JP5073026B2 - Liquid crystal display - Google Patents

Description

  The present invention relates to a liquid crystal display device capable of improving display quality, and in particular, a reflection mode for performing display by reflecting external light (external light) and a liquid crystal display device for performing display by transmitting light from a backlight. It is about.

  In recent years, liquid crystal display devices have been used in a wide range of applications, from large-sized devices used for televisions and personal computers to medium-sized devices used for portable information terminals. These liquid crystal display devices are selectively used according to their respective uses, and transmissive liquid crystal display devices are mainly used for televisions and the like used indoors. Reflection of external light is required for portable information terminals used outdoors. A reflection type liquid crystal surface device provided with means is used.

  In addition, a reflective transflective liquid crystal display device having both reflective and transmissive area functions is used as a reflective type that utilizes light from the outside (external environment) such as sunlight and fluorescent lamps, and is also used for liquid crystal display panels. A transmissive type using light from a backlight disposed on the opposite side of the display surface has been used in combination. In such a liquid crystal display device having both functions, a backlight is disposed on the back surface side (surface opposite to the display surface) of the liquid crystal display panel, and a translucent film is provided on the other transparent substrate on the back surface side. Was forming.

  In these transflective liquid crystal display devices, reflective transflective means are formed in the liquid crystal layer. This reflective semi-transmissive film is formed by forming a metal reflective film substantially in a part of one pixel region, using the region where the metal reflective film is formed as a reflective region, and no metal reflective film is formed. The region was a transmission region. This reflective transflective means is defined by the structure in one pixel region, and a plurality of transparent dielectric layers are stacked over a plurality of pixel regions to form a reflective transflective film, The light is reflected on the surface of the reflective semi-transmissive film or the interface of the dielectric layer, and the light of the backlight is transmitted through the reflective semi-transmissive film. However, when a reflective transflective film is used as the reflective transflective means, there is a problem that the loss of light increases.

  Further, in order to form a reflective region and a transmissive region in the pixel region, a metal such as aluminum is deposited as a metal reflective film and patterned to form a transmissive region.

  FIG. 3 is a cross-sectional view of a conventional transflective liquid crystal display device using a metal reflective film, and FIG. 4 is an enlarged cross-sectional view of one transparent substrate side. The transflective liquid crystal display device includes a liquid crystal display panel and a backlight. Here, the backlight is omitted from the description.

  The liquid crystal display panel LP includes, for example, a glass substrate 2 that is the other transparent substrate on the display surface side, a glass substrate 11 that is one transparent substrate on the back surface side, and a liquid crystal layer 10 disposed therebetween. Yes. A large number of transparent electrodes 4 and 5 are arranged in parallel on the inner surfaces of the glass substrates 11 and 2.

The transparent electrode 5 of the glass substrate 2 is formed so as to extend in the other direction, for example, in the left-right direction in FIG. 3, and the transparent electrode 40 of the glass substrate 11 extends in, for example, one direction, in FIG. It is formed as follows. That is, the glass substrate 2 and the glass substrate 11 are opposed to each other, and the liquid crystal layer 10 is disposed therebetween, and the both substrates 11 and 2 are bonded together by the sealing member. The transparent electrode 40 of the glass substrate 11 and the transparent electrode 5 of the transparent substrate 2 intersect each other, and a pixel region is configured by this intersecting region. Such pixel areas are arranged vertically and horizontally to constitute a display area for displaying predetermined display information as a whole. Then, alignment films 7 and 8 are formed so as to cover the substrates 11 and 2 corresponding to the display area, that is, to cover the plurality of transparent electrodes 40 and 5.

  Although not shown in the drawing, a polarizing plate and a retardation plate are sequentially attached to the outer surface side of the glass substrates 11 and 2 of the liquid crystal display panel.

  A backlight is disposed on the outer surface side of the glass substrate 11. A backlight corresponds to a display area composed of a plurality of pixel areas of the liquid crystal display panel, and light from the backlight is emitted to the display surface through the display area.

