(12) United States Patent
`Naka0 et al.
`
`USOO6774963B1
`US 6,774,963 B1
`Aug. 10, 2004
`
`(10) Patent No.:
`(45) Date of Patent:
`
`(54) LIQUID-CRYSTAL DISPLAY DEVICE
`(75) Inventors: Kenji Nakao, Osaka (JP); Katsuhiko
`Kumagawa, Neyagawa (JP); Tsuyoshi
`Uemura, Kadoma (JP); Naohide
`Wakita, Suita (JP)
`(73) Assignee: Matsushita Electric Industrial Co.,
`Ltd. (JP)
`Subject to any disclaimer, the term of this
`patent is extended or adjusted under 35
`U.S.C. 154(b) by 0 days.
`Appl. No.:
`09/958,658
`Apr. 12, 2000
`PCT Fed:
`PCT/JP00/02396
`
`(*) Notice:
`
`(21)
`(22)
`(86)
`
`PCT No.:
`S371 (c)(1),
`Oct. 12, 2001
`(2), (4) Date:
`PCT Pub. No.: WO00/62120
`PCT Pub. Date: Oct. 19, 2000
`Foreign Application Priority Data
`(30)
`Apr. 13, 1999
`(JP) ........................................... 11/105183
`(51) Int. Cl. .............................................. G02F 1/1335
`(52) U.S. Cl. ......................... 349/104; 349/105; 349/80;
`349/108; 349/106
`(58) Field of Search ................................. 349/104, 105,
`349/80, 108, 106
`
`(87)
`
`(56)
`
`References Cited
`U.S. PATENT DOCUMENTS
`
`4,560,241. A 12/1985 Stolov et al. ................. 349/97
`5,019,808 A * 5/1991 Prince et al. ...
`... 345/88
`5,029.986 A 7/1991 De Vaan ..................... 350/338
`5,267,060 A 11/1993 Colton ........................ 359/15
`5,499,126 A * 3/1996 Abileah et al. ............. 349/106
`
`5,721,600 A * 2/1998 Sumiyoshi et al. ......... 349/119
`5,734,457 A * 3/1998 Mitsui et al. ............... 349/106
`5,739,889 A * 4/1998 Yamada et al. ...
`... 34.9/156
`5,822,029 A * 10/1998 Davis et al. ......
`... 349/115
`5.841,494. A * 11/1998 Hall ..............
`... 349/98
`6,181,399 B1 * 1/2001 Odoi et al. ....
`... 349/113
`6.295,109 B1 * 9/2001 Kubo et al. ................. 349/119
`6,330,100 B2 * 12/2001 Van Aerle et al. .......... 359/254
`6,339,464 B1 * 1/2002 Anderson et al. .....
`... 349/187
`6,359,668 B1 * 3/2002 Iijima et al. .................. 349/61
`6,501,521 B2 * 12/2002 Matsushita et al. ......... 349/106
`6,580,484 B2 * 6/2003 Okamoto et al.
`... 349/119
`6,587,168 B2
`7/2003 Jones et al. ................... 349/96
`
`
`
`FOREIGN PATENT DOCUMENTS
`
`JP
`JP
`JP
`JP
`JP
`JP
`JP
`
`63-043.123
`O2-149881
`O5-323307
`O9-2582O7
`10-197859
`11-038397
`11-160694
`
`2/1988
`6/1990
`12/1993
`10/1997
`7/1998
`2/1999
`6/1999
`
`* cited by examiner
`
`Primary Examiner Jerome Jackson
`ASSistant Examiner-Eugene Lee
`(74) Attorney, Agent, or Firm-Parkhurst & Wendel, L.L.P.
`(57)
`ABSTRACT
`A liquid crystal display device having a back Side light
`Source, which can perform displays of both a transmissive
`type and a reflective type, employs interference filters
`formed with a multilayer film 18, 19 and 20 as color filters
`to be used for color display. The back Side light Source is
`Switched off in use as a reflective type display. The display
`in the liquid crystal display device can be inverted to a
`negative. The normal direction of the multilayer film of the
`interference filter may differ from the normal direction of a
`Substrate.
`
`20 Claims, 11 Drawing Sheets
`
`
`
`17
`
`18
`
`19 20
`
`21
`
`Qualcomm, Exh. 2011, p. 1
`Apple v. Qualcomm, IPR2018-01275
`
`

