(12) United States Patent
`Johnson et al.
`
`(10) Patent No.:
`(45) Date of Patent:
`
`US 6,384,892 B1
`May 7, 2002
`
`US006384892B1
`
`(54) LCD HAVING PARTICULAR DIELECTRIC
`CONSTANT RELATIONSHIP BETWEEN
`ORIENTATION FILM AND LC LAYER
`
`7/1996 Fergason ................... .. 359/93
`5,532,854 A
`
`2/1997 Ohe et al.
`349/123
`5,600,464 A *
`6/1999 Ohe et al. ................. .. 349/132
`5,914,761 A *
`FOREIGN PATENT DOCUMENTS
`
`(75)
`
`Inventors: Mark T. Johnson; Adrianus A. Van
`Der Put, both Of Eindhoven (NL)
`
`(73) Assignee: U.S. Philips Corporation, New York,
`NY (US)
`
`EP
`EP
`
`E1’
`EP
`
`0508227 A3
`0508227 A2
`
`10/1992
`10/1992
`
`....... .. G02F/1/1337
`....... .. G02F/1/1337
`
`0544452 A3
`0644452 A2
`
`3/1995
`3/1995
`
`~~~~~~~ ~~ GOZF/1/1337
`....... .. G02F/1/1337
`
`OTHER PUBLICATIONS
`
`( * ) Notice:
`
`Subject to any disclaimer, the term of this
`patent is extended or adjusted under 35
`U.S.C. 154(b) by 0 days.
`
`(21) Appl. No.: 09/482,930
`
`(22)
`
`Filed:
`
`Jan. 13, 2000
`
`(30)
`
`Foreign Application Priority Data
`
`Jan. 13, 1999
`
`(EP) .......................................... .. 99200074
`
`Int. Cl.7 .............................................. .. C09K 19/02
`(51)
`(52) U.S.Cl.
`...................................... .. 349/177, 349/123
`(58) Field of Search ............................... .. 349/123, 177,
`349/171, 399/123, 171, 177
`
`(56)
`
`References Cited
`U.S. PATENT DOCUMENTS
`
`Chieu T C et al: “Effect of Alignment Layer Conductivity on
`the Bistability of Surface—Stabilized Ferroelectric Liquid
`—Crystal Devices” Applied Physics Letters, US, American
`Institute of Physics. New York, vol. 56, No. 14,Apr. 2, 1990,
`pp. 1326-1328.
`
`* cited by examiner
`
`Primary Examiner—Toan Ton
`(74) Attorney, Agent, or Firm—Aaron Waxler
`
`(57)
`
`ABSTRACT
`
`In a liquid crystal display device, the dielectric constants (E)
`and resistivities (p) of the liquid crystal material and the
`layers of orienting material have such values that the liquid
`crystal display device can be driven by means of a DC
`voltage.
`
`5,165,076 A * 11/1992 Tsuboyama et al.
`
`...... .. 349/184
`
`11 Claims, 3 Drawing Sheets
`
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`

`
`U.S. Patent
`
`May 7, 2002
`
`Sheet 1 of3
`
`US 6,384,892 B1
`
`4wJfllff A
`5 //////////l////// 8
`
`2
`
`
`
`1
`
` 5“E_JJIJI '
`
`K.
`
`
`
`_/10
`
`FIG. 1
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`
`U.S. Patent
`
`May 7, 2002
`
`Sheet 2 of3
`
`US 6,384,892 B1
`
`T
`
`0.20
`
`0.15
`
`AVLC, max
`
`100
`
`F|G. 4
`
` V
`
`FIG. 5
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`
`U.S. Patent
`
`May 7, 2002
`
`Sheet 3 of3
`
`US 6,384,892 B1
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`SEC V. Surpass
`SAM
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`h,
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`|PR2015-00887
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`

`
`US 6,384,892 B1
`
`1
`LCD HAVING PARTICULAR DIELECTRIC
`CONSTANT RELATIONSHIP BETWEEN
`ORIENTATION FILM AND LC LAYER
`
`BACKGROUND OF THE INVENTION
`
`2
`also be given for this effect. Since the display device is now
`DC driven, the electronics for continuously reversing the
`voltage across a pixel may be dispensed with. (Reversing
`can be restricted to e.g. once every minute or five minutes).
