JPH05188395A - Liquid crystal display element - Google Patents

Abstract

PURPOSE:To lower the probability of disconnection and the shorting between scanning lines and signal lines and to improve a yield by disposing two kinds of different picture elements near the respective intersecting points of the scanning lines and the signal lines and applying display signals discretely to these picture elements. CONSTITUTION:The picture element regions consisting of the picture elements A27 constituted of TFTs (thin-film transistors) A22, TFTs A'23 and picture element capacitors A24 and the picture elements B28 constituted of TFTs B 25 and picture element capacitors B26 are formed at the respective intersecting points of the scanning lines 20 and the signal lines 21. The individual picture element capacitors are constituted of respective display picture element electrodes 50, 59, common electrodes and liquid crystal layers clamped by these electrodes. As a result, the common possession of one piece of the scanning line or signal line with the two picture elements is made possible and, therefore, the number of wirings, such as scanning lines and signal lines, and eventually the intersecting parts of the signal lines and the scanning lines are decreased as compared with the ordinary elements.

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 having a display pixel electrode array using thin film transistors (TFTs) as switch devices.

[0002]

2. Description of the Related Art In recent years, as a display element using a liquid crystal, a large-capacity and high-density active matrix type liquid crystal display element for television display or graphic display has been actively developed and put to practical use. In such a liquid crystal display element,
Semiconductor switches are used as means for driving and controlling each pixel so that high-contrast display without crosstalk can be performed. As the semiconductor switch, a TFT or the like formed on an insulating substrate is used because it can be used for transmissive display and can be easily made large in area.

FIG. 6 shows a schematic sectional structure of such a liquid crystal display element described in, for example, Japanese Patent Application Laid-Open No. 56-162793. On the insulating substrate 1, a TFT 2 and a display pixel electrode 3 made of a transparent conductive film connected to the TFT 2 are arrayed. On the other hand, a counter electrode 5 made of a transparent conductive film is formed on the entire surface of the insulating substrate 4. A liquid crystal 6 is sandwiched between the insulating substrate 1 and the insulating substrate 4, and the periphery thereof is further sealed with a sealing agent 7.

As shown in FIG. 6, the above-mentioned TFT 2 is arranged at each intersection of scanning lines 10 and signal lines 11 formed in a matrix, and the gates of the TFTs 2 are connected to the scanning lines 10 row by row. , The drains of the TFTs 2 are connected to the signal line 11 for each column, and the sources are connected to the display pixel electrodes 3. A pixel capacitance is formed by the display pixel electrode 3, the counter electrode 5 and the liquid crystal 6.

FIG. 8 is a plan view of the intersection of the scanning line 10 and the signal line 11, and FIG. 9 is a sectional view thereof. As shown in the figure, the scanning line 10 and the signal line 11 are connected to the gate insulating film 1.
Insulated by 6.

Next, an example of a method of driving the liquid crystal display element will be described. That is, during the period (selection period) in which the scanning line selection voltage is applied to the gate of the TFT 2, the display pixel electrode 3 is set to the same potential as the video signal potential through the signal line 11, and the gate is not scanned line. The display pixel electrode 3 is kept at this video signal potential during the period (holding period) in which the selection voltage is applied. On the other hand, the counter electrode 5 is set to a predetermined potential, and therefore the display pixel electrode 3 and the counter electrode 5 are
A voltage corresponding to the difference between the video signal potential and the counter electrode potential is applied to the liquid crystal 6 held between the two. By changing the alignment state of the liquid crystal according to this voltage, the light transmittance changes, and an image is displayed. Further, when the liquid crystal is driven by direct current, the life is shortened due to electrolysis and deterioration of liquid crystal molecules, so that alternating current drive is generally used.
As an example, a method is used in which the video signal potential is symmetrically set in the even and odd frames with respect to the counter electrode potential set to a predetermined potential.

[0007]

However, this type of liquid crystal display device has the following problems. Due to dust in the manufacturing process, the scanning line 10 and the signal line 11
When a defective insulating portion such as a pinhole occurs in the gate insulating film 16 at the intersection with the scanning line 10 and the signal line 1,
1 causes a short circuit defect, and appears as a line defect on the display screen. Alternatively, the scanning lines 10 and the signal lines 11 themselves may be broken, which is a major factor of yield reduction in a large-screen / high-definition device having many wirings.

[0008]

SUMMARY OF THE INVENTION In order to solve the above-mentioned problems, the present invention crosses a plurality of signal lines and scanning lines in a matrix form, and a thin film transistor and a display connected to the thin film transistor near these intersections. In a liquid crystal display device having a pixel area in which pixel electrodes are arranged, this pixel area is formed by a plurality of different pixels which are periodically repeated and individual display signals are written to each of these pixels. A liquid crystal display element is used.

