JPH0545640A - Liquid crystal display - Google Patents

Abstract

PURPOSE:To improve an opening rate and to brighten a display by forming picture element electrodes via an insulating layer in nonlinear switching elements and the upper parts of the wiring electrodes thereof. CONSTITUTION:A liquid crystal dispersion is applied on a transparent electrode 14 formed on a substrate 1 and is then thermally cured to form a liquid crystal layer 13. On the other hand, TFTs of a reverse stagger type acting as switching elements are formed for each of picture elements to execute the switching operation of the picture element electrodes 9 to which the respective TFTs correspond according to input data. A film consisting of SiNx is formed as the insulating layer in the upper part formed with these TFTs and through-holes 17 are formed in the drain electrode parts of the TFTs. The film consisting of Al is formed in the upper part thereof and is patterned with the picture element electrodes 9. The film consisting of the SiNx is further formed thereon as a passivation layer. The regions which are ineffective for the display are eliminated in this way except that the spacings to allow the electrical sepn. of the picture element electrodes 9 and the picture element electrodes 9 are taken.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a liquid crystal display device that reduces defects during electrode pattern formation and has a bright display.

[0002]

2. Description of the Related Art One of the methods for performing color display is to form a color filter in accordance with a transparent electrode pattern, install a light source on the back surface, and use the transmitted light to recognize the color of the color filter. There is. However, this display method requires an illuminating device, and since it is usually used in the TN mode or STN mode in which two polarizers are installed, the display tends to be dark, so it is necessary to make the illumination very bright, and low power consumption is required. There is a drawback in that it is very difficult to achieve thinning and thinning. In addition, a TFT (Th
An in-film transistor) is provided corresponding to each pixel, a color filter is installed, and a method of realizing color display by light from a light source installed on the back surface also has the same drawbacks as described above. On the other hand, in recent years, polymer dispersion type liquid crystal display devices in which liquid crystals are dispersed in a polymer matrix have been proposed, but these are not easily affected by the thickness of the liquid crystal layer and can have a large area. Has attracted attention because it has features such as not requiring. Further, Japanese Patent Application Laid-Open No. 1-241520 discloses a technique of using this polymer-dispersed liquid crystal to perform color display in correspondence with a color filter. However, the method described in this publication also has the following drawbacks. That is, the state in which the liquid crystal transmits light is “ON”, and the state in which the liquid crystal is scattered is “O”.
Since it is "FF", even when it is "OFF", the front side (display surface side)
Light incident on the LCD is scattered by the liquid crystal layer and transmitted through the color filter, so that it is difficult to obtain sufficient blackness in a "black" display, and it is also difficult to obtain a sufficient contrast ratio. In the case of the structure using the light source from the back surface, the contrast ratio can be improved to some extent by increasing the brightness of this light source, but the display of "black" becomes whitish. Further, if the structure uses reflected light without using the light source from the back surface, the contrast ratio becomes particularly small. In addition, IEICE technique EI
D89-103 is formed by an ultraviolet polymerizable compound 3
By using a polymer network type liquid crystal in which liquid crystal is dispersed in a three-dimensional network structure as a liquid crystal layer of a display element,
It has been shown that advantages such as low voltage driving and excellent steepness can be obtained. However, the document makes no mention of implementing a color display. In addition, Japan Display
ay '89, p572-575 discloses a technique in which an encapsulating liquid crystal is driven by a TFT and a display is performed using an illuminating means. However, since this technique observes liquid crystal particles with transmitted light, color display is not possible. Not done. Therefore,
The applicant of the present invention can obtain a sufficient contrast ratio without using a light source from the back side first, enables color display without requiring illumination from the back side, and is even thinner than the back lighting device. A method of providing a color liquid crystal display device that can be realized is presented. Display methods that utilize the light scattering of the liquid crystal layer include PC type (Phase Change: phase transition), DS type (Dynamic Scattering), thermal effect type, or PDLC (polymer dispersed type liquid crystal or polymer network type liquid crystal) However, when PDLC is used, it is easy to obtain stable display quality because a rubbing process for aligning liquid crystal molecules is not necessary. However, since the PDLC has poor steepness as compared with the conventional STN type liquid crystal or the like, when performing simple matrix drive such as the STN type liquid crystal display, the duty ratio is limited to about 1/60 to 1/100. Therefore, it is difficult to increase the screen size of the display. Therefore, if a non-linear element such as a TFT, a TFD, or an MIM is used for each pixel, the steepness as described above is not necessary, so that stable display quality, a large screen, and a high-definition screen can be realized. come. However, when the TFT is used as the non-linear switching element for each pixel, the following problems occur. That is, since it is not possible to form pixel electrodes in the regions where the TFTs are formed, the gate wirings and the source wirings, and the regions in which the intervals required for their manufacture are aligned, the ratio of the pixel electrodes to the display area ( The aperture ratio) is lowered and the display surface becomes dark. In particular, the higher the resolution is, the more the aperture ratio is significantly reduced. Further, when a liquid crystal display device is normally driven by a TFT, it is necessary to build a capacitor in parallel with the liquid crystal in order to hold the applied voltage written through the source line until the next writing,
The additional capacity as shown in FIG. 1A and the storage capacity method as shown in FIG. 1B are adopted. However, when the additional capacitance method of (a) is adopted as the method of obtaining such capacitance, the capacitance of the gate line increases, the load at the time of driving the gate increases, and the delay of the gate line increases. On the other hand, when the storage capacitance method of (b) is adopted, the capacitance of the gate line does not increase, but when the method of forming the storage capacitance forming electrode at the same time as the gate electrode is used, the number of intersections of the wiring is 2 It doubles, which is a disadvantage in terms of yield. Further, when a bottom gate type TFT is adopted as the non-linear switching element, disconnection or interlayer short circuit easily occurs at the intersection of the gate line and the source line, which is one of the causes that the yield is not improved.

