JP2002229021A - Backlight and display device using the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a backlight properly displaying a moving image and further maintaining the same quality as that of the conventional one is displaying a static image and a display device using the same. SOLUTION: The backlight provides display light to a display panel for image formation from the rear side and has a surface light-emitting element 3 and a light emission control means 7 for turning on/off of drive at least the surface light-emitting element 3, and the display device uses the backlight.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

[0001] 1. Field of the Invention [0002] The present invention relates to a backlight of a surface-emitting element and a display device using the same.

[0002]

2. Description of the Related Art In a conventional color liquid crystal display device, RGB display is performed by dividing pixels corresponding to RGB through a color filter and displaying them. At this time, a cold cathode tube, an LED, or the like is used as the backlight. These are constantly emitting light, and the backlight itself is merely a light source and does not function at all for display.

When a moving image, particularly a fast moving image, is displayed on a liquid crystal display device, an image is blurred and a moving trajectory is seen (tailing phenomenon), which is one of the causes of deterioration in display quality. I was It was thought that the main cause was that the inversion speed of the liquid crystal could not keep up with the television frame frequency. In other words, a signal of one frame is fetched, and the next signal is written before the display is not finished yet, so that a phenomenon in which fast moving pixels cannot catch up occurs. Therefore, image blur,
It has been thought that a tailing phenomenon occurs.

However, it has been reported that the tailing phenomenon does not disappear even when a liquid crystal having a sufficiently high liquid crystal inversion speed (display is completed within one frame) is used. This is because the active drive system, when receiving a signal of a certain frame, holds the signal until the next frame comes, and holds the display. As a method of improving this, a method of resetting the liquid crystal for a certain period of time without holding the entire frame has been proposed (SID9
8; P143-146).

[0005] However, this method requires a high-speed driver IC, which increases the cost. Japanese Patent Application Laid-Open No. 2000-275605 also proposes a method of dividing a backlight. However, in order to link a liquid crystal and the divided backlight, complicated control is required, which leads to an increase in cost.

[0006]

SUMMARY OF THE INVENTION An object of the present invention is to provide a CR
An object of the present invention is to provide a liquid crystal display device having a moving image display performance equivalent to that of T and a light source for realizing the same.

[0007]

That is, the above object is achieved by the following constitution of the present invention. (1) A backlight for providing display light from the back to a display panel on which an image is formed, the backlight having a surface light emitting element and light emission control means for driving at least the surface light emitting element on / off. (2) The backlight according to the above (1), wherein the light emission control means drives the surface light emitting element on / off in accordance with display switching of the display panel. (3) The backlight according to (2), wherein the light emission control unit is turned off at least at the time of switching the display. (4) The light emission control means further turns off the response delay period and / or the transition period.
Backlight. (5) The backlight according to any one of (1) to (4), wherein the light emission control unit can switch between pulse light emission and constant light emission by a display signal of a display panel. (6) The light emission control means performs on / off driving when the image signal displayed on the liquid crystal display panel is a moving image, and stops the on / off driving when the image signal is a still image.
The display device according to any one of (5). (7) The backlight according to any one of (1) to (6), wherein the surface light emitting element is a white light emitting EL element. (8) The backlight according to any one of the above (1) to (7), wherein the surface light emitting element is an organic EL element. (9) A display device having a liquid crystal display panel as a display panel and having the backlight according to any one of (1) to (8). (10) The display device according to (9), wherein the liquid crystal panel has a ferroelectric liquid crystal.

[0008]

DESCRIPTION OF THE PREFERRED EMBODIMENTS A backlight according to the present invention is a backlight for applying display light from the back to a display panel on which an image is formed. The backlight includes a surface light emitting element and at least a surface light emitting element on / off. And a light emission control unit to be driven.

As described above, a good image display can be performed by using the surface light emitting element for the backlight and driving it on and off. That is, by using the surface light emitting source, the display becomes uniform, and a high quality image can be obtained. In addition, by driving the backlight to turn on and off, a so-called tailing phenomenon or the like is suppressed, and favorable moving image display can be performed.

