United States Patent [I91
`Kajimoto et al.
`
`US005920367A
`[ i l l Patent Number:
`[45] Date of Patent:
`
`5,920,367
`Jul. 6,1999
`
`[54] LIQUID CRYSTAL DISPLAY DEVICE
`
`[75]
`
`Inventors: Koichi Kajimoto, Tenri; Takeshi Seike,
`Kitakatsuragi-gun, both of Japan
`
`Primary Examiner-William L. Sikes
`Assistant Exarniner4ung Nguyen
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`Cushman, LLP; David G. Conlin
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`[73] Assignee: Sharp Kabushiki Kaisha, Osaka, Japan
`
`[57]
`
`ABSTRACT
`
`[21] Appl. No.: 081949,128
`
`Oct. 10, 1997
`
`[22] Filed:
`P O I
`Foreign Application Priority Data
`Japan .................................... 8-300116
`Nov. 12, 1996
`[JP]
`Japan .................................... 9-233101
`Aug. 28, 1997
`[JP]
`[51] Int. C1.6 ........................ G02F 111333; G02F 111335
`[52] U.S. C1. .............................. 3491162; 3491114; 349196
`[58] Field of Search .................................. 349151, 62, 96,
`3491113, 162, 114, 68
`
`~ 5 6 1
`
`4,637,687
`4,657,348
`5,724,112
`
`References Cited
`U.S. PATENT DOCUMENTS
`111987 Haim et al. ............................. 3491114
`411987 Ziegler .................................... 3491114
`311998 Yoshida et al. ......................... 3491114
`FOREIGN PATENT DOCUMENTS
`7-333598 1211995 Japan .
`
`In a liquid crystal display device of the present invention, a
`white plate light source such as a cool cathode fluorescent
`tube is provided on a back surface of a liquid crystal cell, i.e.,
`on a surface opposite to a displaying surface of the liquid
`crystal cell. On a surface opposite to the displaying surface
`of the liquid crystal panel, a polarizing plate-equipped
`semitransmitting reflecting plate is provided. The liquid
`crystal panel is composed of active elements such as MIM
`(Metal-Insulator-Metal) elements or TFTs (Thin Film
`Transistors). With this arrangement, discharge of a charge is
`suppressed by switching of the active element when a
`voltage is applied to two types of electrodes sandwitching a
`liquid crystal layer. By setting reflectance and transmittance
`of the polarizing plate-equipped semitransmitting reflecting
`plate such that contrast of the liquid crystal panel is higher
`when the cool cathode fluorescent tube is not lighted than
`when the cool cathode fluorescent tube is lighted, it is
`ensured that visibility both in a reflecting mode and a
`transmitting mode are improved.
`
`12 Claims, 10 Drawing Sheets
`
`Valeo Ex. 1008_001
`
`

`

`U.S. Patent
`
`Jul. 6,1999
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`Sheet 1 of 10
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`Valeo Ex. 1008_002
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`

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`U.S. Patent
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`Jul. 6,1999
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`Sheet 2 of 10
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`Valeo Ex. 1008_003
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`

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`U.S. Patent
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`Jul. 6,1999
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`Sheet 3 of 10
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`FIG. 3
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`Valeo Ex. 1008_004
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`

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`U.S. Patent
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`Jul. 6,1999
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`Sheet 4 of 10
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`FIG. 4
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`Valeo Ex. 1008_005
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`

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`U.S. Patent
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`Jul. 6,1999
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`Sheet 5 of 10
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`Valeo Ex. 1008_006
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`

`

`U.S. Patent
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`Jul. 6,1999
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`Sheet 6 of 10
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`FIG. 6
`
`W
`
`1 z u LO.
`cn
`>
`
`u
`
`--t-
`-m-
`- +
`
`-jt-
`
`+
`
`81
`
`0
`1
`
`100000
`10000
`1 0
`100
`1000
`SURROUNDING BRIGHTNESS ( l x 1
`
`I
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`Valeo Ex. 1008_007
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`

