(19) United States
`(12) Patent Application Publication (10) Pub. No.: US 2006/0203157 A1
`(43) Pub. Date:
`Sep. 14, 2006
`Ozawa et al.
`
`US 200602031.57A1
`
`(54)
`
`(75)
`
`(73)
`(21)
`(22)
`
`LIQUID CRYSTAL DISPLAY AND
`ELECTRONIC DEVICE
`
`Inventors: Kinya Ozawa, Suwa-shi (JP);
`Nobutaka Urano, Chino-shi (JP);
`Tsuyoshi Maeda, Fujimi-machi (JP)
`Correspondence Address:
`OLIFF & BERRIDGE, PLC
`P.O. BOX 19928
`ALEXANDRIA, VA 22320 (US)
`Assignee: Seiko Epson Corporation, Tokyo (JP)
`
`Appl. No.:
`
`11/434,762
`
`Filed:
`
`May 17, 2006
`
`Related U.S. Application Data
`
`(62)
`
`Division of application No. 10/927,076, filed on Aug.
`27, 2004, which is a division of application No.
`10/352,199, filed on Jan. 28, 2003.
`
`
`
`(30)
`
`Foreign Application Priority Data
`
`Jan. 29, 2002 (JP)...................................... 2002-019876
`Dec. 20, 2002 (JP)...................................... 2002-369975
`
`Publication Classification
`
`(51) Int. Cl.
`(2006.01)
`GO2F L/335
`(52) U.S. Cl. .............................................................. 349/114
`(57)
`ABSTRACT
`The invention provides a liquid crystal display capable of
`obtaining light and high-contrast display having a wide
`viewing angle in a transflective liquid crystal display. A
`liquid crystal display of the present invention employs a
`vertical alignment mode using a liquid crystal layer that is
`vertically aligned in the initial alignment state. A transparent
`display area is disposed to Surround the periphery of a
`reflective display area in one dot, and an insulating film is
`provided in the area that corresponds to the reflective display
`area in the center of the dot. The insulating film makes the
`thickness of the liquid crystal layer in the reflective display
`area to be smaller than the thickness of the liquid crystal
`layer in the transparent display area.
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`Page 1
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`Patent Application Publication Sep. 14, 2006 Sheet 1 of 14
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`US 2006/0203157 A1
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`Patent Application Publication Sep. 14, 2006 Sheet 2 of 14
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`Page 3
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`Patent Application Publication Sep. 14, 2006 Sheet 3 of 14
`
`US 2006/0203157 A1
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`Patent Application Publication Sep. 14, 2006 Sheet 4 of 14
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`Page 5
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`Patent Application Publication Sep. 14, 2006 Sheet 5 of 14
`
`US 2006/02031.57 A1
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`Page 6
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`Patent Application Publication Sep. 14, 2006 Sheet 6 of 14
`
`US 2006/0203157 A1
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`Page 7
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`Patent Application Publication Sep. 14, 2006 Sheet 7 of 14
`
`US 2006/0203157 A1
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`Page 8
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`Patent Application Publication Sep. 14, 2006 Sheet 8 of 14
`
`US 2006/0203157 A1
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`FIG. 8
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`Patent Application Publication Sep. 14, 2006 Sheet 9 of 14
`
`US 2006/02031.57 A1
`
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`Page 10
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`Patent Application Publication Sep. 14, 2006 Sheet 10 of 14
`
`US 2006/02031.57 A1
`
`FIG. 10
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`Page 11
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`Patent Application Publication Sep. 14, 2006 Sheet 11 of 14
`FIG. 11
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`US 2006/02031.57 A1
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`Page 12
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`Patent Application Publication Sep. 14, 2006 Sheet 12 of 14
`
`US 2006/0203157 A1
`
`F.G. 12
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`
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`Patent Application Publication Sep. 14, 2006 Sheet 13 of 14
`FIG. 13
`
`US 2006/0203157 A1
`
`
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`Patent Application Publication Sep. 14, 2006 Sheet 14 of 14
`
`US 2006/02031.57 A1
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`601 -
`
`
`
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`US 2006/02031.57 A1
`
`Sep. 14, 2006
`
`LIQUID CRYSTAL DISPLAY AND ELECTRONIC
`DEVICE
`0001) This is a Division of application Ser. No. 10/927,
`076 filed Aug. 27, 2004, which in turn is a Division of
`application Ser. No. 10/352,199 filed Jan. 28, 2003. The
`entire disclosures of the prior applications are hereby incor
`porated by reference herein in their entirety.
