JPH08160462A - Liquid crystal display device - Google Patents

Abstract

PURPOSE: To provide a reflection type liquid crystal display of a low cost without degrading its display grade. CONSTITUTION: A reflection layer 11 is directly formed on a substrate 10. This reflection layer 11 is provided with fine undulations by adequately roughening the surface of the substrate 10 by a sand blasting method, by which irregular reflection is effected. The regions exclusive of pixel capacitor regions are protected with a resist, by which a black matrix is formed without execution of working. TFTs are formed together with the pixel electrodes 13P on an interlayer insulating layer 12 by using a positive stagger type, by which the incorporation of auxiliary capacitors, the prevention of a parallax, the prevention of the distortion of the gate electrode 16 signals and the improvement in the coatability of an oriented film 17 are resulted.

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 which enables a process for reducing the number of masks, and more particularly to a liquid crystal display device having a reflective layer built therein and having significantly reduced power consumption.

[0002]

2. Description of the Related Art Liquid crystal display devices have advantages such as small size, thin shape, and low power consumption, and are being put to practical use in fields such as OA equipment and AV equipment. In particular, the active matrix type using a thin film field effect transistor (hereinafter, abbreviated as TFT) as a switching element is
In principle, static driving with a duty ratio of 100% can be performed in a multiplexed manner, and high-definition and high-contrast ratio moving image display is possible.

The active matrix type liquid crystal display device is
TFTs are formed on the pixel electrodes for driving liquid crystal formed on the substrate.
Are connected to each other, and different voltages are applied to and held by the respective pixel capacitors formed between the common electrodes provided on the substrates arranged at opposite positions with the liquid crystal layer interposed therebetween. The alignment state of the liquid crystal changes for each pixel capacitance to modulate light, and a macroscopic synthesis of these transmitted lights creates a display screen.

FIG. 2 is a sectional view of a conventional reflective liquid crystal display device. A gate electrode (51) made of Cr or the like is formed on an insulating substrate (50) such as glass, and a gate insulating layer (52) such as SiNX is formed on the entire surface covering the gate electrode (51). On the gate insulating layer (52),
An island-shaped semiconductor layer (53) is formed in a region corresponding to the gate electrode (51), and both ends of the semiconductor layer (53) are
The source electrode (54) and the drain electrode (55) are connected to each other to form a TFT. Further, an interlayer insulating layer (56) made of an organic insulating film such as a polyimide resin or an acrylic resin or an SOG film is formed on the entire surface covering the TFT, and a pixel made of Al is formed on the interlayer insulating layer (56). The electrode (57) is formed, and the source electrode (5) is formed by the contact hole (CT) opened in the interlayer insulating layer (56).
4) is connected. The inter-layer insulation layer (56) is formed with a fine concavo-convex pattern on the surface by photoetching, and the pixel electrode (57) is also formed into a fine wavy shape accordingly. Further, an alignment film (58) made of polyimide or the like is formed on the entire surface covering the pixel electrode (57).

On the other hand, a color filter layer (6) is formed on the transparent substrate (60) which is arranged to face the liquid crystal layer (70).
1) is formed, and a common electrode (62) made of ITO and an alignment film (6) such as polyimide are formed on the entire surface covering the same.
3) is formed. The reflection type liquid crystal display device having such a configuration does not require a backlight, which is a transmission type and occupies most of the power consumption, so that the power consumption is significantly reduced. That is, the Al pixel electrode (5
7) also serves as a reflection layer, and the ambient light incident from the color filter (61) side is modulated and emitted while reciprocating through the liquid crystal layer (70) and is recognized again.

[0006]

Conventionally, in order to reduce the reflectance distribution of ambient light depending on the viewing angle, the pixel electrode (5
In the inter-layer insulation layer (56) which is the base of 7), fine irregularities are formed on the surface by photoetching, and accordingly, the surface of the reflecting layer wavy in a wavy state has an appropriate roughness and is irregularly reflected. Was there. Therefore, in the liquid crystal display device having the structure shown in FIG. 2, the photo-etching step in the manufacture of the TFT substrate includes a gate electrode (51), a semiconductor layer (53), a source
Each patterning of the drain electrode (54, 55) and the pixel electrode (57), the gate insulating layer (52), the interlayer insulating layer (5
At least seven times were required for the contact hole formation of 6) and the surface processing of the interlayer insulating layer (56). One photo-etching process includes pre-cleaning, resist coating, pre-baking, exposure,
It involves many steps such as development, post-baking, etching, resist stripping, and post-cleaning, resulting in high cost, and reduction of photoetching steps is desired.

