Liquid crystal display

The present invention relates to a transflective liquid crystal display device having a wide viewing angle.

Currently, wide-viewing-angle transmissive liquid crystal displays such as the IPS (In Plane Switching) method and VA (Vertical Alignment) method are widely used as liquid crystal monitors, and further improved video characteristics as liquid crystal televisions. Is also beginning to be used. While these LCD monitors and LCD TVs are used indoors, LCD display devices are also widespread in portable information devices such as mobile phones and digital cameras. A display device for a portable information device is used by an individual, but a wide viewing angle is still desired because it may be observed from an oblique direction like a digital camera. There is an opinion that a wide viewing angle is disadvantageous for the protection of privacy, but some kind of peep prevention device is required, and a narrow viewing angle characteristic is not desired.

Since the display device for portable information devices is used in a wide environment from outdoors to dark rooms in fine weather, it is desirable that the display device is semi-transparent. The transflective liquid crystal display device has a reflective display unit and a transmissive display unit in one pixel.

The reflective display uses a reflector to reflect the light incident from the surroundings and display it, and since the contrast ratio is constant regardless of the ambient brightness, it is in a relatively bright environment from outdoors to indoors in fine weather. A good display can be obtained.

Since the transmissive display unit uses a backlight, it is possible to obtain a display with a high contrast ratio in a relatively dark environment from indoors to a dark room.

A semi-transmissive liquid crystal display device that has both a reflective display unit and a transmissive display unit can obtain a display with a high contrast ratio in a wide environment from outdoors to a dark room in fine weather.

In the current transflective liquid crystal display device, the liquid crystal layer has a homogeneous orientation or a twisted orientation, and an electric field is applied to the liquid crystal layer in the normal direction of the substrate, which has the same configuration as the TN (Twisted Nematic) type liquid crystal display device. And the electric field application method. Further, a plurality of phase plates are used in order to improve the contrast ratio in a configuration in which the reflector is built in the liquid crystal cell. Therefore, its visual characteristics were not wide enough.

Therefore, for example, Patent Document 1 below describes a method for semi-transparent display with a wide viewing angle by changing the IPS system known for transparent display with a wide viewing angle to a semi-transparent type.

That is, for example, as shown in FIGS. 21 to 24, the comb tooth electrodes 21 and 22 are used as reflection electrodes to form a reflection display unit, and the gap 20 between the comb tooth electrodes 21 and 22 is used as a transmission display unit. In the reflection display unit, light passes through the liquid crystal layer twice, whereas in the transmission display unit, it passes only once, but in order to eliminate the optical path difference between the two, between the comb tooth electrodes 21 and 22 and the gap between them. A step is formed to make the liquid crystal layer thickness of the transmissive display unit about twice that of the reflective display unit.

In this case, the comb tooth electrodes 21 and 22 project on the substrate, and the cross section of the comb tooth electrodes 21 and 22 is approximately square in the cross section perpendicular to the comb tooth direction, and the upper surface thereof is flat. Further, a plurality of phase plates are added to improve the contrast ratio of the reflection display unit, and the retardation of the liquid crystal layer is also adjusted to make the reflection display unit equivalent to a quarter wavelength.

Further, in Patent Document 2, Patent Document 3 and Patent Document 4 below, a diffuse reflection electrode is formed by forming finer irregularities on the comb tooth electrode.<patcit num="1"><text>Japanese Unexamined Patent Publication No. 11-242226</text></patcit><patcit num="2"><text>Japanese Patent Application Laid-Open No. 2002-139737</text></patcit><patcit num="3"><text>Japanese Patent Application Laid-Open No. 2003-21824</text></patcit><patcit num="4"><text>Japanese Unexamined Patent Publication No. 2003-21825</text></patcit>

<p> In the transmissive IPS system, for example, as shown in FIG. 23, the liquid crystal molecules 50 between the comb tooth electrodes were mainly operated. The conventional comb-tooth electrodes 21 and 22 are flat, and the lateral electric field, which is a line of electric force component parallel to the plane of the substrate, is extremely weak on the upper part, so that the liquid crystal molecules 50 on the upper part hardly move. In the semi-transmissive IPS system in which the comb tooth electrodes 21 and 22 are used as the reflection display, the reflection display is always dark unless the liquid crystal molecules 50 on the upper part of the comb tooth electrodes operate, so that the reflection display cannot be performed.</p><p> Further, if the upper surface of the electrode is flat, the light is not diffusely reflected, so that the reflected brightness perceived by the user is lowered. Therefore, if unevenness is formed on the upper surface of the electrode, it becomes a diffuse reflection electrode that diffusely reflects light, but the pitch of the unevenness becomes about 5 to 10 μm due to the resolution limit of the liquid crystal display device manufacturing process. It is about the same as the width required for 22. Therefore, if a plurality of rows of irregularities are to be arranged on the comb tooth electrodes 21 and 22, the width of the comb tooth electrodes 21 and 22 must be widened, the area ratio of the transmission display portion decreases, and the comb tooth electrodes Since the upper surface cannot be reflected and displayed, the effective aperture ratio is reduced.</p><p> As described above, the conventional semi-transmissive IPS system could not display the reflection. Therefore, the present invention enables reflection display in the transflective IPS system.</p>

<p> In the present invention, in order to enable reflection display, the cross-sectional shape of the comb tooth electrode portion, which is square in the conventional transflective IPS system, is changed to a shape including a slope. At this time, on the slope, electric lines of force are generated toward the opposing comb tooth electrodes (which also have the slope). As shown in FIG. 7, a transverse electric field is mainly generated at the ends of the comb tooth electrodes 21 and 22 as the voltage application means, and as shown in FIG. 6, the ends of the comb tooth electrodes 21 and 22 are mainly generated. Then, the liquid crystal molecule 50 on the upper part of the comb tooth electrode can operate.</p><p> The cross-sectional shape including the slope is created by using, for example, the lower layers of the comb tooth electrodes 21 and 22 as an organic insulating film. When the organic insulating film is heated and fired, it becomes a molten state, but the surface tension in the molten state is used to form an arc-shaped cross-sectional shape. A metal film having a high reflectance such as aluminum is formed on the metal film, and the metal film is patterned by a photolithography to selectively form only the upper part of the organic insulating film.</p><p> Since the ends of the comb-tooth electrodes 21 and 22 are inclined while the angle is continuously changing, the ends of the comb-tooth electrodes 21 and 22 diffuse and reflect light in the same manner as the uneven structure of the diffuse-reflecting plate. As a result, as shown in FIG. 4, the light incident from an oblique direction is reflected mainly in the direction of the user 70 observed from the normal direction of the substrate, so that the reflected brightness felt by the user is improved.</p><p> Until now, reflection display was not possible with the semi-transmissive IPS system due to two causes: the liquid crystal on the comb tooth electrode did not work and diffuse reflection did not occur. Since the above two causes can be solved at the same time by using the comb tooth electrodes 21 and 22 having an arcuate cross section, reflection display becomes possible in the transflective IPS system.</p><p> The user often observes the display device from the direction of the substrate normal, but when focusing on any minute slope on the comb tooth electrode, each minute slope is incident from within the plane including the reflective surface normal and the substrate normal. The light is reflected in the normal direction of the substrate. If the directions of the comb tooth electrodes 21 and 22 are constant within one pixel, the direction of the reflection surface normal is also constant within one pixel, and the reflection characteristics have strong directivity. When the reflection characteristics are directional, particularly good display characteristics can be obtained under certain conditions of use.</p><p> On the other hand, if the directivity is reduced, good display characteristics can be obtained in a wide range of environments regardless of the usage conditions. In the present invention, by diversifying the directions of the comb-tooth electrodes 21 and 22 within one pixel, the distribution in the azimuth direction is given to the reflection surface normal of each minute slope. Specifically, the comb tooth electrodes 21 and 22 have a bent structure, a wavy structure in which the width of the electrodes changes periodically or aperiodically, or a minute uneven structure is added on the comb tooth electrodes. As a result, the directivity is reduced and the reflection characteristic becomes more isotropic.</p><p>If the distribution shapes of the comb tooth electrodes 21 and 22 are regular, iridescent coloring occurs due to the interference of reflected light. If a layer having light diffusivity is arranged inside or outside the facing substrate to diffuse the light incident on the comb tooth electrodes 21 and 22 and the reflected light, the interference of the reflected light can be reduced. In order to eliminate the interference of reflected light more completely, it is effective to reduce the distribution regularity of the comb tooth electrodes 21 and 22. Specifically, the adjacent pixel electrodes and the common electrodes have different distribution shapes. Alternatively, a wavy structure or an uneven structure introduced to reduce the directivity is also effective, and the wavy structure or the uneven structure is introduced with an irregular distribution. As a result, the effect of reducing the interference of the reflected light can be obtained at the same time as reducing the directivity.</p>

