JP4761628B2 - Reflective liquid crystal display - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a reflective liquid crystal display device provided with a light diffusing plate.
[0002]
[Prior art]
Conventionally, a so-called reflection type liquid crystal display device has been proposed in which light incident from an observation direction is reflected to display a display.
[0003]
FIG. 7 shows a cross-sectional view of a conventional reflective liquid crystal display device.
[0004]
As shown in the figure, the conventional reflective liquid crystal display device forms a thin film transistor (hereinafter referred to as “TFT”) as a switching element on an insulating substrate 10 made of quartz glass, non-alkali glass or the like. .
[0005]
First, a gate electrode 11 made of a refractory metal such as chromium (Cr) and molybdenum (Mo), a gate insulating film 12 and an active layer 13 made of a polycrystalline silicon film are sequentially formed on an insulating substrate (TFT substrate) 10. Form.
[0006]
The active layer 13 has a channel 13c located above the gate electrode 11, and a source 13s and a drain 13d formed by ion implantation on both sides of the channel 13c using the stopper insulating film 14 on the channel 13c as a mask. Is provided.
[0007]
Then, on the entire surface of the gate insulating film 12, the active layer 13, and the stopper insulating film 14, SiO 2 ₂ Film, SiN film and SiO ₂ An interlayer insulating film 15 configured by sequentially stacking films is formed, and a drain electrode 16 is formed by filling a contact hole provided corresponding to the drain 13d with a metal such as aluminum (Al). Further, a planarizing insulating film 17 made of, for example, an organic resin and flattening the surface is formed on the entire surface. Then, a contact hole is formed at a position corresponding to the source 13 s of the planarization insulating film 17, and the reflective display electrode 19 is a reflective electrode made of Al that is in contact with the source 13 s through the contact hole and also serves as the source electrode 18. Is formed on the planarization insulating film 17. Then, an alignment film 20 made of an organic resin such as polyimide is aligned on the reflective display electrode 19 to align the liquid crystal 21.
[0008]
Further, the counter electrode substrate 30 made of an insulating substrate facing the TFT substrate 10 is provided with a black matrix 32 having red (R), green (G), and blue (B) colors and a light shielding function on the TFT substrate 10 side. And a protective film 33 made of a resin formed thereon, a counter electrode 34 and an alignment film 35 formed on the entire surface of the color filter 31. A polarizing plate 45 is disposed. Then, the periphery of the counter electrode substrate 30 and the TFT substrate 10 is bonded with a seal adhesive (not shown), and the twisted nematic (TN) liquid crystal 21 is sandwiched in the gap formed thereby.
[0009]
A description will be given of how light travels when observing the reflective liquid crystal display device described above.
[0010]
In FIG. 7, natural light 100 incident from the outside is incident from the polarizing plate 45 on the viewer 101 side as indicated by a broken line arrow, and the retardation plate 44, the counter electrode substrate 30, the color filter 31, the protective film 33, The counter electrode 34, the alignment film 35, the TN liquid crystal 21, and the alignment film 20 on the TFT substrate 10 are transmitted and reflected by the reflective display electrode 19. 30 exits from the phase difference plate 45 and enters the observer's eye 101.
[0011]
The brightness measurement of the reflected light of the reflective liquid crystal display device will be described with reference to FIG.
[0012]
FIG. 8A shows a method for measuring the luminance of the surface of the reflective display device, and FIG. 8B shows a measurement diagram showing the measurement results.
[0013]
As shown in FIG. 8A, the reflective liquid crystal display panel including the TFT substrate 10 and the counter electrode substrate 30 is displayed with its display surface facing up. Then, light is incident on the display panel from a direction inclined by a certain angle θin from the normal direction of the display surface. The incident light 105 is reflected by the reflective display electrode, and the reflected light emitted from the display panel is measured by the light intensity detector 106 at every predetermined emission angle. The light intensity detector 106 moves in the θout direction from the normal line of the liquid crystal display panel in FIG. 8A (indicated by a broken line in the figure) to detect and measure the reflected light at each angle θout.
