JP2006023721A - Reflection type display device and method for producing same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To improve an aperture ratio and utilizing efficiency of light while maintaining the alignment stability of a liquid crystal. <P>SOLUTION: A reflection-type display device 200 includes: an active switch layer 201s including a plurality of switching elements 201t; a plurality of pixel electrodes 207 each connected to a corresponding one of the plurality of switching elements 201t; a reflective layer 205 formed between the active switch layer 201s and the plurality of pixel electrodes 207; and a modulation layer 213 provided at a side of the pixel electrodes 207 facing a viewer and capable of being switched between a first state and a second state of respectively different optical characteristics. The reflective layer 205 is connected to neither the plurality of switching elements 201t nor the plurality of pixel electrodes 207. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a reflective display device and a method for manufacturing the same.

  A reflection type liquid crystal display device that performs display by using ambient light as a light source is known. Unlike a transmissive liquid crystal display device, a reflective liquid crystal display device does not require a backlight, and thus is suitably used for various devices that are required to be lightweight and thin. In particular, an active matrix driven reflective liquid crystal display device is provided with a switching element for each pixel, so that high-definition and high-quality display is possible.

  In order to further improve the display performance of the reflective liquid crystal display device, a retroreflective liquid crystal display device having a retroreflective plate as a reflective layer for reflecting ambient light has been proposed. A “reflexive reflector” is an element that reflects incident light on a plurality of reflecting surfaces to reflect the light in the original direction regardless of the incident direction. For example, a fine unit structure is arranged two-dimensionally. It has the structure.

  Since the retroreflective liquid crystal display device does not require a polarizing plate, it is possible to suppress a decrease in light use efficiency due to the use of the polarizing plate and to perform brighter display. In addition, it is expected because the contrast ratio of the display can be improved.

  Hereinafter, the configuration of a retroreflective liquid crystal display device driven by an active matrix will be described with reference to the drawings. FIG. 1A is a schematic cross-sectional view of a retroreflective liquid crystal display device, and FIG. 1B is a diagram illustrating a planar shape of a reflective electrode in the display device of FIG. A configuration as shown in FIGS. 1A and 1B is disclosed, for example, in Patent Document 1 by the same applicant as the present application.

  As shown in FIG. 1A, a front substrate 110 provided with a color filter 119, a transparent counter electrode 111 and an alignment film 112, a back substrate 109 disposed so as to face the front substrate 110, and these substrates And a liquid crystal layer 113 provided between 110 and 109. The back substrate 109 includes a TFT substrate 101 having a plurality of switching elements (TFTs), an insulating layer 102 having a surface shape showing retroreflectivity, a plurality of reflective electrodes 105 and an alignment layer 118 provided on the TFT substrate 101. Have. The reflective electrode 105 is formed on the insulating layer 102 and has irregularities reflecting the surface shape of the insulating layer 102. As shown in FIG. 1B, the plurality of reflective electrodes 105 are arranged apart from each other for each pixel that is a unit of image display. Each reflective electrode 105 is connected to the drain electrode 103 of the corresponding switching element in the TFT substrate 101 through a contact hole 104 formed in the insulating layer 102. The alignment layer 118 is formed on the insulating layer 102 and the reflective electrode 105 and has irregularities reflecting the surface shape of the insulating layer 102. In addition, the liquid crystal layer 113 changes, for example, between a transmission state that transmits light and a scattering state that scatters light (forward scattering) by changing a voltage applied between the counter electrode 111 and the reflection electrode 105. It is a scattering type liquid crystal that can be switched.

  In the display device having such a configuration, the plurality of reflective electrodes 105 exhibit a function as a pixel electrode and a function as a retroreflective layer. Hereinafter, the operation of this display device will be described.

  When the liquid crystal layer 113 is controlled to be in a transmissive state, light from the light source outside the display device and surrounding light passes through the front substrate 110 and the liquid crystal layer 113 and is then reflected by the reflective electrode 105 in the direction in which the light is incident. . At this time, since the image reaching the observer from the display device is the eyes of the observer himself, a “black” display state is obtained.

  On the other hand, when the liquid crystal layer 113 is controlled to be in a scattering state, light from the light source and the surroundings passes through the front substrate 110 and is then scattered by the liquid crystal layer 113. In the case where the liquid crystal layer 113 is a forward scattering liquid crystal layer, the scattered light is reflected by the reflective layer 105 and further emitted in the observation direction through the liquid crystal layer 113 in a scattered state. Since the reflexivity of the reflective layer 105 is lost due to scattering by the liquid crystal layer 113, the incident light does not return to the incident direction. Therefore, a “white” display state is obtained.

  The retroreflective display device described above has the following problems.

  First, the planar reflective electrode 105 as shown in FIG. 1B is typically formed by patterning a metal film having a concavo-convex shape. Therefore, it is difficult to perform patterning with high accuracy. In particular, when using a metal film having a complicated surface shape, for example, a metal film with a corner cube array formed as an uneven shape, the metal film is easily etched depending on the size and arrangement pattern of the corner cube, so as designed. It is difficult to form the reflective electrode 105. Accordingly, there is a problem that the interval between the adjacent reflective electrodes 105 cannot be kept small, and the aperture ratio is lowered. Furthermore, since the light incident on the gap of the reflective electrode 105 is not reflected, the light utilization efficiency is also lowered. On the other hand, although the present applicant has proposed in Patent Document 1 that the reflective electrode 105 is patterned so as to match the arrangement pattern of the corner cubes, the interval between the adjacent reflective electrodes 10 is reduced. As the size of the corner cube becomes smaller, it becomes difficult to apply this method. In addition, the degree of freedom in designing the reflective electrode 105 is limited.

  Second, the surface profile of the alignment film 118 of the back substrate 109 has an uneven shape, and it is difficult to stably align the liquid crystal layer 113. Further, when the level difference between the concave and convex portions on the surface of the alignment film 118 is large, the variation in the thickness of the liquid crystal layer 113 may affect the display characteristics.

  In the above description, the retroreflective liquid crystal display device has been described as an example. However, the reflective liquid crystal display device including a reflective plate having a diffuse reflection characteristic as the reflective layer is also similar to the configuration of FIG. And has the same problems as those described above.

The configuration of such a diffuse reflection type liquid crystal display device is disclosed in Patent Document 2, for example. In the configuration of Patent Document 2, an insulating film having a large refractive index is formed between the reflective electrode having an uneven surface and the liquid crystal layer. Therefore, since the uneven shape of the reflective electrode is flattened to some extent by the insulating film, it is considered that the second problem described above can be improved. However, instead, a voltage drop is caused by the insulating film formed between the reflective electrode and the liquid crystal layer, so that a high driving voltage is required.
JP 2003-195788 A Japanese Patent No. 3166377

  As described above, in a conventional reflective liquid crystal display device, it is necessary to pattern a metal film having irregularities on the surface to form reflective electrodes spaced apart from each other for each pixel. However, it is difficult to pattern such a metal film with high accuracy. Further, when patterning is performed using unevenness, there is a problem that the degree of freedom in designing the reflective electrode is low. Therefore, it is difficult to further increase the aperture ratio and the light utilization efficiency by keeping the width between the reflective electrodes small. Furthermore, since the liquid crystal layer is formed on the surface having irregularities, there is a problem that the alignment of the liquid crystal layer cannot be stably controlled.

  The present invention has been made in view of the above-mentioned points, and its main object is to improve the aperture ratio and the light utilization efficiency while maintaining the alignment stability of the liquid crystal in the reflective liquid crystal display device.

  The reflective display device of the present invention includes an active switch layer including a plurality of switching elements, a plurality of pixel electrodes each connected to a corresponding switching element, and between the active switch layer and the plurality of pixel electrodes. A reflection layer formed on the viewer side of the pixel electrode, and a modulation layer that can be switched between a first state and a second state having different optical characteristics, and the reflection layer includes the plurality of reflection layers. The switching element and the plurality of pixel electrodes are not connected.

  It is preferable that the reflective layer exists under a gap between adjacent pixel electrodes.

  The reflective layer is preferably not separated in pixel units.

  In a preferred embodiment, the reflective layer has a plurality of openings, and the plurality of pixel electrodes and the corresponding switching elements are connected via the corresponding openings of the reflective layer.

  In a preferred embodiment, the device includes a plurality of contact portions that connect the plurality of pixel electrodes and the corresponding switching elements, and the plurality of contact portions are provided through corresponding openings of the reflective layer, The diameter of the contact portion is smaller than the diameter of the opening.

  In a preferred embodiment, the reflective layer has retroreflective properties.

  The reflective layer has a structure in which a plurality of unit structures are two-dimensionally arranged, and a gap between adjacent pixel electrodes may not be aligned with the unit structure of the reflective layer.

The pixel electrode has a substantially rectangular planar shape, and the arrangement pitch in the short side direction of the pixel electrode is P _{pix (S)} , and the arrangement pitch in the long side direction of the pixel electrode is P _{pix (L).} If the pitch of the corner cube is P _cc , ((√3) / 6 × P _{pix (L)} × P _cc + P _{pix (S)} × P _cc / 2) / (P _{pix (L)} × P _{pix (S)} )> 0.005, and more preferably ((√3) / 6 × P _{pix (L)} × P _cc + P _{pix (S)} × P _cc / 2) / (P _{pix (L) XPpix (S)} )> 0.01 is satisfied.

When the pixel electrode pitch is P _pix and the corner cube pitch is P _cc ,
It is preferable that ((√3) +3) / 6 × P _cc / P _pix > 0.005 is satisfied, more preferably ((√3) +3) / 6 × P _cc / P _pix > 0.01 is satisfied. To do.

  In a preferred embodiment, the modulation layer can be switched between a light scattering state and a light transmission state.

  According to another aspect of the present invention, there is provided a reflective display device manufacturing method including a step of preparing a substrate on which an active switch layer including a plurality of switching elements is formed, a step of forming an insulating layer on the active switch layer, and the insulating layer. A step of forming a reflective layer having a plurality of openings thereon, a step of forming a planarizing resin layer on the reflective layer, and a switching element connected to each of the planarizing resin layer Forming a plurality of pixel electrodes, and providing a modulation layer on the pixel electrode that can be switched between a first state and a second state having different optical characteristics. The electrode is connected to the switching element through the opening of the reflective layer.

  According to the present invention, since the reflective layer and the pixel electrode are provided separately, it is not necessary to separate the reflective layer for each pixel. Therefore, since the area of the reflective layer can be increased, the light utilization efficiency can be improved. Further, since the pixel electrode can be patterned regardless of the uneven shape of the reflective layer, the aperture ratio can be improved by reducing the gap between the pixel electrodes. Therefore, a bright display with a high contrast ratio can be realized.

