JP4585071B2 - Active matrix liquid crystal display device - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to an active matrix type liquid crystal display device in which display pixel electrodes are formed using thin film transistors as switching elements.
[0002]
[Prior art]
In recent years, liquid crystal display devices capable of providing high-performance and high-definition display with high density and large capacity have been put into practical use. There are various types of liquid crystal display devices. Among them, crosstalk between adjacent pixels is small, high contrast image display is obtained, transmission type display is possible, and large area is easy. Many active matrix liquid crystal display devices are used.
[0003]
In general, an active matrix type liquid crystal display device includes an array substrate, and the array substrate is arranged in a matrix in a plurality of regions partitioned by a plurality of scanning lines and a plurality of signal lines provided in a direction intersecting each other. Each pixel electrode is connected to a scanning line and a signal line through a thin film transistor (hereinafter referred to as TFT) functioning as a switching element.
[0004]
In addition, this type of liquid crystal display device includes a backlight provided on the back side of the array substrate. In order to reduce the power consumption of the backlight, it is desirable that the pixel has a structure with a high aperture ratio. As a structure capable of obtaining a high aperture ratio, a structure is known in which a wiring BM (black matrix) that shields a gap between a signal line and a pixel electrode is formed by arranging the signal line and the pixel electrode so as to overlap each other. In the case of this wiring BM structure, the parasitic capacitance between the signal line and the pixel electrode is large.
[0005]
The display quality of the TFT liquid crystal display device depends on the parasitic capacitance between the signal line and the pixel electrode. The effect of this parasitic capacitance is to form an auxiliary capacitance line or to insulate the shield electrode fixed at a constant potential between layers. It can be suppressed by arranging the pixel electrode and the signal line so as to overlap with each other through the film.
[0006]
In addition, it is known that in the wiring BM structure, a liquid crystal misalignment region is generated near the end of the signal line on the downstream side in the rubbing direction, which causes a display defect such as a decrease in contrast. For this reason, the alignment defect region of the liquid crystal must be shielded by wiring, and the overlapping width between the signal line and the pixel electrode needs to be increased. However, in this case, there arises a problem that the parasitic capacitance between the signal line and the pixel electrode increases.
[0007]
[Problems to be solved by the invention]
In view of this, a so-called one-side shield structure has been proposed in which the overlapping width of the signal line and the pixel electrode is increased only on the side where the liquid crystal misalignment region occurs, and the shield electrode is arranged along one side edge of the signal line. In this structure, by adjusting the length of the shield electrode, the capacitance between the signal line and the pixel electrode located on one side of the pixel electrode, and the capacitance between the signal line and the pixel electrode located on the other side of the pixel electrode, , And the occurrence of display defects such as crosstalk can be suppressed.
[0008]
On the other hand, in a liquid crystal display device having a pixel-mounted structure, the pixel electrode and the TFT source electrode cannot be directly connected. Therefore, a through hole is formed in the organic insulating film, and the pixel electrode and the TFT source electrode are connected via the pixel connection electrode and the through hole formed simultaneously with the signal line.
[0009]
In this case, the pixel connection electrode needs to be larger than the through hole in consideration of the formation accuracy of the through hole. However, since the pixel connection electrode is formed at the same time as the signal line, the maximum size of the pixel connection electrode is a dot. Determined by pitch, minimum feature size, and signal line width. When the dot hitch is small, the size of the pixel connection electrode is inevitably small, and the through-hole diameter of the organic image separation film is also small.
[0010]
Usually, since the film thickness of the organic insulating film is as thick as 2 to 4 μm, the workability of the through hole is poor, and when the through hole diameter is small, a point defect failure due to poor formation of the through hole is likely to occur. In order to prevent this, a method of increasing the through hole diameter of the organic insulating film in the direction along the signal line can be considered, but in this case, the aperture ratio is lowered.