  Here, the structure of the reflection region and the transmission region will be described. As shown in FIG. 4, the transparent electrode 40 is formed so as to correspond to the pixel region of the glass substrate 11 which is one of the transparent substrates. Then, the metal reflective film 30 is formed in a part of the region corresponding to the pixel region with the transparent electrode 40. That is, the region where the metal reflection film 30 is formed functions as a reflection region. In addition, a region where the metal reflective film 30 is not formed in the pixel region can transmit the light of the backlight and becomes a transmission region.

  Further, an insulating film 60 is formed so as to cover the metal reflective film 30 formed on the transparent electrode 40. The insulating film 60 is formed across a plurality of pixel areas, that is, over the entire display area. Further, an alignment film 7 made of resin is formed on the upper surface of the insulating film 60. The alignment film 7 controls the twist of the liquid crystal molecules of the liquid crystal layer 10 and is subjected to a rubbing process after the alignment film 7 is formed. The insulating film 60 is formed by laminating a metal reflective film 30 smaller than the shape of the transparent electrode 40 on the transparent electrode 40, and relaxes the edge of the transparent electrode 40 and the stepped portion of the metal reflective film 30, thereby aligning the alignment film 7. When the film is formed and rubbed, the alignment film 7 is prevented from being peeled off, and a short circuit caused by a foreign matter that occurs when a conductive foreign matter is present in the liquid crystal layer 10 is prevented. Reference numeral 9 denotes a spacer for making the thickness of the liquid crystal layer 10 constant between one transparent substrate 2 and the other transparent substrate 1.

Japanese Patent Laid-Open No. 10-282488

  In the above-described transflective liquid crystal display device, in particular, the STN transflective liquid crystal display device in which the twist of the liquid crystal molecules of the liquid crystal layer 10 is set to 180 to 270 °, the glass substrate 11 which is a transparent substrate is used. If the wiring resistance of the transparent electrode 40 is high, display characteristics such as crosstalk and concentration gradient deteriorate, so the wiring resistance must be made as small as possible. In view of this, a device has been devised in which a metal reflection film is formed in the display region and a metal film is formed in the wiring portion to reduce the resistance of the wiring portion. Therefore, the metal reflective film 30 tends to be thicker as a result.

However, when the metal reflection film 30 is made thick, the level difference of the metal reflection film 30 in the pixel region becomes large, and there is a problem that the insulating film 60 can be cracked. The crack of the insulating film 60 at the step portion is generated at a portion B in FIG. This is because the film thickness of the insulating film 60 increases on the transparent electrode 40 on which the metal reflective film 30 is formed, particularly around the metal reflective film 30, as the film thickness of the metal reflective film 30 increases. This is because when the film thickness exceeds a certain level, the internal stress of the film concentrates and cracks occur.

  As a result, the alignment film 7 on the insulating film 60 is peeled off from the crack portion of the insulating film 60. As a result, the liquid crystal molecules in the liquid crystal layer 10 cannot be controlled and stable display cannot be performed. It was.

  The present invention has been devised in view of the above-mentioned problems, and its purpose is to improve the three-part structure of a transparent electrode, a metal reflection film, and an insulating film, and peeling or cracking occurs in the insulating film. Therefore, the present invention provides a liquid crystal display device that can stably maintain the alignment film and can stabilize the liquid crystal display.

One aspect of the liquid crystal display device of the present invention is provided with a transparent substrate of a pair, and a liquid crystal layer interposed between the pair of transparent substrates, on one of the transparent substrate of the pair of transparent substrates a reflective film, said comprising: a transparent electrode which is the provided on one transparent substrate so as to cover the reflective film, and an insulating film provided on the transparent conductive electrode, wherein the transparent electrode, the reflective layer A first part located above, a second part located outside the end of the reflective film and having a smaller thickness than the reflective film, and connecting the first part and the second part It has the 3rd site | part which becomes thin as it approaches the said 2nd site | part, It is characterized by the above-mentioned .

