16.4L: Late-News
`
`Paper: A Novel Wide-Viewing-Angle
`Ultra-Trans
`ViewTM
`S. H. Lee, S. L. Lee, H. K Kim, Z Y Eom
`Hvundai Electronics
`Industries,
`Kvunaki-Do,
`..-
`
`Korea
`
`-.
`
`Technology:
`
`Abstract
`A novel nematic liquid crystal display of in-
`plane switching controlled by fringe-field has been
`developed. The device exhibits wide viewing angle
`over 160° and high transmittance
`comparable
`to
`the twisted nematic (TN) cell, a solution for long
`standing problem of previous wide viewing angle
`technologies with low transmittance.
`In this paper,
`the device with optimized design, i.e., less sensitive
`to process will be discussed.
`
`1. Introduction
`Recently,
`several new technologies minimizing
`viewing angle dependency of image quality have been
`introduced in nematic liquid crystal displays (LCDS).
`Among them are in-plane switching (IPS),’ multi-
`domain
`vertical
`alignment
`(MVA)~
`surrounding
`electrode (SE),3 optically compensated bend (OCB),4
`and four-domain VA (FDVA) controlled by in-plane
`field5. The IPS mode can realize wide viewing angle
`due to in-plane rotation of LC director without further
`optical
`compensation
`fUm. However,
`the
`using
`demerit
`in the IPS is low light eflkiency due to the
`low aperture ratio. The MVA, SE and FDVA modes
`also have
`low transmittance problem due to the
`existence of disclination lines in light-transmitted area.
`Fig.
`1
`shows
`the
`relationship
`between
`the
`transmittance
`and viewing angle of the LCDS for
`several display modes. As indicated, any previous
`modes do not satisfj both high transmittance and wide
`viewing
`angle
`characteristics
`at
`the
`same
`time.
`However, we have developed a novel TFT-LCD
`controlled by fringe-field switching (FFS)
`to meet
`both requirements.6 In this paper, we describe
`the
`optimized pixel design with less sensitive to process,
`and its electro-optic
`characteristics.
`2. Switching Principle of Fringe-Field Switching
`the
`Figure 2 shows the schematic features of
`the
`conventional
`IPS and FFS cells describing
`difference in light
`transmitted area (TA) and array
`structure.
`In the IPS cell,
`the distance (1) between
`electrodes is larger than the cell gap (d) and the width
`of electrode (w) such that
`the parallel
`field to the
`substrate (/lY) mainly exists between electrodes with
`bias voltage. Then homogeneously
`aligned liquid
`crystal molecules do mainly twist deformation in x-v
`plane by dielectric
`torque,
`giving rise
`to light
`
`Fig. 2 Features of the IPS and the FFS modes
`
`ISSN0099-0966X/99/3001-0180-$1.00 + .00 (c) 1999 SID
`
`n‘bMVA
`
`m
`
`m
`
`/
`
`&$
`
`Viewing Angle
`
`~
`
`Wide
`
`Fig, 1 Relationship between viewing angle and
`transmittance for several LCD modes.
`
`above
`the LC molecules
`transmittance. However,
`electrodes do not go through twist deformation. As a
`result, the area that light can be transmitted is reduced
`compared to the TN cell.
`In the FFS cell, the pixel and counter electrodes
`are transparent and 1 is zero or smaller than d and w
`so that the electric field parallel
`to the substrate can
`not be formed but
`instead the fringe field lines are
`formed in the whole area. In other words, such field
`lines having vertical
`components
`(EJ
`as well as
`horizontal ones (E”) exist. The interaction probability
`between E, and LC director for negative type of LC is
`about zero because the pretilt angle of LC director is
`
`FFS
`
`.x2- Y
`
`FFS
`<1 or (1
`<1 or ()
`Ey, E,
`ITO
`
`I
`I
`
`II
`
`I I
`
`IRS
`>1
`>1
`E,
`I Metals or ITO I
`
`E’s
`
`I
`I
`
`l/d
`l/w
`Field
`Electrode
`
`Page 1
`
`JDI/PLD - EX. 2009
`TIANMA MICROELECTRONICS
`CO. LTD. v. JDI/PLD
`IPR2021-01060
`
`

