JP2009175561A - Liquid crystal display device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a FFS (Fringe Field Switching) mode liquid crystal display device that suppresses a burn-in phenomenon caused by an upper electrode and is excellent in display picture quality. <P>SOLUTION: This liquid crystal display device 10A has a pair of substrate (array substrate AR and color filter substrate CF) disposed opposite to each other with a liquid crystal layer 25 interposed, and the pair of substrates have display areas where a plurality of sub-pixels are arrayed in a matrix. On one of the pair of substrates, a switching element, a first electrode (lower electrode) 15a, and a second electrode (upper electrode) 18a having a plurality of striped slits 17a formed on the first electrode 15a with an insulating film 16 interposed are formed for each sub-pixel, and a surface of the insulating film 16 is recessed at a position corresponding to the second electrode 18a, so that the surface of the second electrode 18a and the surface of the insulating film 16 are nearly in the same plane with each other. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a fringe field switching (hereinafter referred to as “FFS”) mode liquid crystal display device, and more particularly to an FFS mode liquid crystal display device that suppresses a burn-in phenomenon caused by an upper electrode on the liquid crystal layer side. About.

  As a liquid crystal display device capable of achieving a wide viewing angle, an IPS (In-Plane Switching) mode or FFS mode liquid crystal display device having a pair of electrodes consisting of a pixel electrode and a common electrode on only one substrate is known. .

  Among them, the IPS mode liquid crystal display device has a pair of electrodes arranged in the same layer and rearranges liquid crystal molecules in a direction parallel to the substrate, with the direction of the electric field applied to the liquid crystal being substantially parallel to the substrate. . Therefore, the IPS mode liquid crystal display device is also called a horizontal electric field type liquid crystal display device, and has an advantage of a very wide viewing angle as compared with a conventional vertical electric field type liquid crystal display device. However, in the IPS mode liquid crystal display device, since a pair of electrodes for applying an electric field to the liquid crystal are provided in the same layer, the liquid crystal molecules located above the pixel electrode are not driven sufficiently, and the transmittance and the like are reduced. There is a problem that invites.

  In order to solve such problems of the IPS mode liquid crystal display device, an FFS mode liquid crystal display device, which should be called a so-called oblique electric field method, has been developed (see Patent Documents 1 to 4 below). In an FFS mode liquid crystal display device, a pixel electrode for applying an electric field to a liquid crystal layer and a common electrode are arranged in different layers with an insulating film interposed therebetween. A conventional FFS mode liquid crystal display device will be described with reference to FIG.

  FIG. 9A is a plan view of one subpixel of a conventional liquid crystal display device, and FIG. 9B is a cross-sectional view taken along line IXB-IXB in FIG. 9A.

The liquid crystal display device 10E includes an array substrate (first substrate) AR and a color filter substrate (second substrate) CF. The array substrate AR, the surface of the display area of the first transparent substrate 11 such as a glass substrate, intersect in a state where a plurality of scan lines in a matrix G _L and the signal line S _L is insulated by the gate insulating film 12g to each other It is formed as follows. Further, common wiring (not shown) is formed at the peripheral edge of the display area. Each area surrounded by the scanning lines G _L and the signal line S _L forms a sub-pixel. In addition, a thin film transistor (hereinafter referred to as “TFT”) element, for example, is formed as a switching element for each sub-pixel on the first transparent substrate 11, and is formed on the entire surface of the first transparent substrate 11 including the TFT. A passivation film 12p made of, for example, a silicon nitride layer or a silicon oxide layer is laminated.

  An interlayer film 13 (also referred to as a planarization film) made of an organic material is formed on the surface of the passivation film 12p, and the interlayer film 13 and the passivation film 12p are contacted at a position corresponding to the drain electrode D of the TFT. A hole 14 is formed. Then, a lower electrode 15e made of a transparent conductive material such as ITO (Indium Tin Oxide) or IZO (Indium Zinc Oxide) is formed for each sub-pixel, and each lower electrode 15e is individually formed in the contact hole 14 portion of the TFT. It is electrically connected to the drain electrode D. Accordingly, the lower electrode 15e functions as a pixel electrode.

  Furthermore, an insulating film 16 made of a silicon nitride layer or a silicon oxide layer is formed on the entire surface of the first transparent substrate 11 on which the lower electrode 15e is formed. On the surface of the insulating film 16, an upper electrode 18e having a plurality of slits 17e formed for each sub-pixel region is formed in a solid shape, and this upper electrode 18e is not shown in the periphery of the display region but is used as a common wiring. Electrically connected. Therefore, the upper electrode 18e functions as a common electrode. Further, a rubbing alignment film (not shown) is provided on the entire surface including the upper electrode 18e of the display region. In some cases, the upper electrode 18e is connected to the drain electrode D of the TFT to function as a pixel electrode, and the lower electrode 15e is connected to a common wiring to function as a common electrode.

Further, as shown in FIG. 9B, the color filter substrate CF is formed on the surface of the second transparent substrate 21 such as a glass substrate, with the individual scanning lines G _L , signal lines S _L and TFTs of the liquid crystal display device 10E. A light shielding film 22 is formed at the opposing position. Further, a color filter layer 23 of a predetermined color is formed on the surface of the second transparent substrate 21 surrounded by the light shielding film 22. An overcoat layer 24 is formed so as to cover the surfaces of the light shielding film 22 and the color filter layer 23. An alignment film (not shown) is formed on the surface of the overcoat layer 24.

  The array substrate AR and the color filter substrate CF are opposed so that the upper electrode 18e of the array substrate AR and the color filter layer 23 of the color filter substrate CF are opposed to each other, and the liquid crystal layer 25 is sealed therebetween. Further, a backlight device (not shown) is disposed outside the array substrate AR to complete the FFS mode liquid crystal display device 10E.