<p> As described above, according to the present invention, a semi-transmissive ISP liquid crystal display device that performs reflection display and transmission display having various reflection characteristics can be realized, and this display device can be used in various environments from outdoors to dark rooms in fine weather. It is an all-environment type display device that can display below, and a transparent display provides a wide-field display comparable to a monitor.</p><p> Therefore, a high-quality display device similar to a monitor can be carried around, which makes it possible to handle high-definition image information. Further, if it is used in a digital camera, it becomes easy to check the captured image. Furthermore, with the spread of terrestrial digital broadcasting, it is predicted that the reception status of portable TVs will improve significantly in the future, but if used for portable TVs, high-quality image information can be reproduced anywhere. Become.</p>

Hereinafter, the best mode for carrying out the present invention will be described in more detail with reference to Examples.

A cross section of the liquid crystal display device of the present invention is shown in FIG. 2, and a top view of the second substrate 12 is shown in FIG. FIG. 2 is a cross-sectional view taken along the dotted line 1-2 of FIG. 1A, and the liquid crystal display device of the present invention is mainly composed of a first substrate 11, a liquid crystal layer 10, and a second substrate 12. , The first substrate 11 and the second substrate 12 sandwich the liquid crystal layer 10. The first substrate 11 has a first alignment film 13, a flattening layer 19, and a color filter 18 on the side close to the liquid crystal layer 10.

FIG. 1 (a) shows the distribution state of the common electrode 22 on the second substrate 12, and FIG. 1 (b) shows the distribution state of the structure below the common electrode 22 excluding the common electrode 22 from FIG. 1 (a). The second substrate 12 has a second alignment film 14 on the side close to the liquid crystal layer 10 and a thin film transistor 28 as a driving means. The thin film transistor 28 has an inverted staggered structure, and the channel portion is formed of an amorphous silicon layer 26.

The scanning wiring 27 and the signal wiring 25 intersect, and the thin film transistor 28 is located at the intersection. The thin film transistor 28 is connected to the scanning wiring 27, the signal wiring 25, and the source wiring 23. The scanning wiring 27 and the signal wiring 25 are insulated by the first insulating layer 15, and the signal wiring 25 and the pixel electrode 21 as a voltage applying means are insulated by the second insulating layer 16 and the third insulating layer 17. There is. Further, the pixel electrodes 21 as the voltage applying means are distributed in parallel with the signal wiring 25, and the source wiring 23 is connected. The pixel electrode 21 and the source wiring 23 of the thin film transistor 28 are connected by a through-hole portion 24. There is a second alignment film 14 on the pixel electrode 21, and the orientation direction is defined in the vicinity of the liquid crystal layer 10.

The first substrate 11 is made of Hokeisan glass and has a thickness of 0.5 mm. In the color filter 18, each portion exhibiting red, green, and blue is repeatedly arranged in a stripe shape, and the unevenness caused by the color filter is flattened by the resin flattening layer 19. The first alignment film 13 is a polyimide-based organic film and has a layer thickness of 0.2 μm.

The second substrate 12 is made of Hokeisan glass like the first substrate 11 and has a thickness of 0.5 mm. The second alignment film 14 is a photo-oriented organic film. The scanning wiring 27 and the signal wiring 25 are made of chromium, the first insulating film 15 and the second insulating film 16 are silicon nitride films, and the third insulating film 17 is an organic film. The pixel electrode 21 and the common electrode 22 are made of aluminum and have a layer thickness of 0.14 μm. Both the pixel electrode 21 and the common electrode 22 are comb-shaped and are distributed so that the comb teeth are inserted in parallel in one pixel, and a transverse electric field is formed between the pixel electrode and the common electrode when a voltage is applied. Will be done.

The third insulating layer 17 is distributed in the same manner as the pixel electrode 21 and the common electrode 22, and the pixel electrode 21 and the common electrode 22 are formed on the third insulating film 17. The third insulating film 17 has the same distribution as the pixel electrodes 21 and the common electrodes 22 by patterning the organic film with a photolithography.

The patterned organic film becomes a molten state in the process of heating and firing, but the cross section becomes a symmetric structure having a symmetric quadratic curve due to the surface tension in the molten state.

Since the pixel electrode 21 and the common electrode 22 are made of aluminum having a high reflectance, the portion where the pixel electrode 21 and the common electrode 22 are present is a reflection display portion. The gap 20 between the pixel electrode 21 and the common electrode 22 is transparent and is a transmissive display because it transmits backlight light. Since the pixel electrode 21 and the common electrode 22 are distributed on the third insulating film 17, they project onto the second substrate 12, so that the thickness of the liquid crystal layer of the reflection display portion is smaller than that of the transmission display portion.

The pixel electrode 21 and the common electrode 22 are distributed on the third insulating film 17 so as to completely cover the quadratic curved cross section. As a result, the thickness of the liquid crystal layer in the reflection display unit is set smaller than that in the transmission display unit, and the thickness of the liquid crystal layer in the transmission display unit is made substantially constant. Since the third insulating film 17 has a quadratic curved cross section, the liquid crystal layer thickness of the reflection display portion is not constant. The average value of the liquid crystal layer thickness of the transmissive display unit is about 1.7 to 1.9 times the average value of the reflective display unit.

As described above, in order to completely eliminate the optical path difference between the reflective display unit and the transmissive display unit, the liquid crystal layer thickness of the transmissive display unit should be double that of the reflective display unit. Since the retardation of the liquid crystal layer of the reflective display is one-fourth the wavelength, the retardation of the liquid crystal layer of the transmission display should be twice that wavelength. However, if the retardation of the liquid crystal layer of the transmissive display unit is reduced to half the wavelength, the brightness of the transmissive display is maximized, but the display color is colored yellow. In order to eliminate coloring while keeping the brightness of the transmissive display close to the maximum value, the thickness of the liquid crystal layer of the transmissive display is increased from 1.7 times to 1.9 times, which is slightly smaller than twice that of the reflective display.

Focusing on the third insulating layer 17, the portion covered by the pixel electrode 21 and the common electrode 22 is the reflection display portion, and the rest is the transmission display portion. When the pixel electrode 21 and the common electrode 22 completely cover the third insulating layer 17, the entire third insulating layer 17 becomes a reflection display unit. At this time, the transmissive display portion is limited to the inter-electrode portion, and the inter-electrode portion is flat, so that the liquid crystal layer thickness of the transmissive display portion is constant. When the pixel electrode 21 and the common electrode 22 partially cover the third insulating layer 17, a part (end) on the third insulating layer 17 also becomes a transmissive display portion, so that the liquid crystal layer of the transmissive display portion is also formed. The thickness is not constant.

Therefore, in this embodiment in which the IPS method of giving a transparent display with a wide viewing angle is applied for the purpose of improving the visual characteristics of the transparent display, the liquid crystal layer thickness of the transparent display unit is made constant, and the design gives priority to the transparent display quality. .. As a result, the dark display transmission is sufficiently reduced and the contrast ratio of the transmission display is increased.

For the liquid crystal layer 10, a liquid crystal composition mainly composed of a fluorine-based liquid crystal material and exhibiting positive dielectric anisotropy was used. Its birefringence is 0.073 and it has a nematic phase over a wide temperature range, including room temperature. In addition, it exhibits a high resistance value sufficient to sufficiently maintain the reflected brightness and the transmitted brightness during the holding period of the drive using the thin film transistor 28.

