KR100576113B1 - Method for fabricating thin film transistor substrate for reflective LCD - Google Patents

Abstract

The present invention discloses a method of manufacturing a thin film transistor substrate for a reflective liquid crystal display which can improve reflection efficiency and at the same time realize a high contrast ratio. In the method of manufacturing a reflective liquid crystal display, a photosensitive alignment film such as polycinnamate capable of photo alignment and exposure is coated on the entire surface on a substrate on which a reflective electrode having an uneven structure is formed. Then, the photosensitive alignment film is baked at a predetermined temperature. By baking, the photosensitive alignment film located at the partial apex of the reflective electrode flows to the valley portion to realize flattening. Next, portions requiring contact or the like are developed by removing the exposed photosensitive alignment layer. At the same time, the alignment process of the thin film transistor substrate is completed.

Description

Method for manufacturing thin film transistor substrate for reflective liquid crystal display {Method for fabricating thin film transistor substrate for reflective LCD}

1 is a partial cross-sectional view of a thin film transistor substrate of a conventional reflective liquid crystal display.

FIG. 2 is an explanatory diagram for explaining a role of a reflective electrode in the thin film transistor substrate of FIG. 1; FIG.

3 is a schematic diagram illustrating a process of planarizing an alignment layer of a thin film transistor substrate for a reflective liquid crystal display according to an exemplary embodiment of the present invention.

4 is a schematic diagram illustrating a process of planarizing an alignment layer of a thin film transistor substrate for a reflective liquid crystal display according to another exemplary embodiment of the present invention.

FIG. 5 is a schematic diagram illustrating a process of planarizing an alignment layer of a thin film transistor substrate for a reflective liquid crystal display according to still another embodiment of the present invention. FIG.

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a reflective liquid crystal display device, and more particularly, to planarization of an alignment film formed on a thin film transistor substrate for a reflective liquid crystal display having a reflective electrode having an uneven structure.

Cathode ray tubes (CRTs) employed in displays such as televisions and computer monitors are limited in their installation and movement because of their large weight, device space, and power consumption. In order to compensate for these disadvantages, display panels using flat panel panels, such as liquid crystal displays using liquid crystals, plasma display panels (PDPs) using surface discharge, and displays using electroluminescence, have been proposed and are widely used.

Among the flat panel displays, the liquid crystal display has low power consumption, low voltage operation, high definition, full color display, close to the cathode ray tube, and other electronic devices due to the ease of manufacturing process. It is applied in the field.

Such liquid crystal displays include a projection type liquid crystal display using an external light source and a reflection type liquid crystal display using natural light instead of an external light source.

The reflective liquid crystal display has the advantages of low power consumption, a thin, light weight requiring no backlight device, and excellent display outdoors. Because of this feature, portable devices have the best conditions.

However, since the display screen of the current reflective liquid crystal display is dark and does not support high-definition display and color display, it has been used only in extremely low price products requiring only simple pattern display such as numbers among portable devices.

In order to use the reflective liquid crystal display in a portable information device having a function such as a Document Viewer, Internet Viewer, etc., not only the improvement of reflection luminance but also high definition and colorization are required. In order to make a monochromatic display liquid crystal display mainly displaying characters in a portable information device easy to see, reflection luminance improvement and definition are required, and an active matrix substrate including a switching element such as a thin film transistor is required for the realization.

However, since the displayable information is limited in a monochromatic display device, the price setting of the entire device is inevitably low, and the adoption of a thin film transistor having a high panel cost is fatal for a monochromatic display device.

In addition, in the future, the coloration of the portable information device is essential, and thus, the product life of the monochromatic display device may be short. Accordingly, the development of the reflective liquid crystal display is in progress in the coloration direction.

However, despite the large development in both the panel technology and the market, the reflective color liquid crystal display has not been practically used until now. The reason is the lack of performance in terms of brightness, contrast and response speed.

The improvement of brightness is realized by the combination of two techniques, namely, the technique of increasing the reflection efficiency of the reflective electrode and the ultra-high opening ratio technique. A technique for improving the reflection efficiency has already been used in the conventional guest host liquid crystal, and a technique for maximizing the reflection efficiency by making fine irregularities in the electrode provided with the reflection function is disclosed in US Patent No. 5,408,345.

