EP0717305A2 - Flüssigkristallelement und Flüssigkristallvorrichtung - Google Patents

Flüssigkristallelement und Flüssigkristallvorrichtung Download PDF

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Publication number
EP0717305A2
EP0717305A2 EP96102488A EP96102488A EP0717305A2 EP 0717305 A2 EP0717305 A2 EP 0717305A2 EP 96102488 A EP96102488 A EP 96102488A EP 96102488 A EP96102488 A EP 96102488A EP 0717305 A2 EP0717305 A2 EP 0717305A2
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EP
European Patent Office
Prior art keywords
liquid crystal
voltage signal
voltage
gradation
applying
Prior art date
Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
Granted
Application number
EP96102488A
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English (en)
French (fr)
Other versions
EP0717305B1 (de
EP0717305A3 (de
Inventor
Shuzo Kaneko
Ryoji Fujiwara
Akio Yoshida
Tomoko Maruyama
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Canon Inc
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Canon Inc
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Filing date
Publication date
Priority claimed from JP03192048A external-priority patent/JP3143497B2/ja
Application filed by Canon Inc filed Critical Canon Inc
Publication of EP0717305A2 publication Critical patent/EP0717305A2/de
Publication of EP0717305A3 publication Critical patent/EP0717305A3/de
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Publication of EP0717305B1 publication Critical patent/EP0717305B1/de
Anticipated expiration legal-status Critical
Expired - Lifetime 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
    • G09G3/3611—Control of matrices with row and column drivers
    • G09G3/3648—Control of matrices with row and column drivers using an active matrix
    • G09G3/3651—Control of matrices with row and column drivers using an active matrix using multistable liquid crystals, e.g. ferroelectric liquid crystals
    • G—PHYSICS
    • G09—EDUCATION; CRYPTOGRAPHY; DISPLAY; ADVERTISING; SEALS
    • G09G—ARRANGEMENTS OR CIRCUITS FOR CONTROL OF INDICATING DEVICES USING STATIC MEANS TO PRESENT VARIABLE INFORMATION
    • G09G2310/00—Command of the display device
    • G09G2310/06—Details of flat display driving waveforms
    • G—PHYSICS
    • G09—EDUCATION; CRYPTOGRAPHY; DISPLAY; ADVERTISING; SEALS
    • G09G—ARRANGEMENTS OR CIRCUITS FOR CONTROL OF INDICATING DEVICES USING STATIC MEANS TO PRESENT VARIABLE INFORMATION
    • G09G2310/00—Command of the display device
    • G09G2310/06—Details of flat display driving waveforms
    • G09G2310/061—Details of flat display driving waveforms for resetting or blanking
    • G—PHYSICS
    • G09—EDUCATION; CRYPTOGRAPHY; DISPLAY; ADVERTISING; SEALS
    • G09G—ARRANGEMENTS OR CIRCUITS FOR CONTROL OF INDICATING DEVICES USING STATIC MEANS TO PRESENT VARIABLE INFORMATION
    • G09G2310/00—Command of the display device
    • G09G2310/06—Details of flat display driving waveforms
    • G09G2310/065—Waveforms comprising zero voltage phase or pause
    • 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
    • G09G3/2011—Display of intermediate tones by amplitude modulation
    • 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
    • G09G3/207—Display of intermediate tones by domain size control