Such an FFS mode liquid crystal display device has a wider viewing angle and higher contrast than an IPS mode liquid crystal display device, and can be driven at a lower voltage and has a higher transmittance, thereby enabling bright display. It has features. In addition, in the FFS mode liquid crystal display device, since the overlapping area between the upper electrode and the lower electrode is larger in plan view than in the IPS mode liquid crystal display device, a larger auxiliary capacitance is generated secondarily. There is also an advantage that it is not necessary to provide an auxiliary capacity line.
JP 2001-235863 A JP 2002-182230 A JP 2001-083540 A JP 2007-226175 A

  By the way, it is known that a liquid crystal display device causes a burn-in phenomenon when used under a constant condition for a long time. The burn-in phenomenon occurs similarly in the case of the IPS mode liquid crystal display device and the case of the FFS mode liquid crystal display device. However, it has been found that in the FFS mode liquid crystal display device as described above, the image sticking phenomenon appears greatly as compared with the conventional IPS mode liquid crystal display device.

  One of the causes of the image sticking phenomenon is that a step is generated in the FFS mode liquid crystal display device because the upper electrode having a slit is provided on the surface of the insulating film. That is, since the pixel electrode and the common electrode are formed on the same plane in the IPS mode liquid crystal display device, the path of the electric force lines from the pixel electrode to the liquid crystal and the path of the electric force lines from the liquid crystal to the common electrode are symmetric. It becomes. On the other hand, in the FFS mode liquid crystal display device, the path of electric lines of force from the upper electrode to the liquid crystal and the path of electric lines of force from the liquid crystal to the lower electrode are asymmetric. Therefore, the image sticking phenomenon is larger in the FFS mode liquid crystal display device than in the IPS mode liquid crystal display device.

  In order to suppress the burn-in phenomenon, it can be solved by reducing the level difference of the upper electrode. Therefore, the thickness of the upper electrode is reduced. However, when the thickness of the upper electrode is reduced, the upper electrode is made of a transparent conductive material having a high resistance value such as ITO or IZO, and thus the resistance value of the upper electrode becomes higher. In addition, since a plurality of slits are formed in the upper electrode for each pixel region, the resistance value of the upper electrode is higher than when the upper electrode is formed in a solid shape. Therefore, particularly when the upper electrode is used as a common electrode, the signal applied to the upper electrode is deteriorated due to the increase in resistance of the upper electrode, and the occurrence of lateral crosstalk is observed. The occurrence of such horizontal crosstalk appears particularly in the case of a horizontally long liquid crystal display device called a wide size.

  The present invention has been made to solve the above-described problems of the FFS mode liquid crystal display device. That is, an object of the present invention is to provide an FFS mode liquid crystal display device that suppresses the image sticking phenomenon caused by the upper electrode on the liquid crystal layer side and has a good display image quality.

  In order to achieve the above object, a liquid crystal display device according to the present invention includes a pair of substrates arranged to face each other with a liquid crystal layer interposed therebetween, and a plurality of subpixels are arranged in a matrix on each of the pair of substrates. In the liquid crystal display device having a region, on one of the pair of substrates, a switching element, a first electrode, and an insulating film are interposed on the first electrode for each subpixel. A second electrode having a plurality of stripe-shaped slits is formed, and a recess is formed on the surface of the insulating film at a position corresponding to the second electrode, and the surface of the second electrode and the second electrode It is characterized in that it is formed so that the surface of the insulating film located in the slit portion of the electrode is in the same plane.

  In the liquid crystal display device of the present invention, the second electrode (upper electrode) provided on the surface of the insulating film has a plurality of stripe-like slits for each subpixel. The liquid crystal display device of the present invention can exhibit the fringe field effect by the electric field applied between the first electrode (lower electrode) and the second electrode for each sub-pixel region through the slit. The plurality of striped slits need to be formed in directions parallel to each other, but may be parallel, inclined, or orthogonal to one periphery of the sub-pixel. . Furthermore, there may be a group formed in a plurality of different directions in one subpixel. With such a configuration, it is possible to reduce image quality degradation due to viewing angle.

  According to the liquid crystal display device of the present invention, the surface of the insulating film has a recess formed at a position corresponding to the second electrode, and the surface of the insulating film located at the surface of the second electrode and the slit portion of the second electrode. Are formed in the same plane. With such a configuration, the flatness of the portion of the array substrate in contact with the liquid crystal is improved, and the concentration of electric charges is alleviated. Therefore, the image sticking phenomenon is significantly larger than that of the conventional FFS mode liquid crystal display device as described above. To drop. In addition, since it is not necessary to reduce the thickness of the second electrode in particular, the resistance value of the second electrode can be lowered even when a transparent conductive material having a high resistance value such as ITO or IZO is used as the second electrode. Therefore, the occurrence of lateral crosstalk is greatly reduced.

  In the present invention, a transparent conductive material such as ITO or IZO is used as the first electrode and the second electrode, but the first electrode and the second electrode are different even if they have the same composition. It may be of composition. The first electrode may be formed directly on the surface of the one substrate, or may be formed on an interlayer film formed on the surface of the one substrate. In the present invention, a p-Si (polysilicon) type TFT element, an a-Si (amorphous silicon) type TFT element, and a low temperature polysilicon (LTPS) type TFT element are used as the switching element. Or a two-terminal nonlinear element represented by a thin film diode (TFD) element or the like can be used.

  In the liquid crystal display device of the present invention, the first electrode may be formed on an interlayer film formed in the display region.