  Furthermore, since the uneven shape of the reflective layer is flattened, the orientation of the liquid crystal can be controlled stably. At this time, since a layer for planarization (a planarization layer) is not formed between the liquid crystal layer and the pixel electrode, a problem of a voltage drop due to the provision of the planarization layer does not occur.

  The present invention is particularly advantageous when applied to a retroreflective liquid crystal display device including a reflective layer having retroreflective properties.

  The reflective liquid crystal display device according to the present invention is characterized in that a reflective layer not connected to the pixel electrode or the switching element is provided between the active switch layer including the switching element and the pixel electrode. That is, a reflective layer for using ambient light or light from an external light source for display and a pixel electrode for applying a voltage to the liquid crystal layer are provided independently.

  Hereinafter, the configuration of a reflective liquid crystal display device according to the present invention will be described with reference to a retroreflective liquid crystal display device as an example, with reference to FIGS. 2A is a plan view of the reflective display device 200, and FIGS. 2B and 2C are cross-sectional views 2b-2b ′ and 2c-2c in the plan view of FIG. 2A, respectively. 'Cross section.

  The reflective display device 200 is provided between a front substrate 210 provided with a color filter 219, a transparent counter electrode 211 and an alignment film 212, a rear substrate 209 facing the front substrate 210, and the substrates 210 and 209. And a liquid crystal layer 213. The back substrate 209 includes a substrate 201 having an active switch layer 201s including a plurality of switching elements 201t. On the substrate 201, there are an insulating layer 202 having a shape showing retroreflectivity, a reflective layer 205 formed on the insulating layer 202, a planarizing resin layer 206, a plurality of transparent pixel electrodes 207, and an alignment layer 218. They are formed in this order. The surface of the alignment layer 218 is in contact with the liquid crystal layer 213. The substrate 201 is, for example, a TFT substrate including an active switch layer 201s including a plurality of thin film transistors 201t. The reflective layer 205 has irregularities that reflect the surface shape of the insulating layer 202. Since the unevenness is flattened by the flattening resin layer 206, the pixel electrode 207 and the alignment layer 218 have substantially flat surfaces. A plurality of contact holes 204 are formed in the insulating layer 202 and the planarizing resin layer 206. Each pixel electrode 207 is connected to the drain electrode 203 of the corresponding switching element 201t through the contact hole 204.

  As shown in FIG. 2A, the reflective layer 205 is not separated for each pixel unlike the reflective electrode 105 in the conventional reflective display device (FIG. 1). The reflective layer 205 is formed over the display area of the TFT substrate 201 and has an opening 220 corresponding to the contact hole 204. In addition, since the diameter of each opening 220 is larger than the diameter of the corresponding contact hole 204, the reflective layer 205 is insulated from the switching element and the pixel electrode 207.

  The liquid crystal layer 213 may be a modulation layer that can be switched between the first state and the second state having different optical characteristics. For example, it may be a scattering type liquid crystal layer that can be switched between a light scattering state and a light transmitting state, or an electric field control birefringence mode (ECB mode) that can take two or more states having different retardations. It may be a liquid crystal layer. Further, it may be a TN liquid crystal layer that utilizes the optical rotation of the liquid crystal layer.

  Although not shown, the reflective display device 200 further includes a gate drive circuit for selectively driving the thin film transistor 201t of the TFT substrate 201, a source driver circuit for supplying a signal to the pixel electrode 207, and the like. The gate drive circuit is connected to the gate electrode of the thin film transistor 201t through a gate line. The source drive circuit is connected to the pixel electrode 207 through the source line and the thin film transistor 201t.

  The reflective liquid crystal display device of the present invention is not limited to a retroreflective liquid crystal display device. The reflective layer 205 may be a diffuse reflection type liquid crystal display device using a reflective layer having scattering reflection (also referred to as diffuse reflection) characteristics.

  The reflective display device 200 has the following advantages over the conventional reflective display device described with reference to FIG.

  In the conventional reflective display device, the reflective electrode 105 has a function of retroreflecting or diffusely reflecting light and a function of applying a voltage to the liquid crystal layer (function as a pixel electrode). In order to retroreflect or diffusely reflect light, the reflective electrode 105 needs to have irregularities on the surface. On the other hand, in order to function as a pixel electrode, the reflective electrodes 105 must be separated from each other for each pixel, and such a reflective electrode 105 is formed by patterning a reflective metal layer made of Ag or the like. It is formed. However, it is difficult to perform highly accurate patterning on the reflective metal layer having irregularities on the surface.

  In particular, when a reflective metal layer having a complicated retroreflective shape in which unit structures such as corner cubes are arranged is used, if the patterning of the reflective metal layer is performed along the boundary line of the unit structure, the adjacent reflective electrode 105 There is a problem that the distance is relatively large, the aperture ratio is reduced, and the effective reflection area is reduced. In this specification, “aperture ratio” refers to the ratio of the area that contributes to display with respect to the entire display area, that is, the ratio of the pixel electrode area to the display area area, and the “effective reflection region” is formed by a reflective surface in the display area. Refers to the area that was created. However, it is extremely difficult to pattern the reflective metal layer regardless of the surface shape of the reflective metal layer so that the interval between the adjacent reflective electrodes 105 is sufficiently small. Even if such patterning can be realized, a part of the surface constituting each unit structure (for example, a corner cube) is removed at the peripheral portion of the reflective electrode 105 (near the pattern edge). Retroreflective characteristics cannot be obtained.

  On the other hand, according to the reflective display device 200, since the reflective layer 205 does not need to be patterned, the above-described problem does not occur. Since the reflective layer 205 is continuously formed over the surface of the substrate 201, it has a sufficient reflective function even at the pattern edge of the pixel electrode 207. The pixel electrode 207 can be formed by patterning a conductive film such as an ITO film formed on the planarizing resin layer 206. Such patterning of the conductive film can be freely performed without being restricted by the unevenness of the reflective layer 205. In addition, since the conductive film has a substantially flat surface shape, high-accuracy patterning can be relatively easily performed on the conductive film, so that the interval between the adjacent pixel electrodes 207 is sufficiently small. Can do. Further, since the unevenness on the surface of the reflective layer 205 is flattened, the liquid crystal of the liquid crystal layer 213 can be favorably aligned by the alignment layer 218.

Note that the interval between adjacent pixel electrodes 207 is preferably 1 μm or more. When the thickness is 1 μm or more, sufficient insulation can be secured between the pixel electrodes 207. Further, although the upper limit value of the interval between the adjacent pixel electrodes 207 varies depending on the pitch P _pix of the pixel electrodes 207, for example, if it is 30 μm or less, a sufficiently large aperture ratio can be secured.

  The diameter of the opening 220 may be larger than the diameter of the contact hole 204, but is preferably small enough to ensure a sufficient effective reflection region (area of the reflection layer 205), depending on the resolution of the display device. For example, it is 30 μm or less. On the other hand, the diameter of the contact hole 204 is preferably large enough to be surely insulated from the contact portion made of a conductive material provided inside the contact hole 204, for example, 1 μm or more.

  The back substrate 209 in the reflective display device 200 can be manufactured by, for example, the method described below.

  First, as shown in FIG. 3A, after an insulating layer 202 having a retroreflective shape is formed on the surface of a TFT substrate 201 having a plurality of TFTs, the TFT drains on the TFT substrate 201 are formed on the insulating layer 202. A plurality of contact holes 204a reaching the electrode 203 are formed. Instead of the TFT substrate 201, a substrate having other types of switching elements may be used.

  Thereafter, as shown in FIG. 3B, a reflective layer metal (for example, Ag) 205 ′ is deposited inside the contact hole 204 a and on the insulating layer 202.

  Next, as shown in FIG. 3C, the opening 220 is formed by removing the portion of the metal 205 ′ located inside the contact hole 204 and above the contact hole 204. The diameter of the opening 220 is set to be larger than the diameter of the contact hole 204. Thereby, the reflective layer 205 is obtained.

  Subsequently, as shown in FIG. 3D, a planarizing resin layer 206 is formed so as to level the unevenness in the retroreflective shape of the reflective layer 205. A contact hole 204b is also formed in the planarizing resin layer 206 so as to substantially match the contact hole 204a in the insulating layer 202.

  Thereafter, as shown in FIG. 3E, a transparent conductive film such as an ITO film is formed on the planarizing resin layer 206 and in the contact holes 204a and 204b, and patterning is performed. Thereby, the pixel electrode 207 is formed. The pixel electrode 207 is electrically connected to the drain electrode 203 of the TFT through the contact holes 204a and 204b. On the pixel electrode 207 and the planarizing resin layer 206, an alignment layer 218 for aligning liquid crystals is formed. Thereby, the back substrate 209 is obtained.

  The reflective display device 200 can be manufactured by using the back substrate 209 obtained as described above in the same process as that performed when manufacturing a conventional reflective liquid crystal display device. Specifically, a back substrate 209 and a front substrate 210 having a color filter layer 219, a transparent conductive film 211, and an alignment layer 212 with an RGB color pattern bordered in black are bonded together, and the space between these substrates 209, 210 is bonded. A liquid crystal layer 213 is formed.

(First embodiment)
Hereinafter, a first embodiment of a reflective liquid crystal display device according to the present invention will be described.

  FIG. 4A is a plan view showing the configuration of the back substrate (TFT side substrate) 300 in the reflective liquid crystal display device of this embodiment, and FIG. 4B is a plan view shown in FIG. FIG. 4 is a cross-sectional view taken along line 4b-4b ′.

  The back substrate 300 has a configuration in which an active switch layer 301s, an insulating layer 307, a reflective layer 308, a planarizing resin layer 309, and a pixel electrode 310 are formed in this order on a substrate 301. Yes. In the present embodiment, the active switch layer 301s includes a plurality of thin film transistors 301t. Each thin film transistor 301t includes, for example, a gate electrode 302, a gate insulating film 303 covering the gate electrode 302, a semiconductor layer 304 formed on the gate insulating film 303, a source line and source bus 305, and a drain electrode 306. have. The thin film transistor 301t has a bottom gate structure, but may have a top gate structure. The surface of the insulating layer 307 has a retroreflective shape in which a plurality of corner cubes are arranged. Therefore, the reflective layer 308 is a retroreflective layer. The pixel electrode 310 is connected to the drain electrode 306 of the thin film transistor 301 t through the contact portion 311 provided in the planarizing resin layer 309 and the insulating film 303. Since the reflective layer 308 has an opening 311 ′ so as not to contact the contact portion 311, the reflective layer 308 and the pixel electrode 310 are not conductive.