`5 Moreover, there is no flicker.
`
`The invention relates to a liquid crystal display device
`comprising pixels and electrodes for driving the pixels, each
`pixel comprising a display element defined by picture
`electrodes, which dis la
`element com rises la ers of ori-
`enting material and a ltayelr of liquid crystal materrial between 10
`the picture electrodes.
`Sheh hqhrd Crystal drspray deVrees are geherahy kh0Wh
`and used, for example,
`in monitors, but also in portable
`applleatlehs (ergahlZers’ rheblle telephones)’
`OBJECTS AND SUMMARY OF THE
`INVENTION
`
`15
`
`V,c(t)\[R»«+((i/Ci)_R*)_eXr,_(_,/r)I_VlCICE”
`
`(1)
`
`These ahh Other aspeets 0rI the rhVehtr0h are appareht
`from ahd Wrh he ehlerdated Wrth rererehee to the erhhedr'
`rhehts deserrbed hererharter
`BRIEF DESCRIPTION OF THE DRAWINGS
`In the drawings;
`FIG. 1 shows diagrammatically a part of a liquid crystal
`display device,
`FIG. 2 shows an equivalent circuit diagram of the display
`Cell 1“ rre‘ 1’
`FIG. 3 shows the maximum change with respect to time
`AV,C max across the liquid crystal layer as function of the
`annifed drive Voltage, Whiie
`A known phenomenon in such liquid crystal display
`FIGI 4 Shows the influence of R=p I/pLC on the Siope
`devices is the displacement of ions inIthe liquid, so that 20
`d(AV
`)/dv
`e
`degradation occurs, which becomes manifest as image reten-
`.
`.
`.
`le""“x
`’
`tion. To prevent this, liquid crystal display devices are driven
`FIG‘ 5 shows the rhaxlrhhrh ehahge Wlthrespeet te tlrhe
`with an inverting or alternating voltage across the pixels.
`A.V1C»Wx as a ruhetleh er the apphed drlye voltage for
`This is notably detrimental in portable applications because
`the use of an inverting voltage is accompanied by a high 25 dlrrereht hqulds’ ahd
`energy consumption and a high battery voltage for the drive
`FIG 6 sh0Ws dragrarhrhatreahy 3 drspray deVree~
`electronics. This in Iturn leadsI to higherIcosts.
`I
`I
`DESCRIPTION OF THE PREFERRED
`Aliquid crystal display device according to the invention
`EMBODIMENTS
`is characterized in that, for the quotient Q of a dielectric
`FIG. 1 is a diagrammatic cross-section of a part of a liquid
`constant Ere of the liquid crystal material and the dielectric 30
`crystal display device comprising a liquid crystal cell 1 with
`constant of the layers of orienting material Ear, it holds that
`a twisted nematic liquid crystal material 2 which is present
`Q=ELC/Eo,>0.7 poi/pre, in which, for a liquid crystal mate-
`between two substrates 3, 4 of, for example, glass, provided
`rial having a negative dielectric anisotropy (AE<0) Ere, the
`with electrodes 5, 6. The device further comprises two
`dielectric constant perpendicular to the directors of the
`liquid crystal material
`is (Ei), and for a liquid crystal 35 orientation layers 7, 8 which orient the liquid crystal mate-
`material having apositive dielectric anisotropy (AE>0) ELC,
`rial on the inner walls of the substrates, in this example in
`the dielectric constant parallel to the directors of the liquid
`the direction of the axes of polarization of polarizers (not
`crystal material is (531 it) and po, and pre are the resistivities
`shown), such that the cell has a twist angle of 90°. In this
`of the liquid crystal material and the layers of orienting
`example, the liquid crystal material has a positive optical
`material, respectively.
`40 anisotropy and a positive dielectric anisotropy. If the elec-
`The orientation layer may comprise sub-layers of different
`trodes 5» 6 are ehergrZedI Wrth ah eteetrre Vertagea the
`rnateriaII In that easeI no] is nnderstnnd to rnean the average
`molecules, and henceI the directors, are directed towards the
`resistivity of the Orientation IayerI
`field. The display device Ifurther comprises a backlight 10 (in
`The value Q is preferably between 0.4 and 4, while values 45 thls er.rarhple)' Alterhatlyely’ the dlsplay deylee may be
`of between 1.2 and 3 look optimal.