[0011]
The present invention has been made in view of the above points, and an object thereof is to provide an active matrix liquid crystal display device in which image defects are reduced and display quality is improved. Another object of the present invention is to reduce image defects and improve display quality, and to prevent defective formation of through holes when electrically connecting a pixel electrode and a pixel connection electrode, thereby reducing an aperture ratio. It is an object of the present invention to provide an active matrix type liquid crystal display device capable of performing high-quality display without lowering.
[0013]
[Means for Solving the Problems]
An active matrix type liquid crystal display device according to an aspect of the present invention includes first and second substrates disposed to face each other with a liquid crystal layer interposed therebetween,
The first substrate includes a plurality of scanning lines provided substantially in parallel on the insulating substrate, a plurality of signal lines provided on the scanning lines via an insulating film so as to intersect the scanning lines, A plurality of shield electrodes having electrostatic shielding properties extending from the scanning line and formed along the signal line, and provided in each region surrounded by the signal line and the scanning line, at least a part of the signal line being provided. And a plurality of pixel electrodes connected to the intersections of the signal lines and the scanning lines via the switching elements, and overlapping with the scanning lines,
Each shield electrode includes first and second electrode portions extending in a direction opposite to each other from the scan line along the signal line, and the signal line located between two adjacent pixel electrodes is: a first side edge portion provided to overlap with one pixel electrode, located below the downstream side of the liquid crystal orientation direction relative to the first side edge, the second is provided to overlap with the other pixel electrode Two side edges, and the first and second electrode parts of the shield electrode are provided so as to overlap only with the other pixel electrode and the second side edge of the signal line,
The width of the other pixel electrode overlapping the second side edge of the signal line and the shield electrode is larger than the width of the first pixel electrode overlapping the first side edge of the signal line. Yes.
[0014]
According to the liquid crystal display device having the above configuration, the shield electrode having electrostatic shielding properties extends along the signal line in a direction opposite to each other from the scanning line , and overlaps only with one side edge of the signal line. The arrangement eliminates the need for the interval between the shield electrodes, which is necessary in the past, and the signal line and the shield electrode only need to be provided on one side so that the signal line can be formed with the minimum processing line width. It becomes possible. As a result, a high aperture ratio can be realized while maintaining the electrostatic shielding effect, and a display with improved display quality can be achieved by reducing image quality defects such as crosstalk and luminance unevenness.
[0015]
In addition, the portion of each signal line that overlaps the scanning line and the shield electrode is notched and has a narrower width than the other portions, and accordingly, the scanning line side end of the pixel connection electrode, In addition, the size of the through hole of the organic insulating film can be enlarged. Accordingly, it is possible to realize an active matrix type liquid crystal display device which prevents formation of through holes and has high display quality with few point defects.
[0016]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, an active matrix liquid crystal display device according to an embodiment of the present invention will be described in detail with reference to the drawings.
As shown in FIGS. 1 and 3, the active matrix type liquid crystal display device 10 is configured as a light transmission type liquid crystal display device having a rectangular display region 15, and includes a rectangular array substrate 12 and a counter substrate 14, respectively. It has. These substrates 12 and 14 are arranged to face each other with a predetermined gap by bonding their peripheral portions with a sealing agent (not shown). A liquid crystal layer 90 is sealed between the array substrate 12 and the counter substrate 14 via alignment films 88 and 89, respectively.
[0017]
As shown in FIGS. 1 to 3, the array substrate 12 has a glass substrate 60 as an insulating substrate, and on this glass substrate, a large number of signal lines 50 and a large number of scanning lines 62 are substantially orthogonal as wirings. It is provided in a matrix form. The signal line 50 is formed on the scanning line 62 via the interlayer insulating film 75. On the glass substrate 60, an auxiliary capacitance line 52 extending in parallel with these scanning lines is provided between two adjacent scanning lines 62. The auxiliary capacitance line 52 is formed by patterning the same layer as the scanning line 62.