[0003]

[Objective] The present invention provides a structure capable of forming a storage capacitor in a reflective / direct-viewing type liquid crystal display device while preventing a decrease in aperture ratio and without causing a decrease in yield. In addition, regardless of whether the liquid crystal display device is of a reflective type, a direct-view type, or a transmissive type, when a bottom gate type TFT is used as a non-linear switching element, disconnection at a crossing of a gate line and a source line or a short circuit between layers occurs. It is intended to provide a structure that lowers and improves the yield.

[0004]

[Structure] Conventionally, in a liquid crystal display device using a TFT and a TFD, the structure shown in FIGS. 2C and 2D has been used, so that the region where the TFT or the TFD is formed and the source line are Since the pixel electrodes cannot be formed in the formed regions and the manufacturing margins necessary for actually forming these regions, the aperture ratio is lowered. Therefore, according to the present invention, the pixel electrode provided on the back substrate is formed on the flattening, insulating or passivation layer of the non-linear switching element formed on the back substrate through a contact hole or a through hole, so that the pixel electrode of FIG. As shown in (a) and (b), since the non-linear switching element / wiring is formed under the pixel electrode, the aperture ratio can be improved. In FIG. 2, the bottom gate type TFT has been described as an example, but the same effect can be obtained in the case of a positive stagger type TFT or a planar type TFT. In FIG. 2, 1 is a substrate, 2 is a gate electrode, 3 is a gate insulating film, 4 is amorphous silicon, 5
Is an ohmic layer, 6 is a channel stopper, 7 is a source electrode, 8 is a drain electrode, and 9 is a pixel electrode. Also,
Reference numeral 19 is a metal layer a, 20 is a metal layer b, and 11 is an insulating layer.

