JPH1010580A - Display device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a structure of a pixel capable of obtaining sufficient capacity without substantially lowering a numerical aperture in an active matrix liquid crystal display device. SOLUTION: A metallic common electrode 22 sharing a black matrix is arranged so as to cover a peripheral part of a pixel electrode 24 consisting of a transparent conductive film. At this time, the common electrode 22 functions as the black matrix covering the peripheral part of the pixel, and is held to fixed potential. Therefore, an area that the pixel electrode 24 is overlapped the common electrode 22 functions as auxiliary capacity 25. The auxiliary capacity is constituted through an insulation film 23. Then, for enlarging the auxiliary capacity 25, the common electrode 22 is formed on an insulation layer 21 having a flattened surface. Thus, even when the insulation film 23 is thinned to a 1μm extent, a pin hole, a leakage, etc., between the common electrode and the pixel electrode are prevented, and larger auxiliary capacity is obtained.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a pixel structure of an active matrix type display device (particularly, a liquid crystal display device). More specifically, a storage capacitor and a black matrix (BM) connected in parallel with the pixel electrode
Related to the configuration. Further, the present invention relates to a configuration of a pixel of a flat panel display that requires a wide black matrix.

[0002]

2. Description of the Related Art A display device having an active matrix circuit is known. It has a plurality of source lines for transmitting image data, a plurality of gate lines for intersecting the source lines, and a plurality of gate lines for transmitting a switching signal, and a plurality of pixels provided at the intersection thereof. It has a structure, and a transistor (especially a thin film transistor) is usually used as a switching element.

A pixel has not only a transistor for switching but also a pixel electrode, and has a structure in which a gate electrode of the transistor is connected to a gate wiring, a source is connected to a source wiring, and a drain is connected to the pixel electrode. Note that in the operation of a transistor, the distinction between the source and the drain is not a steady one, but varies according to a signal in the definition of an ordinary electric circuit. Of these, the one connected to the source wiring is called the source, and the one connected to the pixel electrode is called the drain.

[0004] Each pixel has one or more transistors. In particular, an arrangement in which two or more transistors are connected in series is effective because the leak current can be reduced even when the transistors are not selected. Even in such a case, the above definition is applied, and the impurity region not connected to any of the source wiring and the pixel electrode is not particularly defined.

The pixel electrode forms a capacitance (capacitor) between the pixel electrode and the electrode facing the liquid crystal. The above-described transistor functions as a switching element for taking charge in and out of the capacitor. However, in actual operation,
The capacitance of the pixel electrode portion alone is too small to hold necessary charges for a sufficient time. Therefore, it is necessary to provide an auxiliary capacity separately.

Conventionally, this auxiliary capacitor (also referred to as a storage capacitor) is formed by separately providing an opaque conductive material such as metal.
A capacitor is formed between the pixel electrode and the semiconductor layer. Usually, the gate wiring in the next row was used as the counter electrode. However, when the pixel area is large, the capacitance formed by using the gate wiring is sufficient. It was required to expand the gate wiring more than necessary to secure it. In such a structure, a portion that blocks light is present in the pixel, so that the aperture ratio is reduced.

[0007]

SUMMARY OF THE INVENTION The present invention has been made in view of the above problems, and provides a pixel structure capable of obtaining a sufficient capacity without substantially lowering the aperture ratio. That is the task.

[0008]

In particular, in an active matrix type liquid crystal display device, around a pixel electrode,
A light shielding member called a black matrix is required. In general, in a region where a source wiring and a gate wiring arranged in a lattice are formed, the upper part thereof rises.

As a result, the rubbing treatment on the alignment film in this portion does not work well, and the alignment of the liquid crystal molecules in that portion is disturbed. As a result, in the peripheral portion of the pixel, there occurs a phenomenon that light leaks or conversely light does not sufficiently pass. Further, in this portion, it becomes impossible to perform a predetermined electro-optical operation on the liquid crystal.

[0010] When the above phenomenon occurs, the display around the pixels becomes blurred, and the sharpness of the entire image is lost. As a configuration for solving this problem, there is a configuration in which a light-shielding film is arranged so as to cover an edge portion of a pixel electrode. This light-shielding film is called a black matrix (BM).

