent pixels in the extending direction of the video signal line 10 to produce an electric field having a component almost parallel to the substrate surface, thereby controlling the liquid crystal.

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, and more particularly to a liquid crystal of a horizontal electric field type which controls a liquid crystal molecule in a direction parallel to a substrate surface of a liquid crystal panel constituting the liquid crystal display to display an image. It relates to a display device.

[0002]

2. Description of the Related Art A liquid crystal display device has been widely used as a display device capable of high-definition and color display for a notebook computer or a display monitor.

In a liquid crystal display device, a pair of substrates having a large number of electrodes arranged in parallel are bonded so that the electron guns cross each other, and a liquid crystal display device of a simple matrix type (generally, a liquid crystal is sandwiched in a bonding gap). , STN type liquid crystal display devices) and active matrix type liquid crystal display devices provided with switching elements for pixel selection for each unit pixel.

[0004] In particular, as a so-called active matrix type liquid crystal display device, a so-called twisted nematic (TN) system is used, which is a so-called liquid crystal panel using a pixel selection electrode group formed on each of a pair of upper and lower substrates. A so-called horizontal electric field type liquid crystal display using a vertical electric field type liquid crystal display device (generally called a TN type liquid crystal display device) and a liquid crystal panel in which an electrode group for pixel selection is formed on only one of a pair of upper and lower substrates. Device (generally referred to as an IPS mode liquid crystal display device).

In a liquid crystal panel constituting the former TN mode liquid crystal display device, the liquid crystal is twisted by 90 ° in a pair of (two) substrates, and the absorption axis directions are arranged on the outer surfaces of the upper and lower substrates of the liquid crystal panel. Two polarizing plates are arranged in a crossed Nicols state and the absorption axes on the incident side are parallel or perpendicular to the rubbing direction. When the rubbing direction is parallel to the absorption axis of the polarizing plate, it is called an "O" mode, and when it is perpendicular, it is called an "E" mode.

In such a TN type liquid crystal display device, when no voltage is applied, incident light becomes linearly polarized light by an incident side polarizing plate.
The linearly polarized light propagates along the twist of the liquid crystal layer, and when the transmission axis of the exit-side polarizing plate matches the azimuth of the linearly polarized light, all of the linearly polarized light is emitted to form a white display (a so-called “no”). Mari open arrangement).

When a voltage is applied, the direction (director) of a unit vector indicating the average alignment direction of the liquid crystal molecular axes constituting the liquid crystal layer is oriented in a direction perpendicular to the substrate surface, and the azimuth of the incident side linearly polarized light. Since the angle does not change, the display coincides with the absorption axis of the exit-side polarizing plate, resulting in black display (see "Basic and Application of Liquid Crystal", published by the Industrial Research Institute in 1991).

On the other hand, an electrode group for pixel selection and an electrode wiring group are formed only on one of a pair of substrates, and a voltage is applied between adjacent electrodes (between a pixel electrode and a counter electrode) on the substrate by applying a voltage. In an IPS type liquid crystal display device in which layers are switched in a direction parallel to the substrate surface, a polarizing plate is arranged so as to display black when no voltage is applied (a so-called normally closed arrangement).

The liquid crystal layer of this IPS mode liquid crystal display device is
In the initial state, the director of the liquid crystal layer is in a homogeneous orientation parallel to the substrate surface, and in a plane parallel to the substrate, the director of the liquid crystal layer is parallel or somewhat angled with the electrode wiring direction when no voltage is applied, and the liquid crystal layer is oriented when the voltage is applied. The direction of the director shifts in a direction perpendicular to the electrode wiring direction with the application of the voltage, and the director direction of the liquid crystal layer is 45 times smaller than the director direction when no voltage is applied.
° When tilted in the electrode wiring direction, the liquid crystal layer at the time of applying the voltage has an azimuth of 90 degrees of polarization as if it were a half-wave plate.
And the azimuth of the polarized light coincides with the transmission axis of the exit-side polarizing plate, and a white display is obtained.