`

`U.S. Patent
`
`Aug. 10, 2004
`
`Sheet 1 of 11
`
`US 6,774,963 B1
`
`
`
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`
`2. I
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`IZ
`
`Qualcomm, Exh. 2011, p. 2
`Apple v. Qualcomm, IPR2018-01275
`
`

`

`U.S. Patent
`
`Aug. 10, 2004
`
`Sheet 2 of 11
`
`US 6,774,963 B1
`
`
`
`KNNNNNNNNNNNNNNNNNNNNNNNNNNNN?KNNNN?KNNNNN?NNNNNNNNNNNNNNN
`(LZ,
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`99 Z9
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`Qualcomm, Exh. 2011, p. 3
`Apple v. Qualcomm, IPR2018-01275
`
`

`

`U.S. Patent
`
`Aug. 10, 2004
`
`Sheet 3 of 11
`
`US 6,774,963 B1
`
`
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`Qualcomm, Exh. 2011, p. 4
`Apple v. Qualcomm, IPR2018-01275
`
`

`

`U.S. Patent
`
`Aug. 10, 2004
`
`Sheet 4 of 11
`
`US 6,774,963 B1
`
`2. I
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`Qualcomm, Exh. 2011, p. 5
`Apple v. Qualcomm, IPR2018-01275
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`

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`U.S. Patent
`
`Aug. 10, 2004
`
`Sheet 5 of 11
`
`US 6,774,963 B1
`
`WC)
`
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`Qualcomm, Exh. 2011, p. 6
`Apple v. Qualcomm, IPR2018-01275
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`

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`U.S. Patent
`
`Aug. 10, 2004
`
`Sheet 6 of 11
`
`US 6,774,963 B1
`
`FIG. 6
`
`21
`
`Display Unit (TFT),
`Keyboard
`and the like
`
`
`
`Qualcomm, Exh. 2011, p. 7
`Apple v. Qualcomm, IPR2018-01275
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`

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`U.S. Patent
`
`Aug. 10, 2004
`
`Sheet 7 of 11
`
`US 6,774,963 B1
`
`
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`
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`
`Qualcomm, Exh. 2011, p. 8
`Apple v. Qualcomm, IPR2018-01275
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`

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`U.S. Patent
`
`Aug. 10, 2004
`
`Sheet 8 of 11
`
`US 6,774,963 B1
`
`FIG. 8
`
`
`
`Qualcomm, Exh. 2011, p. 9
`Apple v. Qualcomm, IPR2018-01275
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`U.S. Patent
`
`Aug. 10, 2004
`
`Sheet 9 of 11
`
`US 6,774,963 B1
`
`V
`W
`V
`V
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`W
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`V ) III
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`III
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`
`Qualcomm, Exh. 2011, p. 10
`Apple v. Qualcomm, IPR2018-01275
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`U.S. Patent
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`Aug. 10, 2004
`
`Sheet 10 of 11
`
`US 6,774,963 B1
`
`FIG. O
`
`(a)
`
`Qualcomm, Exh. 2011, p. 11
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`U.S. Patent
`
`Aug. 10, 2004
`
`Sheet 11 of 11
`
`US 6,774,963 B1
`
`FIG. 11
`
`1OO
`
`Blue
`
`Yellow
`
`Red
`
`Wavelength
`
`
`
`OO
`
`Wavelength
`
`Qualcomm, Exh. 2011, p. 12
`Apple v. Qualcomm, IPR2018-01275
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`