TF is used as a non-linear switching element.
When T is adopted, disconnection or interlayer short circuit easily occurs at the intersection of the gate line and the source line, which is one of the reasons why the yield is not improved. Therefore, the present invention adopts a configuration in which the TFT is formed on an insulating layer formed on a substrate and the gate electrode of the TFT and its wiring portion are embedded in the insulating layer (FIG. 3).
Since the step difference due to the gate wiring is not generated, it is possible to prevent disconnection of the source line formed above the gate wiring via the insulating layer.

Further, when a liquid crystal display device is driven by a TFT or TFD, it is necessary to install a capacitor in parallel with the liquid crystal in order to hold the applied voltage written through the source line until the next writing. The additional capacity as shown in (a) and the storage capacity method as shown in (b) are adopted. However, when the additional capacitance method of (a) is adopted, the capacitance of the gate line increases, the load at the time of driving the gate increases, and the delay of the gate line increases. On the other hand, when the storage capacitance method of (b) is adopted, the capacitance of the gate line does not increase, but when the method of forming the storage capacitance forming electrode at the same time as the gate electrode is used, the number of intersections of the wiring is 2 There is a possibility that it will be doubled and the yield will decrease. Therefore, in order to solve the above problems, the present invention provides an electrode for forming a storage capacitor under the TFT or TFD via an insulating layer, and connects the electrode for forming the storage capacitor and the electrode of the counter substrate. Then, a means of functioning as a storage capacity is adopted (see FIG. 4). That is, the electrode does not need to be patterned for each pixel, and a step is not formed on the electrode because of the electrode. Further, this storage capacity can be appropriately controlled by the film thickness of the insulating layer and its material.

A liquid crystal display device having a structure in which a liquid crystal layer is sandwiched between a pair of substrates provided with liquid crystal driving electrodes of the present invention, and each pixel is driven by a non-linear switching element provided for each pixel is specific. The structure is not limited to the above. Further, in the case of a direct-viewing type liquid crystal display device, that is, when the user of the display device faces the front side and the opposite side is the back side,
A back substrate provided with a structure that absorbs light transmitted through the front substrate, or a reflection type liquid crystal display device, that is, to reflect light transmitted through the front substrate on the front or back surface of the back substrate. A liquid crystal display device of the present invention is also provided with such a structure.

Further, the constitution of the liquid crystal phase and the kind of material constituting the liquid crystal phase are not particularly limited, but for example, (a) a polymer in which liquid crystal is dispersed so as to be surrounded by a three-dimensional network structure formed of the polymer. Examples thereof include a film composed of a network type liquid crystal layer or (b) a film composed of a polymer dispersed liquid crystal phase in which particulate liquid crystals are dispersed in a polymer matrix. Further, a color liquid crystal display device in which a dye is dispersed in these liquid crystal phases may be used.