More specifically, the pixel area includes a plurality of first areas.
A first thin film transistor which is formed of the display pixel electrode and a plurality of second display pixel electrodes and is connected between the signal line and the first display pixel electrode, and between the signal line and the second display pixel electrode. A second thin film transistor and a third thin film transistor connected in series, the gates of the first thin film transistor and the second thin film transistor are connected to a common scan line, and the gate of the third thin film transistor is connected to a different scan line. A liquid crystal display element is used in which, while being connected, a period in which these two scanning lines are simultaneously selected and a period in which only a common scanning line is selected are periodically repeated.

[0010]

In the liquid crystal display element of the present invention, there are two different
A pixel region is formed using a plurality of pixels to which a signal voltage is written only when one scanning line is selected and a plurality of pixels to which a signal voltage is written when one scanning line is selected from the pixels. Since one scanning line or signal line can be shared by two pixels, the number of wiring lines such as scanning lines and signal lines can be reduced, and the number of intersections between signal lines and scanning lines can be greatly reduced compared to the conventional one. Can be made

[0011]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described in detail below with reference to the drawings.

FIG. 1 is an equivalent circuit diagram showing an embodiment of the present invention. At each intersection of the scanning line 20 and the signal line 21, TF
Pixel A 27 composed of TA 22, TFT A ′ 23 and pixel capacitance A 24, TFT B 25 and pixel capacitance B 26
A pixel region is formed by the pixel B 28 configured by the above. Each pixel capacitance is composed of a display pixel electrode, a common electrode 68, and a liquid crystal layer 70 held between them.

FIG. 2 shows a plan view of each pixel. That is, in the pixel A, the drain electrode 55 of the TFT A 22 is connected to the signal line 21, and the source electrode 58 is connected to the drain electrode 63 of the TFT A ′ 23. The source electrode 60 of the TFT A'23 is the display pixel electrode A 5
It is connected to 0. The gate electrode 56 of the TFTA 22 is connected to the nth row of the scanning line 20, and the gate electrode 62 of the TFTA ′ 23 is connected to the (n−1) th row of the scanning line 20.

On the other hand, in the pixel B 28, the TFT B 2
The drain electrode 54 of No. 5 is connected to the signal line 21, and the source electrode 51 is connected to the display pixel electrode B 59. The gate electrode 53 is connected to the nth row of the scanning line 20.

FIG. 3 shows a sectional view along the line BB 'of FIG. The gate electrode 53 is formed on the insulating substrate 73, and the semiconductor layer 52 is formed on the gate electrode 53 with the gate insulating film 72 interposed therebetween. Further, the semiconductor layer 52 is connected to each of the source electrode 51 and the drain electrode 54 through the ohmic layer 64 to form the TFTB 25. Further, an alignment film 71 is laminated on the entire surface to form an array substrate 74.

On the other hand, a common electrode 68 made of a transparent conductive layer is formed on the entire surface of the insulating substrate 67, and an alignment film 69 is further laminated thereon to form a counter substrate 66. Then, the liquid crystal layer 70 is sandwiched between the array substrate 74 and the counter substrate 66 to form a liquid crystal display device.

Next, the driving method and operating principle of the liquid crystal display element of this embodiment will be described. FIG. 5 shows a partial view of FIG. 1, and FIG. 4 shows a timing chart of a scanning line voltage and a signal line voltage for driving each pixel shown in FIG.

The scanning line 20 has one frame period (Tf).
The scanning line selection voltage (hereinafter, referred to as Vg, on) is applied twice. On the other hand, the signal line 21 has a central voltage (Vsig, c)
On the other hand, a signal line voltage that is inverted every frame is applied. Table 1 below shows the operation of each pixel when such a driving method is used.

[0019]

[Table 1] Note) The broken line indicates the period during which the signal voltage to be applied to other pixels is applied.

From time t _{1 to} t ₂ , Vg, on is applied to the (n-1) th row and the nth row of the scanning line 20, and TFTA
The signal line voltage V1 is written in the pixel capacitance A (n, m) 36 by the simultaneous conduction of the (n, m) 35 and the TFT A '(n, m) 37. In addition, TFTB (n-1, m) 41 and TFTB (n, m) 4
3 becomes conductive, the signal line voltage V1 is similarly applied to each of the pixel capacitance B (n-1, m) 42 and the pixel capacitance B (n, m) 44.
Is written.

From time t2 to t3, Vg, on is applied only to the (n-1) th row of the scanning line 20, and TFTB (n-1, m)
The voltage V ₁ written in the pixel capacitance B (n-1, m) 42 is rewritten to the signal line voltage V ₃ by the conduction of 41. On the other hand, TFTA (n, m) 35 and TFTB (n, m) 43
Becomes non-conductive, and the pixel capacitance A (n, m) 36 and the pixel capacitance B (n, m
m) 44 is held at V ₁ so that pixel A (n, m) 45
Is determined.

