JP4496724B2 - Liquid crystal display element - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a liquid crystal display element.
[0002]
[Prior art]
Some conventional active matrix liquid crystal display elements include a thin film transistor as a switching element (see, for example, Patent Document 1). In this case, the thin film transistor is a bottom gate type, and includes a gate electrode provided on the active substrate, a gate insulating film covering the gate electrode, a semiconductor thin film provided on the gate insulating film, and a central portion of the upper surface of the semiconductor thin film. A channel protective film provided, a pair of ohmic contact layers provided on the semiconductor thin film on both sides of the channel protective film and on both sides thereof, and a source electrode and a drain electrode provided on each ohmic contact layer ing.
[0003]
A pixel electrode is provided on the gate insulating film so as to be connected to the source electrode, and an overcoat film and an alignment film are provided on the pixel electrode and the thin film transistor. On the other hand, a counter electrode and an alignment film are provided on a surface of the counter substrate facing the active substrate. The active substrate and the counter substrate are bonded to each other through a substantially rectangular frame-shaped sealing material, and liquid crystal is sealed between the alignment films of both substrates inside the sealing material.
[0004]
[Patent Document 1]
Japanese Patent Laid-Open No. 2-151834
By the way, in the thin film transistor having the above structure, the thin film transistor is turned on when a positive voltage is applied to the gate electrode and turned off when a negative voltage is applied. Specifically, the thin film transistors arranged in each row are sequentially turned on, and when the thin film transistors arranged in a certain row are on, the thin film transistors arranged in other rows are off. Therefore, the time for which the thin film transistor is turned on is only an instant, and most of the time is in the off state. That is, most of the negative voltage is applied to the gate electrode of the thin film transistor.
[0006]
[Problems to be solved by the invention]
By the way, in the conventional liquid crystal display element, a gate insulating film, a semiconductor thin film (an insulator when the thin film transistor is off), a channel protective film, an overcoat film, and an alignment film are formed on the gate electrode between the source electrode and the drain electrode. However, since these are all insulators, when the thin film transistor is off, ionic impurities in the liquid crystal are formed on the alignment film made of polyimide (organic material) on the gate electrode to which a negative voltage is applied. It is attracted electrically. Examples of the ionic impurities in the liquid crystal include ionic impurities eluted from those formed by an organic material such as a sealing material, and ionic impurities mixed in the liquid crystal itself.
[0007]
The ionic impurities electrically attracted to the alignment film on the gate electrode to which a negative voltage is applied are adsorbed and accumulated on the surface of the alignment film, and further penetrate into the alignment film. There is a problem that the electric field caused by the accumulated charge of the ionic impurities affects the operation of the thin film transistor, and the thin film transistor may malfunction.
[0008]
Accordingly, an object of the present invention is to provide a liquid crystal display element capable of preventing a malfunction of a thin film transistor due to ionic impurities in the liquid crystal.
[0009]
[Means for Solving the Problems]
According to the first aspect of the present invention, a plurality of pixel electrodes arranged in a matrix on the inner surface, a plurality of thin film transistors respectively connected to the pixel electrodes, an overcoat film covering at least the thin film transistor, and the overcoat film And an active substrate having an alignment film formed on the pixel electrode, and a counter electrode on the inner surface, and a counter substrate having an alignment film covering the counter electrode are bonded to each other via a substantially rectangular frame-shaped sealing material, In a liquid crystal display element in which liquid crystal is sealed between the alignment films of the two substrates inside the sealing material, in order to prevent adsorption of ionic impurities in the liquid crystal on the side of the thin film transistor facing the counter substrate provided the ionic impurity adsorption preventing means, the ionic impurities adsorbed preventing means, the alignment film of the active substrate Has an opening provided in order to expose the overcoat film, corresponding to the opening of the alignment layer of the active substrate, that opening is provided on the alignment layer of the counter substrate It is a feature .
The invention according to claim 2 is the invention according to claim 1 , wherein the overcoat film is formed of an inorganic material.
According to a third aspect of the invention, a plurality of pixel electrodes arranged in a matrix on the inner surface, a plurality of thin film transistors respectively connected to the pixel electrodes, an overcoat film covering at least the thin film transistor, and the overcoat film And an active substrate having an alignment film formed on the pixel electrode, and a counter electrode on the inner surface, and a counter substrate having an alignment film covering the counter electrode are bonded to each other via a substantially rectangular frame-shaped sealing material, In the liquid crystal display element in which liquid crystal is sealed between the alignment films of the two substrates inside the sealing material, a first opening for exposing the overcoat film is provided in the alignment film of the active substrate, A second opening is provided in the alignment film of the counter substrate corresponding to the first opening.
The invention according to claim 4 is the invention according to claim 3, wherein the first opening and the second opening are provided so as to overlap each other .
According to the present invention, since the alignment film of the active substrate has the first opening and the alignment film of the counter substrate has the second opening corresponding to the first opening , The malfunction of the thin film transistor due to the ionic impurities in the liquid crystal can be prevented.