`
`BACKGROUND OF THE INVENTION
`
`0002)
`1. Field of Invention
`0003. The present invention relates to a liquid crystal
`display and an electronic device. More specifically, the
`invention relates to a technique of obtaining a high-contrast
`display having a wide viewing angle in a transflective liquid
`crystal display that performs display in both a reflective
`mode and a transparent mode.
`0004 2. Description of Related Art
`0005 Since reflective liquid crystal displays have no light
`Sources, such as a backlight, they consume low power, and
`thus can be used for various portable electronic devices.
`However, the reflective liquid crystal displays perform dis
`play using outside light, such as Sunlight and illumination
`light. Thus, these displays are subject to low visibility in a
`dark place. Therefore, the related art includes liquid crystal
`displays capable of making display visible using outside
`light in a light place, as in general reflective liquid crystal
`displays, and using an inside light source, such as a back
`light, in a dark place. In other words, Such liquid crystal
`displays employ a reflective and transparent display system,
`thereby allowing clear display even in low light while
`reducing power consumption by Switching the display sys
`tem between the reflective mode and the transparent mode
`depending on the Surrounding brightness. Hereinafter, in this
`specification, liquid crystal displays of this type are referred
`to as “transflective liquid crystal displays.”
`0006 Such related art transflective liquid crystal displays
`include a liquid crystal display having a structure in which
`a liquid crystal layer is sandwiched between an upper
`substrate and a lower substrate. A reflective film having a
`light-transmitting window in a metallic film made of alu
`minum or the like is provided on the inner surface of the
`lower substrate, and this reflective film functions as a
`transflective film. In this case, in a reflective mode, outside
`light that has entered from the upper Substrate passes
`through the liquid crystal layer, is then reflected by the
`reflective film, again passes through the liquid crystal layer,
`and outgoes from the upper Substrate, thus contributing to
`display. On the other hand, in a transparent mode, light from
`the backlight, which has entered from the lower substrate,
`passes through the liquid crystal layer from the window of
`the reflective film, and then emerges from the upper sub
`strate to the exterior, thereby contributing to display.
`Accordingly, in the reflective-film formed area, the area
`which has the window serves as a transparent display area
`and the other area serves as a reflective display area.
`0007 Liquid crystal alignment modes include a twisted
`nematic (hereinafter “TN) mode in which liquid crystal
`molecules exhibit a twisted alignment substantially parallel
`to the substrate surface and vertical to the substrate; and a
`vertical alignment mode in which liquid crystal molecules
`exhibit vertical alignment, under a no voltage applied State.
`
`Although, in the related art, the TN mode can be viewed as
`reliable, the related art also includes liquid crystal displays
`that in the vertical alignment mode can provide some
`excellent characteristics.
`0008 For example, in the vertical alignment mode, since
`the state in which the liquid crystal molecules are aligned
`vertically to the substrate surface (there is no optical retar
`dation as viewed from the normal) is used as black display,
`the black display is Superior in quality, thus providing high
`contrast. In Vertical-alignment LCDS which are Superior in
`front contrast, the range of viewing angle in which a fixed
`contrast can be obtained is wider than that of the horizontal
`alignment-mode TN liquid crystal. Furthermore, employing
`an alignment dividing (multidomain) technique of dividing
`the alignment orientation of a liquid crystal in pixels pro
`vides a remarkably wide viewing angle.
`0009. In the transflective liquid crystal display with the
`aforesaid structure, the retardation of the liquid crystal in the
`reflective display area is expressed by: 2xAnd, because the
`incident light passes through the liquid crystal layer two
`times and then reaches the observer, where the thickness of
`the liquid crystal layer is d, the refractive index anisotropy
`of the liquid crystal is: An, and the retardation of the liquid
`crystal which is expressed as their integrated value is: And.
`On the other hand, the retardation of the liquid crystal in the
`transparent display area is expressed by: 1XAnd, because
`the light from the backlight passes through the liquid crystal
`layer only once.