[0018]
In a region surrounded by the two signal lines 50 and the two auxiliary capacitance lines 52, pixel electrodes 51 made of ITO are provided, and each pixel electrode is connected to the signal line 50 via the TFT 18 as a switching element. And the scanning line 62 are connected to each other. Each pixel electrode 51 is formed in a substantially rectangular shape and constitutes one pixel. The source electrode 67 of the TFT 18 is connected to the pixel connection electrode 78, and this pixel connection electrode is connected to the pixel electrode 51 through a through hole 82 formed in the organic insulating layer 81.
[0019]
A signal line drive circuit unit 20 is formed at the end of the long side of the array substrate 12, and a scan line drive circuit unit 22 is formed at the end of the short side. The plurality of signal lines 50 are drawn to the long side of the array substrate 12 and are connected to the signal line driving circuit unit 20. The plurality of scanning lines 62 are drawn to the short side of the array substrate 12 and connected to the scanning line driving circuit unit 22.
[0020]
More specifically, as shown in FIGS. 2 to 4, each signal line 50 is formed in a straight line shape, and as will be described later, in the vicinity of each auxiliary capacitance line 52, one side edge side, For example, the right edge side is notched and formed with a width narrower than other portions. The array substrate 12 includes a shield electrode 53 having electrostatic shielding properties formed by extending a part of each auxiliary capacitance line 52 along each signal line 50. Each shield electrode 53 has first and second electrode portions 53 a and 53 b extending in the opposite directions from the auxiliary capacitance line 52.
[0021]
The first electrode portion 53a and the second electrode portion 53b are provided eccentric to the right side with respect to the signal line 50 in FIG. The signal line 50 has a portion 50a that is overlapped with the auxiliary capacitance line 52 and the first and second electrode portions 53a and 53b of the shield electrode 53, and is narrower than the other portions. The second electrode portions 53a and 53b are provided so as to slightly overlap the side edge portions.
[0022]
In addition, each pixel electrode 51 is provided such that the side edges on the pair of short sides overlap the auxiliary capacitance lines 52 on both sides with a predetermined width. Further, the right long side edge of each pixel electrode 51 is formed in a straight line, and is provided so as to overlap with the left side edge (first side edge) of the signal line 50 by a predetermined width W1. The edge portion is formed in a step shape, and overlaps the side edge portions of the first and second electrode portions 53a and 53b of the shield electrode 53 and the right edge portion (second side edge portion) of the signal line 50 by a predetermined width W2. Is provided.
[0023]
Thus, the signal line 50 and the shield electrode 53 that are partially overlapped with the pixel electrode 51 also serve as a light shielding body that shields a gap between the pixel electrode 51 and the pixel electrode. The direction indicated by the arrow D in FIG. 2 is the orientation vector of the orientation film 88, and the misalignment region NA of the liquid crystal layer 90 is likely to occur at the right edge portion of each signal line 50. Therefore, the overlap width W2 between the pixel electrode 51 and the shield electrode 53 is formed to be larger than the overlap width W1 between the pixel electrode 51 and the signal line 50.
[0024]
The electrode length L1 of the first electrode portion 53a and the electrode length L2 of the second electrode portion 53b of the shield electrode 53 are set to be equal to each other, and the influence of two signal lines adjacent to each other with the pixel electrode 51 interposed therebetween. Are adjusted to be equal. As a result, the influence of the signal line 50 to which the TFT 18 is connected, that is, the signal line on the left side of the pixel electrode, and the signal line 50 to which the TFT is not connected, that is, the right side of the pixel electrode, are connected. The influence of the signal line is approximately the same, and the influence of the parasitic capacitance between the two signal lines and the pixel electrode 51 can be minimized.