`reheetlye
`I
`I
`I
`I
`I
`To inhibit image retention even further, a first embodi-
`lh a hrst apprexlrhatleh’ both the eerhblhed erlehtatleh
`ment is characterized in that poi/pLC<10 (and preferably<5)
`layers 7’ 8 and the layer or llqhld Crystal rrlaterlal 2 (LC
`at 25° C. To prevent lateral conduction in the orientation
`layer) earl be deserlbed as a parallel elrehlt er a reslster ahd
`iayerSI pd is Chosen to be >107 Ohmmeter (T=25o CI)I
`50 a capacitor, as is shown in FIG. 2. Upon DC drive, the
`A further embodiment is characterized in that the liquid
`eeheyler of the Voltage “.055 the LC layer (V’C(t)’ male‘
`.
`.
`.
`.
`gous to a step response, will be.
`.
`crystal display device comprises means for presenting drive
`voltages in one polarity across the pixels (DC drive). In this
`connection, one polarity is understood to mean that no
`measures have been taken to change the polarity across the 55 in WhiCh
`pixels during operations over a longer period of time (e.g.
`Re=RLC/(R"’tR‘C) and Ce=(C"’+CLC)/C"’
`1000 or 2000 frame times), but measures may be taken to
`(R and C represent the resistance per surface unit and the
`drive the Pixels With Opposite Polarity Wheh modes are
`capacitance per surface unit,
`respectively, R=p.d (p:
`re'hsed Or ehahged (rer exarhptea swrtehrhg rrerh or to 3
`standby mode in a display in a portable application or 50 resistiVityI dt
`Iayer thickness) and C=(EO.Er)/dI Whiie
`switching between use of modes,
`Internetpages etc.
`in
`.r=R*C*IROICOII (VIC Ce”: Vnitage annhed across the eeII)I
`computer applications) of the display device.
`The rnaxirnnrn Change in VIC(t) then is
`The inventors have surprisingly found that the display
`device can be DC-driven without degradation or image
`retention occurring in said combination of dielectric con- 65
`stants of the orienting material and of the liquid crystal
`material. By approximation, a theoretical explanation can
`
`A‘/lC=VlC(t=0)—VlCet=%)=[R*—e1eC*):|'VlCvCEll
`
`or
`
`A‘/l¢:,mi1>c=[1/(1+R‘D)_1/(1+(D/E(V)):|
`
`(2)
`
`(3):
`
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`
`in which
`
`D=dol/dLC R=pol/pLC and E(V)=Eol/Pcell(V)
`
`(4)
`
`4
`appeared that these slopes did not change at a change of the
`temperature (measurements at 30 and 60° C.).
`EXAMPLES
`
`US 6,384,892 B1
`
`The voltage dependence of ECe,,(V) is the result of the
`change of the average dielectric constant in the liquid crystal
`
`5
`
`(Ell) is the dielectric constant parallel to the directors (the in
`axes of the liquid crystal molecules) of the liquid crystal
`material (V=VLC Calla LC)
`it
`AE=E _E
`’
`i
`th
`h id
`V0 age 0
`H
`. 4» Vth‘
`res 0
`Equation (5) applies to V>Vth'
`Since the thickness of the orientation layer is much 15
`smaller in practice than that of the layer of liquid crystalline
`materiai (D<<i)> tne term i/(i+D) in equation (3) Can be
`aPPr0Ximated by (i'D)- Equation (3) may tnen be Written a5
`
`f th
`
`e
`
`(In all examples, the LC layer has a thickness of 4 yin and
`the Orientation iayers have an Overall thiraknese of 01 rim)‘
`L . ol_ ‘
`>
`LC 151-
`oI~ ‘
`‘
`t
`iL3°édS/$hai?0;:SLé‘3;1é’~§3‘§“§°?‘Ef’233:
`01 LC_
`LC
`ol~ ‘
`01 LC‘
`d(AVzc,ma.x)/‘iv, 3 Yaine Or 0-025 W35 r0nn.d-
`2- For a eeii With a iiqiiid erystai materiai> Witri E81 =8 and
