Abstract:
The present invention provides a liquid crystal display device which can prevent a phenomenon that an abnormal picture-frame-like frame is displayed outside an effective display region of a liquid crystal display panel even when burrs are generated in a dicing step. A liquid crystal display device is provided with a liquid crystal display panel which includes a pair of substrates constituted of a first substrate and a second substrate, and a liquid crystal layer which is sandwiched between the pair of substrates, wherein the first substrate includes a common electrode on a surface thereof which faces the second substrate in an opposed manner, the second substrate includes a plurality of reflective electrodes, a first conductive film which is arranged to surround a periphery of the plurality of reflective electrodes, and a second conductive film which is arranged to surround a periphery of the first conductive film, a common voltage which is applied to the common electrode is applied to the first conductive film, and a reference voltage (GND) is applied to the second conductive film.

Description:
BACKGROUND OF THE INVENTION  
       [0001]     1. Field of the Invention  
         [0002]     The present invention relates to a liquid crystal display device and a projector, and more particularly to a liquid crystal display device which uses a reflective liquid crystal display panel and a projector.  
         [0003]     2. Description of the Related Art  
         [0004]     As a liquid crystal display device used for a projector, there has been known a reflective liquid crystal display device (see JP-A-2003-271108 (liquid crystal display device)).  
         [0005]     As one of the reflective liquid crystal display devices, there has been known a liquid crystal display device which adopts an electrically controlled birefringence mode.  
         [0006]      FIG. 6  is a view for explaining a single polarizer twisted nematic mode (SPTN) which is one of the electrically controlled birefringence modes.  
         [0007]     As shown in the drawing, an incident light L 1  from a light source (not shown in the drawing) is divided into two polarized lights by a polarization beam splitter  15  and light L 2  which is constituted of a linearly polarized light is radiated.  
         [0008]     As shown in  FIG. 6A , when a voltage is not applied to liquid crystal, the light which is incident on a liquid crystal panel  100  becomes an elliptically polarized light due to the birefringence of a liquid crystal composition  3  and becomes a circularly polarized light on a reflection electrode  5 . The light which is reflected on the reflection electrode  5  passes through the liquid crystal composition  3  again and becomes the elliptically polarized light, and returns to the linearly polarized light at the time of irradiation, and is radiated as a light L 3  (Spolarized wave) which has a phase thereof rotated by 90 degrees with respect to the incident light L 2 . Although the radiation light L 3  is incident on the polarized beam splitter  15  again, the radiation light L 3  is reflected on a polarization surface and becomes an irradiation light L 4 . This irradiation light L 4  is radiated to a screen or the like for performing a display.  
         [0009]     The above constitutes a display method which is referred to as a so-called normally white (normally open) in which the light is radiated when the voltage is not applied to the liquid crystal.  
         [0010]     To the contrary, as shown in  FIG. 6B , when the voltage is applied to the liquid crystal composition  3 , liquid crystal molecules are aligned in the direction of an electric field and hence, a rate that the birefringence is generated in the inside of the liquid crystal is reduced. Accordingly, the light L 2  which is incident on the liquid crystal panel  100  as the linearly polarized light is directly reflected on the reflection electrode  5  as it is, and is radiated as a light L 5  having the same polarization direction as the incident light L 2 . The radiated light L 5  passes through the polarization beam splitter  15  and returns to the light source. Accordingly, the light is not radiated to the screen or the like thus performing a black display,  
       SUMMARY OF THE INVENTION  
       [0011]     The conventional reflective liquid crystal display device is configured such that liquid crystal is sandwiched between a transparent substrate (for example, a glass substrate) at a side on which the light is incident and a drive circuit substrate (for example, a silicon substrate) which includes a reflective electrode on which the incident light is reflected.  
         [0012]      FIG. 7  is a schematic plan view for explaining the drive circuit substrate of the conventional reflective liquid crystal display device. In the drawing, symbol AR indicates an effective display region in which pixels having reflective electrodes are arranged in a matrix array. A first conductive film  115  is formed around the effective display region (AR) in a state that the first conductive film  115  surrounds the effective display region (AR).  
         [0013]     A voltage of Vcom which is applied to a counter electrode is applied to the first conductive film  115 . Due to such a constitution, it is possible to prevent a phenomenon that a picture-frame-like irregular frame is displayed outside the effective display region due to the voltage difference between the first conductive film  115  and the counter electrode.  
         [0014]     In general, the reflective liquid crystal display device is manufactured by manufacturing a large number of above-mentioned constitutions on one sheet of silicon substrate and, thereafter, by cutting (dicing) the silicon substrate.  
