JP2009175557A - Liquid crystal display device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a liquid crystal display device in which a highly precise pixel division using PSA technology is performed, while suppressing deterioration of display quality. <P>SOLUTION: The liquid crystal display device (100) has a pixel (P) including a first region (SPa) and a second region (SPb). The pixel (P) has a pair of oriented films (228, 248) disposed between a pair of electrodes (226, 246) and a liquid crystal layer (260) respectively, orientation maintaining layers (232, 252) disposed between each of the pair of the oriented films (228, 248) and the liquid crystal layer (260), and an ultraviolet light modulation layer (230) having an ultraviolet light high transmission region (230a) corresponding to the first region (SPa) of the pixel (P), and an ultraviolet light low transmission region (230b) corresponding to the second region (SPb) of the pixel. A threshold voltage in a V-T curve representing relationships between a voltage applied to the liquid crystal layer of the first region (SPa) and the transmission differs from a threshold voltage in a V-T curve of the second region (SPb). <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a liquid crystal display device.

  The liquid crystal display device is used not only as a small display device such as a display unit of a mobile phone but also as a large television. The viewing angle of a TN mode liquid crystal display device often used in the past has been relatively narrow. However, a relatively wide viewing angle has been realized in a VA mode liquid crystal display device. However, since a general VA mode liquid crystal display device does not have a good viewing angle dependency of the γ characteristic, when the liquid crystal display device displays an intermediate gray level, when the liquid crystal display device is viewed from an oblique direction, a so-called white floating occurs. Will occur. As a method for improving the viewing angle dependency of such γ characteristics, a plurality of regions having different brightnesses are formed in one pixel.

  Regions having different brightness can be realized by providing sub-pixel electrodes obtained by dividing the pixel electrode and applying different effective voltages to the liquid crystal layer. However, when the pixel electrode is divided, the aperture ratio decreases. Therefore, as another method for forming regions with different brightness, a method using Polymer Sustained Alignment Technology (hereinafter referred to as “PSA technology”) is known (see Patent Documents 1 and 2).

  The PSA technology is produced by mixing a small amount of polymerizable material (for example, photopolymerizable monomer) in a liquid crystal material, assembling a liquid crystal panel, and then irradiating the polymerizable material with active energy rays (for example, ultraviolet light). In this technique, the pretilt direction of liquid crystal molecules is controlled by the polymer to be used. The pretilt direction is represented by a pretilt azimuth and a pretilt angle. When the PSA technology is used, the alignment state of the liquid crystal molecules when the polymer is formed is maintained (stored), so the change in the alignment direction of the liquid crystal molecules with respect to the pretilt direction of the liquid crystal molecules and / or the applied voltage can be determined. Can be controlled.

  With reference to FIG. 13, the manufacturing method of the liquid crystal display device 700 currently disclosed by patent document 1 is demonstrated. In this manufacturing method, ultraviolet light is irradiated through a photomask in order to form regions A and B having different brightness in one pixel. The light shielding portion of the photomask corresponds to the region A, and the opening of the photomask corresponds to the region B. Irradiation with ultraviolet light is performed with no voltage applied. In the region B irradiated with ultraviolet light, a layer of ultraviolet cured material (not shown in FIG. 13) that restricts the movement of the liquid crystal molecules 762 is formed. Therefore, the anchoring strength of the liquid crystal molecules 762 by this layer in the region B is large. Therefore, when a VT curve indicating a change in transmittance with respect to each applied voltage in the regions A and B is measured, the threshold voltage of the VT curve in the region B is the threshold of the VT curve in the region A. Shifting to a higher voltage side than the value voltage, the region A is brighter than the region B in the intermediate gradation display.

With reference to FIG. 14, the manufacturing method of the liquid crystal display device 800 currently disclosed by patent document 2 is demonstrated. In the liquid crystal display device 800, an insulating layer 830 is selectively provided in the region A, and the liquid crystal layer 860 in the region A is thinner than the liquid crystal layer 860 in the region B. Irradiation with ultraviolet light is performed with a voltage applied. Since the insulating layer 830 is selectively provided in the region A, the pretilt angle of the liquid crystal molecules in the region A is larger than the pretilt angle of the liquid crystal molecules in the region B, and the threshold voltage of the VT curve in the region A Is shifted to a higher voltage side than the threshold voltage of the V-T curve of the region B, and the region B is brighter than the region A in the intermediate gradation display.
JP 2006-139046 A JP 2004-301979 A

  According to the manufacturing method disclosed in Patent Document 1, pixel regions A and B are formed corresponding to the light shielding portion and the opening of the photomask. However, the region A and the region B cannot be formed with high accuracy. This is because light that has passed through the opening of the photomask passes through a transparent substrate 722 such as a relatively thick glass substrate, so that a relatively large region B is formed with respect to the opening of the photomask. If a manufacturing method using a photomask is employed in this way, it is difficult to manufacture with high accuracy.

  Further, in the liquid crystal display device 800 disclosed in Patent Document 2, the insulating layer 830 is selectively formed in the region A, and the liquid crystal molecules are aligned along the step formed by the insulating layer 830. Leaks and the contrast ratio decreases. Further, since the thickness of the region A of the liquid crystal layer 860 is different from that of the region B, the alignment of the liquid crystal molecules in the pixel is not stable, and the display quality is deteriorated.

  The present invention has been made in view of the above problems, and an object of the present invention is to provide a liquid crystal display device in which high-precision pixel division using the PSA technology is performed while suppressing deterioration in display quality. .