  The size of the pixel electrode 310 is, for example, 60 μm × 180 μm, and the gap width between adjacent pixel electrodes 310 is, for example, 3 μm or more and 8 μm or less. The arrangement pitch of the unit structures (corner cubes) in the retroreflective layer 308 is, for example, 3 μm to 20 μm, and the level difference between the concave portion and the convex portion in the retroreflective layer 308 is, for example, 3 μm to 16 μm.

  The back substrate 300 in the reflective liquid crystal display device can be manufactured by a method similar to the method described above with reference to FIG. 3, for example. Hereinafter, the method for forming the back substrate 300 will be described more specifically with reference to the drawings. FIGS. 5A to 5C are plan views for explaining a process of forming the back substrate 300, and FIGS. 6A to 6C are respectively the views of FIGS. 5A to 5C. It is 6a-6a ', 6b-6b', and 6c-6c 'sectional drawing.

  First, as shown in FIGS. 5A and 6A, a TFT substrate is formed. The TFT substrate can be formed as follows, for example. A gate line made of tantalum (Ta) or the like and a gate bus 302 are formed on the substrate 301, and then a gate insulating film 303 is formed thereon using a tantalum oxide film or the like. Thereafter, a semiconductor layer 304 made of amorphous silicon or the like is formed. A source line and a source bus 305 made of titanium (Ti) or the like are formed so as to be in contact with one end portion of the semiconductor layer 304, and a drain electrode 306 is formed so as to be in contact with the other end portion of the semiconductor layer 304. In order to simplify the process, the source line / source bus 305 and the drain electrode 306 are preferably formed in the same layer. Thereafter, an insulating film such as silicon nitride may be formed in order to increase the reliability of the TFT.

  Next, as shown in FIGS. 5B and 6B, an insulating layer 307 having a contact hole 311a and a reflection formed on the insulating layer 307 and having an opening 311 ′ larger than the contact hole 311a. Layer 308 is formed. Specifically, the insulating layer 307 and the reflective layer 308 can be formed as follows.

  The insulating layer 307 (thickness: 5 μm, for example) is formed by forming a resin layer made of a transfer resin material on the TFT substrate and then embossing the shape of the master on the resin layer using a master having a concave and convex shape. It can be formed by transferring by a method or the like. The material of the insulating layer 307 is not particularly limited, and is, for example, an acrylic resin. Thereafter, a resist mask is formed on the insulating layer 307 using a photolithography method or the like, and the insulating layer 307 is etched using the resist mask, whereby a contact hole (diameter: 5 μm, for example) 311 reaching the drain electrode 306 of the TFT. Form.

  The reflective layer 308 is formed by depositing a layer made of a reflective metal (for example, an Ag layer) over the surface of the contact hole 311a and the insulating layer 307 of the insulating layer 307, and is positioned inside and above the contact hole 311a in the Ag layer. It is formed by etching a portion to be etched. The reflective layer 308 needs to have an opening 311 ′ having a diameter (for example, 10 μm) larger than the contact hole 311a on the contact hole 311a so as not to come into contact with a conductive layer formed later in the contact hole 311a. is there. Such a reflective layer 308 can be formed, for example, by forming an etching mask that exposes a portion of the Ag layer where the opening 311 ′ is formed, and performing dry etching or wet etching using the etching mask. Alternatively, when wet etching is performed on the Ag layer using an etching mask having substantially the same shape as the resist mask used when forming the contact hole 311a in the insulating layer 307, over-etching causes the Ag layer to have a larger thickness than the contact hole 311a. A large opening 311 can be formed.

  Thereafter, as shown in FIG. 5C and FIG. 6C, the planarizing resin layer 309 and the pixel electrode 310 are formed, whereby the rear substrate 300 is obtained.

  The planarizing resin layer 309 is obtained by forming a resin layer covering the reflective layer 308 and then forming a contact hole 311b in the resin layer. The contact hole 311b is aligned with the contact hole 311a and has substantially the same size. As a material of the planarizing resin layer 309, a material that can easily form the contact hole 311b is preferably used. For example, a resin material that can be used for photolithography can be used. Further, it is necessary to use a material having a high transmittance so as not to deteriorate the retroreflection characteristics in the reflective layer 308. For example, an acrylic resin that can be patterned by ultraviolet exposure can be used as a material that can be photolithography and has high transmittance. The planarizing resin layer 309 is preferably sufficiently thick (for example, 5 μm or more) so that the retroreflective shape in the reflective layer 308 can be leveled.

  On the other hand, the pixel electrode 310 is formed of a transparent conductive film using indium / tin oxide (ITO) or the like on the planarizing resin layer 309 and in the contact holes 311a and 311b (also referred to as “contact holes 311”). The transparent conductive film can be formed and patterned into a pixel electrode shape. At this time, if the step L of the contact hole 311 (the total step of the contact holes 311a and 311b) L is as small as several micrometers or less, or if the contact hole 311 has a forward tapered cross-sectional shape, a normal method using sputtering or the like is used. A transparent conductive film can be formed inside the contact hole 311 by a vapor deposition method. However, in the case where the step L is large and is, for example, twice or more the diameter d of the contact hole 311 (L / d ≧ 2), the transparent conductive film reaching the surface of the drain electrode 306 inside the contact hole 311 by vapor deposition. Is difficult to form. In such a case, it is preferable to use a solution type conductive material as the material of the transparent conductive film, and form the transparent conductive film inside the contact hole 311 by an ink jet method.

  Further, a contact portion formed inside the contact hole 311 and a pixel electrode formation portion formed on the planarizing resin layer 309 in the transparent conductive film may be formed using different materials. For example, the contact portion may be formed using a material that can form a thick film, and the pixel electrode formation portion may be formed using a material that can be formed by vapor deposition or the like. Note that the material of the transparent conductive film (pixel electrode 310) needs to have a high transmittance so as not to deteriorate the retroreflection characteristics of the reflective layer 308 regardless of the formation method.

  The reflective liquid crystal display device of the present embodiment can be manufactured by using the back substrate 300 obtained as described above in the same process as that performed when manufacturing a conventional reflective liquid crystal display device. A specific method will be described below.

  First, a polyimide film is formed on the back substrate 300, and an alignment layer that defines the direction of the liquid crystal is formed by rubbing (rubbing) it with a cloth. On the other hand, a front substrate having a color filter layer, a transparent conductive film and an alignment layer is formed. The alignment layer on the front substrate can also be formed in the same manner as the alignment layer on the back substrate 300. Next, the back substrate 300 and the front substrate are bonded together, and a liquid crystal layer is formed therebetween. The liquid crystal layer may be formed from a polymer dispersed liquid crystal (PDLC). It is also preferable to use a so-called reverse type PDLC that is transparent when no voltage is applied. Thereby, the reflective liquid crystal display device of this embodiment is manufactured.

  The liquid crystal layer in the present embodiment is formed of a reverse type PDLC having a liquid crystal skeleton (mesogen group) in a polymer structure. As described below, the liquid crystal layer displays black by changing the voltage applied to the liquid crystal layer. And white display can be switched. The operation will be described below.

  When the voltage applied to the liquid crystal layer is sufficiently low (when no voltage is applied), the liquid crystal layer becomes transparent. At this time, if the orientation between the mesogenic group of the polymer and the nematic liquid crystal is sufficiently high, transparency can be obtained without depending on the viewing angle, so that the retroreflective performance can be utilized to the maximum, and good Black characteristics can be realized. On the other hand, when a predetermined voltage is applied to the liquid crystal layer, the nematic liquid crystal moves depending on the electric field, but the mesogenic group in the polymer structure hardly moves. As a result, a difference in refractive index occurs between the nematic liquid crystal and the mesogenic group, and light incident on the liquid crystal layer is scattered, so that white characteristics can be obtained.

  In the above “when no voltage is applied”, when the voltage applied to the liquid crystal layer is 0 V, the voltage applied to the liquid crystal layer causes an optical change in the liquid crystal layer, and scattering of light incident on the liquid crystal layer is observed. Including the case where the voltage is lower than the voltage to be generated.

The reverse type PDLC as described above can be formed by irradiating a prepolymer liquid crystal mixture in which a low-molecular liquid crystal composition and an unpolymerized prepolymer are compatible with each other with ultraviolet rays and polymerizing the unpolymerized prepolymer. Here, a prepolymer liquid crystal mixture obtained by adding 4% of a monoacrylate having a mesogenic group, 2% of a diacrylate having a mesogenic group, and 1% of a reaction initiator to a low-molecular liquid crystal material is irradiated with ultraviolet rays (for example, 1 mW / cm ² ). It is obtained by irradiating for minutes. However, the composition and curing conditions of the liquid crystal material are not limited to the above composition and conditions.

  Instead of the reverse type PDLC, a normal type scattering liquid crystal that does not include a liquid crystal skeleton in the polymer structure may be used. The liquid crystal layer becomes a scattering state when no voltage is applied and becomes transparent when a voltage is applied. A normal type PDLC has a structure in which a nematic liquid crystal is included in a polymer structure like a reverse type PDLC, but unlike a reverse type PDLC, it does not have a mesogenic group in the polymer structure. In this case, when no voltage is applied, the liquid crystal molecules are randomly arranged, so that the liquid crystal layer scatters light (scattered state), and white display is obtained. On the other hand, when a voltage is applied, the refractive index of the nematic liquid crystal aligned depending on the electric field matches the refractive index of the polymer, so that the liquid crystal layer becomes transparent and a black display is obtained. At this time, it is extremely difficult to match the refractive index of the nematic liquid crystal having birefringence and the refractive index of the polymer having no birefringence over the entire viewing angle. There is a problem that it tends to be low. However, since the transparency is sufficiently practical and high scattering characteristics can be obtained when no voltage is applied, normal PDLC is advantageous depending on the intended use.

  In the case of forming a normal type PDLC, the alignment treatment is generally not performed. However, if necessary, for example, an organic film such as polyimide may be applied to the substrate surface on the side where the liquid crystal layer is formed.

When PDLC is used as a material constituting the liquid crystal layer, flatness required for the planarization layer may be lower than when other materials (for example, cholesteric liquid crystal described later) are used. Moreover, the thickness of the planarization layer should just be more than the thickness which does not conduct | electrically_connect a reflective metal and a pixel electrode, for example, is 3 micrometers.