Further, since the pixel electrode (57) also serves as a reflection layer, the area of the pixel electrode (57) is increased by the amount of the wavy undulation due to irregular reflection, the resistance is increased, and as a result, the charging characteristics are increased. Was causing the deterioration of. Further, an alignment film (58) for controlling the alignment of the liquid crystal is formed on the pixel electrode (57) by printing or the like, but the adhesiveness and coverage with the surface of the wavy pixel electrode (57) are poor. Has become. In addition, the pixel electrode (57) is an interlayer insulating layer (56).
Corresponding to the uneven surface of the pixel electrode (5) in order to prevent disconnection, and to improve the aperture ratio, each pixel electrode (5
7) There is a gap between them, and at this part the alignment film (58)
Therefore, the adhesiveness and the coating property of were further deteriorated.

Further, in the structure of FIG. 2, in order to improve the aperture ratio, the inter-layer insulating layer (56) is interposed so that T
The pixel electrode (57) is formed in a layer above the FT. The interlayer insulating layer (56) is formed by coating a resin film that has a relatively small effect on the semiconductor layer (53) and can be formed relatively easily. However, when the interlayer insulating layer (56) made of such a material is formed by coating, for example, the film thickness may vary due to compatibility with contact with various underlying metals, and the step difference in the TFT part may cause a difference in pixel electrode. Since part of (57) is raised, the flatness of the reflecting surface is impaired, and there is a problem in that the reflectance distribution becomes viewing angle dependent.

The organic insulating film forming the interlayer insulating layer (56) covering the TFT is formed by applying a liquid resin material and baking at about 200 ° C., but the substrate on which the TFT is formed is heat-treated. There is a problem that the characteristics of a-Si change. Further, when an SOG film is used as the interlayer insulating layer (56), the volume is reduced and the internal stress is increased by firing, and the film is cracked. Further, in order to improve the film quality, baking at a high temperature of 700 to 900 ° C. is required, which causes a problem in the heat resistance of glass, resulting in a decrease in reliability and yield.

[0010]

SUMMARY OF THE INVENTION The present invention has been made to solve the above problems. First, liquid crystal is sealed between two substrates, which are respectively supported and opposed by the two substrates. A plurality of pixel capacitors composed of two transparent electrodes and the liquid crystal interposed between the two transparent electrodes are provided, a thin film transistor is connected to each pixel capacitor, and a voltage can be applied and held for each pixel capacitor. In the possible liquid crystal display device, a reflective layer is formed in a layer different from the pixel capacitance.

Secondly, in the first structure, the reflective layer is formed entirely on one of the two substrates,
The surface of the reflective layer is processed into fine irregularities, and the transparent electrode and the thin film transistor that form one of the pixel capacitors are formed on an interlayer insulating layer that covers the reflective layer. Thirdly, in the first or second configuration, the thin film transistor includes a source electrode and a drain electrode made of the same material as a transparent electrode forming one of the pixel capacitors, and laminated on the source electrode and the drain electrode in the same shape. And a gate electrode.

Fourthly, in any one of the first to third structures, the reflective layer is composed of Al containing a minute amount of Nd. Fifthly, in any one of the second to fourth configurations, the surface of the substrate on which the reflective layer is formed has fine irregularities formed by a sandblasting method, and the irregularity causes the reflective layer to have a fine wavy shape. It has been configured.

Sixthly, in any one of the second to fifth configurations, the surface of the reflective layer is configured so that only a region corresponding to the pixel capacitance is processed into fine unevenness. Seventhly, in the sixth configuration, a region corresponding to the pixel capacitance on the surface of the substrate on which the reflective layer is formed is finely divided by a sand blast method with a protective film covering the outside of the region corresponding to the pixel capacitance. Unevenness is formed, and the reflecting layer is formed into a fine wavy shape in accordance with the unevenness.