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`U.S. Patent
`
`Jul. 6,1999
`
`Sheet 7 of 10
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`LUMINANCE OF DISPLAYING
`SURFACE ( cd/m2)
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`Valeo Ex. 1008_008
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`

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`U.S. Patent
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`Jul. 6,1999
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`Sheet 8 of 10
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`FIG. 8
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`Valeo Ex. 1008_009
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`

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`U.S. Patent
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`Jul. 6,1999
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`Sheet 9 of 10
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`Valeo Ex. 1008_010
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`

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`U.S. Patent
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`Jul. 6,1999
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`Sheet 10 of 10
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`Valeo Ex. 1008_011
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`

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`5,920,367
`
`A
`
`1
`LIQUID CRYSTAL DISPLAY DEVICE
`
`2
`display element. Note that, the reflecting means is composed
`of, for example, (1) aluminium (Al) or Silver (Ag) and (2)
`FIELD OF THE INVENTION
`a film substrate. Thus, in the reflective-type liquid crystal
`. -
`The present invention relates to a liquid crystal display
`display device, unlike the transmitting-type liquid crystal
`device, and more particularly to a semitransmitting-type s display device which is required to be provided with illu-
`liquid crystal display device having transmitting type and
`minating means, it is not required to provide illuminating
`means. As a result, in the reflective-type liquid crystal
`reflecting type displaying systems.
`display device, it is possible to lower the power
`BACKGROUND OF THE INVENTION
`consumption, also it is possible to realize a light, thin liquid
`In recent years, due to its light weight and low power 10 crystal display device with ease which is a characteristic of
`a liquid crysta1
`device.
`consumption, a liquid crystal display device has been used
`However, since the reflective-t~~e liquid
`
`display
`in a variety of fields. Specifically, the liquid crystal display
`device uses the surrounding light, the brightness of the
`device, for example, is used as (1) a display device such as
`display is largely influenced by the lighting condition of the
`an office automation equipment (for example, word proces-
`sor and personal computer), and an audio and visual equip- Is environment where the reflective-type liquid crystal display
`device is used. That is to say, for example, when the
`ment dealing with an image, (2) an information display
`device for use in (a) instmments of a car and an air plane etc,
`reflective-type liquid crystal display device is used in a dark
`and (b) portable information terminals, and (3) an informa-
`environment, it becomes difficult to see the display. For this
`tion display device for use in a watch and a measuring
`reason, the reflective-type liquid crystal display device is not
`20 suitable in a dark environment.
`device.
`1" Contrast, a semitransmitting-t~~e liquid crystal display
`
`Generally, the liquid crystal display device itself is non-
`device, like the transmitting-type, is provided with illumi-
`light emitting, Thus, by providing the liquid crystal display
`nating means such as (1) the small fluorescent lamp, e.g. the
`device with illuminating means of some sort or means
`cool cathode fluorescent tube, and (2) an EL light-emitting
`serving the same function, it is possible to adopt the liquid
`crystal display device as a display which is available in 25 element. The illuminating means is provided on the back
`various forms. The liquid crystal display device can be
`surface of the liquid crystal display element, namely, the
`broadly classified into three types on the basis of the
`illuminating means is provided on a surface opposite to the
`displaying surface of the liquid crystal display element.