  A liquid crystal display device according to the present invention is a liquid crystal display device having pixels including a first region and a second region, and the pixels are provided so as to sandwich a liquid crystal layer containing a liquid crystal material and the liquid crystal layer. A pair of electrodes, a pair of alignment films provided between the pair of electrodes and the liquid crystal layer, an alignment maintaining layer provided between each of the pair of alignment films and the liquid crystal layer, Corresponding to one of the first region and the second region of the pixel corresponding to one of the ultraviolet light high transmittance region and the other region of the first region and the second region of the pixel. And a threshold voltage in a VT curve indicating a relationship between a voltage applied to the liquid crystal layer in the one region and the transmittance. Threshold voltage in the VT curve of the other region Different.

  In one embodiment, in the ultraviolet light modulation layer, the thickness of the ultraviolet light low transmittance region is substantially equal to the thickness of the ultraviolet light high transmittance region.

  In one embodiment, the pretilt angle of the liquid crystal molecules of the liquid crystal layer due to the portion corresponding to the ultraviolet light high transmittance region of the alignment maintaining layer corresponds to the ultraviolet light low transmittance region of the alignment maintaining layer. The threshold voltage in the VT curve of the one region is lower than the threshold voltage in the VT curve of the other region, which is smaller than the pretilt angle of the liquid crystal molecules of the liquid crystal layer.

  In one embodiment, the anchoring strength of the portion corresponding to the ultraviolet light high transmittance region in the orientation maintaining layer is higher than the anchoring strength of the portion corresponding to the ultraviolet light low transmittance region in the orientation maintaining layer. The threshold voltage in the VT curve of the one region is higher than the threshold voltage in the VT curve of the other region.

  In one embodiment, the visible light transmittance in the low ultraviolet light transmittance region is substantially equal to the visible light transmittance in the high ultraviolet light transmittance region.

  In one embodiment, the semiconductor device further comprises an active matrix substrate including a switching element, a plurality of wirings, and an insulating layer together with one electrode of the pair of electrodes and one alignment film of the pair of alignment films, An insulating layer functions as the ultraviolet light modulation layer.

  In one embodiment, the insulating layer is made of a photosensitive resin.

  ADVANTAGE OF THE INVENTION According to this invention, the liquid crystal display device by which the highly accurate pixel division using PSA technology was performed, suppressing the display quality fall can be provided.

  Hereinafter, embodiments of a liquid crystal display device according to the present invention will be described with reference to the drawings.

  FIG. 1 shows a schematic diagram of a liquid crystal display device 100 of the present embodiment. The liquid crystal display device 100 includes a liquid crystal panel 200 and a backlight 300 that emits light toward the liquid crystal panel 200. The liquid crystal panel 200 includes an active matrix substrate 220, a counter substrate 240, and a liquid crystal layer 260 disposed between the active matrix substrate 220 and the counter substrate 240. Here, the liquid crystal display device 100 is a transmissive liquid crystal display device.

  The active matrix substrate 220 includes a transparent substrate 222, a thin film transistor (TFT) 224 that functions as a switching element, a pixel electrode 226, and a first alignment film 228. Although not shown in FIG. 1, a plurality of wirings connected to the TFT 224 are provided.

  The counter substrate 240 includes a transparent substrate 242, a colored layer 244, a counter electrode 246, and a second alignment film 248. The transparent substrate 222 and the transparent substrate 242 are, for example, a glass substrate or a plastic substrate.

  The liquid crystal layer 260 is a vertical alignment type. The liquid crystal layer 260 has a negative dielectric anisotropy nematic liquid crystal material. Although not shown, a polarizing plate is provided on each of the active matrix substrate 220 and the counter substrate 240, and the two polarizing plates are disposed so as to face each other with the liquid crystal layer 260 interposed therebetween. The transmission axes (polarization axes) of the two polarizing plates are arranged so as to be orthogonal to each other, with one arranged along the horizontal direction (row direction) and the other along the vertical direction (column direction). A normally black mode display is performed by combining the liquid crystal layer 260 with the polarizing plates arranged in crossed Nicols in this way.

  A first alignment sustaining layer 232 is provided between the active matrix substrate 220 and the liquid crystal layer 260, and a second alignment maintaining layer 252 is provided between the counter substrate 240 and the liquid crystal layer 260. . In FIG. 1, the first and second alignment sustaining layers 232 and 252 are shown as films covering the entire surfaces of the first and second alignment films 228 and 248, but the first and second alignment maintaining layers 232, 252 may not be provided so as to cover the entire surfaces of the first and second alignment films 228 and 248, and may be provided in an island shape.

  The first orientation maintaining layer 232 and the second orientation maintaining layer 252 are made of a polymer. The first and second alignment maintaining layers 232 and 252 are formed by irradiating the photopolymerizable composition (not shown in FIG. 1) mixed with the liquid crystal material 262 with ultraviolet light. In the following description, the process of forming the first and second alignment sustaining layers 232 and 252 is also referred to as a PSA process. Before performing the PSA process, the first and second alignment sustaining layers 232 and 252 are not formed, and unless a voltage is applied between the pixel electrode 226 and the counter electrode 246, the liquid crystal molecules 262 in the liquid crystal layer 260 are formed. Are aligned approximately perpendicular to the principal surfaces of the first and second alignment films 228 and 248, and the pretilt angle of the liquid crystal molecules is approximately 90 °. The pretilt angle is an angle between the main surfaces of the first and second alignment films 228 and 248 and the major axis direction of the liquid crystal molecules. The first and second alignment films 228 and 248 are vertical alignment films. Here, when the first and second alignment maintaining layers 232 and 252 are formed by performing the PSA process in a state where a voltage is applied between the pixel electrode 226 and the counter electrode 246, the first and second alignment maintaining is performed. Since the alignment of the liquid crystal molecules inclined according to the electric field is maintained by the layers 232 and 252, the pretilt angle of the liquid crystal molecules 262 is lower than 90 °.