[0014]
The measurement result is shown by the dashed curve in FIG. In the figure, the horizontal axis indicates the detection angle of the reflected light, and the vertical axis indicates the reflected light intensity at each detection angle.
[0015]
[Problems to be solved by the invention]
However, as shown by the dashed curve in FIG. 8B, according to the above-described conventional reflective liquid crystal display device, the reflected light intensity is strong depending on a specific angle, but in a wide range of the display panel. There was a drawback that a bright display could not be seen.
[0016]
In order to solve this drawback, it is conceivable to provide a light diffusion layer between the protective film 33 and the counter electrode 34 on the counter electrode substrate 30 in FIG.
[0017]
The relationship between the emission angle of the reflected light at that time and the intensity of the reflected light is shown by a solid curve in FIG. As shown by the solid line in the figure, compared to the dashed curve, strong reflected light can be obtained at each angle, that is, in a wide range, and a bright display can be seen.
[0018]
However, the intensity of the reflected light is small in the angle range θ1 in FIG. That is, since the brightness changes abruptly in the angle range θ1 compared to the reflected light in other angle ranges, when the observer looks at the display surface by changing the angle from the normal direction to the horizontal direction, Appears as uneven brightness.
[0019]
As described above, the conventional reflection type liquid crystal display device has a defect that brightness unevenness appears depending on the viewing angle.
[0020]
Accordingly, the present invention has been made in view of the above-described conventional drawbacks, and provides a reflective liquid crystal display device capable of increasing the luminance of each display pixel and obtaining a display with uniform brightness. With the goal.
[0021]
[Means for Solving the Problems]
In the reflective liquid crystal display device of the present invention, a liquid crystal is sandwiched between first and second substrates disposed to face each other, and the first substrate is connected to a switching element and the switching element. A display electrode made of a conductive reflective material, and the second substrate has a counter electrode facing the display electrode, and the surface of the display electrode has a flat portion and a first substrate side direction. The reflective liquid crystal display device includes a concave recess, and has an inclined portion between a bottom surface of the recess and the flat portion.
[0022]
In the reflection type liquid crystal display device of the present invention, the liquid crystal is sandwiched between the first and second substrates arranged to face each other. The first substrate has a switching element and an upper surface of the switching element. And an insulating film having a recessed portion recessed in the first substrate side direction, and a conductive reflective material that is formed on the insulating film so that the surface is flat and the first substrate side. A reflective liquid crystal display device having a display electrode provided with a concave portion in a direction, and a counter electrode facing the display electrode on the second substrate.
[0023]
In addition, the above-described reflective liquid crystal display device is a reflective liquid crystal display device in which a diffusion layer for diffusing light is provided on one of the first and second substrates.
[0024]
Furthermore, the above-described reflective liquid crystal display device is a reflective display device in which the angle of elevation of the inclined portion with respect to the bottom surface portion of the hollow portion is greater than 0 ° and not greater than 8 °.
[0025]
Furthermore, the above-mentioned reflection type liquid crystal display device is a reflection type liquid crystal display device in which the degree of diffusion of the diffusion layer is a haze value of 19% or more and 70% or less.
[0026]
DETAILED DESCRIPTION OF THE INVENTION
The reflective liquid crystal display device of the present invention will be described below.
[0027]
FIG. 1 shows a cross-sectional view of a reflective liquid crystal display device of the present invention.
[0028]
As shown in the figure, in the case of the present embodiment, a TFT as a switching element is formed on an insulating substrate 10 made of quartz glass, non-alkali glass or the like.
[0029]
Since the structure from the formation of the gate electrode 11 made of a refractory metal such as Cr or Mo on one insulating substrate 10 to before the formation of the planarization insulating film 70 is almost the same as the conventional structure, the description thereof is omitted. A manufacturing method after the formation of the planarization insulating film 70 will be described later.
[0030]
On the planarization insulating film 70, a reflective display electrode 50 made of a conductive reflective material such as Al or silver (Ag) connected to the source 13s of the active layer 13 made of a polycrystalline silicon film is formed. In addition, the reflective display electrode 50 has a concave portion in which the center of the display electrode is concave in the direction of the TFT substrate 10, that is, a concave portion in which the central portion of the display electrode is concave in the direction of the TFT substrate 10. Shape. An alignment film 20 made of polyimide or the like and for aligning liquid crystal is formed thereon.