  According to the present invention, the display area has the reflection area and the transmission area, and the reflection area has the metal reflection film. A metal reflection film that defines the reflection region is formed between the transparent substrate and the transparent electrode. That is, on one glass substrate, a metal reflective film is formed in a reflective region, and a transparent electrode is formed continuously in the reflective region and the transmissive region where the metal reflective film is formed, and a display region including the transparent electrode. An insulating film is formed on the insulating film, and an alignment film is formed on the insulating film.

  For this reason, since the metal reflection film is covered with the transparent electrode, the edge portion of the metal reflection film is relaxed, and disconnection at this portion can be effectively prevented.

  Furthermore, in order to reduce the resistance of the transparent electrode and the wiring part connected to the transparent electrode, the thickness of the metal reflective film formed simultaneously with the wiring part is set thick, and as a result, the thickness of the metal reflective film increases. However, since there is a transparent electrode around the metal reflective film, and an inorganic insulating film is formed on the transparent electrode, the thickness of the inorganic insulating film is the thickness of the inorganic insulating film above the metal reflective film. And the difference in thickness of the inorganic insulating film around the metal reflective film is reduced, and the inorganic insulating film can be made uniform. This makes it possible to effectively use the internal stress of the inorganic insulating film around the metal reflective film, which was easily concentrated in the past. As a result, there is no generation of cracks in the inorganic insulating film, the peeling of the alignment film is eliminated, the alignment film can be stably maintained, and the liquid crystal display is stabilized.

It is a schematic sectional drawing of the liquid crystal display panel used for the liquid crystal display device of this invention. It is an expanded sectional view of the glass substrate of the state which omitted the alignment film of FIG. It is a schematic sectional drawing of the liquid crystal display panel used for the conventional liquid crystal display device. It is an expanded sectional view of the glass substrate of the state which omitted the alignment film of FIG.

  The liquid crystal display device of the present invention will be described below with reference to the drawings.

  FIG. 1 is a cross-sectional view of the liquid crystal display device of the present invention, and FIG. 2 is an enlarged cross-sectional view of one transparent substrate side. The liquid crystal display device of the present invention comprises a liquid crystal display panel Lp and a backlight BL. In addition, the same code | symbol is attached | subjected to FIG. 3, FIG. 4 and an identical location.

  A liquid crystal display panel LP constituting the liquid crystal display device shown in FIG. 1 includes, for example, a glass substrate 1 that is one transparent substrate, a glass substrate 2 that is the other transparent substrate, and a liquid crystal layer 10 disposed therebetween. It is configured.

  On each inner surface side of one glass substrate 1 and the other glass substrate 2, a large number of transparent electrodes 4 and 5 for constituting a pixel region are arranged in parallel. For example, the transparent electrode 4 of one glass substrate 1 is formed to extend in one direction, for example, the depth direction in FIG. 1, and the transparent electrode 5 of the other glass substrate 2 is formed in the other direction, for example, left and right in FIG. Extending in the direction. That is, when one glass substrate 1 and the other glass substrate 2 are arranged to face each other, the transparent electrodes 4 and 5 of both substrates 1 and 2 intersect each other. Thereby, when visually observed from the other glass substrate 2 side, the intersection of the transparent electrodes 4 and 5 becomes a pixel region. A plurality of the pixel areas are arranged vertically and horizontally, and the whole constitutes a display area. Then, alignment films 7 and 8 are formed on the transparent electrodes 4 and 5 so as to be in contact with the liquid crystal layer 10.

  The liquid crystal layer 10 is composed of nematic liquid crystal molecules or the like, and spacers 9 are dispersed so as to keep the thickness of the liquid crystal layer 10 constant. The liquid crystal molecules of the liquid crystal layer 10 are controlled to be twisted by 180 ° to 270 ° in a state where no driving voltage is applied, by controlling the alignment treatment direction of the alignment film 7 and the chiral substance contained in the liquid crystal layer 10. Yes. Although not shown in the drawing, both the substrates 1 and 2 are bonded together by a sealing member, and the liquid crystal layer 10 is filled in the bonded region.