  The active matrix substrate 220 of the liquid crystal display device 100 of the present embodiment is provided with an ultraviolet light modulation layer 230. The ultraviolet light modulation layer 230 has an ultraviolet light high transmittance region 230a and an ultraviolet light low transmittance region 230b having a lower ultraviolet light transmittance than the ultraviolet light high transmittance region 230a. Here, the ultraviolet light low transmittance region 230b mainly absorbs ultraviolet light, but the ultraviolet light low transmittance region 230b may mainly reflect ultraviolet light. The visible light transmittance of the ultraviolet light low transmittance region 230b is substantially equal to the ultraviolet light high transmittance region 230a. The thickness of the ultraviolet light high transmittance region 230a is substantially equal to that of the ultraviolet light low transmittance region 230b.

  In the following description, the ultraviolet light modulation layer, the ultraviolet light high transmittance region, and the ultraviolet light low transmittance region are also referred to as a UV modulation layer, a UV high transmittance region, and a UV low transmittance region, respectively. In the liquid crystal display device 100 shown in FIG. 1, the interlayer insulating layer disposed between the transparent substrate 222 and the pixel electrode 226 functions as the UV modulation layer 230. However, the UV modulation layer 230 may be provided separately from the interlayer insulating layer. Further, the UV modulation layer 230 may be arranged at a position different from between the transparent substrate 222 and the pixel electrode 226. For example, the UV modulation layer 230 may be provided closer to the backlight 300 than the transparent substrate 222.

  The liquid crystal display device 100 is provided with a plurality of pixels P in a matrix of a plurality of rows and columns. In the liquid crystal display device 100, one pixel P is defined by the pixel electrode 226. In general, the counter electrode 236 is a single electrode common to a plurality of pixels P. One pixel P has a first region SPa and a second region SPb. The first region SPa corresponds to the UV high transmittance region 230a, and the second region SPb corresponds to the UV low transmittance region 230b. In FIG. 1, in the liquid crystal layer 260, a region corresponding to the first region SPa is indicated as a liquid crystal region 260a, and a region corresponding to the second region SPb is indicated as a liquid crystal region 260b. The thickness of the liquid crystal region 260a is substantially equal to the thickness of the liquid crystal region 260b.

  In the liquid crystal display device 100, the VT curve in the first region SPa is different from the VT curve in the second region SPb, and the viewing angle dependency of the γ characteristic is improved. Here, the pretilt angle of the liquid crystal molecules 262 in the liquid crystal region 260a is smaller than the pretilt angle of the liquid crystal molecules 262 in the liquid crystal region 260b. That is, in the state where no voltage is applied, the inclination of the alignment direction of the liquid crystal molecules 262 in the liquid crystal region 260a with respect to the normal direction of the main surfaces of the first and second alignment films 228 and 248 is larger than the liquid crystal molecules 262 in the liquid crystal region 260b. In this specification, the angle of inclination of the liquid crystal molecules 262 with respect to the normal direction of the main surfaces of the first and second alignment films 228 and 248 in the voltage-free state is referred to as an inclination angle. The sum of the tilt angle and the pretilt angle is 90 °. Since the tilt angle of the liquid crystal molecules 262 in the liquid crystal region 260a is larger than the tilt angle of the liquid crystal molecules 262 in the liquid crystal region 260b, even if a voltage is applied to the liquid crystal layer 260 of the pixel P, the method of the principal surface of the first alignment film 228 is performed. The inclination of the liquid crystal molecules 262 in the liquid crystal region 260a with respect to the line direction is larger than the inclination of the liquid crystal molecules 262 in the liquid crystal region 260b, and the first region SPa is brighter than the second region SPb when displaying an intermediate gradation. .

  In the liquid crystal display device 100 of the present embodiment, the UV modulation layer 230 changes the illuminance of ultraviolet light in the PSA process, and thereby, the UV high transmittance region 230a and the UV low transmittance region 230b of the UV modulation layer 230 are changed. Correspondingly, the first region SPa and the second region SPb are formed with high accuracy. The UV modulation layer 230 has a UV high transmittance region 230a and a UV low transmittance region 230b corresponding to the first region SPa and the second region SPb, and the boundary between the first region SPa and the second region SPb. The step of the first alignment film 228 is small or substantially absent. For this reason, light leakage is suppressed, and disorder of alignment of the liquid crystal molecules 262 can be suppressed.

  Next, with reference to FIG. 2, the manufacturing method of the liquid crystal display device 100 of this embodiment is demonstrated.

  As shown in FIG. 2A, an active matrix substrate 220 provided with a TFT 224, a UV modulation layer 230, a pixel electrode 226, and a first alignment film 228 on a transparent substrate 222 is prepared. Although not shown in FIG. 2A, a wiring or the like connected to the TFT 224 is provided between the transparent substrate 222 and the pixel electrode 226.

  Next, as shown in FIG. 2B, a counter substrate 240 provided with a colored layer 244, a counter electrode 246 and a second alignment film 248 is prepared on a transparent substrate 242.