Eighth, in any one of the second to seventh configurations, the overlapping portion of the transparent electrode forming one of the pixel capacitors and the light shielding layer assists in holding the voltage applied to the pixel capacitors. It is a structure that is an auxiliary capacity.

[0015]

With the first structure, the reflective layer can be formed outside the pixel capacitor, regardless of the pixel capacitor electrode and the thin film transistor. This prevents the flatness of the reflective layer from being impaired, avoids contact of the reflective layer surface-treated for irregular reflection with the alignment film of the liquid crystal, and improves the adhesion of the alignment film to the underlying layer. .

In the second structure, the reflecting layer is directly formed on the substrate, so that high flatness can be obtained. Also,
Pixel electrodes and thin film transistor layers are formed on the reflective layer by interposing an interlayer insulating layer formed by various deposition methods that are highly adaptable to the underlying shape, such as vapor deposition, vapor deposition, and sputtering. Therefore, even in a structure in which fine irregularities are processed on the surface of the reflective layer due to diffused reflection, deterioration in adhesion and coverage can be prevented. Further, since the interlayer insulating layer is formed before the thin film transistor layer is formed, it is possible to prevent the characteristics of the thin film transistor from changing even in the high temperature process.

In the third structure, the thin film transistor structure in which the gate electrode is arranged in the upper layer prevents the distance between the pixel electrode and the reflective layer from becoming too large and prevents parallax.
That is, in the structure in which the gate electrode is arranged in the lower layer, the distance between the pixel electrode and the reflective layer is increased due to the thickness of the interlayer insulating layer plus the film thickness of the gate insulating layer, but the gate electrode is formed in the upper layer. The arranged structure prevents an increase in the separation distance.

In the fourth structure, the heat resistance is enhanced by forming the reflective layer from a material containing a slight amount of Nd in Al. Therefore, even if the reflective layer is formed as a lower layer on the substrate, Even when exposed to a high temperature in each film forming process or heat treatment, generation of hillocks is suppressed and interlayer short circuit is prevented. In the fifth configuration, by appropriately roughening the substrate surface using the sandblast method, it is possible to relatively easily form fine unevenness, and the reflecting layer is wavy in accordance with the unevenness. Diffuse reflection is performed.

In the sixth structure, the unevenness for irregular reflection is formed on the surface of the reflective layer only in the region corresponding to the pixel capacitance, so that the reflective layer is re-emitted by irregular reflection only in the pixel capacitance region. Outside the area of the pixel capacitance, reflected light is emitted in one direction and is not visible, and it functions as a black matrix, and the contrast ratio is improved. In the seventh configuration, when sandblasting, areas other than the area corresponding to the pixel capacity are protected by a resist or the like to prevent unevenness, so that diffused reflection light emission is performed only in the pixel capacity area and an area outside the pixel capacity. Does not emit light, and the contrast ratio improves.

In the eighth structure, the storage capacity of the voltage applied to the pixel capacitance is improved by forming the auxiliary capacitance for holding the voltage at the overlapping portion of the transparent electrode and the reflective layer which constitutes one of the pixel capacitances. .

[0021]

EXAMPLES Next, examples of the present invention will be described with reference to FIG. First, an insulating substrate such as glass (10)
The surface of the pixel capacitance region is roughened into fine irregularities by the sandblast method. At this time, in a state in which a resist was formed on the surface of the substrate (10) outside the pixel capacitance by photolithography, in a high pressure atmosphere of Ar gas, a pressure of 0.
Si-based crystal fine particles having a diameter of 5 to 2.0 μm are sprayed to form fine irregularities on the surface of the substrate (10).

After the resist is peeled off, a deposited layer containing 1 to 2 atm% of Nd in Al is formed by sputtering to form a reflective layer (11). Reflective layer (11)
Is formed on the entire surface of the substrate (10), but in the pixel capacitance region, it is wavy in accordance with the unevenness of the surface of the substrate (10) and is irregularly reflected. The Al-Nd alloy forming such a reflective layer (11) is a highly heat-resistant material, and there is no problem that hillocks and voids are generated even in the subsequent high temperature process.

