JP2004264876A - Liquid crystal display device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a liquid crystal display device which obtains a wide angle-of-view characteristic and improves the reduction of electric power consumption. <P>SOLUTION: The liquid crystal display device is so constituted that the angle of visibility can be narrowed when there is a need for displaying personal information or secret information in the form of videos. <P>COPYRIGHT: (C)2004,JPO&NCIPI

Description

  The present invention relates to a liquid crystal display device, and more particularly to a so-called backlight type liquid crystal display device.

  A color liquid crystal display device called a so-called backlight system is configured by arranging a backlight unit on the back surface of a liquid crystal display panel having a pair of transparent substrates disposed opposite to each other via a liquid crystal layer as an envelope. ing.

  The liquid crystal display panel has, on its main surface, a display section in which a large number of pixels capable of independently controlling the degree of light transmission are arranged in a matrix in the liquid crystal layer. It is configured so that light emitted from the backlight unit can be transmitted.

  However, the liquid crystal display device configured as described above has one of its advantages in that it has low power consumption, and a configuration for further lowering power consumption is demanded.

  On the other hand, in recent years, there has been known a liquid crystal display device which is capable of recognizing a clear image even when observed from a large angle field of view with respect to its display surface, and is excellent in a so-called wide angle field of view.

  In this case, observation at a wide viewing angle in such a liquid crystal display device is effective when necessary. For example, when a small number of observers observe in front without moving, the effectiveness is not so large. It will not be demonstrated.

  The present invention has been made based on such circumstances, and an object of the present invention is to provide a liquid crystal display device that achieves both low power consumption and a wide-angle view.

  The following is a brief description of an outline of typical inventions disclosed in the present application.

  That is, in a liquid crystal display device including a backlight unit and a liquid crystal display panel having a wide viewing angle characteristic for transmitting light from the backlight unit, the backlight unit has a configuration in which the brightness can be varied. An optical element is disposed between the backlight unit and the liquid crystal display panel, and the optical element is configured to be capable of varying the degree of scattering of light from the backlight unit to the liquid crystal display panel. Is what you do.

  The liquid crystal display device configured as described above is configured so that the brightness of the backlight unit and the light scattering property of the optical element can be changed.

  Therefore, for example, when a small number of observers observe the liquid crystal display device while moving, or when a large number of observers observe the liquid crystal display device without moving, the brightness of the backlight is increased. At the same time, by increasing the degree of light scattering of the optical element, the liquid crystal display device can be observed and its wide viewing angle characteristics can be fully utilized.

  In particular, when the wide viewing angle characteristic of the liquid crystal display device is not required, for example, when a small number of observers observe the liquid crystal display device without moving, the brightness of the backlight is reduced and the light of the optical element is reduced. The degree of scattering can be reduced.

  In any of the above cases, the observer can recognize that the image on the liquid crystal display panel surface has substantially uniform luminance.

  Therefore, when observing the liquid crystal display device in a state where the wide viewing angle characteristic is not required, the power consumption required for the backlight unit can be reduced by reducing the luminance of the backlight unit.

  As is clear from the above description, according to the liquid crystal display device of the present invention, it is possible to obtain a wide viewing angle characteristic and to improve the power consumption.

Embodiment 1 FIG.
FIG. 2 is a schematic configuration diagram showing one embodiment of the liquid crystal display device according to the present invention.

  In FIG. 1, there is a so-called active matrix type liquid crystal display panel 100 first. The liquid crystal display panel 100 is configured such that its display unit is constituted by a set of a plurality of pixels arranged in a matrix, and each pixel is capable of independently controlling the modulation of transmitted light from a backlight unit 300 described later. Have been.

  The light modulation in each pixel employs a method called a so-called lateral electric field method, and the structure thereof will be described in detail later, but the light modulation is generated in a liquid crystal layer interposed between transparent substrates disposed to face each other. The electric field to be applied is parallel to the transparent substrate.

  Such a liquid crystal display panel 100 is known to be capable of recognizing clear images even when viewed from a large angle field of view with respect to its display surface, and to be excellent in a so-called wide angle field of view.

