JP4215708B2 - Active matrix liquid crystal display device - Google Patents

Description

  The present invention relates to an active matrix liquid crystal display device that can be used as a flat display such as an AV / OA device.

  Currently, display devices using liquid crystal have been applied in various fields such as video camera viewfinders, pocket TVs, high-definition projection TVs, personal computers, word processors, and other information display terminals. It is active.

  In particular, an active matrix type TN (Twisted Nematic) liquid crystal display device using a thin film transistor (TFT) as a switching element has a great feature that a high contrast is maintained even when a large capacity display is performed. It has been actively developed and commercialized as a favorite of large-scale, large-capacity full-color displays for laptop computers, notebook computers, and engineering workstations with extremely high demands.

  In such an active matrix liquid crystal display element, a widely used liquid crystal display mode TN (Twisted Nematic) system is a panel having a structure in which liquid crystal molecules are twisted by 90 ° between electrode substrates sandwiching a liquid crystal layer. It is sandwiched between two polarizing plates.

  The two polarizing plates are arranged such that their polarization axes are orthogonal to each other, and one polarizing plate is arranged so that its polarization axis is parallel or perpendicular to the major axis direction of the liquid crystal molecules in contact with one substrate. When no voltage is applied, white display is performed. However, when a voltage is applied in the vertical direction between two substrates, that is, with respect to the liquid crystal panel, the light transmittance gradually decreases to display black.

  Such display characteristics are obtained when a voltage is applied to the liquid crystal panel, the liquid crystal molecules attempt to align in the direction of the electric field while unwinding the twisted structure, and the alignment state of the molecules causes the light transmitted through the panel to be aligned. This is because the polarization state changes and the light transmittance is modulated.

  However, even in the same molecular arrangement state, the polarization state of the transmitted light changes depending on the incident direction of the light incident on the liquid crystal panel. Therefore, the light transmittance varies depending on the incident direction. That is, the characteristics of the liquid crystal panel have a viewing angle dependency. This viewing angle characteristic causes a luminance reversal phenomenon when the viewpoint is tilted with respect to the main viewing angle direction (the major axis direction of the liquid crystal molecules in the intermediate layer of the liquid crystal layer), which is an important issue in the image quality of the liquid crystal panel.

In order to solve this problem, an IPS (In-Plane Switching) in which the direction applied to the liquid crystal is a direction substantially parallel to the substrate, rather than applying an electric field in the direction perpendicular to the substrate as in the TN liquid crystal display system. ) Method, for example, proposed in Patent Document 1 and Patent Document 2.
Japanese Examined Patent Publication No. 63-21907 JP-A-6-160878

FIG. 3A shows a configuration of a pixel portion of an array substrate of a conventional IPS liquid crystal display device. FIG. 3B is a schematic cross-sectional view of the cross-sectional configuration of the liquid crystal display device taken along the alternate long and short dash line in FIG.
As shown in this figure, a plurality of scanning lines 2 and signal lines 7 are formed so as to be orthogonal to each other, and a TFT 11 serving as a switching element is provided at each intersection of the scanning lines 2 and the signal lines 7. In one pixel surrounded by two adjacent scanning lines 2 and two adjacent signal lines 7, a plurality of, for example, two pixel electrodes 8 are formed substantially parallel to the signal line 7. A plurality of, for example, three common electrodes 3 are formed in a comb shape between the signal wiring 7 and the pixel electrode 8 and between the adjacent pixel electrodes 8, and are engaged with the pixel electrode 8. The storage capacitor portion 9 is formed between the pixel electrodes 8 and above the scanning wiring 2.