The first invention disclosed in the present specification, as shown in FIG. 1 and FIG. 2, shows an electrode (covering a constant potential) covering visible light by covering a source wiring and a gate wiring. (Referred to as a common electrode). The periphery of the pixel electrode overlaps with the common electrode. The common electrode is formed on the flattened surface of the organic resin layer. This overlapped region has a feature that it functions as an auxiliary capacitance.

In the above configuration, all regions other than the pixel electrode and a part of the source and drain of the transistor can be shielded from incident light by the common electrode.
In particular, the source wiring and the gate wiring can be completely shielded from the outside. By doing so, it is possible to prevent an electromagnetic wave from jumping into the source wiring or the gate wiring from the outside, thereby causing a malfunction or a malfunction of the device.

Further, the auxiliary capacitance can be formed without lowering the aperture ratio. This is because the black matrix itself is originally required, and in the present invention, the auxiliary capacitance is formed in the black matrix. Here, this configuration is effective in increasing the capacity. If the common electrode has severe irregularities, it is necessary to increase the thickness of the insulating layer interposed between the common electrode and the pixel electrode in order to increase the insulating property between the common electrode and the pixel electrode. In particular, when an organic resin film is used as the insulating layer, a thickness of usually 2 μm or more is required.

However, when the irregularities of the common electrode are small, the thickness of the insulating layer between them is 1 μm or less. Since the capacitance is inversely proportional to the thickness of the insulating layer therebetween, the thinner the insulating layer, the higher the capacitance. In the above configuration, the pixel electrode is formed of a transparent conductive film such as ITO (indium tin oxide). In the basic configuration, one pixel electrode is provided for each pixel. However, a configuration in which one pixel electrode is divided into a plurality of pixels may be employed.

The common electrode (black matrix) arranged so as to overlap the peripheral edge of the pixel electrode is made of titanium or chromium. As is clear from the above description, the common electrode also functions as one of the electrodes constituting the storage capacitor. It is preferable that the common electrode overlaps in the entire periphery of the pixel electrode for the purpose of enhancing light-shielding properties. In this case, the area of the auxiliary capacitance increases and the capacitance increases.

When the dielectric constant of the insulating layer existing between the pixel electrode and the common electrode is higher than the dielectric constant of the organic resin layer formed on the surface of the common electrode, the auxiliary capacitance is naturally increased. Can be larger. In general, since the capacitance coupling between wirings is increased, it has been avoided to increase the dielectric constant of an insulating layer in a semiconductor circuit. However, in the present invention, the source wiring which is the main wiring,
The gate wiring is shielded by the common electrode, and there is no wiring that is capacitively coupled to the pixel electrode via the insulating layer. Therefore, there is no problem in using the insulating layer as a high dielectric material.

According to a second aspect of the present invention, a common electrode is placed over the periphery of the pixel electrode to block light and to maintain a constant potential. The pixel electrode and the common electrode form a capacitor via an insulating film. The common electrode is characterized in that the surface provided on the source wiring and the gate wiring is disposed on an organic resin layer whose surface is flattened. The operation and effect of the second invention are the first.
This is the same as that described with respect to the invention of the above.

The structure of the third invention is, for example, shown in FIGS.
As an example, a layer of a pixel electrode made of a transparent conductive film, a layer of a common electrode made of a light-shielding material, an organic resin layer having a planarized surface, a layer of a source wiring, a layer of a gate wiring, and a common layer with the pixel electrode It has a feature that a capacitance is formed between the electrode and the electrode.

In the above structure, the pixel electrode is arranged on the side closest to the incident light, and then the common electrode (black matrix) is arranged, so that the source line and the gate line arranged below the pixel electrode and the transistor are completely formed. Can be shielded from light. This configuration is very useful not only for shading but also for eliminating the effects of external electromagnetic waves.

In the third aspect, an organic resin layer may be provided between the pixel electrode and the common electrode. Further, it is preferable that the common electrode be overlapped with the edge portion of the pixel electrode because an auxiliary capacitance can be formed at the portion. Further, when the dielectric constant of the insulating layer existing between the pixel electrode and the common electrode is higher than the dielectric constant of the organic resin layer formed on the surface of the common electrode, the auxiliary capacitance can be naturally increased.