The first alignment film 13 was formed by applying and firing Sun Ever manufactured by Nissan Chemical Industries, Ltd. to form a film, and the alignment treatment was performed by a rubbing method. The second alignment film 14 was coated and formed on the second substrate 12 in a solution state, and then irradiated with ultraviolet rays for alignment treatment. Since there is a step of 1.5 μm at the boundary between the reflection display portion and the transmission display portion on the second substrate 12, the boundary portion is not sufficiently oriented by the rubbing method, resulting in poor orientation. By using a photo-oriented organic film for the second alignment film 14, it became possible to sufficiently align the boundary portion, and it was possible to uniformly align the top of the second substrate 12. The orientation directions of the first alignment film 13 and the second alignment film 14 are such that when the first substrate 11 and the second substrate 12 are assembled and the liquid crystal material is sealed to form a liquid crystal panel, the liquid crystal layers are aligned in parallel. Moreover, the orientation direction is set to be 75 degrees with respect to the electric field direction formed between the pixel electrode 21 and the common electrode 22 when observed from the substrate normal direction.

The first substrate 11 of the liquid crystal panel is referred to as the upper side, and the second substrate 12 is referred to as the lower side. This is because the second substrate 12 includes a pixel electrode 21 that reflects incident light and a common electrode 22, and is located on the lower side when viewed from the user under normal use conditions. On the upper side of the liquid crystal panel, a first phase plate 53 and a first polarizing plate 51 are provided in order of proximity to the first substrate 11. A second phase plate 54, a third phase plate 55, and a second polarizing plate 52 are provided on the lower side of the liquid crystal panel in the order of proximity to the second substrate 12.

Although the liquid crystal layer thickness of the reflection display unit is not constant, attention is paid to a minute portion having a typical liquid crystal layer thickness (for example, an average value in the reflection display unit) of the reflection display unit. In the transmissive IPS system, the dark display is obtained when no voltage is applied so that the liquid crystal orientation becomes uniform within one pixel, but this is the same in the semi-transmissive IPS system. If the incident light in the dark display is circularly polarized when it reaches the pixel electrode 21 or the common electrode 22, it becomes linearly polarized parallel to the absorption axis when it reaches the first polarizing plate 51 again after reflection. , It is completely absorbed by the first polarizing plate 51, and the reflectance of dark display can be reduced. Moreover, if the above can be realized in a wide range of visible wavelengths, it is possible to realize an achromatic and low reflectance dark display.

The optical conditions of the first polarizing plate 51, the first phase plate 53, and the liquid crystal layer of the reflection display unit should be determined so as to realize the above, which can be obtained by using the Poincare sphere display shown in FIG. You can. The Poincare sphere display is defined in a space centered on the Stokes parameters (S1, S2, S3) that describe the polarization state, and each point on the Poincare sphere has a one-to-one correspondence with the polarization state. For example, the line of intersection (equatorial line) with the (S1, S2) plane on the Poancare sphere corresponds to linearly polarized light, the intersection with the S3 axis (north pole and south pole) corresponds to circularly polarized light, and the others correspond to elliptical polarized light. To do. Further, (S1, S2, S3) is expressed by the following equations using an arbitrary X-axis component Ex of an electric vector, an arbitrary Y-axis component Ey, and a phase difference δ between Ex and E, respectively.

S1 = (Ex²-Ey²) / (Ex²+ Ey²) S2 = 2ExEycosδ / (Ex²+ Ey²) S3 = 2ExEysinδ / (Ex²+ Ey²)

The conversion of the polarized state by the phase plate and the untwisted liquid crystal layer is expressed as rotation around a line contained in the (S1, S2) plane on the Poancare sphere and passing through the center of the Poancare sphere. The rotation angle at this time is 1/2 rotation if the retardation of the phase plate is 1/2 wavelength, and 1/4 rotation if the retardation of the phase plate is 1/4 wavelength.

Incident light of a typical wavelength in the visible light region (for example, a wavelength of 550 nm that maximizes human visual sensitivity) passes through the first polarizing plate 51, the first phase plate 53, and the liquid crystal layer of the reflection display unit in sequence. Then, pay attention to the process of reaching the pixel electrode 21 or the common electrode 22.

As shown in FIG. 3 (a), the incident light L1 polarized linearly by the first polarizing plate 51 is located at the equator on the Poancare sphere, but is rotated 1/2 by the first phase plate 53. It moves to another point L2 on the equator, rotates 1/4 by the liquid crystal layer, moves to the North Pole NP, and is converted to circularly polarized light.

Next, focusing on the incident light of other wavelengths, the retardation has wavelength dependence, and the retardation is larger on the short wavelength side and smaller on the long wavelength side in both the phase plate and the liquid crystal layer. Therefore, the rotation angle differs depending on the wavelength, and in the rotation by the first phase plate 53, the light having a wavelength other than 550 nm moves to a point off the equator without being halved.

More specifically, the blue light on the short wavelength side has a retardation larger than 1/2 wavelength, so it rotates more than 1/2 rotation and deviates from the equator, and the red light on the long wavelength side has a retardation of 1. Since it is smaller than / 2 wavelength, it rotates less than 1/2 rotation and deviates from the equator. However, in the next 1/4 rotation by the liquid crystal layer, the moving direction is substantially opposite, so that the difference in the rotation angle depending on the wavelength is compensated. As a result, the light of each wavelength is concentrated in the vicinity of the Arctic NP, that is, the light of each wavelength becomes substantially the same circularly polarized light. When this is observed as the display state of the liquid crystal, an achromatic dark display with reduced reflectance can be obtained in a wide range of visible wavelengths.

Since the actions of the first phase plate 53 and the liquid crystal layer of the reflection display unit on the poancare sphere are 1/2 rotation and 1/4 rotation, respectively, the first phase plate 53 and the liquid crystal layer of the reflection display unit at this time The retardation is 1/2 wavelength and 1/4 wavelength, respectively. Further, since the central axis of rotation on the Poancare sphere corresponds to the azimuth angle of the slow phase axis, the azimuth angle θ of the slow phase axis of the first phase plate 53_PH1And the azimuth angle θ in the orientation direction of the liquid crystal layer of the reflection display unit_LCIs defined counterclockwise with the azimuth angle of the transmission axis of the first polarizing plate 51 as 0 degrees, and is expressed by the following equation. 2θ_PH1= 225 ° + θ_LC.........(1)

Further, as shown in FIG. 3 (b), the incident light of each wavelength can be concentrated on the Antarctic SP of the Poincare sphere in the same manner. In this case as well, the retardations of the first phase plate 53 and the liquid crystal layer of the reflection display unit are 1/2 wavelength and 1/4 wavelength, respectively, and θ_PH1And θ_LCIs expressed by the following equation. 2θ_PH1= -45 ° + θ_LC......... (2) In this example, equation (2) was used, and θPH1 = 15 ° and θLC = 75 °.

Next, the optical conditions of the second phase plate 54, the third phase plate 55, and the second polarizing plate 52 are determined. The second phase plate 54, the third phase plate 55, and the second polarizing plate 52 are considered as a pair of the transmission display unit liquid crystal layer, the first phase plate 53, and the first polarizing plate 51, respectively. Here, the reason why the pair of the second phase plate 54 is not the reflection display unit but the liquid crystal layer of the transmission display unit is that the incident light does not pass below the second phase plate 54 in the case of the reflection display. This is because they pass through only in the case of transparent display.

The retardation of the second phase plate 54 is the same as that of the paired transmission display liquid crystal layer, and its slow phase axis is perpendicular to the orientation direction of the transmission display liquid crystal layer (equal to the reflection display liquid crystal layer). To do. As a result, the retardation of the second phase plate 54 and the liquid crystal layer of the transmissive display unit is canceled out.