At times t3 to t4, Vg, on is applied to the nth row and the (n + 1) th row of the scanning line 20, and TFTA
Since the (n + 1, m) 38 and the TFT A ′ (n + 1, m) 40 are simultaneously conducted, the signal line voltage V _{2 is} applied to the pixel capacitance A (n + 1, m) 39.
Is written. Further, since the TFT B (n, m) 43 becomes conductive, V ₁ held in the pixel capacitance B (n, m) 44
Is rewritten to the signal line voltage V ₂ . On the other hand, TFTB (n-
(1, m) 41 is rendered non-conductive, and the voltage of the pixel capacitor B (n-1, m) 42 is held at V ₃ to determine the transmittance of the pixel B (n-1, m). It

From time t _{4 to} t ₅ , Vg, on is applied only to the nth row of the scanning line 20, and the TFT B (n, m) 43 becomes conductive and is held in the pixel capacitance B (n, m) 44. The V ₂ that has been written is rewritten to V ₄ . On the other hand, the TFT A (n + 1, m) 38 becomes non-conductive, and the voltage of the pixel capacitor A (n + 1, m) 39 is held at V ₃ , so that the pixel A (n + 1, m) ) 46 transmission is determined.

When the nth row of the scanning line 20 becomes the non-selection voltage (Vg, off) at the time t ₅ , the TFT B (n, m) 43 becomes non-conductive and the pixel capacitance B (n, m) 44 becomes V _4. Since the pixel B (n, m) 48 is held at, the transmittance of the pixel B (n, m) 48 is determined.

Thus, the transmittance of each pixel in FIG. 5 is determined. At this time, for example, in the pixel capacitance B (n, m) 44, the voltages V ₁ and V ₂ for determining the transmittance of other pixels are written immediately before the voltage V ₄ for determining the transmittance is written. , The period is so short that it does not adversely affect the original display. This also applies to other pixels.

In the active matrix type liquid crystal display device of this embodiment, a plurality of pixels to which a signal voltage is written only when two different scanning lines are selected and one scanning line among them are selected. Since a pixel region is formed by using a plurality of pixels to which a signal voltage is written in, a single signal line can be shared by two pixels, without significantly changing the process of a conventional liquid crystal display device. The number of signal lines can be reduced to half that of the conventional one.

[0027]

According to the liquid crystal display device of the present invention, a plurality of pixels to which a signal voltage is written only when two different scanning lines are selected, and a signal when one scanning line among them are selected. Since a pixel region is formed by using a plurality of pixels to which voltage is written, one scan line or signal line can be shared by two pixels, so that the number of wirings can be significantly reduced as compared with a conventional one. Therefore, the intersection of the scanning line and the signal line can be greatly reduced.
Therefore, the probability of signal line disconnection or short between signal lines and scanning lines, which is a problem in a large-screen / high-definition device having a large number of wirings, can be reduced, and the yield can be significantly improved.

[Brief description of drawings]

FIG. 1 is an equivalent circuit diagram showing an embodiment of a liquid crystal display element of the present invention.

FIG. 2 is a plan view showing two pixels of the liquid crystal display element of FIG.

3 is a cross-sectional view taken along the line BB ′ of FIG.

FIG. 4 is a timing chart showing driving waveforms of the liquid crystal display element of the present invention.

5 is an equivalent circuit diagram showing a part of the liquid crystal display element of FIG.

FIG. 6 is a cross-sectional view showing a conventional liquid crystal display element.

7 is an equivalent circuit diagram of one pixel of the liquid crystal display element of FIG.

8 is a plan view showing an intersection of a signal line and a scanning line of the liquid crystal display element of FIG.

9 is a cross-sectional view taken along the line AA ′ of FIG.

[Explanation of symbols]

 20 ... Scanning line 21 ... Signal line 22 ... TFTA 23 ... TFTA '24 ... Pixel capacitance A 25 ... TFTB 26 ... Pixel capacitance B 27 ... Pixel A 28 ... Pixel B 50 ... Display pixel electrode A 59 ... Display pixel electrode B

Claims (4)

[Claims] 1. A liquid crystal display device having a pixel area in which a plurality of signal lines and scanning lines are crossed in a matrix and a thin film transistor and a display pixel electrode connected to the thin film transistor are arranged in the vicinity of these crossing points. Is formed by a plurality of different pixels which are periodically repeated and arranged, and an individual display signal is written in each of the pixels. 2. The pixel region is formed of a plurality of first display pixel electrodes and a plurality of second display pixel electrodes, and is connected between the signal line and the first display pixel electrode. 2. The liquid crystal display device according to claim 1, further comprising: the thin film transistor, and a second thin film transistor and a third thin film transistor connected in series between the signal line and the second display pixel electrode. 3. The gates of the first thin film transistor and the second thin film transistor are connected to a common scan line,
The liquid crystal display element according to claim 2, wherein a gate of the third thin film transistor is connected to a scanning line different from the common scanning line. 4. The liquid crystal display element according to claim 3, wherein a period in which the two scanning lines are selected and a period in which only the common scanning line is selected are periodically repeated.