  Next, as shown in FIG. 2C, the active matrix substrate 220 and the counter substrate 240 are arranged so that the first alignment film 228 and the second alignment film 248 face each other. Thereafter, a liquid crystal material 262 mixed with the photopolymerizable composition 264 is applied between the first alignment film 228 and the second alignment film 248. Thereby, the liquid crystal panel 200 is produced. The photopolymerizable composition is, for example, a photopolymerizable monomer, a photopolymerizable oligomer, or a mixture thereof. As the photopolymerizable monomer, for example, a diacrylate or dimethacrylate monomer having a liquid crystal skeleton is used. The photopolymerizable composition 264 is added at a concentration of about 0.3 wt% with respect to the liquid crystal material 262.

  Then, as shown in FIG.2 (d), an ultraviolet light is irradiated. During irradiation with ultraviolet light, a voltage is applied between the pixel electrode 226 and the counter electrode 246. By applying a voltage, the liquid crystal molecules 262 are aligned in a predetermined alignment direction, and the liquid crystal molecules 262 are tilted from the normal direction of the main surfaces of the first and second alignment films 228 and 248. Although not shown in FIGS. 1 and 2, the pixel electrode 226 and the counter electrode 246 are provided with slits and / or ribs, and the liquid crystal molecules are aligned according to the alignment regulating force generated due to the slits and ribs. To do. Alternatively, the pixel electrode 226 and the counter electrode 246 may not be provided with slits and / or ribs, and the liquid crystal molecules may be aligned according to an oblique electric field generated due to the shape of the pixel electrode 226.

  The ultraviolet light is applied to the liquid crystal panel 200 from the active matrix substrate 220 side. For example, a light source that mainly emits ultraviolet light (i-line) having a wavelength of 365 nm can be suitably used, and the irradiation time is, for example, about 500 seconds. The ultraviolet light passes through the UV modulation layer 230 and reaches the liquid crystal layer 260. Thereby, the photopolymerizable composition 264 in the liquid crystal layer 260 is polymerized, and the first and second alignment maintaining layers 232 and 252 are formed. In this case, since the light transmittance of the UV high transmittance region 230a of the UV modulation layer 230 is higher than that of the UV low transmittance region 230b, the first and second orientation maintaining layers 232 and 252 formed in the first region SPa. The alignment maintaining force of the liquid crystal region 260a on the liquid crystal molecules 262 is stronger than the alignment maintaining force of the liquid crystal region 260b on the liquid crystal molecules 262 by the first and second alignment maintaining layers 232 and 252 formed in the second region SPb. In addition, since the distance between the UV modulation layer 230 and the liquid crystal layer 260 is short, the first and second regions SPa and SPb having different alignment maintaining forces by the first and second alignment maintaining layers 232 and 252 are formed with high accuracy. The alignment error is also small.

  After that, when the voltage between the pixel electrode 226 and the counter electrode 246 is removed, the liquid crystal molecules 262 of the liquid crystal layer 260 have a force in a direction to return in parallel to the normal direction of the main surfaces of the first and second alignment films 228 and 248. However, the alignment direction of the liquid crystal molecules during the PSA process is maintained by the first and second alignment maintaining layers 232 and 252 formed in the PSA process. As described above, the alignment maintaining force of the liquid crystal region 260a on the liquid crystal molecules 262 by the first alignment maintaining layer 232 formed in the first region SPa is the liquid crystal region formed by the second alignment maintaining layer 252 formed in the second region SPb. Since it is different from the alignment maintaining force of 260b on the liquid crystal molecules 262, due to the difference in alignment maintaining force, the tilt angle of the liquid crystal molecules 262 in the liquid crystal region 260a is larger than the tilt angle of the liquid crystal molecules 262 in the liquid crystal region 260b.

  In this case, when a voltage is applied between the pixel electrode 226 and the counter electrode 246 in order for the liquid crystal display device 100 to display an intermediate gray level, the liquid crystal region 260 a in the normal direction of the main surface of the first alignment film 228 is displayed. The inclination of the liquid crystal molecules 262 is larger than the inclination of the liquid crystal molecules 262 in the liquid crystal region 260b. Thus, the first region SPa is brighter than the second region SPb. Thereafter, the liquid crystal display device 100 is manufactured by assembling the liquid crystal panel 200 and the backlight 300 shown in FIG.

  Note that the photopolymerizable composition 264 may remain in the liquid crystal layer 260 even after the PSA process. For this reason, the concentration of the photopolymerizable composition 264 in the liquid crystal layer 260 may be lowered by further irradiating ultraviolet light after the PSA process. As described above, irradiation with ultraviolet light performed to reduce the concentration of the photopolymerizable composition 264 in the liquid crystal layer 260 is also called secondary irradiation. Even if secondary irradiation is performed, the tilt angle hardly changes. For example, when the tilt angle before performing the secondary irradiation is 5.0 °, the tilt angle after performing the secondary irradiation is 4.7 to 4.8 °.

  Hereinafter, with reference to FIG. 3, the change of the VT curve according to the change of the inclination angle will be described. FIG. 3A shows a VT curve corresponding to the change in the tilt angle, and FIG. 3B shows an enlarged view of the voltage range of 1.5 to 2.5 V in FIG. Show.

  As the applied voltage increases, the transmittance also increases. However, as shown in FIG. 3A, the transmittance increases rapidly when the applied voltage is around 2.5V. Thus, the point where the transmittance increases rapidly is called the rise of the VT curve.

