JP3920822B2 - Display device - Google Patents

Description

  The present invention relates to a display device incorporating a reflective layer.

  A liquid crystal display device has advantages such as a small size, a thin shape, and low power consumption, and is practically used in fields such as OA equipment and AV equipment. In particular, an active matrix type using a thin film field effect transistor (hereinafter abbreviated as TFT) as a switching element can in principle perform static driving with a duty ratio of 100% in a multiplexed manner by line sequential scanning driving. High definition and high contrast ratio video display.

  In an active matrix liquid crystal display device, a TFT is connected to a plurality of pixel electrodes for driving a liquid crystal formed on a substrate, and is formed between common electrodes provided on a substrate disposed at opposite positions with a liquid crystal layer interposed therebetween. In this configuration, different voltages are applied to and held in the respective pixel capacitors. The liquid crystal modulates the light by changing the alignment state for each pixel capacitance, and creates a display screen by macroscopic synthesis of these transmitted lights.

FIG. 2 is a cross-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 SiN _X is formed on the entire surface covering the gate electrode (51). . An island-shaped semiconductor layer (53) is formed on the gate insulating layer (52) in a region corresponding to the gate electrode (51), and a source electrode (54) and a drain electrode are formed at both ends of the semiconductor layer (53). (55) is connected to constitute a TFT. Further, an interlayer insulating layer (56) made of an organic insulating film such as polyimide resin or 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). An electrode (57) is formed and connected to the source electrode (54) by a contact hole (CT) opened in the interlayer insulating layer (56). The interlayer insulating layer (56) has a fine concavo-convex pattern formed on the surface by photoetching, and the pixel electrode (57) is also shaped into a fine wavy shape accordingly. Further, an alignment film (58) such as polyimide is formed on the entire surface covering the pixel electrode (57).

  On the other hand, a color filter layer (61) is formed on the transparent substrate (60) arranged opposite to each other with the liquid crystal layer (70) interposed therebetween, and a common electrode (62) made of ITO and polyimide on the entire surface covering the color filter layer (61). An alignment film (63) is formed.

Since the reflective liquid crystal display device having such a configuration is particularly transmissive and does not require a backlight that occupies most of the power consumption, the power consumption is significantly reduced. That is, the Al pixel electrode (57) also serves as a reflective layer, and ambient light incident from the color filter (61) side is modulated and emitted and re-recognized while reciprocating the liquid crystal layer (70).
JP 59-72479 A

  Conventionally, for the purpose of reducing the reflectance distribution of ambient light depending on the viewing angle, fine irregularities are formed on the surface by photoetching on the interlayer insulating layer (56) which is the base of the pixel electrode (57), and according to this The surface of the reflective layer in a wavy state was diffusely reflected with an appropriate roughness. For this reason, in the liquid crystal display device having the structure shown in FIG. 2, the photoetching process in the manufacture of the TFT substrate includes the gate electrode (51), the semiconductor layer (53), the source / drain electrodes (54, 55), and the pixel electrode (57). Each of the above patterning, contact hole formation of the gate insulating layer (52) and the interlayer insulating layer (56), and surface processing of the interlayer insulating layer (56) were required at least seven times. One photo-etching process includes many processes such as pre-cleaning, resist coating, pre-baking, exposure, development, post-baking, etching, resist stripping, and post-cleaning, and the cost is high, and it is desired to reduce the photo-etching process.

  In addition, since the pixel electrode (57) also serves as a reflection layer, the area of the pixel electrode (57) increases due to the wavy undulations for irregular reflection, resulting in increased resistance, resulting in deterioration of charging characteristics, etc. Was causing.

  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 adhesion and coverage with the surface of the wavy pixel electrode (57) are poor. It has become. In addition, the pixel electrode (57) is made relatively thick in order to prevent disconnection corresponding to the uneven surface of the interlayer insulating layer (56), and each pixel electrode (57) is used to improve the aperture ratio. There is a gap between them, and the adhesion and covering properties of the alignment film (58) are further lowered at this portion.