The retardation of the third phase plate 55 is made identical to the paired first phase plate 53, and its slow phase axis is perpendicular to the slow phase axis of the first phase plate 53. As a result, the retardation of the third phase plate 55 and the first phase plate 53 is offset. The transmission axis of the second polarizing plate 52 is perpendicular to the transmission axis of the first polarizing plate 51.

In this example, θPH2 = 165 °, θPH3 = 105 °, and θPL2 = 90 °, and the retardation of the second phase plate 54 and the third phase plate 55 was set to half the wavelength. Since the retardation of the two sets of birefringent media existing between the second polarizing plate 52 and the first polarizing plate 51 was canceled out, the distance between the second polarizing plate 52 and the first polarizing plate 51 was isotropic. By equalizing the phases and orthogonalizing the second polarizing plate 52 and the first polarizing plate 51, an ideal dark display is realized in the normal direction.

Under the optical conditions determined as described above, the first phase plate 53 and the first polarizing plate 51 are on the upper side of the liquid crystal panel, and the second phase plate 54 and the third phase plate 55 are on the lower side of the liquid crystal panel. The second polarizing plate 52 was laminated. In addition to these, the light diffusion layer 56 was arranged between the first phase plate 53 and the first substrate 11.

The light diffusion layer 56 has a structure in which a large number of transparent microspheres having a refractive index different from that of the adhesive layer are mixed inside the adhesive layer that adheres the first phase plate 53 and the first substrate 11. It has the effect of expanding the optical path of incident light by utilizing the effect of refraction caused by the difference in refractive index between the adhesive layer and the microsphere. As a result, it is possible to reduce the iridescent coloring caused by the interference of the reflected light between the pixel electrode and the common electrode.

4 to 7 are semi-transmissive IPS liquid crystal display devices manufactured as described above, and FIG. 4 is a cross-sectional view showing the relationship between the user 70 at the time of reflection display and the incident light and the emitted light. FIG. 5 is a cross-sectional view showing the orientation state of the liquid crystal molecule 50 when no voltage is applied, and FIG. 6 is a cross-sectional view showing the orientation state of the liquid crystal molecule 50 when no voltage is applied. Is a cross-sectional view showing an electric power line 49 when a voltage is applied.

This semi-transmissive IPS liquid crystal display device was connected to the drive device, and a backlight was placed behind it to observe the display state. When observing in a bright place with the backlight turned off, the display image by the reflection display could be confirmed. Next, when the backlight was turned on and observed in a dark place, a display image by transparent display could be confirmed. As described above, it was possible to confirm the displayed image in both the reflection display and the transmission display in the semitransparent IPS system.

Further, the cross section of the pixel electrode 21 and the common electrode 22 has a substantially symmetrical structure, and exhibits the same reflectance with respect to light incident from either the right direction or the left direction of the cross section. Therefore, in the reflection display, the change in reflectance depending on the incident direction of the light source light was small.

Figure 18 (a) shows the results of evaluating the viewing angle characteristics of the transmissive display of the semi-transmissive IPS liquid crystal display device of this example. FIG. 18A shows the polar dependence of the transmission efficiency measured in the transmission axis direction (solid line) of the first polarizing plate and the absorption axis direction (broken line) of the first polarizing plate. The polar angle of 0 degrees coincides with the substrate normal direction, and the polar angle increases as the distance from the substrate normal direction increases. Focusing on the transmission efficiency in dark display in Fig. 18 (a), there is almost no change in the transmission efficiency within the range of the polar angle ± 20 degrees in any direction, and the effect of improving the viewing angle characteristics by adopting the IPS method. Can be seen.

The pixel structure of the liquid crystal display device of the present invention is not limited to that shown in FIG. For example, as shown in FIG. 14A, the common wiring 29 may be arranged parallel to the scanning wiring 27, and the common electrode may be arranged so as to conduct to the common wiring through the contact hole 24. The pixel structure shown in FIG. 14 (a) is more complicated than that in FIG. 1, but since each common electrode is connected to a common wiring formed on a flat substrate, there is an advantage that defects such as disconnection are unlikely to occur. is there.

Further, in FIGS. 1 and 14 (a), there are two common electrodes for each pixel and one pixel electrode for each pixel. For example, as shown in FIG. 14 (b), there are three common electrodes for each pixel. , The pixel electrode may be two for each pixel. Alternatively, as shown in FIG. 14 (c), the number of common electrodes may be 4 for each pixel and the number of pixel electrodes may be 3 for each pixel, and the number of common electrodes and pixel electrodes is increased to more than that of FIG. 14 (c). You may.

The aperture ratio, drive voltage, and response time of the liquid crystal display device are affected by the distance between the common electrode and the pixel electrode. For example, when the size of one pixel is fixed, by optimizing the number of common electrodes and pixel electrodes in one pixel, it is possible to perform an optimum design to satisfy the required display characteristics in a well-balanced manner. .. Since the present invention is simple, the simplest pixel structure shown in FIG. 1 will be described as an example.

As shown in FIG. 8, in this embodiment, the cross-sectional shapes of the pixel electrode 21 and the common electrode 22 are changed to further improve the reflection characteristics. The cross sections of the pixel electrode 21 and the common electrode 22 of this embodiment are the same as those of the first embodiment in that they have a symmetrical structure. The flat part in the center is reduced and the proportion of slopes is increased as compared with Example 1.

The cross-sectional shape of the pixel electrode 21 and the common electrode 22 were produced as follows. When the third insulating film 17 was patterned using a photolithography, a grating mask capable of changing the exposure amount stepwise was used. The space between the comb tooth electrodes was completely exposed to completely remove the insulating film. The ends of the comb tooth electrodes 21 and 22 were incompletely exposed, leaving a thinner insulating film. The central part of the comb tooth electrodes 21 and 22 was not exposed, and the insulating film thickness was left thicker. By heating and melting this, a cross-sectional shape having a large proportion of slopes at the pixel ends and a smooth change in inclination angle was obtained.

In addition to this, for example, even if an organic insulating film is additionally formed by selectively stacking it on a flat portion in the center and the organic insulating film is heated and melted, the proportion of the slope is increased as compared with Example 1, and the pixel electrode has a cross-sectional shape. A common electrode 22 can be formed with 21.

By increasing the proportion of the slope as compared with Example 1, the strength of the lateral electric field on the pixel electrode 21 and the common electrode 22 is increased, so that the orientation change of the liquid crystal occurs more greatly when the electric field is applied. In addition to this, the ratio of diffuse reflection of light incident from an oblique direction in the normal direction also increased, so that a brighter reflection display was obtained. Since the cross sections of the pixel electrode 21 and the common electrode 22 have a substantially symmetrical structure as in Example 1, the change in reflectance depending on the incident direction of the light source light is also small.

As shown in FIG. 9, in this embodiment, the cross-sectional shapes of the pixel electrode 21 and the common electrode 22 are asymmetrical. It is similar to Example 2 in that the flat portion is reduced as compared with Example 1, but the flat portion is not in the center and is asymmetric.

The asymmetric cross-sectional shape was prepared as follows. A grating mask was used in the same manner as in Example 2, and the portion of the comb tooth electrodes 21 and 22 deviated from the central portion was not exposed and the insulating film thickness was left thicker. In addition to this, for example, an organic insulating film can be additionally formed by selectively overlapping a portion biased from the center of the organic insulating film, and the same cross-sectional shape can be formed by heating and melting the organic insulating film.

Due to the asymmetric cross-sectional shape, light incident from one side of the cross-section can be diffusely reflected in the normal direction at a higher rate. When the display state was confirmed in a bright place, a particularly good reflection display was obtained in a specific case where light was incident from the direction in which the slope normal was facing.

10 to 13 show an example in which the directivity of the reflection display is reduced. Specifically, the structure of the comb tooth electrode is improved to obtain a good reflection display in a wider environment. I made it possible. If the orientation of the comb tooth electrode is constant, the slope at the end of the comb tooth electrode is oriented in one direction, and as a result, the reflection characteristics are directional. In order to solve this, the orientation of the comb tooth electrode is diversified within one pixel. As the method, a method of forming the entire comb tooth electrode into a bent structure, a method of imparting a minute uneven structure to the comb tooth electrode, or a combined use of both can be considered.