  When the applied voltages are equal, the greater the tilt angle, the higher the transmittance. Further, the larger the tilt angle, the lower the rising voltage of the VT curve. A threshold voltage is used as an index of the rising voltage of the VT curve. Here, when the transmittance at the lowest gradation level is 0% relative transmittance and the transmittance at the highest gradation level is 100% relative transmittance, the relative transmittance is 10%. % Is defined as the applied voltage. When the inclination angle is 1.28 °, 2.1 °, 2.93 °, 3.28 °, 4 °, 4.4 °, the threshold voltage Vth is 2.93, 2.88, respectively. 2.85, 2.80, 2.78, 2.75V. Thus, the threshold voltage is lower as the tilt angle is larger.

The tilt angle of the liquid crystal molecules after the PSA process changes according to the irradiation amount of ultraviolet light during the PSA process. FIG. 4 shows a change in the tilt angle of the liquid crystal molecules after the PSA process with respect to the ultraviolet light irradiation amount during the PSA process. Here, the result of measuring the change of the tilt angle with respect to the dose without providing the UV modulation layer is shown. The monomer concentration is 0.3 wt%, the applied voltage is 15 V, and the irradiation intensity of ultraviolet light is 23 mW / cm ² .

The greater the irradiation amount, the greater the alignment maintaining force by the alignment maintaining layer and the greater the tilt angle after removing the voltage. In order to improve the viewing angle dependency of the γ characteristic, the difference ΔVth between the threshold voltage of the first region SPa and the threshold voltage of the second region SPb is preferably about 0.3 V or more. . In order to obtain ΔVth of 0.3 V or more, the difference Δθ between the tilt angle of the liquid crystal molecules in the liquid crystal region 260a and the tilt angle of the liquid crystal molecules in the liquid crystal region 260b is preferably 3 ° or more. [Delta] [theta] = 3 ° in order to achieve, for example, a liquid crystal region 260a, the irradiation amount of 260b each may be a ^{10J / cm 2, 15J / cm} 2, such irradiation dose, UV high transmittance region 230a This can be realized if the UV light transmittance of the UV low transmittance region 230b is 40% and 60%, respectively. Thus, it is preferable that the ultraviolet light transmittance of the UV high transmittance region 230a is about 1.5 times the ultraviolet light transmittance of the UV low transmittance region 230b. In addition, when the ultraviolet light transmittance of the UV high transmittance region 230a and the UV low transmittance region 230b is 90% and 50%, respectively, and the irradiation amount is 20 J / cm ² , the first region is shown in FIG. The inclination angles of the liquid crystal molecules 262 in the SPa and the second region SPb are 8 ° and 1.5 °, respectively.

With reference to FIG. 5, the change of the inclination angle according to the irradiation intensity of the ultraviolet light at the PSA process will be described. FIG. 5 shows a change in tilt angle with respect to the irradiation intensity of ultraviolet light during the PSA process. Here, the result of measuring the change in the tilt angle with respect to the irradiation intensity of the ultraviolet light without providing the UV modulation layer is shown. Here, the dose is kept constant at 20 J / cm ² . Therefore, when the irradiation intensity is 20 mW / cm ² , the irradiation time is 1000 seconds, and when the irradiation intensity is 50 mW / cm ² , the irradiation time is 400 seconds. In the measurement of FIG. 5, a material different from that of FIG. 4 is used, and the inclination angle is different.

As understood from FIG. 5, the higher the irradiation intensity (that is, the shorter the irradiation time), the lower the inclination angle. However, when the irradiation intensity is 20 to 50 mW / cm ² , the inclination angle is It is almost constant. FIG. 5 shows the results when the applied voltage in the PSA process is changed to 5V, 10V and 15V. As can be seen from FIG. 5, the higher the applied voltage, the larger the tilt angle.

  As described above, the interlayer insulating layer may function as the UV modulation layer 230. Before describing the ultraviolet light transmittance and forming method of the interlayer insulating layer functioning as the UV modulation layer 230, the ultraviolet light transmittance and forming method of a general interlayer insulating layer will be described with reference to FIGS. To do.

  In FIG. 6, the insulating layer is made of a photosensitive resin. This photosensitive resin is a positive type. As understood from FIG. 6, the transmittance of the interlayer insulating layer is relatively low at a wavelength of less than 400 nm corresponding to the ultraviolet light region, and the transmittance of the interlayer insulating layer is compared at a wavelength of 400 nm or more corresponding to the visible light region. High. In FIG. 6, the thickness of the insulating layer is 3.0 μm.

  Here, a general method for forming an interlayer insulating layer will be described with reference to FIG.

  As shown in FIG. 7A, the insulating layer D1 is formed on the transparent substrate 522 by spin coating. The insulating layer D1 is made of a positive photosensitive resin. After the formation of the insulating layer D1, pre-baking is performed.

  Next, as shown in FIG. 7B, exposure is performed through a photomask. This exposure is also called mask exposure. In the insulating layer D1, the characteristics of the portion irradiated with the light that has passed through the opening of the photomask change. As light in mask exposure, for example, gh line or ghi line is used.

  Next, as shown in FIG. 7C, when the phenomenon is performed, the portion of the insulating layer D1 that has been irradiated with light and whose characteristics have changed is dissolved and removed. Thereby, an interlayer insulating layer 530 provided with contact holes is formed. The drain electrode of the TFT is exposed from the contact hole.

  Next, as shown in FIG. 7D, post exposure is performed. By this post-exposure, light is irradiated to the portion of the insulating layer D1 that has not been irradiated with light in the previous mask exposure, so that the characteristics of the interlayer insulating layer 530 change and the transmittance of the interlayer insulating layer 530 increases. . This post exposure is also referred to as photo bleach exposure.