         [0015]     However, when burrs are generated in such a dicing step, the first conductive film  115  which is formed in a state that the first conductive film  115  surrounds the effective display region (AR) and a conductive layer (for example, a GND wiring layer) which is formed on the drive circuit substrate and to which a reference voltage (GND) is applied are short-circuited due to such burrs and hence, there exists a possibility that the reference voltage (GND) is applied to the first conductive film  115 .  
         [0016]     Then, when the first conductive film  115  and a conductive layer which is formed in a drive circuit substrate and to which the reference voltage (GND) is applied are short-circuited due to the burrs which are produced in the dicing step, the reference voltage (GND) is applied to the first conductive film  115 .  
         [0017]     Accordingly, there has been a drawback that a frame-like abnormal frame is displayed outside the effective display region of the reflective liquid crystal display device thus deteriorating a display quality of the reflective liquid crystal display device.  
         [0018]     The present invention has been made to overcome the above-mentioned drawback of the prior art and it is an object of the present invention to provide a technique which can prevent the displaying of an abnormal picture-frame-like frame outside an effective display region of a liquid crystal display panel even when burrs are generated in a dicing step in a liquid crystal display device or a projector.  
         [0019]     The above-mentioned and other objects and novel features of the present invention will become apparent by the description of this specification and attached drawings.  
         [0020]     To briefly explain the typical inventions among the inventions described in this specification, they are as follows.  
         [0021]     To overcome the above-mentioned drawbacks of the related art, the present invention provides a liquid crystal display device which includes a liquid crystal display panel which has a pair of substrates constituted of a first substrate and a second substrate, and a liquid crystal layer which is sandwiched between the pair of substrates, wherein the first substrate includes a common electrode on a surface thereof which faces the second substrate in an opposed manner, the second substrate includes a plurality of reflective electrodes, a first conductive film which is arranged around the plurality of reflective electrodes such that the first conductive film surrounds the plurality of reflective electrodes, and a second conductive film which is arranged around the first conductive film such that the second conductive film surrounds the first conductive film on a surface thereof which faces the first substrate in an opposed manner, and a common voltage which is applied to the common electrode is applied to the first conductive film, and a reference voltage (GND) is applied to the second conductive film.  
         [0022]     Further, the present invention is directed to a projector which includes a light source, a plurality of liquid crystal display devices which modulate light radiated from the light source, and a screen on which the light which is modulated by the respective liquid crystal display devices is projected, wherein one of the plurality of liquid crystal display devices is constituted of the liquid crystal display device described above.  
         [0023]     To briefly explain advantageous effects obtained by the typical inventions disclosed in this specification, they are as follows.  
         [0024]     According to the liquid crystal display device and the projector of the present invention, it is possible to prevent a phenomenon that an abnormal picture-frame-like frame is displayed outside an effective display region of the liquid crystal display panel even when burrs are generated in a dicing step. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0025]      FIG. 1  is a block diagram showing a projector which uses three reflective liquid crystal display devices of R, G and B;  
         [0026]      FIG. 2  is a cross-sectional view showing the structure of the reflective liquid crystal display device of an embodiment of the present invention;  
         [0027]      FIG. 3  is a schematic plan view for explaining one example of a drive circuit substrate of the reflective liquid crystal display device of an embodiment of the present invention;  
         [0028]      FIG. 4  is a cross-sectional view for explaining a reason that a picture-frame-like frame is not displayed outside an effective display region even when burrs are generated in a dicing step in the reflective liquid crystal display device of the present invention;  
         [0029]      FIG. 5  is a schematic plan view for explaining another example of the drive circuit substrate of the reflective liquid crystal display device of the embodiment of the present invention;  
         [0030]      FIG. 6  is a view for explaining a single polarizer twisted nematic mode (SPTN) which constitutes one of electrically controlled birefringence modes;  
         [0031]      FIG. 7  is a schematic plan view for explaining a drive circuit substrate of a conventional reflective liquid crystal display device; and  
         [0032]      FIG. 8  is a cross-sectional view for explaining a reason that a picture-frame-like frame is displayed outside an effective display region when burrs are generated in a dicing step in the conventional reflective liquid crystal display device. 
     
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0033]     Hereinafter, embodiments of the present invention are explained in conjunction with attached drawings.  
         [0034]     Here, in all drawings for explaining an embodiment, parts having identical functions are given same symbols and their repeated explanation is omitted.  
         [0035]      FIG. 1  is a block diagram showing a projector which uses three reflective liquid crystal display devices of R, G and B and constitutes an embodiment of the present invention.  
         [0036]     As shown in the drawing, from a white light radiated from a lamp  10 , ultraviolet rays and infrared rays are removed using an IR filter  11  and a UV filter  12  thus producing a visible light necessary for a display.  