The core of this technology is as shown in Fig. 2, in the external environment using the reflective liquid crystal display, the reflected light (shown in dotted lines) reflected by the reflective electrode 126 under the assumption that light is incident from all directions, the position seen by the user, That is, it changes the path to the front and gathers them. Adoption of such a structure improves the reflectance by about two times or more, compared to the structure using a diffuser film in a flat reflector.

By the way, in order to realize a high-quality reflective liquid crystal display, in addition to improving the reflectance, a high contrast ratio is required.

When the alignment film is directly formed on the reflective electrode of the uneven structure, and the liquid crystal is directly oriented on the surface of the alignment film, the alignment film has the same uneven structure as the reflective electrode, so that the black characteristic, which is a key of high contrast ratio characteristics for high quality, is inevitable. Is lowered.

Therefore, in order to improve the contrast ratio, a technique of forming an alignment layer on the planarization insulating layer 128 by applying the planarization insulating layer 128 to the uneven structure reflective electrode 126 as shown in FIG.

According to this technique, it is inevitable to add another photo process due to the need for a pad opening for connecting the reflective electrode and the external terminal after planarization.

Accordingly, an object of the present invention is to planarize the reflective film using the alignment film itself without applying an additional material for planarizing the reflective film in the reflective liquid crystal display.

Another object of the present invention is to be able to perform planarization and photo alignment of the reflective film through a single exposure.

In order to achieve the above object, a method of manufacturing a reflective liquid crystal display according to an aspect of the present invention is an alignment film having a viscosity of 10 cps ~ 50 cps on the surface of the reflective electrode of the thin film transistor substrate formed on the reflective electrode of the uneven structure Is applied, and the post-baking process for flowing the applied orientation film is performed. The application of the post-baking process causes planarization as the flow of the alignment layer proceeds from the partial peak of the reflective electrode to the valley portion.

According to another aspect of the present invention, a method of manufacturing a reflective liquid crystal display includes acrylic, polyimide, and polyamic acid having a viscosity of 10 cps to 50 cps on a reflective electrode surface of a thin film transistor substrate having an uneven structured reflective electrode formed thereon. The alignment film is applied, and a post-baking step for flowing the applied alignment film is performed. The application of the post-baking process causes planarization as the flow of the alignment layer proceeds from the partial peak of the reflective electrode to the valley portion.

According to another aspect of the present invention, there is provided a method of manufacturing a reflective liquid crystal display, by applying polycinnamate to a thickness of 1 μm-10 μm on a reflective electrode surface of a thin film transistor substrate on which a reflective electrode having an uneven structure is formed. The baking process for flowing the mate film is carried out at a predetermined temperature. The application of the post-baking process causes planarization as the polycinnamate film flows from the partial peak of the reflective electrode to the valley. Next, an exposure process is performed to expose and photoalign the active regions (ie, pixel regions) where the alignment of the liquid crystals occurs by application of a contact hole portion for contact with the pad electrodes and an electric field, respectively. When the polycinnamate film is a positive type, the mask used for exposure is a mask in which a transmissive area where no chrome pattern exists in the contact hole portion for contact with the pad electrode is located and faces the active area of the applied polycinnamate film. In the active region of the polarizer is coated on the surface so that the polarized light is irradiated.

Optionally, a mask with a separate polarizer can be used to photo-align the active region of the applied polycinnamate film.

Next, a developing step for exposing the pad electrode by removing the exposed polycinnamate film corresponding to the contact hole region is performed. Here, when the photosensitive region band of the used polycinnamate is one wavelength, the alignment region reacts to the developing solution during the developing process, and therefore, careful adjustment of the exposure amount and the developing time is required. In the case where the region band for the photoreaction and the region band for the light alignment are different from each other, two lamps having different wavelengths should be used to ensure stability during the developing process.

When using a mask in which polarizers are integrally formed in the active region of the contact hole forming mask, it is also possible to incline the mask to simultaneously perform contact hole formation and photo alignment.

Optionally, in the case where a polarizer is not provided in the active region of the contact hole forming mask and a separate polarizer is provided in the corresponding region, the polarizer may be inclined or the light source may be inclined to irradiate. Next, an exposure process is performed to expose and photoalign the active regions (ie, pixel regions) where the alignment of the liquid crystals occurs by application of a contact hole portion for contact with the pad electrodes and an electric field, respectively.

Other objects, features and advantages of the present invention will become more apparent from the following detailed description with reference to the accompanying drawings.

Hereinafter, preferred embodiments of the present invention will be described with reference to the accompanying drawings.