  Thereafter, post-baking is performed. The post-baking removes the remaining liquid such as a developing solution and improves the adhesion of the interlayer insulating layer 530. As described above, the interlayer insulating layer 530 is formed.

  In order for the interlayer insulating layer to function as the UV modulation layer 230 of the liquid crystal display device 100 of the present embodiment, it is necessary to form an insulating layer having regions with different ultraviolet light transmittances. Hereinafter, with reference to FIGS. 8 to 11, a change in the ultraviolet light transmittance of the insulating layer and a method for forming the interlayer insulating layer functioning as the UV modulation layer 230 will be described.

  As described above, the transmittance of the insulating layer is increased by performing the post exposure. FIG. 8 shows the transmission spectrum of the insulating layer that has been post-exposed and the transmission spectrum of the insulating layer that has not been post-exposed.

When the post-exposure is not performed, the transmittance of the insulating layer is low at a wavelength of 600 nm or less, but when the post-exposure is performed, the transmittance of the insulating layer increases particularly in the visible light region, and the transmittance of the interlayer insulating layer in the visible light region. The rate is almost constant. Here, the same light source as that for mask exposure is used as a light source for post exposure, and light of gh line or ghi line is irradiated. The wavelength of g-line is 436 nm, the wavelength of h-line is 405 nm, and the wavelength of i-line is 365 nm. Moreover, the irradiation amount of ultraviolet rays in the post-exposure is 300 mJ / cm ² .

  An interlayer insulating layer functioning as the UV modulation layer 230 can be formed by utilizing the fact that the UV transmittance of the insulating layer changes depending on the presence or absence of post-exposure. Hereinafter, a method for forming an interlayer insulating layer functioning as the UV modulation layer 230 of the liquid crystal display device 100 of the present embodiment will be described with reference to FIG.

  As shown in FIG. 9A, the insulating layer D1 is formed on the transparent substrate 222 by spin coating. Here, TFTs and the like are omitted. The insulating layer D1 is made of a positive photosensitive resin. After the formation of the insulating layer D1, pre-baking is performed.

  Next, as shown in FIG. 9B, exposure is performed through a photomask. The photomask has openings and light shielding portions arranged in a predetermined pattern. Note that the opening of the photomask corresponds to the first region SPa of the pixel P, and the light shielding portion corresponds to the second region SPb of the pixel P. The characteristic of the portion of the insulating layer D1 irradiated with light that has passed through the opening of the photomask changes.

  Next, as shown in FIG. 9C, when the phenomenon is performed, the portion of the insulating layer D1 that has been irradiated with light and changed in characteristics is dissolved and removed, and the insulating layer 230x is formed. The insulating layer 230x thus formed is referred to as a first insulating layer.

  Next, as shown in FIG. 9D, post-exposure is performed on the first insulating layer 230x. The transmittance of the first insulating layer 230x is improved by the post exposure. Thereafter, post baking is performed on the first insulating layer 230x. Post-baking is performed by heating at a temperature of 220 ° C. for 1 hour in a clean oven. The post-baking improves the adhesion of the first insulating layer 230x.

  Next, as shown in FIG. 9E, an insulating layer D2 that covers the first insulating layer 230x is formed by spin coating. The insulating layer D2 is formed of a positive photosensitive resin similar to the first insulating layer D1. After the formation of the insulating layer D2, pre-baking is performed.

  Next, as shown in FIG. 9F, exposure is performed through a photomask. The opening of the photomask is provided so as to correspond to the first insulating layer 230x.

  Next, as shown in FIG. 9G, an insulating layer 230y disposed between the first insulating layers 230x is formed by performing the phenomenon. Thus, the insulating layer 230y formed between the first insulating layers 230x is referred to as a second insulating layer.

  Next, as shown in FIG. 9H, post baking is performed on the first insulating layer 230x and the second insulating layer 230y without performing post exposure. Post-baking is performed by heating at a temperature of 220 ° C. for 1 hour in a clean oven. Thereby, the adhesiveness of the 1st insulating layer 230x and the 2nd insulating layer 230y improves. Note that a contact hole may be formed as necessary, and the contact hole is preferably formed before pre-baking. As described above, an interlayer insulating layer is formed.

  The post-exposure is performed on the first insulating layer 230x, whereas the post-exposure is not performed on the second insulating layer 230y. As described above with reference to FIG. 8, the transmittance of the first insulating layer 230x is higher than the transmittance of the second insulating layer 230y. Therefore, the first insulating layer 230x and the first insulating layer 230y correspond to the UV high transmittance region 230a and the UV low transmittance region 230b of the UV modulation layer 230, respectively, and the interlayer insulating layer functions as the UV modulation layer 230. To do.

  In the above description, in order to form an insulating layer having regions having different ultraviolet light transmittances, a change in ultraviolet light transmittance due to post-exposure is used. However, the present invention is not limited to this. An insulating layer having regions with different ultraviolet light transmittances may be formed by utilizing a change in ultraviolet light transmittance due to additional baking after post-baking. In the following description, baking performed additionally to post baking is also referred to as “additional baking”.

  FIG. 10 shows the transmission spectrum of the insulating layer according to the presence or absence of additional firing and the change in temperature during additional firing. FIG. 10 shows a transmission spectrum of an insulating layer post-baked by heating at 220 ° C. for 1 hour in a clean oven, and additional firing by heating at 220 ° C. and 250 ° C. for another hour in the clean oven after the post-baking. The transmission spectrum of an insulating layer when performing is shown.