  In addition to PDLC, cholesteric liquid crystal having a reflection band in the infrared region can be used as the scattering liquid crystal. A cholesteric liquid crystal is formed by adding a chiral agent having a chiral center to a nematic liquid crystal material. The addition amount of the chiral agent is adjusted so that a spiral pitch that reflects light in a desired band is obtained. In the liquid crystal layer using cholesteric liquid crystal, the driving voltage and the scattering characteristics differ depending on the thickness. Therefore, it is preferable to suppress variation in the thickness of the liquid crystal layer.

  Although the present embodiment is a liquid crystal display device in a scattering display mode, the liquid crystal display device of the present invention may use a dynamic scattering mode or another phase transition type mode as a display mode.

  The reflective liquid crystal display device of this embodiment can reduce the width between the electrodes as compared with a reflective liquid crystal display device (for example, the display device shown in FIG. 1) having a reflective electrode having a function as a reflective layer and a pixel electrode. Has the advantage. This will be described in detail below.

  First, referring to FIG. FIG. 7 is a plan view for explaining the shape of the pixel electrode 701 in the conventional display device shown in FIG. The pixel electrode 701 in the conventional display device is formed by patterning a reflective metal layer (for example, a layer made of Ag) having a retroreflection shape. The reflective metal layer has a shape in which unit structures 702 are arranged. The unit structure 702 is, for example, a corner cube, preferably a cubic corner cube. When a pixel electrode designed as indicated by a dotted line 703 is formed from a reflective metal layer having a retroreflective shape, the reflective metal layer has large irregularities and the light used for photolithography is recurred due to its recursion. Therefore, it is quite difficult to form the pixel electrode pattern edge as designed, that is, along the dotted line 703. The pattern edge of the pixel electrode 701 actually formed by patterning deviates from the dotted line 703 depending on the shape of the unit structure 702. As a result, the gap 701g between the adjacent pixel electrodes 701 is aligned with the unit structure 702 and becomes considerably larger than the design. Specifically, the width of the gap 701g is equal to the pitch of the unit structure or n times (n is an integer of 2 or more).

More specifically, when the width of the designed gap is equal to or less than the pitch of the unit structure, the width of the gap 701g of the pixel electrode 701 actually formed is equal to the pitch of the unit structure or n times (n Is an integer of 2 or more. When the design gap width is greater than (m−1) times the unit structure pitch (m is an integer of 2 or more) and less than m times, the gap width 701 g actually obtained is m of the unit structure pitch. Or (m + k) times the pitch of the unit structure (k is an integer of 1 or more). For example, when the designed gap width is 6 μm and the unit structure pitch is 10 μm, the gap width 701 g is 10 μm, or n times 10 μm (20 μm, 30 μm, etc.), and the designed gap width is 10 μm. When the structure pitch is 6 μm, the gap width 701 g is 12 μm, or (2 + k) times 6 μm (18 μm, 24 μm, etc.).

  Reference is now made to FIG. FIG. 8 is a plan view for explaining the shape of the pixel electrode 801 in the present embodiment. In the present embodiment, the pixel electrode 801 is provided via a planarizing resin layer on the retroreflective layer on which the unit structures 802 are arranged. The pixel electrode 801 is formed by forming a transparent conductive film on the planarizing resin layer and patterning the transparent conductive film. Since the transparent conductive film has a planarized surface, photolithography when patterning the transparent conductive film is performed at a normal resolution without being affected by the uneven shape of the retroreflective layer. Therefore, when the pixel electrode pattern is designed as indicated by the dotted line 703, the transparent conductive film can be patterned almost as designed, and therefore the width of the gap 801g between the adjacent pixel electrodes 801 can be suppressed small.

  As described above, the width of the gap 801g between the adjacent pixel electrodes 801 is determined without depending on the pitch of the unit structure. For example, when the design gap width is 6 μm and the unit structure pitch is 10 μm, the gap is actually formed. The gap width 801g of the pixel electrode 801 is 6 μm. When the designed gap width is 10 μm and the unit structure pitch is 6 μm, the gap width 801g is 10 μm.

  Therefore, according to the present embodiment, since the width of the gap 801g of the pixel electrode 801 can be made smaller than before, the aperture ratio of the display device can be improved.

  Next, referring to the drawings, the gap width of the pixel electrode in the case where the unit structures 702 and 802 in the reflective metal layer and the retroreflective layer are cubic corner cubes composed of three substantially square surfaces orthogonal to each other. The relationship between the design value and the actual value will be described in more detail. Note that the size in the following description corresponds to the size in the plan view.

  FIGS. 16A and 16B are diagrams for explaining the relationship between the design value and the actual value of the gap width of the pixel electrode provided along the x direction and the y direction in the conventional display device, respectively. FIG. 8 is a plan view further enlarging the plan view of the conventional display device shown in FIG. 7. FIGS. 17A and 17B are diagrams showing the relationship between the design value and the actual value of the gap width of the pixel electrode provided along the x direction and the y direction in the present embodiment, respectively. FIG. 9 is a plan view further enlarging the plan view of the display device of the present embodiment shown in FIG. 8.

In the following description, the distance between the bottom points 702b and 802b of the adjacent corner cubes 702 ′ and 802 ′ is the pitch P _cc of the corner cubes 702 ′ and 802 ′, and the bottom points of the adjacent corner cubes 702 ′ and 802 ′. A direction in which 702b and 802b are aligned on a straight line is an x direction, and a direction orthogonal to the x direction is a y direction. The length of one side of the square forming each corner cube 702 ′, 802 ′ is (√3) / 3 × Pcc. Note that the pixel electrode is designed to have a rectangular shape whose short side or long side is substantially parallel to the x direction. Accordingly, the gap between the pixel electrodes is constituted by a gap extending in the x direction and a gap extending in the y direction.

  First, the gap extending in the x direction among the gaps between the pixel electrodes will be described with reference to FIG.

In the conventional display device, the pixel electrode is obtained by forming a resist pattern on the metal reflection layer in which the corner cubes 702 ′ are arranged, and etching the metal reflection layer using the resist pattern as a mask. The resist pattern can be formed by exposing a resist film formed on the metal reflective layer and developing the resist film. The resist film is exposed using a photomask. Here, the width of the gap extending in the x direction defined by the photomask (hereinafter referred to as “gap design value”) Dd _x is equal to or less than the length of one side of the corner cube 702 ′ (Dd _x ≦ (√3) / A photomask designed to be 3 × P _cc ) is used. Further, the photomask is arranged so that the gap in the x direction defined by the photomask is located between the straight lines Ad1 and Au1 connecting the saddle points of the corner cube 702 constituting the row X.

When attempting to pattern a resist film on a metal reflective layer using such a photomask, the light used in photolithography is retroreflected in the recesses of each corner cube. A region wider than the region to be removed is removed. As a result, the gap width (hereinafter referred to as “resist pattern gap width”) Dr _x of the pixel electrode 701 defined by the resist pattern actually obtained after development is larger than the gap design value Dd _x and the corner cube. 702 ′ y-direction width (2√3) /
3 × _Pcc or less.

Typically, the resist pattern gap width Dr _x is between (√3) / 3 × P _cc and (2√3) / 3 × P _cc along the y-direction width at the outer periphery of the corner cube 702 ′. It changes with. In this case, the area of the gap of the resist pattern is larger than the areas of the triangles S1 and S2 in the corner cube 702 ′ of the row X than the area of the gap defined by the photomask. The triangles S1 and S2 are regions other than the region located between the straight lines Au1 and Ad1 in the corner cube 702 ′ as shown in the figure, and the sum ΔS (x) of the areas of these triangles S1 and S2 is (√3 ) / 6 × P _cc ² . Accordingly, the area of the display area that cannot be used for display is increased by (√3) / 6 × P _cc ² or more per corner cube in row X, compared to the area of the area that cannot be used for design display. End up.

Next, the gap extending in the y direction among the gaps between the pixel electrodes will be described with reference to FIG. Here, the photo mask used for exposing the resist film, the case where the y direction of the gap width (gap design value) Dd _y is designed to be a P _cc / 2 or less. Further, in the photomask, the gap in the y direction defined by the photomask is between the straight lines Al1 and Ar1 passing through the bottom point 702b, the apex and the saddle point (the interval between the straight lines Al1 and Ar1 is P _cc / 2). To be positioned.

When patterning the resist film by using a photomask, as in FIG. 16 (a), the gap width Dr _y of the resist pattern is greater than the gap design value Dd _y, and the width in the x direction of the corner cube 702 ' (Ie, pitch P _cc ) or less.

Typically, the resist pattern gap width Dr _y is equal to the pitch P _cc of the corner cube 702 ′. In this case, the area of the resist pattern gap in the corner cube at the position where the gap is formed is equal to the photomask. in than the area of the gap which is defined, the length of the y direction (√3) × per P _cc, greater than the area of the trapezoid S3 and S4. As shown in the figure, trapezoids S3 and S4 are regions other than the region located between the straight lines Al1 and Ar1 in the corner cube 702 ′, and the sum ΔS (y) of the areas is (√3) / 2 × P _cc ² . Therefore, the area of the display area that cannot be used for display is less than the area of the area that cannot be used for design display, and the length in the y direction in the gap is (√3) × _Pcc per (√3) / It will increase by 2 × P _cc ² or more.

  On the other hand, in the present embodiment, as described above with reference to FIG. 8, the pixel electrode is formed by forming a transparent conductive film via a flat film on the retroreflective layer in which the corner cubes 802 ′ are arranged. It is formed by patterning. The patterning of the transparent conductive film is performed as follows. First, a resist film is formed on a transparent conductive film, and the resist film is exposed and developed to pattern the resist film. At this time, the resist film is patterned in substantially the same shape as the pattern defined by the photomask regardless of the shape and arrangement of the corner cubes 802 'in the retroreflective layer. Thereafter, the transparent conductive film is etched using the resist pattern as a mask.

Accordingly, as shown in FIG. 17 (a) and (b), the width Dr _x, Dr _y gaps of the resist pattern to be used in patterning the transparent conductive film, the gap design value Dd _x in the photomask, and Dd _y Almost equal. Therefore, if the gap design value Dd _x is (√3) / 3 × P _cc or less, the gap width Dr _x be (√3) of the resist pattern / 3 × can be kept below P _cc. Further, if the gap design value Dd _y is less P _cc / 2, the gap width Dr _y of the resist pattern can be suppressed to below P _cc / 2. Thus, according to the present embodiment, the area that cannot be used for display in the conventional display device can be reduced, so that the aperture ratio can be improved.

Here, the relationship between the pixel electrode pitch P _pix and the corner cube pitch P _cc for more effectively improving the aperture ratio will be examined.

