JP3723389B2 - Active matrix display device - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a liquid crystal display (LCD), and more particularly to an active matrix type TFT using a thin film transistor (TFT) and having a TFT structure suitable for miniaturization.
[0002]
[Prior art]
An LCD is a display device in which liquid crystal is injected between two opposing first and second substrates. A TFT serving as a switching element and a pixel electrode formed for each pixel are arranged on the first substrate, and a counter electrode is arranged on the second substrate. FIG. 4 is a plan view showing a first substrate of a conventional active matrix LCD. A plurality of data lines 51 extending in the column direction are arranged in parallel, and a plurality of gate lines 52 intersecting with the data lines 51 and extending in the row direction are arranged in parallel. A TFT 53 and a pixel electrode 54 are arranged corresponding to each intersection of the data line 51 and the gate line 52. FIG. 4 shows a delta arrangement in which adjacent rows are shifted from each other.
[0003]
The TFT 53 has a semiconductor film 62 connected to the data line 51 via a contact 61, and this semiconductor film 62 is further connected to the pixel electrode 54 via a contact 63. The semiconductor film 62 intersects with the gate line 52 at two places to form gates 64 and 65, respectively.
[0004]
When a predetermined voltage is applied to the gate line 52, a channel is formed in the gates 64 and 65 of the semiconductor film 62 of the TFT 53 to become conductive, and the data voltage applied to the data line 51 is applied to the pixel electrode 54. The liquid crystal is driven by the electric field generated by the above and displays according to the data voltage.
[0005]
In this specification, the TFT structure having two gates as described above is referred to as a double gate. By making the TFT 53 into a double gate, when the TFT is made non-conductive, high-resistance TFTs are connected in series, so that an improper current that leaks unintentionally when non-conductive, that is, an off-leakage current can be reduced. effective.
[0006]
The TFT 53 further has a gate electrode 66. The gate electrode 66 is a conductive film formed on the opposite side to the gate line 52 across the semiconductor film 62 in a cross-sectional view. The gate electrode 66 is connected to the gate line 52 through a contact 67 and overlaps with the gates 64 and 65. are doing.
[0007]
In this specification, such a structure in which the semiconductor film 62 of the TFT 53 is sandwiched between the gate line 52 and the gate electrode 66 is referred to as a dual gate. Since the gate electrode 66 is connected to the gate line 52, it has the same potential as the gate line 52. By using dual gates, a channel is formed in the semiconductor film 62 by the electric field of each of the upper and lower gates. Therefore, compared to a TFT having a structure without the gate electrode 66, the resistance during conduction is small, and the back channel Therefore, the off-leakage current can be reduced.
[0008]
The semiconductor film 62 has a capacitor region 62 a that overlaps with the pixel electrode 54. An auxiliary capacitance electrode 55 having a wide area extending in the row direction and overlapping with the capacitance area 62a on the pixel electrode 54 is disposed. The auxiliary capacitance electrode 55 is formed in the same layer as the gate line 52, forms an auxiliary capacitance with the capacitance region 62 of the semiconductor film 62, and plays a role of holding a voltage applied to the pixel electrode 54.
[0009]
In addition, a counter electrode and a black matrix are formed on the second substrate arranged to face the first substrate having the above structure. The counter electrode is formed on the entire surface so as to face the plurality of pixel electrodes. The black matrix faces the data line 51 and the TFT 53 in order to prevent light from leaking from between the data line 51 and the pixel electrode 54, or to prevent leakage current from flowing due to light hitting the TFT 53. It is a light-shielding film formed in the region. The black matrix is formed to be about 6 μm thicker than the data line 51 so that light does not leak even if misalignment between the substrates occurs. In FIG. 4, the black matrix is not shown and its width is represented as BM for the sake of simplification of the drawing.
[0010]
FIG. 5 is a cross-sectional view taken along line AA ′ in FIG. The auxiliary capacitance electrode 55 is disposed on the glass substrate 71, and the semiconductor film 62 of the TFT 53 is disposed via the first gate insulating film 72. A data line 51 is arranged on the semiconductor film 62 with an interlayer insulating film 73 interposed therebetween. Further, a planarizing film 74 and the like are formed, the pixel electrode 54 is disposed, and an alignment film 75 is formed to cover the plurality of pixel electrodes 54. Further, a liquid crystal and a counter substrate (not shown) are disposed thereon. The data line 51 and the pixel electrode 54 are formed separated by a predetermined distance d in order to reduce the parasitic capacitance. The distance d is, for example, about 1 μm. The black matrix is formed across the pixel electrode 54 and the pixel electrode 54 ′ adjacent to the pixel electrode 54 in order to prevent light leakage from the interval d.
