GB2293260A - Liquid crystal device - Google Patents

Liquid crystal device Download PDF

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Publication number
GB2293260A
GB2293260A GB9418866A GB9418866A GB2293260A GB 2293260 A GB2293260 A GB 2293260A GB 9418866 A GB9418866 A GB 9418866A GB 9418866 A GB9418866 A GB 9418866A GB 2293260 A GB2293260 A GB 2293260A
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United Kingdom
Prior art keywords
liquid crystal
crystal device
pixels
alignment
group
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Granted
Application number
GB9418866A
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GB2293260B (en
GB9418866D0 (en
Inventor
Edward Peter Raynes
Paul Bonnett
Michael Geraint Robinson
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Sharp Corp
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Sharp Corp
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Publication date
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Priority to GB9418866A priority Critical patent/GB2293260B/en
Publication of GB9418866D0 publication Critical patent/GB9418866D0/en
Priority to JP7238397A priority patent/JPH08101392A/en
Publication of GB2293260A publication Critical patent/GB2293260A/en
Application granted granted Critical
Publication of GB2293260B publication Critical patent/GB2293260B/en
Anticipated expiration legal-status Critical
Expired - Fee Related legal-status Critical Current

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Classifications

    • G—PHYSICS
    • G09—EDUCATION; CRYPTOGRAPHY; DISPLAY; ADVERTISING; SEALS
    • G09G—ARRANGEMENTS OR CIRCUITS FOR CONTROL OF INDICATING DEVICES USING STATIC MEANS TO PRESENT VARIABLE INFORMATION
    • G09G3/00—Control arrangements or circuits, of interest only in connection with visual indicators other than cathode-ray tubes
    • G09G3/20—Control arrangements or circuits, of interest only in connection with visual indicators other than cathode-ray tubes for presentation of an assembly of a number of characters, e.g. a page, by composing the assembly by combination of individual elements arranged in a matrix no fixed position being assigned to or needed to be assigned to the individual characters or partial characters
    • G09G3/34—Control arrangements or circuits, of interest only in connection with visual indicators other than cathode-ray tubes for presentation of an assembly of a number of characters, e.g. a page, by composing the assembly by combination of individual elements arranged in a matrix no fixed position being assigned to or needed to be assigned to the individual characters or partial characters by control of light from an independent source
    • G09G3/36—Control arrangements or circuits, of interest only in connection with visual indicators other than cathode-ray tubes for presentation of an assembly of a number of characters, e.g. a page, by composing the assembly by combination of individual elements arranged in a matrix no fixed position being assigned to or needed to be assigned to the individual characters or partial characters by control of light from an independent source using liquid crystals
    • G09G3/3607—Control arrangements or circuits, of interest only in connection with visual indicators other than cathode-ray tubes for presentation of an assembly of a number of characters, e.g. a page, by composing the assembly by combination of individual elements arranged in a matrix no fixed position being assigned to or needed to be assigned to the individual characters or partial characters by control of light from an independent source using liquid crystals for displaying colours or for displaying grey scales with a specific pixel layout, e.g. using sub-pixels
    • 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
    • G02F1/1337—Surface-induced orientation of the liquid crystal molecules, e.g. by alignment layers
    • G02F1/133753—Surface-induced orientation of the liquid crystal molecules, e.g. by alignment layers with different alignment orientations or pretilt angles on a same surface, e.g. for grey scale or improved viewing angle
    • 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
    • G02F1/1337—Surface-induced orientation of the liquid crystal molecules, e.g. by alignment layers
    • G02F1/133753—Surface-induced orientation of the liquid crystal molecules, e.g. by alignment layers with different alignment orientations or pretilt angles on a same surface, e.g. for grey scale or improved viewing angle
    • G02F1/133757—Surface-induced orientation of the liquid crystal molecules, e.g. by alignment layers with different alignment orientations or pretilt angles on a same surface, e.g. for grey scale or improved viewing angle with different alignment orientations
    • 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
    • G02F1/137—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 characterised by the electro-optical or magneto-optical effect, e.g. field-induced phase transition, orientation effect, guest-host interaction or dynamic scattering
    • G02F1/139—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 characterised by the electro-optical or magneto-optical effect, e.g. field-induced phase transition, orientation effect, guest-host interaction or dynamic scattering based on orientation effects in which the liquid crystal remains transparent
    • G02F1/141—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 characterised by the electro-optical or magneto-optical effect, e.g. field-induced phase transition, orientation effect, guest-host interaction or dynamic scattering based on orientation effects in which the liquid crystal remains transparent using ferroelectric liquid crystals
    • 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
    • G02F2203/00—Function characteristic
    • G02F2203/30—Gray scale
    • G—PHYSICS
    • G09—EDUCATION; CRYPTOGRAPHY; DISPLAY; ADVERTISING; SEALS
    • G09G—ARRANGEMENTS OR CIRCUITS FOR CONTROL OF INDICATING DEVICES USING STATIC MEANS TO PRESENT VARIABLE INFORMATION
    • G09G3/00—Control arrangements or circuits, of interest only in connection with visual indicators other than cathode-ray tubes
    • G09G3/20—Control arrangements or circuits, of interest only in connection with visual indicators other than cathode-ray tubes for presentation of an assembly of a number of characters, e.g. a page, by composing the assembly by combination of individual elements arranged in a matrix no fixed position being assigned to or needed to be assigned to the individual characters or partial characters
    • G09G3/2007—Display of intermediate tones
    • G09G3/2014—Display of intermediate tones by modulation of the duration of a single pulse during which the logic level remains constant

