JP2005128233A - Liquid crystal display device and electronic appliance - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a liquid crystal display device in which a wide viewing angle is obtained in a transmissive display in the case of using a wide band circularly polarizing plate in the liquid crystal display device using a vertical alignment mode. <P>SOLUTION: In the liquid crystal display device, each of upper and lower circularly polarized light incident means has a half-wave plate 16 or 18, a quarter-wave plate 162 or 182 and a linear polarizing plate 17 or 19. Regarding the half-wave plates 16, 18, when refractive indexes in mutually perpendicularly intersecting azimuth angle directions in the plane and that in the thickness direction are represented by nx1, ny1 and nz1 respectively, and Nz1 is defined by an equation Nz1=(nx1-nz1)/(nx1-ny1), an inequality 0.5≤Nz1≤1.0 is satisfied, and at the same time, in relation to the quarter-wave plates 162, 182, when refractive indexes in mutually perpendicularly intersecting azimuth angle directions in the plane and that in the thickness direction are represented by nx2, ny2 and nz2 respectively, and Nz2 is defined by an equation Nz2=(nx2-nz2)/(nx2-ny2), an inequality 1.5≤Nz2≤2.0 is satisfied. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to a configuration of a liquid crystal display device and an electronic apparatus, particularly a vertical alignment mode liquid crystal display device.

  As a liquid crystal display device, a transflective liquid crystal display device having both a reflection mode and a transmission mode is known. As such a transflective liquid crystal display device, a liquid crystal layer is sandwiched between an upper substrate and a lower substrate, and a reflective film in which a window for light transmission is formed on a metal film such as aluminum is used as a lower substrate. In order to make this reflective film function as a semi-transmissive reflector, it has been proposed. (In this specification, the surface on the liquid crystal layer side of the pair of substrates is referred to as the inner surface, and the opposite surface is referred to as the outer surface.) In this case, the external light incident from the upper substrate side is reflected after passing through the liquid crystal layer in the reflection mode. The light is reflected by the reflective film on the inner surface of the substrate, passes through the liquid crystal layer again, is emitted from the upper substrate side, and contributes to display. On the other hand, in the transmissive mode, light from the backlight incident from the lower substrate side passes through the liquid crystal layer from the window portion of the reflective film, and then is emitted to the outside from the upper substrate side, contributing to display. Accordingly, of the reflective film formation region, the region where the window is formed is the transmissive display region, and the other region is the reflective display region.

However, the conventional transflective liquid crystal display device has a problem that the viewing angle in transmissive display is narrow. This is because a transflective plate is provided on the inner surface of the liquid crystal cell so that parallax does not occur, and there is a limitation that reflection display must be performed with only one polarizing plate provided on the viewer side. This is because the degree of freedom in design is small. Therefore, in order to solve this problem, a new liquid crystal display device using vertically aligned liquid crystal has been proposed in the following Patent Document 1 and Non-Patent Document 1. The characteristics are the following three.
(1) A “VA (Vertical Alignment) mode” is adopted in which a liquid crystal having a negative dielectric anisotropy is aligned perpendicularly to a substrate, and the liquid crystal is tilted by applying a voltage.
(2) A “multi-gap structure” is employed in which the liquid crystal layer thickness (cell gap) is different between the transmissive display area and the reflective display area (refer to, for example, Patent Document 2).
(3) The transmissive display area is a regular octagon, and a projection is provided at the center of the transmissive display area on the counter substrate so that the liquid crystal tilts in eight directions within this area. In other words, “alignment division structure” is adopted.
JP 2002-350853 A Japanese Patent Laid-Open No. 11-242226 "Development of transflective LCD for high contrast and wide viewing angle by using homeotropic alignment", M. Jisaki et al., Asia Display / IDW'01, p.133-136 (2001)

  In Patent Document 1 and Non-Patent Document 1 described above, in order to make circularly polarized light incident on the liquid crystal layer, a circularly polarizing plate combining a linearly polarizing plate and a quarter-wave plate (retardation plate) is provided on the outer surface side of the substrate. It has. Although the characteristics of such a circularly polarizing plate have a great influence on the viewing angle characteristics, the above-mentioned document does not mention that detailed conditions are prescribed for the circularly polarizing plate, and the contrast ratio may decrease depending on the viewing angle. . Further, it is known that a linearly polarizing plate, a half-wave plate, and a quarter-wave plate are used in combination as a wide-band circular polarizing plate that covers the entire visible light range. Realization of a liquid crystal display device capable of obtaining a high contrast ratio with a wide viewing angle when this configuration is employed is desired. The problem has been described with reference to the example of the transflective liquid crystal display device. However, this is not limited to the transflective type, and is a problem common to the transmissive liquid crystal display device.