As shown in FIG. 10 (a), in this embodiment, the method of forming the entire inner comb tooth electrode into a bent structure was applied. In Example 1, the comb tooth electrode was perpendicular to the scanning line direction. In this embodiment, the comb tooth electrodes 21 and 22 are V-shaped, and the comb tooth electrodes 21 and 22 are tilted with respect to the scanning line direction. The angles of the comb tooth electrodes 21 and 22 are defined counterclockwise with the direction perpendicular to the scanning line as 0 degree. Assuming that the upper half and the lower half of FIG. 10A are region 1 and region 2, respectively, the inclinations of the comb tooth electrodes 21 and 22 with respect to the scanning line direction in region 1 and region 2 are 20 degrees and -20 degrees, respectively. As a result, the direction of the slope at the end of the comb tooth electrode is increased from the two directions of Example 1 to four directions (61 to 64), the directivity of the reflection characteristic is reduced, and the direction is closer to isotropic, which is a wider range of conditions. A good display can be obtained.

Further, since the directivity of the reflection characteristic is reduced, the diffusivity of the light diffusing layer can be reduced. When the light diffusing layer 56 is arranged between the first substrate 11 and the first phase plate 53, the light diffusing layer 56 and the pixel electrode 21 are separated by the first substrate 11, which is sufficiently larger than the pixel size. Since the incident optical path is expanded by the light diffusing layer 56 at a distant position, the resolution may decrease depending on the usage environment. In this embodiment, the diffusivity of the light diffusing layer can be reduced, so that the resolution can be prevented from being lowered.

When the semi-transmissive IPS liquid crystal display device manufactured as described above was connected to the drive device and the display state was observed in a bright place, the display image by the reflection display could be confirmed. Even if the incident direction of the reflected light was changed in various ways, the change in reflectance was relatively small, a good reflection display was obtained in a wider environment, and the effect of reducing the directivity of the reflection display could be confirmed.

As shown in FIG. 10 (b), in this example, an attempt was made to further reduce the directivity of the reflection display by using a method in which the entire electrode has a bent structure. The electrode structure of this example is based on the V-shape of Example 4, but the bending points of the comb tooth electrodes 21 and 22 are increased from 1 point of Example 4 to 3 points. The inclinations of the comb tooth electrodes 21 and 22 are changed in about a quarter of the pixel end. The direction of the slope at the end of the comb tooth electrode further increased to 8 directions (61 to 68), which was closer to the isotropic reflection characteristic than in Example 4.

Further, the electro-optical characteristics of the IPS system, that is, the threshold voltage and the saturation voltage depend on the angle formed by the initial orientation direction and the electric field direction. In this embodiment, since the inclinations of the comb tooth electrodes 21 and 22 with respect to the scanning line direction are changed, there are regions where the angles formed by the initial orientation direction and the electric field direction are different, and the electro-optic characteristics are different. Since the electro-optical characteristics of the entire pixel are the superposition of the electro-optical characteristics of each part, the dependence of the transmittance on the drive voltage becomes gentle, and more detailed gradation display becomes possible.

As shown in FIG. 11 (a), in this example, an attempt was made to further reduce the directivity of the reflection display by using a method in which the entire electrode has a bent structure. This is an example in which the comb tooth electrodes 21 and 22 are U-shaped, and the inclinations of the comb tooth electrodes 21 and 22 with respect to the scanning line direction are continuously changed. At this time, the direction of the slope at the end of the comb tooth electrode also changes continuously, so that the direction of the slope at the end of the comb tooth electrode is distributed over a wide range. It is closer to the isotropic reflection characteristic than in Example 5.

As shown in FIG. 11 (b), in this embodiment, irregularities are given to the shapes and distributions of the comb tooth electrodes 21 and 22, and the iridescent coloration caused by the interference of the reflected light between the pixel electrodes 21 and the common electrodes 22. Attempted to reduce. If the shapes and distributions of the pixel electrode 21 and the common electrode 22 are within the coherent length, there is an angle condition in which the reflected light generated at different parts of the pixel electrode 21 and the common electrode 22 is strengthened by interference. Since the angle condition changes continuously depending on the wavelength, it is observed as a rainbow-colored striped pattern. If interference occurs, a rainbow-colored striped pattern is superimposed on the display information, which impairs visibility.

In Example 6, the comb tooth electrodes 21 and 22 were U-shaped and their inclinations were continuously changed, but in this example, in addition to this, the adjacent pixel electrodes 21 and the common electrodes 22 have different shapes. Scan with one of the comb teeth made by any pixel electrode 21 or common electrode 22 in order to minimize the part where the orientation direction of the liquid crystal and the angle generated by the electric field are close to 90 degrees and reduce the generation of dark lines. As shown by the dotted line in Fig. 11 (b), only one part is perpendicular to the wiring.

In liquid crystal display devices of mobile phones, relatively high precision with about 200 pixels per inch is becoming the standard. In this case, the size of one pixel is about 40 x 120 μm, so if the resolution of the process is about 5 μm, each pixel has one pixel electrode in the center of the pixel and one common electrode at both ends of the pixel. The structure is arranged one by one. In order to make the light scattering property of each pixel the same, the configuration of each pixel must be the same, but in order to make the adjacent pixel electrodes and the common electrodes different in shape, all the pixel electrodes must be the same. The structure may be the same, and all common electrodes may have the same structure.

As a specific shape of the pixel electrode 21 and the common electrode 22, for example, one of the pixel electrode 21 and the common electrode 22 is formed of an S-shaped structure having a larger curvature, and the other is formed of an S-shaped structure having a smaller curvature. In FIG. 11B, the curvature of the common electrode 22 is larger than that of the pixel electrode 21.

The coherent length, which represents the coherent nature of light existing in nature, is about 20 μm, and is almost the same for artificial lighting such as fluorescent lamps. The approaching pixel electrode 21 and the common electrode 22 are included in the coherent length range, but as shown in FIG. 11 (b), the shapes of the approaching pixel electrode 21 and the common electrode 22 are different, so that they are the same as the pixel electrode 21. The distance between the electrodes 22 changes continuously.

In the U-shaped comb tooth electrodes 21 and 22 of Example 7, there is a portion where the angle between the orientation direction of the liquid crystal and the electric field direction is close to 90 degrees, and this corresponds to the vicinity of the dotted line portion in FIG. 11 (b). To do. In this portion, it is difficult to determine the direction of the change in the orientation of the liquid crystal layer in the electric field application character. That is, the liquid crystal layer rotates clockwise or counterclockwise in the plane of the substrate when the electric field is applied, but it is just as easy if the angle between the orientation direction of the liquid crystal and the electric field direction approaches 90 degrees. Therefore, it is difficult to determine the direction of rotation. As a result, there is a possibility that a dark line portion in which the orientation does not change even when a voltage is applied and the transmittance does not increase when the voltage is applied may occur in a wide range around the vicinity of the broken line portion. If a dark line part is generated, the transparency and the reflectance are reduced, which is not preferable.

Therefore, in this embodiment, as shown in FIG. 11 (c), protrusions are added to the comb tooth electrodes 21 and 22 in the portion corresponding to the dotted line portion in FIG. 11 (b). In the vicinity of the protrusions, the angle between the orientation direction of the liquid crystal and the electric field direction is sufficiently smaller than 90 degrees due to the local electric field caused by the protrusions, and the rotation direction when a voltage is applied is determined. In addition, the orientation change in the vicinity of the protrusion propagates to the periphery thereof, so that the rotation direction when a voltage is applied is determined in a wide area around the protrusion. As described above, since the dark line portion is limited to the narrow region at the tip of the protrusion, the area of the dark line portion can be reduced.