[0021]

1 and 2 show a configuration of a pixel of an active matrix type liquid crystal display device utilizing the invention disclosed in this specification. FIG. 1 schematically shows a cross-sectional view of a manufacturing process of this embodiment, and FIG. 2 shows an arrangement of wirings, common electrodes, pixel electrodes, semiconductor layers, and the like of this embodiment. The numbers in FIG. 2 correspond to those in FIG. FIG. 1 shows a cross section along the dotted line XY in FIG. 2A, but FIG. 1 is conceptual and is not exactly the same as the arrangement in FIG.

Also, what is shown in FIGS. 1 and 2 is
This is only the configuration on the substrate side on which the thin film transistors are arranged. Actually, there is also an opposing substrate (opposite substrate), and the liquid crystal has a gap of several μm between the opposing substrate and the substrate shown in FIG. Will be retained. Hereinafter, the manufacturing process will be described with reference to FIG. As shown in FIG. 1A, a semiconductor layer (active layer) 12 of a transistor is provided over a glass substrate 11 provided with a base silicon oxide film (not shown).

The active layer 12 is composed of a crystalline silicon film obtained by crystallizing an amorphous silicon film by heating or irradiating a laser beam. A gate insulating film 13 covering the active layer 12
Is formed. The material of the gate insulating film 13 is preferably silicon oxide or silicon nitride.
A silicon oxide film formed by a VD method may be used.
A gate wiring (gate electrode) 1 is formed on the gate insulating film using an aluminum-titanium alloy by a known sputtering method.
4 are formed. (Fig. 1 (A))

FIG. 2A shows the circuit arrangement in this state. (FIG. 2A) Next, using a gate wiring as a mask, an N-type or P-type impurity is introduced into the active layer by a known ion doping method to form a source 15 and a drain 16. After the introduction of the impurities, if necessary, activation of the impurities by thermal annealing or laser annealing (recrystallization of the semiconductor film)
May be performed. After the above steps, a silicon nitride film (or silicon oxide film) 17 is deposited by a plasma CVD method. This functions as a first interlayer insulator. (Figure 1
(B))

Next, the source 15 is applied to the first interlayer insulator 17.
And a contact hole reaching the drain 16 is formed. Then, a multilayer film of titanium and aluminum is formed by a known sputtering method, and this is etched to form a source wiring 18 and a drain electrode 19. After the above steps, a silicon nitride film (or silicon oxide film) 20 is deposited by a plasma CVD method. This functions as a second interlayer insulator. It is preferable to use silicon nitride as the second interlayer insulator. This is effective in preventing impurities existing in the upper organic resin layer from penetrating into the lower transistor. (FIG. 1C) The circuit arrangement in this state is shown in FIG. (Figure 2
(B))

Next, the first organic resin layer 21 is formed by spin coating. When a printing method is used instead of the spin coating method, mass productivity can be improved. The upper surface of the organic resin layer is formed flat. Then, a chromium film is formed by a known sputtering method, and the chromium film is etched to form the common electrode 22. Titanium other than chromium may be used. (FIG. 1D) FIG. 2C shows the circuit arrangement in this state. As can be seen from the figure, the common electrode is formed so as to cover the source wiring and the gate wiring. (Fig. 2 (C))

Further, the second coating is performed by a spin coating method.
Is formed. Its thickness needs to be greater than the thickness of the common electrode, but is typically
The thickness is preferably 5 to 1 μm. In this case, the thickness at the portion on the common electrode can be 0.3 μm or more. Then, the second organic resin layer 23 and the first organic resin layer 21, and further,
The second interlayer insulator 20 is continuously etched to form a contact hole reaching the drain electrode 19.

Next, an ITO film is formed by a known sputtering method, and the ITO film is etched to form pixel electrodes 24a, 2b.
4b and 24c are formed. The pixel electrode 24c is a pixel electrode of the transistor, and the pixel electrodes 24a and 2
4b is an adjacent pixel electrode. Pixel electrodes 24a to 2
Capacitors 25 a, 25 b, and 25 c are formed at portions where 4 b overlaps with the common electrode 22 via the second organic resin layer 23. Since the surface of the first organic resin layer 21 is flat, there are few irregularities on the common electrode.
The organic resin layer 23 can be made thin. Therefore, the capacitances 25a to 25c can be large. (FIG. 1 (E))

FIG. 2D shows the circuit arrangement in this state. Note that, in the figure, the positions of the pixel electrode and the overlapping portion of the pixel electrode and the common electrode (that is, the portion where the capacitor exists) are shaded for easy understanding. As can be seen from the figure, the pixel electrode is formed so as to overlap the common electrode, and the common electrode functions as a black matrix. For example, generation and accumulation of electric charge due to irradiation of strong light can be prevented.