`

`1
`LIQUID-CRYSTAL DISPLAY DEVICE
`
`US 6,774,963 B1
`
`TECHNICAL FIELD
`The present invention relates to color filters and liquid
`crystal display devices (or display elements, display units).
`More particularly, the invention relates to color filters and
`liquid crystal display devices which are used for portable
`data terminals or the like and further relates to color filters
`and liquid crystal display devices of types uSable for both
`transmission and reflection.
`
`BACKGROUND OF THE INVENTION
`
`General Background Art
`Liquid crystal display devices are roughly divided into
`transmissive type and reflective type devices.
`First, with regard to transmissive type devices, commonly
`used transmissive type color liquid crystal display devices
`employ absorption type color filters. The transmissive type
`color liquid crystal display device has a Structure as shown
`in FIG.1. In the figure, the reference numeral 11 denotes a
`light guide plate provided with a reflection plate (not shown
`in the figure) on its lower side or the like. The reference
`numeral 12 denotes a polarizer. The reference numeral 14
`denotes a back (lower) side Substrate. The reference numeral
`15 denotes a front (upper; Viewers operate and watch the
`display Screen there) side Substrate. The reference numeral
`17 denotes a polarizer on the front side. The reference
`numeral 61 denotes an absorption type color filter for
`transmitting red light (absorbing light of wavelengths other
`than red). The reference numeral 62 denotes an absorption
`type color filter for transmitting green light. The reference
`numeral 63 denotes an absorption type color filter for
`transmitting blue light. The reference numeral 21 denotes a
`light Source as a Sidelight or a backlight.
`Basic function, Structure, material and the like of each of
`these portions are So-called well-known arts; therefore gen
`eral descriptions thereof are not provided herein.
`Actually, in addition to the above, TFT (Thin Film
`Transistor) for pixels and for driving pixels is formed on
`either of the upper and lower Substrates, and transparent
`conductive film and alignment film are disposed on the sides
`on which those Substrates face a liquid crystal layer. The
`TFT, the transparent conductive film and the alignment film
`also are So-called well-known arts and additionally are not
`directly related to the Scope of the present invention; there
`fore illustrations and descriptions thereof are not provided
`herein.
`Only contents, functions and the like which are directly
`related to the Scope of the present invention are described
`below in principle.
`The backlight disposed on the back Side of a liquid crystal
`panel is a So-called white light Source (which comprises
`light of any wavelength So as not to make light of particular
`colors observable).
`Each pixel is provided with an absorption type color filter
`which transmits only predetermined light corresponding to a
`color of the pixel and absorbs light other than the predeter
`mined light. Thus, each color of red, green and blue is
`displayed.
`The use of the absorption type color filter, however,
`causes an extremely great loSS of light due to the absorption
`of approximately two-thirds (or more in Some cases) of the
`light. Accordingly, it has been proposed that an interference
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`filter should be substituted for the absorption type color filter
`(for example, Japanese Unexamined Patent Publications No.
`11-38397, No. 10-197859 and Japanese Patent Application
`No. 9-273042). An interference filter transmits light of
`particular colors and reflects light other than the light of
`particular colors, in other words, reflects light of unneces
`sary colors for the pixel on the side of the light source. This
`reflected light thereby is reflected again in a display Surface
`by a reflection plate or the like on the lower side of the light
`guide plate 11 to be reused for display, resulting in the
`improvement of utilization efficiency of light as well as the
`decrease of power consumption and the improvement of
`luminance.
`An example Such that an interference filter is applied to a
`reflective type liquid crystal element is disclosed in Japanese
`Unexamined Patent Publication No. 11-38397, a model Such
`that an interference filter is formed under a color filter is
`disclosed in Japanese Unexamined Patent Publication No.
`10-197859, and an example of a backlight for color sepa
`ration using an interference filter is disclosed in Japanese
`Patent Application No. 9-273042.
`An interference filter is generally formed with a multi
`layer film, while a type Such that an interference filter is
`formed by curing cholesteric liquid crystal has been pro
`posed in recent years (for further details, refer to the
`development of color filters by using cholesteric liquid
`crystal presented by Tokuhisa MORIYA in DAI NIPPON
`PRINTING CO.,LTD. at the 6th research report meeting of
`HLC).
`Next, with regard to reflective type devices, commonly
`used reflective type color liquid crystal display devices also
`employ absorption type reflection plates. The reflective type
`color liquid crystal display device has a structure shown in
`FIG. 2 such that a reflection plate 71 which reflects only
`predetermined light and absorbs light other than the prede
`termined light is formed on a Substrate on the back Side of