[0010]
DETAILED DESCRIPTION OF THE INVENTION
(First embodiment)
FIG. 1 shows a cross-sectional view of a main part of a liquid crystal display device as a first embodiment of the present invention. This liquid crystal display element is an active matrix type, and includes an active substrate 1 made of glass or the like and a counter substrate 21. A plurality of pixel electrodes 2 arranged in a matrix and a plurality of thin film transistors 3 respectively connected to these pixel electrodes 2 are provided on the inner surface side of the active substrate 1 (the surface facing the counter substrate 21). Yes.
[0011]
That is, the gate electrode 4 made of an aluminum-based metal or the like is provided at a predetermined location on the upper surface (inner surface) of the active substrate 1. A gate insulating film 5 made of silicon nitride is provided on the upper surface of the active substrate 1 including the gate electrode 4. A semiconductor thin film 6 made of intrinsic amorphous silicon is provided at a predetermined position on the upper surface of the gate insulating film 5 on the gate electrode 4. A channel protective film 7 made of silicon nitride is provided at substantially the center of the upper surface of the semiconductor thin film 6.
[0012]
Ohmic contact layers 8 and 9 made of n-type amorphous silicon are provided on both sides of the upper surface of the channel protective film 7 and on the upper surface of the semiconductor thin film 6 on both sides thereof. A source electrode 10 made of a chromium-based metal or the like is provided on the upper surface of one ohmic contact layer 8. A drain electrode 11 made of a chromium metal or the like is provided on the upper surface of the other ohmic contact layer 9.
[0013]
The gate electrode 4, the gate insulating film 5, the semiconductor thin film 6, the channel protective film 7, the ohmic contact layers 8 and 9, the source electrode 10 and the drain electrode 11 constitute a bottom gate type thin film transistor 3.
[0014]
A pixel electrode 2 made of ITO is provided at a predetermined location on the upper surface of the gate insulating film 5. In this case, the pixel electrode 2 is connected to the source electrode 10 and one ohmic contact layer 8. An overcoat film 12 made of silicon nitride is provided on the upper surface of the gate insulating film 5 including the thin film transistor 3. In this case, an opening 13 is provided in a region corresponding to most of the pixel electrode 2 of the overcoat film 12.
[0015]
An alignment film 14 made of polyimide is provided on the upper surfaces of the overcoat film 12 and the pixel electrode 2. In this case, an opening 15 is provided in the alignment film 14 in a region corresponding to the gate electrode 4. Here, the opening 15 may be formed at least in the alignment film 14 in a region corresponding to the space between the source electrode 10 and the drain electrode 11.
[0016]
On the other hand, the counter electrode 22 made of ITO is provided on the inner surface of the counter substrate 21 (the surface facing the active substrate 1), and the alignment film 23 made of polyimide is provided on the inner surface thereof. The active substrate 1 and the counter substrate 21 are bonded to each other via a substantially rectangular frame-shaped sealing material (not shown) made of an epoxy resin. Further, a liquid crystal 24 is sealed between the alignment films 14 and 23 of both the substrates 1 and 21 inside the sealing material.
[0017]
As described above, in this liquid crystal display element, the opening 15 is provided in the alignment film 14 in the region corresponding to the gate electrode 4, and therefore, in the region where the opening 15 exists, an overlayer made of silicon nitride (inorganic material) is formed. The coat film 12 is exposed and comes into contact with the liquid crystal 24. Since the overcoat film 12 made of silicon nitride (inorganic material) is difficult to electrically attract ionic impurities in the liquid crystal 24 and is difficult to adsorb ionic impurities, the thin film transistor caused by the ionic impurities in the liquid crystal 24 3 malfunctions can be prevented.
[0018]
(Second Embodiment)
FIG. 2 shows a cross-sectional view of a main part of a liquid crystal display device as a second embodiment of the present invention. In this liquid crystal display element, the difference from the case shown in FIG. 1 is that the alignment film 23 provided on the inner surface of the counter substrate 21 corresponds to the opening 15 of the alignment film 14 provided on the inner surface of the active substrate 1. It is the point which provided the opening part 31 in. Even if it does in this way, the effect similar to the case of the said 1st Embodiment can be acquired.
[0019]
(Third embodiment)
FIG. 3 shows a cross-sectional view of a main part of a liquid crystal display device as a third embodiment of the present invention. This liquid crystal display element is different from the case shown in FIG. 1 in that a columnar insulator 32 made of a resin or the like is provided on the upper surface of the overcoat film 12 in a region corresponding to the gate electrode 4. In this case, the alignment film 14 is provided on the surface of the columnar insulator 32, and this alignment film 14 is brought into contact with the alignment film 23 of the counter substrate 21, but the alignment film 14 is not formed on the surface of the columnar insulator 32. The upper surface of the columnar insulator 32 may be brought into contact with the alignment film 23 of the counter substrate 21.