Next, the backlight of the present invention will be described with reference to the drawings. FIG. 1 is a block diagram showing the basic structure of the backlight of the present invention. The backlight of the present invention includes a surface light emitting element 3 serving as a backlight main body, a drive circuit 5, and a light emission control unit 7, as shown in the illustrated example. In addition, a liquid crystal panel 2 serving as a display screen, a drive circuit 4 and a display control means 6 are arranged in the backlight, and are integrated. Since the surface light emitting element 3 functions as a backlight of the liquid crystal panel 2, it is usually arranged in close contact with the back surface of the liquid crystal panel.

In the backlight having such a configuration,
When the image signal Vd is input, the display control means 6 generates a display signal required for display on the liquid crystal panel 2. This display signal is usually a scanning signal and a data signal applied to the scanning line and the data line in the case of TFT driving. Further, the display control means 6 can use a control circuit, a control IC, or the like used for normal liquid crystal driving.

On the other hand, part of the image signal Vd is also input to the light emission control means 7. This light emission control means performs the following control on the image signal input according to the mode.

(1) Simple ON / OFF drive (pulse drive). (2) The surface light emitting element is turned on / off following the display switching. That is, the display is turned off for a certain period when the display is switched. (3) In the above (2), at least the response delay period and / or the transition period are turned off.

In each of the above (2) and (3), the liquid crystal display itself performs the conventional line-sequential scanning.
By turning on and off the backlight, the apparent upper surface is sequentially scanned. In a holding type display using a TFT or the like, line-sequential scanning can display without flicker, but has a problem in displaying a moving image as described above. On the other hand, in the field sequential scanning, flicker may occur because the backlight is turned on and off (however, it can be solved by increasing the repetition period as described above), but a clear moving image plane can be displayed. .

According to the present invention, these switchings can be performed by the preference of the user or automatically with one backlight.

The above-mentioned control mode includes a liquid crystal panel to be used,
What is necessary is just to make it suitable according to the content of the display image, the specifications of the image display device, and the like.

The light emission control means for performing such control includes, for example, a signal processing circuit for analyzing the image signal Vd and extracting an image switching timing, and a timing for generating an on / off drive timing signal from the extracted image switching signal. It can be composed of a generation circuit, a clock circuit that can obtain a clock signal at a predetermined cycle, a synchronization circuit that generates an on / off signal in synchronization with an image signal using the obtained timing signal and clock signal, and the like. Further, a part of these circuits can be replaced by a processor and a control program, and the display control means 6 can also be used as a control circuit, a control IC, a control processor, and the like used for normal liquid crystal driving. it can.

Next, the driving method of each mode will be described in detail. (1) Simple ON / OFF driving (pulse driving) In this case, ON / OFF timing at the time of driving may or may not be synchronized with image switching timing. The ON / OFF cycle is preferably about 10 to 20 times the frame cycle.

For example, when an organic EL panel is used as a backlight, the permissible current can be increased by pulse driving as compared with the conventional continuous lighting method, so that the instantaneous luminance can be increased and a brighter display can be achieved. Becomes

At this time, dividing the light emitting section (EL panel section) into two or more areas has the following merits. For example, by forming two subdivided light-emitting portions in a comb shape interdigitated with each other and by pulse-driving each light-emitting portion alternately at a high speed, the load on each light-emitting portion is reduced. Moreover,
When viewed as a whole, the lighting state appears to be effectively continued, so that a bright display with no flicker can be realized. The timing of the pulse driving may be set to an optimum state based on, for example, the driving conditions of the EL panel and the driving circuit to be used.

Also, for example, an EL panel is manufactured so that the emission colors of the subdivided portions are different, and the user can freely adjust the color of the backlight by controlling the emission brightness of each area during driving. It can be set. Although this is possible without pulse driving, pulse driving is desirable to realize bright display.

(2) A case where the surface light emitting element is driven on / off following the display switching In this case, at least a period of 3 to 6 ms until the writing from the first line to the last line on the liquid crystal display is completed. In particular, it is turned off for about 3 to 5 ms, and turned on when one screen is completed. Further, an off period may be provided once or more, preferably about 2 to 6 times during the display period. The off period in that case is preferably about 0.5 to 1 ms.