Definitions

  • the present invention relates to a liquid crystal element and apparatus exhibiting spontaneous polarization and, more particularly, to a liquid crystal element and apparatus using a ferroelectric liquid crystal (FLC).
  • FLC ferroelectric liquid crystal
  • a ferroelectric liquid crystal (FLC) as a liquid crystal exhibiting the spontaneous polarization has received a great deal of attention in favor of advantages such as high-speed response and good memory characteristics and has been actively developed to obtain a light bulb and the like.
  • Targets utilizing the above advantages are an optical shutter array, a high-definition display unit by simple matrix driving, a light bulb for high-density recording combined with a photoconductive body.
  • the ferroelectric liquid crystal is expected to display a motion picture by active matrix driving using thin film transistors (TFTs).
  • One of the problems is a decrease in response speed of the liquid crystal when a direct current (DC) component is continuously applied to the FLC for a long period of time due to the following reason. Localization of internal ions in the liquid crystal is assumed to be induced to form an electric field.
  • DC direct current
  • a liquid crystal panel used in the present invention is a liquid crystal panel of an active matrix drive scheme, as shown in Fig. 17.
  • the liquid crystal panel comprises switching elements (TFTs obtained by using thin film semiconductors such as amorphous silicon and polysilicon) arranged along a plurality of rows (scanning lines) and a plurality of columns (data lines), first wiring lines (gate lines) commonly connecting the first terminals (gates) of the switching elements in units of rows, second wiring lines (source lines) connecting the second terminals (sources) of the switching elements in units of columns, a plurality of pixel electrodes (transparent electrodes) connected in units of third terminals (drains) of the switching elements, counter electrodes (transparent electrodes) arranged to oppose the pixel electrodes, and a liquid crystal (chiral smectic C, H, I, G, F liquid crystal exhibiting ferroelectric properties) exhibiting spontaneous polarization and arranged between the plurality of pixel electrodes and the counter electrodes.
  • switching elements TFTs obtained by
  • the distance between each pixel electrode and the corresponding counter electrode is set to be a minimum distance (about 5 ⁇ m or less) capable of sufficiently suppressing formation of a helical structure of the chiral smectic liquid crystal.
  • the formation of the helical structure need not be suppressed in the present invention.
  • Thermal control may be performed during driving of the liquid crystal to maintain the liquid crystal within a desired temperature range.
  • an auxiliary voltage signal V SX having a magnitude corresponding to that of the recording voltage signal V W is applied, thereby controlling an internal electric field to be described below.
  • Figs. 2A and 2B show a pseudo equivalent circuit model of an FLC element.
  • Fig. 3 shows an ionic localization diagram obtained when an external DC component is applied for a long period of time.
  • P s spontaneous polarization
  • Figs. 4A and 4B show ionic localization by spontaneous polarization (PS) itself.
  • PS spontaneous polarization
  • the DC component can be controlled by an external voltage applied to the liquid crystal.
  • the auxiliary voltage V s serves as a DC component, and the ionic localization is kept “constant” regardless of the state of the spontaneous polarization P s .
  • the term “constant” indicates a total amount of ionic localization.
  • the “constant” value may be a predetermined value or zero. However, the “constant” value need not always be zero.
  • a method of adjusting the ionic localization to be "constant" will be described with reference to Figs. 5A to 5C.
  • a total amount of ionic localization is apparently maintained to be an amount with which the "black" state as shown in Fig. 4A is kept set.
  • the ionic localization sate of the "black" state shown in Fig. 5A is taken as an initial state.
  • a drive signal having a waveform shown in Fig. 1(a) is applied to the liquid crystal in advance.
  • a drive signal having a waveform shown in Fig. 6A is applied to obtain the "black” state.
  • the superposition amount of the DC component by the auxiliary voltage V SX may be zero.
  • the ionic localization state to be obtained by this display is as shown in Fig. 18A.
  • an auxiliary voltage +V SX1 shown in Fig. 6A is applied to add the ionic localization of Fig. 18B.
  • an auxiliary voltage +V SX2 (Fig. 6C) is applied to maintain the state of Fig. 19A (i.e., the ionic localization state formed by this display) to the total amount obtained in the case of the "black" display.
  • the numerical control of the auxiliary voltages V SX1 and V SX2 is appropriately performed in accordance with the magnitude of the instantaneous polarization P S and the ambient temperature. It is advantageous if the magnitude of the spontaneous polarization P S is set not so large (i.e., 10 nC/cm 2 or less, and preferably 5 nC/cm 2 or less) in the liquid crystal used in the present invention since then an excessive increase in the amplitude of the auxiliary voltage signal V SX can be suppressed.
  • the numerical value for the amplitude of the signal V SX1 preferably falls within the following range: V SX to 2 P s ⁇ a Ci (where ⁇ a is the gradation at the end of application of the voltage V W and satisfies condition 0 ⁇ ⁇ a ⁇ 1, and Ci is the capacitance of the insulating layer)