FIG. 12A shows an example of the pixel structure of this embodiment. In this example, the planar structure of the comb tooth electrodes 21 and 22 was changed to give the comb tooth electrodes 21 and 22 a minute protrusion structure in an attempt to reduce the directivity of the reflection display. The straight electrode structure of Example 1 was continuously provided with minute protrusions to form a wavy structure, and the orientation of the end of the comb tooth electrode was diversified within one pixel. In addition, irregularity was added to the distribution of minute protrusions to make the distribution of the reflecting surface irregular. As a result, in addition to the isotropic reflection characteristics, the effect of reducing the iridescent interference color was obtained at the same time.

As an example of the pixel structure is shown in FIG. 12 (b), in this embodiment, as in the case of the ninth embodiment, the comb tooth electrodes 21 and 22 are provided with a minute protrusion structure to further reduce the directivity of the reflection display. I tried. The third insulating film 17 and the comb tooth electrodes 21 and 22 are formed by photolithography, and these shapes change the shape of the photomask to change the boundary line between the light irradiation part and the light-shielding part on the photoresist. It can be changed arbitrarily. The minute protrusion structure can be imparted by changing the shape of the photomask used for forming the third insulating film 17 and the comb tooth electrodes 21 and 22.

The V-shaped electrode structure was continuously provided with minute protrusions to form a wavy structure, and the orientation of the ends of the comb tooth electrodes was diversified within one pixel. Since the distribution of the directions of the comb-tooth electrodes 21 and 22 of the V-shaped electrode structure is superimposed on the distribution of minute protrusions, the distribution of the directions of the comb-tooth electrodes 21 and 22 is more diversified and more isotropic reflection. I was able to get closer to the characteristics.

FIG. 13 (a) shows an example of the pixel electrode of this embodiment. In this example, an attempt was made to reduce the directivity of the reflection display by superimposing a minute uneven structure 90 without changing the planar structure of the comb tooth electrodes 21 and 22. A minute uneven structure 90 is superimposed on the comb tooth electrodes 21 and 22 of Example 1. Since each unevenness is a rotating body having a quadric curved surface in general, it has an inclined surface over 360 degrees around the center of rotation. By superimposing the minute uneven structure 90, the orientation of the reflective surface normals on the comb tooth electrodes 21 and 22 could be diversified as compared with Example 1.

A structure in which a circular uneven structure was superimposed on a comb-shaped protrusion structure was produced as follows. When the third insulating film 17 was patterned using a photolithography, a grating mask capable of changing the exposure amount stepwise was used. The space between the comb tooth electrodes was completely exposed to completely remove the insulating film. The recesses on the comb tooth electrodes were incompletely exposed, leaving a thinner insulating film. The convex portion on the comb tooth electrode was not exposed, leaving a thicker insulating film. Then, the third insulating film 17 was fired to make the cross-sectional shape of each part on a quadric surface. By using the grating mask, a more complicated structure in which the thickness of the insulating film thickness changes stepwise can be produced without increasing the number of steps. In addition, since the distribution of the minute uneven structure 90 is given irregularity, the effect of reducing the iridescent interference color is obtained at the same time in addition to the isotropic reflection characteristic.

As shown in FIG. 13 (b), in this example, the directivity of the reflection display was reduced by superimposing the minute uneven structure 90 as in the case of the eleventh embodiment. A minute uneven structure 90 was superimposed on the comb tooth electrodes 21 and 22 of Example 6. The comb tooth electrodes 21 and 22 of Example 6 have a distribution in the direction of the reflective surface normal due to their U-shaped structure, but since the distribution due to the minute uneven structure is superimposed on this, the direction of the reflective surface normal is further increased. I was able to diversify. This made it possible to make the reflection characteristics more isotropic. Further, since the comb tooth electrodes 21 and 22 themselves are U-shaped and the comb tooth electrodes 21 and 22 are bent, the arrangement of the uneven structure 90 finer than that of the eleventh embodiment can be made irregular. , The iridescent interference color caused by the minute uneven structure could be reduced.

Hereinafter, in Example 1, a case where the third insulating film 17 is produced by changing from the organic film according to the present invention to the conventional silicon nitride film will be briefly described. For example, as shown in FIGS. 21 to 24, The cross-sectional shape of the third insulating film 17 is approximately square. As a result, the reflective surfaces of the common electrode 22 and the pixel electrode 21 distributed on the third insulating film 17 became flat.

This semi-transmissive IPS liquid crystal display device was connected to the drive device, and a backlight was placed behind it to observe the display state. When the backlight was turned on and observed in a dark place, a display image by transparent display could be confirmed as in Example 1. However, when the backlight was turned off and the observation was performed in a dark place, the display image by the reflection display could not be confirmed.

The reason why the reflection display could not be confirmed when the flat common electrode and the pixel electrode were used is considered as follows. FIG. 21 shows the relationship between the observation direction of the user 70 in the reflection display and the optical paths of the incident light and the emitted light. Since the light incident from the oblique direction is reflected by the flat common electrode 22 and the pixel electrode 21, the incident angle and the exit angle are substantially equal to the macroscopic substrate plane. The light is emitted in the direction opposite to the incident direction and at an angle inclined with respect to the normal direction, and in many cases does not go in the normal direction observed by the user 70.

Further, FIG. 24 shows an electric line of force 49 formed when a voltage is applied between the flat common electrode 22 and the pixel electrode 21. There is almost no electric field above the common electrode 22 and the pixel electrode 21. In FIG. 7, which shows the distribution of electric lines of force in the liquid crystal display device of Example 1, a transverse electric field also exists above the common electrode 22 and the pixel electrode 21. The orientation state of the liquid crystal molecules 50 at this time is shown in FIG. Reflecting the absence of electric lines of force above the common electrode 22 and the pixel electrode 21, the orientation of the liquid crystal molecules 50 hardly changed in the same portion, and the orientation was almost the same as that shown in FIG. 22 showing no voltage applied. It is in a state. The upper portions of the common electrode 22 and the pixel electrode 21, which are reflection display units, always remain dark when no voltage is applied and when a voltage is applied, and the reflectance hardly changes.

As described above, when a flat common electrode and a pixel electrode are used, the reflected light cannot be directed to the user and the liquid crystal layer of the reflected display unit does not operate, so that the reflected display cannot be performed. The invention solved these two reasons.

As for the viewing angle characteristic of the transmission display of the liquid crystal display device of the first embodiment, as shown in FIG. 18A, the dark display transmission efficiency is almost constant up to the polar angle 20 in any direction. However, at a polar angle of ± 20 degrees or more, the dark display transmission efficiency increases as the polar angle increases, and the contrast appears to decrease when observed from this direction. Therefore, the semi-transmissive IPS liquid crystal display device of the first embodiment needs to reduce the dark display transmission efficiency especially in a high polar angle region.

FIG. 19 shows factors involved in the viewing angle characteristics of the birefringent medium and a method for determining the optical characteristics of the birefringent medium in an arbitrary viewing angle direction 84. Factors involved in the viewing angle characteristics of the birefringent medium are the directional of the slow axis, the directional of the advancing axis, and the refractive index at both positions, and these apply the following geometric operations to the refractive index ellipsoid 80. It is required by.

The refractive index elliptical body is an elliptical body whose three axes are the refractive index nx in the x direction, the refractive index ny in the y direction, and the refractive index nz in the z direction. It is parallel to the z direction. Assuming a straight line passing through the center of the refractive index ellipsoid parallel to the viewing angle direction 84 of interest, a cross section 81 including the center of the refractive index ellipsoid perpendicular to this straight line is created. The cross section 81 is generally elliptical, the direction of the major axis 82 is the slow axis acting on the incident light in the viewing angle direction of interest, and the length of the major axis is the refractive index of the slow axis. Similarly, the direction of the minor axis 83 is the phase-advancing axis acting on the incident light in the viewing angle direction of interest, and the length of the minor axis is the refractive index of the phase-advancing axis.