The present invention will be described in detail below based on examples. Embodiment 1 FIG. 5 shows an embodiment of a reflective liquid crystal display device according to the present invention. Although glass was used as the substrate 1,
Transparent polymer substrates such as polyethylene terephthalate, polycarbonate, polyether sulfone, polyarylate and the like can also be used. As the liquid crystal layer 13, the following so-called polymer dispersion type liquid crystal was used. A cyanobiphenyl nematic liquid crystal was mixed at a ratio of 4: 1 by weight to a liquid prepared by mixing a predetermined amount of an epoxy resin and a curing agent. A liquid crystal dispersion prepared by uniformly mixing this with a homogenizer was applied onto the transparent electrode 14 and then heated and cured at 80 ° C. to form a liquid crystal layer. Instead of the epoxy resin, polyvinyl alcohol, a bifunctional photocurable acrylic resin, or the like can be used. As the liquid crystal, a normal nematic liquid crystal such as an ester type, a pyrimidine type, or a mixture thereof can be used in addition to the cyanobiphenyl type.
A suitable size of the liquid crystal particles is about 10 μm or less, and a suitable content is about 10 to 50 wt%. The thickness of the liquid crystal layer was about 15 μm. TFTs acting as switching elements are formed on the substrate 1'for each pixel, and switch the corresponding pixel electrode 9 in accordance with the input data. SiNx is formed as an insulating layer with a film thickness of 2 μm on the upper portion of these TFTs, and a through hole is formed in the drain electrode portion 8 of the TFT. On top of this, 1.
A film having a film thickness of 5 μm is formed, and the pixel electrode 9 is patterned. Further, a film of SiNx having a film thickness of 5000 Å was formed on the upper portion to form a passivation layer. Although the inverse stagger type TFT is used as the switching element in this embodiment, it is also possible to use another type of TFT or another switching element such as MIM. The thickness of the insulating layer is 1
-5 μm is suitable, but preferably 2-3 μm, and other materials such as SiO ₂ can be used. When forming a through hole in this, the angle between the inner surface of the through hole and the substrate surface is preferably 30 to 70 °, and more preferably 45 to 60 °. The film thickness of Al is preferably 5000 Å to 2 μm, and more preferably 1 to 1.5 μm. The material of the pixel electrode 9 is Cu
And Cr can be used. The film thickness of the passivation layer on the pixel electrode 9 is preferably 2000Å to 2 μm,
More preferably, it is 5000 Å to 1 μm.
Although a reflective liquid crystal display device is taken as an example in this embodiment, in the case of a direct-view liquid crystal display device, a light absorption layer may be provided on the pixel electrode, which is formed on the passivation layer. It doesn't matter.

Embodiment 2 FIG. 6 shows an embodiment of a direct-view type color liquid crystal display device according to the present invention. A so-called polymer network type liquid crystal was used as the liquid crystal layer 13 in the same manner as in Example 1. The procedure for producing the liquid crystal layer 13 is as follows. 15 of polymethylmethacrylate resin (PMMA)
The nematic liquid crystal was added to the wt% toluene solution at a weight ratio of 10: 1. Uniform by stirring, transparent electrode 1
A liquid crystal layer is formed by applying the coating liquid on 4 and heating to remove the solvent. Examples of the polymer used for this polymer network type liquid crystal include acrylic resin, polystyrene, polycarbonate, polyvinyl alcohol, siloxane-based, ester-based and other polymer liquid crystals, and epoxy resin, polyamide and other ordinary polymer compounds. The same as the polymer dispersion type is exemplified. It is easier to increase the liquid crystal content than the polymer dispersion type, and the higher the liquid crystal content is, the higher the scattering efficiency in the light scattering state is, so about 60 to 90 wt% is appropriate. Board 1 '
A color filter is formed on the upper side, and when the liquid crystal layer 13 is in a state of scattering light, a display corresponding to the color of each filter is performed. SiNx is formed as a lower insulating layer 11 on the substrate 1'in a film thickness of 2 .mu.m, and an inverted stagger type TFT is formed on the SiNx. At this time, the gate electrode 2 of the TFT has a shape embedded in the lower insulating layer 11. Gate electrode 2 of this structure
The method of forming is as follows. SiNx is deposited to a thickness of 2 μm as the lower insulating layer 11 ′. An inverted pattern of the gate electrode 2 pattern is formed using a negative resist. Using the resist pattern as a mask, the lower insulating layer is removed by the thickness of the gate electrode 2 by dry etching. Cr is deposited as a gate electrode with a film thickness of 3000 Å while leaving the pattern of the negative resist. The negative resist is peeled off to form the gate electrode 2 on the lower insulating layer.
To form. That is, the gate electrode 2 pattern embedded in the lower insulating layer 11 'was formed by the lift-off method. Further, on top of this, SiNx as an insulating layer that also serves as the gate insulating film 3 is formed.
Is formed, and an inverted stagger type TFT is sequentially formed for each pixel. Keep all the pixel electrodes 9 in a positive voltage application state,
Polyaniline was formed to a thickness of 2.0 μm by an electrolytic polymerization method to form a light absorption layer (not shown). Further, a film of SiNx having a film thickness of 5000 Å was formed on the upper portion to form a passivation layer. As the material of the gate electrode 2, Al, Ta, Cu or the like can be used in addition to Cr, and the film thickness thereof is preferably 1000Å to 1.0 μm, more preferably 2000Å to 5000Å.