[0031]
The other counter electrode substrate 30 is provided on the side where the liquid crystal 21 is provided, from a color filter 31 including each color exhibiting R, G, and B and a black matrix 32 having a light shielding function, an acrylic resin that protects the color filter 31, and the like. A protective film 33 is provided. On the protective film 33, a counter electrode 34 is provided on the entire surface so as to face the reflective display electrodes 50. Further, an alignment film 35 made of polyimide is formed on the entire surface.
[0032]
Further, on the side of the counter electrode substrate 30 on which the liquid crystal is not provided, that is, the viewer 101 side, a diffusion layer 43 that diffuses light, a retardation (λ / 4) plate 44 and a polarizing plate 45 are sequentially arranged from the counter electrode substrate 30 side. Is provided. As the liquid crystal 21, for example, TN liquid crystal is used.
[0033]
A description will be given of how light travels when observing the reflective liquid crystal display device described above.
[0034]
Natural light 100 incident from the outside enters from the polarizing plate 45 on the viewer 101 side as shown by a solid line arrow in FIG. 1, passes through the phase difference plate 44, and reaches the light diffusion layer 43. Light is diffused by the light diffusion layer 43, and the diffused light passes through the counter electrode substrate 30, the color filter 31, the protective film 33, the counter electrode 34, the alignment film 35, the liquid crystal 21, and the alignment film 20 on the TFT substrate 10. The light passes through and reaches the reflective display electrode 50 made of a reflective material and having a recess. The reached light is reflected by the reflective display electrode 50.
[0035]
Here, the shape of the reflective display electrode 50 will be described.
[0036]
FIG. 2 shows an enlarged view of the reflective display electrode in FIG. 1 and how the incident light and outgoing light travel, and FIG. 3 shows a plan view on the TFT substrate side of the reflective liquid crystal display device of the present invention. . The enlarged view shown in FIG. 2 is an enlarged view of a cross section taken along the line CC in FIG.
[0037]
As described above, the reflective display electrode 50 is made of a metal having a high light reflectance such as Al and Ag. As shown in FIG. 2, the cross-sectional shape has a flat portion FL at the peripheral portion of the reflective display electrode 50, and has an inclined portion SL that is continuously inclined from the flat portion FL toward the central portion of the reflective display electrode. Further, a flat bottom surface BA is formed substantially at the center of the reflective display electrode continuously to the inclined portion SL (D or E). The inclination angle of the inclined portion SL is an elevation angle θp with reference to the surface of the bottom surface portion BA of the reflective display electrode 50.
[0038]
In FIG. 3, an inclined portion SL that is hatched continuously from the flat portion FL is formed inside the rectangular flat portion FL that is hatched from the upper right to the lower left direction, A rectangular bottom surface BA is formed with a diagonal line from the upper left to the lower right.
[0039]
Thus, the reflective display electrode 50 including the flat portion FL, the inclined portion SL, and the bottom surface portion BA is formed.
[0040]
In FIG. 2, the region B includes a region in the display panel up to the polarizing plate 45 of the reflective display panel, that is, the liquid crystal 21 in contact with the alignment film 20 on the reflective display electrode 50 of the display panel. The area | region provided with each layer to the polarizing plate 45 shown in FIG. 1 is shown. A region A indicates the outside of the display panel, that is, the air on the viewer 101 side.
[0041]
Here, how the incident light that has entered the inclined portion SL and the bottom portion BA travels will be described.
[0042]
The angle (outgoing angle) θout at which light incident on the display panel from the air is reflected by the reflective display electrode 50 and is emitted again from the display panel into the air is expressed by the following equations (1) and (2). expressed.