  The liquid crystal display panel 100 includes a vertical scanning circuit 5 and a video signal driving circuit 6 as external circuits, and the vertical scanning circuit 5 sequentially supplies a scanning signal (voltage) to each of the scanning signal lines 2. The video signal drive circuit 6 supplies a video signal (voltage) to the video signal line 3 in accordance with the timing.

  Power is supplied to the vertical scanning circuit 5 and the video signal driving circuit 6 from the liquid crystal driving power supply circuit 7, and image information from the CPU 8 is divided into display data and control signals by the controller 9 and input. It has become.

  In addition, the liquid crystal display panel 100 having the above-described configuration is particularly provided with the reference signal line 4, and the reference voltage signal applied to the reference signal line 4 is also supplied from the liquid crystal drive power supply circuit 7.

  A backlight unit 300 is disposed on the rear surface of the liquid crystal display panel 100 via an optical element 200. Light from the backlight unit 300 irradiates the liquid crystal display panel 100 via the optical element 200. It is supposed to.

  Although the configuration of the optical element 200 will be described in detail later, the optical element 200 has a function of changing the degree of light scattering of light irradiation from the backlight unit 300 to the liquid crystal display panel 100, and the degree of light scattering is controlled by the drive voltage application circuit 40. Is to be done. The voltage applied to the optical element 200 via the drive voltage application circuit 40 is controlled by the viewing angle controller 60.

  The backlight unit 300 includes a backlight power supply circuit 50 for applying a voltage to a cold cathode ray tube constituting a part of the backlight unit 300. The voltage applied to the cold cathode ray tube via the backlight power supply circuit 50 has a viewing angle. It is controlled by the controller 60. Thereby, the brightness of the backlight unit 300 itself can be changed.

  Next, an embodiment of a method of using the liquid crystal display device having such a configuration will be described with reference to FIG.

  FIG. 3A is a side view showing a state of an optical path when light from the backlight unit 300 passes through the liquid crystal display panel 100 via the optical element 200, and FIG. 3A shows a low power consumption mode (low power consumption mode). (B) shows a wide viewing angle mode (mode in which a wide viewing angle is prioritized).

Low power consumption mode In this case, the illuminance is reduced by reducing the power supply to the backlight unit 300, and at the same time, the drive voltage to the optical element 200 is set to a predetermined value, and the light scattering property is completely eliminated. .

In such a case, as shown in FIG. 6 (a), light from the backlight unit 300, as it passes through the optical element 200, the liquid crystal has a spread in the drawing theta ₁ (emission angle theta ₁₎ The light will pass through the display panel 100.

  When the liquid crystal display device is observed in front of the liquid crystal display device without moving, for example, a small number of observers, the liquid crystal display device does not particularly require characteristics of a wide viewing angle. It becomes.

  Thus, the liquid crystal display device can be driven with low power consumption.

Wide viewing angle mode In this case, by increasing the power supply to the backlight unit 300, the brightness is increased, and at the same time, the driving voltage to the optical element 200 is made lower than the predetermined value, and the light scattering is made high. .

In this case, the light from the backlight 300 is scattered by the optical element 200 and has a spread of θ ₂ (radiation angle θ ₂ ) in the drawing, as shown in FIG. 100 will be transmitted.

  In front of the liquid crystal display device, for example, when a small number of observers observe the liquid crystal display device while moving, or when a large number of observers observe the liquid crystal display device without moving, particularly in the liquid crystal display device. Since a wide viewing angle characteristic is required, it is sufficient to use this mode when necessary.

  Thus, the liquid crystal display device can be driven at a wide viewing angle.

  FIG. 11 shows the change in the degree of scattering of the optical element 200 described above, and the brightness of the liquid crystal display panel 100 at the front (not the brightness of the backlight unit 300 itself, but the brightness of the surface of the liquid crystal display panel 100 recognized by the observer). 6 is a graph showing the relationship between power consumption (W) and light emission angle (θ) when the supply voltage to the backlight unit 300 is changed so as to be constant. Here, the radiation angle θ is defined as an angle including an angle range in which the luminance of light is 50% or more of the front luminance.

  In this case, it was confirmed that 150 was achieved as the front contrast ratio. In addition, it was confirmed that the viewing angle under the condition that the contrast ratio was 10 or more exceeded 70 ° in each of the vertical and horizontal directions.