  The present invention has been made to solve the above-described problems, and in a liquid crystal display device using a vertical alignment mode, a wide viewing angle is particularly obtained in a transmissive display using the broadband circularly polarizing plate as described above. An object is to provide an obtained liquid crystal display device. Another object of the present invention is to provide an electronic apparatus provided with this type of liquid crystal display device as a display unit.

  In order to achieve the above object, a liquid crystal display device of the present invention is a liquid crystal display device in which a liquid crystal layer is sandwiched between a pair of substrates, and the liquid crystal layer is a dielectric whose initial alignment state exhibits vertical alignment. The circularly polarizing means is provided on the outer surfaces of the pair of substrates, each of which has a phase difference of approximately ½ of the wavelength of incident light. An azimuth angle direction orthogonal to each other in the plane of the half-wave plate, having a quarter-wave plate having a phase difference of approximately ¼ of the wavelength of the incident light and a linearly polarizing plate Is defined as Nz1 = (nx1-nz1) / (nx1-ny1) where nx1 and ny1 and the refractive index in the thickness direction are nz1, satisfying 0.5 ≦ Nz1 ≦ 1.0. At the same time, the quarter-wave plate When the refractive index in the azimuth angle direction orthogonal to nx2 and ny2 and the refractive index in the thickness direction as nz2 are defined as Nz2 = (nx2-nz2) / (nx2-ny2), 1.5 ≦ Nz2 ≦ 2.0 is satisfied.

  As described above, the liquid crystal display device of the present invention is premised on a combination of a liquid crystal layer in a vertical alignment mode with a liquid crystal display device, and a linearly polarizing plate, a half-wave plate, a quarter-wave plate as circularly polarizing means. A broadband circularly polarizing plate made of is used. Here, the present invention defines optical characteristics suitable for widening the viewing angle for the half-wave plate and the quarter-wave plate constituting the broadband circularly polarizing plate. The inventor pays attention to Nz (Nz1, Nz2) defined as described above among various parameters representing the optical characteristics of the retardation plate, and changes the value of Nz in various ways to determine the contrast viewing angle characteristics. A simulation was performed to see how the change occurred (the simulation result will be described later). As a result, when a half-wave plate and a quarter-wave plate in which the value of Nz satisfies the above range are used, the transmissive display can be achieved as compared with a liquid crystal display device having a wave plate having a value of Nz of 1. I found that I could widen my viewing angle.

The retardation value Δn · d when the refractive index anisotropy of the liquid crystal layer is Δn and the layer thickness is d is preferably in the range of 0.4 to 0.5.
When the retardation value Δn · d of the liquid crystal layer is within the above range, the value of Nz of each wave plate can be optimized to widen the viewing angle in transmissive display. For example, if the retardation value Δn · d is larger than this, it is necessary to increase Nz of the quarter-wave plate beyond the above range, which is not practical.

In addition, the polarization axis of the linearly polarizing plate provided on the outer surface of one of the pair of substrates and the polarizing axis of the linearly polarizing plate provided on the outer surface of the other substrate are substantially orthogonal to each other, The slow axis (or fast axis) of the half-wave plate and quarter-wave plate provided and the slow axis (or fast axis of the half-wave plate and quarter-wave plate provided on the outer surface of the other substrate). It is desirable to arrange the optical axes of the constituent elements so that the phase axes are substantially orthogonal to each other.
When the optical axis is arranged as described above, a larger contrast ratio can be obtained in a range where the polar angle (angle formed with the normal line of the liquid crystal panel surface) is small.

Alternatively, the polarization axis of the linearly polarizing plate provided on the outer surface of one substrate and the polarizing axis of the linearly polarizing plate provided on the outer surface of the other substrate are substantially parallel to each other, and are 1/2 provided on the outer surface of the one substrate. The slow axis (or fast axis) of the wave plate and quarter wave plate and the slow axis (or fast axis) of the half wave plate and quarter wave plate provided on the outer surface of the other substrate You may arrange | position the optical axis of each component so that it may be substantially parallel mutually.
Alternatively, the polarization axis of the linearly polarizing plate provided on the outer surface of one substrate and the polarizing axis of the linearly polarizing plate provided on the outer surface of the other substrate are approximately 45 °, and 1/2 provided on the outer surface of the one substrate. The slow axis (or fast axis) of the wave plate and quarter wave plate and the slow axis (or fast axis) of the half wave plate and quarter wave plate provided on the outer surface of the other substrate You may arrange | position the optical axis of each component so that it may make about 45 degrees.
In both the former case and the latter case, the contrast ratio in a range where the polar angle is small is lower than in the case of the orthogonal case. However, since the region having a sufficiently small contrast ratio is a region having a large polar angle, that is, a direction that forms a small angle with respect to the liquid crystal panel surface, such an arrangement of optical axes is effective in increasing the viewing angle. It can be said that there is.