[0025]
In addition, as described above, the portion of each signal line 50 that overlaps the auxiliary capacitance line 52 and the shield electrode 53 has a portion 50a on the through hole 82 side cut out, and is narrower than the other portions. Therefore, the dimension of the pixel connection electrode 78 on the side of the auxiliary capacitance line 52 and the through hole 82 of the organic insulating film 52 can be enlarged accordingly. Thereby, formation defects of the through holes 82 can be prevented, and an active matrix type liquid crystal display device with few point defect defects and high display quality can be realized.
[0026]
Next, the configuration of the liquid crystal display device 10 will be described in detail together with its manufacturing method.
First, an a-Si film is deposited to a thickness of about 50 nm on a light-transmitting insulating substrate 60 such as a high strain point glass substrate or a quartz substrate by a CVD method or the like. This a-Si film is annealed at 450 ° C. for 1 hour, and then irradiated with a XeCl excimer laser to polycrystallize a-Si. Thereafter, polycrystalline Si is patterned by a photoetching method to form a polysilicon film 19 that becomes a channel layer of a TFT (hereinafter referred to as a pixel TFT) 18 constituting a pixel portion in the display region 15.
[0027]
Next, a gate insulating film 61 made of a SiOx film is deposited on the entire surface of the substrate 60 by a CVD method to a thickness of about 100 nm. Subsequently, a single layer of Ta, Cr, Al, Mo, W, Cu or the like, or a laminated film or alloy film thereof is deposited on the entire surface of the gate insulating film 61 to a thickness of about 200 to 400 nm, and is formed into a predetermined shape by a photoetching method. By patterning, the scanning line 62 and the auxiliary capacitance line 52 having the gate electrode 63 integrally formed are formed. At this time, the shield electrode 53 is formed in a predetermined shape at a predetermined position simultaneously with the auxiliary capacitance line 52.
[0028]
Thereafter, impurities are implanted into the polysilicon film 19 by ion implantation or ion doping using the gate electrode 62 as a mask, and a drain electrode 66 and a source electrode 67 of the pixel TFT 18 are formed. Impurity is implanted, for example, at a accelerating voltage of 80 keV and a dose of 5 × 10 ¹⁵ atmos / cm ² , and phosphorus is implanted at a high concentration by PH ₃ / H ₂ . Thereafter, the substrate 60 is annealed to activate the impurities.
[0029]
Subsequently, impurities are implanted into the pixel TFT 18 to form N channel type LDD (Lightly Doped Drain) 74a and 74b, and the array substrate is annealed to activate the impurities.
[0030]
Further, for example, an interlayer insulating film 75 made of SiO ₂ is deposited to a thickness of about 500 to 700 nm on the entire surface of the insulating substrate 60 by using PECVD. Then, a contact hole 76 reaching the drain electrode 66 of the pixel TFT 18 and a contact hole 77 reaching the source electrode 67 are formed by photoetching.
[0031]
Next, a single layer of Ta, Cr, Al, Mo, W, Cu or the like, or a laminated film or alloy film thereof is applied to a thickness of about 500 to 700 nm, and is patterned into a predetermined shape by a photoetching method, so that the signal lines 50, pixels Various wirings for connecting the connecting electrode 78, the drain electrode 66 of the pixel TFT 18 and the signal line 50, and connecting the source electrode 67 and the pixel connecting electrode are performed.
[0032]
Further, a protective insulating film 79 made of SiNx is formed on the entire surface of the insulating substrate 60 by PECVD, and a through hole 80 reaching the pixel connection electrode 78 is formed by photoetching. Next, after an organic insulating film 81 is applied to the entire surface of the substrate to a thickness of 2 to 4 μm, a through hole 82 reaching the pixel connection electrode 78 is formed.
[0033]
Next, lTO is deposited on the organic insulating film 81 to a thickness of about 100 nm by a sputtering method, and patterned into a predetermined shape by a photoetching method to form the pixel electrode 51, and the pixel electrode through the through holes 80 and 82. 51 and the pixel connection electrode 78 are connected. Through the above steps, the array substrate 12 of the liquid crystal display device 10 is obtained.