The common electrode 22 functions not only as a simple light shield but also as a shield against external electromagnetic waves. That is, it has a function of preventing intrusion of unnecessary signals due to the gate wiring 14 and the source wiring 18 serving as antennas. (FIG. 2 (D)) As is clear from FIG. 2 (C), the common electrode 22
Are arranged so as to cover the channel of the thin film transistor. This is to prevent the operation of the thin film transistor from being affected by light irradiation.

Here, the structure in which the second organic resin layer 23 is a single layer is shown, but a multilayer structure may be used. Further, it may be made of an inorganic material or a material having a higher dielectric constant.
This is because there is no capacitive coupling between the pixel electrode and the lower wiring via the insulating layer corresponding to the second organic resin layer. When the insulating layer corresponding to the second organic resin layer is made of a high dielectric material, it is effective in increasing the auxiliary capacitance.

[0032]

According to the present invention, the black matrix covering the peripheral portion of the pixel electrode and the pixel electrode are partially overlapped with an insulating film interposed therebetween, so that the portion can be constituted as an auxiliary capacitor.
This itself is not a factor that lowers the aperture ratio of the pixel. Further, since the thickness of the insulating film can be reduced, the capacitance value can be increased.

The invention disclosed in this specification is not limited to an active matrix type liquid crystal electro-optical device, but also includes a flat panel display which requires a black matrix covering a pixel electrode and its periphery and an auxiliary capacitor connected to a thin film transistor. Can be used generally. As described above, the present invention is industrially useful.

[Brief description of the drawings]

FIG. 1 is a sectional view showing a manufacturing process according to one embodiment of the present invention.

FIG. 2 shows an arrangement of wiring and the like according to the embodiment.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 11 Glass substrate 12 Active layer 13 Gate insulating film 14 Gate wiring (gate electrode) 15 Source 16 Drain 17 First interlayer insulator 18 Source wiring 19 Drain electrode 20 Second interlayer insulator 21 First organic resin layer 22 Common Electrode 23 second organic resin layer 24 pixel electrode 25 storage capacitor

Claims (7)

[Claims] A source line and a gate line arranged in a lattice pattern, wherein at least one pixel electrode is provided in a region surrounded by the source line or the gate line; And a common electrode that is made of a material that covers the source wiring and the gate wiring and that blocks visible light and that is held at a constant potential, between the layer of the source wiring and the gate wiring. An active matrix type display device, wherein a portion overlaps the common electrode, the common electrode is formed on a flattened surface of the organic resin layer, and the overlapped region functions as an auxiliary capacitor. 2. A semiconductor device comprising: a source wiring and a gate wiring arranged in a lattice; and a region surrounded by the source wiring or the gate wiring has at least one pixel electrode. A common electrode that is made of a material that blocks visible light and is superposed on the common electrode, the pixel electrode and the common electrode form a capacitor via an insulating film, and the common electrode An active matrix display device characterized in that a surface provided on the source wiring and the gate wiring is disposed on a flattened organic resin layer. 3. A pixel electrode layer made of a transparent conductive film, a common electrode layer made of a light-shielding material, a source wiring layer, and a gate wiring layer in this order from the incident light side. An active matrix display device, wherein an organic resin layer whose surface is planarized is provided between layers of the source wiring, and a capacitor is formed between the pixel electrode and the common electrode. 4. The active matrix type display device according to claim 1, wherein an organic resin layer exists between the pixel electrode and the common electrode. 5. The display device according to claim 3, wherein the common electrode is arranged so as to overlap an edge portion of the pixel electrode. 6. The display device according to claim 3, wherein the source wiring and the gate wiring are shielded from incident light by the common electrode. 7. The semiconductor device according to claim 1, wherein a dielectric constant of an insulating layer existing between the pixel electrode and the common electrode is higher than a dielectric constant of an organic resin layer formed on the surface of the common electrode. An active matrix display device characterized by the above-mentioned.