The IPS mode liquid crystal display device has a feature that a change in hue and contrast is small even at a viewing angle, and a wide viewing angle is achieved (Japanese Patent Laid-Open No. 5-50).
No. 5247).

In the IPS mode liquid crystal display device, since it is necessary to form an electric field parallel to the substrate, a structure in which a pixel electrode and a reference electrode are formed in a comb shape on one substrate is employed. A signal voltage is supplied from a video signal line to a pixel electrode through a switching element (generally, a thin film transistor: TFT; the switching element is hereinafter described as a thin film transistor TFT), and a reference voltage is supplied from a reference signal line to a reference electrode. You.

A TFT is formed by using a plurality of steps of a photolithography technique.
In order to reduce the number of photolithography steps, a direction perpendicular to the extending direction of the video signal line, a direction parallel to the scanning signal line, and a direction perpendicular to the pixel electrode and the reference electrode are formed.

[0013]

However, in the conventional arrangement of the reference signal lines, the electrodes are formed in the openings of one pixel, so that the so-called aperture ratio is reduced and the brightness of the screen is reduced. was there.

When the reference signal line is formed integrally with the reference electrode in a direction parallel to the extending direction of the video signal line, a decrease in aperture ratio can be prevented, but an intersection with the scanning signal line occurs. Accordingly, there is a problem that the capacity of the scanning signal line is increased, the waveform rounding of the scanning signal line is increased, the writing characteristics of the TFT are deteriorated, and the display quality is reduced.

SUMMARY OF THE INVENTION An object of the present invention is to provide a liquid crystal display device which can solve the above-mentioned problems of the prior art, and which enables bright and high quality display.

[0016]

Means for Solving the Problems In order to achieve the above-mentioned object, the present invention is characterized by having the following constitutions (1) to (5).

(1) A switching element for selecting a pixel, a video signal line, a scanning signal line, and a pixel electrode to which a video signal is supplied by the switching element and the pixel electrode are provided on one of the pair of substrates. A reference electrode for controlling a liquid crystal by forming an electric field having a parallel component; and a reference signal line for applying a reference signal to the reference electrode. A liquid crystal layer is sandwiched between opposing gaps between the pair of substrates. A liquid crystal panel having a polarizing plate laminated on each of the outer surfaces of the pair of substrates, and at least a drive circuit for applying a voltage waveform for pixel selection to a source electrode of the switching element via the wiring, A plurality of reference electrodes are formed in the extending direction of the video signal line, and the reference signal line for supplying a reference signal to the reference electrode is also used at least as one of the reference electrodes. At least one of the reference electrode, passed over the switching element via an insulating film, connecting between two pixels adjacently provided in the extending direction of the video signal lines.

According to this configuration, a decrease in the aperture ratio of the pixel is suppressed, and there is no increase in the crossing capacity, so that a bright and high-quality image display can be obtained.

(2) A switching element for selecting a pixel, a video signal line, a scanning signal line, and a pixel electrode to which a video signal is supplied by the switching element and the pixel electrode are provided on one of the pair of substrates. A reference electrode for controlling a liquid crystal by forming an electric field having a parallel component; and a reference signal line for applying a reference signal to the reference electrode. A liquid crystal layer is sandwiched between opposing gaps between the pair of substrates. A liquid crystal panel having a polarizing plate laminated on each of the outer surfaces of the pair of substrates, and at least a drive circuit for applying a voltage waveform for pixel selection to a source electrode of the switching element via the wiring, A plurality of reference electrodes are formed in the extending direction of the video signal line, and the reference electrode is connected to one of the reference signal lines for supplying a reference signal to the reference electrode within one pixel, and A signal line passed over the switching element via an insulating film, connecting between two pixels adjacently provided in the extending direction of the video signal lines.

According to this configuration, a decrease in the aperture ratio of the pixel is suppressed, and a bright and high-quality image display can be obtained.