`difference in illuminating methods: a transmitting type, a
`Between the illuminating means and the liquid crystal
`reflecting type, and a semitransmitting type.
`A transmitting-type liquid crystal display device is pro- 30 display element, there is provided a semitransparent reflect-
`ing plate such as a magic mirror. The main portion of the
`vided with illuminating means such as (1) a small fluores-
`reflecting plate is made of (a) a scattering
`cent lamp, e,g,, a cool cathode fluorescent tube, and (2) an
`plate such as a
`plastic sheet, (b) a scattering
`EL (electroluminescence) light-emitting element. Such illu-
`plate in which a meshed
`reflecting
`has been
`rninating means is provided on the back surface of a liquid
`crystal display element, namely, the illuminating means are 35 patterned on the scattering plate of (a), or (c) a scattering
`plate On which pear' resin etc. has been spread.
`provided on a surface opposite to the displaying surface of
`With this arrangement, in a luminous environment, dis-
`the liquid crystal display device. With this arrangement, the
`playing is carried out without lighting of the illuminating
`transmittance of the light from the illuminating means is
`adjusted by the liquid crystal display element such that the 40 means, but by the reflection of surrounding light such as
`light is transmitted to the front surface of a display panel,
`'"door illumination by the semi-reflecting plate. Namely, in
`thereby displaying an image on the displaying surface of the
`this case, the surrounding light is used as reflecting illumi-
`liquid crystal display element. Thus, since the liquid crystal
`nation. Note that, displaying without lighting of the illumi-
`display device is provided with illuminating means, such
`nating means in this manner will be referred to as a reflecting
`liquid crystal display device can be used in a dark environ- 45 mode hereinafter.
`ment in the same manner as a self-light-emitting element.
`In contrast, in a dark environment, displaying is carried
`Further, by controlling the intensity of the light from the
`out by lighting of the illuminating means. Namely, in this
`illuminating means, it is possible to adjust the brightness of
`case, the light from the illuminating means is used which
`the display screen.
`transmits through the semitransmitting reflecting plate. Note
`However, in the liquid crystal display device of this type, so that, displaying by lighting of the illuminating means in this
`even when used in a luminous environment, the illuminating
`manner will be referred to as a transmitting mode hereinaf-
`means is required to carry out illumination with certain
`ter.
`As described, since the liquid crystal display device of
`intensity. For this reason, even though the liquid crystal
`this type is provided with both the transmitting type and the
`display device is, in general, said to have low power
`consumption, the power consumption is increased. Also, 5s reflecting type displaying systems, a suitable displaying
`because it is required to provide a power source for supply-
`system can be adopted in accordance with a lighting envi-
`ing power to the illuminating means, the liquid crystal
`ronment so as to complement each other the shortcoming of
`display device has a drawback in that the liquid crystal
`each displaying system. Namely, the semitransmitting-type
`display device becomes large and heavy.
`liquid crystal display device has an advantage in that the
`On the other hand, a reflective-type liquid crystal display 60 power consumption is low, and the device is suited for use
`device uses, as reflecting illumination, surrounding light
`not only in a luminous environment but also in a dark
`such as the sun light and indoor illumination which are
`environment.
`available in the environment where the reflective-type liquid
`Incidentally, the characteristic of the semitransmitting-
`crystal display device is used. Hence, the reflective-type
`type liquid crystal display device is defined fixedly by
`liquid crystal display device is provided with reflecting 65 setting of the transmittance and the reflectance of a material
`means for reflecting the surrounding light. The reflecting
`of the semitransmitting reflecting plate. That is to say, in the
`means is provided on the back surface of the liquid crystal
`case of using, for example, a semitransmitting reflecting
`
`Valeo Ex. 1008_012
`
`