  Further, the viewing angle controller 60 shown in FIG. 2 controls the change in the luminance of the backlight unit 300 and the change in the degree of light scattering of the optical element 200 by the operation of the operator (observer), for example, in the relationship shown in FIG. The control signals are transmitted to the drive voltage application circuit 40 and the backlight power supply circuit 50.

  In this case, the operation performed by the operator on the viewing angle controller 60 includes, for example, the case where the luminance of the backlight unit 300 is reduced and the degree of light scattering of the optical element 200 is reduced, and the case where the luminance of the backlight unit 300 is increased and The operation may be performed in two stages, that is, when the degree of light scattering of the element 200 is increased. In addition, the present invention is not limited to this. In the case where the luminance of the backlight unit 300 is reduced and the degree of light scattering of the optical element 200 is reduced, the luminance of the backlight unit 300 is increased and the degree of light scattering of the optical element 200 is increased. Needless to say, the operation may be performed linearly and continuously until the operation is performed.

  The above-described operation by the operator is performed by, for example, a view angle adjustment switch or the like, and the view angle controller 60 is driven by an output from the view angle adjustment switch, whereby a simple configuration can be achieved. .

  Further, it goes without saying that the variable brightness of the backlight unit 300 and the variable degree of light scattering of the optical element 200 may be independently operated.

  Hereinafter, an embodiment of a specific configuration of the liquid crystal display panel 100, the optical element 200, and the backlight unit 300 will be sequentially described.

[Liquid crystal display panel 100]
As shown in FIG. 3, there is a liquid crystal display panel 100, and one of the transparent substrates 1A and 1B disposed opposite each other via the liquid crystal of the liquid crystal display panel 100 has its x A scanning signal line 2 and a reference signal line 4 extending in the direction (row direction) and juxtaposed in the y direction (column direction) are formed.

  In this case, in this figure, from above the transparent substrate 1A, a reference signal line 4, a scanning signal line 2 relatively separated from the reference signal line, a reference signal line 4 close to the scanning signal line 2, The scanning signal lines 2, which are relatively spaced apart from the reference signal line 4, are arranged sequentially.

  Further, a video signal line 3 which is insulated from the scanning signal line 2 and the reference signal line 4 and extends in the y direction and is juxtaposed in the x direction is formed.

  Here, a rectangular region having a relatively large area surrounded by each of the scanning signal line 2, the reference signal line 4, and the video signal line 3 is a region where a unit pixel is formed. And constitute a display surface.

  FIG. 4 is a plan view showing an embodiment of the unit pixel (corresponding to a region surrounded by a dotted line in FIG. 3). FIG. 5 is a sectional view taken along line VV of FIG. 4, FIG. 6 is a sectional view taken along line VI-VI, and FIG. 7 is a sectional view taken along line VII-VII.

  In FIG. 4, on a main surface of a transparent substrate 1A, a reference signal line 4 extending in the x-direction, and a scanning signal line 2 spaced from and parallel to the reference signal line 4 are formed.

  Here, three reference electrodes 14 are formed integrally with the reference signal line 4. That is, two of the reference electrodes 14 are in the y-direction side of the pixel region formed by the pair of video signal lines 3 described later, that is, in the (−) y direction in proximity to the respective video signal lines 3. It is formed to extend to the vicinity of the scanning signal line 2, and the remaining one is formed between them.

  The surface of the transparent substrate 1A on which the scanning signal lines 2, the reference signal lines 4, and the reference electrodes 14 are formed covers the scanning signal lines 2 and the like, and covers the insulating film 15 made of, for example, a silicon nitride film (FIG. 5). , FIG. 6, FIG. 7). This insulating film 15 accumulates as an interlayer insulating film at an intersection with the scanning signal line 2 and the reference signal line 4 for a video signal line 3 described later, and as a gate insulating film for a region where the thin film transistor TFT is formed. The region where the capacitance Cstg is formed functions as a dielectric film.

