JPH11212059A - Liquid crystal display - Google Patents

Abstract

(57) [Summary] [PROBLEMS] To provide a liquid crystal display device which improves crosstalk, uneven contrast, roughness, and the like, and realizes good display quality. A liquid crystal layer is provided between a pair of substrates, and a plurality of source lines are provided on one of the substrates.
A liquid crystal display device that includes a pixel electrode 5 and supplies a signal from each source line 7 to a corresponding pixel electrode 5 via a mechanical switch to apply a voltage to each pixel. In a liquid crystal display device, a gate electrode 3 and a drain forming the mechanical switch are provided. When a capacitance value Cgd between the electrode 6 and ΔV ^MIN is a voltage difference applied to a liquid crystal layer at which a luminance difference is recognized on a display screen, ΔVg is an amplitude value voltage of a gate signal pulse, and Cpix is a pixel capacitance value, Cgd <(ΔV ^MIN / ΔVg) × Cpi
Design to satisfy the relationship of x.

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 an active matrix type liquid crystal display device suitably used for a television set, a personal computer, a word processor, and other OA equipment.

[0002]

2. Description of the Related Art An a-Si TFT active matrix type liquid crystal display device has become widespread as a thin, lightweight and low power consumption display. However, a-Si TFT is
There is a problem that the mobility of a-Si is low and the leak current at the time of off is large. For this reason, as the size of the screen increases and the definition increases, a voltage cannot be sufficiently applied to each pixel, crosstalk, unevenness and reduction in contrast occur, and the display quality deteriorates. Therefore, in order to solve this problem, a liquid crystal display device having a configuration using a mechanical switch as a switching element of each pixel has been proposed in JP-A-58-18675 and JP-A-9-92909. I have.

A configuration example of such a conventional mechanical switch will be described with reference to FIG. 6 showing a plan view of an active matrix substrate and FIG. 7 showing a cross-sectional view taken along line BB in FIG.

On the active matrix substrate 51, an insulating film 54 is formed on a gate electrode 53 branched from a gate line 52. A drain electrode 56 extended from the pixel electrode 55 is connected to a gate electrode 53 with an insulating film 54 interposed therebetween.
Is formed on. Further, a source electrode 58 extending from the source line 57 with a hollow portion provided thereon is formed.

On the other hand, the common electrode 60
Are formed, a liquid crystal is sealed between the active matrix substrate 51 and the counter substrate 59, and a liquid crystal layer 61 is formed.

FIG. 8 shows an equivalent circuit of each pixel.
As shown in the figure, in the mechanical switch 62 shown in the dotted circle, the gate electrode 53 and the drain electrode 56
Are formed, and a capacitance Csd64 between the source electrode 58 and the drain electrode 56 is formed. The liquid crystal capacitance Clc65 is configured as a pixel capacitance Cpix.

In the mechanical switch 62 having the above structure, when a potential difference is applied between the gate electrode 53 and the source electrode 58, an electrostatic attraction acts between the two electrodes. The electrode 58 is the gate electrode 53
Side and comes into contact with the drain electrode 56, and the switch is turned on.

[0008] Again, the potential difference is equal to or less than the on-voltage Von, and in some cases, hysteresis occurs, and the source electrode 58 is separated from the drain electrode 56 at a value lower than the on-voltage Von, and the switch is turned off.

As described above, since the on / off of the switch resistance is determined by the contact / non-contact of the electrodes, the resistance at the time of on is sufficiently small, and the switch operates as an ideal resistance switch having no leakage current at the time of off. .

[0010]

However, since the mechanical switch is a minute operation switch utilizing electrostatic attraction,
As described above, the capacitance is formed between the gate electrode, the source electrode, and the drain electrode. Therefore, when the above-described conventional switch is used for driving the liquid crystal, even when the switch is off, a change in the gate signal or the source signal has a considerable effect on the drain potential, and the voltage written to each pixel fluctuates. The problem arises.