  When the first electrode is formed on the interlayer film formed in the display area, the surface of the first electrode that overlaps the switching element or the like in plan view, and further, the first electrode is formed with an insulating film sandwiched between the surfaces of the first electrode. It is possible to prevent a step from being formed on the surface of the two electrodes. Therefore, according to the liquid crystal display device of the present invention, the thickness of the liquid crystal layer, that is, the cell gap can be made constant, so that the display image quality is improved. In addition, the interlayer film in the present invention can be used as long as a transparent organic insulating film having at least a surface flatness can be obtained at the time of manufacture. For example, a transparent resin such as acrylic resin or polyimide can be used. Good.

  Further, in the liquid crystal display device of the present invention, the surface of the interlayer film is formed with a recess at a position corresponding to the second electrode, and the first electrode and the insulating film are each formed with an uneven shape on the surface of the interlayer film. It can be formed to have a constant thickness so as to follow.

  The concave portion formed at a position corresponding to the second electrode of the interlayer film can be easily formed without particularly increasing the number of manufacturing steps by forming the interlayer film with a photoresist and performing exposure using a multi-tone mask. Then, after forming the recess at a position corresponding to the second electrode on the surface of the interlayer film, an insulating film made of an inorganic insulating material such as silicon nitride having a certain thickness by a CVD (chemical vapor deposition) method or a sputtering method and The second electrode can be formed sequentially. Therefore, according to the invention of the liquid crystal display device of the present invention, an FFS mode liquid crystal display device in which the image sticking phenomenon does not easily occur can be manufactured.

  In the liquid crystal display device of the present invention, the insulating film may be made of an inorganic material composed of a silicon nitride layer or a silicon oxide layer.

  Since an inorganic material such as a silicon nitride layer or a silicon oxide layer has very good insulating properties, it can also serve as a passivation film. In order to form a recess at a position corresponding to the second electrode of the insulating film made of an inorganic material and form a contact hole, exposure is performed using a multi-tone mask by a lithography method without particularly increasing the number of manufacturing steps. Can be formed. In the liquid crystal display device of the present invention, the first electrode can be directly formed on the surface of the one substrate or the surface of the gate insulating film. Therefore, according to the liquid crystal display device of the present invention, since it is not necessary to form an interlayer film, the number of manufacturing steps can be reduced, and an FFS mode liquid crystal display device in which no burn-in phenomenon occurs can be easily manufactured. .

  In the liquid crystal display device of the present invention, the insulating film can be made of an organic material.

  Since the insulating film disposed between the first electrode and the second electrode is not necessarily required to have high insulating properties, an insulator made of an organic material is used instead of an inorganic insulating film such as silicon oxide or silicon nitride. May be. By using a photoresist as the organic material and performing exposure using a multi-tone mask, a recess is formed at a position corresponding to the second electrode on the surface of the insulating film made of the organic material without particularly increasing the number of manufacturing steps. Can do. In the liquid crystal display device of the present invention, the first electrode can be directly formed on the surface of the one substrate, usually the surface of the passivation film. Therefore, according to the liquid crystal display device of the present invention, since it is not necessary to form an interlayer film, the number of manufacturing steps can be reduced, and an FFS mode liquid crystal display device in which no burn-in phenomenon occurs can be easily manufactured. .

  In the liquid crystal display device of the present invention, the thickness of the insulating film is preferably 2000 mm to 4000 mm.

  If the thickness of the insulating film is less than 2000 mm, electrostatic breakdown is likely to occur, and if the thickness of the insulating film exceeds 4000 mm, a high voltage is required to drive the liquid crystal, which is not preferable. In addition, when an insulating film made of an organic material is directly formed with a photoresist, the film thickness is usually on the order of μm. However, by performing exposure using a multi-tone mask, the thickness can be easily set to 2000 mm to 4000 mm, A recess can be formed at a position corresponding to the second electrode.

  In the liquid crystal display device of the present invention, the first electrode is electrically connected to the electrode of the switching element for each sub-pixel, and the second electrode is formed at a peripheral portion of the display region. It is preferable to be connected to common wiring.

  In the liquid crystal display device of the present invention, the first electrode operates as a pixel electrode, and the second electrode operates as a common electrode. In the FFS mode liquid crystal display device, both the first electrode and the second electrode can be operated as a pixel electrode or a common electrode. However, as in the present invention, the first electrode is operated as a pixel electrode and the second electrode. If the first electrode is operated as a common electrode, the number of manufacturing steps can be reduced as compared with the case where the first electrode is operated as a common electrode and the second electrode is operated as a pixel electrode. In general, when the FFS mode liquid crystal display device is operated using the second electrode as a common electrode, the image sticking phenomenon increases. However, according to the liquid crystal display device of the present invention, even if the second electrode is operated as a common electrode, the image sticking phenomenon is greatly suppressed, so that the effect is remarkable.

  Hereinafter, the best embodiment of the present invention will be described with reference to the drawings. However, each embodiment shown below exemplifies an FFS mode liquid crystal display device as a liquid crystal display device for embodying the technical idea of the present invention, and the present invention is applied to the FFS mode liquid crystal display device. It is not intended to be specific and is equally applicable to other embodiments within the scope of the claims. In addition, in each drawing used for the description in this specification, each layer and each member are displayed at different scales so that each layer and each member can be recognized on the drawing. However, it is not necessarily displayed in proportion to the actual dimensions.