`a liquid crystal panel. Thus, only pixels for brightly display
`ing predetermined light reflect the predetermined light; the
`reflection plate reflects the predetermined light on the dis
`play side (the Side of viewers);...and only the pixels for
`brightly displaying predetermined light absorb the predeter
`mined light, while a circular light plate and a liquid crystal
`layer shut off (absorb) the predetermined light in the case of
`pixels for not brightly displaying predetermined light. In
`FIG. 2, corresponding numbers are given to members and
`portions having the same function, Structure and the like as
`in FIG. 1. Similarly, these numbers apply to liquid crystal
`display devices according to embodiments of the present
`invention described after. The reference numeral 71 in FIG.
`2 is a reflection plate as well as an electrode.
`It is noted for confirmation that transmitted light in this
`type passes back and forth through a liquid crystal layer,
`namely, passes through twice for display (this is related to
`embodiments described after).
`In addition to the above, partially transmissive type liquid
`crystal display devices are mentioned as an intermediate
`type between the transmissive type and the reflective type.
`This type is Such that a half mirror is disposed on the upper
`or lower side of the back side substrate 14 of the liquid
`crystal display device shown in FIG. 1 to transmit a certain
`quantity of light and reflect a certain quantity of light. A
`liquid crystal display element of this type is used as the
`transmissive type when an AC power Supply can be used and
`is used as the power-saving reflective type when battery
`operated, being widely used particularly for portable data
`terminals or the like.
`
`Qualcomm, Exh. 2011, p. 13
`Apple v. Qualcomm, IPR2018-01275
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`US 6,774,963 B1
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`Furthermore, a type of device usable as both a transmis
`Sive type and a reflective type device was announced in
`recent years (in a news release by SHARP CORPORATION
`on Apr. 1, 99). This type of device is an improved conven
`tional partially transmissive type device and is characterized
`in that a reflection plate is partially formed at every pixel.
`Background Art in View of the Problems to be
`Solved by the Present Invention
`Brightness, however, is not Sufficiently Secured in liquid
`crystal display elements described above. Since polarized
`light has, from the Start, been utilized in liquid crystal
`display devices, utilization efficiency of light is reduced to
`approximately a half in principle even for mere black-and
`white display.
`In particular, brightness is further reduced in a type of
`device uSable as both a transmissive type and a reflective
`type device. For example, if, for the Sake of Simplicity of
`explanation, transmittance of a half mirror is assumed to be
`50%, only 50% of brightness of a backlight is utilized in the
`case of transmissive type display, while only 50% of
`reflected light is utilized in the case of reflective type
`display. Resultingly, utilization efficiency of light is reduced
`to half in both types of display. This reduction is caused also
`when a reflection plate is formed at pixels (actually, in use
`as a transmissive type device employing a backlight, the
`transmittance will frequently be less than 50% as compared
`with use as a reflective type device because of having extra
`possible luminance).
`Moreover, an absorption type color filter is used for a
`color filter So that two-thirds (or more in Some cases) of light
`is not utilized; therefore utilization efficiency of light is
`reduced to approximately one-sixth in principle for color
`display. The use of the above-mentioned half mirror can
`reduce utilization efficiency of light to approximately one
`twelfth in the worst case.
`In a model Such that an interference filter is used as a
`measure against the reduction, the display Screen is observed
`in Such a manner that colors thereon change when viewing
`from an oblique direction. That is, an interference filter is
`formed with a multilayer film or the like having periodicity
`and Selectively reflects light of wavelengths corresponding
`to the thickness thereof. Consequently, the effective thick
`neSS of the interference filter is increased when the display
`Screen is viewed from an the oblique direction, leading to a
`change in wavelengths which are transmitted.
`LeSS power consumption and brighter display, therefore,
`have been desired in transmissive type devices and reflective
`type devices as well as particularly a type usable as both of
`the types and additionally a liquid crystal display device for
`color display. It has been desired that colors not change with
`the direction from which the display screen is viewed and
`that color Saturation be improved.
`DISCLOSURE OF THE INVENTION
`The present invention is intended for solving the above
`mentioned problems and employs a nonabsorption type
`color filter as a color filter.
`According to the invention, transmissive type display and
`reflective type display are performed.
`According to the invention, a back Side light Source Such
`as a backlight and a Sidelight can be Switched off indepen
`dently of a pixel unit for use of the device as a reflective type
`device.
`According to the invention, an interference filter is used
