US20080278668A1 - Liquid crystal device and projection display device - Google Patents
Liquid crystal device and projection display device Download PDFInfo
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- US20080278668A1 US20080278668A1 US12/124,242 US12424208A US2008278668A1 US 20080278668 A1 US20080278668 A1 US 20080278668A1 US 12424208 A US12424208 A US 12424208A US 2008278668 A1 US2008278668 A1 US 2008278668A1
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- liquid crystal
- compensating plate
- optical compensating
- optical
- light
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- G—PHYSICS
- G02—OPTICS
- G02F—OPTICAL DEVICES OR ARRANGEMENTS FOR THE CONTROL OF LIGHT BY MODIFICATION OF THE OPTICAL PROPERTIES OF THE MEDIA OF THE ELEMENTS INVOLVED THEREIN; NON-LINEAR OPTICS; FREQUENCY-CHANGING OF LIGHT; OPTICAL LOGIC ELEMENTS; OPTICAL ANALOGUE/DIGITAL CONVERTERS
- G02F1/00—Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics
- G02F1/01—Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics for the control of the intensity, phase, polarisation or colour
- G02F1/13—Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics for the control of the intensity, phase, polarisation or colour based on liquid crystals, e.g. single liquid crystal display cells
- G02F1/133—Constructional arrangements; Operation of liquid crystal cells; Circuit arrangements
- G02F1/1333—Constructional arrangements; Manufacturing methods
- G02F1/1335—Structural association of cells with optical devices, e.g. polarisers or reflectors
- G02F1/13363—Birefringent elements, e.g. for optical compensation
-
- G—PHYSICS
- G02—OPTICS
- G02F—OPTICAL DEVICES OR ARRANGEMENTS FOR THE CONTROL OF LIGHT BY MODIFICATION OF THE OPTICAL PROPERTIES OF THE MEDIA OF THE ELEMENTS INVOLVED THEREIN; NON-LINEAR OPTICS; FREQUENCY-CHANGING OF LIGHT; OPTICAL LOGIC ELEMENTS; OPTICAL ANALOGUE/DIGITAL CONVERTERS
- G02F1/00—Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics
- G02F1/01—Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics for the control of the intensity, phase, polarisation or colour
- G02F1/13—Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics for the control of the intensity, phase, polarisation or colour based on liquid crystals, e.g. single liquid crystal display cells
- G02F1/133—Constructional arrangements; Operation of liquid crystal cells; Circuit arrangements
- G02F1/1333—Constructional arrangements; Manufacturing methods
- G02F1/1335—Structural association of cells with optical devices, e.g. polarisers or reflectors
-
- G—PHYSICS
- G02—OPTICS
- G02F—OPTICAL DEVICES OR ARRANGEMENTS FOR THE CONTROL OF LIGHT BY MODIFICATION OF THE OPTICAL PROPERTIES OF THE MEDIA OF THE ELEMENTS INVOLVED THEREIN; NON-LINEAR OPTICS; FREQUENCY-CHANGING OF LIGHT; OPTICAL LOGIC ELEMENTS; OPTICAL ANALOGUE/DIGITAL CONVERTERS
- G02F1/00—Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics
- G02F1/01—Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics for the control of the intensity, phase, polarisation or colour
- G02F1/13—Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics for the control of the intensity, phase, polarisation or colour based on liquid crystals, e.g. single liquid crystal display cells
- G02F1/133—Constructional arrangements; Operation of liquid crystal cells; Circuit arrangements
- G02F1/1333—Constructional arrangements; Manufacturing methods
- G02F1/1335—Structural association of cells with optical devices, e.g. polarisers or reflectors
- G02F1/13363—Birefringent elements, e.g. for optical compensation
- G02F1/133634—Birefringent elements, e.g. for optical compensation the refractive index Nz perpendicular to the element surface being different from in-plane refractive indices Nx and Ny, e.g. biaxial or with normal optical axis
-
- G—PHYSICS
- G02—OPTICS
- G02F—OPTICAL DEVICES OR ARRANGEMENTS FOR THE CONTROL OF LIGHT BY MODIFICATION OF THE OPTICAL PROPERTIES OF THE MEDIA OF THE ELEMENTS INVOLVED THEREIN; NON-LINEAR OPTICS; FREQUENCY-CHANGING OF LIGHT; OPTICAL LOGIC ELEMENTS; OPTICAL ANALOGUE/DIGITAL CONVERTERS
- G02F2413/00—Indexing scheme related to G02F1/13363, i.e. to birefringent elements, e.g. for optical compensation, characterised by the number, position, orientation or value of the compensation plates
- G02F2413/01—Number of plates being 1
-
- G—PHYSICS
- G02—OPTICS
- G02F—OPTICAL DEVICES OR ARRANGEMENTS FOR THE CONTROL OF LIGHT BY MODIFICATION OF THE OPTICAL PROPERTIES OF THE MEDIA OF THE ELEMENTS INVOLVED THEREIN; NON-LINEAR OPTICS; FREQUENCY-CHANGING OF LIGHT; OPTICAL LOGIC ELEMENTS; OPTICAL ANALOGUE/DIGITAL CONVERTERS
- G02F2413/00—Indexing scheme related to G02F1/13363, i.e. to birefringent elements, e.g. for optical compensation, characterised by the number, position, orientation or value of the compensation plates
- G02F2413/10—Indexing scheme related to G02F1/13363, i.e. to birefringent elements, e.g. for optical compensation, characterised by the number, position, orientation or value of the compensation plates with refractive index ellipsoid inclined, or tilted, relative to the LC-layer surface O plate
Definitions
- the present invention relates to a liquid crystal device and to a projection display device.
- liquid crystal projectors projection display devices
- a structure has been suggested in which a liquid crystal device, which is driven in a ‘VA (Vertical Alignment) mode’ where liquid crystal having negative dielectric anisotropy is vertically aligned on a substrate and liquid crystal molecules are tilted by applying a voltage, is included as a light valve.
- VA Vertical Alignment
- most liquid crystal projectors in the related art have a contrast ratio of substantially 1:500 in a projected image, they are not as good as projectors, such as DMDs (registered trademark) using mechanical shutters, which have a contrast ratio of 1:3000.
- Japanese Unexamined Patent Application Publication No. 7-69536 discloses a technology in which an optical compensating plate is employed to compensate for the incident angle dependency of the liquid crystal device, thereby realizing a display having a higher contrast.
- a refractive index anisotropic body serving as the optical compensating plate is arranged in a vertical-alignment-type liquid crystal cell, so that it is possible to compensate for a phase difference occurring in the liquid crystal cell due to inclined light.
- the effect of the optical compensating plate decreases as the pretilt angle decreases from 90°.
- An advantage of the invention is that it provides a projection display device which is capable of performing excellent optical compensation even when the liquid crystal is pretilted, and of performing image display having a high contrast by including a liquid crystal device of the invention.
- a liquid crystal device includes a pair of substrates; a liquid crystal layer interposed between the pair of substrates, the liquid crystal layer being composed of liquid crystal having negative dielectric anisotropy representing that an initial alignment state thereof is vertical; and an optical compensating plate which is provided outside at least one substrate of the pair of substrates and has negative refractive index anisotropy.
- the liquid crystal is pretilted in a predetermined direction, and an optical axis direction of the optical compensating plate is substantially parallel to the pretilt direction of the liquid crystal.
- the optical compensating plate be disposed parallel to one substrate, and the optical axis direction of the optical compensating plate be substantially parallel to the pretilt direction of the liquid crystal, at an angle deviating from the normal line of the optical compensating plate.
- the optical axis direction of the optical compensating plate is substantially parallel to the normal line direction of the optical compensating plate, and the optical compensating plate be disposed to be inclined from a location parallel to one of the pair of substrates such that the optical axis direction of the optical compensating plate is substantially parallel to the pretilt direction of the liquid crystal.
- the optical axis direction of the optical compensating plate is inclined according to the pretilt of the liquid crystal, so that it is possible to entirely compensate for a phase difference due to the pretilt of the liquid crystal and a phase difference due to the light in a inclined direction.
- a projection display device including the above-mentioned liquid crystal device as an optical modulating unit.
- the projection display device further includes an adjuster that adjusts an arrangement angle of the optical compensating plate such that the optical axis direction of the optical compensating plate aligns with the pretilt direction of the liquid crystal.
- the adjuster be composed of a rotation mechanism for rotating the optical compensating plate on two axes.
- the optical axis direction of the optical compensating plate can be freely adjusted by the adjusting mechanism, it is possible to cope with the design change such as the change of the pretilt angle of the liquid crystal without requiring the design change of the optical compensating plate.
- FIG. 1 is an equivalent circuit diagram of a liquid crystal panel
- FIG. 2 is a diagram showing the planar structure of the liquid crystal panel
- FIG. 3 is a cross-sectional view taken along the line III-III of FIG. 2 ;
- FIG. 4 is an exploded perspective view of a liquid crystal device according to a first embodiment of the invention.
- FIG. 5 is a diagram showing an index ellipsoid of an optical compensating plate
- FIG. 6 is a graph showing black transmittance when changing an inclined angle of the optical compensating plate and a pretilt angle of liquid crystal
- FIG. 7 is an exploded perspective view of a liquid crystal device according to a second embodiment of the invention.