  As shown in FIG. 10, the transmittance of the insulating layer after post-baking is relatively high, but the additional layer is subjected to additional baking after the post-baking, so that the transmittance of the insulating layer is lowered particularly in the ultraviolet light region. Moreover, the transmittance | permeability falls largely, so that the temperature at the time of additional baking is high. Thus, the additional baking is performed after post-baking, whereby the transmittance of the insulating layer can be reduced. Moreover, the difference in UV transmittance can be increased as the temperature during additional baking is higher. However, the higher the temperature during additional baking, the more constant the transmittance in the visible light region.

  An interlayer insulating layer functioning as a UV modulation layer can be formed by utilizing the additional baking and the fact that the UV transmittance of the insulating layer changes according to the temperature. Hereinafter, a method for forming an interlayer insulating layer functioning as the UV modulation layer 230 of the liquid crystal display device 100 of the present embodiment will be described with reference to FIG.

  As shown in FIG. 11A, the insulating layer D1 is formed on the transparent substrate 222 by spin coating. The insulating layer D1 is made of a positive photosensitive resin. After the formation of the insulating layer D1, pre-baking is performed.

  Next, as shown in FIG. 11B, exposure is performed through a photomask. The photomask has openings and light shielding portions arranged in a predetermined pattern. The opening portion of the photomask corresponds to the second region SPb of the pixel P, and the light shielding portion corresponds to the first region SPa of the pixel P. The characteristic of the portion of the insulating layer D1 irradiated with light that has passed through the opening of the photomask changes.

  Next, as shown in FIG. 11C, when the phenomenon is performed, the portion of the insulating layer D1 that has been irradiated with light and changed in characteristics is dissolved and removed, and the first insulating layer 230x is formed.

  Next, as shown in FIG. 11D, post-baking is performed. Post-baking is performed by heating at a temperature of 220 ° C. for 1 hour in a clean oven. The post-baking improves the adhesion of the first insulating layer 230x. Thereafter, additional firing is performed. The additional baking is performed, for example, by heating to a temperature of 220 to 250 ° C. for 1 hour using a clean oven that has been post-baked as it is.

  Next, as shown in FIG. 11E, an insulating layer D2 that covers the insulating layer 230x is formed by spin coating. The insulating layer D2 is made of the same photosensitive resin as the insulating layer D1. After the formation of the insulating layer D2, pre-baking is performed.

  Next, as shown in FIG. 11F, exposure is performed through a photomask. The opening of the photomask is provided so as to correspond to the first insulating layer 230x.

  Next, as shown in FIG. 11G, by performing the phenomenon, a second insulating layer 230y disposed between the first insulating layers 230x is formed.

  Next, as shown in FIG. 11 (h), post-baking is performed. Post-baking is performed by heating at a temperature of 220 ° C. for 1 hour in a clean oven. As described above, an interlayer insulating layer is formed.

  The additional baking is performed on the first insulating layer 230x, whereas the additional baking is not performed on the second insulating layer 230y. Therefore, as described above with reference to FIG. 10, the transmittance of the first insulating layer 230x is lower than the transmittance of the second insulating layer 230y. Therefore, the first insulating layer 230x and the second insulating layer 230y correspond to the UV low transmittance region 230b and the UV high transmittance region 230a of the UV modulation layer 230, respectively, and the interlayer insulating layer functions as the UV modulation layer 230. To do.

In the mask exposure shown in FIG. 9 and FIG. 11, the dose at the time of mask exposure is, for example, 20 to 40 mJ / cm ² , and the region that becomes the first insulating layer 230x is shielded from light by the photomask. This is to prevent the photosensitive resin from being dissolved in the developer by preventing the photosensitive resin from being irradiated with light. On the other hand, as described above with reference to FIG. 2, the UV modulation layer 230 formed from a photosensitive resin is irradiated with ultraviolet light in the PSA process. The irradiation amount at the PSA step is, for example, 10 J / cm ² , which is not much different from the irradiation amount at the time of mask exposure. However, since the post-baking is performed in advance, such a large irradiation amount is obtained in the PSA step. The ultraviolet light transmittance of the UV modulation layer 230 hardly changes even when irradiated with ultraviolet light.

  FIG. 12 shows the transmission spectrum of the interlayer insulating layer before and after the PSA process. Here, as the PSA process, ultraviolet light with an irradiation amount of 10 J is irradiated. As can be understood from FIG. 12, the ultraviolet light transmittance of the insulating layer hardly changes before and after the PSA process. This is because by performing post-baking when forming the insulating layer, the ultraviolet light transmittance of the insulating layer hardly changes with irradiation of ultraviolet light.

  In the above description, different pre-tilt angles are used to form regions with different VT curves, but the present invention is not limited to this. As disclosed in Patent Document 1, different anchoring strengths may be used to form regions having different VT curves. For example, when ultraviolet light is irradiated through the UV modulation layer 230 having the UV high transmittance region 230a and the UV low transmittance region 230b without applying a voltage in the PSA process, the pretilt of the liquid crystal molecules in the liquid crystal regions 260a and 260b is applied. Anchoring strength can be varied while the angle remains approximately 90 °. In this case, since the anchoring strength of the liquid crystal region 260a corresponding to the UV high transmittance region 230a is larger than the anchoring strength of the liquid crystal region 260b corresponding to the UV high transmittance region 230b, the pixel electrode 226 and the counter electrode 246 When a voltage is applied between them, the inclination of the liquid crystal molecules 262 in the liquid crystal region 260a corresponding to the UV high transmittance region 230a with respect to the normal direction of the main surface of the first alignment film 228 is in the UV low transmittance region 230b. It is smaller than the liquid crystal molecules 262 in the corresponding liquid crystal region 260b. For this reason, the threshold voltage of the first region SPa is shifted to a lower voltage side than the threshold voltage of the second region SPb. Alternatively, both the pretilt angle and the anchoring strength may be different.