`EO,=3.6, it holds that ELC1/3E0,=Ell/EO,z2.22. Furthermole
`it holds that po,=4.10
`ohmmeter en pLC=5.10
`ohmmeter, so that
`it holds that po,/pLC=0.8 and pLC/
`p z2.77 p /p
`. For the slope d(AV
`)/dV a value of
`lC’'”“x
`0063 was fgluifdc
`’
`3. For a Cell with a liquid Crystal material with EH=8.7 and
`EO,=3.6, it holds that ELC/Eo,=Ell/EO,z2.42. Furthermore
`it holds that po,=4.1012 ohmmeter and pLC=6.1012
`ohmmeter, so that it holds that poi/pLC=0.66 and ELC/
`EOI26 3.66 pa,/DLC. For the slope d(AV,e mm)/d\/, a value
`A‘/Ic.max=[i‘RD‘(i‘(D/E(V))]-V=[(i/Er‘/)‘R]-DV
`(5) 20
`It ailfprefri Eigfnftillilenrlfliirst three examples that d(AVlC)m-X)/dv
`When equation (5) is used for E(V), this yields with (4):
`23:35::$331.23:°::::::g.i:1::r::.,%.§a::e:::;:£.:
`<v>
`for 25 examples, it was shown that a slope of approximately zero
`l:lG. 3 Shows the Variation of AVIC mm (formula
`a display Cell with dOl=i00 Hm’ dLC=’4 am’ pOl=pLC=1013
`is reached at Qz1.5. For 1<Q<<1.8, the slope is substantially
`ohmmeter, Eo,=3.5, while ELC(V) is defined by formula (5),
`neghglble’ Certalnly When poi: pic’
`.
`.
`.
`.
`.
`For a cell with a liquid crystal material with E =8 and
`In which E“=8 and Ei=3’ or ELC/601:6“/Ei=2'3’ While
`E =3 it holds that E /E =E /E 26 2 66 Furthermore it
`poi/pLC=1. It appears from FIG. 3 that the maximum voltage 30 hgids’ that
`_1 8Li%12°’ hi‘ Oil
`'
`'
`_1 5 1012
`change AVIC max for V>Vth varies practically linearly; the
`p°i_ '
`.'
`0 mme er en pLC_ '
`'
`slope of the curve has a value which is defined by
`Ohmgngéen jo trialat
`it hneiris th(aaEAQ]ol/pLC)=/é arid1ELC£
`poiz .
`poi pLC.
`or t e s ope
`kamax
`, a Va ue o
`(8)
`it/eV’°'”“‘)/dV=[re“/E"’)_R'D]
`($04 Y“ foumii 1 F
`11
`'th
`1'
`‘d
`t 1
`t
`'
`1
`oun erexamp e
`:
`or a ce wi
`a iqui crys a ma eria
`This derived function is practically constant for V>Vth, 35
`with Ell=8.3 and Eo,=3,
`it holds that ELC/Eo,=Ell/
`while it has a value of 0 for ELC/Eo,=po,/pLC. FIG. 4 shows
`Eo,z2.77. Furthermore it holds that po,=1.8.1015 ohmme-
`the influence of R=po,/pLC on d(AV,C)max)/dV. The Figure
`ter and pLC=1014 ohmmeter, so that it holds that poi/pLC=
`shows that for R<2.7, the slope of the curve reaches said
`10 and ELC/Eo,z0.27. poi/pLC. For the slope d(AV,C)m_x)/
`constant value fairly rapidly (at R~0,1). Since the maximum
`dV, a value of 0.20 was found.
`change of the drive voltage remains limited to approxi- 40 Counterexample 2: For a cell with a liquid crystal material
`mately 4 V (in a voltage range between Vth and the satura-
`with Ell=8 and Eo,=3.5,
`it holds that ELC/Eo,=Ell/
`tion voltage Vmt) for (super)twisted nematic LCDs, and the
`Eo,z2.29. Furthermore it holds that po,=1013 ohmmeter
`maximum value of the slope is of the order of 0.06, voltage
`and pLC=3.1012 ohmmeter, so that it holds that poi/pLC=
`corrections remain limited to values of approximately 0.25
`3.33 and ELC/Eo,z0.69. poi/pLC. For the slope d(AV,C)
`V (see also FIG. 3). Amaximum change of the slope of 0.10 45
`max)/dV, a value of 0.10 was found.
`is admissible; at a small number of grey values and an
`FIG. 6 is an equivalent circuit diagram of a part of a
`average correction voltage for all grey values, even a larger
`display device 1 in which the invention has been applied.