(3) In the above (2), at least the response delay period and / or the transition period are turned off. Here, the response delay period refers to the time required for the transmittance change from 0% to 10% or from 100% to 90% after the voltage is applied (modulated). In the above definition, "rise (fall) time" plus "delay time" refers to "turn-on (off) time. In addition, the transition period is a so-called" transition period "that defines a change in transmittance of a liquid crystal panel. The term includes at least a part of “rise time”, “fall time”, “time obtained by adding delay time to rise time”, and “time obtained by adding delay time to fall time”. The “rise time” and “fall time” are times defined by the so-called transmitted light intensity increasing or decreasing from 10% → 90% or 90% → 10% in a steady state.

By the way, in order to improve the hold display of the liquid crystal, it is only necessary to turn off the light for a certain period of time, which is good for displaying a moving image. Becomes Therefore, it is preferable to have a switching unit 7a for switching between pulse light emission and continuous light emission according to the input image signal. It is preferable that the switching unit automatically switches to pulse emission only when a moving image signal such as a television signal is input. Also,
The user may switch the state as desired.

As the switching means 7a, a circuit for discriminating between a moving image and a still image may be added to a signal processing circuit for analyzing the image signal Vd and extracting the image switching timing. The processing may be performed by a processor or the like.

Specifically, a configuration as shown in FIG. 4 can be adopted. That is, the switching unit 7a in the illustrated example includes a specific signal extracting unit 71 that extracts a luminance or chromaticity signal of a specific pixel from an input image signal, a signal holding unit 72 that holds the extracted signal, Comparing means 73 is provided for comparing the signal held in the signal holding means 72 with an extracted signal of the same pixel in the next (subsequent) frame.

Then, based on the comparison result from the comparing means 73, there is provided a judging means 74 for judging whether it is a moving image or a still image based on the presence or absence of a change in the luminance or chromaticity signal of the extracted specific pixel. If there is no change in the luminance or chromaticity signal of the pixel, the image is determined to be a still image, and if there is a change, it is determined to be a moving image. Then, based on the result, the light emission control unit switches between the pulse light emission and the continuous light emission.
In this case, the pixels used for the determination need not be all pixels, and may be arbitrarily extracted or may be extracted every predetermined number, for example, every several hundred to several thousand pixels. Further, the determination unit 74 may include a storage unit 75, and may store a plurality of comparison results, and then make a composite determination on them.

Note that the rate of change of the signal when judging whether the image is a moving image or a still image may be derived from an empirical rule, or may be arbitrarily set by the user.

The surface light emitting device used as the backlight includes an organic EL device and an inorganic EL device. The present invention is advantageous in that it can be easily formed into a thin film, can be driven at a low voltage, and operates. An organic EL element is particularly preferable because of its high speed.

The color of the light source of the surface emitting element is preferably white so that the existing liquid crystal panel can be used as it is. When the light source is colored, it is necessary to adjust the color of the color filter.

FIG. 2 shows the structure of an organic EL device suitably used in the present invention. The organic EL element in the illustrated example is a substrate 11
/ Hole injection electrode 1 / hole injection transport layer 2 / light emitting layer 3 /
It has a structure in which the electron injection transport layer 4 / electron injection electrode 5 are sequentially stacked, and white light emission is possible by selecting the material of the light emitting layer.

In order to emit white light, there is a method of emitting three primary colors of RGB, for example, a method of emitting complementary colors such as blue and yellow.

As the electron injection electrode, a substance having a low work function is preferable. For example, K, Li, Na, Mg, La, C
e, Ca, Sr, Ba, Al, Ag, In, Sn, Z
It is preferable to use a single metal element such as n or Zr, or a two-component or three-component alloy system containing them for improving the stability. The electron injection electrode can be formed by an evaporation method or a sputtering method.

The thickness of the electron injecting electrode thin film may be a certain thickness or more capable of sufficiently injecting electrons.
Preferably, the thickness may be 1 nm or more. The upper limit is not particularly limited, but the thickness may be generally about 1 to 500 nm.