Therefore, the optical properties of the birefringent medium in any viewing direction are determined by the ratio of nx, ny, nz, which is generally expressed by the Nz coefficient. The Nz coefficient is defined by the following equation in the presentation by Yasuo Fujimura, Tatsuki Nagatsuka, Hiroyuki Yoshimi, Takefumi Simomura et al. (SID '91 DIGEST (1991) pp. 739-742). Nz = (nx-nz) / (nx-ny) ......... (3)

If the Nz coefficient is different, the viewing angle characteristics will be different. As a specific example, consider a birefringent medium 1 having Nz = 1.0 arranged so that the slow axis is 45 degrees when observed from the normal direction of the substrate. FIG. 20A shows a change in the optical characteristics of the birefringent medium 1 when the incident direction changes so that the polar angle increases at an azimuth angle of 90 degrees. The refractive index ellipsoid of the birefringent medium 1 has a rugby ball-like shape having the longest slow-phase axial direction when observed from the substrate normal direction. Therefore, the cross section of the refractive index ellipsoid changes so as to approach a state parallel to the horizontal direction as the polar angle increases. At the same time, the long axis direction of the cross section also changes so as to approach the horizontal direction.

Next, consider the birefringence medium 2 having Nz = 0.0 arranged so that the slow axis is 135 degrees when observed from the normal direction of the substrate. FIG. 20 (b) shows the change in the optical characteristics of the birefringent medium 2 when the incident direction changes so that the polar angle increases at an azimuth angle of 90 degrees in the same manner as in FIG. 20 (a). The refractive index ellipsoid has a convex lens-like shape, which is the shortest in the phase-advancing axis direction when observed from the substrate normal direction and the longest in the vertical direction. Therefore, the cross section of the refractive index ellipsoid changes so that the thickness in the normal direction appears as the polar angle increases and swells in the vertical direction. At the same time, its long axis also changes so as to approach the vertical direction.

FIG. 20 (c) shows a state in which the birefringence medium 1 and the birefringence medium 2 are observed at the same time. In FIG. 20 (c), 85 and 86 are shown to distinguish the slow-phase axes of the birefringent medium 1 and the birefringent medium 2, respectively. The birefringent medium 1 and the birefringent medium 2 are arranged so that their slow-phase axes are orthogonal to each other in the normal direction of the substrate. When the polar angle increases at an azimuth angle of -90 degrees, the long axis of the cross section of the refractive index ellipsoid of the birefringence medium 1 changes toward the horizontal direction as the polar angle increases, and the refractive index ellipsoid of the birefringence medium 2 changes. The long axis of the cross section changes so as to approach the vertical direction.

That is, both of them change so as to rotate counterclockwise, and the speed of rotation is the same as the polar angle increases. Therefore, even if the polar angle increases, the slow axes of both are kept orthogonal. Also, this is true not only at the azimuth of -90 degrees, but also when the polar angle is changed at all azimuths. Therefore, the slow axes of the birefringent medium 1 and the birefringent medium 2 are kept orthogonal in all viewing angle directions.

From the above, if one of the pair of birefringent media whose slow-phase axes are orthogonal to each other in the normal direction of the substrate is set to Nz = 1 and the other is set to Nz = 0, the retardation of both can be widened in a wider viewing angle range. Since they can be offset, the viewing angle characteristics of dark display can be improved. In Example 1, the slow-phase axes are orthogonal to each other when viewed from the normal direction of the substrate: two sets of the transparent display unit liquid crystal layer and the second phase plate, and the first phase plate and the third phase plate. Is.

First, considering the pair of the transmissive display unit liquid crystal layer and the second phase plate, the transmissive display unit liquid crystal layer is composed of a nematic liquid crystal, and its orientation state is homogenic orientation. Since the nematic liquid crystal is positively uniaxial, the liquid crystal layer of the transmissive display unit is nx&gt; nz = ny, and Nz = 1. Therefore, the second phase plate, which is one of the pair, is set to Nz = 0. For the first phase plate and the third phase plate, the first phase plate may be Nz = 0, the third phase plate may be Nz = 1, or the first phase plate may be Nz = 1. In addition, the third phase plate may be set to Nz = 0. The latter is selected here.

FIG. 18 (b) shows the transmission display viewing angle characteristics of the semi-transmissive IPS liquid crystal display device of this embodiment. Compared with FIG. 18 (a), the dark display transmittance in the high polar angle region was reduced, and the effect of improving the phase difference compensation in the viewing angle direction by the combinatorial optimization of the Nz coefficient was confirmed.

In the liquid crystal display device of Example 1, the upper and lower alignment films were replaced with vertical alignment films. The vertical alignment film is a polyimide-based organic polymer having an alkyl group in the side chain. As the liquid crystal material, a nematic liquid crystal having a positive dielectric anisotropy was used as in Example 1.

A cross-sectional view of the liquid crystal display device of this embodiment is shown in FIG. FIG. 15 shows a state in which no voltage is applied to the liquid crystal layer, and the liquid crystal layer is roughly oriented in the normal direction of the substrate by replacing the upper and lower alignment films with vertical alignment films.

Since the orientation state of the liquid crystal layer is vertical orientation when no voltage is applied, the retardation of both the reflection display portion and the transmission display portion is almost zero at the substrate normal. In order to make this state dark, the optical conditions of the phase plate and the polarizing plate were changed.

First, the optical conditions of the phase plate and the polarizing plate arranged on the upper side of the first substrate were determined in order to make the reflection display unit dark. A first phase plate is placed on the upper side of the first substrate, and its retardation is reduced to a quarter wavelength. Taking the vertical direction of the comb tooth electrode as a reference, the slow axis of the first phase plate was arranged so as to form 45 degrees with respect to the vertical direction of the comb tooth electrode. Further, the first polarizing plate was arranged on the upper side of the first phase plate, and the transmission axis thereof was arranged so as to form 90 degrees with respect to the vertical direction of the comb tooth electrode.

Circularly polarized light is created by the first phase plate and the first polarizing plate. Since the retardation of the liquid crystal layer is zero, the circularly polarized light formed by the first phase plate and the first polarizing plate is directly incident on the common electrode and the pixel electrode, and the dark display of the reflection display is realized. Further, if the first phase plate is an inversely dispersed phase plate in which the retardation increases with wavelength, the reflectance can be reduced in a wide wavelength range within the visible wavelength range, so that a lower reflectance and achromatic reflection display can be obtained. ..

Next, the optical conditions of the phase plate and the polarizing plate to be arranged under the second substrate in order to make the transmission display unit dark are determined. A second phase plate is used under the second substrate, its retardation is the same quarter wavelength as that of the first phase plate, and its slow phase axis is the slow phase axis of the first phase plate. It was arranged so as to be orthogonal to. As a result, the retardation of the first phase plate is canceled out, and the retardation of the laminate of the first phase plate, the liquid crystal layer, and the second phase plate becomes zero. Further, the transmission axis of the second polarizing plate is arranged so as to be orthogonal to the transmission axis of the first polarizing plate to realize dark display of the transmission display unit.

When a voltage is applied between the pixel electrode and the common electrode, electric lines of force similar to those in FIG. 7 are formed, and the orientation state of the liquid crystal layer at this time is shown in FIG. Since the dielectric anisotropy of the liquid crystal material is positive, the liquid crystal layer changes its orientation so as to be parallel to the lines of electric force. As a result, retardation occurs in the liquid crystal layer, and both the reflective display unit and the transmissive display unit are clearly displayed.

Looking at FIG. 16 in detail, the liquid crystal layer is vertically oriented at the center of the upper surface of the pixel electrode and the common electrode, because there is no electric field in this portion. Further, the liquid crystal layer is also vertically oriented between the pixel electrode and the common electrode, because the orientations are opposite to each other on the pixel electrode side and the common electrode side, and both are opposed to each other in the middle. Focusing on the liquid crystal layer between any pixel electrode and the common electrode, the inclination of the lines of electric force is opposite on the pixel electrode side and the common electrode side. Are in opposite directions. As a result, the liquid crystal layer is divided into two domains when a voltage is applied, and a wide viewing angle is obtained.