`

`5,920,367
`
`3
`4
`With this arrangement, since the liquid crystal panel is
`plate which has been set so as to have high transmittance and
`provided with the active elements which control supplying
`low reflectance, the illuminating characteristic of the liquid
`of a charge to the first transparent electrodes, in the case of
`crystal display device becomes transmission-oriented. On
`applying a voltage to the respective first transparent elec-
`the other hand, in the case of using, for example, a semi-
`transmitting reflecting plate which has been set so as to have s trodes and the second transparent electrodes of the first
`low transmittance and high reflectance, the illuminating
`substrate and the second substrate sandwitching the liquid
`characteristic of the liquid crystal display device becomes
`crystal layer, discharge of the charge can be suppressed by
`reflection-oriented. Note that, in the semitransmitting-type
`switching of the active elements. This prevents the contrast
`liquid crystal display device, ignoring the light loss due to
`from lowering when the illuminating means is lighted,
`scattering in the semitransmitting reflecting plate, the trans- 10 thereby permitting to design a reflection-oriented liquid
`mittance and the reflectance substantially trade off with each
`crystal display device.
`
`other. Recently, a semitransmitting-t~~e liquid crystal dis-
`In accordance with this arrangement, the reflectance and
`play device which is highly transmitting as well as highly
`the transmittance of the polarizing plate-equipped semi-
`reflecting has been developed; however, the transmittance
`transparent reflecting plate are set so as to make contrast of
`and the reflectance still trade off with each other.
`15 the liquid crystal panel higher when the illuminating means
`is not lighted (referred to as transmitting mode hereinafter)
`A semitransmitting-type liquid crystal display device, for
`than when the illuminating means is lighted (referred to as
`example, adopting the STN (Super Twisted Nematic) system
`reflecting mode hereinafter).
`is designed, considering the visibility in both the transmit-
`ting mode and the reflecting mode, SO that the respective
`With this arrangement, in the reflecting mode, a prede-
`contrast in the transmitting mode and in the reflecting mode 20 termined amount of surrounding light such as the sun light
`are substantially the s a m e . Therefore, in the
`andindoorilluminationisreflectedbythepolarizingplate-
`semitransmitting-type liquid crystal display device adopting
`equipped semitransparent reflecting plate such that a display
`the STN system, both the transmitting type and the reflecting
`having relatively high contrast can be obtained. On the other
`type displaying systems can be adopted. Note that, the
`hand, in the transmitting mode, compared with the reflecting
`contrast refers to the ratio of respective luminance values 25 mode, contrast lowers due to a decrease in the transmittance
`when displaying white and when displaying black, while
`in the transmitting mode; however, since transmitting light
`driving the liquid crystal display element.
`from the illuminating means is constantly supplied to the
`liquid crystal display element, visibility does not become
`However, in the semitransmitting-type liquid crystal dis-
`poor due to a change in the surrounding brightness.
`play device adopting the STN system, due to its
`arrangement, if a large number of scanning lines are 30
`Thus, with this arrangement, despite the fact that the
`employed, a charge stored during a period of (a) applying a
`liquid crystal display device is designed so as to be
`voltage to two transparent electrodes sandwitching the liquid
`reflection-oriented, contrast can be increased both in the
`crystal layer and (b) applying the next voltage to the two
`transmitting mode and the reflecting mode, thereby permit-
`transparent electrodes is discharged so as to lower the
`ting to improve visibility in the both modes irrespective of
`contrast. Also, the contrast in the transmitting mode is 35 the surrounding brightness.
`lowered compared with, for example, the transmitting-t~~e
`For a fuller understanding of the nature and advantages of
`liquid crystal display device or the reflecting type liquid
`the invention, reference should be made to the ensuing
`crystal display device. This presents a problem in that the
`detailed description taken in conjunction with the accom-
`displaying becomes dark in the reflecting mode and pale in 40 panying drawings,
`the transmitting mode such that the visibility of the dis-
`played image becomes poor.
`
`BRIEF DESCRIPTION OF THE DRAWINGS
`FIG. 1 is a cross sectional view showing an example of a
`structure of a liquid crystal display device of the present
`invention.
`It is an object of the present invention to provide a liquid 45
`FIG. 2(a) is a perspective view showing a schematic
`crystal display device which permits to improve visibility
`arrangement of a liquid crystal panel provided with two-
`both in a transmitting mode and the reflecting mode irre-
`terminal non-linear resistance elements; and FIG. 2(b) is an
`spective of surrounding brightness.
`enlarged drawing of the portion A of FIG. 2(a).
`In order to achieve the above-mentioned object, a liquid
`FIG. 3 is a cross sectional view showing a schematic
`crystal display device of the present invention includes a so arrangement when measuring contrast in a transmitting
`liquid crystal panel provided with (1) a first substrate having
`mode of the liquid crystal display device.
`first transparent electrodes provided in a form of matrix, (2)
`view showing a
`is a
`a second substrate, having second transparent electrodes,
`arrangement when measuring contrast in a reflecting mode
`provided so as to face the first substrate, and (3) a liquid
`the liquid crysta1
`device.
`crystal layer sandwiched between the first substrate and the ss
`FIG. 5 is a graph of a relationship between contrast and
`second substrate, a polarizing plate-equipped semitransmit-
`a character size, indicating easiness to read characters.
`ting reflecting plate provided on a side opposite to a dis-
`FIG. 6 is a graph showing a relationship between sur-
`playing surface of the liquid crystal panel, and illuminating
`rounding brightness and visibility with respect to each
`means for illuminating the liquid crystal panel through the
`polarizing plate-equipped semitransmitting reflecting plate, 60 contrast in the reflecting mode.
`FIG. 7 is a graph showing a relationship between lumi-
`wherein the liquid crystal panel includes active elements
`nance of a displaying surface of the liquid crystal panel and
`which control supplying of a charge to the first transparent
`visibility with respect to each contrast in the transmitting
`electrodes by their switching, and reflectance and transmit-
`mode.
`tance of the polarizing plate-equipped semitransmitting
`FIG. 8 is a cross sectional view showing another example
`reflecting plate are set so as to make contrast of the liquid 65
`crystal panel higher when the illuminating means is not
`of a structure of a liquid crystal display device of the present
`lighted than when the illuminating means is lighted.
`invention.
`
`SUMMARY OF THE INVENTION
`
`Valeo Ex. 1008_013
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`