SiO2 is laminated on the reflective layer (11) by plasma CVD to form an interlayer insulating layer (12),
A drain electrode (13D), a source electrode (13S), and a pixel electrode (13P) are formed on the interlayer insulating layer (12) by sputtering ITO and photoetching.
The area of the substrate (10) where the unevenness is formed is formed to be smaller than the area corresponding to the pixel electrode (13P) by about 2 to 3 μm due to the alignment margin and the peripheral light shielding.
Further, by forming the interlayer insulating layer (12) with a plasma film, the adhesion and the covering property with the base can be improved, and the reliability can be improved by adapting to the unevenness of the reflective layer (11). The reflective layer (11) also serves as an auxiliary capacitance electrode, and the pixel electrode (1
3P), the inter-layer insulating layer (12) is used as a dielectric layer to form a storage capacitor. Since the auxiliary capacitance is formed on the entire surface of the pixel electrode (13P) and a large capacitance value can be obtained, the shape of the surface of the reflective layer (11) can be obtained by forming the interlayer insulating layer (12) to a thickness of about 1 μm. The unevenness according to
The lower ground of the source / drain electrode wiring (13) is smoothed, and the reflection layer (11) and the drain electrode (13) are
The parasitic capacitance between D) is also reduced and signal distortion is prevented.

In this case, the reflective layer (11) has an interlayer insulating layer (12) formed by a contact hole formed at the end of the substrate.
A voltage is applied to the interlayer insulating layer (12) through a capacitor and controlled by the electric field effect, or a voltage is applied through the capacitor and controlled electrically. On the source / drain electrodes (13S, 13D), the same a-Si (14) as the channel layer, the SiNx gate insulating layer (15), and the gate electrode (16) made of Al or Al-Nd alloy are the same. It is laminated in a pattern to form a TFT. a-Si and SiNx are continuously formed by plasma CVD without breaking the vacuum, and subsequently,
Al (Al-Nd) is formed into a film by sputtering.
l (Al-Nd), SiNX, and a-Si are etched using the mask of the gate electrode (16).

An alignment film (17) of polyimide or the like is formed on the entire surface covering these. On the other hand, the liquid crystal layer (30)
Insulating substrates such as glass (2
0) is arranged, and a color filter layer (21) such as RGB and a common electrode (2) of ITO are arranged on the substrate (20).
2) is formed on the entire surface, and a polyimide alignment film (2
3) is formed on the entire surface.

As described above, the reflective layer (1
Since 1) is directly formed on the substrate (10), there are no undulations on the entire surface, and the reflection layer (11) undulates in a small wavy shape due to the unevenness formed on the surface of the pixel capacitance region of the substrate (10). As a result, diffuse reflection is performed, and the viewing angle dependence of the reflected light intensity is eliminated as a whole. Further, since the irregular reflection processing of the reflection layer (11) is performed on the substrate (10) by using the sandblast method, it is more cost effective than using photoetching.

Further, by making only the pixel capacitance region the region to be processed into the concavo-convex pattern, the light re-emitted by the irregular reflection of the reflection layer (11) is finely modulated by the pixel capacitance and emitted, and also outside the pixel capacitance region. The light reflected by is emitted in another direction and becomes invisible. That is, since the reflective layer (11) functions as a black matrix outside the pixel capacitance region, the contrast ratio is improved.

When the reflection layer (11) is arranged outside the pixel capacitance, a positive stagger type having the gate electrode (16) arranged on the upper layer is adopted as the TFT, so that the gate insulating layer (15) is formed in the pixel. Since it is located above the electrode (13P), the reflective layer (11) and the pixel electrode (13P) are separated from each other only by the film thickness of the interlayer insulating layer (12) and are not too far apart. Therefore, parallax, that is, parallax, generated between the display image formed of the pixel capacitance layer and the shadow of the display image captured on the reflective layer (11) can be suppressed. Further, in an inverted stagger type in which the gate electrode is arranged in the lower layer, if it is attempted to eliminate parallax, the film thickness of the gate insulating layer (15) is
It is necessary to reduce the distance between the reflective layer (11) and the pixel electrode (13P) by thinning the interlayer insulating layer (12), which increases the parasitic capacitance formed between the gate electrode line and the reflective layer.
Distortion occurs in the gate electrode signal, causing a problem such as a decrease in contrast ratio.