In the conventional display device, the actual area of the gap between the pixel electrodes is larger than the designed area of the gap between the pixel electrodes, but the increased area per pixel ΔS = ΔS (x) + ΔS (y ) _Varies depending on the pitch P _{pix of the} pixel electrodes and the pitch P _{cc of the} corner cubes as shown in the following formula (1). If the pitch in the x direction of the pixel electrode is P _{pix (x)} and the pitch in the y direction is P _{pix (y)} ,
ΔS = ΔS (x) + ΔS (y) = P _{pix (x)} / P _cc × (S 1 + S 2) + P _{pix (y)} / ((√3) × P _cc ) × (S 3 + S 4)
= P _{pix (x)} / P _cc × (√3) / 6 × P _cc ² + P _{pix (y)} / ((√3) × P _cc ) × (√3) / 2 × P _cc ²
Therefore, ΔS = (√3) / 6 × P _{pix (x)} × P _cc + P _{pix (y)} × P _cc / 2 (1)

When the ratio of the increased area ΔS to the pixel area (P _{pix (x)} × P _{pix (y)} ) exceeds 0.5%, more preferably more than 1%, the aperture ratio is greatly improved as compared with the prior art. Can do. Accordingly, the pixel electrode pitch P _pix (P _{pix (x)} or P _{pix (y)} ) and the corner cube pitch P _cc preferably satisfy the following formula (2), more preferably the following formula (3). Satisfied. Thereby, a brighter display than before can be realized.
ΔS / (P _{pix (x)} × P _{pix (y)} )
= ((√3) / 6 × P _{pix (x)} × P _cc + P _{pix (y)} × P _cc / 2) / (P _{pix (x)} × P _{pix (y)} )> 0.005 (2)
ΔS / (P _{pix (x)} × P _{pix (y)} )
= ((√3) / 6 × P _{pix (x)} × P _cc + P _{pix (y)} × P _cc / 2) / (P _{pix (x)} × P _{pix (y)} )> 0.01 (3)

Incidentally, when the pitch P _pix and _(y) are equal to each other _{(P pix (x) × P} pix (y) = P pix) in the pitch P _{pix (x)} and y-direction of the x-direction in the pixel electrode, the above equation (2) and (3) are respectively expressed by the following equations.
((√3) +3) / 6 × P _cc / P _pix > 0.005 (4)
((√3) +3) / 6 × P _cc / P _pix > 0.01 (5)

For example, if the resolution of the display device is about 200 ppi (ppi: pixels per inch), the corner cube pitch P _cc is 1 μm or more, and the aperture ratio can be greatly improved compared to the conventional case. If the pitch P _cc is about 2 μm, the aperture ratio can be greatly improved when the resolution of the display device is about 85 ppi or more.

In the above, the case where the pixel electrode having a rectangular shape has sides parallel to the x direction and the y direction has been described, but in this embodiment, the direction of the long side or the short side of the pixel electrode is the x direction in the corner cube. It does not have to coincide with the y direction, and even in this case, the same relationship as the above equations (2) and (3) is established. That is, if the arrangement pitch in the short side direction of the pixel electrode is P _{pix (S)} and the arrangement pitch in the long side direction is P _{pix (L)} , the following expression (4), more preferably the following expression (5) is satisfied. Thus, the aperture ratio can be effectively improved.
((√3) / 6 × P _{pix (L)} × P _cc + P _{pix (S)} × P _cc / 2) / (P _{pix (L)} × P _{pix (S)} )> 0.005 (6)
((√3) / 6 × P _{pix (L)} × P _cc + P _{pix (S)} × P _cc / 2) / (P _{pix (L)} × P _{pix (S)} )> 0.01 (7)

  Furthermore, according to this embodiment, as will be described in detail below, it is possible to realize display characteristics superior to those of the conventional retroreflective display device.

  FIGS. 9A and 9B are schematic cross-sectional views showing a black state and a white state of a conventional retroreflective display device, respectively, and FIGS. 10A and 10B are respectively It is typical sectional drawing which shows the black state and white state of the retroreflection type display apparatus of this embodiment. Each display device is an active matrix drive type using TFT as a switching element.

  A conventional retroreflective display device has a configuration similar to that described above with reference to FIG. That is, a back substrate 509, a front substrate 510, and a liquid crystal layer 505 sandwiched between the back substrate 509 and the front substrate 510 are provided. The back substrate 509 includes a TFT substrate 501 having a plurality of thin film transistors 501t on the surface, and an electrode (reflective electrode) 503 having a retroreflective property formed on the TFT substrate 501. The reflective electrodes 503 are spaced apart from each other corresponding to the pixels, and a non-reflective layer 504 that does not exhibit a reflective function is provided between the adjacent reflective electrodes 503. A color filter 507 and a black mask 506 are formed on the surface of the front substrate 510 on the liquid crystal layer 505 side. The color filter 507 is arranged corresponding to the pixel. The black mask 506 is disposed between the adjacent color filters 507 so as to cover the non-reflective layer 504. In this figure, the thin film transistor 501t is disposed under the non-reflective layer 504, but only the wiring (source wiring) of the TFT substrate 501 may be disposed under the non-reflective layer 504. The liquid crystal layer 505 is formed of PDLC, for example, and displays “black” when the liquid crystal layer 505 is in a transparent state and “white” when in a scattering state.

  Here, the display principle of the conventional diffuse reflection type liquid crystal display device will be described. First, the operation of black display will be described. When light is incident from the light source 500, the incident light is generally reflected along a path indicated by an arrow 500a in FIG. That is, light from the light source 500 passes through the color filter 507, then passes through the transparent liquid crystal layer 505, and is reflected by the retroreflector 503, and passes through the liquid crystal layer 505 and the color filter 507 and passes through the light source 500. Go back to the direction. At this time, since the observer recognizes the image of his / her eyes, the display is black.

  On the other hand, the light incident obliquely on the end of the color filter 507 (near the black mask 506) out of the light from the light source 500 has passed through the color filter 507 and the transparent liquid crystal layer 505 as indicated by an arrow 500b. Thereafter, the light enters the non-reflective layer 504. This light passes through the non-reflective layer 504, reaches the surface of the thin film transistor 501t, and is reflected there. Note that the thin film transistor 501t may not be disposed under the non-reflective layer 504, and a wiring in the TFT substrate 501 may be disposed instead. In this case, light transmitted through the non-reflective layer 504 is transmitted through the wiring. Reflected on the surface. Reflection on the surface of the thin film transistor 501t or the wiring is usually metal reflection. Depending on the design of the panel, most of the light reflected by the surface of the thin film transistor 501t or the like is absorbed by the black mask 506. However, when the width of the black mask 506 is set to be small for the purpose of improving display brightness, a part of the light reflected by the surface of the thin film transistor 501t or the like is different from the color filter 507 that has passed at the time of incidence. The light passes through the color filter 507 and is emitted (arrow 500b ′), and the black characteristic is deteriorated.

  Next, the white display operation will be described. When light from the light source 500 is incident, as shown by an arrow 500c in FIG. 9B, a part of the incident light passes through the color filter 507 and is then scattered by the liquid crystal layer 505 in a scattering state. When the liquid crystal layer (PDLC) 505 has forward scattering characteristics, light incident on the liquid crystal layer 505 is scattered (forward scattered) toward the retroreflecting plate 503 and reflected by the retroreflecting plate 503. The reflected light reaches the observer's eyes again through the liquid crystal layer 505 and the color filter 507. When the liquid crystal layer 505 has a backscattering characteristic, most of the incident light is scattered in the observation direction by the liquid crystal layer 505, but a part of the incident light is scattered forward and reflected by the retroreflecting plate 503. Reach the eyes. In any case, since the retroreflectivity of the light reflected by the retroreflective plate 503 is destroyed by the scattering characteristics of the liquid crystal layer 505, most of the reflected light does not return to the direction of the light source 500 and contributes to white display.

  On the other hand, light incident on the end of the color filter 507 (near the black mask 506) obliquely from the light source 500 passes through the color filter 507 and is scattered by the liquid crystal layer 505 as indicated by an arrow 500d. However, part of the scattered light enters the non-reflective layer 504 between the adjacent reflective electrodes 503 and reaches the surface of the thin film transistor 501t, where it is reflected (reflected by metal). The reflected light is designed to be absorbed by the black mask 506. However, since the light scattered by the liquid crystal layer 505 is reflected by the surface of the thin film transistor 501t and further scattered by the liquid crystal layer 505, the reflected light is not absorbed by the black mask 506 but passes through the color filter 507 and is observed by the observer. There is also light emitted to the side. Among these, the light emitted through the color filter 507 different from the color filter 507 that has passed at the time of incidence causes color mixing. Note that the amount of reflected light that passes through the same color filter 507 as the incident light again and is used for display is very small.

  On the other hand, the retroreflective display device of this embodiment operates as follows. First, the black display operation will be described with reference to FIG. The retroreflective display device shown in FIG. 10A is formed using the back substrate 300 described with reference to FIG. The configuration of the liquid crystal layer and the front substrate is the same as that of the liquid crystal layer 505 and the front substrate 510 in the conventional display device described above.

  When light is incident from the light source 500, the incident light is generally reflected along a path indicated by an arrow 600a in FIG. That is, the light from the light source 500 passes through the color filter 507, passes through the transparent liquid crystal layer 505, the transparent pixel electrode 310, and the flattening resin layer 309, and then is reflected by the retroreflective plate 308 and is again flattened resin layer. 309, the pixel electrode 310, the liquid crystal layer 505, and the color filter 507 are returned to the direction of the light source 500.

  On the other hand, of the light from the light source 500, the light incident on the end of the color filter 507 (near the black mask 506) is, as indicated by the arrow 600b, the color filter 507, the transparent liquid crystal layer 505, and the transparent pixel electrode. After passing through 310 and the planarizing resin layer 309, it is reflected by the retroreflecting plate 308 and absorbed by the black mask 506. However, a part of the light reflected by the retroreflecting plate 308 does not enter the black mask 506 but passes through the color filter 507 again and returns to the light source 500. In this way, the light that has passed through the end of the color filter 507 is absorbed by the black mask 506, or returns to the direction of the light source 500 by retroreflection and does not exit in the viewing direction, so that good black display characteristics can be obtained. It is done.