Next, the manufacturing process will be described.
Aluminum (Al) is laminated on the glass substrate 1, and the scanning wiring 2 and the common electrode 3 are simultaneously patterned by photolithography. A first insulator layer 4 of silicon nitride (SiNx) serving as a gate insulating film of the TFT is laminated on the scanning wiring 2 and the common electrode 3. Further, an amorphous silicon (α-Si) semiconductor layer 5 that controls the switching function of the TFT is laminated on the first insulator layer 4. Thereafter, a second insulator layer 6 of silicon nitride (SiNx) is laminated and patterned as a channel protective film of the TFT. Then, three layers of n + amorphous silicon (n + -α-Si), titanium (Ti), and aluminum (Al) are continuously deposited to form a collective pattern, and the signal wiring 7, the pixel electrode 8, and the storage capacitor portion 9 are shown in FIG. Formed as follows. Here, since n + amorphous silicon (n + -α-Si) is in ohmic contact with the semiconductor layer 5, the signal wiring 7, and the pixel electrode 8, titanium (Ti) is made of aluminum (Al) and amorphous silicon (α-Si). It was provided to prevent diffusion into the semiconductor layer 5. Further, a third insulator layer 10 of silicon nitride (SiNx) is laminated as a TFT protective film.

  An alignment film is applied to the array substrate 12 and the counter substrate 13 configured as described above, and a rubbing process is performed. Then, the array substrate 12 and the counter substrate 13 are bonded to each other with a certain gap, and liquid crystal is injected between them to form a liquid crystal layer 14. On the counter substrate 13, the light shielding film 15 exists at a position corresponding to the scanning wiring 2 and the signal wiring 7, but the light shielding film 15 does not exist at a position corresponding to the common electrode 3 and the pixel electrode 8.

  However, in the above configuration, the signal wiring 7 and the pixel electrode 8 have the same film thickness. It is necessary to increase the film thickness of the signal wiring 7 in order to allow a tolerance for disconnection failure and to reduce the wiring resistance. Therefore, the film thickness of the pixel electrode 8 is also increased, and the rubbing process is not performed in the vicinity of the pixel electrode 8. For this reason, in the panel display, non-aligned light leakage occurs at that portion, and the contrast is lowered. In addition, since the outermost surface of the pixel electrode 8 is made of aluminum (Al) having a high reflectance, light outside the panel is reflected, and there is a problem that the contrast is further lowered.

The active matrix liquid crystal display device of the present invention includes a plurality of signal lines and scanning lines arranged in a matrix, one or more switching elements provided at each intersection of the signal lines and the scanning lines, and the switching An array substrate having a pixel electrode connected to an element; a common electrode formed by meshing with the pixel electrode; a counter substrate disposed opposite to the array substrate; the array substrate and the counter substrate; An active matrix liquid crystal display device in which an electric field in a direction substantially parallel to the array substrate is applied to the liquid crystal layer , wherein the signal wiring has a plurality of layers. from made, the pixel electrode, together with includes a part of the conductive material constituting the signal wiring as a component, a layer the pixel electrode excluding the uppermost layer of the plurality of layers Characterized in that it is made.

According to the present invention, the pixel electrode can be thinned, lapping can be performed, and occurrence of non-aligned light leakage in the vicinity of the pixel electrode can be suppressed .

Active matrix liquid crystal display device of the present invention, in the IPS mode liquid crystal display device can achieve good multi-tone display with a wide viewing angle, the simple configuration of reducing the thickness of the pixel electrode, tolerance for bad break Can reduce non-aligned light leakage in the vicinity of the pixel electrode, and can suppress reflection of light outside the panel without increasing the wiring resistance or increasing the wiring resistance, and a high-contrast image can be obtained. .

The active matrix liquid crystal display device of the present invention includes a plurality of signal lines and scanning lines arranged in a matrix, one or more switching elements provided at each intersection of the signal lines and the scanning lines, and the switching An array substrate having a pixel electrode connected to the element; a common electrode formed by meshing with the pixel electrode; a counter substrate disposed opposite to the array substrate; the array substrate and the counter substrate; An active matrix liquid crystal display device in which an electric field in a direction substantially parallel to the array substrate is applied to the liquid crystal layer , wherein the signal wiring has a plurality of layers. from made, the pixel electrode, together with includes a part of the conductive material constituting the signal wiring as a component, a layer the pixel electrode excluding the uppermost layer of the plurality of layers By being made, it enables lapping process, since it is possible to reduce the pixel electrode, it is possible to suppress the occurrence of omission unoriented light in the pixel electrode neighboring districts, screen high contrast can be obtained.