`

`5,920,367
`
`DESCRIPTION OF THE EMBODIMENTS
`
`5
`FIG. 9 is a graph showing a relationship between lumi-
`nance of a white plate light source provided in the liquid
`crystal display device and power consumption.
`FIG. 10 is a perspective view showing a schematic
`arrangement of a liquid crystal panel provided with three- 5
`terminal non-linear resistance elements.
`
`6
`the light guiding plate 10 and the polarizing plate-equipped
`semitransmitting reflecting plate 7. The reflecting plate 12 is
`provided on the side opposite to the scattering sheet 11 with
`respect to the light guiding plate 10.
`In the case of using the liquid crystal display device
`having the described arrangement in a dark environment,
`displaying is carried out by lightning of the cool cathode
`fluorescent tube 8. In this case, the illuminating light from
`the cool cathode fluorescent tube 8 incidents on the light
`[First Embodiment]
`10 guiding plate 10 of the white plate light source 2 from one
`describe One embodiment of the
`The
`end surface of the light guiding plate 10 so as to be guided
`present invention referring to FIG. 1 through FIG. 7.
`into the light guiding plate 10. The illuminating light thus
`FIG. 1 shows a cross sectional view of a semitransmitting-
`guided into the light guiding plate 10 is uniformly scattered
`type liquid crystal display device of the present embodi-
`by the scattering sheet 11 and the reflecting sheet 12 so as to
`ment. As shown in FIG. 1, the liquid crystal display device 1s be emitted towards the liquid crystal cell 1. Then, the
`of this type is provided with a liquid crystal cell 1 and a
`illuminating light transmits through the polarizing plate-
`white plate light source 2. The white plate light source 2 is
`equipped semitransmitting reflecting plate 7 of the liquid
`provided on a back surface of the liquid crystal cell 1.
`crystal cell 1 so as to be emitted towards the front surface
`Namely, the white plate light source 2 is provided on a
`side of the liquid crystal display device. In short, displaying
`surface opposite to a displaying surface of the liquid crystal 20 is carried out by using the transmitting light from the white
`cell 1. Note that, the screen size of the liquid crystal display
`plate light source 2. Note that, displaying by lighting of the
`device, for example, is 11 cm in diagonal line.
`cool cathode fluorescent tube 8 in this manner will be
`referred to as a transmitting mode hereinafter.
`The liquid crystal cell 1 is provided with a liquid crystal
`panel l a . the liquid crystal panel l a is composed of a
`On the other hand, in the case of using the liquid crystal
`transparent upper side glass substrate 3 (first substrate), a 25 display device in a luminous environment, displaying is
`carried out without lighting of the cool cathode fluorescent
`lower side glass substrate 4 (second substrate), and a liquid
`crystal layer 5 which is sandwiched between the upper side
`tube 8. In this case, surrounding light such as indoor
`glass substrate 3 and the lower side glass substrate 4 via a
`illumination transmits through the polarizing plate 6, the
`seal material 5a.
`upper side glass substrate 3, liquid crystal layer 5, the lower
`On the liquid crystal layer 5 side, as shown in FIG. 2(a) 30 side glass substrate 4 in this order so as to reach the
`polarizing plate-equipped semitransmitting reflecting plate
`and FIG. 2(b) which is an enlarged drawing of the portion A
`7. The surrounding light thus reached to the polarizing
`of FIG. 2(a), the glass substrate 3 is provided with (1) a
`plate-equipped semitransmitting reflecting plate 7 is then
`plurality of transparent electrodes 31 (first transparent
`reflected by the polarizing plate-equipped semitransmitting
`electrodes) provided in a form of matrix, (2) signal elec-