[0020]
In this case, since the liquid crystal 24 does not exist between the alignment films 14 and 23 in the region corresponding to the gate electrode 4 due to the presence of the columnar insulator 32, the thin film transistor caused by the ionic impurities in the liquid crystal 24. 3 malfunctions can be prevented. Further, by controlling the height of the columnar insulator 32, the columnar insulator 32 can be given a role as a gap control spacer. Here, the columnar insulator 32 may be formed on at least the upper surface of the overcoat film 12 in a region corresponding to the space between the source electrode 10 and the drain electrode 11.
[0021]
(Fourth embodiment)
FIG. 4 is a cross-sectional view of a main part of a liquid crystal display device as a fourth embodiment of the present invention. In this liquid crystal display element, the difference from the case shown in FIG. 1 is that the opening 15 is not formed in the alignment film 14 provided on the inner surface of the active substrate 1, and instead, in the region corresponding to the channel protective film 7. This is that a ground potential ionic impurity adsorption preventing electrode 33 made of an aluminum-based metal or the like is provided between the overcoat film 12 and the alignment film 14.
[0022]
In this case, since the electric field from the gate electrode 4 is shielded by the ionic impurity adsorption preventing electrode 33 at the ground potential, the ions in the liquid crystal 24 are formed on the alignment film 14 on the ionic impurity adsorption preventing electrode 33. Adsorption or accumulation of ionic impurities does not occur, and therefore malfunction of the thin film transistor 3 due to ionic impurities in the liquid crystal 24 can be prevented. Here, the ionic impurity adsorption preventing electrode 33 may be formed at least between the overcoat film 12 and the alignment film 14 in a region corresponding to between the source electrode 10 and the drain electrode 11.
[0023]
(Other embodiments)
In each of the above-described embodiments, the channel protection type amorphous silicon thin film transistor has been described. However, the present invention is not limited to this, and a channel etch type amorphous silicon thin film transistor, a bottom gate type polysilicon thin film transistor, or the like may be used.
[0024]
【The invention's effect】
As described above, according to the present invention, the alignment film of the active substrate has the first opening, and the alignment film of the counter substrate has the second opening corresponding to the first opening. Thus, malfunction of the thin film transistor due to ionic impurities in the liquid crystal can be prevented.
[Brief description of the drawings]
FIG. 1 is a cross-sectional view of a main part of a liquid crystal display device as a first embodiment of the invention.
FIG. 2 is a cross-sectional view of a main part of a liquid crystal display device as a second embodiment of the invention.
FIG. 3 is a cross-sectional view of a main part of a liquid crystal display device as a third embodiment of the invention.
FIG. 4 is a cross-sectional view of a main part of a liquid crystal display device as a fourth embodiment of the invention.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 Active substrate 2 Pixel electrode 3 Thin film transistor 4 Gate electrode 5 Gate insulating film 6 Semiconductor thin film 7 Channel protective film 8, 9 Ohmic contact layer 10 Source electrode 11 Drain electrode 12 Overcoat film 14 Orientation film 15 Opening part 21 Opposite substrate 22 Counter electrode 23 Alignment film 24 Liquid crystal 31 Opening 32 Columnar insulator 33 Electrode for preventing adsorption of ionic impurities

Claims (4)

A plurality of pixel electrodes arranged in a matrix on the inner surface, a plurality of thin film transistors respectively connected to these pixel electrodes, an overcoat film covering at least the thin film transistor, and formed on the overcoat film and the pixel electrode An active substrate having an alignment film, a counter electrode on the inner surface, and a counter substrate having an alignment film covering the counter electrode are bonded together via a substantially rectangular frame-shaped sealing material, and both the substrates inside the sealing material In the liquid crystal display element in which liquid crystal is sealed between the alignment films, ionic impurity adsorption preventing means for preventing adsorption of ionic impurities in the liquid crystal is provided on a side of the thin film transistor facing the counter substrate. is, the ionic impurities adsorbed prevention means, the overcoat layer to the alignment layer of the active substrate Has a first opening provided in order to out, in response to first opening of the alignment layer of the active substrate, the second opening is provided on the alignment layer of the counter substrate A liquid crystal display element characterized by comprising: 2. The liquid crystal display element according to claim 1 , wherein the overcoat film is made of an inorganic material. A plurality of pixel electrodes arranged in a matrix on the inner surface, a plurality of thin film transistors respectively connected to these pixel electrodes, an overcoat film covering at least the thin film transistor, formed on the overcoat film and the pixel electrode An active substrate having an alignment film, a counter electrode on the inner surface, and a counter substrate having an alignment film covering the counter electrode are bonded together via a substantially rectangular frame-shaped sealing material, and both the substrates inside the sealing material In the liquid crystal display element in which liquid crystal is sealed between the alignment films, a first opening for exposing the overcoat film is provided in the alignment film of the active substrate, and the first opening corresponds to the first opening. A liquid crystal display element, wherein a second opening is provided in the alignment film of the counter substrate. 4. The liquid crystal display element according to claim 3, wherein the first opening and the second opening are provided so as to overlap each other.

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