  Note that the response speed can be improved by controlling the liquid crystal molecules in the VA mode liquid crystal display device to be inclined from the normal direction of the main surface of the alignment film. In addition, by defining the pretilt azimuth so that the alignment direction of the liquid crystal molecules in the pixel is symmetric, a good viewing angle characteristic can be realized.

  In the above description, the liquid crystal display device is a transmissive type, but the present invention is not limited to this. The liquid crystal display device may be a transflective liquid crystal display device.

  In the above description, the UV modulation layer is provided between the transparent substrate and the first alignment film, but the present invention is not limited to this. The UV modulation layer may be provided so as to face the first alignment film through the transparent substrate.

  In the above description, the pixel P has the two regions SPa and SPb, but the present invention is not limited to this. The pixel P may have three or more regions.

  In the liquid crystal display device according to the present invention, pixel division is performed with high accuracy using the PSA technique, and a decrease in aperture ratio is suppressed. In addition, a UV modulation layer is provided for different regions where the pixels are divided, so that deterioration in display quality is suppressed.

1 is a schematic view of an embodiment of a liquid crystal display device according to the present invention. (A)-(d) is a schematic diagram for demonstrating the manufacturing method of the liquid crystal display device of this embodiment, respectively. (A) is a graph which shows the change of the VT curve with respect to the change of an inclination angle, (b) is a graph which expanded a part of (a). It is a graph which shows the change of the inclination angle according to the change of the irradiation amount at the time of a PSA process. It is a graph which shows the change of the inclination angle with respect to irradiation intensity. It is a graph which shows the change of the transmittance | permeability with respect to the wavelength of a common interlayer insulation layer. (A)-(d) is a schematic diagram for demonstrating the formation method of a common interlayer insulation layer, respectively. It is a graph for demonstrating the improvement of the transmittance | permeability by post exposure. (A)-(h) is a schematic diagram for demonstrating the formation method of the interlayer insulation layer in the liquid crystal display device of this embodiment, respectively. It is a graph for demonstrating the fall of the transmittance | permeability by additional baking. (A)-(h) is a schematic diagram for demonstrating another formation method of the interlayer insulation layer in the liquid crystal display device of this embodiment, respectively. It is a graph which shows the change of the transmittance | permeability of the interlayer insulation film before and behind a PSA process. It is a schematic diagram of the conventional liquid crystal display device. It is a schematic diagram of another conventional liquid crystal display device.

Explanation of symbols

DESCRIPTION OF SYMBOLS 100 Liquid crystal display device 200 Liquid crystal panel 220 Active matrix substrate 222 Transparent substrate 224 TFT
226 Pixel electrode 228 First alignment film 230 UV modulation layer 230a UV high transmittance region 230b UV low transmittance region 232 First alignment maintaining layer 240 Counter substrate 242 Transparent substrate 244 Colored layer 246 Counter electrode 248 Second alignment film 252 Second Alignment maintaining layer 260 Liquid crystal layer 300 Backlight

Claims (7)

A liquid crystal display device having a pixel including a first region and a second region,
The pixel is
A liquid crystal layer containing a liquid crystal material;
A pair of electrodes provided to sandwich the liquid crystal layer;
A pair of alignment films respectively provided between the pair of electrodes and the liquid crystal layer;
An alignment maintaining layer provided between each of the pair of alignment films and the liquid crystal layer;
Corresponding to one of the first region and the second region of the pixel corresponding to one of the ultraviolet light high transmittance region and the other region of the first region and the second region of the pixel. An ultraviolet light modulation layer having an ultraviolet light low transmittance region,
A liquid crystal display device in which a threshold voltage in a VT curve indicating a relationship between a voltage applied to the liquid crystal layer in one region and a transmittance is different from a threshold voltage in the VT curve in the other region .   2. The liquid crystal display device according to claim 1, wherein in the ultraviolet light modulation layer, the thickness of the ultraviolet light low transmittance region is substantially equal to the thickness of the ultraviolet light high transmittance region. The pretilt angle of the liquid crystal molecules of the liquid crystal layer due to the portion corresponding to the ultraviolet light high transmittance region of the alignment maintaining layer is the liquid crystal layer due to the portion corresponding to the ultraviolet light low transmittance region of the alignment maintaining layer. Smaller than the pretilt angle of the liquid crystal molecules of
3. The liquid crystal display device according to claim 1, wherein a threshold voltage in the VT curve of the one region is lower than a threshold voltage in the VT curve of the other region. The anchoring strength of the portion corresponding to the ultraviolet light high transmittance region of the orientation maintaining layer is larger than the anchoring strength of the portion corresponding to the ultraviolet light low transmittance region of the orientation maintaining layer,
3. The liquid crystal display device according to claim 1, wherein a threshold voltage in the VT curve of the one region is higher than a threshold voltage in the VT curve of the other region.   The liquid crystal display device according to claim 1, wherein a visible light transmittance in the low ultraviolet light transmittance region is substantially equal to a visible light transmittance in the high ultraviolet light transmittance region. An active matrix substrate further including a switching element, a plurality of wirings, and an insulating layer together with one of the pair of electrodes and one of the pair of alignment films;
The liquid crystal display device according to claim 1, wherein the insulating layer functions as the ultraviolet light modulation layer.   The liquid crystal display device according to claim 6, wherein the insulating layer is made of a photosensitive resin.

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