  1A is a plan view of one subpixel of the liquid crystal display device according to the first embodiment, and FIG. 1B is a cross-sectional view taken along line IB-IB in FIG. 1A. 2A to 2F are cross-sectional views corresponding to the line IB-IB in FIG. 1A, which sequentially shows the manufacturing process of the liquid crystal display device of the first embodiment. FIG. 3A is a plan view of one subpixel of the liquid crystal display device of the second embodiment, and FIG. 3B is a cross-sectional view taken along line IIIB-IIIB in FIG. 3A. 4A to 4G are cross-sectional views corresponding to the line IIIB-IIIB in FIG. 3A, showing the manufacturing process of the liquid crystal display device of the second embodiment step by step. FIG. 5A is a plan view of one sub-pixel of the liquid crystal display device of the third embodiment, and FIG. 5B is a cross-sectional view taken along line VB-VB in FIG. 5A. 6A to 6F are cross-sectional views corresponding to the line VB-VB in FIG. 5A, showing the manufacturing process of the liquid crystal display device of the third embodiment step by step. 7A is a plan view of one sub-pixel of the liquid crystal display device of the fourth embodiment, and FIG. 7B is a cross-sectional view taken along the line VIIB-VIIB in FIG. 7A. 8A to 8D are cross-sectional views corresponding to the line VIIB-VIIB in FIG. 7A, showing the manufacturing process of the liquid crystal display device of the fourth embodiment step by step.

[First Embodiment]
The configuration of the FFS mode liquid crystal display device 10A according to the first embodiment of the present invention will be described in the order of manufacturing steps with reference to FIGS. 1A, 1B, and 2A to 2F. In the FFS mode liquid crystal display device 10A of the first embodiment, the same components as those of the conventional liquid crystal display device shown in FIGS. 9A and 9B are denoted by the same reference numerals.

The array substrate AR of the FFS mode liquid crystal display device 10A of the first embodiment is manufactured as follows. First, a plurality of scanning lines _GL are formed in the display region of the first transparent substrate 11 such as a glass substrate so as to be parallel to each other, and then the entire surface is gate-insulated with a silicon nitride layer or a silicon oxide layer. Cover 12 g of membrane. Thereafter, a semiconductor layer made of, for example, an a-Si layer is formed in the TFT formation region. The region of the scanning line _{GL at} the position where the semiconductor layer is formed becomes the gate electrode G of the TFT.

Then, forming a common line Com like to form a signal line S _L including the source electrode S so as to intersect the scan lines G _L, to form a drain electrode D on the TFT forming region, around the display region in the display region To do. The common wiring Com may be formed between the gate insulating film 12g and the first transparent substrate. Thereafter, the entire surface of the first transparent substrate 11 obtained in the above process is covered with a passivation film 12p. As the passivation film 12p, a film made of a silicon nitride layer or a silicon oxide layer can be used, but a silicon nitride layer is more desirable from the viewpoint of insulation. Since the process so far is the same as the manufacturing process of the conventional FFS mode liquid crystal display device, the detailed illustration thereof is omitted. Thereafter, an interlayer film 13 made of, for example, a photoresist is laminated on the entire surface of the passivation film 12p (see FIG. 2A).

  Next, exposure and development are performed using a multi-tone mask, for example, a halftone mask 30 (see FIG. 2B). Multi-tone masks are used for the purpose of leaving different photoresist film thicknesses in a substrate, and halftone masks and gray tone masks are known. In the halftone mask 30, a portion having the same configuration as the light transmission portion itself of the binary mask 31 becomes a total light amount transmission portion 31a, and a light absorbing member 32 that absorbs part of the exposure light is absorbed in the light transmission portion of the binary mask 31. The provided part becomes the intermediate light quantity transmission part 31b. The transmittance of the intermediate light quantity transmission part 31b can take various numerical values by changing the absorbance of the light absorbing member 32.

  If the absorbance of the intermediate light quantity transmission part 31b is less than 20%, considering the variation of the luminance of the light source of the exposure device, the light quantity transmission 31a is substantially the same. In addition, when the absorbance of the intermediate light amount transmitting portion 31b exceeds 60%, the amount of transmitted light is excessively reduced and it takes time for complete exposure even for a thin photoresist layer. Therefore, the optimal absorbance of the intermediate light amount transmission part 31b is 20% to 60%. A gray tone mask can also be used as a multi-tone mask. The gray tone mask has a portion in which the intermediate light amount transmission portion 31b is formed with a plurality of slit patterns having a resolution limit or less, and the intermediate light amount can be changed by changing the width of the slit or the number of slits per predetermined width. The light transmittance of the transmission part 31b can be changed.

  In the first embodiment, the concave portion 13a of the interlayer film 13 is a portion for obtaining an intermediate light amount of the multi-tone mask, and a thick photoresist layer at the peripheral portion of the display region including the contact hole 14 and the formation position of the common wiring Com. Is a portion for obtaining the total light quantity of the multi-tone mask, and each is exposed in a lump. Then, the photoresist layer in the recess 13a of the interlayer film 13 and the thick photoresist layer at the periphery of the contact hole 14 and the display region are adjusted by appropriately adjusting the light transmittance of the portion that obtains the intermediate light quantity of the multi-tone mask. Thus, it is possible to perform exposure at the same time with the optimum exposure amount. By performing development processing thereafter, the recess 13a can be formed in the interlayer film 13, and the contact hole 14 forming portion and the photoresist layer at the peripheral portion of the display region can be removed (see FIG. 2C).

  Next, the portion of the passivation film 12p where the contact hole 14 is to be formed is removed by an etching method. For the formation of the contact hole 14, a plasma etching method, which is a kind of dry etching method, can be employed. Further, a lower transparent conductive layer made of ITO or IZO is laminated by sputtering or the like. At this time, since the formed transparent conductive layer is laminated with a certain thickness on the inside of the recess 13a of the interlayer film 13, it is formed in a shape that accurately reflects the shape of the recess 13a of the interlayer film 13. In addition, the drain electrode D is electrically connected. Thereafter, the lower electrode 15a is formed in a predetermined pattern for each sub-pixel in the display region by photolithography and etching (see FIG. 2D). In the liquid crystal display device 10A of the first embodiment, the lower electrode 15a corresponds to the first electrode of the present invention and functions as a pixel electrode.