         [0037]     The visible light which passes through the UV filter  12  is subjected to the color separation of R, G, B by a dichroic mirror  13 , and the respective color-separated lights pass through respective polarizers ( 14 R,  14 G,  14 B), respective polarization beam splitters ( 15 R,  15 G,  15 B) and phase plates ( 16 R,  16 G,  16 B) and are incident on the reflective liquid crystal display devices ( 17 R,  17 G,  17 B).  
         [0038]     As mentioned previously, in case of the white display performed by the normally-white-method reflective liquid crystal display device, the linearly polarized light which is incident on the reflective liquid crystal display devices ( 17 R,  17 G,  17 B) becomes a circularly polarized light after passing a liquid crystal layer of a liquid crystal display panel and, thereafter, the circularly polarized light becomes a linearly polarized light which has a phase thereof rotated by 90° with respect to an incident polarization angle after passing through the liquid crystal layer again at the time of reflection.  
         [0039]     The linearly polarized lights which are radiated form the reflective liquid crystal display devices ( 17 R,  17 G,  17 B) pass through the polarization beam splitters ( 15 R,  15 G,  15 B) and half mirrors  18  and are subjected to color synthesis, and the synthesized light is projected to a projection screen  20  by way of a radiation lens  19 . Accordingly, an enlarged image is displayed on the projection screen  20 .  
         [0040]     Next, the structure of the reflective liquid crystal display device according to this embodiment is explained.  
         [0041]     In  FIG. 2 , numeral  100  indicates a liquid crystal display panel, numeral  1  indicates a drive circuit substrate which constitutes a second substrate, numeral  2  indicates a transparent substrate (for example, glass substrate) which constitutes a first substrate, numeral  3  indicates liquid crystal composition, and numeral  4  indicates spacers. The spaces  4  define a cell gap “d” which is a fixed distance between the drive circuit substrate  1  and the transparent substrate  2 . The liquid crystal composition  3  is sandwiched in this cell gap “d”.  
         [0042]     Numeral  5  indicates reflective electrodes (pixel electrodes) which are formed on the drive circuit substrate  1 . Numeral  6  indicates a counter electrode and a voltage is applied to the liquid crystal composition  3  between the counter electrode  6  and the reflective electrode  5 . Numerals  7 ,  8  are orientation films which align the liquid crystal molecules in fixed directions.  
         [0043]     Numeral  30  indicates an active element and supplies a gray scale voltage to the reflective electrode  5 . Numeral  34  indicates a source region of the active element  30 . Numeral  35  indicates a drain region of the active element  30 , and numeral  36  indicates a gate electrode of the active element  30 .  
         [0044]     Numeral  38  indicates an insulation film, numeral  31  indicates a first electrode which forms a pixel capacitance, and numeral  40  indicates a second electrode which forms a pixel capacitance. The first electrode  31  and the second electrode  40  form the capacitance by way of the insulation film  38 .  
         [0045]     Numeral  41  indicates a first interlayer film and numeral  42  indicates a first conductive film. The first conductive film  42  electrically connects the drain region  35  and the second electrode  40 .with each other. Numeral  43  indicates a second insulation film, numeral  44  indicates a first light blocking film, numeral  45  indicates a third insulation film, and numeral  46  indicates a second light blocking film. A through hole  42 CH is formed in the second interlayer film  43  and the third interlayer film  45  thus electrically connecting the first conductive film  42  and the second light blocking film  46 . Numeral  47  indicates a fourth interlayer film, numeral  48  indicates a second conductive film which forms the reflective electrode  5 , and numeral  49  indicates a conductive layer. A gray scale voltage is transmitted to the reflective electrode  5  from the drain region  35  of the active element  30  via the first conductive film  42 , the through hole  42 CH and the second light blocking film  46 .  
         [0046]     The liquid crystal display device of this embodiment is of a reflective type and the liquid crystal display panel  100  is irradiated with a large quantity of light. The light blocking film blocks the light such that the light is not incident on the semiconductor layers of the drive circuit substrate. In the reflective liquid crystal display device, the light which is radiated to the liquid crystal display panel  100  is incident from the transparent substrate  2  side (upper side in  FIG. 2 ), passes through the liquid crystal composition  3  and is reflected on the reflective electrode  5 , and again, passes through the liquid crystal composition  3  and the transparent substrate  2 , and is radiated form the liquid crystal display panel  100 .  
         [0047]     However, a portion of the light which is radiated to the liquid crystal display panel  100  leaks into the drive circuit substrate side from a gap between the reflective electrodes  5 . The first light blocking film  44  and the second light blocking film  46  are provided for preventing the light from being incident on the active element  30 .  