Further, the uppermost layer of the pixel electrode is preferably formed of a different conductive material than the top layer of the signal lines, further, the top layer of the pixel electrode is formed by small conductive reflective material than aluminum Luke, by the pixel electrode is formed of a transparent conductive material, the reflection of the panel outside light is suppressed, higher contrast screen is obtained.

Hereinafter, the active matrix type liquid crystal display device of the present invention will be described based on each embodiment.
(Embodiment 1)
FIG. 1A schematically shows a planar configuration of a pixel portion of an array substrate in (Embodiment 1) of the present invention, and FIG. 1B is a liquid crystal display device taken along a dashed line in FIG. The schematic sectional drawing of this sectional structure is shown.

  In the glass array substrate 1 shown in FIG. 1, a plurality of scanning wirings 2 and signal wirings 7 are formed so as to be orthogonal to each other, and TFTs 11 serving as switching elements are provided corresponding to the intersections of the scanning wirings 2 and the signal wirings 7. . In one pixel surrounded by two adjacent scanning lines 2 and two adjacent signal lines 7, a plurality of, for example, two pixel electrodes 8 are formed substantially parallel to the signal line 7.

  A plurality of, for example, three common electrodes 3 are formed in a comb shape between the signal wiring 7 and the pixel electrode 8 and between the adjacent pixel electrodes 8, and are engaged with the pixel electrode 8. The storage capacitor portion 9 is formed between the pixel electrodes 8 and above the scanning wiring 2.

The manufacturing process is as follows.
Aluminum is used as the scanning wiring 2 and a pattern is formed on the glass substrate 1 by a photolithography method in a substantially parallel manner with a predetermined interval as shown in the figure. At the same time, a common electrode 3 that is substantially parallel to each other is patterned between two adjacent scanning lines 2.

  The film thickness of the scanning wiring 2 and the common electrode 3 is 150 nm, and the material is not limited to aluminum, and a conductive single layer film or a multilayer film such as chromium (Cr) or a metal mainly composed of aluminum may be used. Good.

  On the scanning wiring 2 and the common electrode 3, a first insulator layer 4 made of, for example, silicon nitride (SiNx), which functions as a gate insulating film of the TFT 11 functioning as a switching element, is laminated. Further, on the first insulator layer 4, for example, a semiconductor layer 5 made of amorphous silicon (α-Si) that controls the switching function of the TFT is laminated. Thereafter, a second insulator layer 6 of silicon nitride (SiNx) is laminated and patterned as a channel protective film of the TFT. Then, two layers of n + amorphous silicon (n + -α-Si) and titanium (Ti) were continuously deposited, and a collective pattern was formed by dry etching to form the pixel electrode 8 and the storage capacitor portion 9 as shown in the figure. A pixel electrode 8 is formed between two adjacent common electrodes 3 so as to be substantially parallel to the common electrode 3. Here, the film thickness of titanium (Ti) was 100 nm.

  Further, 300 nm of aluminum (Al) was deposited, and using this, a pattern was formed by wet etching so that the signal wiring 7 was substantially orthogonal to the scanning wiring 2 and substantially parallel to each other.

  On the scanning wiring 2 with the first insulator layer 4 and the semiconductor layer 5 interposed therebetween, the storage capacitor portion 9 is formed so as to overlap the two pixel electrodes 8. The storage capacitor unit 9 is provided to hold a voltage supplied to the pixel. As a protective film, a third insulator layer 10 such as silicon nitride (SiNx) was laminated.

  An alignment film was applied to the array substrate 12 and the counter substrate 13 configured as described above, and a rubbing process was performed. The array substrate 12 and the counter substrate 13 were bonded to each other with a gap of 3 μm, and liquid crystal was injected between them to form a liquid crystal layer 14. In this way, the film thickness of the pixel electrode 8 is 200 nm thinner than the signal wiring 7, and the rubbing process can be performed in the vicinity of the pixel electrode 8, and the pixel electrode 8 is formed of titanium having a reflectance lower than that of aluminum. . When a lighting image inspection of this liquid crystal display device was performed, it was confirmed that an image with high contrast was obtained without any non-oriented light missing in the vicinity of the pixel electrode 8.