`slope may be admitted.
`This device comprises a matrix of pixels 18 at the area of
`It is also apparent from FIG. 4 that, for R>2.7, the value
`crossings of m row or selection electrodes 5 and n column
`of the slope rapidly increases (in absolute value). Up to Rz5 50 or data electrodes 6. The row electrodes are successively
`(which corresponds to ELC/Eo,=0.7 poi/pLC), the maximum
`selected by means of a row driver 16, while the column
`value of the slope remains below approximately 0.06, so that
`electrodes are provided with data via a data register 15. If
`the same considerations apply as above.
`necessary, incoming data signals 11 are first processed for
`To prevent image retention, pLC should not be too high
`this purpose in a processor 12. Mutual synchronization
`with respect to p0,. Therefore, preferably, poi/pLC<10 (and 55 between the row driver 16 and the data register 15 takes
`<5 in practice). To prevent lateral conduction occurring on
`place via drive lines 17.
`the row
`a substrate between the electrodes in adisplay device having
`Drive signals from the row driver 16 select
`a plurality of electrodes, po, is at least 107 ohmmeter (and
`electrodes 5. The signal present at the column electrode 6
`preferably at least 108 ohmmeter).
`defines the information to be displayed. Although a display
`FIG. 5 shows measured values for the voltage AV,C)max as 60 device of the passive type is shown,
`the invention also
`a function of the (DC) drive voltage for different types of
`applies to an active matrix. In that case, separate pixels are
`display cells (different combinations of materials for the
`connected to the row electrodes via switches (for example,
`orientation layers and the liquid crystal material). In all
`thin-film transistors or two-pole circuits). Selection may also
`cases, ELC/Eo,=Ell/E0, approximately 8/3z2.7 and R=po,/
`take place by means of plasma channels (Plasma Addressed
`pLCz1.5, so that it holds that ELC/Eo,z1.8 poi/pLC. Also for 65 Liquid Crystal Display).
`this comparatively high value of R, it appears that constant
`As shown above, the values of AV,C)max remain within
`values of the slopes d(AV,C)max)/dV are found. Moreover, it
`admissible limits at the chosen value for the slope d(AV,C)
`
`1
`d.
`lsp ay Ce
`
`ll
`
`‘
`
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`
`5
`
`US 6,384,892 B1
`
`5
`
`10
`
`6
`acterized in that, for the quotient Q of a dielectric constant
`max)/dV. The value of AV,C)m_x is dependent on the presented
`voltage (the grey value). In a simple solution, either all
`ELC of the liquid crystal material and the dielectric constant
`voltages on the column electrodes or all voltages on the row
`of the layers of orienting material E0, it holds that Q=ELC/
`electrodes may be given the same correction voltage (offset).
`Eo,>0.7pO,/pLC, in which, for a liquid crystal material having
`a negative dielectric anisotropy (AE<0)ELC, the dielectric
`Thls eerreetleh Veltage Wlll usually be deterlhlhed by the
`constant perpendicular to the directors of the liquid crystal
`aVerage Value Of the Veltage rahge t0 be used-
`material is (El), and for a liquid crystal material having a
`lh a deylee lh Whleh lhahy grey seales are dlsplayed> the
`positive dielectric anisotropy (AE>0)ELc, the dielectric con-
`data Voltage Oh the eelhlhh eleetlede ls adapted preferably
`stant parallel to the directors of the liquid crystal material is
`for each Value of the lheelhlhg Slghal 11’ for example’ by
`.
`.
`.
`.
`.
`.
`means of a look-up table 13 in the processor 12.
`(Ell) and he’ and the are the leslstlyltles of the hquld Crystal
`Althou h the above-mentioned exam les are based on
`l and the la ers of orientin material
`res ectivel
`.
`.
`g
`.
`.
`p .
`.
`.
`.
`matena
`.
`.y
`.
`.
`g
`.
`’
`p
`y’
`liquid crystal materials having a positive dielectric
`.
`.
`ahd Wherelh the dlehlay devlee le DC dhV.eh'
`anisotropy, a similar consideration applies to liquid crystal
`2' A lhlhld erystal dlsplay deyéee as elahhed lh elahh 1’
`materials having a negative dielectric anisotropy.