The present invention provides a high contrast ratio without any additional planarization insulating film formed on the surface of the alignment film, in all embodiments for forming a thin film transistor substrate having a concave-convex structure in which the surface of the reflective electrode serves as a micro lens to increase the reflectance. Disclosed are a method of manufacturing various reflective liquid crystal displays that enable the achievement of the above.

Prior to describing an alignment layer forming process according to an exemplary embodiment of the present invention, a method of manufacturing a thin film transistor substrate having a reflective electrode having a concave-convex structure in manufacturing a reflective liquid crystal display panel will be described with reference to FIG. 1.

That is, a gate bus line, a gate electrode 105 extending from the gate bus line, a gate insulating film 106, and amorphous silicon (a-Si) are formed on a transparent or light-shielding insulating substrate 102 such as a glass substrate. The contact layers 110a and 110b are formed of a semiconductor layer 108 serving as a channel layer and an amorphous silicon (n + a-Si) layer doped with n-type impurities at a high concentration.

Then, a source electrode 113a and a drain electrode 113b integral with the source bus line and the source bus line and extending from the source bus line are formed. By this process, a TFT substrate on which thin film transistors 120 (hereinafter referred to as "TFT") are formed for each unit pixel region is prepared.

Next, an insulating film 122 covering the thin film transistor substrate is formed, and a reflective electrode 126 electrically connected to the drain electrode 113b of the thin film transistor through a contact hole formed in the insulating film in the pixel region on the insulating film 122. Is formed.

Various methods for forming the reflective electrode 126 into the uneven structure have been proposed, one of which is to form the insulating film 122 formed on the lower portion of the reflective electrode first using the photosensitive organic insulating film into the uneven structure, The reflective electrode 126 is formed thereon.

The reflective electrode 126 formed on the organic insulating layer 122 having the uneven structure has the same uneven structure along the uneven surface of the organic insulating layer 122.

A method of forming a flattened alignment layer in order to manufacture a thin film transistor substrate having excellent black characteristics using a substrate having a reflective electrode having an uneven structure prepared according to the above method will be described with reference to FIGS. 3 to 5.

<Example 1>

Referring to FIG. 3, an alignment layer 132 such as polyimide is printed on the reflective electrode 126 having the uneven structure. Here, since the alignment layer 132 is formed only on a desired portion by a printing method, a pad opening process for electrically connecting the input / output terminal of the driving drive to the reflective electrode can be omitted. On the other hand, the spin coating method is formed on the front surface including the reflective electrode 126 shown in FIG. 1, so that the process for opening the pad electrode must be performed essentially, and thus it is difficult to apply compared to the printing method.

In the present embodiment 1, the polyimide used as the alignment layer 132 has a viscosity of about 10 cps to 50 cps, and thus may sufficiently function as a fluid.

In general, the alignment film is formed in a thickness range of about 400 to 800 kPa, but in the present embodiment, the alignment film 132 is applied to a thickness of 500 to 1,000 kPa. If the printing facility cannot print the above thicknesses at one time, it is also possible to print two or more times.

Next, the board | substrate with which the oriented film 132 was apply | coated was placed in a fin plate, and post-baking is performed at the temperature of about 100-130 degreeC. As shown in FIG. 3, in the post-baking process, the alignment film located at the peak portion of the peak of the reflective electrode 126 flows to the valley portion to planarize. Thereafter, the main bake is performed at a temperature higher than the post bake temperature to proceed with imidization.

When the post bake process is completed, the rubbing process and subsequent assembly process are performed.

As described above, according to the present embodiment 1, the alignment film is formed thick by a printing method, and flows through two baking processes to achieve flattening, thereby forming a film for flattening and a patterning process-photosensitive film for contact with the pad. Even if the coating step, the exposure step, and the developing step are omitted, a reflective liquid crystal display having a high contrast ratio and a high contrast ratio excellent in black characteristics can be manufactured.

<Example 2>

On the other hand, unlike the polyimide used in Example 1, it is also possible to use the organic film which has photosensitivity in formation of a planarization oriented film.

The reflective electrode of the microlens structure mentioned above with a thickness in the range of 1 μm to 10 μm by spin coating the photosensitive organic film such as acrylic resin, photosensitive polyimide, photosensitive polyamic acid, etc. having a viscosity of 10 to 50 cps. It applies to the board | substrate which has. Here, the rotation speed of the applied spin coater is in the range of about 100 rpm to 1000 rpm, and the photosensitive organic film is formed to reach the above thickness for a time of several seconds to several tens of seconds.