Since the cross section of the pixel electrode and the common electrode is inclined, the liquid crystal on the pixel electrode and the common electrode operates even in the case of this embodiment in which the liquid crystal orientation when no voltage is applied is vertically oriented, and the liquid crystal is reflected as the voltage is applied. A rate change is obtained. Further, in the liquid crystal display device of the present invention, since the cross section of the pixel electrode and the common electrode is inclined, the liquid crystal layer thickness of the reflection display portion is not uniform and has a distribution. In this embodiment, since the liquid crystal orientation when no voltage is applied is vertical orientation, the retardation of the liquid crystal layer is almost zero regardless of the thickness of the liquid crystal layer. Therefore, the retardation of the liquid crystal layer becomes uniform (zero) over the entire inclined portion. As a result, the dark display of the reflection display has a lower reflectance, and a reflection display having a high contrast ratio can be obtained.

In this example, a liquid crystal material having a negative dielectric anisotropy was used, and the liquid crystal orientation when no voltage was applied was set to vertical orientation. FIG. 17 shows a cross-sectional view of the liquid crystal display device of this embodiment when a voltage is applied. Since the liquid crystal layer changes its orientation so as to be perpendicular to the electric lines of force, the liquid crystal orientation changes in the direction opposite to that of Example 14 shown in FIG.

That is, focusing on the liquid crystal layer between the arbitrary pixel electrode and the common electrode, in Example 14, as shown in FIG. 16, the liquid crystal layer changes its orientation so as to face the intermediate point between the pixel electrode and the common electrode. In the example, as shown in FIG. 17, the orientation changes so as to face the end on the pixel electrode side and the end on the common electrode side. Also in this case, a reflection display having a high contrast ratio and a reflection display and a transmission display having a wide viewing angle can be obtained.

In this embodiment, in a liquid crystal display device having a pixel electrode having a bent planar structure and a common electrode as shown in FIGS. 10 and 11, the liquid crystal orientation when no voltage is applied is vertically oriented. In this case, the liquid crystal orientation direction when a voltage is applied is divided into four or more directions, and the liquid crystal layer is divided into four or more domains. Therefore, the viewing angle characteristics of each domain are more uniformly made uniform, and a reflection display and a transmission display with a wider viewing angle can be obtained.

<figref num="1">It is a figure which shows the pixel structure in Example 1, FIG. 1 (a) is a figure which shows the distribution of a pixel electrode 21 and common electrode 22, and the reflection surface normal distribution 61, 62, and FIG. 1 (b) is a figure which shows. , The scanning wiring 27, the signal wiring 25, the thin film transistor 28, and the pixel electrode 21 are shown in the figure.</figref><figref num="2">Cross-sectional view between dotted lines 1-2 of FIG. 1 (a) mainly consisting of the pixel electrode 21 and the common electrode 22 in the first embodiment.</figref><figref num="3">The figure which obtains the optical condition of the 1st polarizing plate 51, the 1st phase plate 53, and the liquid crystal layer of a reflection display part in Example 1.</figref><figref num="4">Cross-sectional view showing the relationship between the user 70 at the time of reflection display in Example 1 and the incident light and the emitted light.</figref><figref num="5">In Example 1, a cross-sectional view showing the orientation state of the liquid crystal molecules 50 when no voltage is applied.</figref><figref num="6">In Example 1, a cross-sectional view showing the orientation state of the liquid crystal molecules 50 when a voltage is applied.</figref><figref num="7">FIG. 1 is a cross-sectional view showing an electric line of force 49 when a voltage is applied.</figref><figref num="8">In Example 2, a cross-sectional view showing the orientation state of the liquid crystal molecules 50 when a voltage is applied.</figref><figref num="9">FIG. 3 is a cross-sectional view showing the orientation state of the liquid crystal molecules 50 when a voltage is applied.</figref><figref num="10">It is a figure which shows the pixel structure in Examples 4 and 5, and FIG. 10 (a) is a figure which shows the distribution of the pixel electrode 21 and the common electrode 22 in Example 4, and the distribution 61-64 in the reflection surface normal direction. FIG. 10 (b) is a diagram showing the distribution of the pixel electrode 21 and the common electrode 22 and the distribution 61 to 68 in the normal direction of the reflecting surface in the fifth embodiment.</figref><figref num="11">It is a figure which shows the pixel structure in Examples 6, 7 and 8, and FIG. 11 (a) is a figure which shows the distribution of the pixel electrode 21 and the common electrode 22 in Example 6, and also FIG. 11 (b). Is a diagram showing the distribution of the pixel electrode 21 and the common electrode 22 in Example 7, and FIG. 11 (c) is a diagram showing the distribution of the pixel electrode 21 and the common electrode 22 in Example 8.</figref><figref num="12">It is a figure which shows the pixel structure in Examples 9 and 10, FIG. 12 (a) is a figure which shows the distribution of a pixel electrode 21 and common electrode 22 in Example 9, and FIG. 12 (b) is a figure which shows Example. It is a figure which shows the distribution of the pixel electrode 21 and the common electrode 22 in 10.</figref><figref num="13">It is a figure which shows the pixel structure in Examples 11 and 12, FIG. 13 (a) is a figure which shows the distribution of a pixel electrode 21 and common electrode 22 in Example 11, and FIG. 13 (b) is a figure which shows. It is a figure which shows the distribution of the pixel electrode 21 and the common electrode 22 in Example 12, and FIG. 13C is a cross-sectional view between 3-4 of FIG. 13A.</figref><figref num="14">It is a figure which shows the pixel structure using the common wiring, and the example which changed the number of common electrodes and pixel electrodes in this.</figref><figref num="15">It is sectional drawing which shows the liquid crystal orientation state at the time of no voltage application of the liquid crystal display device of Example 14.</figref><figref num="16">It is sectional drawing which shows the liquid crystal orientation state at the time of applying a voltage of the liquid crystal display device of Example 14.</figref><figref num="17">It is sectional drawing which shows the liquid crystal orientation state at the time of applying a voltage of the liquid crystal display device of Example 15.</figref><figref num="18">It is a figure which shows the visual angle characteristic in the transmission display of the liquid crystal display device of this invention.</figref><figref num="19">It is a figure which shows the factor which is involved in the visual angle characteristic of a birefringent medium, and the method of determining the optical characteristic of a birefringent medium in an arbitrary visual angle direction.</figref><figref num="20">It is a figure which shows the change of the cross-sectional shape of the refractive index ellipsoid with the increase of the polar angle.</figref><figref num="21">A cross-sectional view showing the relationship between the user 70 and the incident light and the emitted light at the time of the conventional reflection display.</figref><figref num="22">Cross-sectional view showing the orientation state of the liquid crystal molecules 50 when no voltage is applied in the conventional manner.</figref><figref num="23">Cross-sectional view showing the orientation state of the liquid crystal molecules 50 when a conventional voltage is applied.</figref><figref num="24">Cross-sectional view showing electric lines of force 49 when a conventional voltage is applied</figref>

Code description

10 ... liquid crystal layer, 11 ... first substrate, 12 ... second substrate, 13 ... first alignment film, 14 ... second alignment film, 15 ... th One insulating film, 16 ... second insulating film, 17 ... third insulating film, 18 ... color filter, 19 ... flattening film, 20 ... gap, 21 ... Pixel electrode, 22 Common electrode, 23 Source wiring, 24 Through hole part, 25 Signal wiring, 26 Amorphous silicon layer, 27 Scanning wiring, 28 Thin film, 29 common wiring, 49 electric power line, 50 liquid crystal molecule, 51 first plate, 52 second plate, 53 1st phase plate, 54 ... 2nd phase plate, 55 ... 3rd phase plate, 56 ... light diffusion layer, 61 to 68 ... tilt direction of the reflective surface in the reflective display 70: User, 80: Refractive index ellipse, 81: Cross section including the center of the refractive index ellipse, 82: Long axis of the cross section of the refractive index ellipse, 83: Refractive index Short axis of the cross section of the elliptical body, 84 ... viewing angle direction, 85 ... slow axis of the phase plate with Nz = 1.0, 86 ... slow axis of the phase plate with Nz = 0.0, 90 ... minute Concavo-convex structure