As a result, when a full screen is displayed by a conventional liquid crystal display device using switches, unevenness and roughness are noticeable in the screen, and good display quality cannot be obtained.

Also, when a so-called window pattern is displayed, band-like crosstalk occurs above and below the window pattern.

That is, when the drain potential fluctuates due to a gate signal or a source signal when the switch is turned off, a deterioration in display quality such as a crosstalk phenomenon, uneven contrast, roughness, etc. is caused, and a switch having an excellent on / off ratio as a resistance switch is provided. Although the performance can be obtained, the capacitance between the electrodes newly causes display deterioration, and the expected effect of improving the display quality of the liquid crystal display device cannot be obtained.

The present invention has been made in view of the above problems, and has as its object to provide a liquid crystal display device which improves crosstalk, unevenness of contrast, roughness, etc., and realizes good display quality. It is in.

[0015]

According to a first aspect of the present invention, there is provided a liquid crystal display device including a liquid crystal layer between a pair of substrates, wherein a plurality of substrates are provided on one of the pair of substrates. A gate line and a source line are arranged so as to intersect with each other, a pixel electrode is provided in each region surrounded by the gate line and the source line, and a pixel electrode is provided from each source line to a corresponding pixel electrode via a mechanical switch. In a liquid crystal display device that supplies a signal and applies a voltage to each pixel, a capacitance value Cgd between a gate electrode and a drain electrode that forms the mechanical switch is ΔV ^MIN, and a liquid crystal in which a luminance difference is recognized on a display screen. a layer applied voltage difference, and amplitude voltage of the gate signal pulse [Delta] Vg, when the pixel capacitance value Cpix, satisfy the relation of ^{Cgd <(ΔV MIN / ΔVg)} × Cpix And

According to the above configuration, when the mechanical switch is turned off, a change in the drain potential caused by a change in the gate signal hardly affects the display quality, and unevenness and roughness can be prevented.

As described above, when a full screen is displayed on a liquid crystal display device using a conventional switch, unevenness and roughness are conspicuous in the screen, and good display quality cannot be obtained. As a result of analyzing this phenomenon, it was found that the cause was a capacitance formed between the gate electrode and the drain electrode. Such a conventional mechanism of generating unevenness and roughness will be described below with reference to FIG.

At the start of writing T1, a pulse of a gate signal is input, the potential difference between the gate signal and the source signal exceeds the threshold value Von of the switch, and the switch is turned on. This allows the drain electrode to conduct to the source electrode,
A source signal is written to the drain potential.

At the end of writing T2, the pulse of the gate signal falls, and when the potential difference between the gate signal and the source signal becomes equal to or less than the switch off voltage Voff, the switch is turned off.

However, since a capacitance is formed between the gate electrode and the drain electrode, the drain potential varies with a change in the gate signal when the switch is turned off.
The variation amount ΔVd1 of the drain potential at this time follows the following equation.

ΔVd1 = ΔVg × Cgd / Cpix ΔVg: Amount of change in gate signal Cgd: Capacitance between gate electrode and drain electrode Cpix: Pixel capacitance As long as all switches have the same Voff, there is no contrast unevenness. Vo in the switch
It is very difficult to prevent variations in the ff voltage. As a result, the variation amount ΔVd1 of the drain potential varies in the plane, causing unevenness, roughness, and the like.

On the other hand, in the configuration of the present invention, as described above,
When the capacitance value Cgd between the gate electrode and the drain electrode is C
gd <(ΔV ^MIN / ΔVg) × Cpix, so that the fluctuation of the drain potential due to the change of the gate signal is suppressed, and the unevenness due to the capacitance between the gate electrode and the drain electrode is suppressed. Roughness can be prevented.
Therefore, it is possible to provide an active matrix type liquid crystal display device which is excellent in display quality and is suitable for enlargement of screen size and high definition.