Embodiment 3 FIG. 7 shows an embodiment of a direct-view type color liquid crystal display device according to the present invention. A so-called polymer network type liquid crystal was used for the liquid crystal layer, and the same procedure as in Example 2 was performed. A color filter 16 is formed on the substrate 1, and when the liquid crystal layer 13 is in a light scattering state, a display corresponding to the color of each filter is performed. A Cr electrode having a film thickness of 2000 Å is formed on the substrate 1 ′ as an electrode 18 of the storage capacitor, and this electrode is connected to the transparent electrode 14 formed on the substrate 1 in the non-display portion. SiNx is formed as a lower insulating layer 11 'on the upper part of the film with a film thickness of 2.5 .mu.m, and an inverted stagger type TFT is formed on the upper part of the film. In this embodiment, SiNx is used as the lower insulating layer 11 ', but since this insulating layer 11' is used as the dielectric of the storage capacitor,
The storage capacitance can be controlled by adjusting the film thickness. In addition, in addition to SiNx, S in some cases
It is also possible to use iO ₂ or the like, and it is effective to use a laminated film of these.

Embodiment 4 FIG. 8 shows an embodiment of a direct-view type color liquid crystal display device according to the present invention. A so-called polymer network type liquid crystal was used as the liquid crystal layer 13 and produced in the same manner as in Example 2. A color filter is formed on the substrate 1, and when the liquid crystal layer 13 is in a light scattering state, a display corresponding to the color of each filter is performed. On the substrate 1 ', a Cr electrode as an electrode of the storage capacitor is formed with a film thickness of 2000Å, and this electrode is connected to the transparent electrode 14 formed on the substrate 1 in the non-display portion. On top of this, SiNx is used as the lower insulating layer 11 '.
The film is formed with a film thickness of 5 μm, and an inverted stagger type TFT is formed on this film. At this time, the gate electrode of the TFT has a shape embedded in the lower insulating layer 11 '. The gate electrode 2 having this structure was formed by using the lift-off method as in the second embodiment. That is, using the negative resist pattern as a mask, the lower insulating layer 11 'is removed by the thickness of the gate electrode 2 by dry etching, and the negative resist pattern is left as it is to form Cr as the gate electrode 2.
Film is formed to a thickness of 3000 Å, the negative resist is peeled off to form the gate electrode 2 on the lower insulating layer 11 ′, so that the gate electrode 2 embedded in the lower insulating layer 11 ′ is formed.
A pattern was formed. The Cr electrode pattern formed by the above method is used for the gate wiring and the inverted stagger type T as the gate electrode.
The FT is formed for each pixel, and the switching operation of the corresponding pixel electrode 9 is performed according to the input data. On top of these TFTs, S is formed as an insulating layer 11.
iNx is deposited to a film thickness of 2 μm, and a through hole is formed in the drain electrode portion 8 of the TFT. An Al film to be the pixel electrode 9 is formed thereon to a film thickness of 1.5 μm, and the pixel electrode 9 is patterned. Further, SiNx was formed into a film having a film thickness of 5000 Å on the upper portion to form the passivation layer 12.

[0013]

According to the present invention, since the pixel electrode is formed on the non-linear switching element and the wiring electrode thereof via the insulating layer, the pixel electrode and the pixel electrode are electrically separated from each other. There is no region other than display that is invalid for display, and the aperture ratio can be improved. Therefore,
It is possible to realize a brighter liquid crystal display device than before.
According to another aspect of the present invention, since the insulating layer is provided below the gate electrode and the gate electrode is embedded in the insulating layer, a step due to the gate line is not generated, and thus the insulating layer is formed above the gate wiring. It is possible to prevent disconnection of the source wiring. Therefore, defects at the time of forming the electrode wiring pattern can be reduced and the manufacturing yield can be improved. In the present invention, since the storage capacitor is formed by the pixel electrode and the electrode formed below the TFT or TFD via the insulating layer, this electrode does not need to be patterned for each pixel, and therefore this electrode is not necessary. Because of this, there is no step on the top.