[0043]
θout = sin ^-1 [(N ₂ / N ₁ ) Sin {sin ^-1 ((N ₁ / N ₂ ) Sin θin)} + 2θp}] (Equation 1)
θout = sin ^-1 [(N ₂ / N ₁ ) Sin {sin ^-1 ((N ₁ / N ₂ ) Sin θin)} − 2θp}] (Formula 2)
Here, in each formula (1), (2), n ₁ Is the refractive index in air and n ₁ = 1. N ₂ Is the refractive index in the display panel and n ₂ ≒ 1.5.
[0044]
First, light that has entered the left inclined portion D in the figure enters the display panel from the air at an angle θin1, proceeds according to Equation (1), is reflected by the inclined portion D, and is emitted from the display panel. Then, it exits into the air at an angle of θout 1. At this time, θout1> θin1.
[0045]
The light incident on the bottom surface portion BA is incident on the display panel from the air at an angle θin2 according to the equation (1) or (2), reflected by the bottom surface portion BA, and emitted from the display panel. The light is emitted at an angle of θout2. At this time, there is a relationship of θout2 = θin2.
[0046]
The light that has entered the right inclined portion E in the figure enters the display panel from the air at an angle θin3, proceeds according to Equation (2), is reflected by the inclined portion E, and is emitted from the display panel. The light is emitted at an angle of θout3. At this time, θout3 <θin3.
[0047]
Thus, the incident light is reflected by each part of the reflective display electrode and emitted.
[0048]
Below, the formation method of the reflective display electrode provided with the flat part, the inclination part, and the bottom face part is demonstrated.
[0049]
FIG. 4 shows a cross-sectional view of the manufacturing process of the reflective liquid crystal display device of the present invention along FF in FIG.
[0050]
As shown in FIG. 4D, a reflective display electrode 50 made of a reflective material is provided near the intersection of a gate signal line 51 having a part of the gate electrode 11 and a drain signal line 52 having a part of the drain electrode 16. A connected TFT is provided. The reflective display electrode 50 is provided extending over the TFT. A flat portion FL, an inclined portion SL, and a bottom portion BA are formed on the surface of the reflective display electrode 50.
[0051]
Step 1 (FIG. 4A): a first gate electrode made of a refractory metal such as Cr or Mo on an insulating substrate 10 made of quartz glass, non-alkali glass or the like and forming part of the gate signal line 51. 11. SiN film and SiO ₂ A gate insulating film 12 made of a film and an active layer 13 made of a polycrystalline silicon film are sequentially formed.
[0052]
The active layer 13 is provided with a channel 13c above the gate electrode 11, and a source 13s and a drain 13d formed by ion implantation on both sides of the channel 13c.
[0053]
On the channel 13c, SiO that functions as a mask that covers the channel 13c so that ions do not enter the channel 13c during ion implantation when forming the source 13s and the drain 13d. ₂ A stopper insulating film 14 made of a film is provided.
[0054]
Then, on the entire surface of the gate insulating film 12, the active layer 13, and the stopper insulating film 14, SiO 2 ₂ Film, SiN film and SiO ₂ An interlayer insulating film 15 in which films are sequentially stacked is formed. The interlayer insulating film 15 may be composed of a single organic film made of an organic material such as SiO, SiN, or acrylic, or a multilayer body of any combination thereof.
[0055]
Next, contact holes C1 and C2 are provided at positions corresponding to the drain 13d and the source 13s of the interlayer insulating film 15, respectively. The contact hole C1 corresponding to the drain 13d is formed by laminating Al alone or Mo and Al in this order and filling the metal with the metal to form the drain electrode 16.
[0056]
The drain signal line 52 is provided on the interlayer insulating film 15 simultaneously with the formation of the drain electrode 16 constituting a part thereof.
[0057]
Step 2 (FIG. 4B): Photosensitivity made of an insulating resin having photosensitivity and a flat surface on the entire surface of the interlayer insulating film 15, the drain signal line 52, and the drain electrode 16 including the contact hole C2. A resin film 70 is applied. A first mask 71 having an opening corresponding to the inclined portion SL and the bottom portion BA of the reflective display electrode 50 to be formed later is disposed thereon. Then, a first exposure 75 is performed. The exposure amount at this time may be such an exposure amount that exposure light reaches a shallow region from the surface of the photosensitive resin 70, and the exposure amount is 20 mJ to 60 mJ, preferably 25 mJ to 50 mJ, more preferably 30 mJ to 40 mJ. is there.