  Further, although not shown in the drawing, a polarizing plate and a retardation plate are respectively attached to the outer surface side of one glass substrate 1 and the other glass substrate 2 of the liquid crystal display panel LP. Moreover, you may provide the light-scattering layer for scattering and diffusing light as needed.

  The backlight BL is composed of, for example, a light guide plate and a light source, and is disposed outside one glass substrate 1. Specifically, the liquid crystal display panel LP and the backlight BL are fixed in a predetermined positional relationship by a frame member that supports and fixes them. That is, the display area composed of a plurality of pixel areas of the liquid crystal display panel LP and the light emission surface of the light guide plate of the backlight BL are arranged to face each other.

  Here, as shown in the enlarged sectional view of FIG. 2, a metal reflection film 3 constituting a reflection region is formed in the pixel region between the inner surface of one glass substrate 1 and the transparent electrode 4. And the area | region in which this metal reflective film is not formed in a pixel area turns into a transmissive area | region. That is, the layer structure is different between the reflective region and the transmissive region formed in one pixel region.

  On the inner surface of the glass substrate 1, for example, a metal reflective film 3 made of aluminum, chromium, silver or the like having a film thickness of 500 to 5000 mm is formed. In addition to aluminum, chromium, and silver, an aluminum alloy, a chromium alloy, a silver alloy, and the like may be used.

The metal reflection film 3 is formed before the transparent electrode 4 is formed. The metal reflection film 3 simply reflects external light, and the metal reflection film 3 is used as a wiring portion for reducing the resistance value of the transparent electrode 4. it can. The metal reflection film 3 that defines the reflection region can be formed in a stripe shape in the depth direction of the paper surface of FIGS. As a result, the metal film continuous to the plurality of pixel regions is present below the transparent electrode 4, and is used as a wiring portion for supplying a predetermined driving voltage to the transparent electrode 4 outside the display region. The The transparent electrode 4 is formed of ITO (indium tin / tin oxide), tin oxide ITO or the like having a thickness of 500 to 2000 mm on the metal reflective film 3 so as to cover the step of the metal reflective film 3. Since the transparent electrode 4 is made of a metal oxide film such as ITO (indium tin oxide) or tin oxide, the resistance value is higher than that of a single metal. By forming a metal film (metal reflective film) having a small resistance value below the transparent electrode 4 as described above, the resistance value of the entire transparent electrode 4 can be reduced, and the voltage drop of the driving voltage can be effectively prevented and stabilized. It is effective for performing liquid crystal display.

  As described above, in the transparent electrode 4, the metal reflective film 3 is formed in a band shape in the vicinity of the central portion in the width direction of the transparent electrode 4 to be a reflective region, and both end portions in the width direction of the transparent electrode 4 are transmissive regions. . That is, light from the backlight passes through this transmission region.

  A common inorganic insulating film 6 is formed on the plurality of transparent electrodes 4. That is, the inorganic insulating film 6 is formed in a display area composed of pixel areas arranged vertically and horizontally. For this reason, it forms on the glass substrate 1 exposed from between the transparent electrodes 4 and the transparent electrodes 4.

  This inorganic insulating film 6 is formed in order to prevent short circuit between substrates and short circuit between transparent electrodes when a conductive foreign matter is mixed in the liquid crystal layer 10, and at the same time, the alignment film 7 formed on the upper surface thereof. It improves the adhesive strength.

  The inorganic insulating film 6 is formed of a transparent inorganic material made of SiOx typified by SiO2, SiNx typified by Si3N4, TiOx typified by TiO2, ZrO2, Al2O3, Ta2O5, Nb2O3, or the like. At this time, the film thickness of the inorganic insulating film 6 is in the range of 300 to 1500 mm.

  At this time, since the step portion of the upper edge portion of the metal reflection film 3 is covered with the transparent electrode 4, the step is relaxed, and it is not necessary to increase the thickness of the inorganic insulating film 6 more than necessary. Thus, it can be formed with 300 to 1500 mm, and the internal stress generated in proportion to the thickness of the film thickness can be reduced.