[0011]
In recent years, active matrix display devices have been adopted as display devices for portable electronic devices, such as digital still cameras and digital video camera finders, but the number of pixels has been maintained for installation in portable devices. There is a demand for reducing the screen size and making it finer.
[0012]
[Problems to be solved by the invention]
The capacitance value of the auxiliary capacitance is proportional to the area where the auxiliary capacitance electrode 55 and the semiconductor film 62 overlap. When the screen size is reduced while maintaining the number of pixels, simply by reducing the size in a similar manner and miniaturizing, the capacity value of the auxiliary capacitance becomes insufficient with the reduction, and the voltage applied to the pixel electrode 54 is appropriately set. It can no longer be held.
[0013]
Therefore, if an attempt is made to secure the capacity of the auxiliary capacity even if the pixel size is reduced, the proportion of the area occupied by the auxiliary capacity electrode 55 in the pixel relatively increases. However, since the auxiliary capacitance electrode 55 that forms the auxiliary capacitance is formed of a metal film such as chromium, the region where the auxiliary capacitance electrode 55 is formed does not transmit light. Therefore, if the area of the auxiliary capacitor is made constant while reducing the pixel size, there arises a problem that the aperture ratio of the pixel is lowered.
[0014]
Accordingly, an object of the present invention is to provide an LCD having an auxiliary capacitance electrode with a higher aperture ratio while ensuring a constant area of the auxiliary capacitance.
[0015]
[Means for Solving the Problems]
The present invention has been made in order to solve the above-described problem, and is formed in a matrix corresponding to each of intersections of gate lines and data lines, a plurality of gate lines arranged in the row direction, a plurality of data lines arranged in the column direction, A thin film transistor having a semiconductor electrode which is connected to the data line and the pixel electrode and intersects with a part of the gate line, and extends in a direction parallel to the gate line and is opposed to the semiconductor film of the thin film transistor. In an active matrix display device having a storage capacitor electrode for forming a capacitor and switching pixels using a thin film transistor, the storage capacitor electrode and the semiconductor film each have a branch portion extending along the data line. Device.
[0016]
The branch portion of the auxiliary capacitance electrode is disposed so as to overlap with at least a part of the data line, and the branch portion of the semiconductor film is disposed so as not to overlap with the data line.
[0017]
In addition, a light-shielding portion with a thick data line is formed in a region between the end of the branch portion of the auxiliary capacitance electrode and the gate line in the adjacent row. The parts are superimposed.
[0018]
DETAILED DESCRIPTION OF THE INVENTION
FIG. 1 is a plan view of an LCD according to the first embodiment of the present invention. A plurality of data lines 1 extending in the column direction are arranged in parallel, and a plurality of gate lines 2 extending in the row direction intersecting the data lines 1 are arranged in parallel. A TFT 3 and a pixel electrode 4 are arranged corresponding to each intersection of the data line 1 and the gate line 2.
[0019]
The gate line 2 and the capacitor electrode 21 are disposed on the first substrate, and the semiconductor film 12 is disposed with an insulating film interposed therebetween. Further, the data line 1 is arranged through an insulating film. The data line 1 is connected to the semiconductor film 12 of the TFT 3 through the contact 11 and further connected to the pixel electrode 4 through the contact 13. The TFT 3 has a so-called double gate structure in which it intersects with the gate line 2 at two points, and each has a gate 14 and a gate 15. Further, it has a gate electrode 16 disposed in a layer opposite to the gate line 2 with the semiconductor film 12 interposed therebetween, and the gate electrode 16 is connected to the gate line 2 through a contact 17 in a so-called dual gate structure. is there.
[0020]
The above points are the same as those of the conventional LCD. This embodiment is characterized by the shape of the auxiliary capacitance electrode 21 indicated by a thick solid line and the capacitance region 12a of the TFT 3 indicated by a one-dot chain line. The auxiliary capacitance electrode 21 is made of a metal such as chromium formed in the same layer as the gate electrode 2. The auxiliary capacitance electrodes 21 are connected to each other in the row direction, and have a branch portion 21 a extending in the column direction along the data line 1 in a region overlapping the pixel electrode 4 indicated by a dotted line. The capacitor region 12a of the semiconductor film 12 is also continuously formed from the region where the TFT 3 is formed so as to extend in the column direction along the data line 1 in accordance with the shapes of the auxiliary capacitor electrode 21 and the branch portion 21a. Have
[0021]
The tip portion 21b of the auxiliary capacitance branch portion 12a is formed indented to prevent a short circuit between the semiconductor film 12 ′ of the TFT 3 ′ in the next row and the capacitance region 12a, and the auxiliary capacitance electrode 21 is also formed in the capacitance region 12a. In addition, it has the same shape.