[Brief description of drawings]

FIG. 1A shows an additional capacitance system of a conventional liquid crystal display device. (B) shows a storage capacity method of a conventional liquid crystal display device.

FIG. 2A is a sectional view of an inverted stagger type TFT liquid crystal display device of the present invention. (B) is a sectional view of a liquid crystal display device using the TFD of the present invention. FIG. 3C is a sectional view of a conventional inverted stagger type TFT liquid crystal display device. (D) is a cross-sectional view of a liquid crystal display device using a conventional TFD.

FIG. 3 shows a cross-sectional view of a TFT of the present invention in which a gate electrode is embedded in a lower insulating layer.

FIG. 4 shows a cross-sectional view of a TFT of the present invention in which the lower insulating layer is a storage capacitor dielectric.

FIG. 5 is a sectional view of a liquid crystal display device of the present invention in which a through hole is formed in a drain electrode portion of a TFT.

FIG. 6 is a TFT in which a gate electrode is embedded in a lower insulating layer.
FIG. 3 is a sectional view of a liquid crystal display device of the present invention using

FIG. 7 is a cross-sectional view of a liquid crystal display device of the present invention using a TFT in which a lower insulating layer is a storage capacitor dielectric.

FIG. 8 is a cross-sectional view of a liquid crystal display device of the present invention using a TFT in which a gate electrode is embedded in a lower insulating layer which is a dielectric of a storage capacitor.

[Explanation of symbols]

1 Front substrate 1'Back substrate 2 Gate electrode 3 Gate insulating layer 4 Amorphous silicon 5 Ohmic layer 6 Channel stopper 7 Source electrode 8 Drain electrode 9 Pixel electrode 10 n ^-- a-Si layer 11 Insulating layer 11 'Lower insulating layer 12 Passivation Layer 13 Liquid crystal layer 14 Transparent electrode 15 Protective layer 16 Color filter 17 Through hole 18 Storage capacitance electrode 19 Additional capacitance electrode 20 Metal layer a 21 Metal layer b 22 Source line 23 Gate line

Claims (4)

[Claims] 1. A structure having a liquid crystal layer sandwiched between a pair of substrates provided with liquid crystal driving electrodes, wherein the liquid crystal layer scatters light when a voltage is applied and when a voltage is not applied, and a light state. In a liquid crystal display device in which each pixel is driven by a non-linear switching element provided for each pixel, the pixel electrode is flattened on the non-linear switching element, or on the insulating or passivation layer. A liquid crystal display device characterized in that it is formed through a contact hole or a through hole. 2. A structure in which a liquid crystal layer is sandwiched between a pair of substrates provided with liquid crystal driving electrodes, and a state in which the liquid crystal layer scatters light depending on whether a voltage is applied or not and a light state. And a bottom gate type TF in which the driving of each pixel is provided for each pixel.
In the liquid crystal display device using T, the TFT is formed on an insulating layer formed on a substrate, and the gate electrode of the TFT and its wiring portion are formed in a state of being embedded in the insulating layer. A liquid crystal display device characterized by the above. 3. A storage capacitor is provided in association with a non-linear switching element for driving each pixel electrode, and the associated capacitance is composed of the pixel electrode and an electrode provided below the non-linear switching element via an insulating layer. Claim 1 or 2
The described liquid crystal display device. 4. The liquid crystal display device according to claim 1, wherein the liquid crystal display device is a direct-view type or a reflection type liquid crystal display device.