[0034]
On the other hand, the counter substrate 14 is a transparent electrode made of, for example, lTO by sputtering, for example, by forming a colored layer 85 in which a pigment or the like is dispersed on a glass substrate 84 as an insulating substrate having transparency. It is obtained by forming the counter electrode 86.
[0035]
Alignment films 88 and 89 made of low-curing polyimide are printed and applied to the entire surface of the array substrate 12 on the pixel electrode 51 side and the entire surface of the counter substrate 86 side of the counter substrate 14 formed as described above, respectively. Are rubbed so that the orientation axes differ by 90 degrees. Thereafter, the array substrate 12 and the counter substrate 14 are arranged facing each other and assembled into a cell, and a nematic liquid crystal 90 is injected into the gap and sealed. Then, by attaching the deflecting plates 92 and 94 to the outer surface sides of the insulating substrates 60 and 84 of both the substrates 12 and 14, respectively, the liquid crystal display device 10 is obtained.
[0036]
In the liquid crystal display device configured as described above, the shield electrode 53 formed for each pixel on the array substrate 12 is formed only on one side with respect to the signal line 50. Accordingly, the interval between the shield electrodes, which was conventionally necessary, is no longer necessary, and the signal line 50 and the shield electrode 53 need only be overlapped on one side, so that the signal line 50 is formed with the minimum processing line width. Is possible.
[0037]
As a result, a high aperture ratio can be realized while maintaining the same electrostatic shielding effect as that of the prior art, and display with improved display quality can be achieved by reducing image quality defects such as crosstalk and luminance unevenness.
[0038]
In addition, the portion of each signal line 50 that overlaps the auxiliary capacitance line 52 and the shield electrode 53 is cut out at a portion 50a on the through hole 82 side and is narrower than the other portions, and accordingly, only that much. The dimension of the auxiliary capacitor line 52 side end of the pixel connection electrode 78 and the through hole 82 of the organic insulating film 52 can be enlarged. Thereby, formation defects of the through holes 82 can be prevented, and an active matrix type liquid crystal display device with few point defect defects and high display quality can be realized.
[0039]
The present invention is not limited to the above-described embodiment, and various modifications can be made within the scope of the present invention. For example, according to the second embodiment shown in FIG. 5, the electrode length L1 of the first electrode portion 53a of the shield electrode 53 and the electrode length L2 of the second electrode portion 53b are equal to the first electrode portion 53a and the scanning line. The minimum distance between the second electrode portion 53b and the scanning line 62 is adjusted to be equal to each other, and the influences of two signal lines adjacent to each other with the pixel electrode 51 interposed therebetween are equal. Have been adjusted so that.
[0040]
Even with such a configuration, the same effects as those of the above-described first embodiment can be obtained. In addition, since the distance between the scanning line 62 and the first and second electrode portions 53a and 53b is adjusted to be the widest, the scanning line 62 and the shield electrode 53, that is, the auxiliary capacitance line 52 are short-circuited. Establishment can be reduced and the yield of the array substrate 10 can be further improved.
[0041]
Furthermore, according to the third embodiment shown in FIG. 6, the storage capacitor line 52 is omitted, and the scanning lines 62 are provided at the positions of the storage capacitor lines in the first and second embodiments, respectively. A part of each scanning line 62 is extended along each signal line 50 to form a shield electrode 53 having electrostatic shielding properties. Each shield electrode 53 has first and second electrode portions 53 a and 53 b extending in opposite directions from the scanning line 62. The second electrode part 53 b is formed longer than the first electrode part 53 a, and the extended end forms the gate electrode 18. The through holes 80 and 82 connecting the pixel connection electrode 78 and the pixel electrode 51 are provided so as to overlap the scanning line 62.
[0042]
Other configurations are the same as those of the first embodiment, and the same parts are denoted by the same reference numerals, and detailed description thereof is omitted. Also in the third embodiment, the same operational effects as those of the above-described embodiment can be obtained, the auxiliary capacitance line is not necessary, and a higher aperture ratio can be obtained.