`0010. As described above, when the alignment of the
`liquid crystal molecules of the liquid crystal layer is con
`trolled, even with the structure having different retardation
`values in the reflective display area and in the transparent
`display area, an electric field has been applied to the liquid
`crystal at the same driving Voltage in both display modes. In
`such a case, when the liquid crystal with different display
`modes, in other words, the liquid crystal with different
`retardations between the transparent display area and the
`reflective display area is aligned at the same driving Voltage,
`it poses a problem of obtaining no high-contrast display. In
`order to address or solve the problem, a liquid crystal display
`is disclosed in Japanese Unexamined Patent Application
`Publication No. 11-242226 that has a structure having
`different thicknesses of the liquid crystal layer in the trans
`parent display area and in the reflective display area.
`
`SUMMARY OF THE INVENTION
`0011. As described above, using the vertical alignment
`mode can also be used to achieve high contrast. Therefore,
`a liquid crystal display with a combination of the transflec
`tive liquid crystal display and the vertical alignment mode
`can be beneficial. However, problems exist with such a
`structure, including a problem of decreased contrast due to
`the difference in retardation in the reflective and transparent
`display modes, problems of alignment control and alignment
`division in the vertical alignment mode, and so on, thus
`preventing Such a display from becoming realized.
`0012. The present invention addresses or solves the
`above and/or other problems, and provides a liquid crystal
`display capable of obtaining light and high-contrast display
`having a wide viewing angle in a transflective liquid crystal
`display.
`
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`US 2006/02031.57 A1
`
`Sep. 14, 2006
`
`0013 In order to address or achieve the above, a liquid
`crystal display according to the present invention includes a
`liquid crystal layer sandwiched between a pair of Substrates,
`and separately having a transparent display area for trans
`parent display and a reflective display area for reflective
`display in one dot area. The liquid crystal layer exhibits
`vertical alignment in the initial alignment state. An insulat
`ing film is provided between at least one of the pair of
`Substrates and the liquid crystal layer and in at least the
`reflective display area, the insulating film making the thick
`ness of the liquid crystal layer in the reflective display area
`and in the transparent display area different owing to its film
`thickness.
`0014. The liquid crystal display of the present invention
`is a combination of a transflective liquid crystal display and
`a liquid crystal in a vertical alignment mode. A transflective
`liquid crystal display can be provided with a structure in
`which, in order to address or solve the problem of reduction
`in contrast due to the difference of retardation between the
`reflective and the transparent display modes, the thickness of
`the liquid crystal layer is varied in the reflective display area
`and in the transparent display area by forming an insulating
`film with a fixed thickness in the reflective display area on
`the lower substrate so as to project toward the liquid crystal
`layer. The applicants have studied this type of liquid crystal
`display. With such a structure, the thickness of the liquid
`crystal layer in the reflective display area can be made to be
`Smaller than that of the liquid crystal layer in the transparent
`display area owing to the presence of the insulating film.
`Therefore, the retardation in the reflective display area and
`the retardation in the transparent display area can be suffi
`ciently close to or substantially equal to each other, thereby
`allowing an increase in contrast.
`0.015 The inventors have found that the alignment ori
`entation of the liquid crystal in a vertical alignment mode
`during the application of an electric field can be controlled
`by combining a liquid crystal layer in a vertical alignment
`mode to the liquid crystal display having the above insulat
`ing film. More specifically, a negative liquid crystal is
`generally used when the vertical alignment mode is
`employed. However, the direction in which the liquid crystal
`molecules fall cannot be controlled without any consider
`ations (unless a pre-tilt is given) because the liquid crystal
`molecules are brought down from a state of standing verti
`cally to the Substrate surface in the initial alignment state,
`thus generating disturbance of alignment (disclination) to
`cause imperfect display Such as light dropout, resulting in a
`decrease in display quality. Therefore, when the vertical
`alignment mode is employed, an important factor is to
`control the alignment orientation of the liquid crystal mol
`ecules in applying an electric field. In the liquid crystal
`display having the aforesaid insulating film, the insulating
`film projects toward the liquid crystal layer, which serves as
`a projection. Thus, a pre-tilt that corresponds to the shape of
`the projection can be given with the liquid crystal molecules
`vertically aligned in the initial state. Due to this action, the
`alignment orientation when an electric field is applied to the
`liquid crystal molecules can be controlled. Consequently,
`high-contrast display can be achieved without imperfect
`display, Such as light drop.