According to another aspect of the present invention, a liquid crystal display device includes a liquid crystal layer between a pair of substrates, and a plurality of gate lines and source lines on one of the pair of substrates. Are arranged so as to intersect with each other, a pixel electrode is provided in each region surrounded by the gate line and the source line, and a signal is supplied from each source line to a corresponding pixel electrode via a mechanical switch. In a liquid crystal display device that applies a voltage to a pixel, a capacitance value Csd between a source electrode and a drain electrode forming the mechanical switch is represented by ΔV ^MIN and a liquid crystal layer applied voltage difference at which a luminance difference is recognized on a display screen, Assuming that ΔV ^{B / W} is a voltage difference applied to the liquid crystal layer for obtaining a white display and a black display, and Cpix is a pixel capacitance value, a relationship of Csd <(ΔV ^MIN / ΔV ^{B / W} ) × Cpix is satisfied. doing.

According to the above configuration, when the mechanical switch is turned off, the fluctuation of the drain potential caused by the change of the source signal hardly affects the display quality, and the crosstalk can be prevented.

As described above, when a so-called window pattern is displayed on a liquid crystal display device using a conventional switch, band-like crosstalk occurs above and below the window pattern. As a result of analyzing this phenomenon, it was found that the cause was a capacitance formed between the source electrode and the drain electrode. Such a conventional crosstalk generation mechanism will be described below with reference to FIG.

As a result of the formation of the capacitance between the source electrode and the drain electrode, the drain potential changes with the change of the source signal when the switch is turned off. At this time, the fluctuation amount ΔVd2 of the drain potential follows the following equation.

ΔVd2 = ΔVs × Csd / Cpix ΔVs: Source signal change amount Csd: Source electrode-drain electrode capacitance Cpix: Pixel capacitance Therefore, when a window pattern is displayed, the change in the source signal after writing is in-plane. In contrast, a crosstalk phenomenon occurs.

On the other hand, in the configuration of the present invention, as described above,
The capacitance value Csd between the source electrode and the drain electrode is C
Since it is set so as to satisfy the relationship of sd <(ΔV ^MIN / ΔV ^{B / W} ) × Cpix, the fluctuation of the drain potential due to the change of the source signal is suppressed, and the capacitance between the source electrode and the drain electrode is reduced. The resulting crosstalk can be prevented.
Therefore, it is possible to provide an active matrix type liquid crystal display device which is excellent in display quality and is suitable for enlargement of screen size and high definition.

According to a third aspect of the present invention, there is provided a liquid crystal display device according to the first or second aspect, wherein the difference in the luminance ratio in the liquid crystal layer applied voltage difference ΔV ^MIN is smaller than 5%. It is characterized by:

According to the above configuration, the value of the voltage difference ΔV ^MIN applied to the liquid crystal layer is set so that the difference in luminance ratio is smaller than 5% even if the drain potential fluctuates. Is almost unrecognized.

According to a fourth aspect of the present invention, there is provided a liquid crystal display device according to any one of the first to third aspects, wherein the pixel capacitance is opposed to the pixel electrode and the pixel electrode. The liquid crystal capacitance between the common electrode and the pixel electrode and an additional capacitance between the pixel electrode and an additional capacitance line disposed on the same substrate are arranged in parallel.

According to the above configuration, the pixel capacitance can be set to an arbitrary value equal to or larger than the liquid crystal capacitance, and the fluctuation of the drain potential can be easily suppressed.

[0033]

DESCRIPTION OF THE PREFERRED EMBODIMENTS One embodiment of the present invention will be described below with reference to FIGS.

FIG. 3 is a plan view showing a schematic configuration of an active matrix substrate 1 which is one substrate of the liquid crystal display device according to one embodiment of the present invention. FIG. 4 is a cross-sectional view taken along line AA in FIG. 3, and also shows the counter substrate 11 and the liquid crystal layer 13. That is, the present liquid crystal display device has a panel in which liquid crystal is sealed between an active matrix substrate 1 and a counter substrate 11, which are a pair of insulating substrates, and a liquid crystal layer 13 is formed.

