JP2845487B2 - Active matrix type liquid crystal display - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Object of the Invention] (Industrial Application Field) The present invention relates to an active matrix type liquid crystal display device using, for example, a thin film transistor (TFT) as an active device.

2. Description of the Related Art In a display device using a liquid crystal, a large-capacity, high-density active matrix type liquid crystal display element for television display, graphic display and the like is actively developed and put into practical use. In such a display device, a semiconductor switch is used as a means for driving and controlling each pixel so that high-contrast display without crosstalk can be performed. As the semiconductor switch, a TFT formed on a transparent insulating substrate is usually used because a transmissive display is possible and the area can be easily increased.

The driving method of this type of liquid crystal display element is as follows.
That is, during a period (switching period) in which the scanning line selection voltage (Vg, on) is applied to the TFT gate, the potential of the display pixel electrode is set to the same potential as the video signal potential, and the scanning line non-scanning is applied to the TFT gate. While the selection voltage (Vg, off) is being applied, the display pixel electrode holds this potential. As a result, a potential difference according to the video signal voltage is applied to the liquid crystal layer sandwiched between the display pixel electrode and the counter electrode set to a predetermined potential. When the arrangement state of the liquid crystal layer changes in accordance with the potential difference, the light transmittance of this portion also changes, and an image is displayed. When the liquid crystal layer is driven by a direct current, the liquid crystal layer is degraded due to electrolysis of liquid crystal molecules and the life is shortened. Generally, the AC drive is performed by setting the potential of the counter electrode to a DC potential and setting the video signal voltage to be symmetrical between the potential of the counter-electrification in the even and odd frames. That is, the video signal voltage is obtained by adding a certain DC voltage (Vsc) and a positive / negative symmetric AC voltage (Vsa) corresponding to the video signal.

Here, generally, a parasitic capacitance (Cgs) exists between the gate and the source of the TFT. Because of this Cgs, the scanning signal voltage is V
When switching from g, on to Vg, off, the capacitance is shifted to the negative side by ΔVp of the display pixel electrode due to capacitance division. This shift amount has a relationship of ΔVp to ΔVg * Cgs / (Cgs + C1c).
Here, ΔVg = Vg, on−Vg, off, and C1c represents the capacity of the liquid crystal layer. Therefore, the voltage applied to the liquid crystal layer is made equal in the even-odd frame by shifting the electric field of the counter electrode to the negative side by ΔVp.

However, since C1c shows a change in capacitance with respect to the applied voltage, the value of ΔVp differs for each video signal. That is, the optimum counter electrode potential differs for each video signal. Generally, the counter electrode potential is set to the same potential for all pixels at the same time. Therefore, in a display screen to which various video signal voltages are applied, the optimum counter electrode potential cannot be set for all pixels at the same time. . As a result, flicker, which is a flicker of the display screen, occurs.

Therefore, in this type of liquid crystal display device, for example,
As described in Japanese Patent Application Laid-Open No. 162793, the storage capacitance (Cs) having no capacitance change with respect to the applied voltage is set to Clc
In some cases, it is attempted to reduce the dependence of ΔVp on the video signal voltage by newly inserting the video signal in parallel with.

4 (a) and 4 (b) are a cross-sectional view and a plan view, respectively, of one pixel in a conventional TFT array substrate. FIG. 4 (a) is a view of the CC ′ plane of FIG. It corresponds to the cross section at the time. As shown in the figure, a TFT 1 is formed on a glass substrate 2 and connected to a gate electrode 4 and a gate insulating film 5 integrated with a scanning line 3, a drain electrode 7 integrated with a signal line 6, and a display pixel electrode 8. It comprises a source electrode 9 and a semiconductor film 10. In a direction substantially parallel to the scanning line 3, an auxiliary capacitance forming wiring 11 is formed so as to partially face the display pixel electrode 8 with the gate insulating film 5 interposed therebetween, and the display pixel electrode 8 is An impermissible storage capacitance (Cs) is obtained at the overlapping portion of the capacitance forming wiring 11.

(Problems to be Solved by the Invention) However, as shown in FIG.
When the CS is formed between the display pixel electrode 8 and the auxiliary capacitance forming wiring 11 due to dust in the manufacturing process, a large number of point defects occur in the image. I was

Accordingly, the present invention has been made in view of such circumstances, and an object of the present invention is to provide an active matrix type liquid crystal display element in which point defects caused by a short circuit between a pixel electrode and a capacitance forming wiring are reduced. .