The present invention can be applied to a transflective liquid crystal display device provided with a transmissive display region for performing transmissive display and a reflective display region for performing reflective display within one dot region.
According to this configuration, it is possible to obtain a liquid crystal display device that is excellent in visibility regardless of the brightness of the place of use and particularly has a wide viewing angle for transmissive display.

An electronic apparatus according to the present invention includes the liquid crystal display device according to the present invention.
According to this configuration, an electronic apparatus including a liquid crystal display unit having a wide viewing angle particularly in transmissive display can be realized.

[First Embodiment]
Hereinafter, a first embodiment of the present invention will be described with reference to the drawings.
The liquid crystal display device of this embodiment is an example of an active matrix liquid crystal display device using a thin film transistor (hereinafter abbreviated as TFT) as a switching element.
FIG. 1 is an equivalent circuit diagram of a plurality of dots arranged in a matrix constituting the image display area of the liquid crystal display device of the present embodiment, and FIG. 2 is a plan view showing the structure of a plurality of adjacent dots on the TFT array substrate. 3A is a plan view showing the structure of the liquid crystal display device, and FIG. 3B is a cross-sectional view. In each of the following drawings, the scale of each layer and each member is different in order to make each layer and each member recognizable on the drawing.

  In the liquid crystal display device according to the present embodiment, as shown in FIG. 1, a plurality of dots arranged in a matrix that forms an image display region include a pixel electrode 9 and a switching element for controlling the pixel electrode 9. Each of the TFTs 30 is formed, and the data line 6 a to which an image signal is supplied is electrically connected to the source of the TFT 30. Image signals S1, S2,..., Sn to be written to the data line 6a are supplied line-sequentially in this order, or are supplied for each group to a plurality of adjacent data lines 6a. Further, the scanning line 3a is electrically connected to the gate of the TFT 30, and the scanning signals G1, G2,..., Gm are applied to the plurality of scanning lines 3a in a pulse-sequential manner at a predetermined timing. Further, the pixel electrode 9 is electrically connected to the drain of the TFT 30, and by turning on the TFT 30 as a switching element for a certain period, the image signals S1, S2,. Write at the timing. A predetermined level of image signals S1, S2,..., Sn written to the liquid crystal via the pixel electrode 9 is held for a certain period with the common electrode described later. The liquid crystal modulates light by changing the orientation and order of the molecular assembly according to the applied voltage level, thereby enabling gradation display. Here, in order to prevent the held image signal from leaking, a storage capacitor 70 is added in parallel with the liquid crystal capacitor formed between the pixel electrode 9 and the common electrode. Reference numeral 3b denotes a capacity line.

Next, the planar structure of the TFT array substrate constituting the liquid crystal display device of the present embodiment will be described with reference to FIG.
As shown in FIG. 2, on the TFT array substrate, a plurality of rectangular pixel electrodes 9 (contours are indicated by broken lines 9A) are provided in a matrix, and data along the vertical and horizontal boundaries of the pixel electrodes 9 is provided. A line 6a, a scanning line 3a, and a capacitor line 3b are provided. In the present embodiment, the inside of each pixel electrode 9 and the region where the data line 6a, the scanning line 3a, the capacitance line 3b, etc., which are arranged so as to surround each pixel electrode 9 are formed is one dot region, The display is made possible for each dot area arranged in a matrix.

  The data line 6a is electrically connected to a source region, which will be described later, of the semiconductor layer 1a that constitutes the TFT 30, for example, a polysilicon film, via a contact hole 5, and the pixel electrode 9 is connected to the semiconductor layer 1a. Among these, it is electrically connected to a drain region described later via a contact hole 8. Further, in the semiconductor layer 1a, the scanning line 3a is disposed so as to face the channel region (the region with the oblique line rising to the left in the drawing), and the scanning line 3a functions as a gate electrode in a portion facing the channel region. . The capacitance line 3b is formed from a main line portion (that is, a first region formed along the scanning line 3a in plan view) extending substantially linearly along the scanning line 3a and a location intersecting the data line 6a. And a protruding portion (that is, a second region extending along the data line 6 a when viewed in a plan view) protruding toward the previous stage (upward in the drawing) along the data line 6 a. In FIG. 2, a plurality of first light shielding films 11 a are provided in a region indicated by a diagonal line rising to the right.