  Next, the white display operation will be described. The light from the light source 500 is scattered by the liquid crystal layer 505 after passing through the color filter 507 as indicated by an arrow 600c in FIG. At this time, when the liquid crystal layer 505 has forward scattering characteristics, the light incident on the liquid crystal layer 505 is scattered (forward scattered) in the direction of the retroreflective plate 503 and passes through the transparent pixel electrode 310 and the planarizing resin layer 309. Reflected by the retroreflector 503. When the liquid crystal layer 505 has backscattering characteristics, most of the incident light is scattered in the observation direction by the liquid crystal layer 505 and exits through the color filter 507, but a part of the incident light is scattered forward and recursively. Reflected by the reflector 503. In any case, since the retroreflectivity of the light reflected by the retroreflective plate 503 is destroyed by the scattering characteristics of the liquid crystal layer 505, most of the light reflected by the retroreflective plate 503 passes through the color filter 507 again. To exit in the observation direction. Further, although there is light that is scattered in the direction of the light source 500 by the liquid crystal layer 505 and does not contribute to display, the amount of light is very small.

  On the other hand, light incident on the end of the color filter 507 (in the vicinity of the black mask 506) out of the light from the light source 500 is scattered by the liquid crystal layer 505 through the color filter 507 as indicated by an arrow 600d. Regardless of the scattering characteristics (forward scattering type, back scattering type) of the liquid crystal layer 505, part of the scattered light is reflected by the retroreflector 308 through the transparent pixel electrode 310 and the planarizing resin layer 309. A part of the reflected light is absorbed by the black mask 506, but the remaining light does not enter the black mask 506, but exits in the observation direction through the same color filter 507 as that at the time of incidence. As described above, light from the light source 500 that passes from the pixel region through the end of the color filter 507 to the black mask region also returns to the observation direction using the retroreflective property. Improve and achieve brighter display.

  As described above, according to the retroreflective liquid crystal display device of the present embodiment, it is possible to suppress deterioration in display characteristics due to light incident from the end of the black mask 506. Therefore, good display characteristics can be obtained in the black display state, and brighter display can be realized while suppressing color mixing even in the white display state.

  Furthermore, according to this embodiment, there are the following merits.

  In the conventional reflective display device (FIG. 9), since the surface of the liquid crystal layer 505 on the back substrate side has an uneven shape, even when the liquid crystal layer 505 is in a uniform alignment state, due to scattering of PDLC present in the recesses, There is a problem that the black display characteristic is deteriorated. This is because light is reflected by a plurality of surfaces forming the concave portion, and light incident on the PDLC in the concave portion from different directions is scattered by the birefringence of the PDLC. When a planarization layer is provided between the liquid crystal layer 505 and the reflective electrode 503, the black display characteristics can be prevented from being deteriorated, but a voltage loss is caused by the planarization layer. On the other hand, in this embodiment, the back substrate side surface of the liquid crystal layer 505 is flattened, and the PDLC scattering as described above does not occur, so that the black display characteristics can be improved and a display with high contrast can be realized. . In addition, since the pixel electrode 308 and the drain electrode 306 of the thin film transistor 501t are in contact (conduction), there is no voltage loss due to the planarization resin layer 309.

  The configuration and manufacturing method of the retroreflective liquid crystal display device of the present embodiment are not limited to the above configuration and method. For example, the back substrate 300 in the present embodiment can be manufactured using a columnar resist pattern (resist column) having a shape corresponding to the contact hole. Hereinafter, a manufacturing method using a resist pillar will be described with reference to the drawings.

  First, as shown in FIG. 11A, a resist pattern (resist pillar) corresponding to the size (for example, diameter 5 μm) of a contact hole to be formed on the drain electrode 1202 of the TFT substrate 1200 by photolithography. 1203 is formed. The height of the resist pillar 1203 is set to be larger than the thickness of the insulating layer 1204 to be formed in a later step, and is, for example, 8 μm.

  Next, as shown in FIG. 11B, a transfer resin 1204 ′ such as an acrylic resin is applied to the TFT substrate 1200.

  After that, as shown in FIG. 11C, the surface shape of the master 1220 is transferred to the transfer resin 1204 'by an embossing method or the like. Specifically, a master 1220 having a corner cube array shape is attached to the surface of the transfer resin 1204 ', and the transfer resin 1204' is cured. Curing of the transfer resin can be performed using thermoplasticity, thermosetting property, photocuring property, or the like. For example, when an acrylic resin is used as the transfer resin 1204 ′, the transfer resin 1204 ′ can be cured by being irradiated with ultraviolet rays. A curing accelerator may be added to the transfer resin 1204 as necessary.

  The curing method and curing conditions of the transfer resin 1204 ′ are not particularly limited, but it should be noted that if the resist column 1203 is cured in the curing step of the transfer resin 1204, it is difficult to remove the resist column 1203 in a later-described step. There is a need. For example, when the resist pillar 1203 is formed using a positive resist material, the transfer resin 1204 ′ is formed using a photocurable resin material, and the transfer resin 1204 ′ is cured by irradiation with light. This is because in the curing step of the transfer resin 1204 ′, the resist pillar 1203 is also irradiated with light, but this does not cause the resist pillar 1203 to cure. On the other hand, since the resist pillar 1203 can be peeled off relatively easily if not subjected to the main baking, a transfer resin 1204 ′ is formed using a thermosetting resin material and transferred at a temperature lower than the main baking temperature of the resist pillar 1203. The resin 1204 ′ may be cured. Note that when the transfer resin 1204 ′ is cured using photocuring property, there is an advantage that the process time can be shortened as compared with the case of curing using thermosetting property.

  Next, when the TFT substrate 1200 and the master 1220 are released, an insulating layer 1204 having a corner cube array shape is obtained as shown in FIG. As shown in FIG. 11E, a reflective metal layer (for example, Ag layer) 1205 is formed on the surface of the insulating layer 1204 by, for example, sputtering or vapor deposition.

  Subsequently, as shown in FIG. 11F, a planarizing material is applied on the reflective metal layer 1205 to form a planarizing resin layer 1207, and a contact hole 1207c is formed in the planarizing resin layer 1207 by photolithography. Form. The contact hole 1207c is aligned with the resist pillar 1203. For example, the same mask as that used when the resist pillar 1203 is formed may be used.

  Thereafter, as shown in FIG. 11G, an opening (diameter: 8 μm, for example) 1205c larger than the contact hole 1207c is formed in the reflective metal layer 1205. Specifically, the planarizing resin layer 1207 is used as an etching mask, and a part of the reflective metal layer 1205 is removed by wet etching, for example. At this time, an etching time, an etching solution, or the like is selected so that a portion wider than the portion exposed by the contact hole 1207c in the reflective metal layer 1205 is removed (overetching).

  After the etching of the metal reflective layer 1205, as shown in FIG. 11H, the resist pillar 1203 is peeled off using a solution (peeling liquid) that melts the resist pillar 1203. As the stripping solution, for example, an organic amine-based alkali solution or a polar solvent such as acetone may be used. As a result, a contact hole 1204c is formed in the insulating layer 1204. Since the contact hole 1204c is connected to the contact hole 1207c formed in the planarization resin layer 1207, one contact hole 1208 that penetrates the insulating layer 1204 and the planarization resin layer 1207 and reaches the drain electrode 1202 is obtained.

  Note that, using a solution prepared so that the resist pillar 1203 can be melted and can also be used as an etching solution for the reflective metal layer 1205, the overetching process of the reflective metal layer 1205 shown in FIG. The resist pillar removing step shown in h) can be performed simultaneously.

  Thereafter, as shown in FIG. 11I, coating-type ITO is applied to the inside of the planarizing resin layer 1207 and the contact hole 1208 to form an ITO film 1209 '. Subsequently, as shown in FIG. 11 (j), the pixel electrode 1209 is formed by patterning the ITO film 1209 '. Each pixel electrode 1209 is electrically connected to the drain electrode 1202 of the corresponding thin film transistor through a contact portion 1210 formed inside the contact hole 1208. In this way, the back substrate 1230 is completed.

  In the above description, a retroreflective layer having a corner cube array shape is formed as the reflective metal layer 1205. However, a retroreflective layer of another shape may be formed by the same method, or a diffuse reflective layer may be formed. May be.

  Further, a conductive column may be formed using a conductive material instead of the resist column 1203. In this case, in the rear substrate after completion, the conductive pillar constitutes a part of a contact portion that connects the pixel electrode and the switching element. Hereinafter, a method for manufacturing a back substrate in the case of forming a conductive column (conductive portion) will be described.

  First, as shown in FIG. 12A, a columnar conductive portion 1240 is formed on the drain electrode 1202 of the TFT substrate 1200. The conductive portion 1240 can be formed by depositing and patterning a conductive material, for example. The size and thickness of the conductive portion 1240 may be the same as the size and thickness of the resist pillar 1203 described above.

  Conductive materials include conductive material dispersed resins in which conductive materials (carbon, aluminum, etc.) are dispersed in insulating resins (acrylic resins, etc.), and organic conductive compounds (polyacetylene, etc.) in which the polymer itself is conductive. You may use. When a conductive material-dispersed resin containing a photocurable acrylic resin or the like is used as the insulating resin, patterning using a photolithography method is possible, and the formation process of the conductive portion 1240 can be simplified.

  Subsequently, as described with reference to FIGS. 11B to 11G, after the insulating layer 1204 is formed by the embossing method, the metal reflective layer 1205 having the opening 1205c and the flat having the contact hole 1207c are formed. A plasticized resin layer 1207 is formed (FIGS. 12B to 12G).

  Thereafter, as shown in FIG. 12 (h), an ITO film 1211 'coated with coating-type ITO is formed inside the planarizing resin layer 1207 and the contact hole 1207c. Subsequently, as shown in FIG. 12I, the pixel electrode 1211 is formed by patterning the ITO film 1211 '. The pixel electrode 1211 is electrically connected to the drain electrode 1202 of the corresponding thin film transistor through a contact portion formed of the ITO film formed inside the contact hole 1207c and the conductive portion 1240. In this way, the back substrate 1250 is completed.

(Second Embodiment)
The reflective display device according to the second embodiment of the present invention will be described below.

  FIG. 13A is a plan view showing a configuration of a back substrate (TFT side substrate) 400 in the reflective liquid crystal display device of the present embodiment, and FIG. 13B is a plan view shown in FIG. It is 13b-13b 'sectional drawing in.

  The back substrate 400 has the same configuration as the back substrate 300 described with reference to FIGS. 4 (a) and 4 (b). However, the insulating layer 407 has a diffuse reflection shape instead of a retroreflection shape, and the reflection layer 408 is different in that it has a scattering type reflection characteristic instead of the retroreflection characteristic.

  The back substrate 400 of this embodiment can be formed by, for example, the method described below.