  On the surface of the insulating film 15, first, a semiconductor layer 16 is formed in a region where the thin film transistor TFT is formed. The semiconductor layer 16 is made of, for example, amorphous Si, and is formed on the scanning signal line 2 so as to overlap with a portion close to the video signal line 3. Thus, a part of the scanning signal line 2 also serves as a gate electrode of the thin film transistor TFT.

  Then, on the surface of the insulating film 15 thus formed, as shown in FIG. 4, the video signal lines 3 extending in the y direction and juxtaposed in the x direction are formed.

  The video signal line 3 is integrally provided with a drain electrode 3A formed to extend to a part of the surface of the semiconductor layer 16 of the thin film transistor TFT.

  Further, a display electrode 18 is formed on the surface of the insulating film 15 in the pixel region. The display electrode 18 is formed so as to run between the reference electrodes 14. That is, one end of the display electrode 18 also serves as the source electrode 18A of the thin film transistor TFT, extends in the (+) y direction as it is, further extends in the x direction along the reference signal line 4, and then (-) It has a U-shape extending in the direction and having the other end.

  In this case, a portion of the display electrode 18 that overlaps with the reference signal line 4 forms a storage capacitor Cstg including the insulating film 15 as a dielectric film between the display electrode 18 and the reference signal line 4. The storage capacitor Cstg has an effect of storing video information on the display electrode 18 for a long time when, for example, the thin film transistor TFT is turned off.

  The surface of the semiconductor layer 16 corresponding to the interface between the drain electrode 3A and the source electrode 18A of the thin-film transistor TFT is doped with phosphorus (P) to form a high concentration layer. I am trying to make a contact. In this case, the high-concentration layer is formed over the entire surface of the semiconductor layer 16, and after forming each of the electrodes, the high-concentration layers other than the electrode formation region are etched using the electrodes as a mask. The above configuration can be adopted.

  The protective film 19 made of, for example, a silicon nitride film is formed on the upper surface of the insulating film 15 on which the thin film transistor TFT, the video signal line 3, the display electrode 18, and the storage capacitor Cstg are formed (FIGS. 5, 6, and 7). ) Is formed, and an alignment film 20 is formed on the upper surface of the protective film 19 to constitute a lower substrate of the liquid crystal display panel 100. Note that a polarizing plate 21 is disposed on a surface of the lower substrate opposite to the liquid crystal layer side.

  Then, as shown in FIG. 5, a light-shielding film 22 is formed on a portion on the liquid crystal side of the transparent substrate 1B serving as the upper substrate, as shown in FIG. The light-shielding film 22 has a function of preventing the thin film transistor TFT from being directly irradiated with light and a function of improving display contrast. The light-shielding film 22 is formed in a region indicated by a broken line in FIG. 4, and an opening formed therein constitutes a substantial pixel region.

  Further, a color filter 23 is formed so as to cover the opening of the light-shielding film 22. The color filter 23 has a different color from that of the adjacent pixel region and has a boundary on the light-shielding film 22. ing. A flat film 24 made of a resin film or the like is formed on the surface on which the color filters 23 are formed, and an alignment film 25 is formed on the surface of the flat film 24. Note that a polarizing plate 26 is disposed on the surface of the upper substrate opposite to the liquid crystal layer side.

  Here, the relationship between the alignment film 20 and the polarizing plate 21 formed on the transparent substrate 1A side and the relationship between the alignment film 25 and the polarizing plate 26 formed on the transparent substrate 1B side will be described with reference to FIG.

  The angle of the rubbing direction 208 of each of the alignment films 20 and 25 with respect to the direction 207 of the electric field applied between the display electrode 18 and the reference electrode 14 is φLC. The angle of one polarizing plate 21 in the polarization transmission axis direction 209 is φP. The polarization transmission axis of the other polarizing plate 26 is orthogonal to φP. ΦLC = φP. As the liquid crystal layer LC, a nematic liquid crystal composition having a positive dielectric anisotropy Δε, a value of 7.3 (1 kHz), and a refractive index anisotropy Δn of 0.073 (589 nm, 20 ° C.) is used. Used.

  The configuration of the alignment films 20 and 25 and the polarizing plates 21 and 26 and the like having such a relationship is what is called a normally black mode, and generates an electric field E parallel to the transparent substrate 1A in the liquid crystal layer LC. This allows light to pass through the liquid crystal layer LC. However, in this embodiment, the present invention is not limited to such a normally black mode, and it goes without saying that a normally white mode in which light passing through the liquid crystal layer LC when no electric field is applied may be maximum. Absent.