On the active matrix substrate 1, a plurality of gate lines 2 and source lines 7 are arranged so as to cross each other. Further, a pixel electrode 5 is formed in each region surrounded by the gate line 2 and the source line 7, and a plurality of pixel electrodes 5 are provided in a matrix on the entire substrate.

Each pixel electrode 5 is connected to a corresponding source line 7 via a mechanical switch 14 (see FIG. 5).
A signal corresponding to the display is supplied. On the other hand, an appropriate potential is applied to the common electrode 12 provided on the counter substrate 11.
Thereby, an appropriate voltage is applied to each pixel to control the orientation of the liquid crystal molecules in the liquid crystal layer 13 of each pixel, and light is modulated by incident light such as transmitted light to perform display.

The structure of the active matrix substrate 1 provided in the present liquid crystal display device will be described in more detail. On the active matrix substrate 1, an insulating film 4 is provided on a gate electrode 3 branched from a gate line 2.
The drain electrode 6 extended from the pixel electrode 5 is formed at a distance of about 5 μm from the gate electrode 3, that is, the distance α between the gate electrode 3 and the drain electrode 6.
Is about 5 μm.

Further, the source electrode 8 extending from the source line 7 is formed from above the gate electrode 3 to above the drain electrode 6 via a hollow layer. The overlap β between the source electrode 8 and the drain electrode 6 is set to 5 μm. The width γ of the source electrode 8 is set to 5 μm.

The insulating film 4 is made of Al ₂ O ₃ having a thickness of 0.3 μm.
And the area of the pixel electrode 5 is about 40000 μm ² .

On the active matrix substrate 1, a plurality of additional capacitance lines 9 are provided. The additional capacitance line 9 is formed in parallel with the gate line 2, and forms an additional capacitance 10 at an overlapping portion between the additional capacitance line 9 and the pixel electrode 5.

On the other hand, a common electrode 12 is formed on the entire surface of the opposing substrate 11, and a liquid crystal layer 13 is provided between the substrates 1 and 11. The thickness of the liquid crystal layer 13 is approximately 5 μm.

FIG. 5 shows an equivalent circuit of each pixel.
As shown in the figure, in the mechanical switch 14 shown in the dotted circle, a capacitance Csd15 is formed between the source electrode 8 and the drain electrode 6. Further, a pixel capacitance Cpix18 is configured by paralleling the liquid crystal capacitance Clc16 and the additional capacitance Ccs17.

Next, in manufacturing the liquid crystal display device of the present embodiment, the applied voltage difference ΔV ^{B / W of the} liquid crystal layer for obtaining white display and black display and the applied voltage of the liquid crystal layer for which a luminance difference is recognized on the display screen. A procedure for ^{obtaining the} difference ΔV ^MIN will be described.

The liquid crystal display device of this embodiment is a transmission type TN
Mode is adopted. FIG. 1 is a graph showing the relationship between the voltage applied to the liquid crystal layer 13, that is, the applied voltage V applied between the pixel electrode 5 and the common electrode 12 and the transmittance T. The applied voltage V was measured by applying a voltage directly between the pixel electrode 5 and the common electrode 12, and was actually measured.
3 represents a voltage applied to the reference numeral 3.

From the characteristics shown in the graph of FIG. 1, it is confirmed that the applied voltage V at which the transmittance T changes is 2 to 5 V. That is, it can be seen that the voltage difference ΔV ^{B / W} applied to the liquid crystal layer for obtaining white display and black display is 3V.

Next, regions having different luminances were displayed on the screen, and the boundaries were visually observed. Then, the difference in luminance at which the difference in luminance can be recognized was examined. Table 1 shows the results. As shown in Table 1, it was found that when the difference in luminance ratio exceeded 2%, the difference in luminance was slightly recognized, and when the difference was 5% or more, the difference was surely recognized.