  • Fig. 7 shows a measurement of a divided voltage applied to a liquid crystal layer when a terminal voltage of a liquid crystal pixel is set at 0 V immediately after a gradation recording voltage V W is applied. At this time, the liquid crystal molecules are partially returned to the "black" direction and are set in the gradation state.
  • V SX about 0.5 V can be obtained even in the full "white" state.
  • the initial ionic localization state can be maintained constant.
  • the DC component also serves as a "white" retention voltage of the liquid crystal, high-speed response of the liquid crystal can be obtained and can cope with the motion picture.
  • Figs. 10 and 11 show an optical response test improved by the above driving method.
  • the effective magnitude of the spontaneous polarization P S of the liquid crystal used and the composite capacitance Ci of the alignment layers as important components constituting the element or an insulating layer portion including an additional insulating layer in the element must satisfy the above permanent relationship, thereby performing substantially stable gradation driving.
  • the composite capacitance Ci is preferably set to be large, and the spontaneous polarization value P S of the liquid crystal used is preferably set to be small.
  • insulating layers formed to prevent electrical short-circuiting of the upper and lower electrodes of each cell are formed such that an oxide mixture (Ti-SiO x ) of Ti (titanium) and Si (silicon) is coated on the electrodes and baked to obtain thin films each having a thickness of about 1,000 ⁇ .
  • a 200 ⁇ thick polyimide alignment layer is formed on this insulating film and baked.
  • the resultant structure is rubbed to maximize the composite capacitance Ci.
  • the capacitance Ci can be about several 10 nF/cm 2 .
  • the physical film thickness must be decreased, and a layer having a high dielectric constant is selected.
  • the magnitude of the spontaneous polarization P S of the liquid crystal is a maximum of 10 nC/cm 2 when it is evaluated by a polarization reverse current. This magnitude is preferably 5 nC/cm 2 or less.
  • the value 2P S /Ci is set to be about 0.5 V or less. In order to increase the value Vth, the viscosity of the liquid crystal is adjusted. However, it is generally disadvantageous to increase the drive voltage.
  • the voltage Vth is defined as a DC application voltage limit with which an optical change is substantially not detected during a period of gradation display in driving the element.
  • this driving method cannot control each gradation level in formation of an image by a simple matrix.
  • this driving method can be applied to an arrangement for driving pixels independently of each other as in driving of a single-bit optical shutter or a 7-segment display, or as in active matrix driving of TFTs (Thin Film Transistors).
  • Fig. 12 is a timing chart showing drive waveforms when the present invention is applied to active matrix driving.
  • a reset signal V R for setting a pixel in the "black” state is applied, and a time voltage for sufficiently setting the pixel in the "black” state by utilizing the open characteristics of the TFT is also applied (Vr in Fig. 12).
  • a recording voltage V W is applied, and this gradation level voltage V W is kept applied for a predetermined period of time in accordance with similar open characteristics.
  • a ground signal V E is then applied to the pixel. During application of a ground voltage V e , the gradation transmittance is changed but can be stabilized by the following auxiliary signal.
  • the auxiliary voltage signal V SX is then applied to the pixel.
  • This signal can be selected from V SX1 and V SX2 in accordance with a desired gradation display state.
  • the auxiliary voltage signal is applied as a voltage value containing an appropriate DC voltage. Note that when a sufficiently high voltage is applied as the reset voltage, the voltages V SX1 and V SX2 may be applied as values added with voltages for effecting the DC components corresponding to the gradation levels after the voltage difference between the voltages Vr and V W is compensated to be zero during the frame period.
  • the target DC component value of this auxiliary voltage signal V SX is selected in accordance with the magnitude of the spontaneous polarization Ps of the liquid crystal used.
  • the recording voltage V W or the recording voltage signal V W is a signal for determining the optical state of each pixel and represents a voltage signal (gradation voltage signal) corresponding to display brightness of the pixel.
  • the auxiliary voltage V SX or the auxiliary voltage signal V SX is assumed to be a voltage for substantially stabilizing the gradation display state. This voltage signal is stabilized well at a DC voltage equal to or less than the optical threshold value Vth.
  • the optical threshold value Vth is defined as a value with which an optical change is substantially not detected even if the threshold value Vth is kept applied throughout one frame.
  • the absolute value of the auxiliary voltage signal V SX is preferably set to be about 1/50 to 1/5 that of the gradation voltage signal.
  • the application interval of the ground voltage V e between the voltages V W and V SX is given to stabilize a reaction component as response of the liquid crystal molecules after the gradation voltage signal V W is applied.
  • the V SX value must be appropriately regulated in accordance with a drive waveform.
  • the application intervals of the voltage signals V W and V E can be set equal to that of the reset voltage Vr.
  • a recording period of each line is divided into at least four intervals (if the V E application interval is not provided, only three intervals are required; and the following description exemplifies a case wherein the V E application interval is provided).