[Optical element 200]
FIG. 9A is a cross-sectional view illustrating details of the optical element 200. First, a polymer-dispersed liquid crystal 201 is interposed between a pair of transparent substrates 200A and 200B which are substantially the same size as the liquid crystal panel 100 and are arranged to face each other. Transparent electrodes 202A and 202B are formed over the entire surface of each of the transparent substrates 200A and 200B on the side of the polymer dispersed liquid crystal 201 so that a voltage can be applied to each of the transparent electrodes 202A and 202B. It has become.

  FIG. 3A shows a light transmission state in the polymer dispersed liquid crystal 201 by applying a predetermined voltage between the transparent electrodes 201A and 201B. That is, when a predetermined voltage is applied, each molecule of the polymer dispersed liquid crystal 201 is oriented in the voltage direction, and the incident light 203 is emitted through the polymer dispersed liquid crystal without being scattered.

  In this case, it has been confirmed that the optical element is composed of only the above-described elements and does not include, for example, a polarizing plate or the like, so that about 80% of the incident light can be transmitted.

  FIG. 2B shows the light transmission state of the polymer dispersed liquid crystal 201 by reducing the value of the voltage applied between the transparent electrodes 202A and 202B. That is, as the value of the applied voltage decreases, the orientation of the molecules of the polymer dispersed liquid crystal becomes random, and the incident light 203 is scattered and emitted. This means that the viewing angle of light from the backlight unit 300 can be expanded by the optical element 200.

[Backlight unit 300]
FIG. 10 is a cross-sectional view showing details of the backlight unit 300. In the figure, first, there is a light guide plate 301. The light guide plate 301 is made of a transparent plate material having substantially the same size as the liquid crystal display panel 100, and a cold cathode ray tube 302 is arranged along one end face of the light guide plate 301, and all the light from the cold cathode ray tube 302 A reflection plate 303 is attached so that light can enter the light guide plate 301 from the one end surface side.

  A reflector (not shown) is provided on a surface of the light guide plate 301 farther from the liquid crystal display panel, so that the light from the cold cathode ray tube 302 guided into the light guide plate 301 is transmitted to the liquid crystal display panel. Uniform light is irradiated from the main surface side opposed to the entire surface.

  It is to be noted that the power supplied to the cold cathode ray tube 302 is variable as described above.

Embodiment 2. FIG.
In this embodiment, as shown in FIG. 12, a prism sheet 400 is particularly arranged on the surface of the backlight unit 300 on the liquid crystal display panel 100 side, that is, on the main surface of the light guide plate 301 shown in FIG. .

  The prism sheet 400 is made of, for example, a sheet made of a resin material such as acrylic, and formed with countless triangular pyramid-shaped protrusions on the surface thereof. Light incident from the back side is collected and emitted to the front side. It is configured so that

  In such a configuration, since the light from the backlight unit 300 can be effectively used to the optical element 200 without waste, the effect of reducing the power consumption of the backlight unit 300 in addition to the effect of the first embodiment. To play.

Embodiment 3 FIG.
FIG. 13 shows another embodiment and corresponds to FIG. 2 is different from that of FIG. 2 in that an internal power supply (battery) can be used in addition to the external power supply as the liquid crystal display device, and the external power supply and the internal power supply are used as the power supply for driving the liquid crystal display device. An input power supply monitoring circuit 70 for determining which power supply is used is provided, and the power supply identification information is input to the viewing angle controller 60.

  Then, the viewing angle controller 60 to which the power supply identification information is input automatically switches between the low power consumption mode and the wide viewing angle mode.

  That is, when an external power supply is used, the power consumption of the external power supply is not so noticeable. Therefore, the viewing angle controller 60 is designed to improve the brightness of the backlight unit 300 and the light scattering property of the optical element 200. Is activated. When an internal power supply is used, the power consumption of the power supply is anxious, so that the viewing angle controller 60 reduces the brightness of the backlight unit 300 and the light scattering property of the optical element 200. It is supposed to work.