  Further, an insulating film 16 made of a silicon nitride layer or a silicon oxide layer is formed on the entire surface of the transparent substrate 11 on which the lower electrode 15a is formed to have a predetermined thickness, for example, 2000 mm to 4000 mm. The insulating film 16 is formed under plasma CVD conditions that are milder than the conditions for forming the gate insulating film 12g and the passivation film 12p, so-called low-temperature film forming conditions, so as not to roughen the surfaces of the interlayer film 13 and the lower electrode 15a. At this time, since the formed insulating film 16 is also laminated with a certain thickness inside the uneven portion of the lower electrode 15a, the insulating film 16 is formed in a shape that accurately reflects the shape of the recessed portion 13a of the interlayer film 13. (See FIG. 2E). Next, the common film Com is exposed by removing the insulating film 16 and the passivation film 12p in the contact hole 14a formation portion in the peripheral part of the display region by photolithography and etching.

  Further, an upper transparent conductive layer made of ITO or IZO is laminated by a sputtering method or the like so as to fill the recess 16 a formed on the surface of the insulating film 16. At this time, the transparent conductive layer and the common wiring line Com are electrically connected at the contact hole 14a in the peripheral portion of the display area, and the surface of the insulating film 16 is also covered with the transparent conductive layer. Thereafter, by a photolithography method and an etching method, a predetermined pattern is formed in the periphery of the display region so that the surface of the insulating film 16 at a position corresponding to the slit 17a of the upper electrode 18a is exposed in the display region. The transparent conductive layer is etched. The surface of the insulating film 16 exposed in the display region has the same height as the surface of the upper electrode 18a, and functions as a plurality of slits 17a that generate a fringe field effect. Further, the upper electrode 18a covers the entire display region and is in a state of being electrically connected to the common wiring Com at the contact hole 14a (see FIG. 2F).

  Therefore, in the liquid crystal display device 10A of the first embodiment, the upper electrode 18a corresponds to the second electrode of the present invention and functions as a common electrode. Thereafter, an alignment film (not shown) is provided on the entire surface on the upper electrode 18a side, thereby completing the array substrate AR of the liquid crystal display device 10A of the first embodiment.

The color filter substrate CF facing the array substrate AR may be the same as the color filter substrate for the conventional FFS mode liquid crystal display device shown in FIG. That is, the color filter substrate CF is shielded from light so that the surface of the second transparent substrate 21 such as a glass substrate covers positions corresponding to the individual scanning lines G _L , signal lines S _L, and TFTs of the liquid crystal display device 10A. A film 22 is formed. Further, a color filter layer 23 of a predetermined color is formed on the surface of the second transparent substrate 21 surrounded by the light shielding film 22. An overcoat layer 24 is formed so as to cover the surfaces of the light shielding film 22 and the color filter layer 23. An alignment film (not shown) is formed on the surface of the overcoat layer 24. Next, the liquid crystal is sealed inside with the array substrate AR and the color filter substrate CF facing each other, thereby obtaining the liquid crystal display device 10A of the first embodiment as shown in FIGS. 1A and 1B.

  According to the liquid crystal display device 10A of the first embodiment manufactured as described above, the upper electrode 18a is embedded in the recess of the insulating film 16, so that it is exposed from the surface of the upper electrode 18a. The surface of the insulating film 16 is flattened. Therefore, the flatness of the portion of the array substrate AR in contact with the liquid crystal 25 is improved and the concentration of electric charges is alleviated, so that the image sticking phenomenon is greatly reduced as compared with the conventional FFS mode liquid crystal display device. In addition, since the thickness of the upper electrode 18a can be increased, even if the upper electrode 18a is made of a transparent conductive material having a high resistance value such as ITO or IZO, the resistance value of the upper electrode 18a is very small. Become. Therefore, according to the liquid crystal display device 10A of the first embodiment, the image sticking phenomenon is sufficiently suppressed, and the signal applied to the upper electrode 18a functioning as the common electrode is not deteriorated. Even a display device is a liquid crystal display device with little horizontal crosstalk and good display image quality.

[Second Embodiment]
In the liquid crystal display device 10B of the second embodiment, the insulating film between the lower electrode and the upper electrode is formed of a photoresist layer. The configuration of the liquid crystal display device according to the second embodiment will be described in the order of the manufacturing process with reference to FIGS. 3A, 3B, and 4A to 4G. In the FFS mode liquid crystal display device 10B of the second embodiment, the same components as those of the liquid crystal display device 10A of the first embodiment are denoted by the same reference numerals.

The array substrate AR of the FFS mode liquid crystal display device 10B of the second embodiment is manufactured as follows. First, a plurality of scanning lines _GL are formed in the display region of the transparent substrate 11 such as a glass substrate so as to be parallel to each other, and a common wiring Com is formed around the display region. A gate insulating film 12g made of a silicon nitride layer or a silicon oxide layer is covered. Thereafter, a semiconductor layer made of, for example, an a-Si layer is formed in the TFT formation region. The region of the scanning line _{GL at} the position where the semiconductor layer is formed becomes the gate electrode G of the TFT. Then, forming a common line Com like to form a signal line S _L including the source electrode S so as to intersect the scan lines G _L, to form a drain electrode D on the TFT forming region, around the display region in the display region To do. The common wiring Com may be formed between the gate insulating film 12g and the first transparent substrate. Thereafter, the entire surface of the first transparent substrate 11 obtained in the above process is covered with a passivation film 12p (see FIG. 4A). Since the steps up to here are the same as the manufacturing steps of the conventional FFS mode liquid crystal display device, the detailed illustration thereof is omitted.