- FIG. 8 is a diagram showing the index ellipsoid of the optical compensating plate
- FIG. 9 is a cross-sectional view showing one structural example of the optical compensating plate.
- FIGS. 10A and 10B are diagrams showing one example of a method of manufacturing the optical compensating plate
- FIGS. 11A and 11B are diagrams of contrast curves when an optical axis of the optical compensating plate is inclined and when the optical axis of the optical compensating plate is not inclined, respectively;
- FIG. 12 is a diagram showing an example of a projection display device.
- FIG. 13 is a cross-sectional view showing an example of liquid crystal device applied to the projection display device.
- each member has been adjusted in order to have a recognizable size in the drawings described below.
- one side of each constituent element of a liquid crystal device toward a liquid crystal layer is called an inner side
- the other side of the liquid crystal device is called an outer side.
- the liquid crystal device according to the first embodiment includes a liquid crystal panel with a liquid crystal layer interposed between a pair of substrates, an optical compensating plate disposed outside one substrate of the liquid crystal panel, and polarizers disposed outside the optical compensating plate and the other substrate of the liquid crystal panel, respectively.
- an active-matrix-type transmissive liquid crystal panel which uses a thin film transistor (hereinafter, referred to as a TFT) element serving as a switching element, will be described by way of an example.
- TFT thin film transistor
- FIG. 1 is an equivalent circuit diagram of the liquid crystal panel.
- a plurality of dots arranged in a matrix which constitute an image display region of the transmissive liquid crystal panel are provided with pixel electrodes 9 , respectively.
- a TFT element 30 which serves as a switching element to electrically control the pixel electrode 9 , is provided at one side of the pixel electrode 9 .
- the TFT element 30 has a source electrode electrically connected to a data line 6 a .
- the respective data lines 6 a are supplied with image signals S 1 , S 2 , . . . , and Sn.
- the image signals S 1 , S 2 , . . . , and Sn may be line-sequentially supplied to the respective data lines 6 a in this order, or may be supplied to the plurality of adjacent data lines 6 a constituting each group.
- the TFT element 30 has a gate electrode electrically connected to a scanning line 3 a .
- the respective scanning lines 3 a are supplied with scanning signals G 1 , G 2 , . . . , and Gm with a predetermined timing in a pulsed manner. Further, the scanning signals G 1 , G 2 , . . . , and Gm are line-sequentially applied to the respective scanning lines 3 a in this order.
- the TFT element 30 has a drain electrode electrically connected to the pixel electrode 9 .
- the TFT elements 30 each serving as the switching element are turned on during a predetermined period by the scanning signals G 1 , G 2 , . . .
- the image signals S 1 , S 2 , . . . , and Sn, which are supplied through the data lines 6 a , are written into liquid crystal of the respective pixels with a predetermined timing.
- the image signals S 1 , S 2 , . . . , and Sn which are written into the liquid crystal and having predetermined levels, are held for a predetermined period by a liquid crystal capacitor formed between the pixel electrode 9 and a common electrode, which will be described below.
- a storage capacitor 17 is formed between the pixel electrode 9 and a capacitive line 3 b , and is disposed parallel to the liquid crystal capacitor.
- FIG. 2 is a diagram illustrating the planar structure of the liquid crystal panel.
- the rectangular pixel electrodes 9 (their outlines are shown by broken lines), which are made of transparent conductive materials, such as indium tin oxide (hereinafter, referred to as ITO), are arranged in a matrix.
- the data line 6 a , the scanning line 3 a and the capacitive line 3 b are provided along longitudinal and horizontal boundaries of the pixel electrode 9 .
- a region where the pixel electrode 9 is formed is a dot, and display can be performed by each dot arranged in a matrix.
- the TFT element 30 is formed around a semiconductor layer 1 a made of a polysilicon film.
- the semiconductor layer 1 a has a source region (which will be described below) electrically connected to the data line 6 a via a contact hole 5 .
- the semiconductor layer 1 a has a drain region (which will be described below) electrically connected to the pixel electrode 9 via a contact hole 8 .
- a portion of the semiconductor layer 1 a opposite to the scanning line 3 a is provided with a channel region 1 a ′.
- the scanning line 3 a has a portion opposite to the channel region 1 a ′, serving as a gate electrode.
- the capacitive line 3 b has a main line portion linearly extending along the scanning line 3 a (that is, a first region formed along the scanning line 3 a in plan view) and a protruding portion protruding toward a front stage side (upward in the drawing) along the data line 6 a from an intersection of the data line 6 a and the capacitive line 3 b (that is, a second region extending along the data line 6 a in plan view). Further, in regions shown by an inclined line rising toward a right side in FIG. 2 , first light shielding films 11 a are formed. In addition, the protruding portion of the capacitive line 3 b and the first light shielding film 11 a are electrically connected to each other through a contact hole 13 , thereby forming a storage capacitor, which will be described below.
- FIG. 3 is a diagram illustrating the sectional structure of the liquid crystal panel, which is a cross-sectional view taken along the line III-III of FIG. 2 .
- the liquid crystal panel 60 mainly includes the TFT array substrate 10 , a counter substrate 20 arranged opposite to the TFT array substrate 10 , and a liquid crystal layer 50 interposed between the TFT array substrate 10 and the counter substrate 20 .
- the TFT array substrate 10 mainly includes a substrate body 10 A made of a transmissive material, such as glass or quartz, and TFT elements 30 , the pixel electrodes 9 , an alignment film 16 or the like formed in the substrate.
- the counter substrate 20 mainly includes a substrate body 20 A made of a transmissive material, such as glass or quartz, and common electrodes 21 , an alignment film 22 or the like formed in the substrate.
- a first light shielding film 11 a and a first interlayer insulating film 12 are formed on a surface of the TFT array substrate 10 .
- the semiconductor layer 1 a is formed on a surface of the first interlayer insulating film 12 , and the TFT element 30 is formed around the semiconductor layer 1 a .
- a channel region 1 a ′ is formed at a portion of the semiconductor layer 1 a opposite to the scanning line 3 a , and the source region and the drain region are formed at both sides of the channel region.
- each of the source and drain regions has a heavily doped region having a relatively high impurity concentration and a lightly doped region (LDD region) having a relatively low impurity concentration. That is, in the source region, a lightly doped source region 1 b and a heavily doped source region 1 d are formed, and in the drain region, a lightly doped drain region 1 c and a heavily doped drain region 1 e are formed.
- LDD lightly doped drain
- a gate insulating film 2 is formed on a surface of the semiconductor layer 1 a .
- the scanning line 3 a is formed on a surface of the gate insulating film 2 , and a portion of the scanning line 3 a constitutes a gate electrode.
- a second interlayer insulating film 4 is formed on surfaces of the gate insulating film 2 and the scanning line 3 a .
- the data line 6 a is formed on the surface of the second interlayer insulating film 4 and is electrically connected to the heavily doped source region 1 d through the contact hole 5 formed in the second interlayer insulating film 4 .
- a third interlayer insulating film 7 is formed on the surfaces of the second interlayer insulating film 4 and the data line 6 a .
- the pixel electrode 9 is formed on a surface of the third interlayer insulating film 7 and is electrically connected to the heavily doped drain region 1 e through a contact hole 8 formed in the second interlayer insulating film 4 and the third interlayer insulating film 7 .
- an inorganic vertical alignment film 16 composed of an oblique vapor deposition film is formed in order to cover the pixel electrode 9 .
- the semiconductor layer 1 a is extended to form a first storage capacitor electrode 1 f .
- the gate insulating film 2 a is extended to form a dielectric film, and a capacitive line 3 b is disposed on a surface of the dielectric film to form a second storage capacitor electrode.
- the above-mentioned storage capacitor 17 is constructed.
- the first light shielding film 11 a is formed on the surface of the TFT array substrate 10 corresponding to regions where the TFT elements 30 are formed.
- the first light shielding film 11 a serves to prevent the light incident on the liquid crystal panel from leaking into the channel region 1 a ′ of the semiconductor layer 1 a , the lightly doped source region 1 b and the lightly doped drain region 1 c .
- the first light shielding film 11 a is electrically connected to the capacitive line 3 b located at a front or rear stage through the contact hole 13 formed in the first interlayer insulating film 12 .
- the first light shielding film 11 a functions as a third storage capacitor electrode, and a new storage capacitor is formed between the first light shielding film 11 a and the first storage capacitor electrode 1 f using the first interlayer insulating film 12 as the dielectric film.
- a second light shielding film 23 is formed on a surface of the counter substrate 20 corresponding to regions where the data line 6 a , the scanning line 3 a , and the TFT element 30 are formed.
- the second light shielding film 23 serves to prevent the light incident on the liquid crystal panel from leaking into the channel region 1 a ′ of the semiconductor layer 1 a , the lightly doped source region 1 b , and the lightly doped drain region 1 c .
- the common electrode 21 which is made of a conductive material, such as ITO, is formed on substantially the entire surfaces of the counter substrate 20 and the second light shielding film 23 .
- an inorganic vertical alignment film 22 composed of an oblique vapor deposition film is formed on a surface of the common electrode 21 .
- liquid crystal molecules are aligned to be inclined in a predetermined direction from a horizontal plane of the substrate in a state in which a voltage is not applied to the liquid crystal.