  • the lower timing chart represents a case wherein the recording period A of the nth line is divided into four intervals.
  • the recording period A is divided into a division interval a for enabling a gate corresponding to a subsequent line a few lines after the current line to reset the pixels of the subsequent line, a division interval b for enabling a gate of the nth line to perform recording of the nth line itself, a division interval c for enabling a gate corresponding to a previous line a few lines before the current line to apply the ground voltage to the recorded pixels of the previous line, and a division interval d for enabling a gate corresponding to another previous line a few lines before the above previous line to apply an auxiliary voltage signal to the recorded pixels of this other previous line.
  • the division intervals a , b , c , and d in the recording period A of the nth line may have any one of the following orders: abcd, abdc, acdb, acbd, bacd, badc, bcad, bcda, bdac, bdca, cabd,....
  • Fig. 12 shows optical states 101 to 104 of a liquid crystal pixel of the nth line. These states are enlarged in Fig. 13.
  • Fig. 14 is a view showing an FLC sandwiched between an upper electrode substrate 11 having a TFT active matrix and a lower substrate with its entire surface serving as an electrode.
  • each frame is driven for about 33 msec. For this reason, a recording period assigned to each line is about 33 ⁇ sec per frame.
  • the recording period of 33 ⁇ sec for applying a recording voltage every nth line according to the present invention is divided into four intervals (i.e., each interval is about 8 ⁇ sec or less).
  • a satisfactory image display could be obtained by the material used by the present inventor at maximum V R and V W voltages of about 7 V.
  • the DC component was superposed on the auxiliary voltage V SX by a voltage equal to or less than the threshold value Vth corresponding to the gradation level to stabilize the gradation display state.
  • the pulse peak value of the auxiliary voltage signal V SX can be determined as follows.
  • peak values V S1 , V S2 , and V S3 are defined as follows if the reset voltage is sufficiently high, the number of scanning lines is 1,000, and a 24-line period is provided as the frame interval (blanking period) as follows.
  • V S1 ' V 0 ⁇ S 2 - V 1 ⁇ S 3 1024 - ⁇ S 2 + S 3 + S 4 - S 3 + 1 ⁇
  • the auxiliary voltage signal V SX may be calculated in accordance with the analog recording signal voltage V W on the spot, or may be automatically output from a prestored table T (V W and V SX ) if the recording signal V W is a digital signal.
  • the driving method of the present invention can be easily realized by arranging a frame memory or a line memory of at least S 4 lines in principle.
  • Fig. 15 shows a simple block diagram of a driver circuit. All signal tuning operations are performed in response to a clock (shown in Fig. 15). Gate signal output timings of the lines, reset signals for the source electrodes, and recording and auxiliary signal output timings are controlled by this clock.
  • the ionic localization state is stabilized when the FCL state is the full “black” state.
  • this localization may be stabilized when the FCL state is a full “white” state.
  • ionic localization in the initial "white” state is caused to occur to start the operation.
  • a waveform in Fig. 16(d) is continuously applied.
  • the DC component source for maintaining the ionic localization in the "black” state is 2 P s ⁇ a Ci and this component is applied as the auxiliary signal. If the "white" domain ratio is given as ⁇ a, in order to maintain the ionic localization amount in the "white” state with respect to the remaining black domain ratio (1 - ⁇ a), an auxiliary voltage having the following DC component superposing amount is applied (Figs.
  • the DC component value -2 P s (1 - ⁇ a ) Ci is always smaller than Vth.
  • a good liquid crystal display As has been described above, there is provided a good liquid crystal display.
  • a high-precision direct viewing flat display or a projection display can be arranged.
  • a color filter on each pixel, or by using a plurality of liquid crystal elements of the driving method of the present invention so as to perform color light projection, a transmission or reflection type high-definition flat color television or projection color television can be arranged.
  • the present invention is not limited to the driving techniques in the above embodiment.
  • the present invention is widely applicable as optical elements consisting of liquid crystals having spontaneous polarization to perform stable gradation display.
  • a liquid crystal apparatus including a liquid crystal panel having a pair of electrodes and a liquid crystal exhibiting spontaneous polarization and arranged between the pair of electrodes, first means for applying a gradation voltage signal corresponding to gradation information to the pair of electrodes, and second means for applying, a DC component serving as a reverse bias of an internal electric field generated upon application of the gradation voltage signal, to the liquid crystal during one vertical scanning period.
  • a liquid crystal element comprising a liquid crystal exhibiting spontaneous polarization, a pair of electrode substrates for sandwiching said liquid crystal therebetween, characterized in that insulating layers are formed between said electrode substrates and said liquid crystal, wherein a spontaneous polarization P S value of said liquid crystal, an interelectrode composite capacitance Ci of said insulation layers, and a voltage threshold value Vth of optical response of said liquid crystal in said liquid crystal element satisfy the following condition: 2P s Ci > Vth