[Constitution of the Invention] (Means for Solving the Problems) According to the present invention, a thin film transistor including a gate electrode, a gate insulating film, a semiconductor film, a source electrode and a drain electrode on a first insulating substrate is integrated with the gate electrode. And an array substrate in which pixel electrodes are connected to the source electrodes of the thin film transistors, and a common electrode is formed on the second insulating substrate. An active matrix type liquid crystal display device comprising a liquid crystal sandwiched between an opposing substrate formed thereon, and a liquid crystal display element having a shape along an outer peripheral portion of a pixel electrode on an array substrate, and a pixel electrode, a gate insulating film, and a semiconductor film. A capacitance forming electrode is provided to face the electrode.

(Operation) In the present invention, since the semiconductor film is interposed between the capacitance forming electrode and the pixel electrode in addition to the gate insulating film, the capacitance forming electrode is compared with the case where only the gate insulating film is present. The short circuit between the pixel electrode and the pixel electrode is reduced. In addition, by devising the shape of the semiconductor film or the source electrode, the non-conduction due to disconnection of the step between the portion where Cs is formed and the portion where the Cs is not formed between the pixel electrode and the capacitor forming electrode is achieved without significantly reducing the aperture ratio. Can be prevented.

Hereinafter, the present invention will be described in detail with reference to the drawings.

FIG. 1 is a sectional view of one pixel in one embodiment of the present invention. In the figure, on one main surface of an insulating substrate 20 made of, for example, glass, for example, a Cr (chromium) film, which is a light-shielding material, is coated by a sputtering method, and then photo-etched into a predetermined shape to form a gate electrode 21. And a capacitor forming electrode 22 are simultaneously formed, and a gate insulating film 23 made of, for example, silicon oxide (SiOx) is formed by a plasma CVD method so as to cover this. Then, the gate insulating film 2
For example, an i-type hydrogenated amorphous silicon (a-Si: H) film is coated by plasma CVD on a portion facing the gate electrode 21 on the upper surface 3 and then photo-etched into a predetermined shape to form a semiconductor film. 24 are provided. And
The pixel electrode 25 is provided on the gate insulating film 23 adjacent to the source region side of the semiconductor film 24 by, for example, coating an ITO (indium tin oxide) film by a sputtering method and then performing photoetching into a predetermined shape. Have been. One end of an electrode 26 is connected to the source region, and is connected to the pixel electrode 25 at the other end of the source electrode 26. Further, one end of a drain electrode 27 is connected to the drain region. Here, the drain electrode 27 and the source electrode 26
Means, for example, Mo (molybdenum) film and Al (aluminum)
The film is formed by the same process of sequentially coating the film with a sputtering method and then performing photoetching into a predetermined shape. Thus, an array substrate 29 of a bookstore having a TFT 28 including the gate electrode 21, the gate insulating film 23, the semiconductor film 24, the source electrode 26, and the drain electrode 27 is obtained. On the other hand, on one main surface of the insulating substrate 30 made of, for example, glass, for example, ITO
By forming the common electrode 31 made of
Is configured. On one main surface of the array substrate 29, for example, a low-temperature curing type polyimide (PI)
An alignment film 33 made of
Similarly, an alignment film 34 made of, for example, a low-temperature curing type polyimide is formed on the entire main surface of the substrate. And
Each alignment film is formed on one main surface of the array substrate 29 and the counter substrate 32.
By rubbing the cloths 33 and 34 in a predetermined direction with a cloth or the like, rubbing alignment treatments are respectively performed. Furthermore,
The array substrate 29 and the opposing substrate 32 are combined such that one main surface side faces each other and their respective alignment axes form approximately 90 °, and a liquid crystal 35 is sandwiched in a gap obtained thereby.

FIG. 2 is a schematic plan view showing one pixel on the array substrate 29 of this embodiment, and FIG. 1 corresponds to a cross-sectional view taken along the line AA 'in FIG. In the figure, a row selection line 40 integrated with the gate electrode 21 and a column selection line 41 integrated with the drain electrode 27 are substantially orthogonal, and a TFT 28 is arranged near the intersection. In addition, the capacitance forming electrode 22 has a shape along the outer peripheral portion of the pixel electrode 25, and further, the semiconductor film 24 is partially cut at a portion facing the connection portion between the source electrode 26 and the pixel electrode 25. .