- vapor deposition angles of the alignment films 16 and 22 are set to about 50° with respect to the normal line of the substrate and thicknesses thereof are set to 40 nm.
- the liquid crystal molecules are aligned in a state in which they are inclined at an angle of about 86° in a predetermined direction from the horizontal plane of the substrate (4° with respect to the normal line of the substrate).
- the inclined direction of the liquid crystal molecules that is, the director of the liquid crystal molecules when a voltage is not applied
- a pretilt direction of the liquid crystal is referred to as a pretilt direction of the liquid crystal.
- the liquid crystal layer 50 is interposed between the TFT array substrate 10 and the counter substrate 20 .
- the liquid crystal layer 50 is composed of nematic liquid crystal showing negative dielectric anisotropy. That is, the liquid crystal molecules constituting the liquid crystal layer 50 are vertically aligned when an electrical field is not applied (an initial alignment state) and are horizontally aligned when the electrical field is applied.
- FIG. 4 is an exploded perspective view of the liquid crystal device according to the present embodiment.
- the liquid crystal device 100 includes the above-mentioned liquid crystal panel 60 , an optical compensating plate 70 disposed outside the TFT array substrate 10 of the liquid crystal panel 60 , and polarizers 62 and 64 disposed outside the optical compensating plate 70 and the counter substrate 20 , respectively.
- the polarizer 62 is disposed at one side of the liquid crystal panel 60 where light is incident and the polarizer 64 is disposed at the other side of the liquid crystal panel 60 where the light is emitted.
- its transmission axis is parallel to a Y direction of FIG. 4 .
- the polarizer 64 disposed at the other side of the liquid crystal panel where light is emitted its transmission axis is parallel to an X direction of FIG. 4 .
- the directions of the transmission axes of these polarizers 62 and 64 are inclined with respect to a direction P′ of a projection vector obtained by reflecting the pretilt direction P of the above-mentioned liquid crystal on the substrate plane.
- the liquid crystal panel 60 when the light is incident on the liquid crystal device 100 from the lower side of the polarizer 62 , only linearly polarized light aligned with the transmission axis of the polarizer 62 is transmitted through the polarizer 62 .
- the liquid crystal molecules In the liquid crystal panel 60 when the electrical field is not applied, the liquid crystal molecules are vertically aligned in a state in which they are pretilted in one direction with respect to the substrate plane. Therefore, the polarization state of the linearly polarized light incident on the liquid crystal panel 60 is changed due to a phase difference according to the pretilt, and the light is then emitted from the liquid crystal panel 60 as elliptically polarized light.
- the liquid crystal panel 60 since the elliptically polarized light is almost orthogonal to the transmission axis of the polarizer 64 , it is almost impossible to transmit it through the polarizer 64 . Therefore, in the liquid crystal panel 60 , when the electrical field is applied, black display is performed (normally black mode). On the other hand, in the liquid crystal panel 60 , when the electrical field is applied, the liquid crystal molecules are vertically aligned. For this reason, the polarization direction of the linearly polarized light incident on the liquid crystal panel 60 is changed in a direction orthogonal to the incident light due to birefringence.
- the optical compensating plate 70 is disposed between the polarizer 62 and the substrate 20 of the liquid crystal panel 60 where the light is emitted.
- FIG. 5 is a schematic diagram showing an index ellipsoid of the optical compensating plate 70 .
- n x and n y indicate principal refractive indices in a plane direction of the optical compensating plate
- n z indicates a principal refractive index in a depthwise direction of the optical compensating plate.
- the refractive index n z in an optical axis direction D is smaller than those of refractive indices in the other directions, and forms a disc shape in the index ellipsoid.
- the index ellipsoid is aligned parallel to the horizontal plane 70 a of the optical compensating plate 70 , and the optical-axis direction D of the optical compensating plate 70 (a minor-axis direction of the index ellipsoid) is parallel to the normal direction of the optical compensating plate 70 .
- a thickness-direction phase difference of the optical compensating plate 70 ((n x ⁇ n z ) ⁇ d, where d is the thickness of the optical compensating plate) is 0.2 ⁇ m, and the retardation of the liquid crystal panel 60 is 0.32. Therefore, the thickness-direction phase difference of the optical compensating plate 70 is set to be slightly smaller than the retardation of the liquid crystal panel 60 .
- the above-mentioned optical compensating plate 70 is mounted on a supporting substrate.
- the supporting substrate is made of a transmissive material, such as non-alkali glass, or sapphire or quartz having high thermal conductivity.
- the optical compensating plate 70 mounted on the supporting substrate is disposed in the liquid crystal device 100 at a predetermined distance from the surface of the liquid crystal panel 60 shown in FIG. 4 . As a result, it is possible to prevent the optical compensating plate 70 from deteriorating due to the heat irradiated from the liquid crystal panel 60 .
- the optical compensating plate 70 is disposed so as to be inclined at an angle of ⁇ 2 with respect to a substrate plane of the liquid crystal panel 60 , such that its optical axis direction D is substantially parallel to the pretilt direction P of the liquid crystal panel 60 .
- the pretilt angle ⁇ 1 of the liquid crystal molecules is set to 86° with respect to the horizontal plane of the substrate 10 (4° with respect to the normal line of the substrate)
- a plate face 70 a of the optical compensating plate 70 is disposed in a state in which it is rotated at an angle of 4° from a position parallel to the substrate 10 .
- the inclined angle ⁇ 2 of the optical compensating plate 70 can be adjusted by means of a predetermined rotating mechanism (adjuster) to rotate the optical compensating plate 70 or the supporting substrate for supporting the optical compensating plate 70 .
- a predetermined rotating mechanism adjuster
- a rotating mechanism can rotate the optical compensating plate 70 about two axes.
- FIG. 6 is a graph showing the transmittance at the time of performing black display in the case of changing the pretilt angle ⁇ 1 of the liquid crystal and the inclined angle ⁇ 2 of the optical compensating plate 70 .
- FIG. 6 shows the transmittance at the time of performing black display in the case in which a lamp light source has an intensity distribution in a cone of substantially 10°.
- a region shown by a sign A has the lowest transmittance
- regions shown by signs B, C, D, . . . have transmittances increasing in this order.
- the transmittance at the time of performing the black display becomes lowest when the optical axis direction D of the optical compensating plate 70 is substantially parallel to the pretilt direction P of the liquid crystal, and the transmittance increases as it deviates from the condition. For this reason, it can be apprehended that high contrast display, in which bright black display is suppressed by aligning the optical axis direction D with the pretilt direction P, can be achieved.
- the optical compensating plate 70 is disposed to be inclined with respect to the liquid crystal panel 60 (that is, not parallel to each other), such that the pretilt direction P of liquid crystal aligns with the optical axis direction of the optical compensating plate 70 . For this reason, it is possible to entirely compensate for the phase difference due to the pretilt of the liquid crystal and the phase difference due to the light in an oblique direction, so that high contrast display can be achieved as compared to the related art.
- the number of optical compensating plates 70 is one, but two or more may be provided.
- the optical compensating plate 70 may be composed of a plurality of optical compensating plates, and a new optical compensating plate may be provided between the polarizer 62 and the counter substrate 20 of the liquid crystal panel 60 .
- the optical compensating plate 70 allows the slow axes of two positive refractive index anisotropic bodies to be orthogonal to each other, so that it may be provided as a negative refractive index anisotropic body.
- the liquid crystal device according to the present embodiment has the same basic configuration as that of the first embodiment, except that an optical compensating plate is disposed parallel to a liquid crystal panel and only its optical axis is inclined from a horizontal plane. Therefore, in FIGS. 7 to 9 , constituent elements common to FIGS. 1 to 6 are denoted by the same reference numerals, and the description thereof will be omitted.
- FIG. 7 is an exploded perspective view of the liquid crystal device according to the second embodiment of the invention.
- a liquid crystal device 200 includes a liquid crystal panel 60 , an optical compensating plate 80 disposed outside a TFT array substrate 10 of the liquid crystal panel 60 , and polarizers 62 and 64 disposed outside the optical compensating plate 80 and a counter substrate 20 .
- the optical compensating plate 80 is disposed parallel to the substrate 10 of the liquid crystal panel 60 .
- FIG. 8 is a schematic diagram showing the index ellipsoid of the optical compensating plate 80 .
- n x and n y indicate principal refractive indices in a plane direction of the optical compensating plate
- n z indicates a principal refractive index in a depthwise direction of the optical compensating plate.
- the refractive index n z in an optical axis direction D is smaller than the refractive indices n x and n y in the other directions, and forms a disc shape in the index ellipsoid.
- the index ellipsoid is aligned so as to be inclined to the horizontal plane 80 a of the optical compensating plate 80 , and the optical-axis direction D of the optical compensating plate 80 (a minor-axis direction of the index ellipsoid) is inclined at an angle of ⁇ 1 with respect to the normal direction of the optical compensating plate 80 .
- the inclined angle ⁇ 1 of the optical axis is substantially equal to a pretilt angle of the liquid crystal panel 60 , so that the optical axis direction D of the optical compensating plate 80 is substantially parallel to the pretilt direction P of the liquid crystal.
- the pretilt angle ⁇ 1 of the liquid crystal is set to 88° with respect to the horizontal plane of the substrate 10 (2° with respect to the normal line of the substrate), and the optical axis direction D of the optical compensating plate 80 is set to a direction inclined at an angle of 2° with respect to the normal line direction of the horizontal plane 80 a of the optical compensating plate 80 .