  More specifically, each of the first light shielding films 11a is provided at a position that covers the TFT 30 including the channel region of the semiconductor layer 1a when viewed from the TFT array substrate side, and is opposed to the main line portion of the capacitor line 3b. The main line portion extending linearly along the scanning line 3a and the protruding portion protruding from the portion intersecting with the data line 6a to the rear side (that is, downward in the figure) adjacent to the data line 6a. The tip of the downward protruding portion in each stage (pixel row) of the first light shielding film 11a overlaps the tip of the upward protruding portion of the capacitor line 3b in the next stage under the data line 6a. A contact hole 13 for electrically connecting the first light-shielding film 11a and the capacitor line 3b to each other is provided at the overlapping portion. In other words, in the present embodiment, the first light-shielding film 11a is electrically connected to the upstream or downstream capacitor line 3b through the contact hole 13. Further, as shown in FIG. 2, a reflective film 20 is formed in one dot area, and the area where the reflective film 20 is formed becomes a reflective display area R, and the reflective film 20 is not formed. The region, that is, the inside of the opening 21 of the reflective film 20 becomes the transmissive display region T.

Next, a planar structure and a cross-sectional structure of the liquid crystal display device of the present embodiment will be described with reference to FIG.
FIG. 3A is a schematic plan view showing a planar structure of the color filter layer provided in the liquid crystal display device of the present embodiment, and FIG. 3B is a red color in the plan view of FIG. It is a cross-sectional schematic diagram of the part corresponding to a layer.
As shown in FIG. 2, the liquid crystal display device according to the present embodiment has a dot region including a pixel electrode 9 inside a region surrounded by the data line 6a, the scanning line 3a, the capacitor line 3b, and the like. doing. In this dot area, as shown in FIG. 3A, one colored layer of the three primary colors is arranged corresponding to one dot area, and three dot areas (D1, D2, D3) are arranged. This constitutes a pixel including the colored layers 22B (blue), 22G (green), and 22R (red).

  On the other hand, as shown in FIG. 3B, the liquid crystal display device according to the present embodiment is a dielectric having an initial alignment state of vertical alignment between the TFT array substrate 10 and a counter substrate 25 disposed opposite thereto. A liquid crystal layer 50 made of a liquid crystal material having negative rate anisotropy is sandwiched. In the TFT array substrate 10, a reflective film 20 made of a highly reflective metal film such as aluminum or silver is partially formed through an insulating film 24 on the surface of a substrate body 10 A made of a light-transmitting material such as quartz or glass. The configuration is made. As described above, the reflective film 20 formation region is the reflective display region R, and the non-reflective region of the reflective film 20, that is, the opening 21 of the reflective film 20 is the transmissive display region T. As described above, the liquid crystal display device according to the present embodiment is a vertical alignment type liquid crystal display device including the vertical alignment type liquid crystal layer 50, and is a transflective liquid crystal display device capable of reflective display and transmissive display. It is.

  The insulating film 24 formed on the substrate body 10A has an uneven shape 24a on its surface, and the surface of the reflective film 20 has unevenness following the uneven shape 24a. Since the reflected light is scattered by such irregularities, reflection from the outside is prevented, and a wide viewing angle display can be obtained. An insulating film 26 is formed on the reflective film 20 at a position corresponding to the reflective display region R. That is, the insulating film 26 is selectively formed so as to be positioned above the reflective film 20, and the thickness of the liquid crystal layer 50 is made different between the reflective display region R and the transmissive display region T as the insulating film 26 is formed. ing. The insulating film 26 is made of an organic film such as an acrylic resin having a film thickness of about 2 to 3 μm, for example, and is inclined so that its layer thickness continuously changes in the vicinity of the boundary between the reflective display region R and the transmissive display region T. It has an inclined area with 26a. The thickness of the liquid crystal layer 50 where the insulating film 26 does not exist is about 4 to 6 μm, and the thickness of the liquid crystal layer 50 in the reflective display region R is about half of the thickness of the liquid crystal layer 50 in the transmissive display region T. Yes.

Thus, the insulating film 26 functions as a liquid crystal layer thickness adjusting layer (liquid crystal layer thickness control layer) that varies the thickness of the liquid crystal layer 50 between the reflective display region R and the transmissive display region T depending on its own film thickness. is there. In the case of the present embodiment, the edge of the flat surface on the upper side of the insulating film 26 and the edge of the reflective film 20 (reflective display area) substantially coincide with each other, and the inclined area of the insulating film 26 becomes the transmissive display area T. Will be included. Then, on the surface of the TFT array substrate 10 including the surface of the insulating film 26, a pixel electrode 9 made of a transparent conductive film such as indium tin oxide (hereinafter abbreviated as ITO), an orientation made of polyimide or the like. A film 27 is formed. In the present embodiment, the reflective film 20 and the pixel electrode 9 are separately provided and laminated. However, in the reflective display region R, a reflective film made of a metal film can be used as the pixel electrode.
On the other hand, in the transmissive display region T, the insulating film 24 is formed on the substrate body 10A, and the reflective film 20 and the insulating film 26 are not formed on the surface thereof. That is, the pixel electrode 9 and the alignment film 27 made of polyimide or the like are formed on the insulating film 24.