         [0048]     In this embodiment, the light blocking film is formed of a conductive layer, the second light blocking film  46  is electrically connected to the reflective electrode  5 , and a pixel potential control signal is supplied to the first light blocking film  44  thus allowing the light blocking film to function also as a part of the pixel capacitance.  
         [0049]     Further, in this embodiment, an opaque silicon substrate is used as the drive circuit substrate  1 . Accordingly, the active elements  30  and lines can be formed below the reflective electrodes  5  and hence, it is possible to obtain an advantage that the reflective electrodes  5  which constitute the pixels can be enlarged thus realizing the so-called high numerical aperture. Further, it is also possible to obtain an advantage that heat generated by the light radiated to the liquid crystal display panel  100  can be dissipated from a back surface of the drive circuit substrate  1 .  
         [0050]      FIG. 3  is a schematic plan view for explaining the drive circuit substrate of the reflective liquid crystal display device of this embodiment. In the drawing, symbol AR indicates an effective display region in which the pixels having the reflective electrodes are arranged in a matrix array. A first conductive film  115  is formed around the effective display region (AR) such that the first conductive film  115  surrounds the effective display region (AR).  
         [0051]     A voltage of Vcom which is applied to the counter electrode is applied to the first conductive film  115 . Accordingly, it is possible to prevent a phenomenon that an abnormal picture-frame-like frame is displayed outside the effective display region due to the voltage difference between the first conductive film  115  and the counter electrode.  
         [0052]     Further, in this embodiment, a second conductive film  116  is formed around the first conductive film  115  such that the second conductive film  116  surrounds the first conductive film  115 . A reference voltage (GND) is applied to the second conductive film  116 . Here, the first conductive film  115  and the second conductive film  116  are constituted of a metal film.  
         [0053]     As mentioned previously, the reflective liquid crystal display devices are manufactured by manufacturing a large number of liquid crystal display devices on one sheet of the silicon substrate and, thereafter, by cutting (dicing) the silicon substrate.  
         [0054]     However, as shown in  FIG. 8 , in the conventional reflective liquid crystal display panel, there may be a case that due to a burr  120  which is generated during a dicing step, a first conductive film  115  which is arranged to surround an effective display region and a conductive layer (for example, a GND wiring layer) (M 1 ) which is formed in the drive circuit substrate and to which a reverence voltage (GND) is applied are short-circuited. In such a case, the reference voltage (GND) is applied to the first conductive film  115  and hence, an abnormal picture-frame-like frame is displayed outside the effective display region of the reflective liquid crystal display device thus deteriorating the display quality of the reflective liquid crystal display device.  
         [0055]     Here,  FIG. 8  is a view showing the cross-sectional structure of a side of the drive circuit substrate  1  cut in the dicing step.  
         [0056]     However, in this embodiment, the second conductive film  116  is formed around the first conductive film  115  such that the second conductive film  116  surrounds the first conductive film  115  and, at the same time, the reference voltage (GND) is applied to the second conductive film  116 .  
         [0057]     Accordingly, as shown in  FIG. 4 , in this embodiment, even when the burr  120  is generated in the dicing step, a component which is short-circuited with the conductive layer (M 1 ) in the drive circuit substrate is the second conductive film  116  and hence, even when the burr  120  is generated in the dicing step, there is no possibility that the first conductive film  115  and the conductive layer (M 1 ) in the drive circuit substrate are short-circuited.  
         [0058]     Accordingly, in this embodiment, it is possible to eliminate a phenomenon that the abnormal picture-frame-like frame is displayed outside the effective display region of the reflective liquid crystal display device.  
         [0059]     Here,  FIG. 4  is a view showing the cross-sectional structure of a side of the drive circuit substrate  1  cut in the dicing step.  
         [0060]     Here, as is evident from the explanation described heretofore, it is not always necessary to apply the reference voltage (GND voltage) to the second conductive film  116 . Depending on cases, the voltage may not be applied to the second conductive film  116 .  
         [0061]     Further, the second conductive film  116  may not be formed in a strip shape provided that the second conductive film  116  is configured to surround the first conductive film  115 . For example, as shown in  FIG. 5 , the second conductive film  116  in a floating state may be formed around the conductive film  115  in an island shape. That is, the second conductive film  116  may be configured such that a plurality of island-like conductors are formed on each side such as an upper side in  FIG. 5 , while one island like conductor is formed on one side as in the case of the lower side in  FIG. 5 .  
         [0062]     Although the invention made by inventors of the present invention has been specifically explained in conjunction with the above-mentioned embodiments, it is needless to say that the present invention is not limited to the above-mentioned embodiments and various modifications can be made without departing from the gist of the present invention.