`The value AV,C max is also dependent on the voltage across 15 ehalaetellzed lh that Q.=ELC/E01 ?pol/pLC' .
`.
`.
`the cell. In color) images, a mixed color is formed by the
`3' A llqhld erystal dlsplay deylee as elahhed lh elahh l>
`images of’ for example’ a red’ a green and a blue pixel. If’
`characterized in that Q=ELC/E0, has a value of between 1
`for example, the red pixel receives a low voltage (maximum
`ahd 4'
`.
`.
`.
`.
`.
`.
`.
`transmission in the case of crossed polarizers), while the two
`4' A llqhld erystal dlsplay deylee as elahhed lh elahh 3>
`other pixels receive, for example, an average voltage, on 20 ehalaetehzed lh that l;Q§l'8'
`.
`.
`.
`.
`which average voltage also an average correction voltage for
`5' A llqhld erystal dlsplay deylee as flahhed lh elahh l>
`all pixels is based, this leads to discoloration due to a too
`ehalaetehzed lh that p91/pLC<10 (T=25 C;)'
`.
`.
`high correction for the red pixel. Image retention may also
`6' A llqhld ‘Crystal dlsplay deVlee7as elahhed lh elahh l>
`occur when the device is driven with the same information
`eharaetehzed lh that po{ ls at least ‘lo Ohlhlheter (T=25 C')'
`for a longer period of time. This is largely prevented by 25
`7' A llehld elystal dlsplay deylee as elahhed lh elahh l’
`driving the display device cclcpsedueutiallv. lu that case’
`characterizedin that the display dCV1CC.COII1pI‘1SCS means for
`the backlight 10 supplies one of the three colors in the case
`plesehtlhg ahye Voltages lh ehe Pelallty aeless the plXels'
`of a full color display by means of three sub-images (red,
`8' A llqhld erystal dlsplay deylee aselahhed lh elahh. 7>
`green’ blue) for 1/3 of a frame time’ While the liquid crystal
`characterized in that
`the display .dCV1C.C comprises drive
`display device comprises information of the relevant sub- 30 lheahs for presehtlhg row seleetloh. slghals to the row
`image. Since the voltage across the pixel is generally dif_
`electrodes and drive means for presenting data signals to the
`ferent for the three sub-images, the above-mentioned image
`eelhlhh eleetledes
`.
`.
`.
`.
`.
`retention occurs less rapidly. This is of course also possible
`9' A llqhld erystal dlsplay deylee as elahhed lh elahh 8>
`with images composed of two sub_images of a different
`characterized in that the drive means for presenting data
`color.
`35 signals comprise correction means for adapting the voltage
`the invention relates to a liquid crystal
`In summary,
`of the data slghals lh depehdeheehpeh plesehtee data'
`display device whose dielectric constants ELC of the liquid
`10' A hqhld. elystal dlsplay deylee. as elallhee lh elahh 7’
`crystal material and of the layers of orienting material, as
`eharaeterlzed lh that the alsplay deylee ls proylded Wlth ah
`well as the resistivity of the liquid crystal material and the
`lllhlhlhatleh hhlt eelhpllslhg lheahs for seqhehtlally pleseht'
`layers of orienting material are chosen to be such that the 40 lhg hght lh at least W0 Wayelehgth rahges> ahd thehhye
`display device can be driven by means of a DC voltage.
`means are provided with means for presenting, to the display
`The invention resides in each and every novel character-
`deVlee> the data slghals of a WaVeleHgth rahge'ass0elated
`istic feature and each and every combination of character-
`shh'llhage at ah hhage ‘to he dlsplayell
`.
`.
`.
`istic features.
`11. A liquid crystal display device as claimed in claim 1,
`What is claimed is.
`45 characterized in that the display device comprises driving
`means for inverting the voltages over the display elements at
`1. A liquid crystal display device comprising pixels and
`switching on the display device or after a period of one
`electrodes for driving the pixels, each pixel comprising a
`minute.
`display element defined by picture electrodes, which display
`element comprises layers of orienting material and a layer of
`liquid crystal material between the picture electrodes, char-
`
`SEC v. Surpass Tech, |PR2015—OO887
`SAMSUNG EX. 1023 — 7/7
`
`SEC v. Surpass Tech, IPR2015-00887
`SAMSUNG EX. 1023 - 7/7