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  • Physics & Mathematics (AREA)
  • Chemical & Material Sciences (AREA)
  • Crystallography & Structural Chemistry (AREA)
  • Nonlinear Science (AREA)
  • General Physics & Mathematics (AREA)
  • Engineering & Computer Science (AREA)
  • Spectroscopy & Molecular Physics (AREA)
  • Mathematical Physics (AREA)
  • Optics & Photonics (AREA)
  • Computer Hardware Design (AREA)
  • Theoretical Computer Science (AREA)
  • Liquid Crystal (AREA)

Abstract

A liquid crystal device (8) is provided in which pixels are organised into groups (10). The twist angle varies between individual pixels (2, 4, 6) in a given group (10) such that the switching threshold varies between pixels within the group. The pixels within each group (10) share common addressing electrodes but are controllable such that some of the pixels can be switched without switching other pixels. Such a device is therefore capable of providing several grey levels. <IMAGE>

Description

LIQUID CRYSTAL DEVICE The present invention reiates to a liquid crvstal device. Such a device is suitable for use as a display device having the ability to display a plurality of grey levels.
It is known that material, such as terroelectric liquid crvstals (FLC), having low spontaneous polarisation and minima in their switching time versus control voltage characteristic (known as the T-V characteristic) at suitable voltages are suitable for use in liquid crystal displays (LCD). The minima in the r-V characteristic are utilised by certain drive schemes, such as the Joers/Alvey and Malvern schemes, to obtain high speed addressing and high contrast. However, the basic FLC effect is bistable and does not exhibit the grey scale capability required for high definition television and other high resolution applications.
It has been reported in a paper titled "Molecular alignment of very-largesize FLCD", Y.Hanvu, K.Nakamura, Y.Hotta, S. Yoshihara and J.Knabe SID 93 Digest, p364, that problems in obtaining high contrast, due to the C-directors tending to take a twisted structure between the upper and lower substrates of the LCD, can be reduced or overcome by using crossrubbing of the alignment surfaces of the LCD. The alignment surfaces of each pixel are twisted with respect to one another bv the same amount.
,Accoråing to the present invention, there is provided a liauid crvstal device, comprising a oiuralitv of groups of picture elements, each group of picture elements comprising a plurality of picture eiements having different twist angies of surface alignment.
As used herein, the term "twist angle of surface alignment" refers to the difference in the direction of the alignment induced in a liquid crystal layer at a first surface defining a boundary of the liquid crystal layer and the alignment induced in the liquid crystal layer at a second surface defining a boundary of the liquid crystal laver.
It is thus possible to provide a device in which the switching characteristics of picture elements (pixels) within each group of pixels can be made to vary with respect to one another. Thus a control pulse of a given duration and voltage may switch some pixels within a group but not others. Thus it is possible to provide a display having enhanced grey level capability where one or more of the groups of pixels is controlied to be a super-pixel. The super-pixei may represent one pixel of image data presented to the device.
Preferably the liquid crystal material is a ferroelectric liquid crystal.
Preferably the pixels within each individual group share common electrodes. Thus each pixel within a group is subjected to the same control pulse-length and voltage as each other pixel within the group.
Preferably the alignment means on first and second surfaces defining side walls of each of the pixels produce alignment directions which, for each pixel, are substantially symmetrically disposed about a first direction.
Preferably the alignment directions are defined by optical writing of a photopolymerisable material. Alternatively the alignment directions can be defined by rorming structures, such as grooves, on the first and second surfaces. Such alignment structures may be formed by controlled rubbing ot the first and second surfaces.
Preferably the liquid crystal material exhibits a minimum in its T-V characteristic. Advantageously drive means are provided for driving the apparatus with signals in the vicinitv of the minimum in the T-V characteristic for the pixels within each group such that the driving signal can be selected to switch one or more of the pixels within a group in response to control data.
The present invention will further be described, by way of example, with reference to the accompanying drawings, in which: Figure 1 is a perspective schematic view of part of a liquid crystal device constituting an embodiment of the present invention; and Figure 2 is a graph of a n-V characteristic versus twist angle for the embodiment illustrated in Figure 1.
Figure 1 shows first, second and third pixels 2,4 and 6, respectively, within a liquid crystal device 8. The first, second and third pixels are grouped together to form a single super-pixel 10. The super-pixel 10 is one of a plurality of super-pixels fabricated within the device 8.