- the optical compensating plate 80 can use one obtained by aligning the discotic liquid crystal to be tilt and then polymerizing it.
- FIG. 9 is a cross-sectional view schematically showing an example of the optical compensating plate.
- the optical compensating plate 80 of FIG. 9 is one obtained by proving an alignment film on a supporting body such as cellulose triacetate (TAC) and providing a discotic layer, such as triphenylene derivative, on the alignment film.
- TAC cellulose triacetate
- alignment films 81 a and 82 a made of polyimide or the like are formed on surface of a pair of supporting bodies 81 and 82 , the discotic compound 84 is applied on one supporting body, and a discotic layer 83 is interposed between the two supporting bodies. Then, a discotic nematic (N D ) phase is formed by the heat treatment and is then polymerized by ultraviolet rays, and its alignment state is fixed. When the discotic nematic (N D ) phase is formed, the discotic layer 83 is endowed with the tilt by the alignment films 81 a and 82 a , and is formed in a state in which its optical axis is obliquely inclined.
- the inclined angle ⁇ of the optical axis 84 a is controlled by an alignment process (rubbing process) of the alignment films 81 a and 82 a , so that the optical axis direction D and the pretilt direction P of the liquid crystal are parallel to each other.
- FIG. 10 is a diagram showing an example of a method of forming the optical compensating plate.
- a resin material 85 is heat up to substantially a glass transition point, and are elongated in two directions.
- the resin material 85 is interposed between the pair of heat substrates 91 and 92 , and the substrates 91 and 92 are shifted in directions opposite to each other while putting pressure on the resin material 85 from the outside of one substrate.
- the shearing stresses of the directions opposite to each other are applied on the top and bottom surfaces of the resin material 85 , so that an optical axis direction of an optical body constituting the resin material 85 is obliquely inclined.
- the inclined angle of the optical axis is controlled depending on the intensity of the shearing stress, so that the optical direction D and the pretilt direction P are parallel to each other.
- FIG. 11 is a diagram showing a measuring result of viewing angle characteristics.
- FIG. 11A is a diagram showing contrast curves when the optical axis of the optical compensating plate is not inclined (when the optical axis direction of the optical compensating plate and the pretilt direction of the liquid crystal does not align with each other)
- FIG. 11B are a diagram showing contrast curves when the optical axis of the optical compensating plate is inclined at an angle of 2° in accordance with the pretilt angle of the liquid crystal, as in the present embodiment.
- a region shown by a sign A has the largest contrast
- regions shown by signs B, C, D, . . . have the contrast decreasing in this order.
- FIG. 11 shows a region shown by a sign A has the largest contrast
- FIG. 11 in the case in which the optical axis direction of the optical compensating plate is inclined ( FIG. 11A ), display symmetry is high and a range for performing high contrast display is large as compared to the case in which the optical axis direction of the optical compensating plate is not inclined ( FIG. 11B ). For this reason, it can be apprehended that display having a wide viewing angle and a high contrast can be performed by aligning the optical axis direction D with the pretilt direction P.
- the optical axis direction D of the optical compensating plate 80 is substantially parallel to the pretilt direction P of the liquid crystal, it is possible to entirely compensate for the phase difference due to the pretilt of the liquid crystal and the phase difference due to the light in an oblique direction, so that high contrast display can be achieved as compared to the related art.
- FIG. 12 is a schematic diagram showing the structure of a three-plate-type reflective color liquid crystal projector, which is an example of the projection display device.
- a liquid crystal projector 1000 includes a polarizing illumination device 700 mainly having a light source unit 710 disposed along a system optical axis L, an integrator lens 720 and a polarization conversion element 730 , a polarized beam splitter 740 for reflecting an S polarized beam emitted from the polarizing illumination device 700 from an S polarized beam reflecting surface 741 , a dichroic mirror 742 for separating a blue (B) light component from the light reflected from the S polarized beam reflecting surface 741 of the polarized beam splitter 740 , a reflective liquid crystal light valve 745 B for modulating the separated blue (B) light component, a dichroic mirror 743 for reflecting a red (R) light component, of the light after the blue light component is separated, to separate it, a reflective liquid crystal light valve 745 R for modulating the separated red (R) light component, a reflective liquid crystal light valve 745 G for modulating a green (G) light component of the residual light passing through the dichroic mirror
- the random polarized beam emitted from the light source unit 710 is divided into a plurality of intermediate beams by the integrator lens 720 , is then converted into one kind of polarized beams (S polarized beam) arranged by the polarization conversion element 730 having a second integrator lens formed at the light incident side, and then reaches the polarized beam splitter 740 .
- the S polarized beams emitted from the polarization conversion element 730 are reflected from the S polarized beam reflecting surface 741 of the polarized beam splitter 740 , and a blue (B) beam in the reflected beams is reflected from a blue light reflecting layer of the dichroic mirror 742 and is then modulated by the reflective liquid crystal light valve 745 B.
- a red (R) beam is reflected from a red light reflecting layer of the dichroic mirror 743 and is then modulated by the reflective liquid crystal light valve 745 R.
- a green (G) beam having transmitted the red light reflecting layer of the dichroic mirror 743 is modulated by the reflective liquid crystal light valve 745 G.
- the color light beams are modulated by the reflective liquid crystal light valves 745 R, 745 G, and 745 B.
- the S polarized light component does not transmit the polarized beam splitter 740 which reflect the S polarized light component therefrom, but the P polarized light component is transmitted through it.
- the light passing through the polarized beam splitter 740 forms an image.
- the reflective liquid crystal light valve (light modulating unit) 745 has a liquid crystal panel 60 with a liquid crystal layer interposed between a pair of substrates, and an optical compensating plate 80 disposed outside one substrate 10 A of the liquid crystal panel 60 , and is an active-matrix-type reflective liquid crystal device using a thin film transistor (hereinafter, referred to as a TFT) serving as a switching element.
- a TFT thin film transistor
- the basic configuration of the liquid crystal panel 60 is the same as those shown in FIGS. 1 to 3 , except that the pixel electrode 9 is formed of a conductive material, such as aluminum (Al) or silver (Ag), having high reflectance, and the retardation of the liquid crystal layer 50 is half of that according to the first embodiment (that is, it is suitable for a reflective type). Therefore, its description will be omitted with respect to the structure of the liquid crystal panel 60 .
- a conductive material such as aluminum (Al) or silver (Ag)
- the optical compensating plate 80 has the same configuration as that in the second embodiment. That is, the optical compensating plate 80 is composed of an optically anisotropic body, such as a discotic compound, having negative refractive index anisotropy and has a disc shape in the index ellipsoid, and the refractive index n z in an optical axis direction D is smaller than the refractive indices n x and n y in the other directions.
- an optically anisotropic body such as a discotic compound, having negative refractive index anisotropy and has a disc shape in the index ellipsoid
- the index ellipsoid is aligned so as to be inclined to the horizontal plane 80 a of the optical compensating plate 80 , and the optical-axis direction D of the optical compensating plate 80 (a minor-axis direction of the index ellipsoid) is inclined at an angle of ⁇ 1 with respect to the normal line direction of the optical compensating plate 80 .
- the inclined angle ⁇ 1 of the optical axis is substantially equal to the pretilt angle of the liquid crystal 51 , so that the optical axis direction D of the optical compensating plate 80 is substantially parallel to the pretilt direction P of the liquid crystal 51 .
- the pretilt angle ⁇ 1 of the liquid crystal 51 is set to 86° with respect to the horizontal plane of the substrate 10 (4° with respect to the normal line of the substrate), and the optical axis direction D of the optical compensating plate 80 is set to a direction inclined at an angle of 4° with respect to the normal line direction of the horizontal plane 80 a of the optical compensating plate 80 .
- the optical axis direction D of the optical compensating plate 80 is substantially parallel to the pretilt direction P of the liquid crystal, it is possible to entirely compensate for the phase difference due to the pretilt of the liquid crystal and the phase difference due to the light in a inclined direction. Therefore, in the liquid crystal projector 1000 according to the present embodiment, it is possible to achieve image display having a wider viewing angle and higher contrast than those in the related art.
- the reflective liquid crystal display device is exemplified as the projection display device.
- the invention is not limited thereto, but may be applied to a transmissive liquid crystal projector. In this case, it is necessary to use the transmissive liquid crystal device according to the first or second embodiment as a light modulating unit.
- the transmissive display device having the liquid crystal device is exemplified as an example of the electronic apparatus.
- the liquid crystal of the invention is not limited to the transmissive display device, and may be mounted on various electronic apparatuses.
- Examples of the electronic apparatus may include apparatuses having an electronic book, a personal computer, a digital still camera, a liquid crystal television, a view-finder-type or monitor-direct-view type video tape recorder, a car navigation device, a pager, an electronic organizer, a electronic calculator, a word processor, a work station, a video phone, a POS terminal, and a touch panel, and the liquid crystal device can be properly used as an optical modulating unit of them.
Abstract
A liquid crystal device includes a pair of substrates; a liquid crystal layer interposed between the pair of substrates, the liquid crystal layer being composed of liquid crystal having negative dielectric anisotropy in which an initial alignment state thereof is vertical; and an optical compensating plate which is provided outside at least one substrate of the pair of substrates and has negative refractive index anisotropy. The liquid crystal is pretilted in a predetermined direction, and an optical axis direction of the optical compensating plate is substantially parallel to the pretilt direction of the liquid crystal.