  First, a TFT substrate is formed by a method similar to the method described with reference to FIGS. 5 (a) and 6 (a). Next, a resin layer having a random pattern is formed on the TFT substrate using, for example, an acrylic ultraviolet curable resin. The random pattern may be a plurality of island patterns (size of each island pattern: for example, 10 μm × 10 μm). Next, when the resin layer is heated to 105 ° C., for example, and the resin layer is thermally deformed (heated), an insulating layer 407 having irregularities on the surface is formed.

  Subsequently, a contact hole 311 is formed in the insulating layer 407 by a method similar to the method described with reference to FIGS. 5B and 6B, and then a reflection such as an Ag layer is formed on the insulating layer 407. A metal layer is formed. An opening 311 ′ having a diameter larger than that of the contact hole 311 is provided in the reflective metal layer. As a result, a reflective layer 408 having diffuse reflection characteristics is formed.

  Thereafter, the back substrate 400 is obtained by forming the planarizing resin layer 309 and the pixel electrode 310 by a method similar to the method described with reference to FIGS. 5C and 6C.

  The reflective liquid crystal display device of the present embodiment can be manufactured by using the back substrate 400 obtained as described above in the same process as that performed when manufacturing a conventional reflective liquid crystal display device. A specific method will be described below.

  First, a polyimide film is formed on the back substrate 400, and an alignment layer that defines the direction of the liquid crystal is formed by rubbing (rubbing) it with a cloth. On the other hand, a front substrate having a color filter layer, a transparent conductive film and an alignment layer is formed. The alignment layer on the front substrate can also be formed in the same manner as the alignment layer on the back substrate 400. Next, the back substrate 400 and the front substrate are bonded together, and a birefringence mode liquid crystal layer, for example, is formed between them. Further, unlike the retroreflective liquid crystal display device of Embodiment 1, a polarizing plate and a retardation plate corresponding to the retardation of the liquid crystal layer are attached to the surface of the front substrate. Thereby, the reflective liquid crystal display device of this embodiment is obtained.

  In addition, the manufacturing method of the back substrate 400 and the display device of the present embodiment is not limited to the above method. For example, the back substrate 400 may be manufactured by a method similar to the method using the resist pillar described with reference to FIG. 11 or the method using the columnar conductive portion described with reference to FIG.

  Hereinafter, the advantages of the diffuse reflection type liquid crystal display device of the present embodiment over the conventional diffuse reflection type display device will be described with reference to the drawings. 14A and 14B are schematic cross-sectional views showing a white state and a black state of a conventional diffuse reflection type liquid crystal display device, respectively, and FIGS. 15A and 15B are respectively It is typical sectional drawing which shows the white state and black state of the diffuse reflection type liquid crystal display device of this embodiment. Each display device is an active matrix drive type using TFT as a switching element. Further, as an example of the display mode, a single polarizing plate mode including a polarizing plate, a retardation plate, a liquid crystal layer, and a reflective layer is used. In the following example, an electric field control birefringence mode liquid crystal layer designed to be in a “white” display state when no voltage is applied is used. Note that the liquid crystal layer may be designed to be in a “black” display state when no voltage is applied.

  A conventional diffuse reflection type liquid crystal display device includes a rear substrate 909, a front substrate 910, and a liquid crystal layer 905 sandwiched between the rear substrate 909 and the front substrate 910. The back substrate 909 includes a TFT substrate 901 having a plurality of thin film transistors 901t on the surface, and an electrode (reflective electrode) 903 having a diffuse reflection characteristic formed on the TFT substrate 901. The reflective electrode 903 is provided corresponding to the pixel, and has a non-reflective layer 904 between the adjacent reflective electrodes 903. A color filter 907 and a black mask 906 are formed on the surface of the front substrate 910 on the liquid crystal layer 905 side. The color filter 907 is disposed corresponding to the pixel, and the black mask 906 is disposed between the adjacent color filters 907 so as to cover the non-reflective layer 904. A phase difference plate 921 and a polarizing plate 920 are provided in this order on the surface of the front substrate 910 on the viewer side.

  Here, the display principle of the conventional diffuse reflection type liquid crystal display device will be described. First, the operation of white display will be described. When light is incident on the display device from the light source 900, the incident light is generally reflected along a path indicated by an arrow 900a in FIG. The light from the light source 900 passes through the polarizing plate 920 to become linearly polarized light A1 parallel to the transmission axis direction of the polarizing plate 920, and then passes through the phase difference plate 921, for example, clockwise circularly polarized light B1. It becomes. The circularly polarized light B 1 passes through the color filter 907 and then passes through the liquid crystal layer (retardation Δnd = λ / 4) 905 to become linearly polarized light A 1 and is reflected by the diffuse reflector 903. The reflected light again passes through the liquid crystal layer 905 to become circularly polarized light B1, passes through the color filter 907, and then becomes linearly polarized light A1 by the phase difference plate 921 and is thus emitted from the polarizing plate 920 in the observation direction.

  On the other hand, the light incident on the end of the color filter 907 (near the black mask 906) obliquely from the light source 900 passes through the liquid crystal layer 905 and then is adjacent to the reflective electrode 903 as indicated by an arrow 900b. Between the non-reflective layers 904. Such light passes through the non-reflective layer 904 and reaches the surface of the thin film transistor 901 where it is reflected. The reflection on the surface of the thin film transistor 901 is usually a metal reflection. Depending on the design of the panel, most of the light reflected by the surface of the thin film transistor 901 is absorbed by the black mask 906. However, since the distance between the color filter 907 and the surface of the thin film transistor 901 which is a reflection surface is longer than the distance between the color filter 907 and the diffuse reflection plate 903, a part of the light reflected on the surface of the thin film transistor 901 is black mask. Instead of 906, the color filter 907 that is different from the color filter 907 that has passed at the time of incidence passes (arrow 900b ′). The light that has passed through the color filter 907 different from that at the time of incidence becomes linearly polarized light A1 by the phase difference plate 921, passes through the polarizing plate 920, and returns to the observation direction, which causes color mixing.

  Next, the black display operation will be described. As indicated by an arrow 900c in FIG. 14B, the light from the light source 900 passes through the polarizing plate 920 to become linearly polarized light A1 parallel to the transmission axis direction of the polarizing plate 920, and then the retardation plate 921. , And becomes, for example, clockwise circularly polarized light B1. This circularly polarized light B 1 passes through the liquid crystal layer 905 through the color filter 907. At this time, if a predetermined voltage (saturation voltage or higher) is applied to the liquid crystal layer 905, the retardation Δnd of the liquid crystal layer 905 is substantially zero, so that the polarization state of the light passing through the liquid crystal layer 905 is maintained. In this case, the circularly polarized light B1 that has passed through the liquid crystal layer 905 is reflected by the diffuse reflector 903 to become counterclockwise circularly polarized light B2, and passes through the liquid crystal layer 905 and the color filter 907 again. The light (circularly polarized light B2) that has passed through the color filter 907 passes through the phase difference plate 921, and becomes linearly polarized light A2 that is orthogonal to the linearly polarized light A1. The linearly polarized light A2 is orthogonal to the transmission axis direction of the polarizing plate 920 and is absorbed by the polarizing plate 920, so that the black state is obtained.

  On the other hand, light incident on the end of the color filter 907 (in the vicinity of the black mask 906) from the light source 900 obliquely enters the non-reflective layer 904 after passing through the liquid crystal layer 905 as indicated by an arrow 900d. To do. Such light passes through the non-reflective layer 904 and reaches the surface of the thin film transistor 901 where it is reflected by the metal. The reflection on the surface of the thin film transistor 901 is usually a metal reflection. Depending on the design of the panel, most of the light reflected by the surface of the thin film transistor 901 is absorbed by the black mask 906. A part of the light reflected by the surface of the thin film transistor 901 passes through the color filter 907 different from the incident time without being absorbed by the black mask 906, but is absorbed by the polarizing plate 920, so that the quality of black display is lowered. There is no.

  Note that halftone display can be realized by changing the voltage applied to the liquid crystal layer 905 in a range from zero to a saturation voltage. If the applied voltage is zero, the retardation Δnd of the liquid crystal layer 905 is λ / 4 as described above, so that the light that has been reflected by the diffuse reflector 903 and then passed through the liquid crystal layer 905 is clockwise circularly polarized light B1. is there. When a voltage lower than the saturation voltage is applied to the liquid crystal layer 905, light that has been reflected by the diffuse reflector 903 and then passed through the liquid crystal layer 905 becomes elliptically polarized light, and part of the elliptically polarized light does not pass through the polarizing plate 920. Key is displayed. The larger the voltage applied to the liquid crystal layer 905, the smaller the retardation Δnd of the liquid crystal layer 905, and the proportion of the light emitted from the polarizing plate 920 in the light reflected by the diffuse reflector 903 increases. Get closer.

  Next, the operation of the diffuse reflection type liquid crystal display device of the present embodiment will be described with reference to FIGS. 15 (a) and 15 (b). The diffuse reflection display device shown in FIG. 15 is formed using the back substrate 400 described with reference to FIG. The configuration of the liquid crystal layer and the front substrate is the same as that of the liquid crystal layer 905 and the front substrate 910 in the conventional display device described above.

  First, the operation in the white state will be described. When light is incident on the display device from the light source 900, the incident light is generally reflected along a path indicated by an arrow 1000a in FIG. The light from the light source 900 passes through the polarizing plate 920 to become linearly polarized light A1 parallel to the transmission axis direction of the polarizing plate 920, and then passes through the phase difference plate 921, for example, clockwise circularly polarized light B1. It becomes. The circularly polarized light B 1 passes through the color filter 907 and then passes through the liquid crystal layer (retardation Δnd = λ / 4) 905 to become linearly polarized light A 1, passes through the planarizing resin layer 309, and is reflected by the diffuse reflector 408. The reflected light passes through the planarizing resin layer 309 and then passes through the liquid crystal layer 905 to become circularly polarized light B1. The circularly polarized light B1 passes through the color filter 907 and becomes linearly polarized light A1 by the phase difference plate 921. Therefore, the reflected light (linearly polarized light A1) passes through the polarizing plate 920 and is emitted in the observation direction.

  On the other hand, light incident on the end of the color filter 907 (in the vicinity of the black mask 906) obliquely from the light source 900 passes through the liquid crystal layer 905 and the planarizing resin layer 309 through the same path as indicated by the arrow 1000a. After passing, it is reflected by the diffuse reflector 408, but most of the reflected light is absorbed by the black mask 906 (arrow 1000b). Here, the proportion of the reflected light that is not absorbed by the black mask 906 and passes through the color filter 907 different from that at the time of incidence is much smaller than that in the conventional display device (FIG. 14A). In this embodiment, since the distance between the black mask 906 and the reflection surface (the surface of the diffuse reflection plate 408) is equal to the distance between the color filter 907 and the reflection surface, the spread of the reflected light can be suppressed, and the reflected light is incident. This is because the ratio of passing through the color filter 907 different from the time can be reduced. Therefore, it is possible to suppress color mixing that becomes a problem in the conventional display device.