Next, the board | substrate with which the photosensitive organic film was apply | coated was placed in a fin plate, and post-baking is performed at predetermined temperature. As shown in FIG. 3, in the post-baking process, the photosensitive organic film located in the peak portion of the peak of the reflective electrode 126 flows to the valley portion to planarize.

Next, exposure is performed for several hundred msec to several thousand msec using a mask for exposing a portion where the pad electrode is opened. Thereafter, the exposed part is developed to open the pad.

Thereafter, the unexposed portions are rubbed and a subsequent assembly process is performed.

As described above, according to the second embodiment, the process is complicated as compared with the first embodiment, but since the pad can be opened without applying a separate photosensitive film, the process is simpler than the conventional manufacturing method.

<Example 3>

The method presented in Example 2 has advantages over the conventional method, but after the patterning process for opening the pad, the rubbing of the alignment layer must be performed separately.

Therefore, in the present Example 3, the polycinnamate which has already recognized the possibility as a photo-alignment material is used as a planarization aligning film.

Referring to FIG. 4, a polycinnamate 142 film having a viscosity of 10 to 50 cps is spin-coated to a thickness of 1 μm-10 μm on the front surface of the thin film transistor substrate having the uneven structure reflective electrode 146 formed thereon. Here, the rotation speed of the applied spin coater is in the range of about 100 rpm to 1000 rpm, and proceeds for several seconds to several tens of seconds.

Next, the board | substrate with which the polycinnamate film 142 was apply | coated was placed in a fin plate, and postbaking is performed at predetermined temperature. In the post-baking process, the polycinnamate film 142 located at the peak portion of the reflective electrode 146 is flowed to the valley portion to planarize.

Next, a mask 200 for photoaligning the polycinnamate film in the pixel region is exposed on the substrate while exposing the portion where the pad electrode is opened.

As shown in FIG. 4, the mask 200 includes light transmitting areas 202 and 204 for transmitting incident light and light blocking areas 206 for blocking incident light, and unlike the light transmitting area 202 for opening the pad electrode. In the transmissive region 204 corresponding to the pixel region (or active region), which is an alignment region, a polarizing film is embedded for optical alignment. As such, when using the mask 200 in which the polarizing film is integrally installed in the alignment area of the mask, it is also possible to perform the exposure process by inclining the mask at a predetermined angle to simultaneously perform the pad opening and the light alignment.

Of course, since polarized light having a specific wavelength and intensity is required for the optical orientation of the pixel region, it is also applicable to use the polarization system 230 separated from the mask, as shown in FIG.

Referring again to FIG. 4, when the alignment of the mask 200 is completed, the lamp 220 is driven to expose the polycinnamate film 142 for several hundred msec to several thousand msec.

The pad area is then opened by developing and removing the exposed film of the pad area.

Here, when the photosensitive region band of the polycinnamate film 142 used is one wavelength, the alignment region reacts to the developer during the developing process, and therefore, careful adjustment of the exposure amount and the developing time is required.

After the opening of the pad and the polycinnamate membrane are completed by the above process, a subsequent assembly process is performed.

On the other hand, when the wavelength range in response to the irradiation light for the light alignment of the selected polycinnamate film and the wavelength range in response to the irradiation light for the pad opening is different, in order to ensure stability during the development process, it is shown in FIG. As shown, two lamps 220 with different wavelengths should be used. In FIG. 5, reference numerals 212 and 214 denote transmissive regions through which irradiated light is transmitted, and reference numeral 216 denotes light-shielding regions through which irradiated light is reflected or absorbed.

The process of the alignment film forming method shown in FIG. 5 is the same as the process conditions of FIG. 4 described in the preceding section, except that the polycinnamate film in the pad open area is a light source having a first lamp having a first wavelength in response to the developer. In the polycinnamate film in the active region, an exposure process is performed using a second lamp having a second wavelength as an exposure source so as not to react with a developer for removing the exposed portion of the pad open region.

The light transmitted through the light-transmitting region 214 of the mask 210 is polarized while passing through the lower polarizer 230 to be irradiated onto the polycinnamate film 142 to photo-align the polycinnamate film 142.

When the exposure process is completed, the development process is performed to open the connection portion with the pad electrode. Thereafter, a subsequent assembly process is performed.