Next, on the counter substrate 25 side, a color filter 22 (a red colored layer 22R in FIG. 3B) is provided on the inner surface of a substrate body 25A made of a translucent material such as glass or quartz. Here, the periphery of the colored layer 22R is surrounded by a black matrix BM, and the boundaries of the dot regions D1, D2, and D3 are formed by the black matrix BM (see FIG. 3A).
A common electrode 31 made of a transparent conductive film such as ITO and an alignment film 33 made of polyimide or the like are formed on the liquid crystal layer side of the color filter 22. Here, the common electrode 31 has a recess 32 in the reflective display region R, and the surface of the alignment film 33, that is, the sandwiching surface of the liquid crystal layer 50, has a recess (step) formed substantially along the recess 32. Is formed. The concave portion (step portion) formed on the sandwiching surface of the liquid crystal layer 50 has an inclined surface with a predetermined angle with respect to the substrate plane (or the vertical alignment direction of the liquid crystal molecules), and the liquid crystal molecules are aligned along the direction of the inclined surface. The orientation, particularly the direction in which the vertically aligned liquid crystal molecules fall down, is regulated. In the present embodiment, both the alignment films 27 and 33 of the TFT array substrate 10 and the counter substrate 25 are subjected to vertical alignment processing.

  Next, on the outer surface side of the substrate main body 10A of the TFT array substrate 10, a quarter wavelength plate 182, a half wavelength plate 18, and a linear polarizing plate 19 are provided via an adhesive layer (not shown) from the substrate main body side. It is affixed. Similarly, a quarter wavelength plate 162, a half wavelength plate 16, and a linear polarizing plate 17 are attached to the outer surface side of the substrate body 25A of the counter substrate 25 from the substrate side through an adhesive layer (not shown). ing. These quarter-wave plates 182 and 162, half-wave plates 18 and 16, and linear polarizers 19 and 17 constitute a broadband circular polarizer, and circularly polarized light is applied to the substrate inner surface side (liquid crystal layer 50 side). Incident is possible. The linearly polarizing plates 17 and 19 have a polarization axis in a predetermined direction and transmit only linearly polarized light. The quarter-wave plates 182 and 162 have a phase difference (retardation) that is approximately ¼ of the wavelength of the incident light. In the case of the present embodiment, the quarter-wave plates 182 and 162 are about 130 nm relative to the incident light with a wavelength of 590 nm. A stretched film having a phase difference is used. The half-wave plates 18 and 16 have a phase difference (retardation) that is approximately ½ of the wavelength of the incident light. In the case of this embodiment, the half-wave plates 18 and 16 are about 260 nm with respect to the incident light with a wavelength of 590 nm. A stretched film having a phase difference is used. Further, a backlight 15 serving as a light source for transmissive display is provided outside the polarizing plate 19 attached to the TFT array substrate 10.

  Here, as shown in FIG. 4, the half-wave plates 18 and 16 have a refractive index in the azimuth direction orthogonal to each other in the plane thereof as nx1 and ny1, and a refractive index in the thickness direction as nz1 and Nz1 When defined as = (nx1-nz1) / (nx1-ny1), 0.5 ≦ Nz1 ≦ 1.0 is satisfied, and specifically, for example, Nz1 = 0.5 is set. Similarly, the quarter-wave plates 182 and 162 have Nx2 = (nx2-nz2) / Nz2 = (nx2-nz2) / where the refractive index in the azimuth direction orthogonal to each other in the plane is nx2 and ny2, and the refractive index in the thickness direction is nz2. When defined as (nx2-ny2), 1.5 ≦ Nz2 ≦ 2.0 is satisfied, and specifically, for example, Nz1 = 1.8 is set. The liquid crystal layer 50 is set so that the retardation value Δn · d is in the range of 0.4 to 0.5, where Δn is the refractive index anisotropy and d is the layer thickness. Specifically, for example, Δn · d = 0.42 is set.