`as the nonabsorption type color filter.
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`According to the invention, although modulation charac
`teristics of a liquid crystal layer differ between a transmis
`Sive type mode and a reflective type mode in accordance
`with the thickness of the liquid crystal layer through which
`light passes through (the distance of transmission), either
`mode offers a bright display and excellent contrast.
`According to the invention, a color filter is an interference
`filter formed with a multilayer film, and additionally the
`normal direction of the multilayer film differs from the
`normal direction of a Substrate.
`More specific descriptions are detailed below.
`An aspect of the invention is characterized in that a liquid
`crystal display device for color display (including a projec
`tion display) having a back Side light Source, Such as a
`backlight or a powerful light Source for projecting, employs
`as a color filter corresponding to a color of each pixel
`making up part of a delta, a mosaic, a Stripe or the like on
`a display Surface (in the case of projection display, strictly
`Speaking a Surface as a film used for displaying) not a
`conventional color filter which absorbs light other than light
`of predetermined colors by dispersing colorant into trans
`parent resin, but a nonabsorption type color filter which
`transmits light of predetermined colors and reflects light
`other than the light of predetermined colors (note that the
`nonabsorption type color filter is not limited to the display
`of the three primary colors).
`Another aspect of the invention is characterized in that a
`liquid crystal display device is a combination liquid crystal
`display device (as described above, including elements and
`display units of portable apparatuses) capable of Switching
`between a transmissive type display mode and a reflective
`type display mode by Switching a Switch.
`A further aspect of the invention is characterized in that
`the quantity of light of a backlight can be shutoff (to Zero)
`for the use as a reflective type device.
`A Still further aspect of the invention is characterized in
`that a nonabsorption type color filter is an interference color
`filter, such as one formed with a multilayer film, that
`transmits only light of predetermined colorS Such as red and
`reflects light of complementary colors thereto.
`A Still further aspect of the invention is characterized in
`that color display of red, green and blue is performed in
`transmissive type display and color display of cyan, magenta
`and yellow is performed in reflective type display. For this
`purpose, the device comprises a predetermined Switching
`circuit and the like for Such color displayS.
`A Still further aspect of the invention is characterized in
`that a display can be inverted to a negative by shifting a TFT
`between ON and OFF in order to perform an optimum
`display for each of transmissive type display and reflective
`type display.
`A Still further aspect of the invention is characterized in
`that a liquid crystal display device which can Switch
`between a transmissive type display mode and a reflective
`type display mode comprises reflection means for reflecting
`incident light entering from the display Side or light of a
`predetermined color by each pixel for white display and
`color display when the device is used as a reflective type
`device, and transmission means for transmitting light of
`white color or light of a predetermined color by each pixel
`when the device is used as a transmissive type device.
`A Still further aspect of the invention is characterized in
`that a Voltage Signal for modulation in transmissive type
`display is set to be large in accordance with a type of liquid
`crystal to be used therefor in order to compensate for the fact
`
`Qualcomm, Exh. 2011, p. 14
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`US 6,774,963 B1
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`S
`that the amount of modulation, change in the polarization
`angle of light for display by a liquid crystal layer, is leSS as
`compared with reflective type display.
`A Still further aspect of the invention is characterized in
`that a portion of a cell is thickened in order to thicken the
`liquid crystal layer of the portion through which light for
`display passes when the device is used as a transmissive type
`device.
`A Still further aspect of the invention is characterized in
`that a voltage for modulation is raised in order to increase
`the amount of modulation in use as a transmissive type
`device and in that a liquid crystal is used which greatly
`modulates in response to a high Voltage.
`A Still further aspect of the invention is characterized in
`that reflected light by a reflection means and transmitted
`light by a transmission means are in a complementary color
`relationship and that modulation by a liquid crystal layer can
`be Switched by Switching display mode.
`A Still further aspect of the invention is characterized in
`that a reflection means and a transmission means are non
`absorption types and particularly interference filters.
`A Still further aspect of the invention is characterized in
`that an interference filter is formed with a multilayer film
`and that the multilayer film is formed with inclinations on a
`Surface of the multilayer film at each pixel in the horizontal,