[0022]
By forming the auxiliary capacitance electrode 21 as in the present embodiment, it is possible to minimize the decrease in the aperture ratio while securing the area of the auxiliary capacitance electrode. This is because the side portion of the data line 1 is a region where a black matrix is conventionally formed on the counter substrate and is originally shielded from light. The black matrix is formed thicker than the data line 1 in order to cope with misalignment. Therefore, by forming the auxiliary capacitance electrode 21 along the data line 1, the light shielding regions can be concentrated at the same place, so that the decrease in the aperture ratio can be minimized.
[0023]
Further, the auxiliary capacitor electrode 21 and the capacitor region 12 a have a protrusion 21 c above the drawing along the bent portion of the data line 1. Since the black matrix for shielding the TFT 3 is formed in the area indicated by BM, the shielding area is also formed here. If the TFT 3 is exposed to light, it may cause a malfunction. Therefore, a black matrix is formed on the TFT 3, and the portion where the black matrix and the protruding portion 21c are overlapped increases the area of the capacitance as described above. However, it does not lead to a decrease in aperture ratio.
[0024]
2 is a cross-sectional view taken along line AA ′ of FIG. The auxiliary capacitor electrode 21 is formed on the first substrate 31, and the capacitor region 12 a of the semiconductor film 12 is formed thereon via the insulating film 32. A data line 1 is formed thereon via an insulating film 33. A pixel electrode 4 is formed thereon via a flattening insulating film 34, and an alignment film 35 is further formed.
[0025]
When the facing area between the data line 1 and the pixel electrode 4 is increased, a capacitance is generated here, and the response speed of the LCD is lowered. Therefore, the data line 1 and the pixel electrode 4 are formed apart from each other by a predetermined distance d. Yes. The black matrix formed along the data line described in the section of the prior art is formed because it is necessary to block light leaking from the gap. The storage capacitor electrode 21 of the present embodiment is formed so as to overlap with the region below the data line 1. Therefore, no light leaks from the right side of the data line 1 in the drawing. Therefore, the black matrix BM need not be disposed on the side of the data line 1 where the auxiliary capacitance electrode 21 is formed, and may be disposed only on the adjacent pixel electrode 4a side. Since the black matrix is formed on the counter substrate side, illustration is omitted, but the black matrix is arranged on the counter substrate side in the region indicated by BM in the drawing.
[0026]
It is desirable that the auxiliary capacitance electrode 21 and the data line 1 be separated by 0.5 μm or more in the thickness direction. In the present embodiment, the auxiliary capacitance electrode 21 and the data line 1 are separated by about 0.7 μm in the thickness direction by the interlayer insulating films 32 and 33. Therefore, a capacitance value generated between the auxiliary capacitance electrode 21 and the data line 1 is small, and a predetermined voltage is continuously applied to the auxiliary capacitance electrode 21, so that a capacitance generated between the data line 1 and the auxiliary capacitance electrode 21. It is possible to reduce signal rounding due to. In this embodiment, the insulating film 32 is 0.1 μm and the insulating film 33 is 0.6 μm.
[0027]
In addition, since the capacitance between the data line 1 and the auxiliary capacitance electrode 21 has never been too small, the width of the overlap between the data line 1 and the auxiliary capacitance electrode 21 is a manufacturing error such as a mask shift at the time of manufacturing. It is better to superimpose only. By superimposing at least the manufacturing error, light does not leak from between the data line and the auxiliary capacitance electrode 21 even if mask displacement occurs. Further, even if the overlapping width is equal to or larger than the manufacturing error, the capacitance between the data line 1 and the auxiliary capacitance electrode 21 is merely increased unnecessarily. Therefore, it is preferable that the width for superimposing these is about the manufacturing error. Although a specific numerical value of the width to be overlapped varies depending on a manufacturing error, it may be overlapped by, for example, about 1 μm to 3 μm.