[0058]
Step 3 (FIG. 4C): Next, the first mask 71 is removed, and a second mask 72 is disposed instead. The second mask 72 is a mask having an opening corresponding to a position where a contact hole C3 for contact between the source 13s of the active layer 13 and the reflective display electrode 50 is formed.
[0059]
After the second mask 72 is disposed, a second exposure 76 is performed. The exposure amount in the second exposure 76 is set larger than the first exposure amount. This is because the depth of the contact hole C3 is deeper than the depth of the bottom portion BA. Therefore, it is necessary to increase the exposure amount of the second exposure 76 in order for the exposure light to reach the depth at which the contact hole C3 reaching the source 13s is obtained. Specifically, the exposure amount of the second exposure 76 is 200 mJ to 600 mJ, preferably 250 mJ to 500 mJ, and more preferably 300 mJ to 400 mJ.
[0060]
It should be noted that the order of forming the recessed portion having the flat portion FL, the inclined portion SL, and the bottom surface portion BA and the contact hole C3 may be any first, and the exposure amount when forming the contact hole C3 forms the recessed portion. It may be larger than the exposure amount at the time.
[0061]
Step 4 (FIG. 4D): Next, the second mask 72 is removed, and the photosensitive resin film 70 is developed, whereby the photosensitive resin film 70 is etched, and the bottom surface portion BA, the inclined portion SL, and A contact hole C3 is formed.
[0062]
Step 5 (FIG. 4E): Thereafter, a reflective display electrode 50 made of a reflective material such as Al is formed in a predetermined pattern thereon. Thereby, the reflective display electrode 50 having the flat portion FL, the bottom portion BA, and the inclined portion SL on the surface is obtained.
[0063]
Further, an alignment film for aligning liquid crystal is formed on the reflective display electrode 50 to complete a so-called TFT substrate. Opposite the TFT substrate, a counter electrode substrate is provided in which a counter electrode and an alignment film are formed on the liquid crystal arrangement side, and a retardation plate and a polarizing plate are formed on the side where no liquid crystal is arranged. The TFT substrate and the counter electrode substrate are bonded at the periphery thereof, and a liquid crystal is filled in these gaps to complete a reflective liquid crystal display device.
[0064]
Next, a light diffusion plate that diffuses light will be described.
[0065]
In FIG. 5, as shown in FIG. 1, the reflected light detection angle when the light diffusing plate 43 is provided on the counter electrode substrate 30 on the viewer 101 side and the reflective display electrode 50 dented in the shape as described above is used. And the reflectance. Here, the reflectance refers to a ratio obtained by dividing the brightness of the reflected light of the measured reflective liquid crystal display device by the brightness of the reflected light of the standard diffusion plate. Therefore, the reflectance exceeds 100%. In the figure, the horizontal axis indicates the detection angle of reflected light with the normal direction of the display surface being 0 °, and the vertical axis indicates the reflectance at the detection angle.
[0066]
As shown in the figure, each curve indicating the relationship between the detection angle and the reflectance has a different haze value of the light diffusion plate. Curve b is haze value 7%, curve c is haze value 14%, curve d is haze value 19%, curve e is haze value 25%, curve f is haze value 33%, curve g is haze value 45%, curve h Indicates a haze value of 55%, a curve i indicates a haze value of 70%, and a curve j indicates a haze value of 75%. A curve a indicates a case where no diffusion plate is provided. Further, the graph shown in FIG. 2 shows a case where the incident angle θin of light incident on the display panel from the region A in FIG. 2 is θin = 30 °.
[0067]
In FIG. 5, all pole transitions have a peak of the amount of reflected light in the vicinity of a detection angle of 30 °, and a region protruding in a “hump” shape in the vicinity of detection angles of 12 ° to 15 ° and 45 ° to 47 °. There is. As will be described later, this region is bright because a large amount of reflected light is emitted due to reflection at the inclined portion SL of the reflective display electrode 50.