[0047]

[Table 1]

Here, the difference in the luminance ratio is defined as the difference between the two luminances.
Is the relative ratio difference between the luminances of the two regions, and the luminance ratio difference =
| Luminance difference / Average luminance |. The average brightness is an average value of the brightness of the two regions.

In a transmission type liquid crystal display device, luminance corresponds to transmittance.

Next, from the data in FIG. 1, (ΔT / T) / ΔV was calculated from the transmittance T and the minute transmittance difference ΔT / small voltage change ΔV indicated by the slope for each applied voltage V.

Further, .DELTA.T / T corresponding to the difference in luminance ratio was set to 5%, and .DELTA.V was back calculated to obtain the value of the small voltage change .DELTA.V at which the difference in luminance ratio with respect to each applied voltage V was 5%. The result is shown in FIG.

As described above, the minute voltage change amount ΔV changes with the applied voltage V, and the minimum value thereof is defined as the liquid crystal layer applied voltage difference ΔV ^MIN at which the luminance difference is recognized on the display screen. The minimum value of the small voltage change amount ΔV is set to ΔV ^MIN in order to effectively prevent the influence on the display. In the present embodiment, ΔV ^MIN = 0.025 V.

As described above, the voltage difference ΔV ^{B / W} applied to the liquid crystal layer at which white display and black display can be obtained and the voltage difference ΔV ^MIN applied to the liquid crystal layer at which the luminance difference is recognized on the display screen can be obtained. it can.

The amplitude value voltage ΔV of the gate signal pulse
g can be set according to the characteristics of the mechanical switch.
The ON voltage Von of the mechanical switch 14 of the present embodiment
Was 15 V, the gate signal had the same polarity as the source signal, and the amplitude value voltage ΔVg of the gate signal pulse was 20 V.
V is set. The source signal is 2 to 3 depending on the video signal.
The AC driving is performed by inverting the polarity for each field with an amplitude of 5V.

Therefore, each of the above values is a value unique to the liquid crystal display device determined from the relationship between the voltage applied to the liquid crystal layer and the transmittance and the characteristics of the mechanical switch.

Further, the voltage difference ΔV ^{B / W} applied to the liquid crystal layer for obtaining a white display and a black display obtained in the above-described process, the voltage difference ΔV ^MIN applied to the liquid crystal layer for recognizing the luminance difference on the display screen, and the gate The capacitance Cgd between the gate electrode 3 and the drain electrode 6, the capacitance Csd between the source electrode 8 and the drain electrode 6, and the pixel capacitance Cpix were designed from the amplitude value voltage ΔVg of the signal pulse. Here, the pixel capacitance Cpix
Is a value obtained by adding the additional capacitance Ccs to the liquid crystal capacitance Clc.

Hereinafter, the setting of each capacitance value will be described.

First, regarding the capacitance Cgd, Cgd <
It was designed to satisfy the relationship of (ΔV ^MIN / ΔVg) × Cpix. In the present embodiment, since a gap of 5 μm is provided between the gate electrode 3 and the drain electrode 6 to eliminate the overlap between the two electrodes 3 and 6, the capacitance Cgd between the gate electrode 3 and the drain electrode 6 is The value is set to a value that can be ignored and the value of the capacitance Cgd is Cgd <(ΔV ^MIN / ΔV
g) × Cpix is satisfied.

Here, regarding the value of the capacitance Cgd, Cgd
The reason for designing to satisfy the relationship of <(ΔV ^MIN / ΔVg) × Cpix is as follows.

As already described with reference to FIG. 9, the variation ΔVd1 of the drain potential due to the change of the gate signal follows the following equation.

ΔVd1 = ΔVg × Cgd / Cpix From this, Cgd = (ΔVd1 / ΔVg) × Cpix.