`0016. With the structure of the present invention, the
`transflective liquid crystal display in a vertical alignment
`mode has an insulating film. Accordingly, the problem of
`
`reduction in contrast due to the difference of retardation
`between the reflective and the transparent display modes can
`be addressed or solved, which is a fundamental problem of
`the transflective liquid crystal display, and imperfect display,
`because of the fact that the alignment orientation of the
`liquid crystal molecules in the vertical alignment mode
`cannot be controlled, can be reduced. Consequently, both the
`advantage of the vertical alignment mode and the advantage
`of the transflective type can fully be taken to realize a liquid
`crystal display of high display quality.
`0017. The arrangement of the transparent display area
`and the reflective display area in one dot area can be set
`arbitrarily. However, it is preferable to arrange the transpar
`ent display area So as to Surround the periphery of the
`reflective display area and to arrange the insulating film in
`the area that corresponds to the reflective display area in the
`center of the dot.
`0018 From such a viewpoint, another liquid crystal dis
`play of the present invention includes a liquid crystal layer
`sandwiched between a pair of Substrates, and separately
`having a transparent display area for transparent display and
`a reflective display area for reflective display in one dot area.
`An insulating film is provided between at least one of the
`pair of Substrates and the liquid crystal layer and in at least
`the reflective display area, the insulating film making the
`thickness of the liquid crystal layer in the reflective display
`area and in the transparent display area different owing to its
`film thickness. The thickness of the liquid crystal layer in the
`center of the dot area is set to be smaller than in the
`periphery in the one dot area.
`0019. With such a structure, if a rectangular reflective
`display area is provided in the center of one dot area and a
`rectangular insulating film is disposed therein, around which
`a transparent display area is formed, the alignment orienta
`tions of the liquid crystal molecules are specified to four
`orientations that are perpendicular to each side of the
`rectangle with the insulating film in the center of the dot as
`the center. As a result, four areas that each have a different
`alignment orientation are formed in one dot area to realize
`an alignment dividing structure, thus achieving a wide
`Viewing angle.
`0020. Alternatively, contrarily to the aforesaid structure,
`it is also possible to have a structure in which an insulating
`film is provided between at least one of the pair of substrates
`and the liquid crystal layer and in at least the reflective
`display area, the insulating film making the thickness of the
`liquid crystal layer in the reflective display area and in the
`transparent display area different owing to its film thickness.
`The thickness of the liquid crystal layer in the periphery of
`the one dot area is set to be smaller than in the center. More
`specifically, the reflective display area is provided so as to
`Surround the periphery of the transparent display area in the
`one dot. The insulating film is disposed in the area corre
`sponding to the reflective display area in the periphery of the
`dot.
`0021 With such a structure, if a rectangular reflective
`display area is provided in the center of one dot area, a
`rectangular-frame-shaped insulating film is disposed on the
`outside thereof, and a reflective display area is formed in the
`periphery thereof, the alignment orientations of the liquid
`crystal molecules are specified to four orientations that are
`perpendicular to each side of the rectangular frame from the
`
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`

`US 2006/02031.57 A1
`
`Sep. 14, 2006
`
`insulating film in the periphery of the dot area toward the
`center. As a result, four areas that each have a different
`alignment orientation are formed in one dot area, as in the
`aforesaid structure, to realize an alignment dividing struc
`ture, thus achieving a wide viewing angle.
`0022 Preferably, the insulating film includes an inclined
`area in the vicinity of the boundary between the reflective
`display area and the transparent display area, the inclined
`area having an inclined plane so that its thickness continu
`ously varies.
`0023 The end of the insulating film, which corresponds
`to the boundary between the reflective display area and the
`transparent display area, may have a step-like difference in
`thickness. However, in Such a case, the thickness of the
`liquid crystal layer sharply changes because of the aforesaid
`step in the vicinity of the boundary between the reflective
`display area and the transparent display area, thus causing
`alignment disturbance of the liquid crystal to exert a bad
`influence upon display. On the other hand, when the insu
`lating film has an inclined plane so as to continuously vary
`the thickness thereof, the alignment of the liquid crystal also
`varies continuously depending on the position of the
`inclined plane of the insulating film, thus causing no large or
`Substantial disturbance of alignment to prevent or reduce
`imperfect display. When the insulating film is rectangular, as
`described above, the inclined plane is also inclined in four
`directions perpendicularly crossing each other. Therefore,
`the presence of the inclined plane allows Smooth formation
`of the alignment dividing structure.