(3) A switching element for selecting a pixel, a video signal line, a scanning signal line, and a pixel electrode to which a video signal is supplied by the switching element and the pixel electrode are provided on one of the pair of substrates. A reference electrode for controlling a liquid crystal by forming an electric field having a parallel component; and a reference signal line for applying a reference signal to the reference electrode. A liquid crystal layer is sandwiched between opposing gaps between the pair of substrates. A liquid crystal panel having a polarizing plate laminated on each of the outer surfaces of the pair of substrates, and at least a drive circuit for applying a voltage waveform for pixel selection to a source electrode of the switching element via the wiring, A plurality of reference electrodes are formed in the extending direction of the video signal line, and the reference electrode is connected to the reference signal line that supplies a reference signal to the reference electrode within one pixel, A signal line passes over the switching element via an insulating film, connects two pixels adjacent to each other in the direction in which the video signal line extends, and connects the reference wiring to the reference signal line with the reference wiring. The storage capacitor was formed in the region of the connection wiring portion formed by overlapping with the pixel electrode of the element.

According to this configuration, a decrease in the aperture ratio of the pixel is suppressed, an increase in the rounding of the waveform of the scanning signal line is suppressed, and a deterioration in the writing characteristics of the TFT is prevented. The display is obtained.

(4) The reference electrode in (1), (2) or (3) is formed of a transparent conductive material.

(5) The transparent conductive material in (4) is any one of ITO, SnO ₂ , and In ₂ O ₃ .

The reference electrode formed in the opening of the pixel can avoid a change in the operation characteristics of the TFT due to the light of the backlight.

[0026]

Embodiments of the present invention will be described below in detail with reference to the accompanying drawings.

[Embodiment 1] FIG. 1 is a plan view of an essential part for explaining a plane structure of a pixel portion for explaining a first embodiment of a liquid crystal panel constituting a liquid crystal display device according to the present invention, and FIG. FIG. 3 is a cross-sectional view of a main part along the line BB ′ in FIG. 1.

1, 2 and 3, reference numeral 10 denotes a video signal line, 11 denotes a pixel electrode, 12 denotes a reference electrode, 15 denotes a scanning signal line, 16 denotes a semiconductor layer, 17 denotes a TFT, 30 denotes a gate insulating film, 40 is an insulating film. Note that 1A is a substrate, and BM is an opening edge of a light-shielding layer, and a region shown as “pixel” in the drawing is one pixel.

In this embodiment, three reference electrodes 12A, 12B, 1 are formed in the opening of one pixel in parallel with the video signal line 10 and the pixel electrode 11 as the reference electrode 12 connected to the reference signal line.
2A are arranged, and one of them, that is, the reference electrode 12B located at the center crosses the scanning signal line 15 on the TFT section 17.

As shown in FIG. 2, in this embodiment, the other two reference electrodes 12A and the scanning signal lines 15 are
Intersect at a place other than the part. The reference electrode 12A and the scanning signal line 15 overlap with the gate insulating film 30 and the insulating film 40 interposed therebetween, and a cross capacitance is formed at this portion.

On the other hand, as shown in FIG.
B and the scanning signal line 15 intersect on the TFT 17. The semiconductor layer 16 is formed on the scanning signal line 15 with a gate insulating film 30 interposed therebetween. At the time of writing in a TFT in which the waveform distortion of the scanning signal line becomes a problem, the semiconductor layer 16 is in a state equivalent to that of a metal and supplies a signal from the video signal line 10 to the pixel electrode 11.

That is, at this time, the crossing capacitance formed between the reference electrode 12B and the scanning signal line 15 in the region shown in FIG. 3 has already been formed between the semiconductor layer and the scanning signal line. No cross capacitance to a new scanning signal line is generated due to the presence of the electrode 12B. In this way, the reference signal line, which is also used as the reference electrode, crosses the scanning signal line 15 on the TFT 17, thereby avoiding the generation of a new capacitance, and does not generate a capacitive load on the scanning signal line. The occurrence of dullness is prevented. When a verification test was conducted by embodying the liquid crystal display device according to the configuration of the present embodiment, one of the three reference signal lines formed in one pixel passed through the TFT 17 as described above. The increase in the crossing capacitance with the scanning signal line could be suppressed to 2/3 as compared with the case where the signal did not pass over the TFT 17.