  In the structure of FIG. 2, the pixel electrode (57) is formed in an upper layer than the TFT by interposing an interlayer insulating layer (56) in order to improve the aperture ratio. The interlayer insulating layer (56) is formed by coating a resin film that has a small influence 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 varies due to the compatibility with the various metals underneath, and the step of the TFT portion has a pixel electrode. There is a problem that a part of (57) is raised, the flatness of the reflecting surface is impaired, and the viewing angle dependency occurs in the reflectance distribution.

  In addition, 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. However, in order to heat-treat the substrate on which the TFT is formed, a-Si There was a problem such as the characteristics of the 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, resulting in cracks in the film. Furthermore, in order to improve the film quality, baking at a high temperature of 700 to 900 ° C. is required, so that a problem arises in the heat resistance of the glass, leading to a decrease in reliability and yield.

  The present invention has been made to solve the above problems. First, a first transparent electrode on a substrate, and a reflective layer made of an Al—Nd alloy formed in a different layer from the first transparent electrode, It was set as the structure which has. Second, in the first configuration, the surface of the reflective layer is processed into a fine uneven shape. Third, in the first or second configuration, the first transparent electrode is formed on an interlayer insulating film that covers the reflective layer and flattens the surface.

  Fourth, the substrate has a first transparent electrode and a reflective layer, the first transparent electrode is formed flat, and the reflective layer has a surface processed into fine irregularities, Light input from above is reflected by the reflective layer and output above the substrate.

  Fifth, in the fourth configuration, the reflective layer is made of an Al—Nd alloy. Sixthly, in the third to fifth configurations, a switching element is connected to the first transparent electrode. Seventhly, in the sixth configuration, the switching element includes a source electrode and a drain electrode made of the same material as the first transparent electrode, and a semiconductor laminated in the same shape on the source electrode and the drain electrode. The layer is composed of an insulating layer and a gate electrode. Eighthly, in the second to seventh configurations, the surface of the reflective layer has a configuration in which only a region corresponding to the first electrode is processed into a fine uneven shape. Ninthly, in the first to eighth configurations, the reflective layer is formed on the substrate.

  Tenth, in the first to ninth configurations, further comprising a second transparent electrode made of a transparent electrode corresponding to the first transparent electrode, the first transparent electrode, the second transparent electrode, A structure having at least a liquid crystal layer in between. Eleventhly, in the tenth configuration, an alignment film is provided between the first transparent electrode and the second transparent electrode and the liquid crystal layer.

  According to the present invention, since the heat resistance is increased by forming the reflective layer from a material containing a small amount of Nd in Al, hillocks are generated even when exposed to a high temperature in each subsequent film formation process or heat treatment. It is suppressed and interlayer short-circuit is prevented.

  Further, since the surface of the reflective layer is processed into fine irregularities, irregular reflection is performed, and the viewing angle dependency of the reflected light intensity is lost as a whole. Further, by forming a reflective layer outside the pixel capacitor, the reflective layer can be formed regardless of the pixel capacitor electrode and the thin film transistor. As a result, the flatness of the reflective layer is not impaired, and the reflective layer whose surface is processed for irregular reflection is prevented from coming into contact with the alignment film of the liquid crystal, thereby improving the adhesion of the alignment film to the base. .

  In addition, an inter-layer insulating layer formed by various deposition methods having high adaptability to a base shape such as a vapor deposition method, a vapor deposition method, and a sputtering method is interposed on the reflective layer so that a pixel electrode or a thin film transistor layer is formed. Since it is formed, even in a structure in which fine irregularities are processed on the surface of the reflective layer for irregular reflection, a decrease in adhesion and coverage can be prevented.

  In addition, since the interlayer insulating layer is formed before the thin film transistor layer is formed, the characteristics of the thin film transistor can be prevented from being changed even by a high temperature process. In addition, the thin film transistor structure in which the gate electrode is disposed on the upper layer prevents the distance between the pixel electrode and the reflective layer from being excessively increased 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 by the thickness obtained by adding the thickness of the gate insulating layer to the thickness of the interlayer insulating layer. The arranged structure prevents an increase in the separation distance.