  Next, the black display operation will be described. As indicated by an arrow 1000c in FIG. 15B, the light from the light source 900 passes through the polarizing plate 920 to become linearly polarized light A1 parallel to the transmission axis direction of the polarizing plate 920, and then the retardation plate. It passes through 921 and becomes, for example, clockwise circularly polarized light B1. This circularly polarized light B 1 passes through the liquid crystal layer 905 through the color filter 907. At this time, if a predetermined voltage (saturation voltage or higher) is applied to the liquid crystal layer 905, the retardation Δnd of the liquid crystal layer 905 is substantially zero, so that the polarization state of the light passing through the liquid crystal layer 905 is maintained. In this case, the circularly polarized light B1 that has passed through the liquid crystal layer 905 passes through the flattening resin layer 309, is reflected by the diffuse reflector 408, and becomes counterclockwise circularly polarized light B2. Passes through filter 907. The light (circularly polarized light B2) that has passed through the color filter 907 passes through the phase difference plate 921, and becomes linearly polarized light A2 that is orthogonal to the linearly polarized light A1. Since the linearly polarized light A2 is absorbed by the polarizing plate 920, it becomes a black state.

  On the other hand, light incident on the end of the color filter 907 (in the vicinity of the black mask 906) obliquely from the light source 900 passes through the liquid crystal layer 905 and the flattening resin layer 309 through a path similar to the path indicated by the arrow 1000c. The light passes through and is reflected by the diffuse reflector 408, but most of the reflected light is absorbed by the black mask 906. Part of the light reflected by the diffuse reflector 408 passes through the color filter 907 without being absorbed by the black mask 906, but is absorbed by the polarizing plate 920, so that the quality of black display is not deteriorated.

  As described above, according to the diffuse reflection type liquid crystal display device of the present embodiment, it is possible to suppress deterioration in display characteristics due to light incident from the end of the black mask 906. Therefore, good display characteristics can be obtained in the black display state, and brighter display can be realized while suppressing color mixing even in the white display state.

  Further, according to the present embodiment, there are the following merits.

  In general, in a diffuse reflection type liquid crystal display device, liquid crystal molecules in the liquid crystal layer 905 are aligned in the electric field direction in a black state (here, a voltage application state). Therefore, the refractive index anisotropy in the liquid crystal layer 905 is reduced, and ideally, the phase difference (retardation Δnd) is zero. Actually, since there is a layer (anchoring layer) on the surface of the liquid crystal layer 905 whose alignment state does not change even when the applied voltage is changed, the retardation Δnd of the liquid crystal layer 905 cannot be reduced to zero. By reducing the thickness of the ring layer, the retardation Δnd of the liquid crystal layer 905 can be further reduced.

  In the conventional display device shown in FIG. 14, an alignment film (not shown) is typically formed on the reflective electrode 903 having an uneven shape, and a liquid crystal layer 905 is provided on the alignment film. The alignment film has a surface shape that reflects the shape of the reflective electrode 903. When the liquid crystal layer 905 is provided on the uneven surface, the alignment direction of the liquid crystal molecules is likely to be non-uniform in the vicinity of the unevenness, and the liquid crystal molecule layer that is not aligned in the electric field direction even when a voltage is applied becomes apparently thick. . As a result, the retardation Δnd (phase difference) of the liquid crystal layer 905 cannot be sufficiently reduced, so that excellent black (dark) characteristics cannot be obtained.

  On the other hand, according to the present embodiment, the alignment film is formed on the planarizing resin layer 309, and the alignment surface in contact with the liquid crystal layer 905 is flat. Therefore, the surface layer in the liquid crystal layer 905 can be made thinner than the surface layer in the conventional display device, so that the black characteristics can be greatly improved.

  According to the present invention, it is possible to provide a reflective liquid crystal display device in which the aperture ratio and the light utilization efficiency are improved while maintaining the alignment stability of the liquid crystal. Since the reflective liquid crystal display device of the present invention has a high display characteristic, it is possible to realize a display with higher quality than before.

  The present invention is suitably applied to a retroreflective liquid crystal display device provided with a reflective layer having retroreflective characteristics.

(A) is a cross-sectional schematic diagram which shows the structure of the conventional retroreflection type liquid crystal display device, (b) is a top view of the reflective electrode in the display apparatus of Fig.1 (a). (A)-(c) is a figure which shows the structure of the reflection type liquid crystal display device by this invention, (a) is a top view, (b) and (c) are 2b-2b 'sectional drawing and It is 2c-2c 'sectional drawing. (A)-(e) can be process sectional drawing for demonstrating an example of the manufacturing method of the back substrate in this invention. (A) And (b) is the top view and 4b-4b 'sectional drawing which respectively show the structure of the back substrate in 1st Embodiment by this invention. (A)-(c) is a top view for demonstrating the formation process of the back substrate in 1st Embodiment by this invention. (A)-(c) is 6a-6a ', 6b-6b', and 6c-6c 'sectional drawing of Fig.5 (a)-(c), respectively. It is a top view for demonstrating the shape of the pixel electrode in the conventional retroreflection type liquid crystal display device. It is a top view for demonstrating the shape of the pixel electrode in the retroreflection type liquid crystal display device of 1st Embodiment by this invention. (A) And (b) is a figure for demonstrating operation | movement in the conventional retroreflection type liquid crystal display device. (A) And (b) is a figure for demonstrating the operation | movement in the retroreflection-type liquid crystal display device of 1st Embodiment. (A)-(j) is process sectional drawing for demonstrating the other production methods of the back substrate in 1st Embodiment. (A)-(i) is process sectional drawing for demonstrating the further another manufacturing method of the back substrate in 1st Embodiment. (A) And (b) is the top view and 13b-13b 'sectional view which respectively show the structure of the back substrate in 2nd Embodiment by this invention. (A) And (b) is a figure for demonstrating operation | movement in the conventional diffuse reflection type liquid crystal display device. (A) And (b) is a figure for demonstrating the operation | movement in the diffuse reflection type liquid crystal display device of 2nd Embodiment. (A) And (b) is an expansion schematic diagram for demonstrating the relationship between the design value of the width | variety of the pixel electrode in a conventional retroreflection-type liquid crystal display device, and an actual value. (A) And (b) is an enlarged schematic diagram for demonstrating the relationship between the design value of the width | variety of the pixel electrode in the retroreflection-type liquid crystal display device of 1st Embodiment, and an actual value.

Explanation of symbols

200 retroreflective display device 201 TFT substrate 201s active switch layer 201t TFT (switching element)
203 Drain electrode 204 Contact hole 205 Reflective layer 206 Flattening resin layer 207 Pixel electrode 209 Rear substrate 210 Front substrate 211 Transparent counter electrode 212, 218 Alignment film 213 Liquid crystal layer (modulation layer)
219 Color filter 220 opening

Claims (14)

An active switch layer including a plurality of switching elements;
A plurality of pixel electrodes each connected to a corresponding switching element;
A reflective layer formed between the active switch layer and the plurality of pixel electrodes;
A modulation layer that is provided on the viewer side of the pixel electrode and can be switched between a first state and a second state having different optical characteristics;
The reflection type display device, wherein the reflection layer is not connected to the plurality of switching elements and the plurality of pixel electrodes.   The reflective display device according to claim 1, wherein the reflective layer exists under a gap between adjacent pixel electrodes.   The reflective display device according to claim 1, wherein the reflective layer is not separated in units of pixels.   The reflective layer has a plurality of openings, and the plurality of pixel electrodes and the corresponding switching elements are connected via corresponding openings of the reflective layer. The reflective display device according to any one of the above.   A plurality of contact portions for connecting the plurality of pixel electrodes and the corresponding switching elements; the plurality of contact portions are provided through corresponding openings in the reflective layer; and the diameter of the contact portion is The reflective display device according to claim 1, wherein the reflective display device is smaller than a diameter of the opening.   The reflective display device according to claim 1, wherein the reflective layer has retroreflective properties.   The reflective layer according to claim 6, wherein the reflective layer has a structure in which a plurality of unit structures are two-dimensionally arranged, and a gap between adjacent pixel electrodes is not aligned with the unit structure of the reflective layer. Reflective display device.   The reflective display device according to claim 7, wherein the unit structure of the reflective layer is a cubic corner cube. Each pixel electrode has a substantially rectangular planar shape, and the arrangement pitch in the short side direction of the pixel electrode is P _{pix (S)} , and the arrangement pitch in the long side direction of the pixel electrode is P _{pix (L).} If the corner cube pitch is _Pcc ,
Claims satisfying ((√3) / 6 × P _{pix (L)} × P _cc + P _{pix (S)} × P _cc / 2) / (P _{pix (L)} × P _{pix (S)} )> 0.005 9. A reflective display device according to 8. Each pixel electrode has a substantially rectangular planar shape, and the arrangement pitch in the short side direction of the pixel electrode is P _{pix (S)} , and the arrangement pitch in the long side direction of the pixel electrode is P _{pix (L).} If the corner cube pitch is _Pcc ,
Claims satisfying ((√3) / 6 × P _{pix (L)} × P _cc + P _{pix (S)} × P _cc / 2) / (P _{pix (L)} × P _{pix (S)} )> 0.01 9. A reflective display device according to 8. When the pixel electrode pitch is P _pix and the corner cube pitch is P _cc ,
The reflective display device according to claim 8, wherein ((√3) +3) / 6 × P _cc / P _pix > 0.005 is satisfied. When the pixel electrode pitch is P _pix and the corner cube pitch is P _cc ,
The reflective display device according to claim 8, wherein ((√3) +3) / 6 × P _cc / P _pix > 0.01 is satisfied.   The reflective display device according to claim 6, wherein the modulation layer can be switched between a light scattering state and a light transmission state. Preparing a substrate on which an active switch layer including a plurality of switching elements is formed;
Forming an insulating layer on the active switch layer;
Forming a reflective layer having a plurality of openings on the insulating layer;
Forming a planarizing resin layer on the reflective layer;
Forming a plurality of pixel electrodes each connected to a corresponding switching element on the planarizing resin layer;
Providing a modulation layer on the pixel electrode that can be switched between a first state and a second state having different optical characteristics,
Each pixel electrode is a manufacturing method of a reflective display device in which each pixel electrode is connected to the switching element through the opening of the reflective layer.

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