[0043]
In addition, in the above-described embodiment, an active matrix liquid crystal display device using a polysilicon layer as a semiconductor layer has been described. However, the present invention uses another semiconductor layer such as an amorphous silicon layer as the semiconductor layer. The present invention can also be applied to an active matrix liquid crystal display device.
[0044]
【The invention's effect】
As described above in detail, according to the present invention, the shield electrode having electrostatic shielding formed by extending a part of the auxiliary capacitance line or the scanning line in the opposite direction is provided on one side edge portion of the signal line. The aperture ratio is reduced by narrowing the width by notching one side edge of each signal line that is located on the storage capacitor line or scanning line. Without this, the dimensions of the pixel connection electrode and the through hole of the organic insulating film can be increased. Accordingly, it is possible to realize an active matrix type liquid crystal display device that prevents formation of through-holes and has few point defects and high display quality.
[Brief description of the drawings]
FIG. 1 is a perspective view showing an active matrix liquid crystal display device according to a first embodiment of the invention.
FIG. 2 is a plan view showing a part of an array substrate of the liquid crystal display device.
3 is a cross-sectional view of the liquid crystal display device taken along line AA in FIG. 2;
4 is a cross-sectional view of the liquid crystal display device taken along line BB in FIG. 2;
FIG. 5 is a plan view showing an array substrate of a liquid crystal display device according to a second embodiment of the present invention.
FIG. 6 is a plan view showing an array substrate of a liquid crystal display device according to a third embodiment of the present invention.
[Explanation of symbols]
12 ... Array substrate 14 ... Counter substrate 18 ... TFT
50 ... signal line 51 ... pixel electrode 52 ... auxiliary capacitance line 53 ... shield electrode 53a ... first electrode part 53b ... second electrode part 60, 85 ... glass substrate 75 ... interlayer insulating film 78 ... pixel connection electrodes 80, 82 ... Through hole

Claims (3)

A first substrate and a second substrate disposed opposite to each other with a liquid crystal layer interposed therebetween;
The first substrate includes a plurality of scanning lines provided substantially in parallel on the insulating substrate, a plurality of signal lines provided on the scanning lines via an insulating film so as to intersect the scanning lines, A plurality of shield electrodes having electrostatic shielding properties extending from the scanning line and formed along the signal line, and provided in each region surrounded by the signal line and the scanning line, at least a part of the signal line being provided. And a plurality of pixel electrodes connected to the intersections of the signal lines and the scanning lines via the switching elements, and overlapping with the scanning lines,
Each of the shield electrodes has first and second electrode portions extending in a direction opposite to each other from the scanning line along the signal line,
The signal line which is located between the two pixel electrodes has a first side edge portion provided to overlap with one pixel electrode, the lower flow side of the liquid crystal orientation direction relative to the first side edge adjacent And has a second side edge provided overlapping the other pixel electrode,
The first and second electrode portions of the shield electrode are provided so as to overlap only with the other pixel electrode and the second side edge portion of the signal line,
The width of the other pixel electrode overlapping the second side edge of the signal line and the shield electrode is larger than the width of the one pixel electrode overlapping the first side edge of the signal line. An active matrix liquid crystal display device. Overlapping width between the first and second electrode portions and the other pixel electrode of each of the shield electrodes, according to claim 1, wherein greater than the overlap width between said signal line and said one pixel electrode Active matrix type liquid crystal display device. A connection electrode formed by patterning the same layer as the signal line, wherein the connection electrode has one end connected to the source electrode of the switching element and the other end positioned to overlap the scanning line And the other end is connected to the pixel electrode through a through hole located on the scanning line,
3. The side edge on the through-hole side of a portion of the signal line that overlaps with the scanning line and the shield electrode is cut out and formed thinner than the other portion. 2. An active matrix liquid crystal display device according to item 1.

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