`trodes 32 for supplying a charge to the plurality of trans- 35 reflecting plate 7 so as to be emitted towards the displaying
`surface side of the liquid crystal display device through the
`parent electrodes 31, (3) a plurality of two-terminal Don-
`liquid crystal cell 1 in the reversed order, thereby displaying
`linear resistance element 33 (active elements) for switching
`an image on the displaying surface of the liquid crystal
`continuity and discontinuity between the plurality of trans-
`display device. Note that, displaying without lighting of the
`parent electrodes 31 and the plurality of signal electrodes 32,
`and (4) a liquid crystal element 34. The two-terminal Don- 40 cool cathode fluorescent tube 8 will be referred to as a
`reflecting mode hereinafter.
`linear resistance elements 33 of the present embodiment are,
`for example, MIM elements having a metal-insulator-metal
`The following will explain the method by which the
`structure.
`respective contrast in the transmitting mode and the reflect-
`On the other hand, the lower glass substrate 4 is provided 45 ing mode are measured in the liquid crystal display device.
`FIG. 3 is a cross sectional view showing a structure when
`with scanning electrodes 41 (second transparent electrodes)
`composed of a plurality of transparent electrodes provided in
`measuring contrast in the transmitting mode of the liquid
`stripes so as to face the transparent electrodes 31. Note that,
`crystal display device. Above the displaying surface side of
`it is possible to change the respective positions of the upper
`the liquid crystal cell 1, there are provided in this order a lens
`glass substrate 3 and the lower glass substrate 4.
`13, a visibility correcting filter 14 for correcting visibility of
`light which has transmitted through the lens 13, and a light
`Also, as shown in FIG. 1, on a surface of the liquid crystal
`receiving element 15 for receiving light which has trans-
`panel l a , namely, on a surface opposite to the liquid crystal
`mitted through the lens 13 and the visibility correcting filter
`layer 5 of the upper glass substrate 3, a polarizing plate 6 is
`14.
`provided. Likewise, on the other surface of the liquid crystal
`panel l a , namely, on a surface opposite to the liquid crystal 55 With this arrangement, the light from the white plate light
`layer 5 of the lower glass substrate 4, a polarizing plate-
`source 2 transmits through the liquid crystal cell 1, the lens
`equipped semitransmitting reflecting plate 7 is provided.
`13, and the visibility correcting filter 14 in this order so as
`to be received by the light receiving element 15. According
`The white plate light source 2 is provided with a cool
`to the amount of light received by the light receiving element
`cathode fluorescent tube 8 (illuminating means), a chamber
`9 for supporting the cool cathode fluorescent tube 8, a light 60 15, the respective luminance values when displaying white
`guiding plate 10, a scattering sheet 11, and a reflecting sheet
`and when displaying black are determined so as to measure
`12. The cool cathode fluorescent tube 8 is provided so that
`the ratio of the two luminance values, namely, the contrast
`it can emit light on one end surface of the light guiding plate
`is measured.
`10. The light guiding plate 10 is provided so as to face the
`In contrast, FIG. 4 is a cross sectional view showing a
`liquid crystal cell 1 with respect to the entire back surface 65 structure when measuring contrast in the reflecting mode of
`(surface opposite to the displaying surface of the liquid
`the liquid crystal display device. In a direction of the normal
`crystal cell 1). The scattering sheet 11 is provided between
`with respect to the displaying surface of the liquid crystal
`
`Valeo Ex. 1008_014
`
`