  The film thickness of the pixel electrode 8 may be in the range of 30 to 200 nm, and the material may be a conductive material having a lower reflectance than aluminum such as tantalum (Ta), chromium (Cr), molybdenum (Mo) other than titanium. Alternatively, indium tin oxide (ITO), which is a transparent conductive material, may be used.

In addition, this configuration is effective by applying the matters related to the pixel electrode 8 to the common electrode 3 even when the common electrode 3 is formed in the same layer as the signal wiring 7.
(Embodiment 2)
FIG. 2A schematically shows a planar configuration of a pixel portion of the array substrate according to (Embodiment 2) of the present invention, and FIG. 2B is a liquid crystal display device taken along one-dot chain line in FIG. The schematic sectional drawing of this sectional structure is shown. Descriptions of parts common to those in the first embodiment are omitted, and different parts are described.

  In the second embodiment, after the pattern formation of the second insulator layer 6, two layers of n + amorphous silicon (n + -α-Si) and titanium (Ti) are continuously deposited, and a batch pattern formation is performed by dry etching. The pixel electrode 8, the storage capacitor portion 9, and the signal wiring portion were formed as shown in the figure.

  Further, aluminum (Al) was deposited, and the signal wiring 7 was formed by wet etching so as to overlap the signal wiring portion formed of titanium (Ti). By configuring the signal wiring 7 to have two layers of titanium / aluminum (Ti / Al), it is possible to further increase the tolerance for the disconnection failure of the signal wiring 7 as compared with the first embodiment. The wiring resistance can be further reduced. When a lighting image inspection of this liquid crystal display device was performed, it was confirmed that an image with high contrast was obtained without any non-oriented light missing in the vicinity of the pixel electrode 8.

FIG. 2 is a plan view and a cross-sectional view schematically showing a planar configuration of a pixel portion of an array substrate in the active matrix liquid crystal display device of Embodiment 1 of the present invention. FIG. 6 is a plan view and a cross-sectional view schematically showing a planar configuration of a pixel portion of an array substrate in an active matrix liquid crystal display device according to (Embodiment 2) of the present invention. It is the top view and sectional drawing which show schematically the planar structure of the pixel part of the array substrate in the conventional active matrix liquid crystal display device.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Glass substrate 2 Scanning wiring 3 Common electrode 4 1st insulator layer 5 Semiconductor layer 6 2nd insulator layer 7 Signal wiring 8 Pixel electrode 9 Storage capacity | capacitance part 10 3rd insulator layer 11 TFT
12 array substrate 13 counter substrate 14 liquid crystal layer 15 light shielding film

Claims (3)

A plurality of signal wirings and scanning wirings arranged in a matrix, one or more switching elements provided at each intersection of the signal wirings and the scanning wirings, a pixel electrode connected to the switching elements, and the pixels An array substrate having a common electrode formed by occlusion with the electrode;
A counter substrate disposed to face the array substrate;
A liquid crystal layer sandwiched between the array substrate and the counter substrate;
An active matrix liquid crystal display device in which an electric field in a direction substantially parallel to the array substrate is applied to the liquid crystal layer,
The signal wiring is composed of a plurality of layers,
The pixel electrode includes a part of a conductive material constituting the signal wiring as a constituent element , and the pixel electrode is formed from a layer excluding the uppermost layer of the plurality of layers. Liquid crystal display device. 2. The active matrix liquid crystal display device according to claim 1, wherein the uppermost layer of the pixel electrode is made of a conductive material different from that of the uppermost layer of the signal wiring. Wherein either the top layer of the pixel electrode is formed by small conductive material reflectance than aluminum, an active matrix of claim 1 or claim 2, wherein said pixel electrode, characterized in that it is formed of a transparent conductive material Type liquid crystal display device.

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