[Embodiment 2] FIG. 4 is a plan view of an essential part for explaining a planar structure of a pixel portion for explaining a second embodiment of a liquid crystal panel constituting a liquid crystal display device according to the present invention. The same reference numerals as those in FIG. 1 correspond to the same functional parts.

In this embodiment, the reference electrode 12 connected to the reference signal line is composed of three reference electrodes 12A, 12B and 12A formed by connecting one end in one pixel, and a common connection portion in the pixel. Reference electrode 1 is connected to one reference electrode 12B at 12 '.
2A and 12A are connected. Then, the reference electrode 12B was configured to pass over the TFT 17. As a result, in the present embodiment, an increase in the intersection capacitance with the scanning signal line could be prevented.

With this configuration, a capacitive load is not applied to the scanning signal line, and the occurrence of the rounding of the voltage waveform is prevented.

[Embodiment 3] FIG. 5 is a plan view of a principal part for explaining a planar structure of a pixel portion for explaining a third embodiment of a liquid crystal panel constituting a liquid crystal display device according to the present invention, and FIG. −
FIG. 7 is a cross-sectional view of a main part along a line A ′, and FIG. 7 is a cross-sectional view of a main part along a line BB ′ of FIG. The same reference numerals as those in the drawings of the embodiment correspond to the same functional portions.

In this embodiment, three reference electrodes 12A, 1
2B and 12A are connected to one reference signal line 12B at a common connection portion 12 'in one pixel. Then, the reference signal line 12 </ b> B was made to pass over the TFT 17. Further, a common connection portion 12 'for connecting the reference electrode and the reference signal line is provided.
Are formed so as to overlap the pixel electrode 11 of the TFT 17.

According to the structure of this embodiment, the common connection unit 1
Since a storage capacitor can be formed in a region where 2 ′ overlaps the pixel electrode 11 of the TFT 17, display quality can be improved, and the common connection portion 12 ′ is overlapped with the pixel electrode 11 of the TFT 17, whereby The aperture ratio can be improved as compared with the second embodiment.

[Embodiment 4] In this embodiment, the first embodiment to the first embodiment will be described.
In the third embodiment, a reference electrode 12B serving also as a reference signal line crossing the TFT 17 is formed of a transparent conductive film.

Reference electrode (reference signal line) on TFT section 17
12B is formed of a metal material, and the backlight is
When formed on the back surface of A, if the light from the backlight is sufficiently strong, the light from the backlight is reflected on the metal reference electrode, and this wraps around the semiconductor layer of the TFT 17, and leaks from the TFT 17 due to the photoconductive phenomenon. In particular, the off characteristics of the TFT 17 may be degraded.

In this embodiment, the reference electrode (reference signal line) 12B passing over the TFT 17 is formed of a transparent conductive film, thereby preventing the reflection of light from the backlight and the above-described operation characteristics of the TFT 17. Deterioration can be prevented. In addition, as the transparent conductive film, ITO, SnO ₂ , In ₂ O
Any of ₃ can be used.

Next, the operation and control circuit of the in-plane switching mode liquid crystal display device to which the present invention is applied will be described.

FIG. 8 is a cross-sectional view of the vicinity of an electrode of one pixel and a cross-sectional view of a peripheral portion of the substrate in an image display area of a liquid crystal display substrate of a horizontal electric field type. Lower substrate SUB based on liquid crystal layer LC
On the side of 1 (1A in the above embodiment), a thin film transistor (TFT), a storage capacitor Cstg (not shown), an electrode group CT (reference electrode 12 in the above embodiment), and PX (the same pixel electrode 11) are formed. On the substrate SUB2 side, a pattern of a color filter FIL and a pattern of a black matrix BM for shading are formed. The black matrix BM
Can be formed on the lower transparent glass substrate SUB1 side.