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  • Engineering & Computer Science (AREA)
  • Chemical & Material Sciences (AREA)
  • Crystallography & Structural Chemistry (AREA)
  • Physics & Mathematics (AREA)
  • Computer Hardware Design (AREA)
  • General Physics & Mathematics (AREA)
  • Theoretical Computer Science (AREA)
  • Liquid Crystal (AREA)
  • Liquid Crystal Display Device Control (AREA)
  • Liquid Crystal Substances (AREA)
EP96102488A 1990-08-22 1991-08-21 Flüssigkristallvorrichtung Expired - Lifetime EP0717305B1 (de)

Applications Claiming Priority (10)

Application Number Priority Date Filing Date Title
JP22171090 1990-08-22
JP22170990 1990-08-22
JP221709/90 1990-08-22
JP221710/90 1990-08-22
JP22170990 1990-08-22
JP22171090 1990-08-22
JP19204891 1991-07-31
JP192048/91 1991-07-31
JP03192048A JP3143497B2 (ja) 1990-08-22 1991-07-31 液晶装置
EP91114021A EP0473058B1 (de) 1990-08-22 1991-08-21 Flüssigkristallgerät

Related Parent Applications (2)

Application Number Title Priority Date Filing Date
EP91114021A Division EP0473058B1 (de) 1990-08-22 1991-08-21 Flüssigkristallgerät
EP91114021.8 Division 1991-08-21

Publications (3)

Publication Number Publication Date
EP0717305A2 true EP0717305A2 (de) 1996-06-19
EP0717305A3 EP0717305A3 (de) 1996-11-20
EP0717305B1 EP0717305B1 (de) 2002-11-06

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EP96102488A Expired - Lifetime EP0717305B1 (de) 1990-08-22 1991-08-21 Flüssigkristallvorrichtung

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EP (1) EP0717305B1 (de)
AT (2) ATE150570T1 (de)
DE (2) DE69133146T2 (de)
ES (1) ES2098286T3 (de)

Cited By (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
WO1999005238A1 (de) * 1997-07-25 1999-02-04 Aventis Research & Technologies Gmbh & Co Kg Ferroelektrische flüssigkristallanzeige mit aktiven matrix elementen

Citations (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
EP0294852A2 (de) * 1987-06-12 1988-12-14 Canon Kabushiki Kaisha Vorrichtung mit einem ferroelektrischen Flüssigkristall

Patent Citations (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
EP0294852A2 (de) * 1987-06-12 1988-12-14 Canon Kabushiki Kaisha Vorrichtung mit einem ferroelektrischen Flüssigkristall

Cited By (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
WO1999005238A1 (de) * 1997-07-25 1999-02-04 Aventis Research & Technologies Gmbh & Co Kg Ferroelektrische flüssigkristallanzeige mit aktiven matrix elementen
US6368679B1 (en) 1997-07-25 2002-04-09 Aventis Research & Technologies Gmbh & Co. Kg Ferroelectric liquid-crystal display having active matric elements

Also Published As

Publication number Publication date
EP0717305B1 (de) 2002-11-06
ATE150570T1 (de) 1997-04-15
DE69125228T2 (de) 1997-08-28
DE69125228D1 (de) 1997-04-24
ES2098286T3 (es) 1997-05-01
EP0717305A3 (de) 1996-11-20
DE69133146D1 (de) 2002-12-12
ATE227437T1 (de) 2002-11-15
DE69133146T2 (de) 2004-02-05

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