  Thereafter, a contact hole 14 is formed in the passivation film 12p at the drain electrode D portion of the TFT by photolithography and etching (see FIG. 4B). Next, a lower transparent conductive layer made of ITO or IZO is laminated by sputtering or the like. At this time, the formed transparent conductive layer is electrically connected to the drain electrode D. Thereafter, the lower electrode 15b is formed in a predetermined pattern for each sub-pixel in the display region by photolithography and etching (see FIG. 4C). In the liquid crystal display device 10B of the second embodiment, the lower electrode 15b corresponds to the first electrode of the present invention and functions as a pixel electrode.

  Further, an insulating film 13 ′ made of a photoresist is formed over the entire surface of the first transparent substrate 11 on which the lower electrode 15b is formed (see FIG. 4D). Next, using a multi-tone mask, for example, a half-tone mask 30, a recess 13′b of an insulating film 13 ′ at a position corresponding to an upper electrode 18b described later is a portion for obtaining the intermediate light amount, and on a common wiring Com described below. The thick photoresist layer at the position where the contact hole 14b is formed is a portion that obtains the total amount of light and is exposed in a lump (see FIG. 4E). Further, development processing is performed to form a recess 13′b on the surface of the insulating film 13 ′, and at the same time, the insulating film 13 ′ in the portion where the contact hole 14b is formed on the common wiring Com is removed.

  The insulating film 13 'made of photoresist has a thickness on the order of .mu.m, but operates normally even in this state. However, since the film thickness is too thick to make full use of the characteristics of the FFS mode liquid crystal display device 10B that is driven at a low voltage, the thickness of the insulating film 13 ′ made of this photoresist is preferably set to 2000 to 4000 mm. In this case, a half-tone mask 30 having a three-level gradation is used, and the recess 13'b of the insulating film 13 'is a portion for obtaining the intermediate light amount, and the thick photoresist layer of the contact hole 14b has the total light amount. The other part is a part that obtains a low amount of light, and each part may be exposed collectively. In this way, the thickness of the insulating film 13 ′ can be set to 2000 mm to 4000 mm without particularly increasing the number of manufacturing steps, so that the liquid crystal can be driven with a low voltage. Next, the common wiring Com is exposed by removing the passivation film 12p where the contact hole 14b is formed by etching (see FIG. 4F).

  Further, an upper transparent conductive layer made of ITO or IZO is laminated by sputtering or the like so as to fill the recess 13′b formed on the surface of the insulating film 13 ′. At this time, the common wiring Com is electrically connected by the transparent conductive layer via the contact hole 14b in the peripheral portion of the display area, and the surface of the insulating film 13 ′ is also covered by the transparent conductive layer. Thereafter, by a photolithography method and an etching method, a predetermined pattern is formed in the peripheral portion of the display region so that the surface of the insulating film 13 ′ at a position corresponding to the slit 17b of the upper electrode 18b is exposed in the display region. The transparent conductive layer is etched. Then, the surface of the insulating film 13 ′ exposed in this display region has the same height as the surface of the upper electrode 18 b and functions as a plurality of slits 17 b that generate a fringe field effect. Further, the upper electrode 18b covers substantially the entire display region, and is in a state of being electrically connected to the common wiring line Com through the contact hole 14b (see FIG. 4G).

  Accordingly, in the liquid crystal display device 10B of the second embodiment, the upper electrode 18b corresponds to the second electrode of the present invention and functions as a common electrode. Thereafter, an alignment film (not shown) is provided on the entire surface on the upper electrode 18b side, thereby completing the array substrate AR of the liquid crystal display device 10B of the second embodiment. Next, the same color filter substrate CF as used in the first embodiment is used, and the array substrate AR and the color filter substrate CF obtained as described above are opposed to each other, and liquid crystal is sealed inside. As a result, as shown in FIGS. 3A and 3B, the liquid crystal display device 10B of the second embodiment is obtained.

  The liquid crystal display device 10B of the second embodiment manufactured as described above exhibits the same operations and effects as the liquid crystal display device 10A of the first embodiment, and the manufacturing man-hour is the liquid crystal display device of the first embodiment. Since it is less than 10A, it can be easily manufactured at low cost.

[Third Embodiment]
The configuration of the FFS mode liquid crystal display device 10C according to the third embodiment of the present invention will be described in the order of manufacturing steps with reference to FIGS. 5A, 5B, and 6A to 6F. In the FFS mode liquid crystal display device 10B of the second embodiment, the same components as those of the liquid crystal display device 10A of the first embodiment are denoted by the same reference numerals. Further, as a manufacturing process of the array substrate AR, a scanning line G _L , a signal line S _L , a TFT portion, a drain electrode D, a common wiring Com, a passivation film 12 p and an interlayer are formed on the surface of the first transparent substrate 11 such as a glass substrate. Since the process up to the production of the film 13 (see FIG. 6A) is the same as that in the first embodiment, its detailed description is omitted.

  Next, a contact hole 14 is formed in the interlayer film 13 at a position corresponding to the drain electrode D by a photolithography method and an etching method, and the interlayer film 13 in the peripheral portion of the display region including the formation position of the common wiring Com is removed. (See FIG. 6B). Next, the passivation film 12p on the drain electrode D where the contact hole 14 is to be formed is removed by an etching method. The contact hole 14 can be formed by a plasma etching method which is a kind of dry etching method.