`vertical, or the like directions as viewed by a viewer in order
`not to cause disorder to color display depending on the
`Viewing angle.
`A Still further aspect of the invention is characterized in
`that a cholesteric liquid crystal is used for the multilayer
`film.
`A Still further aspect of the invention is characterized in
`that an interference filter using the cholesteric liquid crystal
`is a complex comprising a cholesteric liquid crystal and a
`polymer.
`A Still further aspect of the invention is characterized in
`that a liquid crystal display device which is not a type usable
`as both a transmissive type device and a reflective type
`device employs a nonabsorption type color filter for full
`color display, dichroic display, monochromatic display and
`the like and that the same techniques as in each of the
`above-mentioned groups of inventions are employed for the
`nonabsorption type color filter.
`BRIEF DESCRIPTION OF THE DRAWINGS
`FIG. 1 is a cross sectional view of a structure of a
`conventional transmissive type liquid crystal display ele
`ment.
`FIG. 2 is a cross sectional view of a structure of a
`conventional reflective type liquid crystal display element.
`FIG. 3 is a cross sectional view of a structure of a liquid
`crystal display element according to Embodiment 1 in the
`present invention.
`FIG. 4 is a view conceptually showing functions in use of
`a liquid crystal display element as a transmissive type
`element according to the above-mentioned Embodiment 1.
`FIG. 5 is a view conceptually showing functions in use of
`a liquid crystal display element as a reflective type element
`according to the above-mentioned Embodiment 1.
`FIG. 6 is a diagram showing principles of a circuit that,
`for example, Switches off a back Side light Source inter
`locked to a negative inversion.
`FIG. 7 is a cross sectional view of a structure of a liquid
`crystal display element according to Embodiment 2 in the
`present invention.
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`FIG. 8 is a diagram showing a regulating System (circuit)
`of driving Voltage.
`FIG. 9 is a view conceptually showing a structure of an
`interference filter according to Embodiment 5 in the present
`invention.
`FIG. 10 is a view conceptually showing an interference
`filter formed with a multilayer film using cholesteric liquid
`crystal.
`FIG. 11 is a graph showing characteristics of an interfer
`ence filter for dichroic display.
`DETAILED DESCRIPTION OF THE
`PREFERRED EMBODIMENTS
`The present embodiment relates to color liquid crystal
`display devices.
`
`EMBODIMENT 1.
`The present embodiment relates to transmissive type color
`liquid crystal display devices.
`FIG. 3 shows a cross sectional view of a liquid crystal
`display element according to the embodiment. In the figure,
`the reference numeral 13 denotes a retardation plate as a
`quarter-wave plate (W/4). The reference numeral 18 denotes
`an interference filter for transmitting red light and reflecting
`cyan light. The reference numeral 19 denotes an interference
`filter for transmitting green light and reflecting magenta
`light. The reference numeral 20 denotes an interference filter
`for transmitting blue light and reflecting yellow light.
`These interference filters are detailed in embodiments
`described after.
`A liquid crystal display element according to the embodi
`ment has the same basic Structure as in FIG. 1, for example,
`a backlight unit is disposed on the back Side of a liquid
`crystal panel holding liquid crystal between Substrates
`thereof. The liquid crystal display element, however, differs
`from FIG. 1 in that the interference filters are formed at each
`pixel on the back Side Substrate. Although these color filters
`are formed on the active matrix Substrate on which TFT
`(Thin Film Transistor) is formed, illustrations of the TFT are
`not provided herein for the previously mentioned reason.
`The interference filters having the above-mentioned char
`acteristics serve as the color filters shown in FIG. 1. Cyan,
`magenta and yellow are a mixture of green and blue, red and
`blue, and red and green respectively. It is noted for confir
`mation that red, green and blue are a complementary color
`to cyan, magenta and yellow respectively. These descrip
`tions are So-called well-known matters, therefore further
`detailed descriptions thereof are not provided herein.
`A liquid crystal layer to be used has a twisted nematic
`structure with a twist of 45. As a result, the liquid crystal
`layer functions as a quarter-wave plate (W/4) with no appli
`cation of Voltage, and meanwhile does not function as a
`quarter-wave plate (w/4) with the application of voltage for
`the reason that liquid crystal therein is aligned in the
`direction of electric field. The switching of electric field (ON
`and OFF, or opening and closing) performs displaying.
`A polarizer 17 is adhered to an upper side substrate 15 so
`that the direction of absorption axis thereof is parallel to the
`rubbing direction of alignment film. A quarter-wave plate
`(W/4) 13 and a polarizer 12 are adhered to a lower side
`substrate 11 so that the direction of absorption axis thereof
`is perpendicular to that of absorption axis of the polarizer on
`the upper Side.
`According to this construction, the liquid crystal display
`element is normally black in transmissive type display and
`
`Qualcomm, Exh. 2011, p. 15
`Apple v. Qualcomm, IPR2018-01275
`
`