The hole injection electrode usually emits light from the substrate side.
Because it is a structure that extracts light, it is transparent or translucent.
Pole is preferred. ITO (tin-doped acid)
Indium oxide), IZO (zinc-doped indium oxide)
), ZnO, SnO_Two, In_TwoO _ThreeAnd the like,
Preferably ITO (tin-doped indium oxide), IZO
(Zinc-doped indium oxide) is preferred.

The hole injection electrode has an emission wavelength band, usually 3
50 to 800 nm, especially 50% light transmittance for each emitted light.
%, Especially 60% or more.

The thickness of the hole injecting electrode may be a certain thickness or more that can sufficiently inject holes, and is preferably 5 or more.
The range is preferably from 0 to 500 nm, more preferably from 50 to 300 nm. The upper limit is not particularly limited, but if the thickness is too large, there is a fear of peeling or the like. If the thickness is too small, there is a problem in the film strength at the time of manufacturing, the hole transport ability, and the resistance value.

This hole injection electrode layer can be formed by a vapor deposition method or the like, but is preferably formed by a sputtering method.

The organic layer of the organic EL device is as follows.

For the light emitting layer, a fluorescent substance which is a compound having a light emitting function is used. Examples of such a fluorescent substance include compounds disclosed in JP-A-63-264892, for example, at least one selected from compounds such as quinacridone, rubrene, and styryl dyes. A quinoline derivative such as a metal complex dye having 8-quinolinol or a derivative thereof as a ligand, such as tris (8-quinolinolato) aluminum;
Tetraphenylbutadiene, anthracene, perylene,
Coronene, 12-phthaloperinone derivatives, and the like. Further, Japanese Unexamined Patent Application Publication No. 8-12600 (Japanese Patent Application No.
Phenylanthracene derivatives described in JP-A-8-12969 (Japanese Patent Application No. 6-1144).
No. 56) can be used.

Such a fluorescent substance can be used as a dopant in combination with a host substance capable of emitting light by itself. In that case, the content of the fluorescent substance in the light emitting layer is 0.01 to 10% by weight, further 0.1 to 5% by weight.
%. When used in combination with a host substance, the emission wavelength characteristics of the host substance can be changed, light emission shifted to a longer wavelength becomes possible, and the luminous efficiency and stability of the device are improved.

As the host substance, a quinolinolato complex is preferable, and an aluminum complex having 8-quinolinol or a derivative thereof as a ligand is preferable. Such an aluminum complex is disclosed in JP-A-63-26469.
No. 2, JP-A-3-255190, JP-A-5-7707
3, JP-A-5-258859, JP-A-6-2158
No. 74 and the like.

Other host materials are disclosed in
Also preferred are phenylanthracene derivatives described in JP-A-12600 and tetraarylethene derivatives described in JP-A-8-12969.

The light emitting layer may also serve as an electron injection / transport layer. In such a case, it is preferable to use tris (8-quinolinolato) aluminum or the like.

As the compound capable of injecting and transporting electrons, it is preferable to use a quinoline derivative, furthermore a metal complex having 8-quinolinol or a derivative thereof as a ligand, particularly tris (8-quinolinolato) aluminum (Alq3). It is also preferable to use the above-mentioned phenylanthracene derivatives and tetraarylethene derivatives.

As the compound for the hole injecting / transporting layer, it is preferable to use an amine derivative having strong fluorescence, for example, a triphenyldiamine derivative, a styrylamine derivative, or an amine derivative having an aromatic condensed ring.

The electron injection / transport layer and the hole injection / transport layer may be formed using an inorganic substance (eg, an oxide such as silicon, germanium, strontium, and rubidium).

After each layer of the organic EL element is formed, SiO 2
A protective film using an inorganic material such as _X, an organic material such as Teflon (registered trademark), a fluorocarbon polymer containing chlorine, or the like may be formed. The protective film may be transparent or opaque, and the thickness of the protective film is about 50 to 1200 nm. The protective film is
In addition to the reactive sputtering method, a general sputtering method,
It may be formed by an evaporation method, a PECVD method, or the like.