`

`the dielectric torque is applied
`very low. However,
`between Ey and the LC director such that
`the liquid
`crystal molecules do twist deformation in plane in the
`whole area,
`resulting in light
`transmission. Fig. 3
`shows a simulational
`result of dynamic
`response
`behavior with applied voltage for a negative LC. The
`light transmittance starts to occur
`near the edge of electrodes and extends to the whole
`area. This implies that the twisting of the LC director
`in the FFS mode does occur due to the dielectric
`torque initially and consecutively elastic force of the
`LC molecules to neighboring ones being at the center
`of electrodes. Another
`interesting characteristic
`in
`transmission
`unlike
`other
`displays
`is
`that
`the
`transmission is alternating along horizontal direction.
`This means that the degree of twist of LC director is
`different due to the alternating amplitude of Ey The
`efficiency of light transmittance also depends on the
`types of liquid crystal.
`
`I
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`x Counter electrode
`
`Pihl
`
`electrode
`
`Fig. 3 Simulational result of dynamic response
`behavior of LC director and corresponding
`transmittance
`
`3. Advantages of the FFS mode
`Fig. 4 shows one pixel design and equivalent
`circuit of the IPS and FFS cells. In the FFS cell, there
`are several advantages over the conventional IPS cells
`as following:
`-High transmittance
`-Crosstalkless
`-Less process dependence
`-No need of planarization for good alignment of LCS
`In the FFS cell, it does not need an additional space
`for storage capacitor (CJ because C, can be formed in
`
`the light-transmitted area, so that it has high aperture
`ratio. And also there is an additional fi-inge capacitor
`(CJ so the total capacitance is much higher than that
`of the IPS cell. This indicates that the fluctuation of
`the pixel electrode potential~ Vp disturbed by change
`of source-bus line potential
`V~ is less than the IPS
`cell and the feedthrough voltage d V is much lower
`than those of
`IPS and TN cells
`and is almost
`independent on applied voltage, owing to large total
`capacitor. This results in low crosstalk and less DC
`applied to cell. For a process view point,
`in the IPS
`mode, the threshold voltage is linearly proportional
`to
`the electrode distance,
`i.e., V,h=x I/d (K22f E .zf E )’12
`so that it is sensitive to the layer to layer misalignment
`and also the etch bias variation
`of
`the metals.
`However,
`in the FFS mode, two approaches to design
`a pixel, i.e., l/d< 1 or Oare possible. In the latter case,
`there is no electrode distance so that the relationship
`between V,h as well as transmittance
`and 1 are not
`linearly dependent. Instead they have a plateau range
`with best
`transmittance
`as varying the distance (Z’)
`between the pixel electrodes for given w, as shown in
`simulational
`results of Fig. 5. For simulation,
`the
`liquid crystal with negative dielectric anisotropy is
`used. The
`results
`show that
`for
`the
`l/d < 0,
`transmittance
`is linearly decreased as 1 and w is
`increasing. For l/d = O, the optimal range does exist
`for best transmission and the transmittance does not
`change
`linearly with increasing ~. This property
`improves uniformity in brightness. However,
`in this
`structure,
`the channel width of TFT and gate high
`voltage should be optimized for enough charging.
`Another issue is liquid crystal alignment. In the IPS
`cell, the pixel and counter electrodes are formed using
`gate and source-drain metals that have thickness at
`least above 1000 A,
`accordingly planarization
`for
`good alignment of LC is necessary. However,
`in the
`FFS cell, the pixel and counter electrodes are ITOS
`having a thickness about 400A,
`so good alignment of
`LC is obtained without extra process.
`
`4. Electro-optic characteristics of the FFS cell
`Fig.
`6
`shows
`again
`the
`voltage-dependent
`transmission curves for the TN, IPS, and FFS mode in
`12.1” SVGA.
`In transmittance
`efficiency,
`the TN
`mode is best and the FFS mode shows comparable
`light efficiency, about 90’% of the TN mode. Fig. 7
`curves
`transmittance
`voltage-dependent
`shows
`depending on the dielectric
`anisotropy of the LC.
`a positive LC is used,
`the maximum-
`When
`transmittance
`is decreased
`although
`the
`driving
`
`ISSN0099-0966X/99/3001-0180-$1.00 + .00 (c) 1999 SID
`
`Page 2
`
`JDI/PLD - EX. 2009
`TIANMA MICROELECTRONICS
`CO. LTD. v. JDI/PLD
`IPR2021-01060
`
`