  With this configuration, the user does not need to be particularly conscious, and gives priority to the wide viewing angle mode when using an external power supply with relatively few restrictions on power consumption, and to lower power consumption. When the internal power supply is used, the mode automatically switches to the low power consumption mode.

  Therefore, in addition to the effects shown in the first embodiment, convenience for the user can be improved.

Embodiment 4. FIG.
In this embodiment, the liquid crystal display device shown in the third embodiment is particularly configured as a notebook PC. FIG. 14 is an external view showing a configuration of a liquid crystal display device of a notebook PC. The liquid crystal display device of the notebook PC has the advantage that its liquid crystal display panel 100 (having the backlight unit 300 built therein) and the keyboard 500 are foldably integrated and its portability is an advantage. An external power supply, which is a commercial power supply, can be used, and a built-in power supply (internal power supply: battery) can be used.

  With such a configuration, power consumption can be suppressed, particularly when a battery must be used.

  Therefore, the effects of wide viewing angle characteristics and low power consumption can be obtained as required.

Embodiment 5 FIG.
In this embodiment, the liquid crystal display device shown in the first embodiment is particularly configured as a liquid crystal monitor. Here, the liquid crystal monitor is configured for the purpose of allowing a large number of observers to observe, and thus the liquid crystal display panel 100 is considerably larger than that of a normal liquid crystal display device.

  The liquid crystal monitor is provided with a viewing angle adjustment switch 600, and the operation of the viewing angle adjustment switch 600 controls the viewing angle controller 60 as described in the first embodiment.

  The liquid crystal monitor configured as described above can perform operations such as narrowing the viewing angle when it is necessary to display personal information or confidential information, and can manage information security.

FIG. 1 is a basic conceptual diagram showing one embodiment of a liquid crystal display device according to the present invention. FIG. 2 is a block diagram showing one embodiment of a liquid crystal display device according to the present invention. FIG. 2 is a schematic plan view showing one embodiment of a liquid crystal display panel used in the liquid crystal display device according to the present invention. FIG. 2 is a plan view showing one embodiment of one pixel of a liquid crystal display panel used in the liquid crystal display device according to the present invention. FIG. 5 is a sectional view taken along line VV in FIG. 4. FIG. 6 is a sectional view taken along line VI-VI of FIG. 4. FIG. 7 is a sectional view taken along line VII-VII in FIG. 4. FIG. 4 is a diagram showing a relationship between an alignment film and a polarizing plate of a liquid crystal display panel used in a liquid crystal display device according to the present invention. FIG. 2 is a configuration diagram showing one embodiment of an optical element used in the liquid crystal display device according to the present invention. FIG. 3 is a configuration diagram showing one embodiment of a backlight unit used in the liquid crystal display device according to the present invention. 4 is a graph illustrating a relationship between power consumption of a backlight unit and a light emission angle due to scattering of an optical element. It is an explanatory view showing another embodiment according to the present invention. It is an explanatory view showing another embodiment according to the present invention. It is an explanatory view showing another embodiment according to the present invention. It is an explanatory view showing another embodiment according to the present invention.

Explanation of reference numerals

100 liquid crystal display panel, 200 optical element, 300 backlight unit, 40 driving voltage application circuit, 50 backlight power supply circuit, 60 viewing angle controller.

Claims (8)

A liquid crystal display device that narrows the viewing angle when it is necessary to display personal information or confidential information. A liquid crystal display device capable of reducing the viewing angle when it is necessary to display personal information or secret information. A liquid crystal display device that can control the security of information by narrowing the viewing angle when it is necessary to display personal information or secret information. A liquid crystal display device that can operate to narrow the viewing angle when personal information or confidential information needs to be displayed, and can manage the security of information. A liquid crystal monitor that narrows the viewing angle when it is necessary to display personal or confidential information. A liquid crystal monitor that can be operated to narrow the viewing angle when it is necessary to display personal or confidential information. A liquid crystal monitor that can narrow the viewing angle and control the security of information when it is necessary to display personal or confidential information. A liquid crystal monitor that can operate to narrow the viewing angle when it is necessary to display personal or confidential information, and can manage the security of information.

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