The substrate may be an amorphous substrate such as glass or quartz, or a crystalline substrate such as Si, GaAs or Z
Examples thereof include nSe, ZnS, GaP, and InP, and a substrate in which a crystalline, amorphous, or metal buffer layer is formed on these crystalline substrates can also be used. A resin substrate may be used to provide flexibility or reduce weight. As the metal substrate, Mo, Al, Pt, I
r, Au, Pd, or the like can be used, and a glass substrate is preferably used. Since the substrate is usually on the light extraction side, it is preferable that the substrate has the same light transmittance as the above-mentioned electrodes.

Further, in order to prevent the deterioration of the organic layer and the electrodes, it is preferable to seal the organic EL structure with a sealing plate or the like. The sealing plate adheres and seals the sealing plate using an adhesive resin layer in order to prevent moisture from entering.

The material of the sealing plate is preferably a flat plate, and examples thereof include materials such as glass, ceramic, metal, and resin. Glass is particularly preferable. The height of the sealing plate may be adjusted by using a spacer and held at a desired height.

The organic EL device may be produced by a conventional vapor deposition method, or may be produced by dissolving it in a solvent and then applying it. When performing the coating method, selection may be made according to the characteristics of the solvent such as a screen printing method, a dipping method, and a spray coating method, but the spray coating method is most preferable.
Further, a vapor deposition method and a coating method can be used in combination.

As the liquid crystal panel used in the present invention, a TN liquid crystal display, an STN liquid crystal display, or the like used as a normal liquid crystal display device can be used. These use a nematic liquid crystal, but it is preferable to use a ferroelectric liquid crystal display capable of responding much faster than a nematic liquid crystal.

The ferroelectric material may be a material used in a usual liquid crystal display device, for example, p-hexyloquine, benzylidene-p'-amino-2-chloro-
α-propyl-cinnamate and the like can be used.

Further, a chiral smectic liquid crystal having no memory property in a voltage-transmittance characteristic is also preferable, and particularly, a thresholdless antiferroelectric liquid crystal (hereinafter, referred to as “TLAFFL”).
C "). TLAFLC is based on the following (1)-
As shown in the document of (3), the optical average molecular axis direction changes continuously in the substrate plane with respect to the applied voltage, and the hysteresis exhibited by the conventional antiferroelectric liquid crystal (AFLC) is exhibited. Has disappeared. Therefore, T
By combining with an active element such as FT, application to a display capable of multi-gradation display with a wide viewing angle can be expected.

Further, a polymer stabilized ferroelectric liquid crystal display (PSFLCD) [H. Furue, T. Miyama, Y. Iimura,
H.Hasebe, H.Takatu and S.Kobayashi: Jpn.J.Appl.Ph
ys. 36 (1997) L1517.]. In this method, a small amount of a UV-curable liquid crystal acrylate monomer is added to a general ferroelectric liquid crystal material, and a liquid crystal cell can be manufactured in exactly the same manner as a bistable ferroelectric liquid crystal. Then, by irradiating the liquid crystal cell with ultraviolet rays while applying a DC electric field, it is possible to realize a high-speed response liquid crystal cell capable of gray scale display (monostable) by the applied voltage.

(1) A full-color thre
shoulderless Antiferroector
ic LCD exciting wide view
ing angle with fast responses
e time, T.E. Yosida et al., SID 97 (So
city for Information Disp
layer 97) DIGEST p841.

(2) Voltage-holding
properties of thresholds
s antiferroelectric liquid
crystals driven by active m
attributes, T .; Saishu et al., SID 96.
(Society for Information D
display 96) DIGEST p703.

(3) "Anti-ferroelectric phase development mechanism in liquid crystal and possibility of thresholdless antiferroelectric phase", Miyachi et al., Applied Physics, Vol. 65, No. 10, (1996), p. 1029.

The form of the liquid crystal panel can be used in combination with a backlight, and any form may be used as long as it is used in a usual liquid crystal display device.

[0061]

<Example 1> A 7059 substrate (trade name, manufactured by Corning Incorporated) was scrubbed using a neutral detergent as a glass substrate.

An ITO hole injection electrode layer having a thickness of 200 nm was formed on this substrate at a substrate temperature of 250 ° C. by an RF magnetron sputtering method using an ITO oxide target.