  Next, a lower transparent conductive layer made of ITO or IZO is laminated by sputtering or the like, and the transparent conductive layer is formed in a predetermined pattern by photolithography and etching, and the lower electrode 15c is formed for each sub-pixel of the display area. Are formed in a predetermined pattern (see FIG. 6C). In the liquid crystal display device 10C of the third embodiment, the lower electrode 15c corresponds to the first electrode of the present invention and functions as a pixel electrode.

  Further, an insulating film 16 made of a silicon nitride layer or a silicon oxide layer is coated to a predetermined thickness over the entire surface of the first transparent substrate 11 on which the lower electrode 15c is formed. The insulating film 16 is formed under plasma CVD conditions, so-called low-temperature film forming conditions, which are gentler than the conditions for forming the gate insulating film 12g and the passivation film 12p so as not to roughen the surfaces of the interlayer film 13 and the lower electrode 15c. . Next, a concave portion 16a is formed on the surface of the insulating film 16 at a position corresponding to a second electrode 18c described later by a photolithography method and an etching method, and the insulating film 16 in the contact hole 14a formation portion in the peripheral portion of the display region and The passivation film 12p and the like are removed to expose the common wiring Com.

  Further, an upper transparent conductive layer made of ITO or IZO is laminated by a sputtering method or the like so as to fill the recess 16 a formed on the surface of the insulating film 16. At this time, the transparent conductive layer and the common line Com are electrically connected through the contact hole 14a in the peripheral portion of the display area, and the surface of the insulating film 16 is also covered with the transparent conductive layer. Thereafter, by a photolithography method and an etching method, a predetermined pattern is formed at the periphery of the display region so that the surface of the insulating film 16 at a position corresponding to the slit 17c of the upper electrode 18c is exposed in the display region. The transparent conductive layer is etched. Then, the surface of the insulating film 16 exposed in this display region becomes the same height as the surface of the upper electrode 18c, and functions as a plurality of slits 17c that generate a fringe field effect. Further, the upper electrode 18c covers substantially the entire display region and is electrically connected to the common wiring line Com through the contact hole 14a (see FIG. 6F). Therefore, in the liquid crystal display device 10C of the third embodiment, the upper electrode 18c corresponds to the second electrode of the present invention and functions as a common electrode.

  Thereafter, an alignment film (not shown) is provided on the entire surface on the upper electrode 18c side to complete the array substrate AR of the liquid crystal display device 10C of the third embodiment. Next, the same color filter substrate CF as used in the first embodiment is used, and the array substrate AR and the color filter substrate CF obtained as described above are opposed to each other, and liquid crystal is sealed inside. As a result, as shown in FIGS. 5A and 5B, the liquid crystal display device 10C of the third embodiment is obtained.

  The liquid crystal display device 10C of the third embodiment manufactured as described above exhibits the same operations and effects as the liquid crystal display device 10A of the first embodiment, and the manufacturing man-hour is the liquid crystal display of the first embodiment. Although the number is higher than that of the device 10A, the upper electrode 18c can be formed with high accuracy, so that the display image quality is very good.

[Fourth Embodiment]
In the liquid crystal display device 10D of the fourth embodiment, the insulating film between the lower electrode and the upper electrode is formed of an inorganic insulating film. The configuration of the liquid crystal display device according to the fourth embodiment will be described in the order of manufacturing steps with reference to FIGS. 7A, 7B, and 8A to 8D. In the FFS mode liquid crystal display device 10D of the fourth embodiment, the same components as those of the liquid crystal display device 10A of the first embodiment are denoted by the same reference numerals.

The array substrate AR of the FFS mode liquid crystal display device 10D of the fourth embodiment is manufactured as follows. First, a plurality of scanning lines _GL and common lines Com are formed in a display region of the transparent substrate 11 such as a glass substrate so as to be parallel to each other. Next, after forming a lower transparent conductive layer made of ITO or IZO by sputtering or the like, an independent lower electrode 15d is formed for each sub-pixel of the display region by photolithography and etching. The lower electrode 15 is in a state of being electrically connected to the common line Com for each sub-pixel, corresponds to the first electrode of the present invention, and functions as a common electrode. Next, the entire surface is covered with a gate insulating film 12g made of a silicon nitride layer or a silicon oxide layer. Thereafter, a semiconductor layer made of, for example, an a-Si layer is formed in the TFT formation region. The region of the scanning line at the position where the semiconductor layer is formed becomes the gate electrode G of the TFT. Then, a signal line S _L including the source electrode S so as to intersect the scan lines G _L in the display area to form a drain electrode D on the TFT forming region. (See FIG. 8A). Since the steps up to here are the same as the manufacturing steps of the FFS mode liquid crystal display device not provided with the interlayer film of the conventional example, the detailed illustration thereof is omitted.

  Thereafter, the entire surface of the first transparent substrate 11 obtained in the above process is covered with an insulating film 16 ′ made of, for example, a silicon nitride layer to a predetermined thickness (see FIG. 8B). The insulating film 16 ′ made of the silicon nitride layer does not have to have a particularly low temperature film formation condition, and can be formed under a film formation condition for a passivation film, so that the insulation is good. Therefore, this insulating film 16 ′ can also be provided with a property as a passivation film. Next, a contact hole 14 is formed in this insulating film 16 'in the drain electrode D portion of the TFT by photolithography and etching, and a recess is formed on the surface of the insulating film 16' at a position corresponding to a second electrode 18d described later. 16′d is formed (see FIG. 8C).