On the other hand, the polycinnamate film of Figs. 4 and 5 has been described in the case where the exposed part is a positive type removed by the developer, for example, it is of course applicable to the case where the unexposed part is a negative type reacting to the developer.

As described above, according to the third embodiment, even when the spin coating method is applied, since the rubbing process is omitted as compared with the second embodiment, the manufacturing process of the reflective liquid crystal display having high reflectance and high contrast ratio is simplified.

As described above, according to the method of manufacturing a reflective liquid crystal display of the present invention, the alignment film is formed thick by a printing method, and flows through two baking processes to achieve flattening, thereby forming a film for the flattening process and a pad. Even if the patterning step for contact with the photoresist—a coating step, an exposure step, and a developing step—is omitted, it is possible to manufacture a reflective liquid crystal display having a high contrast ratio and a high contrast ratio excellent in black characteristics.

In addition, by using the photosensitive alignment film, the pad can be opened without applying a separate photosensitive film, so that the process is simpler than in the conventional manufacturing method.

In addition, since the rubbing process is omitted even when the spin coating method is applied, the manufacturing process of the reflection type liquid crystal display having high reflectance and high contrast ratio becomes simpler.

Meanwhile, although specific embodiments of the present invention have been described and illustrated herein, modifications will be made by those skilled in the art from the detailed description of the present invention. Accordingly, the following claims are to be embraced as including such variations and modifications without departing from the spirit and spirit of the invention.

Claims (12)

Providing a substrate including a reflective electrode having a concave-convex surface and one terminal formed in a pixel area on an insulating layer for insulating the thin film transistor; Opening a pad region on the reflective electrode and selectively forming an alignment film having unevenness corresponding to the uneven surface; Post-baking the alignment layer at a first temperature to planarize the alignment layer; Main baking the planarized alignment layer at a second temperature higher than the first temperature; And And rubbing the alignment layer. The method of claim 1, wherein the alignment layer has a viscosity of 10 to 50 cps, and is formed by a printing method with a thickness of 500 to 1,000 kPa. The method of claim 1, wherein the first temperature is in a range of 100 to 130 ° C. Providing a substrate formed in a pixel area on an insulating film for insulating the thin film transistor, the substrate including a reflective electrode having a terminal and an uneven surface electrically connected to the thin film transistor; Forming a photosensitive alignment layer having unevenness corresponding to the uneven surface on the entire surface of the substrate; Baking the photosensitive alignment layer to planarize the photosensitive alignment layer; Patterning the photosensitive alignment layer to expose a predetermined portion of the reflective electrode; And And rubbing the photosensitive alignment layer to form a thin film transistor substrate for a reflective liquid crystal display. The method of manufacturing a thin film transistor substrate for a reflective liquid crystal display according to claim 4, wherein the photosensitive alignment layer is selected from a group of photosensitive organic films composed of acryl, polyimide, and polyamic acid. The method of claim 5, wherein the photosensitive alignment layer has a viscosity of 10 to 50 cps and is formed to a thickness of 1 to 10 μm. Providing a substrate formed in a pixel region on an insulating film for insulating the thin film transistor, the substrate including a reflective electrode having one terminal electrically connected to the thin film transistor and having an uneven surface; Forming a photosensitive alignment layer having a concave-convex surface corresponding to the concave-convex surface to a predetermined thickness on a front surface of the substrate; Baking the photosensitive alignment layer to planarize the photosensitive alignment layer; Exposing a predetermined portion of the photosensitive alignment layer and photoaligning the photosensitive alignment layer in the pixel region; And And developing the removed photosensitive alignment layer and removing the exposed photosensitive alignment layer. 8. The method of manufacturing a thin film transistor substrate for a reflective liquid crystal display according to claim 7, wherein the photosensitive alignment layer is polycinnamate. The method of claim 8, wherein the polycinnamate has a viscosity of 10 to 50 cps and is formed to a thickness of 1 to 10 μm. The method of claim 7, wherein the mask for photoalignment of the photosensitive alignment layer comprises a polarizing film integrated with the mask in a region corresponding to the pixel region. The method of claim 7, wherein the mask for photoalignment of the photosensitive alignment layer comprises a polarization system separated from the mask in a region corresponding to the pixel region. . 12. The method of manufacturing a thin film transistor substrate for a reflective liquid crystal display according to claim 10 or 11, wherein the mask is inclined with respect to the substrate during exposure.

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