This substrate was patterned into a stripe by the photolithography method. Further, a polyimide resin as an insulating layer was patterned thereon by a photolithography method.

[0064] After the surface of the substrate on which ITO electrode layer, etc. formed by UV / 0 ₃ washing, polyethylene dioxythiophene as a hole injection layer (Polyethlene dioxytiophene:
After applying 100 nm of PEDOT (manufactured by Bayer), a distant dopant (manufactured by Idemitsu, IDE) was used as a blue light emitting body.
102) was dissolved in a toluene solvent using coumarin 6 as a green color and DCMl as a red color using a polyvinyl carbazole (PVK) polymer as a host material. This solution was applied on the previous substrate by spin coating. After performing vacuum drying at 80 ° C. for one hour, L
3 nm of iF and 80 nm of an Al electrode were deposited. Next, the sealing glass was bonded using a UV-curable adhesive to obtain a white light source element.

Next, a liquid crystal panel was prepared using a pair of ITO substrates which were patterned so as to form a matrix. The liquid crystal used was a polymer-stabilized ferroelectric liquid crystal. The rise time of this liquid crystal was 0.5 ms, and the rise time was 0.5 ms. In this liquid crystal panel, a square pattern 21 as shown in FIG.
The display is controlled so as to flow in the screen 20 as indicated by an arrow 22 every 6.7 ms (corresponding to one frame).

The white light source of the present invention was arranged as a backlight behind this liquid crystal, and was turned on and off within one frame period as shown in Table 1 to evaluate lighting. Table 1 shows the results.

[0067]

[Table 1]

As is clear from the table, the trailing phenomenon, which had a problem in the constant lighting, has been improved by the on / off driving.

[0069]

As described above, according to the present invention, it is possible to provide a backlight which can perform a moving image table well and maintain the same quality as a conventional backlight when displaying a still image, and a display device using the same. Can be provided.

[Brief description of the drawings]

FIG. 1 is a block diagram showing a basic configuration of a backlight according to the present invention.

FIG. 2 is a cross-sectional view showing a basic configuration of an organic EL element used for a backlight.

FIG. 3 is a schematic diagram showing a display screen in the embodiment.

FIG. 4 is a block diagram showing a specific configuration example of a switching unit.

[Explanation of symbols]

 2 liquid crystal panel 3 surface light emitting element 4 drive circuit 5 drive circuit 6 display control means 7 light emission control means 7a switching means

Continued on the front page (51) Int.Cl. ⁷ Identification code FI Theme coat II (Reference) G09G 3/36 G09G 3/36 F-term (Reference) 2H091 FA44Z GA11 HA12 LA16 2H093 NC42 NC59 ND10 ND12 NE06 NF17 5C006 AA11 AF42 AF78 BA12 BB11 EA01 FA25 5C080 AA10 BB05 DD01 DD10 EE25 FF09 JJ01 JJ02 JJ06 5G435 AA00 BB12 BB15 EE26 EE30 GG25

Claims (10)

[Claims] 1. A backlight for providing display light from the back to a display panel on which an image is formed, wherein the backlight includes a surface light-emitting element and at least a light-emission control unit for turning on / off the surface light-emitting element. Light. 2. The backlight according to claim 1, wherein said light emission control means drives the surface light emitting element on / off in accordance with display switching of the display panel. 3. The backlight according to claim 2, wherein the light emission control unit is turned off at least when the display is switched. 4. The light emission control unit further turns off a response delay period and / or a transition period.
Backlight. 5. The backlight according to claim 1, wherein said light emission control means can switch between pulse light emission and continuous light emission by a display signal of a display panel. 6. The light emission control means performs on / off driving when the image signal displayed on the liquid crystal display panel is a moving image, and stops the on / off driving when the image signal is a still image.
5. The display device according to any of 5. 7. The backlight according to claim 1, wherein the surface light emitting device is a white light emitting EL device. 8. The backlight according to claim 1, wherein the surface light emitting device is an organic EL device. 9. A display device having a liquid crystal display panel as a display panel, and having the backlight according to claim 1. 10. The display device according to claim 9, wherein the liquid crystal panel includes a ferroelectric liquid crystal.