[0028]
FIG. 3 is a plan view showing a second embodiment of the present invention. The same points as those in the first embodiment are denoted by the same reference numerals and description thereof is omitted. The present embodiment is characterized in that the data line 1 has a light shielding region 1a formed thick. Since the auxiliary capacitance electrode 21 is generally formed in the same layer as the data line 2, the branch portion 21 a of the auxiliary capacitance electrode 21 needs to be formed at a predetermined interval from the gate line 2. As described in the first embodiment, the black matrix is not formed in the region facing the auxiliary capacitance electrode 21 side of the data line 1, so that leakage occurs from the gap between the branch portion 21 a of the auxiliary capacitance electrode 21 and the gate line 2. The light to be emitted may be a problem. Of course, a black matrix may be formed here, but since the black matrix is formed on the counter substrate side, a substrate bonding error occurs, and the black matrix needs to be designed larger than a necessary region. On the other hand, if the light shielding region 1a is formed on the data line 1 as in this embodiment, it is not necessary to consider the substrate bonding error, and the auxiliary capacitance electrode 21 and the gate line can be formed with only the minimum necessary light shielding region. Light leakage from the gap between the two can be prevented.
[0029]
The above embodiment has been described by exemplifying an LCD using a double-gate and dual-gate TFT. However, the present invention is not limited to this, and a single-gate and single-layer TFT may be used.
[0030]
In the above embodiment, the delta arrangement in which the pixel electrodes 4 are shifted by 1/2 in the row direction is illustrated. However, the present invention is not limited to this, and a stripe arrangement in which the pixels are linearly arranged may be used.
[0031]
【The invention's effect】
As described above, according to the present invention, since the capacitor electrode and the semiconductor film each have a branch portion extending along the data line, the light shielding regions can be integrated and the aperture ratio of the pixel can be improved.
[0032]
Since the branch portion of the auxiliary capacitance electrode is arranged so as to overlap with at least a part of the data line, light does not leak from between the data line and the auxiliary capacitance electrode.
[0033]
Further, since the branch portion of the semiconductor film is disposed without overlapping with the data line, the parasitic capacitance generated here can be minimized.
[0034]
In addition, a light-shielding portion having a thick data line is formed in a region between the branch portion end of the auxiliary capacitance electrode and the gate line in the adjacent row, and this light-shielding portion is aligned with the gate line and the auxiliary capacitance electrode. Since the portions overlap, light does not leak from between the end of the auxiliary capacitance electrode and the gate line.
[0035]
By the way, in a large display device with one large pixel, the decrease in the aperture ratio due to the black matrix and the auxiliary capacitor is not so much a problem, and the ratio of the area occupied by the auxiliary capacitor to one pixel is compared with a small display device. And low. Therefore, the present invention is a 4-inch type or smaller, for example, a small display device such as a 2-inch type or a 1.5-inch type, or a high-definition display device such as a 4-inch type or a 6-inch type such as an XGA. It is most effective when applied to a display device in which one pixel is small. Of course, the present invention can also be applied to a large display device, and the aperture ratio can be improved.
[Brief description of the drawings]
FIG. 1 is a plan view of a display device according to a first embodiment.
FIG. 2 is a cross-sectional view of the display device according to the first embodiment.
FIG. 3 is a plan view of a display device according to a second embodiment.
FIG. 4 is a plan view of a conventional display device.
FIG. 5 is a cross-sectional view of a conventional display device.
[Explanation of symbols]
1 data line, 2 gate line,
3 TFT, 4 pixel electrode,
11, 13, 17 contact, 12 semiconductor film,
14,15 gate, 21 auxiliary capacitance electrode

Claims (2)

A plurality of gate lines arranged in the row direction;
A plurality of data lines arranged in the column direction;
Pixel electrodes arranged in a matrix corresponding to the intersections of the gate lines and the data lines;
A thin film transistor having a semiconductor film connected to the data line and the pixel electrode and intersecting a part of the gate line;
An auxiliary capacitance electrode extending in a direction parallel to the gate line and forming an auxiliary capacitance facing the semiconductor film of the thin film transistor;
In an active matrix display device that switches the pixel using the thin film transistor,
The storage capacitor electrode and the semiconductor film, bifurcation and possess respectively extending in the data line direction parallel
A branch portion of the auxiliary capacitance electrode is disposed so as to overlap at least a part of the data line;
An active matrix display device, wherein the branch portion of the semiconductor film is arranged without overlapping with the data line. In a region between the branch portion end of the auxiliary capacitance electrode and the gate line of the adjacent row, a light shielding portion in which the data line is formed thick is formed,
2. The active matrix display device according to claim 1, wherein the light shielding portion partially overlaps with the gate line and the auxiliary capacitance electrode.

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