  In addition, the reflective layer is re-emitted due to irregular reflection only in the pixel capacitance region, and outside the pixel capacitance region, reflected light is emitted in one direction so that it does not enter the eye and functions as a black matrix, improving the contrast ratio. .

  Moreover, high flatness is obtained by forming the reflective layer directly on the substrate. Further, by appropriately roughening the surface of the substrate using the sand blasting method, fine irregularities can be formed relatively easily, and the reflection layer is waved in accordance with the irregularities, and irregular reflection is performed. Also, when sandblasting, by protecting the areas other than the area corresponding to the pixel capacity with a resist or the like so that irregularities are not formed, irregular reflection light emission is performed only in the pixel capacity area, and no light is emitted in the area outside the pixel capacity, The contrast ratio is improved.

  In addition, by forming an auxiliary capacitor for holding a voltage at the overlapping portion of the transparent electrode and the reflective layer forming one of the pixel capacitors, the holding ratio of the voltage applied to the pixel capacitor is improved.

  According to the present invention, a display device with high reliability and high yield can be obtained at low cost without degrading display quality.

  An embodiment of the present invention will be described with reference to FIG. First, the surface of the pixel capacitor region of an insulating substrate (10) such as glass is roughened into fine irregularities by sandblasting. At this time, 0.5 to 2.0 μm diameter Si-based crystal fine particles were sprayed in a high pressure atmosphere of Ar gas in a state where a resist was formed on the surface of the region outside the pixel capacity of the substrate (10) by photolithography. Then, fine irregularities are formed on the surface of the substrate (10).

  After peeling off the resist, a deposited layer containing 1 to 2 atm% Nd in Al is formed by sputtering to form a reflective layer (11). The reflective layer (11) is formed on the entire surface of the substrate (10), but in the pixel capacitance region, it is waved according to the irregularities on the surface of the substrate (10) to perform irregular reflection. The Al—Nd alloy forming such a reflective layer (11) is a high heat resistant material, and there is no problem that hillocks and voids are generated even in a subsequent high temperature process.

  On the reflective layer (11), SiO2 is laminated by plasma CVD to form an interlayer insulating layer (12). On the interlayer insulating layer (12), a drain electrode (13D) and a source are formed by sputtering and photoetching of ITO. Electrodes (13S) and pixel electrodes (13P) are formed. The region where the unevenness of the substrate (10) is formed is formed to be about 2 to 3 μm smaller than the region corresponding to the pixel electrode (13P) for alignment margin and peripheral light shielding. Further, by forming the interlayer insulating layer (12) with a plasma film, it is possible to improve the adhesion and covering properties with the base, and to improve the reliability by adapting to the unevenness of the reflective layer (11). The reflective layer (11) also serves as an auxiliary capacitance electrode, and constitutes an auxiliary capacitance between the pixel electrodes (13P) using the interlayer insulating layer (12) as a dielectric layer. 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) is increased by forming the interlayer insulating layer (12) thick and about 1 μm. Is eliminated, the ground of the source / drain electrode wiring (13) is smoothed, the parasitic capacitance between the reflective layer (11) and the drain electrode (13D) is reduced, and signal distortion is prevented.

  In this case, the reflective layer (11) is taken out on the interlayer insulating layer (12) through a contact hole formed at the edge of the substrate and is electrically controlled, or the interlayer insulating layer (12 via a capacitor). ) Is taken out and controlled by the field effect to apply a voltage.

  On the source / drain electrodes (13S, 13D), the channel layer a-Si (14), SiNx gate insulating layer (15), and the gate electrode (16) made of Al or Al-Nd alloy are the same. Layered in a pattern, it constitutes a TFT. a-Si and SiNx are continuously formed by plasma CVD without breaking the vacuum. Subsequently, Al (Al-Nd) is formed by sputtering, and Al (Al-Nd), SiNx, a-Si. Is etched using the mask of the gate electrode (16). An alignment film (17) such as polyimide is formed on the entire surface covering these.