`

`US 6,774,963 B1
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`15
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`7
`meanwhile is normally white in reflective type display.
`Normally black is a mode such that “black display (light
`does not reach the display Side) is performed with no
`application of Voltage, while normally white is a mode
`Such that white display (light reaches the display Side, that
`is, light corresponding to a color of a pixel to which Voltage
`is not applied reaches the display Side in the case of color
`display; therefore the white display is not limited to a white
`display in terms of chromatics) is performed with no appli
`cation of Voltage.
`Functions of this liquid crystal display element are
`described below.
`FIG. 4 shows functions of transmissive type display, in
`which a backlight is Switched on. In the figure, three kinds
`of pixels R, G and B are shown and interference filters for
`not merely transmitting R (red light), G (green light) and B
`(blue light) but also reflecting light other than red light,
`green light and blue light are formed as color filters at the
`pixels R, G and B respectively. Among white light from the
`backlight, the color filters not only transmit Solely light of
`predetermined colors but also reflect light other than the
`light of predetermined colors on the Side of the backlight.
`This reflected light thereby is reflected again inside a back
`light unit and thereafter reaches the display Side through
`predetermined color filters since it will be rare that there are
`no pixels of the same color as the reflected light on the whole
`display Surface. Even if this is not the case, the reflected light
`is utilized directly or indirectly for the rise of temperature of
`the backlight and the emission of light therefrom, leading to
`notably less loSS of light as compared with absorption type
`color filters.
`The liquid crystal layer in transmissive type display is
`normally black; therefore only a pixel to which Voltage is
`applied, namely, the pixel R transmits R (red light), for
`35
`example, when Voltage is applied to only the pixel R. G
`(green light) and B (blue light), meanwhile, are absorbed in
`the polarizer on the front Side. Consequently, the transmis
`Sion of only R (red light) through the polarizer results in a
`display of red in color display of R, G and B.
`FIG. 5 shows functions of reflective type display, in which
`a backlight is Switched off, external light Such as room light
`enters from the Side of operators, and additionally Voltage is
`applied to only the pixel R.
`The external light is white light. Color filters formed at the
`pixels reflect light of complementary colors to the above
`mentioned colors of transmitted light, as the filters are
`interference filters; therefore in this case the color filter R
`reflects C (cyan light) which is a mixture of G and B.
`However, a Voltage is applied to the pixel R. At this time
`because the liquid crystal layer is normally white in use as
`a reflective type element, pixels to which a Voltage is applied
`become black display. That is, light is absorbed.
`At As a result, C (cyan light) reflected thereby is absorbed
`by the polarizer 17. On the other hand, the interference filters
`at the pixels G and B reflect M (magenta light: a mixture of
`R and B) and Y (yellow light: a mixture of R and G)
`respectively so that M (magenta light) and Y (yellow light)
`reflected thereby are not absorbed in the normally white
`reflective type display Since Voltage is not applied to the
`pixels G and B. Consequently, in reflective type display the
`reflection of M (magenta light) and Y (yellow light) results
`in a display of red in color display of C, M and Y for the
`reason that each of the pixels G and B is Small.
`In reflective type display not employing a backlight,
`because more importance is placed on brightness than on
`color purity, color display of C, M and Y is desirable. On the
`
`8
`contrary, in a transmissive type display employing a
`backlight, because more importance is place on color purity
`than brightness, color display of R, G and B is desirable. The
`liquid crystal display element according to the present
`embodiment Satisfactorily meets the requirements. Actually,
`the liquid crystal display element was used for both of the
`types, offering very excellent display.
`The liquid crystal display device according to the embodi
`ment is Suitable for being applied to mobile apparatuses Such
`as portable data terminals. A backlight thereof can be
`Switched on when there is ample power Supply, and mean
`while can be switched off or dimmed when the battery
`residual quantity is low. More specifically, in accordance
`with the battery residual quantity, brightness of external light
`and the like, the Voltage of the backlight can be decreased or
`only one of two backlights can be Switched on.
`The liquid crystal according to the embodiment is a
`twisted nematic mode with a twist of 45. It is to be noted
`that the liquid crystal is not limited to this mode, in other
`words, the liquid crystal may be homeotropic liquid crystal,
`OCB liquid crystal, STN liquid crystal, ferroelectric liquid
`crystal, ECB liquid crystal or the like.
`The behavior itself of the liquid crystal layer according to
`the embodiment is normally white in reflective type display
`and meanwhile is normally black in transmissive type dis
`play. The reverse of this is also possible, in which case it is
`necessary to adjust the angle at which a po