`

`voltage is relatively lower than that of a negative one.
`For a positive LC, the LC molecules do tilt-up along
`the fringe field as well as twist deformation with bias
`voltage so that the degree of twist above electrodes is
`low,
`resulting in less transmittance
`than that of a
`negative one.
`
`Acknowledgements
`We deeply express our appreciation to Senior
`Vice President Soo Han Choi, Managers W. G. Lee,
`Y. J. Lim, J. Y. Lee, H. S. Park, our hardworking
`engineers, and the process teams for the full support
`of the project.
`
`H.
`
`References
`1, K. Kondo et al., SID ’98 Digest, 389 (1998).
`2. A. Takeda et al., SID ’98 Digest, 1077 (1998).
`3. N. Korea et al., SID ’96 Digest, 558 (1996); K.
`Kim et al., Asia Display ’98,383 (1998)
`4. P. L. Bos and J. A. Rahman, SID ’93 Digest, 273
`(1993); Y. Yamaguchi et al., SID ’93 Digest, 277
`(1993).
`5. S. H. Lee et al., KSID ’97 Digest, 23 (1997); Appl.
`Phys. Lett. 71 (19), 2851 (1997); SID ’98 Digest,
`1077 (1998); K. H. Kim et al., SID ’98 Digest, 175
`(1998).
`6. S. H. Lee et al., Asia Display ’98 Digest, 371
`(1998), Appl. Phys. Lett. 73 (20), 2881 (1998).
`
`180°
`
`270°
`
`90°
`
`0°
`
`Fig. 8 Iso-contrast curve of the FFS cell
`
`We have measured a viewing angle dependence of
`a contrast
`ratio (CR) as shown in Fig. 8. The CR
`greater than 10 with a polar angle of 80° in vertical
`and horizontal directions is obtained. This indirectly
`proves in-plane rotation of the LC director and also
`the CR greater than 250 at normal direction is easily
`obtained.
`
`TFT-LCD
`5. “Ultra-TransView”
`We
`have
`fabricated
`15.0” XGA TFT-LCD
`module utilizing the concept of FFS. It has a trade
`mark “Ultra-TransView” which has meaning of both
`ukra-transmittance
`and Ultra-viewing
`angle. The
`power
`consumption
`is only 19 W with surface
`luminance of 200nits. The crosstalk is less than 1.5%
`for both horizontal and vertical
`one as appeared in
`Table 1.
`
`6. Conclusion
`wide-viewing-angle
`We have developed a novel
`technology with concept of the FFS. This exhibits
`high transmittance
`and wide viewing angle at
`the
`same
`time with use of negative
`liquid crystal,
`the
`drawback
`of previous wide-
`overcoming
`viewing-angle
`technologies. We also optimized the
`device less sensitive to process. We believe that this is
`one of most promising candidates
`for high quality
`active matrix LCD,
`irrespective of panel size and
`uses.
`
`I
`I
`
`Table 1 Specflcations of “Ultra-TransView”
`15.0
`\Dia~onal Size (Inches)
`1024 (’X3)X 768
`lResolution
`99X 297
`lPixel Size (urn)
`6.5
`lSupplied Voltage (V)
`200
`Brightness (nit)
`4CCFL
`Backlight
`19
`Power Consunmtion (W)
`250:1
`Contrast Ratio
`160°
`Viewing Angle (CR>l O)
`<1.5’?/.
`Crosstalk
`
`I
`
`I
`I
`
`1
`
`I
`
`ISSN0099-0966X/99/3001-0180-$1.00 + .00 (c) 1999 SID
`
`Page 3
`
`JDI/PLD - EX. 2009
`TIANMA MICROELECTRONICS
`CO. LTD. v. JDI/PLD
`IPR2021-01060
`
`

`

`IRS
`
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`Fig. 4 Schematic drawing of a pixel layout and equivalent circuit of the IPS and FFS modes.
`
`I
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`Fig. 5 Simulational results of a) 1and b) 1’- dependent transmission
`
`t
`
`6
`
`/iIll
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`
`+W=4
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`5
`
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`o
`
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`
`Voltage(V)
`
`10
`
`Fig. 7 Voltage-dependent
`transmission curve
`depending on different types of liquid cgwtals.
`
`012345678910
`(V)
`Voltage
`Fig. 6 Voltage-dependent
`transmission
`curves for different display modes
`
`ISSN0099-0966X/99/3001-0180-$1.00 + .00 (c) 1999 SID
`
`Page 4
`
`JDI/PLD - EX. 2009
`TIANMA MICROELECTRONICS
`CO. LTD. v. JDI/PLD
`IPR2021-01060
`
`