[0068]
Here, for example, when attention is paid to the vicinity of the detection angle of 45 ° of the curve a that does not use the light diffusing plate, the reflectance decreases to around the detection angle of 30 ° to 42 ° (TP1), and from around that 42 °. The reflectance gradually increases and reaches a peak around a detection angle of 47 °. That is, by forming the reflective surface of the reflective display electrode 50 as shown in FIG. 2, it is possible to observe a bright display at other angles as well as the peak of the reflected light amount in the vicinity of 30 in FIG. And the reflectivity gradually decreases. Thus, when the reflectance increases or decreases depending on the detection angle and the difference in the amount of reflected light increases depending on the angle at which the reflective liquid crystal display device is viewed, the display is observed as having uneven brightness.
[0069]
Therefore, it is preferable to further provide a light diffusion plate as in the reflective liquid crystal display device of the present invention. By adopting the light diffusing plate, compared with the case where the light diffusing plate shown by the curve a in FIG. 5 is not provided, in the curves b to j, the degree of the hump-like protrusion near the detection angles of 15 ° and 45 ° is reduced. The increase / decrease in unevenness of the amount of reflected light is reduced (the possibility of reversal of the amount of reflected light is reduced), and a uniform brightness display can be obtained.
[0070]
From the viewpoint of alleviating luminance unevenness, it is preferable that the reflectance near the detection angle of 47 ° is a reflectance that does not reverse as compared with the reflectance near 40 °. That is, among the curves in the figure, from the point TP1 that decreases from the peak near the detection angle of 30 °, such as the curves d, e, f, g, h, i, and starts increasing again if the curve is a. It is preferable to use a light diffusing plate having a characteristic that does not become higher than the reflectance in TP1 even if the detection angle becomes large. Specifically, by using a diffuser plate having a haze value of 19% or more and 70% or less, a partial inversion phenomenon of the reflected light amount that occurs when the reflected light amount exceeds TP1 near the peak without the light diffuser plate is suppressed. In addition, a uniform brightness display can be obtained in the reflective liquid crystal display device. More preferably, a light diffusion plate having a haze value of 30% to 55% is preferable.
[0071]
The same applies to the case where the detection angle is in the vicinity of 12 ° to 15 °. In TP2 in the vicinity of the detection angle of 12 ° to 15 °, it is preferable that the reversal of the reflectance does not increase, that is, the curves d, e, f, g. H, i of the light diffusing plate for obtaining h, i may be 19% or more and 70% or less. Preferably it is 30% or more and 55% or less.
[0072]
In the present invention, the “haze value” is based on ASTM D1008, which is a transparency evaluation standard, and the measurement principle is as follows.
[0073]
A light source, a sample, and an integrating sphere are arranged on a straight optical path, and a measuring system including a detector for measuring diffused light is used as a part of the integrating sphere.
[0074]
The light beam from the light source passes through the sample to be measured (in the case of the present invention, a light diffusion plate) and enters the integrating sphere. This incident light is uniformly diffused inside a glossy white coated integrating sphere and measured by a detector.
[0075]
The haze value indicates the degree of diffusion of light incident on the light diffusing plate, and is expressed as a percentage of incident light that is 2.5 ° or more on average.
[0076]
Here, the inclination angle of the inclined portion SL of the reflective display electrode will be described.
[0077]
FIG. 6 is a characteristic diagram showing the relationship between the inclination angle of the inclined portion SL of the reflective display electrode and the peak angle of the reflected light. In the figure, the horizontal axis indicates the inclination angle of the inclined portion of the reflective display electrode, and the vertical axis indicates the peak angle of the reflected light emitted. Here, the inclination angle of the inclined portion of the reflective display electrode refers to the elevation angle from the surface of the bottom surface of the reflective display electrode. The peak angle of the emitted light is the angle having the highest reflectance among the angles incident on the reflective liquid crystal display device and reflected and emitted from the light.
[0078]
In the figure, a curve G represents the case where the incident angle of light incident on the reflective liquid crystal display device, that is, the incident angle with respect to the normal direction of the display surface of the reflective liquid crystal display device as a reference (0 °) is 30 °. The case of 25 ° is indicated by a curve H.