`

`5,920,367
`
`~
`
`8
`7
`cell 1, the light receiving element 15 provided with a
`liquid crystal display device, the visibility cannot be
`improved in both modes.
`visibility correcting filter is provided, and in a direction
`inclined by the angle 0 with respect to the normal to the
`In contrast, the contrast of the semitransmitting-type
`liquid crystal display device of the present embodiment in
`polarizing plate-equipped semitransmitting reflecting plate
`7 , a light source 16 and a projector 17 are provided. Note s both the transmitting mode and the reflecting mode are
`that, in the present embodiment, the angle 0 is set to 30°, and
`greatly higher than
`that o f the conventional
`the diameter of a measuring point on the surface of the
`semitransmitting-type liquid crystal display device adopting
`the STN system. This is due to the fact that since the
`polarizing plate 6 is 0.2 mm.
`semitransmitting-type liquid crystal display device of the
`With this arrangement, the light emitted
`Ihe light lo present embodiment is provided with the active elements
`source 16 incidents on the liquid crystal cell 1 through the
`such as the MIM elements, in the case of applying a voltage
`projector 17. The incident light then reaches the polarizing
`to two types of electrodes (transparent electrodes 31 and
`P
`~
`~
`~
`
`
`-~semitransmitting reflecting plate ~ ~ ~ ~ P
`
`
`
`
`
`P
`~
`
`scanning electrodes 41) sandwitching the liquid crystal layer
`the polarizing plate 6 , the upper side glass substrate 3, the
`5 (liquid crystal element 34), discharge of the charge can be
`layer 5, and the lower side glass substrate
`liquid
`suppressed by the switching of the active elements, Thus, in
`the liquid
`in this
`be reflected
`the semitransmitting-type liquid crystal display device of the
`as
`
`~
`the polarizing P
`~
`~
`
`~semitransmitting reflecting - ~ ~ ~ ~
`
`
`
`~~Ppresent embodiment,
`
`
`
`
`with the conventional
`
`P
`plate 7 . The reflected light
`P
`P
`the polarizing P
`~
`~
`-
`~
`~
`~
`~
`~
`~
`~
`~
`
`semitransmitting-type liquid crystal display device adopting
`semitransmitting reflecting plate 7 is emitted towards the
`the STN system, higher contrast can be realized,
`displaying surface side of the liquid crystal display device
`In addition, as a reference, the respective contrast of (1)
`through the liquid crystal cell 1 in the reversed order so as 20 a reflecting-type liquid crystal display device adopting the
`to be received by the light receiving element 15. Then,
`STN system and (2) a reflecting-type liquid crystal display
`according to the amount of light received by the light
`device adopting the active elements are also measured by the
`receiving element 15, the contrast is measured.
`method of FIG. 4. Note that, in this case, the polarizing
`shows the
`of 'Ontrast measurement mea- 25 plate-equipped semitransmitting reflecting plate 7 of FIG. 4
`sured in the described manner in the transmitting mode and
`is replaced with a polarizing plate-equipped reflecting plate,
`the reflecting mode.
`The result shows that the contrast of the (1) a reflecting-type
`Note that, for comparison, the contrast of a conventional
`liquid crystal display device adopting the STN system and
`
`semitransmitting-t~~e liquid crystal display device adopting
`(2) a reflecting-type liquid crystal display device adopting
`the STN (Super Twisted Nematic) system respectively in the 30 the active elements are 13 and 40, respectively. Thus, also in