Description
- This application is a divisional patent application of U.S. Ser. No. 11/211,019 filed Aug. 24, 2005, claiming priority to JP 2004-260753 filed Sep. 8, 2004, all of which are hereby incorporated by reference.
- 1. Technical Field
- The present invention relates to a liquid crystal device and to a projection display device.
- 2. Related Art
- In recent years, liquid crystal projectors (projection display devices) have been used as display devices in which large-screen display can be performed. In such a projector, a structure has been suggested in which a liquid crystal device, which is driven in a ‘VA (Vertical Alignment) mode’ where liquid crystal having negative dielectric anisotropy is vertically aligned on a substrate and liquid crystal molecules are tilted by applying a voltage, is included as a light valve. However, since most liquid crystal projectors in the related art have a contrast ratio of substantially 1:500 in a projected image, they are not as good as projectors, such as DMDs (registered trademark) using mechanical shutters, which have a contrast ratio of 1:3000. That is because of the viewing angle characteristics of the liquid crystal device. In the liquid crystal projector, light incident on the liquid crystal device is not entirely parallel light. However, since the liquid crystal device has incident angle dependence, it causes the contrast ratio of the projected image to decrease. To overcome this problem, Japanese Unexamined Patent Application Publication No. 7-69536 discloses a technology in which an optical compensating plate is employed to compensate for the incident angle dependency of the liquid crystal device, thereby realizing a display having a higher contrast.
- In the technology disclosed in Japanese Unexamined Patent Application Publication No. 7-69536, a refractive index anisotropic body serving as the optical compensating plate is arranged in a vertical-alignment-type liquid crystal cell, so that it is possible to compensate for a phase difference occurring in the liquid crystal cell due to inclined light. However, when the liquid crystal is pretilted to control the alignment of liquid crystal molecules, the effect of the optical compensating plate decreases as the pretilt angle decreases from 90°.
- An advantage of the invention is that it provides a projection display device which is capable of performing excellent optical compensation even when the liquid crystal is pretilted, and of performing image display having a high contrast by including a liquid crystal device of the invention.
- According to an aspect of the invention, a liquid crystal device includes a pair of substrates; a liquid crystal layer interposed between the pair of substrates, the liquid crystal layer being composed of liquid crystal having negative dielectric anisotropy representing that an initial alignment state thereof is vertical; and an optical compensating plate which is provided outside at least one substrate of the pair of substrates and has negative refractive index anisotropy. The liquid crystal is pretilted in a predetermined direction, and an optical axis direction of the optical compensating plate is substantially parallel to the pretilt direction of the liquid crystal. In the above-mentioned liquid crystal device, it is preferable that the optical compensating plate be disposed parallel to one substrate, and the optical axis direction of the optical compensating plate be substantially parallel to the pretilt direction of the liquid crystal, at an angle deviating from the normal line of the optical compensating plate. Further, preferably, the optical axis direction of the optical compensating plate is substantially parallel to the normal line direction of the optical compensating plate, and the optical compensating plate be disposed to be inclined from a location parallel to one of the pair of substrates such that the optical axis direction of the optical compensating plate is substantially parallel to the pretilt direction of the liquid crystal.
- In this case, the optical axis direction of the optical compensating plate is inclined according to the pretilt of the liquid crystal, so that it is possible to entirely compensate for a phase difference due to the pretilt of the liquid crystal and a phase difference due to the light in a inclined direction.
- According to another aspect of the invention, there is provided a projection display device including the above-mentioned liquid crystal device as an optical modulating unit.
- In this case, light leakage in black display can be prevented, and a high contrast ratio in a projected image can be obtained.
- Further, preferably, the projection display device further includes an adjuster that adjusts an arrangement angle of the optical compensating plate such that the optical axis direction of the optical compensating plate aligns with the pretilt direction of the liquid crystal. Furthermore, it is preferable that the adjuster be composed of a rotation mechanism for rotating the optical compensating plate on two axes.
- According to this aspect, since the optical axis direction of the optical compensating plate can be freely adjusted by the adjusting mechanism, it is possible to cope with the design change such as the change of the pretilt angle of the liquid crystal without requiring the design change of the optical compensating plate.
- The invention will be described with reference to the accompanying drawings, wherein like numbers reference like elements, and wherein:
-
FIG. 1 is an equivalent circuit diagram of a liquid crystal panel; -
FIG. 2 is a diagram showing the planar structure of the liquid crystal panel; -
FIG. 3 is a cross-sectional view taken along the line III-III ofFIG. 2 ; -
FIG. 4 is an exploded perspective view of a liquid crystal device according to a first embodiment of the invention; -
FIG. 5 is a diagram showing an index ellipsoid of an optical compensating plate; -
FIG. 6 is a graph showing black transmittance when changing an inclined angle of the optical compensating plate and a pretilt angle of liquid crystal; -
FIG. 7 is an exploded perspective view of a liquid crystal device according to a second embodiment of the invention; -
FIG. 8 is a diagram showing the index ellipsoid of the optical compensating plate; -
FIG. 9 is a cross-sectional view showing one structural example of the optical compensating plate; -
FIGS. 10A and 10B are diagrams showing one example of a method of manufacturing the optical compensating plate; -
FIGS. 11A and 11B are diagrams of contrast curves when an optical axis of the optical compensating plate is inclined and when the optical axis of the optical compensating plate is not inclined, respectively; -
FIG. 12 is a diagram showing an example of a projection display device; and -
FIG. 13 is a cross-sectional view showing an example of liquid crystal device applied to the projection display device. - Hereinafter, embodiments of the invention will be described with reference to the accompanying drawings. The scale of each member has been adjusted in order to have a recognizable size in the drawings described below. In the present specification, one side of each constituent element of a liquid crystal device toward a liquid crystal layer is called an inner side, and the other side of the liquid crystal device is called an outer side.
- First, a liquid crystal device according to a first embodiment of the invention will be described with reference to
FIGS. 1 to 6 . The liquid crystal device according to the first embodiment includes a liquid crystal panel with a liquid crystal layer interposed between a pair of substrates, an optical compensating plate disposed outside one substrate of the liquid crystal panel, and polarizers disposed outside the optical compensating plate and the other substrate of the liquid crystal panel, respectively. In the present embodiment, an active-matrix-type transmissive liquid crystal panel, which uses a thin film transistor (hereinafter, referred to as a TFT) element serving as a switching element, will be described by way of an example. -
FIG. 1 is an equivalent circuit diagram of the liquid crystal panel. A plurality of dots arranged in a matrix which constitute an image display region of the transmissive liquid crystal panel are provided withpixel electrodes 9, respectively. ATFT element 30, which serves as a switching element to electrically control thepixel electrode 9, is provided at one side of thepixel electrode 9. TheTFT element 30 has a source electrode electrically connected to adata line 6 a. Therespective data lines 6 a are supplied with image signals S1, S2, . . . , and Sn. The image signals S1, S2, . . . , and Sn may be line-sequentially supplied to therespective data lines 6 a in this order, or may be supplied to the plurality ofadjacent data lines 6 a constituting each group. - In addition, the
TFT element 30 has a gate electrode electrically connected to ascanning line 3 a. Therespective scanning lines 3 a are supplied with scanning signals G1, G2, . . . , and Gm with a predetermined timing in a pulsed manner. Further, the scanning signals G1, G2, . . . , and Gm are line-sequentially applied to therespective scanning lines 3 a in this order. Furthermore, theTFT element 30 has a drain electrode electrically connected to thepixel electrode 9. In addition, when theTFT elements 30 each serving as the switching element are turned on during a predetermined period by the scanning signals G1, G2, . . . , and Gm supplied through thescanning lines 3 a, the image signals S1, S2, . . . , and Sn, which are supplied through thedata lines 6 a, are written into liquid crystal of the respective pixels with a predetermined timing. - The image signals S1, S2, . . . , and Sn, which are written into the liquid crystal and having predetermined levels, are held for a predetermined period by a liquid crystal capacitor formed between the
pixel electrode 9 and a common electrode, which will be described below. In addition, in order to prevent the held image signals S1, S2, . . . , and Sn from leaking, astorage capacitor 17 is formed between thepixel electrode 9 and acapacitive line 3 b, and is disposed parallel to the liquid crystal capacitor. As such, when a voltage signal is applied to the liquid crystal, alignment states of liquid crystal molecules change according to the applied voltage level. As a result, light incident on the liquid crystal is modulated, and thus gray-scale display can be achieved. -
FIG. 2 is a diagram illustrating the planar structure of the liquid crystal panel. In the liquid crystal panel according to the present embodiment, on the TFT array substrate, the rectangular pixel electrodes 9 (their outlines are shown by broken lines), which are made of transparent conductive materials, such as indium tin oxide (hereinafter, referred to as ITO), are arranged in a matrix. In addition, thedata line 6 a, thescanning line 3 a and thecapacitive line 3 b are provided along longitudinal and horizontal boundaries of thepixel electrode 9. According to the present embodiment, a region where thepixel electrode 9 is formed is a dot, and display can be performed by each dot arranged in a matrix. - The