On the inner surface (on the liquid crystal LC side) of each of the transparent glass substrates SUB1 and SUB2, alignment films ORI11 and ORI12 for controlling the initial alignment of the liquid crystal are provided. Polarizing plates POL1 and POL2 whose polarization axes are orthogonally arranged (crossed Nicol arrangement) are provided on the outer surfaces of each.

FIG. 9 is a schematic explanatory diagram of a peripheral circuit of a liquid crystal display device according to the present invention. As shown in the figure, the liquid crystal panel constituting the liquid crystal display device is composed of a set of a plurality of pixels in which a display unit is arranged in a matrix, and each pixel transmits light from a backlight disposed on the back of the liquid crystal panel. It is configured so that light can be modulated independently.

On a lower substrate (active matrix substrate) SUB1, which is one of the components of the liquid crystal panel, the active pixel region AR extends in the x direction (row direction) and is arranged in the y direction (column direction). The gate signal line GL (also the video signal line 10) and the counter voltage signal line CL (the reference signal line 12 of the above embodiment) are insulated from each other and extend in the y direction, and the drains are arranged in the x direction. A signal line DL is formed.

Here, a unit pixel is formed in a rectangular area surrounded by each of the gate signal line GL, the counter voltage signal line CL, and the drain signal line DL.

The liquid crystal display substrate is provided with a vertical scanning circuit V and a video signal driving circuit H as external circuits, and the vertical scanning circuit V sequentially supplies a scanning signal (voltage) to each of the gate signal lines GL. From the video signal drive circuit H to the drain signal line DL in accordance with the timing.
Is supplied with a video signal (voltage).

The vertical scanning circuit V and the video signal driving circuit H are supplied with power from the liquid crystal driving power supply circuit 3, and input image information from the CPU 1 after being divided into display data and control signals by the controller 2 respectively. It is supposed to be.

FIG. 10 is a perspective view of a notebook personal computer, which is an example of information equipment on which the liquid crystal display device according to the present invention is mounted. The notebook computer (portable personal computer) includes a keyboard unit (main body unit) and a display unit connected to the keyboard unit by a hinge. The keyboard unit accommodates a keyboard and a signal generation function such as a host (host computer) and a CPU, and the display unit has a liquid crystal panel PNL, around which drive circuit boards PCB1 and PCB2, a control chip TCON and a CPU. A PCB 3 mounted with a connector CT or the like for connecting signals, an inverter power supply board serving as a backlight power supply, and the like are mounted.
This liquid crystal panel PNL has the alignment film described in each of the above embodiments.

Various circuit boards PCB1, PCB2, PCB3, an inverter power supply board, and a backlight are integrated with the liquid crystal panel PNL and mounted as a liquid crystal display module MDL.

[0052]

As described above, according to the present invention,
In particular, it is possible to improve the aperture ratio of pixels without causing deterioration of writing characteristics due to an increase in the crossing capacitance between a scanning signal line and a reference signal line formed on a substrate of a liquid crystal panel constituting a liquid crystal display device of a horizontal electric field type, A bright and high-contrast liquid crystal display device can be provided.

[Brief description of the drawings]

FIG. 1 is a main part plan view for explaining a planar structure of a pixel portion for explaining a first embodiment of a liquid crystal panel constituting a liquid crystal display device according to the present invention.

FIG. 2 is a cross-sectional view of a main part along the line A-A 'in FIG.

FIG. 3 is a cross-sectional view of a main part along line B-B 'in FIG.

FIG. 4 is a main part plan view for explaining a plane structure of a pixel portion for explaining a second embodiment of the liquid crystal panel constituting the liquid crystal display device according to the present invention.

FIG. 5 is a main part plan view for explaining a planar structure of a pixel portion for explaining a third embodiment of the liquid crystal panel constituting the liquid crystal display device according to the present invention.

6 is a cross-sectional view of a main part along line A-A 'in FIG.

FIG. 7 is a cross-sectional view of a main part along the line B-B 'in FIG.