In this embodiment, since the gate insulating film 23 and the semiconductor film 24 exist between the capacitance forming electrode 22 and the pixel electrode 25 (Cs portion), the capacitance forming electrode is compared with the case where only the gate insulating film 23 is provided.
The probability of a short between 22 and the pixel electrode 25 has been reduced to about 1/6.
Also, since the semiconductor film 24 is left in the Cs portion, the pixel electrode 25
May occur, and non-conduction may occur between the central portion and the outer peripheral portion of the pixel electrode 25, but the source electrode 26 is formed on the pixel electrode 25 facing the cut portion of the semiconductor film 24 and in the vicinity thereof. Therefore, the electrical connection between the central portion and the outer peripheral portion of the pixel electrode 25 can be obtained by the function of the source electrode 26. Actually, when the cut portion of the semiconductor film 24 is present, the number of point defects in the display image is reduced to about 1/6 as compared with the case where the cut portion is not present.

3 (a) and 3 (b) are a cross-sectional view and a plan view, respectively, of one pixel in another embodiment of the present invention, and FIG. 3 (a) shows an arrow BB 'plane in FIG. 3 (b). It corresponds to the cross section when viewed from the direction. This embodiment differs from the embodiment shown in FIGS. 1 and 2 in the shapes of the capacitance forming electrode 22 and the source electrode 26. That is, the capacitance forming electrode 22 has a shape completely along the outer peripheral portion of the pixel electrode 25, and there is no cut portion as shown in FIG. Further, the source electrode 26 is expanded as compared with the previous case, and extends to the pixel electrode 25 facing the region surrounded by the capacitance forming electrode 22.

This embodiment has the same effect as the embodiment shown in FIG. 1 and FIG. That is, since the gate insulating film 23 and the semiconductor film 24 exist in the Cs portion, the short circuit between the capacitance forming electrode 22 and the pixel electrode 25 is reduced as compared with the case where only the gate insulating film 23 is provided. Further, even if the above-described disconnection occurs in the pixel electrode 25, the source electrode 26 extending to the pixel electrode 25 facing the region surrounded by the capacitance forming electrode 22 is located at the center of the pixel electrode 25. The outer peripheral portion can be electrically connected.

[Effects of the Invention] According to the present invention, point defects in a TFT array substrate can be reduced as compared with the prior art by devising a connection portion between a TFT and a pixel electrode and a shape of a semiconductor film, and the product yield during manufacturing is greatly reduced. improves.

[Brief description of the drawings]

FIG. 1 is a sectional view showing an embodiment of the invention described in claim 1,
FIG. 2 is a plan view showing one embodiment of the present invention, FIG. 3 is a sectional view and a plan view of another embodiment of the present invention, and FIG. 4 is a schematic view showing a conventional active matrix type liquid crystal display device. is there. 20, 30 ... insulating substrate, 21 ... gate electrode 22 ... capacitance forming electrode, 23 ... gate insulating film 24 ... semiconductor film, 25 ... pixel electrode 26 ... source electrode, 27 ... drain electrode 28 … Thin film transistor, 29… Array substrate 31… Common electrode, 32… Counter substrate 35… Liquid crystal, 40… Row select line 44… Column select line

──────────────────────────────────────────────────続 き Continued on the front page (58) Field surveyed (Int.Cl. ⁶ , DB name) G02F 1/136 G02F 1/1343 G09F 9/30 H01L 29/78

Claims (4)

(57) [Claims] 1. A thin-film transistor comprising a gate electrode, a gate insulating film, a semiconductor film, a source electrode and a drain electrode on a first insulating substrate, comprising: a row selection line integral with the gate electrode; and a column selection integral with the drain electrode. Between the array substrate in which a pixel electrode is connected to the source electrode of the thin film transistor and a common electrode formed on a second insulating substrate; In an active matrix type liquid crystal display device sandwiching liquid crystal, a first capacitor is formed on the array substrate along the row selection line, facing the pixel electrode via the gate insulating film and the semiconductor film. An electrode for capacitance formation including an electrode portion for the electrode, and the semiconductor film is arranged along the electrode for capacitance formation. Liquid crystal display device. 2. The capacitor forming electrode is substantially parallel to the first capacitor forming electrode portion, and the first capacitor forming electrode portion is arranged in parallel with the first electrode.
2. The active matrix type liquid crystal display element according to claim 1, wherein the active matrix type liquid crystal display element has a ring shape along the outer peripheral portion of the pixel electrode included in the second capacitance forming electrode portion separated from the capacitance forming electrode portion. 3. The active matrix liquid crystal display device according to claim 2, wherein a part of said semiconductor film along said first capacitance forming electrode portion is cut. 4. The device according to claim 1, wherein the source electrode extends beyond the first capacitance forming electrode portion and is electrically connected to the pixel electrode in a region surrounded by the capacitance forming electrode. The active matrix type liquid crystal display device according to claim 2, wherein