On the other hand, as described above, since the minimum value of the small voltage change amount ΔV at which the luminance difference is recognized on the display screen is set to the liquid crystal layer applied voltage difference ΔV ^MIN , the value of the capacitance Cgd is Cgd <( If it is designed to satisfy the relationship of ΔV ^MIN / ΔVg) × Cpix, the variation ΔVd of the drain potential
1 satisfies ΔVd1 <ΔV ^MIN , and the influence on display can be almost eliminated.

Next, regarding the capacitance Csd, Csd <
It was designed to satisfy the relationship of (ΔV ^MIN / ΔV ^{B / W} ) × Cpix. The reason is as follows.

As already described with reference to FIG. 9, the variation ΔVd2 of the drain potential due to the change of the source signal follows the following equation.

ΔVd2 = ΔVs × Csd / Cpix From this, Csd = (ΔVd2 / ΔVs) × Cpix.

On the other hand, as described above, since the minimum value of the small voltage change amount ΔV at which the luminance difference is recognized on the display screen is defined as the liquid crystal layer applied voltage difference ΔV ^MIN , the value of the capacitance Csd is Csd <( If it is designed so as to satisfy the relationship of ΔV ^MIN / ΔVs) × Cpix, the variation amount ΔVd of the drain potential
2 is ΔVd2 <ΔV ^MIN . Further, as described above, ΔVs in actual driving can be obtained from the voltage difference ΔV ^{B / W} applied to the liquid crystal layer for obtaining white display and black display, so that Csd <(Δ
If the design is made to satisfy the relationship of (V ^MIN / ΔV ^{B / W} ) × Cpix, the influence on the display can be almost eliminated.

In this embodiment, the overlap between the source electrode 8 and the drain electrode 6 is designed to minimize the area thereof, and the capacitance Csd between the source electrode 8 and the drain electrode 6 is given by: Csd = ε ₀ × 8 (ε: LC) × 25 μm ² (area) ÷ 0.3 μm (thickness) = 0.0059 pF

On the other hand, the liquid crystal capacitance Clc is set as follows: Clc = ε ₀ × 8 (ε: LC) × 40000 μm ² (area) ÷ 5 μm (thickness) = 0.566 pF. Also, as described above, ΔV ^MIN =
0.025V, ΔV ^{B / W} = 3V. Putting these values into the following ^{equation, Csd <(ΔV MIN / ΔV} B / W) × Cpix 0.0059pF <(0.025V / 3V) × Cpix ^{Therefore, Csd <(ΔV MIN / ΔV} B / W) × In order to satisfy the relationship of Cpix, it is necessary to satisfy Cpix> 0.708 pF. Therefore, in the present embodiment, the additional capacitance Cc
Let the value of s be Ccs + Clc = Cpix> 0.708 pF
Therefore, it was set so that Ccs> 0.142 pF.

The additional capacitor 10 (see FIG. 3) uses a film similar to the insulating film 4 on the gate electrode 3 as a dielectric layer, and its area is set to 500 μm ² . As described above, the size of the additional capacitance 10 is set according to the liquid crystal capacitance.

In the present embodiment, a driving method as shown in FIG. 9 in which the polarity of a source signal is inverted for each field is employed. However, the present invention is applicable to any other driving method such as inverting the polarity every line writing. Applicable to the method.

Next, a method for manufacturing the liquid crystal display device of the present embodiment will be described. First, for the active matrix substrate 1, Al is formed on a glass substrate and then patterned to form gate lines 2 and gate electrodes 3. Thereafter, anodizing is performed to form an insulating film 4 of Al ₂ O ₃ . Next, a pixel electrode 5 and a drain electrode 6 are formed by patterning after forming an ITO film.

Further, a sacrificial layer (not shown) is formed, and a portion corresponding to the hollow layer is left by patterning. Next, A
1 and SiO ₂ are laminated, and the source line 7 and the source electrode 8 are formed by patterning. Thereafter, the hollow layer was formed by etching the sacrificial layer by isotropic plasma etching, and the active matrix substrate 1 was manufactured.