  Further, the arrangement of the optical axes of the upper circular polarizing plate, that is, the linear polarizing plate 17, the half-wave plate 16 and the quarter-wave plate 162 on the outer surface side of the counter substrate 25 is as shown in FIG. The absorption axis of the linearly polarizing plate 17 is 30.0 ° with respect to the X-axis when two orthogonal axes in the plane as viewed from above the X-axis and the Y-axis are viewed from above. The slow axis of the half-wave plate 16 forms 43.0 ° with respect to the X axis, and the slow axis of the quarter wavelength plate 162 forms 81.0 ° with respect to the X axis. On the other hand, the arrangement of the optical axes of the lower circular polarizing plate, that is, the linear polarizing plate 19, the half-wave plate 18 and the quarter-wave plate 182 on the outer surface side of the TFT array substrate 10 is as shown in FIG. . Similarly to FIG. 5, when viewed from above the linear polarizing plate 17, the absorption axis of the linear polarizing plate 19 is 30.0 ° with respect to the Y axis, and the slow axis of the half-wave plate 18 is with respect to the X axis. 47.0 °, and the slow axis of the quarter-wave plate 182 is 9.0 ° with respect to the X-axis. Therefore, the absorption axis of the upper linear polarizing plate 17 and the absorption axis of the lower linear polarizing plate 19 are orthogonal to each other. Further, the slow axis of the upper half-wave plate 16 and the slow axis of the lower half-wave plate 18 are orthogonal to each other. Further, the slow axis of the upper quarter-wave plate 162 and the slow axis of the lower quarter-wave plate 182 are orthogonal to each other.

  FIG. 7 shows the result of the inventor's calculation of the contrast viewing angle characteristic by simulation on the premise of the liquid crystal display device having the above configuration. FIG. 7 shows an isocontrast curve at coordinates with an azimuth angle of 0 ° to 360 ° and a polar angle of 0 ° (normal direction of the panel) to 80 °. The isocontrast curve has a contrast ratio of 5, 10 from the outside. , 20, 50, 100, 200, 500, 1000. An area having a contrast ratio of 5 or less is indicated by hatching (area D). A region having a contrast ratio of 1000 or more is indicated by dot hatching (region B). According to the liquid crystal display device of the present embodiment, as shown in FIG. 7, the contrast ratio is 5 or more inside the cone where the polar angle is approximately 60 °, and a wide viewing angle is obtained. Was confirmed.

Here, the Nz value of the half-wave plate and the quarter-wave plate constituting the broadband circularly polarizing plate is based on the knowledge that the most significant influence on the contrast ratio is the degree of black sinking during black display. A simulation was conducted on the viewing angle characteristics of black display when the angle was changed. The results are shown in FIGS.
FIG. 8 shows an equiluminance curve of black display when Nz of the half-wave plate is fixed to 0.5 and Nz of the quarter-wave plate is variously changed. Nz of the quarter wave plate is 1.5, Nb of the quarter wave plate is 1.8 in FIG. 8B, and Nz of the quarter wave plate is 2.0 in FIG. 8C. d) shows the case where Nz of the quarter-wave plate is 2.2.
In each figure, there is a portion where the black display is blackened in the center (area of hatched hatching D), and the black display is brightly floated (dot hatching) at the four corners of upper right, upper left, lower right, and lower left. However, as the Nz of the quarter-wave plate increases, the four corners become darker (the area of the code D becomes smaller), which tends to be good. However, on the other hand, as the Nz of the quarter-wave plate becomes larger, the upper, lower, left, and right cross-shaped dark parts begin to float brightly. Therefore, generally, when Nz of the half-wave plate is 0.5, it is considered that Nz of the quarter-wave plate is preferably about 1.8 in FIG.

Next, FIG. 9 shows an isoluminance curve for black display when Nz of the half-wave plate is fixed to 1.0 and Nz of the quarter-wave plate is variously changed. ) Is Nz of the quarter-wave plate is 1.5, FIG. 9B is Nz of the quarter-wave plate is 1.8, FIG. 9C is Nz of the quarter-wave plate is 2.0, FIG. 9D shows the case where Nz of the quarter-wave plate is 2.2.
In each figure, unlike the case where Nz of the half-wave plate is set to 0.5, the portions where the black display at the upper right corner, the upper left corner, the lower right corner, and the lower left corner is brightly floated (region B) are ¼. There is no tendency to improve by increasing the Nz of the wave plate. In addition, due to the increase in Nz of the quarter-wave plate, the upper, lower, left, and right cross-shaped dark portions (regions with reference sign D) do not float extremely. Therefore, generally, when Nz of the half-wave plate is 1.0, Nz of the quarter-wave plate is preferably about 1.8 in FIG. 9B where the bright portions at the four corners are the darkest. I think that the.