It is conventional to align the liquid crystal material in a single predetermined direction at first and second surfaces 12 and 14, respectively, of the device 8. Thus, the alignment of the liquid crystal material at the first and second surfaces would conventionally be the same for each pixel. However, in the embodiment shown in Figure 1, the alignment of the liquid crystal material at the first and second surfaces varies between pixels within a group. The alignment of the liquid crystal material within the first pixel 2 makes and angle of 0 with respect to a first direction at the first surface 12, and -o with respect to the first direction and the second surface 14.The liquid crystal material is aligned with the first direction at both the first and second surfaces 12 and 14 within the region of the second pixel 4 whereas, tor the third pixel 6, the alignment of the liquid crystal makes angles of 9 and +6 with respect to the first direction at the first surface 12 and second surface 14, respectively. In this embodiment 0 has a magnitude of 8 degrees.
Transparent electrodes, for example of indium tin oxide, are provided adjacent the first and second surfaces such that a control signal can be provided to the group of pixels. The device 8 may carry addressing control electronics (not shown) adjacent each group so as to allow the use of column/row type addressing schemes. This structure is repeated for each group of pixels.
The device is enciosed between glass plates (not shown). In use the device is illuminated with polarised light, and the light reflected or transmitted by the device is passed through a further polariser so that the image supplied to the device can be viewed. Alternatively polarising means can be integrally formed within the device.
The first and second surfaces 12 and 14 are provided by rubbed polyimide layers. As an alternative to mechanical treatment to produce the alignment films, photopolymers may be used, as described in "Surtace-induced parallel alignment of liquid crystals by linearly polymerised photopolymers", M.Schadt, K.Schmitt, V.Kozinkov and V.Chigrinov, Jpn. J. App. Phys. Vol 31 (1992) p2153-2164.
Figure 2 shows the relation between pulse time T and the minimum control voltage V-ln for switching a FLC material known as SCE8 within cell having a thickness of approximately 2 ijm. SCE8 is a standard terroelectric liquid crystal material which is available from Merck Limited of Merck House,. Poole, Dorset, BH15 1TD, United Kingdom. The 5-V,,, curves varv for different twist angles, i.e the difference between the direction of alignment at the first surface 12 and the direction of alignment at the second surface 14. The first curve 30 corresponds to the response of the second pixel 4 , the second curve 32 corresponds to the first pixel 2, whereas the third curve 34 corresponds to the third pixel 6.If the pixels are driven with signals in the region of the minima in the :-Vm,n curves, for example with a fixed pulse length of approximately 40 ,u'S and a variable voltage drive, a signal of approximately 41 Volts would switch the third pixel 6 between its bistable states, but would not affect the first and second pixels. A signal having a magnitude of approximately 49 Volts would switch the first and third pixels 2 and 6, but not the second pixel; whereas a voltage of approximately 54 Volts or more would switch all three pixels together.Thus, depending on the magnitude of the control voltage, it is possible to switch the group of pixels to any one of four states, which in a display device correspond to all pixels dark, one pixel dark, two pixels dark and three pixels dark, and hence to a super-pixel capable of displaying four grey levels. If the above voltages were used to switch the pixels from "off" to "on", the pixels could be returned to the "off" state by applying a relatively large reverse polarity so as to ensure that all the pixels are switched.
The display may be controlled so as to blank entire rows at a time.
The display may be used in aoolications in which other grey scale techniques are used, sucn as spatial and temporal digital grey scale techniques. For example, tecnniques using two bits (4 levels) of spatial modulation and 2 bits (4 lexis) of temporal dither in conjunction with a display of the type described hereinabove allowing a further tour grey levels to be defined within each of the grey levels obtainable using the above techniques allows 236 grey levels to be displayed.
Such a device is suitable for use in the display ot a high definition television system and allows 256 grey levels to be displayed at video refresh rates.
Other simpler grey level schemes may be produced using simpler devices. For example, if each super-pixel only contained two pixels of equal size, such a pixel could be driven using a time multiplexed (i.e.
temporal dither) scheme having a time ratio of 1:3 so as to provide a device having a capability of displaying nine grey levels.
Furthermore, the pixels within each super-pixel 10 need not be of equal size. For example, a super-pixel containing two pixels in an area ratio of 1:4 may be driven using a temporal dither having a ratio of 1:2 to provide a device capable of displaying sixteen grey levels.
Spatial modulation of adjacent super-pixels grouped to form an image pixel enables further improvements in grey scale to be achieved. For example if two super pixels 10 have a spatial dither of 1:3 (i.e. one pixel is three times the size of the other or is simulated by grouping three super-pixels together in a device where each super-pixel is the same size), if each super-pixel contains two pixels in an area ratio of 1:1 and a temporal addressing scheme having a temporal dither of 1:9 is employed, such a grouping can dispiav 81 grey levels.
The liquid crystal device 8 may be used in conjunction with polarisers andior reflectors to produce a displav wnich uses the device 8 in either a transmissive or a reflective mode. Adciitionally the liquid crystal material may have a pleochroic dye added thereto. Such a device can be used with only one polariser, which may be separate to or integrally formed with the device 8.