  On the inorganic insulating film 6, an alignment film 7 is formed over the entire display area. For example, the orientation 7 is rubbed after a polyimide resin is applied and cured.

  Thus, in one glass substrate 1, the reflective region which is a part of the pixel region is laminated in the order of the metal reflective film 6, the transparent electrode 4, the inorganic insulating film 6, and the alignment film 7 from the glass substrate 1 side. The transparent region, which is a part of the pixel region, is laminated in the order of the transparent electrode 4, the inorganic insulating film 6, and the alignment film 7 from the glass substrate 1 side.

  The transparent electrode 5 and the alignment film 8 are laminated in this order from the glass substrate 2 side on the inner surface of the other glass substrate 2.

  In one glass substrate 1 having the above-described configuration, a crack caused by the thickness of the inorganic insulating film 6 has conventionally occurred around the metal reflective film 3, but the metal reflective film 6 and the transparent electrode 4 are formed in this order. By covering the entire metal reflective film 6 with the transparent electrode 4, relaxing the stepped portion of the upper edge of the metal reflective film 3, and reducing the thickness of the inorganic insulating film 6, cracks due to internal stress are generated. Can be prevented. That is, the thickness of the A portion shown in FIG. 2 can be made thinner than the thickness of the B portion of FIG. 4 of the conventional example, and the inorganic insulating film can be cracked.

  The inventor investigated the occurrence of cracks in the inorganic insulating film 6 and the insulating film 60 (shown as an insulating film in the table) by changing the film thicknesses of the metal reflective film 6 and the transparent electrode 4 in one glass substrate 1.

  The thickness of the insulating film was set to 800 mm for both the product of the present invention and the conventional example.

  According to Table 1, the display quality of the crosstalk and the density gradient is improved by increasing the thickness of the metal reflective film 3 and the transparent electrode 4, but the conventional film configuration (transparent electrode 4 and metal reflective film 3 In order, if the reflective film 3 exceeds 3000 mm, cracks occur in the portion B of FIG. 4 and peeling of the alignment film occurs.

  However, in the film configuration of the product of the present invention, even if the reflective film exceeds 3000 mm, the inorganic insulating film 6 will not crack if the film thickness of the transparent electrode 4 is set to 1500 mm or more. confirmed.

  Furthermore, in order to obtain good results in crosstalk of display information and display quality of density gradient between pixel areas, it is important to form a reflective film of 4000 mm and a transparent electrode of 1500 mm or more. This is because, by increasing the thickness of the metal reflection film 6, the resistance of the entire transparent electrode 4 can be lowered, and the resistance of the transparent electrode 4 can be lowered. As a result, crosstalk and concentration gradient can be reduced. Furthermore, by forming 5000 mm of the metal reflective film 3 and 2000 mm of the transparent electrode 4, a liquid crystal display device free from crosstalk, concentration gradient, and cracks in the inorganic insulating film 6 could be obtained.

DESCRIPTION OF SYMBOLS 1 ... One glass substrate 2 ... The other glass substrate 3 ... Metal reflective film 4, 5 ... Transparent electrode 6 ... Inorganic insulating film 7, 8 ... Alignment film 9 ... Spacer 10 ... Liquid crystal layer

Claims (3)

And the transparent substrate of a pair,
A liquid crystal layer interposed between the pair of transparent substrates;
A reflective film provided on one of the pair of transparent substrates;
A transparent electrode provided on the one transparent substrate so as to cover the reflective film;
And an insulating film provided on the transparent conductive electrode,
The transparent electrode includes a first part located on the reflective film, a second part located outside the end of the reflective film and having a smaller thickness than the reflective film, the first part and the first part A liquid crystal display device having a third part that connects two parts and has a thickness that decreases as the second part is approached . The liquid crystal display device according to claim 1, wherein a thickness of the first portion is set smaller than a thickness of the reflective film. The thickness of the insulating film located on the second site, the liquid crystal display device according to claim 1 or 2 is set smaller than the thickness of the second portion.