As a comparative example, the inventor of the present invention is outside the scope of the present invention, that is, the Nz of the half-wave plate is less than 0.5 and more than 1.0, and the Nz of the quarter-wave plate is less than 1.5 The simulation is performed in the entire range exceeding zero. As a result, for example, as shown in FIG. 13, the black display floats extremely brightly in all azimuth directions in a region where the polar angle is large (region of reference B) as shown in FIG. ), It has been confirmed that the effect of widening the viewing angle is not obtained at all.
From the above results, when Nz of the half-wave plate is 0.5 to 1.0, and Nz of the quarter-wave plate is 1.8 to 2.0, more preferably around 1.8, It was found that the best viewing angle characteristics can be obtained.

  FIGS. 8 and 9 show the viewing angle characteristics when the retardation value Δn · d of the liquid crystal layer is 0.42, whereas the liquid crystal layer has a retardation value Δn · d of 0.50. The viewing angle characteristic is shown in FIG. FIG. 10 shows an isoluminance curve for black display when Nz of the half-wave plate is 1.0 and Nz of the quarter-wave plate is 2.0. Compared with the viewing angle characteristics (FIGS. 9A to 9D) when Nz of the half-wave plate is 1.0 and Δn · d of the liquid crystal layer is 0.42, the viewing angle characteristics of FIG. Is substantially the same as the viewing angle characteristic when Nz of the quarter-wave plate shown in FIG. From this, it can be seen that when the retardation value Δn · d of the liquid crystal layer is increased, in order to widen the viewing angle, it is necessary to increase Nz of the quarter-wave plate accordingly.

  As shown in FIGS. 5 and 6, the above characteristics are the absorption axes of the upper and lower linear polarizing plates, the slow axis of the upper and lower half-wave plates, and the slow axis of the upper and lower quarter-wave plates. Although it is a characteristic in the case of orthogonal arrangement, the arrangement of these optical axes is not limited to this. For example, FIG. 11 shows a set of lower circularly polarizing plates (linearly polarizing plates, 1/2 with respect to a set of upper circularly polarizing plates (linearly polarizing plate, half-wave plate, and quarter-wave plate). The same contrast curve is shown for the whole of the wave plate and the quarter wave plate rotated by 45 °. That is, the polarization axis of the upper linear polarizing plate and the polarization axis of the lower linear polarizing plate form 45 °, and the slow axis of the upper half-wave plate and quarter-wave plate and the lower 1 / This is a case where the slow axis of the two-wave plate and the quarter-wave plate forms 45 °. FIG. 12 shows an isocontrast curve when the entire set of the lower circular polarizing plates is rotated by 90 ° with respect to the set of the upper circular polarizing plates. That is, the polarization axis of the upper linear polarizing plate and the polarization axis of the lower linear polarizing plate are parallel to each other, and the slow axis of the upper half-wave plate and the quarter-wave plate is lower than the lower half. This is a case where the slow axis of the wave plate and the quarter wave plate is parallel.

  In either case, since the broadband circularly polarizing plates are used for the upper and lower circularly polarizing plates, a sufficient contrast ratio can be obtained even if the upper and lower linearly polarizing plates and the wave plate are not symmetrical with each other. As shown in FIGS. 11 and 12, the contrast ratio in the front (in the normal direction of the panel) is lower than that in FIG. 7 (in the case of being orthogonal), but the portion with a high contrast ratio spreads in the vertical direction. Is 5 or less (outside of the outermost curve). Therefore, it can be said that such an arrangement of optical axes is effective in increasing the viewing angle.

  Thus, according to the liquid crystal display device of the present embodiment, the value of Nz is 1 by optimizing the value of Nz of the half-wave plate and the quarter-wave plate constituting the broadband circularly polarizing plate. Compared with a liquid crystal display device having a wave plate, the viewing angle in transmissive display can be widened.

[Electronics]
Next, specific examples of the electronic apparatus including the liquid crystal display device according to the above embodiment of the present invention will be described.
FIG. 14 is a perspective view showing an example of a mobile phone. In FIG. 14, reference numeral 1000 denotes a mobile phone body, and reference numeral 1001 denotes a display unit using the liquid crystal display device. When the liquid crystal display device of the above embodiment is used for a display unit of such an electronic device such as a mobile phone, an electronic device having a liquid crystal display unit with high contrast and a wide viewing angle can be realized.

  The technical scope of the present invention is not limited to the above embodiment, and various modifications can be made without departing from the spirit of the present invention. For example, in the above-described embodiment, an example in which the present invention is applied to an active matrix liquid crystal display device using TFT as a switching element has been described. However, an active matrix liquid crystal display device using a thin film diode (TFD) as a switching element. The present invention can also be applied to a passive matrix liquid crystal display device or the like. In addition, specific descriptions regarding materials, dimensions, shapes, and the like of various components can be appropriately changed.