TFT element 30 is formed around asemiconductor layer 1 a made of a polysilicon film. Thesemiconductor layer 1 a has a source region (which will be described below) electrically connected to thedata line 6 a via acontact hole 5. Thesemiconductor layer 1 a has a drain region (which will be described below) electrically connected to thepixel electrode 9 via acontact hole 8. On the other hand, a portion of thesemiconductor layer 1 a opposite to thescanning line 3 a is provided with achannel region 1 a′. In addition, thescanning line 3 a has a portion opposite to thechannel region 1 a′, serving as a gate electrode. - The
capacitive line 3 b has a main line portion linearly extending along thescanning line 3 a (that is, a first region formed along thescanning line 3 a in plan view) and a protruding portion protruding toward a front stage side (upward in the drawing) along thedata line 6 a from an intersection of thedata line 6 a and thecapacitive line 3 b (that is, a second region extending along thedata line 6 a in plan view). Further, in regions shown by an inclined line rising toward a right side inFIG. 2 , firstlight shielding films 11 a are formed. In addition, the protruding portion of thecapacitive line 3 b and the firstlight shielding film 11 a are electrically connected to each other through acontact hole 13, thereby forming a storage capacitor, which will be described below. -
FIG. 3 is a diagram illustrating the sectional structure of the liquid crystal panel, which is a cross-sectional view taken along the line III-III ofFIG. 2 . As shown inFIG. 3 , theliquid crystal panel 60 according to the present embodiment mainly includes theTFT array substrate 10, acounter substrate 20 arranged opposite to theTFT array substrate 10, and aliquid crystal layer 50 interposed between theTFT array substrate 10 and thecounter substrate 20. TheTFT array substrate 10 mainly includes asubstrate body 10A made of a transmissive material, such as glass or quartz, andTFT elements 30, thepixel electrodes 9, analignment film 16 or the like formed in the substrate. In addition, thecounter substrate 20 mainly includes asubstrate body 20A made of a transmissive material, such as glass or quartz, andcommon electrodes 21, analignment film 22 or the like formed in the substrate. - On a surface of the
TFT array substrate 10, a firstlight shielding film 11 a and a firstinterlayer insulating film 12, which will be described in detail below, are formed. In addition, thesemiconductor layer 1 a is formed on a surface of the firstinterlayer insulating film 12, and theTFT element 30 is formed around thesemiconductor layer 1 a. Achannel region 1 a′ is formed at a portion of thesemiconductor layer 1 a opposite to thescanning line 3 a, and the source region and the drain region are formed at both sides of the channel region. In addition, since theTFT element 30 has the LDD (lightly doped drain) structure, each of the source and drain regions has a heavily doped region having a relatively high impurity concentration and a lightly doped region (LDD region) having a relatively low impurity concentration. That is, in the source region, a lightly dopedsource region 1 b and a heavily dopedsource region 1 d are formed, and in the drain region, a lightly dopeddrain region 1 c and a heavily dopeddrain region 1 e are formed. - On a surface of the
semiconductor layer 1 a, agate insulating film 2 is formed. In addition, on a surface of thegate insulating film 2, thescanning line 3 a is formed, and a portion of thescanning line 3 a constitutes a gate electrode. In addition, a secondinterlayer insulating film 4 is formed on surfaces of thegate insulating film 2 and thescanning line 3 a. Further, thedata line 6 a is formed on the surface of the secondinterlayer insulating film 4 and is electrically connected to the heavily dopedsource region 1 d through thecontact hole 5 formed in the secondinterlayer insulating film 4. In addition, a thirdinterlayer insulating film 7 is formed on the surfaces of the secondinterlayer insulating film 4 and thedata line 6 a. In addition, thepixel electrode 9 is formed on a surface of the thirdinterlayer insulating film 7 and is electrically connected to the heavily dopeddrain region 1 e through acontact hole 8 formed in the secondinterlayer insulating film 4 and the thirdinterlayer insulating film 7. In addition, an inorganicvertical alignment film 16 composed of an oblique vapor deposition film is formed in order to cover thepixel electrode 9. - In addition, according to the present embodiment, the
semiconductor layer 1 a is extended to form a firststorage capacitor electrode 1 f. Further, the gate insulating film 2 a is extended to form a dielectric film, and acapacitive line 3 b is disposed on a surface of the dielectric film to form a second storage capacitor electrode. As a result, the above-mentionedstorage capacitor 17 is constructed. - In addition, the first
light shielding film 11 a is formed on the surface of theTFT array substrate 10 corresponding to regions where theTFT elements 30 are formed. The firstlight shielding film 11 a serves to prevent the light incident on the liquid crystal panel from leaking into thechannel region 1 a′ of thesemiconductor layer 1 a, the lightly dopedsource region 1 b and the lightly dopeddrain region 1 c. In addition, the firstlight shielding film 11 a is electrically connected to thecapacitive line 3 b located at a front or rear stage through thecontact hole 13 formed in the firstinterlayer insulating film 12. As a result, the firstlight shielding film 11 a functions as a third storage capacitor electrode, and a new storage capacitor is formed between the firstlight shielding film 11 a and the firststorage capacitor electrode 1 f using the firstinterlayer insulating film 12 as the dielectric film. - On the other hand, a second
light shielding film 23 is formed on a surface of thecounter substrate 20 corresponding to regions where thedata line 6 a, thescanning line 3 a, and theTFT element 30 are formed. The secondlight shielding film 23 serves to prevent the light incident on the liquid crystal panel from leaking into thechannel region 1 a′ of thesemiconductor layer 1 a, the lightly dopedsource region 1 b, and the lightly dopeddrain region 1 c. In addition, thecommon electrode 21, which is made of a conductive material, such as ITO, is formed on substantially the entire surfaces of thecounter substrate 20 and the secondlight shielding film 23. Further, an inorganicvertical alignment film 22 composed of an oblique vapor deposition film is formed on a surface of thecommon electrode 21. In addition, by means of thesealignment films alignment films - In addition, the
liquid crystal layer 50 is interposed between theTFT array substrate 10 and thecounter substrate 20. Theliquid crystal layer 50 is composed of nematic liquid crystal showing negative dielectric anisotropy. That is, the liquid crystal molecules constituting theliquid crystal layer 50 are vertically aligned when an electrical field is not applied (an initial alignment state) and are horizontally aligned when the electrical field is applied. -
FIG. 4 is an exploded perspective view of the liquid crystal device according to the present embodiment. - The
liquid crystal device 100 according to the present embodiment includes the above-mentionedliquid crystal panel 60, an optical compensatingplate 70 disposed outside theTFT array substrate 10 of theliquid crystal panel 60, andpolarizers plate 70 and thecounter substrate 20, respectively. Thepolarizer 62 is disposed at one side of theliquid crystal panel 60 where light is incident and thepolarizer 64 is disposed at the other side of theliquid crystal panel 60 where the light is emitted. In thepolarizer 62 disposed at one side of the liquid crystal panel where light is incident, its transmission axis is parallel to a Y direction ofFIG. 4 . In addition, in thepolarizer 64 disposed at the other side of the liquid crystal panel where light is emitted, its transmission axis is parallel to an X direction ofFIG. 4 . The directions of the transmission axes of thesepolarizers - Further, when the light is incident on the
liquid crystal device 100 from the lower side of thepolarizer 62, only linearly polarized light aligned with the transmission axis of thepolarizer 62 is transmitted through thepolarizer 62. In theliquid crystal panel 60 when the electrical field is not applied, the liquid crystal molecules are vertically aligned in a state in which they are pretilted in one direction with respect to the substrate plane. Therefore, the polarization state of the linearly polarized light incident on theliquid crystal panel 60 is changed due to a phase difference according to the pretilt, and the light is then emitted from theliquid crystal panel 60 as elliptically polarized light. In addition, since the elliptically polarized light is almost orthogonal to the transmission axis of thepolarizer 64, it is almost impossible to transmit it through thepolarizer 64. Therefore, in theliquid crystal panel 60, when the electrical field is applied, black display is performed (normally black mode). On the other hand, in theliquid crystal panel 60, when the electrical field is applied, the liquid crystal molecules are vertically aligned. For this reason, the polarization direction of the linearly polarized light incident on theliquid crystal panel 60 is changed in a direction orthogonal to the incident light due to birefringence. Since the polarization axis of the linearly polarized light aligns with the transmission axis of thepolarizer 64, it is transmitted through thepolarizer 64. Therefore, in theliquid crystal panel 60, when the electrical field is not applied, white display is performed. - In the present embodiment, the optical compensating
plate 70 is disposed between thepolarizer 62 and thesubstrate 20 of theliquid crystal panel 60 where the light is emitted. -
FIG. 5 is a schematic diagram showing an index ellipsoid of the optical compensatingplate 70. InFIG. 5 , nx and ny indicate principal refractive indices in a plane direction of the optical compensating plate, and nz indicates a principal refractive index in a depthwise direction of the optical compensating plate. The optical compensatingplate 70 according to the present embodiment is composed of an optically anisotropic body, such as a discotic compound, having negative refractive index anisotropy, and the principal refractive indices nx, ny, and n z satisfy the condition nx=ny>nz. That is, the refractive index nz in an optical axis direction D is smaller than those of refractive indices in the other directions, and forms a disc shape in the index ellipsoid. The index ellipsoid is aligned parallel to thehorizontal plane 70 a of the optical compensatingplate 70, and the optical-axis direction D of the optical compensating plate 70 (a minor-axis direction of the index ellipsoid) is parallel to the normal direction of the optical compensatingplate 70. In the present embodiment, a thickness-direction phase difference of the optical compensating plate 70 ((nx−nz)·d, where d is the thickness of the optical compensating plate) is 0.2 μm, and the retardation of theliquid crystal panel 60 is 0.32. Therefore, the thickness-direction phase difference of the optical compensatingplate 70 is set to be slightly smaller than the retardation of theliquid crystal panel 60. - The above-mentioned optical compensating