  Further, an upper transparent conductive layer made of ITO or IZO is laminated by sputtering or the like so as to fill the recess 16′d formed on the surface of the insulating film 16 ′. At this time, the transparent conductive layer and the drain electrode D of the TFT are electrically connected through the contact hole 14, and the surface of the insulating film 16 'is also covered with the transparent conductive layer. Thereafter, the transparent conductive layer is etched by photolithography and etching so that the surface of the insulating film 16 at a position corresponding to the slit 17d of the upper electrode 18d is exposed in the display region. Then, the surface of the insulating film 16 ′ exposed in this display region has the same height as the surface of the upper electrode 18 d and functions as a plurality of slits 17 d that generate a fringe field effect. Further, the upper electrode 18d is in a state of being electrically connected to the drain electrode D of the TFT through the contact hole 14 (see FIG. 8D). Accordingly, in the liquid crystal display device 10D of the fourth embodiment, the upper electrode 18d corresponds to the second electrode of the present invention and functions as a pixel electrode.

  Thereafter, an alignment film (not shown) is provided on the entire surface on the upper electrode 18d side, thereby completing the array substrate AR of the liquid crystal display device 10D of the fourth embodiment. Next, the same color filter substrate CF as used in the first embodiment is used, and the array substrate AR and the color filter substrate CF obtained as described above are opposed to each other, and liquid crystal is sealed inside. Thus, as shown in FIGS. 7A and 7B, the liquid crystal display device 10D of the fourth embodiment is obtained.

  The liquid crystal display device 10D of the third embodiment manufactured as described above exhibits the same operations and effects as the liquid crystal display device 10A of the first embodiment, and the manufacturing man-hour is the liquid crystal display of the first embodiment. Since the number of devices is smaller than that of the device 10A, it can be manufactured at a low cost, and the upper electrode 18d can be formed with high accuracy, so that the display image quality is very good.

  The example of the FFS mode liquid crystal display device has been described above as each embodiment of the present invention. Such a liquid crystal display device of the present invention can be used for electronic devices such as personal computers, mobile phones, portable information terminals, and portable music players. However, since the basic configuration of these electronic devices is well known to those skilled in the art, detailed description thereof is omitted.

1A is a plan view of one subpixel of the liquid crystal display device according to the first embodiment, and FIG. 1B is a cross-sectional view taken along line IB-IB in FIG. 1A. 2A to 2F are cross-sectional views corresponding to the line IB-IB in FIG. 1A, showing the manufacturing process of the liquid crystal display device of the first embodiment step by step. FIG. 3A is a plan view of one subpixel of the liquid crystal display device of the second embodiment, and FIG. 3B is a cross-sectional view taken along line IIIB-IIIB in FIG. 3A. 4A to 4G are cross-sectional views corresponding to the line IIIB-IIIB in FIG. 3A, showing the manufacturing process of the liquid crystal display device of the second embodiment step by step. FIG. 5A is a plan view of one sub-pixel of the liquid crystal display device of the third embodiment, and FIG. 5B is a cross-sectional view taken along line VB-VB in FIG. 5A. 6A to 6F are cross-sectional views corresponding to the line VB-VB in FIG. 5A, showing the manufacturing process of the liquid crystal display device of the third embodiment step by step. 7A is a plan view of one sub-pixel of the liquid crystal display device of the fourth embodiment, and FIG. 7B is a cross-sectional view taken along the line VIIB-VIIB in FIG. 7A. 8A to 8D are cross-sectional views corresponding to the line VIIB-VIIB in FIG. 7A, showing the manufacturing process of the liquid crystal display device of the fourth embodiment step by step. FIG. 9A is a plan view of one subpixel of a conventional liquid crystal display device, and FIG. 9B is a cross-sectional view taken along line IXB-IXB in FIG. 9A.

Explanation of symbols

10A to 10E: Liquid crystal display device 11: First transparent substrate 12: Passivation film 13: Interlayer film 13a: Recess 14: Contact hole 15a-15d: Lower electrode 16, 16 ': Insulating film 16a, 16'd: Recess 17a ˜17d: slits 18a˜18d: upper electrode 21: second transparent substrate 22: light shielding film 23: color filter layer 24: overcoat layer 25: liquid crystal layer 30: halftone mask 31: binary mask 31a: total light quantity transmission part 31b: Intermediate light quantity transmission part 32: Light absorption member Com: Common wiring G _L : Scanning line S _L : Signal line

Claims (7)

In a liquid crystal display device comprising a pair of substrates opposed to each other with a liquid crystal layer interposed therebetween, each having a display region in which a plurality of subpixels are arranged in a matrix on each of the pair of substrates.
In one of the pair of substrates, a switching element, a first electrode, and a plurality of stripe-shaped slits are formed on the first electrode with an insulating film interposed therebetween for each subpixel. Two electrodes are formed,
The surface of the insulating film is formed with a recess at a position corresponding to the second electrode, and the surface of the second electrode and the surface of the insulating film positioned at the slit portion of the second electrode are formed in the same plane. A liquid crystal display device.   The liquid crystal display device according to claim 1, wherein the first electrode is formed on an interlayer film formed in the display region.   A recess is formed on the surface of the interlayer film at a position corresponding to the second electrode, and the first electrode and the insulating film are each formed to have a constant thickness so as to follow the uneven shape of the surface of the interlayer film. The liquid crystal display device according to claim 2.   The liquid crystal display device according to claim 1, wherein the insulating film is made of an inorganic material including a silicon nitride layer or a silicon oxide layer.   The liquid crystal display device according to claim 1, wherein the insulating film is made of an organic material.   The liquid crystal display device according to claim 1, wherein the insulating film has a thickness of 2000 to 4000 mm.   The first electrode is electrically connected to the electrode of the switching element for each sub-pixel, and the second electrode is connected to a common wiring formed in a peripheral portion of the display region. The liquid crystal display device according to claim 1.

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