As for the counter substrate 11, a light-shielding film (not shown) provided with an opening corresponding to the pixel electrode 5 and a color filter (not shown) are formed on a glass substrate which is an insulating substrate. The common electrode 12 was formed on the entire upper surface.

After forming an alignment film (not shown) on both of the substrates 1 and 11, the substrates 1 and 11 were bonded to each other, and liquid crystal was injected and sealed between them to produce a liquid crystal display device.

It is to be noted that Ti, Mo, Ta, W, Cu and the like can be applied to the material of the wiring / electrode such as the gate line 2 and the source line 7, and the structure and manufacturing method such as the material of the insulating film 4. Is not limited to the embodiment.

The display quality was confirmed by driving the liquid crystal display device of the present embodiment. As a result, it was confirmed that there was no unevenness, roughness, or crosstalk, and excellent display quality was obtained.

Incidentally, the liquid crystal display device of the present invention is not limited to the configuration of the liquid crystal display device of the present embodiment described above. For example, in the present embodiment, the mechanical switch 14 is used.
In the above configuration, the liquid crystal exists in the hollow layer, but another configuration such as providing a cover hood on the mechanical switch 14 may be adopted.

[0078]

As described above, in the liquid crystal display device according to the first aspect of the present invention, the capacitance value Cgd between the gate electrode and the drain electrode forming the mechanical switch is ΔV ^MIN and the luminance difference on the display screen is The difference between the applied voltage of the liquid crystal layer and the Δ
Assuming that Vg is the amplitude value voltage of the gate signal pulse and Cpix is the pixel capacitance value, Cgd <(ΔV ^MIN / ΔVg) ×
This is a configuration that satisfies the relationship of Cpix.

Thus, since the mechanical switch is used as the switching element of each pixel, the switch is turned on / off by contact / non-contact of the conductor, and the on resistance is sufficiently low and the off resistance is sufficiently high. Furthermore, since the amount of change in the drain potential caused by the change in the gate signal is limited through the capacitance between the gate electrode and the drain electrode, and the influence on the display characteristics is prevented, the occurrence of unevenness and roughness is suppressed. Can be

Therefore, there is an effect that it is possible to provide a liquid crystal display device which is excellent in display quality and suitable for enlargement of the screen size and high definition.

In the liquid crystal display device according to the second aspect of the present invention, as described above, the capacitance value Csd between the source electrode and the drain electrode forming the mechanical switch is ΔV ^MIN and the luminance difference is recognized on the display screen. ΔV
Assuming that ^{B / W} is a voltage difference applied to the liquid crystal layer for obtaining a white display and a black display, and Cpix is a pixel capacitance value, Csd <(ΔV
^MIN / ΔV ^{B / W} ) × Cpix.

Thus, since the mechanical switch is used as the switching element of each pixel, the switch is turned on / off by contact / non-contact of the conductor, and the on resistance is sufficiently low and the off resistance is sufficiently high. Further, the amount of change in the drain potential caused by the change in the source signal is limited through the capacitance between the source electrode and the drain electrode, and the change in the drain potential is prevented from being affected, so that the occurrence of crosstalk or the like is suppressed. .

Therefore, there is an effect that it is possible to provide a liquid crystal display device which is excellent in display quality and suitable for enlargement of the screen size and high definition.

According to a third aspect of the present invention, as described above, in the configuration of the first or second aspect, the luminance ratio difference in the liquid crystal layer applied voltage difference ΔV ^MIN is smaller than 5%.

Therefore, even if the drain potential fluctuates, there is an effect that the luminance difference is hardly recognized on the display screen.