plate 70 is mounted on a supporting substrate. The supporting substrate is made of a transmissive material, such as non-alkali glass, or sapphire or quartz having high thermal conductivity. In addition, the optical compensatingplate 70 mounted on the supporting substrate is disposed in theliquid crystal device 100 at a predetermined distance from the surface of theliquid crystal panel 60 shown inFIG. 4 . As a result, it is possible to prevent the optical compensatingplate 70 from deteriorating due to the heat irradiated from theliquid crystal panel 60. In addition, the optical compensatingplate 70 is disposed so as to be inclined at an angle of θ2 with respect to a substrate plane of theliquid crystal panel 60, such that its optical axis direction D is substantially parallel to the pretilt direction P of theliquid crystal panel 60. According to the present embodiment, since the pretilt angle θ1 of the liquid crystal molecules is set to 86° with respect to the horizontal plane of the substrate 10 (4° with respect to the normal line of the substrate), aplate face 70 a of the optical compensatingplate 70 is disposed in a state in which it is rotated at an angle of 4° from a position parallel to thesubstrate 10. The inclined angle θ2 of the optical compensatingplate 70 can be adjusted by means of a predetermined rotating mechanism (adjuster) to rotate the optical compensatingplate 70 or the supporting substrate for supporting the optical compensatingplate 70. As such, by providing the adjuster to adjust a disposition angle of the optical compensatingplate 70, it is possible to easily cope with design changes of theliquid crystal panel 60. Preferably, such a rotating mechanism can rotate the optical compensatingplate 70 about two axes. -
FIG. 6 is a graph showing the transmittance at the time of performing black display in the case of changing the pretilt angle θ1 of the liquid crystal and the inclined angle θ2 of the optical compensatingplate 70. Specifically,FIG. 6 shows the transmittance at the time of performing black display in the case in which a lamp light source has an intensity distribution in a cone of substantially 10°. InFIG. 6 , a region shown by a sign A has the lowest transmittance, and regions shown by signs B, C, D, . . . have transmittances increasing in this order. As shown inFIG. 6 , the transmittance at the time of performing the black display becomes lowest when the optical axis direction D of the optical compensatingplate 70 is substantially parallel to the pretilt direction P of the liquid crystal, and the transmittance increases as it deviates from the condition. For this reason, it can be apprehended that high contrast display, in which bright black display is suppressed by aligning the optical axis direction D with the pretilt direction P, can be achieved. - As described above, according to the present embodiment, the optical compensating
plate 70 is disposed to be inclined with respect to the liquid crystal panel 60 (that is, not parallel to each other), such that the pretilt direction P of liquid crystal aligns with the optical axis direction of the optical compensatingplate 70. For this reason, it is possible to entirely compensate for the phase difference due to the pretilt of the liquid crystal and the phase difference due to the light in an oblique direction, so that high contrast display can be achieved as compared to the related art. - Further, in the present embodiment, the number of optical compensating
plates 70 is one, but two or more may be provided. For example, the optical compensatingplate 70 may be composed of a plurality of optical compensating plates, and a new optical compensating plate may be provided between thepolarizer 62 and thecounter substrate 20 of theliquid crystal panel 60. Also, the optical compensatingplate 70 allows the slow axes of two positive refractive index anisotropic bodies to be orthogonal to each other, so that it may be provided as a negative refractive index anisotropic body. - Next, a liquid crystal device according to a second embodiment of the invention will be described with reference to
FIGS. 7 to 9 . The liquid crystal device according to the present embodiment has the same basic configuration as that of the first embodiment, except that an optical compensating plate is disposed parallel to a liquid crystal panel and only its optical axis is inclined from a horizontal plane. Therefore, inFIGS. 7 to 9 , constituent elements common toFIGS. 1 to 6 are denoted by the same reference numerals, and the description thereof will be omitted. -
FIG. 7 is an exploded perspective view of the liquid crystal device according to the second embodiment of the invention. - A
liquid crystal device 200 according to the present embodiment includes aliquid crystal panel 60, an optical compensatingplate 80 disposed outside aTFT array substrate 10 of theliquid crystal panel 60, andpolarizers plate 80 and acounter substrate 20. In the present embodiment, the optical compensatingplate 80 is disposed parallel to thesubstrate 10 of theliquid crystal panel 60. -
FIG. 8 is a schematic diagram showing the index ellipsoid of the optical compensatingplate 80. InFIG. 8 , nx and ny indicate principal refractive indices in a plane direction of the optical compensating plate, and nz indicates a principal refractive index in a depthwise direction of the optical compensating plate. The optical compensatingplate 80 according to the present embodiment is composed of an optically anisotropic body, such as a discotic compound, having negative refractive index anisotropy, and the principal refractive indices nx, ny, and nz satisfy the condition nx=ny>nz. That is, the refractive index nz in an optical axis direction D is smaller than the refractive indices nx and ny in the other directions, and forms a disc shape in the index ellipsoid. The index ellipsoid is aligned so as to be inclined to thehorizontal plane 80 a of the optical compensatingplate 80, and the optical-axis direction D of the optical compensating plate 80 (a minor-axis direction of the index ellipsoid) is inclined at an angle of θ1 with respect to the normal direction of the optical compensatingplate 80. The inclined angle θ1 of the optical axis is substantially equal to a pretilt angle of theliquid crystal panel 60, so that the optical axis direction D of the optical compensatingplate 80 is substantially parallel to the pretilt direction P of the liquid crystal. In the present embodiment, the pretilt angle θ1 of the liquid crystal is set to 88° with respect to the horizontal plane of the substrate 10 (2° with respect to the normal line of the substrate), and the optical axis direction D of the optical compensatingplate 80 is set to a direction inclined at an angle of 2° with respect to the normal line direction of thehorizontal plane 80 a of the optical compensatingplate 80. - The optical compensating
plate 80 can use one obtained by aligning the discotic liquid crystal to be tilt and then polymerizing it.FIG. 9 is a cross-sectional view schematically showing an example of the optical compensating plate. The optical compensatingplate 80 ofFIG. 9 is one obtained by proving an alignment film on a supporting body such as cellulose triacetate (TAC) and providing a discotic layer, such as triphenylene derivative, on the alignment film. When the discotic compound takes a liquid crystal phase, it shows negative uniaxis optically. In addition,alignment films bodies discotic compound 84 is applied on one supporting body, and adiscotic layer 83 is interposed between the two supporting bodies. Then, a discotic nematic (ND) phase is formed by the heat treatment and is then polymerized by ultraviolet rays, and its alignment state is fixed. When the discotic nematic (ND) phase is formed, thediscotic layer 83 is endowed with the tilt by thealignment films optical axis 84 a is controlled by an alignment process (rubbing process) of thealignment films - The above-mentioned optical compensating
plate 80 can be also formed by applying the shearing stress on a polycarbonate or norbornene resin and elongating it. FIG. 10 is a diagram showing an example of a method of forming the optical compensating plate. In this method, as shown inFIG. 10A , aresin material 85 is heat up to substantially a glass transition point, and are elongated in two directions. In addition, theresin material 85 is interposed between the pair ofheat substrates substrates resin material 85 from the outside of one substrate. As a result, the shearing stresses of the directions opposite to each other are applied on the top and bottom surfaces of theresin material 85, so that an optical axis direction of an optical body constituting theresin material 85 is obliquely inclined. The inclined angle of the optical axis is controlled depending on the intensity of the shearing stress, so that the optical direction D and the pretilt direction P are parallel to each other. -
FIG. 11 is a diagram showing a measuring result of viewing angle characteristics.FIG. 11A is a diagram showing contrast curves when the optical axis of the optical compensating plate is not inclined (when the optical axis direction of the optical compensating plate and the pretilt direction of the liquid crystal does not align with each other), andFIG. 11B are a diagram showing contrast curves when the optical axis of the optical compensating plate is inclined at an angle of 2° in accordance with the pretilt angle of the liquid crystal, as in the present embodiment. InFIG. 11 , a region shown by a sign A has the largest contrast, and regions shown by signs B, C, D, . . . have the contrast decreasing in this order. As shown inFIG. 11 , in the case in which the optical axis direction of the optical compensating plate is inclined (FIG. 11A ), display symmetry is high and a range for performing high contrast display is large as compared to the case in which the optical axis direction of the optical compensating plate is not inclined (FIG. 11B ). For this reason, it can be apprehended that display having a wide viewing angle and a high contrast can be performed by aligning the optical axis direction D with the pretilt direction P. - As described above, also in the present embodiment, since the optical axis direction D of the optical compensating
plate 80 is substantially parallel to the pretilt direction P of the liquid crystal, it is possible to entirely compensate for the phase difference due to the pretilt of the liquid crystal and the phase difference due to the light in an oblique direction, so that high contrast display can be achieved as compared to the related art. - Next, a projection display device, which is an example of an electronic apparatus of the invention, will be described.