It is an equivalent circuit diagram of a plurality of dots of a liquid crystal display device of one embodiment of the present invention. FIG. 6 is a plan view of a plurality of adjacent dots on the TFT array substrate. 3A is a plan view showing the structure of the liquid crystal display device, and FIG. 3B is a cross-sectional view. It is explanatory drawing for showing the refractive index anisotropy of a phase difference plate. It is a figure for demonstrating the optical axis arrangement | positioning of an upper side circularly-polarizing plate. It is a figure for demonstrating the optical axis arrangement | positioning of a lower side circularly-polarizing plate. It is a figure which shows the isocontrast curve of a liquid crystal display device equally. FIG. 6 is a diagram showing an isoluminance curve when Nz of a half-wave plate is 0.5 in the liquid crystal display device. FIG. 6 is a diagram showing an isoluminance curve when Nz of a half-wave plate is 1.0 in the liquid crystal display device. FIG. 6 is a diagram illustrating an isoluminance curve when Δn · d of a liquid crystal is 0.5 in the liquid crystal display device. It is a figure which shows the isocontrast curve when the optical axis arrangement | positioning of a lower side circularly-polarizing plate is shifted 45 degrees. It is a figure which shows the isocontrast curve when the optical axis arrangement | positioning of a lower circularly-polarizing plate is shifted by 90 degrees. It is a figure which shows the equiluminance curve at the time of using the waveplate which has Nz outside the range of this invention as a comparative example. It is a perspective view which shows an example of the electronic device of this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 ... TFT array substrate, 16, 18 ... 1/2 wavelength plate, 17, 19 ... Linear polarizing plate, 25 ... Opposite substrate, 50 ... Liquid crystal layer, 162, 182 ... 1/4 wavelength plate

Claims (7)

A liquid crystal display device having a liquid crystal layer sandwiched between a pair of substrates,
The liquid crystal layer is made of a liquid crystal having a negative dielectric anisotropy in which the initial alignment state is vertical alignment, and circular polarization means are provided on the outer surfaces of the pair of substrates, respectively, and each of the circular polarization means is incident light. A ½ wavelength plate having a phase difference of approximately ½ of the wavelength of λ, a ¼ wavelength plate having a phase difference of approximately ¼ of the wavelength of incident light, and a linearly polarizing plate,
For the half-wave plate, Nz1 = (nx1-nz1) / (nx1-ny1) where the refractive index in the azimuth direction orthogonal to each other in the plane is nx1, ny1 and the refractive index in the thickness direction is nz1. And satisfying 0.5 ≦ Nz1 ≦ 1.0,
The refractive index in the azimuth direction orthogonal to each other in the plane is nx2, ny2 and the refractive index in the thickness direction is nz2, and Nz2 = (nx2-nz2) / (nx2-ny2) When defined as follows, 1.5 ≦ Nz2 ≦ 2.0 is satisfied.   2. The liquid crystal display according to claim 1, wherein a retardation value Δn · d when the refractive index anisotropy of the liquid crystal layer is Δn and the layer thickness is d is in a range of 0.4 to 0.5. apparatus.   The polarization axis of the linearly polarizing plate provided on the outer surface of one of the pair of substrates and the polarization axis of the linearly polarizing plate provided on the outer surface of the other substrate are substantially orthogonal to each other. The half-wave plate and the quarter-wave plate provided on the outer surface of the other substrate and the slow-axis (or fast-axis) of the quarter-wave plate and the quarter-wave plate provided on the outer surface of the other substrate, respectively. 3. The liquid crystal display device according to claim 1, wherein the slow axis (or fast axis) of the wave plate is substantially orthogonal to each other.   The polarization axis of the linearly polarizing plate provided on the outer surface of one of the pair of substrates and the polarization axis of the linearly polarizing plate provided on the outer surface of the other substrate are substantially parallel to each other, The half-wave plate provided on the outer surface of the substrate and the slow axis (or the fast axis) of the quarter-wave plate and the half-wave plate provided on the outer surface of the other substrate and the 1 / 3. The liquid crystal display device according to claim 1, wherein the slow axis (or fast axis) of the four-wavelength plate is substantially parallel to each other.   The polarization axis of the linearly polarizing plate provided on the outer surface of one of the pair of substrates and the polarization axis of the linearly polarizing plate provided on the outer surface of the other substrate form approximately 45 °, The half-wave plate provided on the outer surface of the substrate and the slow axis (or the fast axis) of the quarter-wave plate and the half-wave plate provided on the outer surface of the other substrate and the 1 / 3. The liquid crystal display device according to claim 1, wherein a slow axis (or a fast axis) of the four-wave plate forms approximately 45 °.   6. The liquid crystal display device according to claim 1, further comprising a transmissive display region for performing transmissive display and a reflective display region for performing reflective display within one dot region. An electronic apparatus comprising the liquid crystal display device according to claim 1.

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