  On the other hand, an insulating substrate (20) such as glass is disposed at an opposite position across the liquid crystal layer (30), and a color filter layer (21) such as RGB and an ITO common electrode are disposed on the substrate (20). (22) is formed on the entire surface, and a polyimide alignment film (23) is formed on the entire surface.

  As described above, since the reflective layer (11) is directly formed on the substrate (10) by the configuration of the present invention, the entire surface is free from undulations and is accompanied by the unevenness processed on the surface of the pixel capacitance region of the substrate (10). As a result, the reflective layer (11) undulates in a small wave shape, so that irregular reflection is performed and the viewing angle dependence of the reflected light intensity is lost as a whole. Further, the irregular reflection processing of the reflective layer (11) is performed on the substrate (10) using the sand blast method, so that it is more advantageous in cost than using photoetching.

  Further, by making the region to be processed into irregularities only the pixel capacitance region, the light re-emitted by the irregular reflection of the reflective layer (11) is emitted after being finely modulated by the pixel capacitance and reflected outside the pixel capacitance region. The emitted light is emitted in a different direction and is not visible. That is, since the reflective layer (11) functions as a black matrix outside the pixel capacitance region, the contrast ratio is improved.

  Further, when the reflective layer (11) is disposed outside the pixel capacitor, a positive stagger type in which the gate electrode (16) is disposed on the upper layer is employed as the TFT, so that the gate insulating layer (15) becomes the pixel electrode (13P). ), The distance between the reflective layer (11) and the pixel electrode (13P) is only the film thickness of the interlayer insulating layer (12) and is not too far away. For this reason, the parallax which arises between the display image comprised by a pixel capacity | capacitance layer, and the shadow of the display image reflected on the reflection layer (11), ie, parallax, is suppressed. Further, in the inverted stagger type in which the gate electrode is arranged in the lower layer, if the parallax is to be eliminated, the interlayer insulating layer (12) is made thin by the thickness of the gate insulating layer (15), and the reflective layer (11) and the pixel are formed. The separation distance between the electrodes (13P) must be reduced, the parasitic capacitance generated between the gate electrode line and the reflective layer is increased, the gate electrode signal is distorted, and the contrast ratio is lowered.

  In addition, since the TFT is formed above the reflective layer (11) and the interlayer insulating layer (12), the a-Si (16) semiconductor layer is less exposed to high temperatures such as film formation and heat treatment, TFT characteristics were prevented from deteriorating and reliability and yield were improved.

  Further, since the pixel electrode (13P) is formed using the smooth and flat surface of the interlayer insulating layer (12) as a base, the pixel electrode (13P) is also smooth and flat, thereby preventing an increase in wiring resistance. . In addition, since the alignment film (17) is formed by printing polyimide resin or the like, generally, the step coverage is worse than that of a sputtered film or a CVD film, but in the present invention, a smooth and flat pixel electrode ( 13P) is used as a base, and thus the adhesion and covering properties with the alignment film (17) are good, and the reliability is improved.

  Also, with this structure, the maximum number of TFT substrates required for manufacturing the TFT substrate is such that resist patterning during sandblasting of the substrate (10), ITO patterning for source / drain electrode wiring, and gate electrode wiring for TFT ( 16) The patterning is a minimum of three, and the manufacturing cost is low.

It is sectional drawing of the liquid crystal display device based on the Example of this invention. It is sectional drawing of the 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 (2)

An active matrix liquid crystal display device in which liquid crystal is sealed between a pair of substrates,
One substrate has a TFT, a transparent electrode and a reflective layer,
The transparent electrode is formed flat on the flattened interlayer insulating film by plasma CVD,
The reflective layer is made of an Al—Nd alloy , and is formed below the interlayer insulating film and on the one substrate, and the surface thereof has a fine uneven shape only in a region corresponding to the transparent electrode. Has been processed,
An active matrix liquid crystal display device, wherein light incident from above the other substrate passes through the transparent electrode, is reflected by the reflective layer, and is emitted above the other substrate . 2. The active matrix liquid crystal display device according to claim 1, wherein the Al—Nd alloy contains Al at 1 to 2 atm% Nd.

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