FIG. 12 is a schematic diagram showing the structure of a three-plate-type reflective color liquid crystal projector, which is an example of the projection display device. - A
liquid crystal projector 1000 includes apolarizing illumination device 700 mainly having alight source unit 710 disposed along a system optical axis L, anintegrator lens 720 and apolarization conversion element 730, apolarized beam splitter 740 for reflecting an S polarized beam emitted from thepolarizing illumination device 700 from an S polarizedbeam reflecting surface 741, adichroic mirror 742 for separating a blue (B) light component from the light reflected from the S polarizedbeam reflecting surface 741 of thepolarized beam splitter 740, a reflective liquid crystallight valve 745B for modulating the separated blue (B) light component, adichroic mirror 743 for reflecting a red (R) light component, of the light after the blue light component is separated, to separate it, a reflective liquid crystallight valve 745R for modulating the separated red (R) light component, a reflective liquid crystallight valve 745G for modulating a green (G) light component of the residual light passing through thedichroic mirror 743, and a projectionoptical system 750 composed of projection lenses for synthesizing the light modulated by the three reflective liquid crystallight valves dichroic mirrors polarized beam splitter 740 to project the synthesized light onto ascreen 760. - The random polarized beam emitted from the
light source unit 710 is divided into a plurality of intermediate beams by theintegrator lens 720, is then converted into one kind of polarized beams (S polarized beam) arranged by thepolarization conversion element 730 having a second integrator lens formed at the light incident side, and then reaches thepolarized beam splitter 740. The S polarized beams emitted from thepolarization conversion element 730 are reflected from the S polarizedbeam reflecting surface 741 of thepolarized beam splitter 740, and a blue (B) beam in the reflected beams is reflected from a blue light reflecting layer of thedichroic mirror 742 and is then modulated by the reflective liquid crystallight valve 745B. In addition, in the light beams transmitting the blue light reflecting layer of thedichroic mirror 742, a red (R) beam is reflected from a red light reflecting layer of thedichroic mirror 743 and is then modulated by the reflective liquid crystallight valve 745R. On the other hand, a green (G) beam having transmitted the red light reflecting layer of thedichroic mirror 743 is modulated by the reflective liquid crystallight valve 745G. As described above, the color light beams are modulated by the reflective liquid crystallight valves - Among the color light components reflected from the pixels of the liquid crystal panel, the S polarized light component does not transmit the
polarized beam splitter 740 which reflect the S polarized light component therefrom, but the P polarized light component is transmitted through it. The light passing through thepolarized beam splitter 740 forms an image. - Here, the structure of the reflective liquid crystal
light valves FIG. 13 . Since the three reflective liquid crystal light valves have the same structure, any one of three reflective liquid crystal light valves will be described as one reflective liquid crystallight valve 745. The reflective liquid crystal light valve (light modulating unit) 745 according to the present embodiment has aliquid crystal panel 60 with a liquid crystal layer interposed between a pair of substrates, and an optical compensatingplate 80 disposed outside onesubstrate 10A of theliquid crystal panel 60, and is an active-matrix-type reflective liquid crystal device using a thin film transistor (hereinafter, referred to as a TFT) serving as a switching element. The basic configuration of theliquid crystal panel 60 is the same as those shown inFIGS. 1 to 3 , except that thepixel electrode 9 is formed of a conductive material, such as aluminum (Al) or silver (Ag), having high reflectance, and the retardation of theliquid crystal layer 50 is half of that according to the first embodiment (that is, it is suitable for a reflective type). Therefore, its description will be omitted with respect to the structure of theliquid crystal panel 60. - The optical compensating
plate 80 has the same configuration as that in the second embodiment. That is, the optical compensatingplate 80 is composed of an optically anisotropic body, such as a discotic compound, having negative refractive index anisotropy and has a disc shape in the index ellipsoid, and the refractive index nz in an optical axis direction D is smaller than the refractive indices nx and ny in the other directions. The index ellipsoid is aligned so as to be inclined to thehorizontal plane 80 a of the optical compensatingplate 80, and the optical-axis direction D of the optical compensating plate 80 (a minor-axis direction of the index ellipsoid) is inclined at an angle of θ1 with respect to the normal line direction of the optical compensatingplate 80. The inclined angle θ1 of the optical axis is substantially equal to the pretilt angle of theliquid crystal 51, so that the optical axis direction D of the optical compensatingplate 80 is substantially parallel to the pretilt direction P of theliquid crystal 51. In the present embodiment, the pretilt angle θ1 of theliquid crystal 51 is set to 86° with respect to the horizontal plane of the substrate 10 (4° with respect to the normal line of the substrate), and the optical axis direction D of the optical compensatingplate 80 is set to a direction inclined at an angle of 4° with respect to the normal line direction of thehorizontal plane 80 a of the optical compensatingplate 80. - As described above, since in the
light valve 745 according to the present embodiment, the optical axis direction D of the optical compensatingplate 80 is substantially parallel to the pretilt direction P of the liquid crystal, it is possible to entirely compensate for the phase difference due to the pretilt of the liquid crystal and the phase difference due to the light in a inclined direction. Therefore, in theliquid crystal projector 1000 according to the present embodiment, it is possible to achieve image display having a wider viewing angle and higher contrast than those in the related art. - In the present embodiment, the reflective liquid crystal display device is exemplified as the projection display device. However, the invention is not limited thereto, but may be applied to a transmissive liquid crystal projector. In this case, it is necessary to use the transmissive liquid crystal device according to the first or second embodiment as a light modulating unit. In addition, according to the present embodiment, the transmissive display device having the liquid crystal device is exemplified as an example of the electronic apparatus. However, the liquid crystal of the invention is not limited to the transmissive display device, and may be mounted on various electronic apparatuses. Examples of the electronic apparatus may include apparatuses having an electronic book, a personal computer, a digital still camera, a liquid crystal television, a view-finder-type or monitor-direct-view type video tape recorder, a car navigation device, a pager, an electronic organizer, a electronic calculator, a word processor, a work station, a video phone, a POS terminal, and a touch panel, and the liquid crystal device can be properly used as an optical modulating unit of them.
- As described above, the preferred embodiments according to the invention has been described with reference to the accompanying drawings, but it goes without saying that the invention is limited thereto. The shapes or combinations of the respective constituent elements shown in the drawings are only exemplary, but various changes and modifications can be made based on the design requirement without departing from the spirit and scope of the invention.
Claims (2)
1. A liquid crystal device comprising:
a pair of substrates;
a liquid crystal layer interposed between the pair of substrates, the liquid crystal layer including liquid crystal having negative dielectric anisotropy and a predetermined pretilt direction; and
an optical compensating plate provided outside at least one of the pair of substrates, the optical compensating plate having negative refractive index anisotropy and an optical axis direction, the optical axis direction of the optical compensating plate being substantially parallel to the pretilt direction of the liquid crystal,
wherein the optical axis direction of the optical compensating plate is substantially parallel to the normal line direction of the optical compensating plate, and
the optical compensating plate is inclined with respect to parallel with the substrates, so that the optical axis direction of the optical compensating plate is substantially parallel to the pretilt direction of the liquid crystal.
2. A projection display device comprising the liquid crystal device according to claim 1 as an optical modulating unit.
Priority Applications (1)
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US12/124,242 US20080278668A1 (en) | 2004-09-08 | 2008-05-21 | Liquid crystal device and projection display device |
Applications Claiming Priority (4)
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JP2004260753A JP2006078637A (en) | 2004-09-08 | 2004-09-08 | Liquid crystal device and projection display device |
JP2004-260753 | 2004-09-08 | ||
US11/211,019 US7570328B2 (en) | 2004-09-08 | 2005-08-24 | Liquid crystal device and projection display device |
US12/124,242 US20080278668A1 (en) | 2004-09-08 | 2008-05-21 | Liquid crystal device and projection display device |
Related Parent Applications (1)
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US11/211,019 Division US7570328B2 (en) | 2004-09-08 | 2005-08-24 | Liquid crystal device and projection display device |
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US12/124,242 Abandoned US20080278668A1 (en) | 2004-09-08 | 2008-05-21 | Liquid crystal device and projection display device |
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US8692637B2 (en) | 2008-04-04 | 2014-04-08 | Correlated Magnetics Research LLC | Magnetic device using non polarized magnetic attraction elements |
US8717131B2 (en) | 2008-04-04 | 2014-05-06 | Correlated Magnetics Research | Panel system for covering a glass or plastic surface |
US8704626B2 (en) | 2010-05-10 | 2014-04-22 | Correlated Magnetics Research, Llc | System and method for moving an object |
US8279031B2 (en) | 2011-01-20 | 2012-10-02 | Correlated Magnetics Research, Llc | Multi-level magnetic system for isolation of vibration |
Also Published As
Publication number | Publication date |
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KR20060051065A (en) | 2006-05-19 |
KR100748766B1 (en) | 2007-08-13 |
JP2006078637A (en) | 2006-03-23 |
US20060050215A1 (en) | 2006-03-09 |
US7570328B2 (en) | 2009-08-04 |
CN1746744A (en) | 2006-03-15 |
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