`0024. It is also possible to provide an electrode to drive
`the liquid crystal layer to the Substrate having the insulating
`film and to provide a no electrode formed area where the
`electrode is absent in at least part of the inclined plane of the
`insulating film.
`0025. With the structure of the present invention, as
`described above, merely providing an insulating film that is
`a projection projecting toward the liquid crystal layer allows
`control of alignment orientation. However, when no elec
`trode formed area is provided to at least part of the inclined
`plane of the insulating film, an electric field (potential lines)
`generating between the electrodes on both the substrates is
`distorted in the vicinity of the no electrode formed area. The
`action of the distorted electric field allows smooth or sub
`stantially smooth control of the alignment orientation of the
`liquid crystal molecules.
`0026 Assuming that the center of one dot is a rectangular
`reflective display area, the periphery is a transparent display
`area and a rectangular-frame-shaped no electrode formed
`area is provided in the inclined area of the insulating film,
`which corresponds to the boundary between the reflective
`display area and the transparent display area, the electrode
`of the reflective display area and the electrode of the
`transparent display area are completely separated. There
`fore, it becomes difficult to apply the same driving Voltage
`to both of them at the same time. Accordingly, it is prefer
`able to provide a structure in which the electrode in the
`reflective display area and the electrode in the transparent
`display area, which are provided on both sides of the no
`electrode formed area, are electrically connected through a
`connecting section formed of the same layer as the elec
`trodes. Alternatively, it is also preferable to provide a
`structure in which the electrode in the reflective display area
`
`and the electrode in the transparent display area are electri
`cally connected through a connecting section formed of a
`different layer from the electrodes. With such a structure, the
`same driving Voltage can easily be applied simultaneously to
`the electrode in the reflective display area and the electrode
`in the transparent display area.
`0027. When one of the substrates is an element substrate
`having a pixel electrode and a Switching element and the
`other Substrate is an opposed substrate having a common
`electrode and the insulating film, it is preferable to dispose
`a contact hole to electrically connect the pixel electrode and
`the Switching element on the one Substrate in the position not
`overlapping the inclined area.
`0028. Since the contact hole that electrically connects the
`pixel electrode and the switching element is formed on the
`upper layer of one Substrate, the pixel electrode is generally
`recessed at the portion of the contact hole. Therefore, with
`the aforesaid structure, the electric field that has been
`distorted in the vicinity of the no electrode formed area is
`further distorted because of the recess of the pixel electrode,
`thereby facilitating control of the alignment of the liquid
`crystal molecules.
`0029 Furthermore, when an electrode to drive the liquid
`crystal layer and an insulating film are provided on one of
`the pair of substrates, and an electrode to drive the liquid
`crystal layer is provided on the other substrate, it is prefer
`able that the electrode on the other substrate include a
`window on the outside of the inclined area of the insulating
`film.
`0030. With the structure of the present invention, as
`described above, merely providing the insulating film that is
`a projection projecting toward the liquid crystal layer allows
`control of alignment orientation. However, when the elec
`trode on the other substrate, which is opposed to the insu
`lating film, has a window on the outside of the inclined area
`of the insulating film, an electric field generating between
`the electrodes on both the substrates tilts because there are
`no electrodes at the window. The action of the tilted electric
`field allows smoother control of the alignment orientation of
`the liquid crystal molecules.
`0031 When the insulating film has an inclined plane, it is
`preferable that the inclination angle of the inclined plane of
`the insulating film relative to the substrate surface be in the
`range of 5° to 50°. The inclined plane may be either planar
`or curved. Here, “the inclination angle of the inclined plane'
`means an angle 0 formed by the tangential line S of an
`inclined plane in the position where the layer thickness in the
`inclined area is hi? 2, and a Substrate Surface (planar plane),
`where the thickness of the flat part of the insulating film is
`h.