Further, since the TFT is formed above the reflective layer (11) and the interlayer insulating layer (12), it is a-Si.
The semiconductor layer of (16) is less likely to be exposed to high temperatures such as film formation and heat treatment, deterioration of TFT characteristics is prevented, and reliability and yield are improved. Furthermore, the pixel electrode (1
3P) is formed by using the smooth and flat surface of the interlayer insulating layer (12) as a base, the pixel electrode (13P) is also smooth and flat, and an increase in wiring resistance was prevented. Further, since the alignment film (17) is formed by printing a polyimide resin or the like, it generally has poor step coverage as compared with a sputter film or a CVD film, but in the present invention, a smooth and flat pixel electrode ( 13P) as a base, the adhesiveness and coverage with the alignment film (17) are good, and the reliability is improved.

With this structure, the number of masks required for manufacturing the TFT substrate is such that the patterning of the resist during the sandblasting of the substrate (10), the patterning of the ITO serving as the source / drain electrode wiring, and the gate serving as the TFT. The patterning of the electrode wiring (16) is at least three, and the manufacturing cost is low.

[0031]

As is apparent from the above description, according to the present invention, a reflective liquid crystal display device having a low cost, a high reliability and a high yield can be obtained without degrading the display quality.

[Brief description of drawings]

FIG. 1 is a cross-sectional view of a liquid crystal display device according to an embodiment of the present invention.

FIG. 2 is a cross-sectional view of a conventional liquid crystal display device.

[Explanation of symbols]

 10, 20 Insulating substrate 11 Reflective layer 12 Interlayer insulating layer 13 Source / drain electrode wiring 14 a-Si 15 Gate insulating layer 16 Gate electrode wiring 17, 23 Alignment film

Claims (8)

[Claims] 1. A liquid crystal is sealed between two substrates,
A plurality of pixel capacitors each composed of two transparent electrodes, which are respectively supported and opposed by one substrate and the liquid crystal interposed between the two transparent electrodes, are provided, and a thin film transistor is connected to each pixel capacitor. A liquid crystal display device configured to be able to apply and hold a voltage for each pixel capacitance, wherein a reflective layer is formed in a layer different from the pixel capacitance. 2. The reflective layer is entirely formed on one of the two substrates, and the surface of the reflective layer is processed into fine irregularities to form a transparent film that constitutes one of the pixel capacitors. The electrode and the thin film transistor are formed on an interlayer insulating layer that covers the reflective layer.
The described liquid crystal display device. 3. The thin film transistor includes a source electrode and a drain electrode made of the same material as a transparent electrode forming one of the pixel capacitors, and a semiconductor layer, an insulating layer, and a semiconductor layer stacked on the source electrode and the drain electrode in the same shape. The liquid crystal display device according to claim 1, comprising a gate electrode. 4. The reflective layer is made of Al containing a small amount of Nd.
4. The liquid crystal display device according to claim 1, wherein the liquid crystal display device comprises: 5. The surface of the substrate on which the reflective layer is formed,
The liquid crystal display device according to any one of claims 2 to 4, wherein fine irregularities are formed by a sandblast method, and the reflection layer is finely corrugated in accordance with the irregularities. 6. The liquid crystal display device according to claim 2, wherein only a region corresponding to the pixel capacitance is processed into a fine concavo-convex shape on the surface of the reflective layer. . 7. A fine concavo-convex pattern is formed by a sandblast method in a region corresponding to the pixel capacitance on the surface of the substrate on which the reflective layer is formed, with a protective film covering the outside of the region corresponding to the pixel capacitance. 7. The liquid crystal display device according to claim 6, wherein the reflection layer is formed into a fine wavy shape according to the unevenness. 8. The overlapping portion of the transparent electrode and the light-shielding layer, which constitutes one of the pixel capacitances, is an auxiliary capacitance that assists in holding a voltage applied to the pixel capacitances. 8. The liquid crystal display device according to claim 7.