[0079]
Further, for example, in the curve G, the outgoing light peak on the side where the outgoing light peak angle is larger than 30 ° is due to the inclined surface D on the left side of the reflective display electrode in FIG. 2, and the outgoing light peak angle is 30 °. The lower emission light peak is due to the inclined surface E on the right side of the reflective display electrode in FIG.
[0080]
Here, in general, when an observer views the reflective liquid crystal display device, it is very high that the observer sees the image in an angle range of approximately 0 ° to 60 ° with respect to the normal line of the display surface.
[0081]
Therefore, in FIG. 6, the peak angle of the emitted light only needs to be in the range of about 0 ° to 60 °. Therefore, the inclination angle of the inclined portion SL of the reflective display electrode is such that the emitted light peak appears in that range. Is approximately greater than 0 ° and not greater than about 8 °. Thereby, the peak of emitted light can be set to 0 ° or more and 60 ° or less. More preferably, the inclination angle of the inclined portion SL may be 4 ° or more and 6 ° or less.
[0082]
The reason is as follows.
[0083]
FIG. 5 shows a case where the incident angle θin = 30 °, but the “hump-shaped” protruding portions existing in the vicinity of the detection angles of 12 ° to 15 ° and 45 ° to 47 ° are 0 ° and 30 °. When it appears in the vicinity of 15 ° which is an intermediate angle between and 45 ° which is an intermediate angle between 30 ° and 60 °, unevenness in brightness on the display surface is not noticeable and bright at an angle from 0 ° to 60 °. A display is obtained. In particular, by using the light diffusing plate 43 together as described above, for example, in the example of FIG. 5, a bright display is obtained not only in the vicinity of the detection angle of 30 ° but also in the vicinity of 12 ° to 15 ° and 45 ° to 47 °. In addition, since the inversion of the reflected light amount at the protruding portion can be suppressed, luminance unevenness can be prevented.
[0084]
Therefore, in order to obtain the peak of the emitted light near the angles, that is, in the vicinity of 15 ° and 45 °, the inclination angle in FIG. 6 may be about 4 ° to 6 °.
[0085]
As described above, by providing a light diffusing plate in a reflective liquid crystal display device and defining a haze value indicating the degree of diffusion, uneven brightness occurs even when the display device is observed from various angles. Therefore, a display device with uniform brightness can be obtained.
[0086]
In the present embodiment, the light diffusion plate 43 is provided on the counter electrode substrate 30 on the viewer 101 side opposite to the side on which the color filter 31 is provided. The protective film 33 and the counter electrode 34 are not limited, and are also between the surface of the counter electrode substrate 30 and the color filter 31 or between the color filter 31 and the counter electrode 34 instead of the protective film 33 of the color filter 31. The same effect can be obtained even when placed between the reflective display electrode 50 and the alignment film 20 on the viewer 101 side.
[0087]
In the present embodiment, the case where a flat portion is provided at the periphery of the reflective display electrode has been described. However, the present invention is not limited to this, and the inclined portion and its inclination are not provided without a flat portion at the periphery. Even when a flat bottom surface portion formed continuously with the portion is provided, the same effect as that obtained when the peripheral portion is provided with a flat portion can be obtained.
[0088]
In the above description, a depression is formed in the photosensitive resin film 70 located below the reflective display electrode 50 to form an inclined portion, a flat portion, and a bottom portion in the reflective display electrode 50. However, the present invention is not limited to this. Alternatively, the reflective display electrode material may be formed on the flat film 70 and the electrode surface may be selectively etched.
[0089]
Note that the behavior of the liquid crystal 21 is that in the above-described embodiment, when no voltage is applied to the liquid crystal, light incident from the outside becomes linearly polarized light by the polarizing plate 45 and circularly polarized light by the phase difference plate 44. Then, the light is incident on the liquid crystal 21 and reflected by the reflective display electrode 50 to further change the phase by λ / 2 and pass through the liquid crystal 21 again. It is shaded and appears black.