`0032. When the inclination angle is less than 5°, it forms
`a gentle inclined plane. Therefore, the inclined area
`increases in size to have too large an area where the
`retardation becomes fragmentary, thus increasing optical
`loss. On the other hand, when the inclination angle exceeds
`50, it forms a steeply inclined plane. Therefore, the liquid
`crystal molecules are aligned vertically to the inclined plane
`when non-selected Voltage is applied, thereby generating
`disclination between the liquid crystal molecules on the
`inclined plane and those on the planar plane. Consequently,
`black floating (a leak of light) occurs to decrease in contrast.
`Therefore, it is desirable that the inclination angle be in the
`range of 5° to 50°.
`
`Page 18
`
`JAPAN DISPLAY INC. - EX. 2007
`TIANMA MICROELECTRONICS CO. LTD. v. JAPAN DISPLAY INC
`IPR2021-01058
`
`

`

`US 2006/02031.57 A1
`
`Sep. 14, 2006
`
`0033. The outline of the insulating film in one dot area is
`not particularly limited, and the invention can include vari
`ous shapes. However, when it is an equilateral polygon or a
`circle, the liquid crystal molecules are uniformly divided in
`each direction in one dot area. As a result, a viewing angle
`at which high contrast is obtained can be isotropically
`widened.
`0034) Furthermore, providing a circularly-polarized-light
`radiating device to radiate circularly polarized light to the
`one substrate or the other substrate allows preferable reflec
`tive display and transparent display.
`0035 An electronic device of the present invention
`includes the liquid crystal display according to the present
`invention.
`0.036 With such a structure, electronic devices can be
`provided which have a light and high-contrast liquid crystal
`display having a wide viewing angle irrespective of use
`environment.
`
`BRIEF DESCRIPTION OF THE DRAWINGS
`0037 FIG. 1 is a schematic circuit diagram of a plurality
`of dots arranged in the form of matrix which constitute an
`image display area of a liquid crystal display according to a
`first exemplary embodiment of the present invention;
`0038 FIG. 2 is a plan view showing the structure of an
`adjacent plurality of dots on a TFT array substrate which
`constitutes the liquid crystal display of the same:
`0.039
`FIG. 3 is a sectional view taken along plane A-A
`of FIG. 2, showing the structure of the liquid crystal display
`of the same;
`0040 FIG. 4 is a plan view showing the structure of an
`adjacent plurality of dots on a TFT array substrate, which
`constitutes a liquid crystal display according to a second
`exemplary embodiment of the present invention;
`0041
`FIG. 5 is a sectional view taken along plane A-A
`of FIG. 4, showing the structure of the liquid crystal display
`of the same;
`0.042
`FIG. 6 is a sectional view showing the structure of
`a liquid crystal display according to a third exemplary
`embodiment of the present invention:
`0.043
`FIG. 7 is a plan view showing the structure of an
`adjacent plurality of dots on a TFT array substrate, which
`constitutes a liquid crystal display according to a fourth
`exemplary embodiment of the present invention;
`0044 FIG. 8 is a sectional view taken along plane A-A
`of FIG. 7, showing the structure of the liquid crystal display
`of the same;
`0045 FIG. 9 is a plan view showing the structure of an
`adjacent plurality of dots on a TFT array substrate, which
`constitutes a liquid crystal display according to a fifth
`exemplary embodiment of the present invention;
`0046 FIG. 10 is a sectional view taken along plane A-A
`of FIG. 9, showing the structure of the liquid crystal display
`of the same;
`0047 FIG. 11 is a sectional view showing the structure
`of a liquid crystal display according to a sixth exemplary
`embodiment of the present invention:
`
`0048 FIG. 12 is a sectional view showing the structure
`of a liquid crystal display according to a seventh exemplary
`embodiment of the present invention;
`0049 FIG. 13 is a graph explaining the inclination angle
`of an insulating film of the present invention;
`0050 FIG. 14 is a perspective view showing an example
`of an electronic device of the present invention;
`0051
`FIG. 15 is a perspective view showing another
`example of an electronic device of the present invention; and
`0052 FIG. 16 is a perspective view showing still another
`example of an electronic device of the present invention.
`DETAILED DESCRIPTION OF PREFERRED
`EMBODIMENTS
`0053) Referring to FIGS. 1 to 3, a first exemplary
`embodiment of the present invention is described below.
`0054 A liquid crystal display of this exemplary embodi
`ment is an example of an active-matrix liquid crystal display
`that uses a thin film transistor (hereinafter “TFT) as a
`Switching element.
`0055