`transmitting mode and the reflecting mode are also measured
`the reflective-type liquid crystal display device, higher con-
`by the same method. Here, in order to carry out the mea-
`trast can be obtained in the case of adopting the active
`surement under the same condition, the white plate light
`elements than in the case of adopting the STN system even
`source 2 of the present embodiment is adopted as illumi-
`in the reflective-type liquid crystal display device,
`Dating means of the conventional liquid crystal display 35
`As described, since the semitransmitting-type liquid crys-
`device. Table 1 shows the results of the measurement.
`tal display device of the present embodiment adopting the
`active elements has higher contrast than the conventional
`liquid crystal display device adopting the STN system, even
`in the case of designing the semitransmitting-type liquid
`40 crystal display device so as to make the device reflection-
`oriented by setting of the reflectance and the transmittance
`of the material of the polarizing plate-equipped semitrans-
`mitting reflecting plate 7 , the visibility can be improved both
`in the transmitting mode and the reflecting mode.
`In the present embodiment, the reflectance and the trans-
`mittance of the material of the polarizing plate-equipped
`semitransmitting reflecting plate 7 are set so that the contrast
`of the liquid crystal panel l a is (1) not less than 10 when the
`As shown in Table 1, although the contrast of the con-
`cool cathode fluorescent tube 8 is not lighted and (2) not less
`ventional semitransmitting-type liquid crystal display device so than 3 when the cool cathode fluorescent tube 8 is lighted.
`adopting the STN system is slightly higher in the transmit-
`Note that, it is preferable to set the reflectance and the
`transmittance of the material of the polarizing plate-
`ting mode than that in the reflecting mode, they are sub-
`equipped semitransmitting reflecting plate 7 so that the
`stantially the same. This is due to the fact that considering
`contrast of the liquid crystal panel l a is (a) not less than 20
`the visibility in the transmitting mode and the reflecting
`mode, the conventional semitransmitting-type liquid crystal 5 s when the cool cathode fluorescent tube 8 is not lighted and
`display device adopting the STN system is designed so that
`(b) not less than 10 when the cool cathode fluorescent tube
`8 is lighted. The basis of the setting values of the contrast of
`the contrast in the transmitting mode and the contrast in the
`reflecting mode are the same.
`the liquid crystal panel l a will be mentioned later.
`In the conventional semitransmitting-type liquid crystal
`Note that, the ratio of contrast in the reflecting mode and
`display device, as shown in Table 1, the contrast in the 60 the transmitting mode substantially corresponds to the ratio
`reflecting mode is 8 which indicates poor visibility.
`of the reflectance and the transmittance of the material of the
`However, if a reflection-oriented semitransmitting reflecting
`polarizing plate-equipped semitransmitting reflecting plate
`7 . Hence, the reflectance and the transmittance of the
`plate is adopted, the contrast in the reflecting mode can be
`increased to 12 (not shown), thereby obtaining relatively
`material of the polarizing plate-equipped semitransmitting
`high visibility. However, in this case, the contrast in the 65 reflecting plate 7 can be set so as to make the re