8A and 8B are a cross-sectional view of the vicinity of an electrode of one pixel and a cross-sectional view of a peripheral portion of a substrate in an image display region of a liquid crystal display substrate of a horizontal electric field type.

FIG. 9 is a schematic explanatory diagram of a peripheral circuit of a liquid crystal display device according to the present invention.

FIG. 10 is a perspective view of a notebook personal computer, which is an example of an information device equipped with the liquid crystal display device according to the present invention.

[Explanation of symbols]

REFERENCE SIGNS LIST 10 video signal line 11 pixel electrode 12 (12A, 12B, 12A) reference electrode (also serving as reference signal line) 15 scanning signal line 16 semiconductor layer 17 TFT 30 gate insulating film 40 insulating film 1A substrate.

Claims (5)

[Claims] 1. A switching element for selecting a pixel, a video signal line, a scanning signal line, and a pixel electrode to which a video signal is supplied by the switching element and one of the pair of substrates is parallel to the substrate. A reference electrode for controlling the liquid crystal by forming an electric field having various components, and a reference signal line for applying a reference signal to the reference electrode, while sandwiching a liquid crystal layer in an opposing gap between the pair of substrates. A liquid crystal panel in which a polarizing plate is laminated on each of the outer surfaces of the pair of substrates,
A drive circuit for applying a voltage waveform for pixel selection to the source electrode of the switching element via the wiring, wherein a plurality of the reference electrodes are formed in a direction in which the video signal lines extend. And the reference signal line for supplying a reference signal to the reference electrode is also used as at least one of the reference electrodes, and at least one of the reference electrodes is passed over the switching element via an insulating film to form the image. A liquid crystal display device comprising two pixels adjacent to each other in a direction in which a signal line extends. 2. A switching element for selecting a pixel, a video signal line, a scanning signal line, and a pixel electrode to which a video signal is supplied by the switching element, and one of the pair of substrates being parallel to the substrate. A reference electrode for controlling the liquid crystal by forming an electric field having various components, and a reference signal line for applying a reference signal to the reference electrode, while sandwiching a liquid crystal layer in an opposing gap between the pair of substrates. A liquid crystal panel in which a polarizing plate is laminated on each of the outer surfaces of the pair of substrates,
A drive circuit for applying a voltage waveform for pixel selection to a source electrode of the switching element via the wiring, wherein a plurality of the reference electrodes are formed in a direction in which a video signal line extends. Connecting the reference electrode to one of the reference signal lines for supplying a reference signal to the reference electrode within one pixel, passing the reference signal line over the switching element via an insulating film, A liquid crystal display device, wherein two adjacent pixels are connected in the extending direction of the liquid crystal display. 3. A switching element for selecting a pixel, a video signal line, a scanning signal line, and a pixel electrode to which a video signal is supplied by the switching element and parallel to the substrate on one of the pair of substrates. A reference electrode for controlling the liquid crystal by forming an electric field having various components, and a reference signal line for applying a reference signal to the reference electrode, while sandwiching a liquid crystal layer in an opposing gap between the pair of substrates. A liquid crystal panel in which a polarizing plate is laminated on each of the outer surfaces of the pair of substrates,
A drive circuit for applying a voltage waveform for pixel selection to the source electrode of the switching element via the wiring, wherein a plurality of the reference electrodes are formed in a direction in which the video signal lines extend. In addition, the reference electrode is connected to the reference signal line for supplying a reference signal to the reference electrode within one pixel, and the reference signal line is passed over the switching element via an insulating film to extend the video signal line. By forming a connection wiring portion connecting two pixels adjacent to each other in the existing direction and connecting the reference electrode and the reference signal line to the pixel electrode of the switching element, the connection wiring portion is formed so as to overlap. A liquid crystal display device, wherein a storage capacitor is formed in a region of the connection wiring portion. 4. The liquid crystal display device according to claim 1, wherein said reference electrode is formed of a transparent conductive material. 5. The transparent conductive material is made of ITO, SnO ₂ , I
The liquid crystal display device according to claim 4, characterized in that as either n ₂ O _3.