As described above, the liquid crystal display device of the invention according to claim 4 has the structure according to any one of claims 1 to 3,
The pixel capacitance is a liquid crystal capacitance between the pixel electrode and a common electrode facing the pixel electrode, and an additional capacitance between the pixel electrode and an additional capacitance line disposed on the same substrate as the pixel electrode. Are configured in parallel.

Therefore, it is possible to set the pixel capacitance to an arbitrary value equal to or larger than the liquid crystal capacitance, and it is possible to easily suppress the fluctuation of the drain potential.

[Brief description of the drawings]

FIG. 1 is a graph showing a relationship between an applied voltage and a transmittance of a liquid crystal display device according to an embodiment of the present invention.

FIG. 2 is a graph showing a relationship between an applied voltage and a minute voltage change amount at which a transmittance ratio difference of the liquid crystal display device is 5%.

FIG. 3 is a plan view showing an active matrix substrate which is one substrate of the liquid crystal display device.

FIG. 4 is a cross-sectional view taken along line AA in FIG.

FIG. 5 is an equivalent circuit diagram of each pixel in the liquid crystal display device.

FIG. 6 is a plan view showing an active matrix substrate provided in a conventional liquid crystal display device.

FIG. 7 is a sectional view taken along line BB in FIG. 6;

FIG. 8 is an equivalent circuit diagram of each pixel in a conventional liquid crystal display device.

FIG. 9 is a timing chart showing driving waveforms, and is a diagram for explaining that a change in a gate signal or a source signal changes a drain potential.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 * 11 Substrate (a pair of substrates) 2 Gate line 3 Gate electrode 4 Insulating film 5 Pixel electrode 6 Drain electrode 7 Source line 8 Source electrode 9 Additional capacitance line 10 Additional capacitance 12 Common electrode 13 Liquid crystal layer 14 Mechanical switch

Claims (4)

[Claims] 1. A liquid crystal layer is provided between a pair of substrates, and a plurality of gate lines and source lines are disposed on one of the pair of substrates so as to intersect with each other, and are surrounded by the gate lines and the source lines. A pixel electrode is provided in each of the formed regions, a signal is supplied from each source line to a corresponding pixel electrode via a mechanical switch, and a voltage is applied to each pixel.In a liquid crystal display device, a gate electrode forming the mechanical switch is provided. When a capacitance value Cgd between the drain electrode and ΔV ^MIN is a voltage difference applied to a liquid crystal layer at which a luminance difference is recognized on a display screen, ΔVg is an amplitude value voltage of a gate signal pulse, and Cpix is a pixel capacitance value, Cgd <(ΔV ^MIN / ΔVg) × Cpi
A liquid crystal display device satisfying a relationship of x. 2. A liquid crystal layer is provided between a pair of substrates, and a plurality of gate lines and source lines are arranged on one of the pair of substrates so as to intersect with each other, and are surrounded by the gate lines and the source lines. A pixel electrode is provided in each of the regions, and a signal is supplied from each source line to a corresponding pixel electrode via a mechanical switch, and a voltage is applied to each pixel. In the liquid crystal display device, a source electrode forming the mechanical switch is provided. capacitance Csd between the drain electrode, and a liquid crystal layer applied voltage difference luminance difference can be recognized on the display screen ΔV ^MIN, ΔV B ^{/ W}
Is the voltage difference applied to the liquid crystal layer at which a white display and a black display are obtained.
If pix is a pixel capacitance value, Csd <(ΔV ^MIN / Δ
V ^{B / W} ) × Cpix. 3. The liquid crystal display device according to claim 1, wherein a difference in luminance ratio at the voltage difference ΔV ^MIN applied to the liquid crystal layer is smaller than 5%. 4. The liquid crystal display device according to claim 1, wherein the pixel capacitance is a liquid crystal capacitance between the pixel electrode and a common electrode facing the pixel electrode, and an additional capacitance line disposed on the same substrate as the pixel electrode and the pixel electrode. The liquid crystal display device according to any one of claims 1 to 3, wherein the additional capacitors are arranged in parallel.