Claims (11)

1. A liquid crystal device comprising a plurality of groups of picture elements, each group of picture elements comprising a plurality of picture elements having different twist angles of surface alignment.
2. A liquid crystal device as claimed in Claim 1, including a ferroelectric liquid crystal material.
3. A liquid crystal device as claimed in Claim 1 or 2, in which the picture elements of each group have common control electrodes.
4. A liquid crystal device as claimed in any one of the preceding claims, including liquid crystal material having a minimum in its control voltage versus control pulse length characteristic.
A A liquid crystal device as claimed in any one of the preceding claims, in which each picture element has first and second alignment means, at least one of which comprises a photopolymerisable material.
6. A liquid crystal device as claimed in any one of the preceding claims, in which each picture element has first and second alignment means, at least one of which carries a surface structure for aligning liquid crystal material along a predetermined direction.
A A liquid crystal device as claimed in Claim 6, in which the surface structure is produced by rubbing of a material defining a boundary of the device.
8. A liquid crystal device as claimed in Claims 5 to 7, in which, for each picture element, the directions of alignment of the liquid crystal at the first and second alignment means are symmetrically disposed about a first direction which is common to all of the picture elements.
9. A liquid crystal device as claimed in any one of the preceding claims, in which the liquid crystal incorporates a pleochroic dye.
10. A liquid crystal display comprising a liquid crystal device as claimed in any one of the preceding claims.
11. A liquid crystal device substantially as described hereinbefore with reference to and as illustrated in the accompanying drawings.
GB9418866A 1994-09-19 1994-09-19 Liquid crystal device Expired - Fee Related GB2293260B (en)

Priority Applications (2)

Application Number Priority Date Filing Date Title
GB9418866A GB2293260B (en) 1994-09-19 1994-09-19 Liquid crystal device
JP7238397A JPH08101392A (en) 1994-09-19 1995-09-18 Liquid crystal device and liquid crystal display device

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Application Number Priority Date Filing Date Title
GB9418866A GB2293260B (en) 1994-09-19 1994-09-19 Liquid crystal device

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GB9418866D0 GB9418866D0 (en) 1994-11-09
GB2293260A true GB2293260A (en) 1996-03-20
GB2293260B GB2293260B (en) 1998-07-08

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Cited By (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
WO2000008522A1 (en) * 1998-08-07 2000-02-17 Honeywell Inc. Liquid crystal display with reduced off state luminance

Citations (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
EP0240010A1 (en) * 1986-04-02 1987-10-07 Canon Kabushiki Kaisha Optical modulation device
EP0402984A1 (en) * 1989-06-12 1990-12-19 Koninklijke Philips Electronics N.V. Passive ferro-electric liquid crystal display device and method of manufacturing such a device

Family Cites Families (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US5579140A (en) * 1993-04-22 1996-11-26 Sharp Kabushiki Kaisha Multiple domain liquid crystal display element and a manufacturing method of the same

Patent Citations (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
EP0240010A1 (en) * 1986-04-02 1987-10-07 Canon Kabushiki Kaisha Optical modulation device
EP0402984A1 (en) * 1989-06-12 1990-12-19 Koninklijke Philips Electronics N.V. Passive ferro-electric liquid crystal display device and method of manufacturing such a device

Cited By (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
WO2000008522A1 (en) * 1998-08-07 2000-02-17 Honeywell Inc. Liquid crystal display with reduced off state luminance
US6181401B1 (en) 1998-08-07 2001-01-30 Honeywell International Inc. Liquid crystal display with reduced off state luminance

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Publication number Publication date
JPH08101392A (en) 1996-04-16
GB2293260B (en) 1998-07-08
GB9418866D0 (en) 1994-11-09

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Effective date: 20000919