[0090]
In addition, when a voltage is applied to the liquid crystal, light incident from the outside becomes linearly polarized light by the polarizing plate 45, becomes circularly polarized light by the phase difference plate 44, and enters the liquid crystal 21, and is reflected by the reflective display electrode 50. The light is reflected and the phase further changes by λ / 2, and passes through the liquid crystal 21 again. At this time, it becomes elliptically polarized light, the phase is changed by λ / 4 by the phase difference plate 44, and becomes linearly polarized light from the polarizing plate 45 and appears white.
[0091]
In the above-described embodiment, polycrystalline silicon is used as the active layer of the TFT. However, the present invention is not limited thereto, and the effects of the present invention can be obtained even if an amorphous silicon semiconductor material is used. It is what you play.
[0092]
Furthermore, the above-described configuration can be applied as a reflective display electrode in a passive matrix reflective LCD as well as an active matrix LCD having a switching element in each pixel, and a light diffusion plate can be combined. The same effects as described above can be obtained.
[0093]
Furthermore, the above-described configuration can be applied as a reflective display electrode in a passive matrix reflective LCD as well as an active matrix LCD having a switching element in each pixel, and a light diffusion plate can be combined. The same effects as described above can be obtained.
[0094]
In the above embodiment, a so-called bottom-gate TFT in which the gate electrode is below the active layer is shown. However, the present invention is not limited to this, and the gate electrode is above the active layer. Even the so-called top-gate TFT of the present invention exhibits the effects of the present invention.
[0095]
Furthermore, in the present invention, in addition to Al, a conductive reflective material such as silver may be used as the reflective display electrode material.
[0096]
【The invention's effect】
According to the present invention, it is possible to obtain a reflective liquid crystal display device that can increase the luminance of each display pixel and obtain a uniform and bright display at a wide viewing angle.
[Brief description of the drawings]
FIG. 1 is a cross-sectional view of a reflective liquid crystal display device of the present invention.
FIG. 2 is an enlarged view of a reflective electrode of the reflective liquid crystal display device of the present invention.
FIG. 3 is a manufacturing process diagram of the reflective liquid crystal display device of the present invention.
FIG. 4 is a plan view of the reflective liquid crystal display device of the present invention on the TFT substrate side.
FIG. 5 is a characteristic diagram showing characteristics of the reflective liquid crystal display device of the present invention.
FIG. 6 is a characteristic diagram showing characteristics of the reflective liquid crystal display device of the present invention.
FIG. 7 is a cross-sectional view of a conventional reflective liquid crystal display device.
FIG. 8 is a cross-sectional view showing a reflected light measurement method and characteristics of a conventional reflective liquid crystal display device.
[Explanation of symbols]
10 TFT substrate
13 Active layer
15 Interlayer insulation film
21 liquid crystal
30 Counter electrode substrate
43 Light diffusion layer
50 Reflective display electrode
70 Photosensitive resin film
FL flat part
SL inclined part
BA bottom

Claims (5)

  A liquid crystal is sandwiched between first and second substrates disposed opposite to each other. The first substrate includes a switching element and a display electrode made of a conductive reflective material connected to the switching element. The second substrate includes a counter electrode facing the display electrode, and the surface of the display electrode includes a flat portion and a recessed portion recessed in the first substrate side direction, the recessed portion A reflective liquid crystal having an inclined portion between the bottom surface portion and the flat portion, and an elevation angle of the inclined portion with respect to the bottom surface portion of the hollow portion being greater than 0 ° and not more than 8 °. Display device.   It has an insulating film which is provided on the switching element and has a concave portion in the first substrate side direction, and the display electrode includes the concave portion by being formed on the insulating film. The reflective liquid crystal display device according to claim 1.   3. The reflection type liquid crystal display device according to claim 1, wherein a light diffusion layer for diffusing light is provided on one of the first and second substrates.   The reflective liquid crystal display device according to claim 1, further comprising a color filter disposed between the second substrate and the counter electrode.   The reflection type liquid crystal display device according to claim 3, wherein the light diffusion layer has a haze value of 19% to 70%.

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