Jolume 26
`
`Number 4
`
`April 1999
`
`_uTro'p'aa'n Physical Snclatv
`
`ISSN 0267-8292
`
`
`
`-u
`
`1
`
`Page 1 of 8
`
`Tianma Exhibit 1034
`
`Page 1 of 8
`
`Tianma Exhibit 1034
`
`

`
`
`
`LEQUED CR¥STALS
`an international journal of science and technology
`
`GEORGE W. GRAY
`PO Box 3307, Wimborne, Dorset BH2l 4YD, UK.
`NOEL CLARK
`University of Colorado, Department of Physics, Campus Box 390, Boulder, Colorado 80309, USA.
`
`Editors
`
`J.-P. Bayle (University of Paris XI,
`Orsay, France)
`P. J. Bos (Liquid Crystal Institrrte,
`Kent State University, USA)
`H. Brand (University of Bayreuth,
`Germany)
`H. J. Coles (University of
`Southampton, UK)
`G. Crawford (Xerox Palo Alto
`Research Centre, California, USA)
`A. Fukuda (Department of Kamsei
`Engineering, Japan)
`S. M. Kelly (University of Hull)
`S. Kumar (Kent State University,
`USA)
`S. T. Lagerwall (Chalmers University
`of Technology, Gotenborg, Sweden)
`
`Editorial Board
`
`L. Loriga (Jagiellonian University,
`Krakow, Poland)
`N. V. Madhusudana (Raman
`Research Institute, Bangalore,
`India)
`A. F. Martins (Universidade Nova de
`Lisboa, Portugal)
`H. T. Nguyen (Centre de Recherche
`Parrl Pascal, Pessac, France)
`D. J. Photinos (University of Patras,
`Greece)
`R. Pindak (A.T.&T. Bell
`Laboratories, Murray Hill, USA)
`K. Praefcke (Technische Universitat
`Berlin, Germany)
`C. S. Rosenblatt (Case Western
`Reserve University, Ohio, USA)
`
`Founding Editors
`
`Professor G. R. Luckhurst
`Professor E. Samulski
`
`J. R. Sambles (University of Exeter,
`UK)
`V. P. Shibaev (Moscow State
`University, Moscow, Russia)
`A. Strigazzi (Politecnico di Torino,
`Italy)
`J. K. Vij (Trinity College Dublin,
`Ireland)
`D. M. Walba (University of
`Colorado, Boulder, USA)
`R. Wingen (Hoechst A G, Frankfurt,
`Germany)
`R. Zentel (Bergische Universitat,
`Wuppertal, Germany)
`R. Zharig (Chinese Academy of
`Sciences, Beijing, China)
`
`
`
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`Page 2 of 8
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`Page 2 of 8
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`

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`
`
`Effect of chemical structures of polyimides on photosensitivity of
`liquid crystal alignment using a polarized UV exposure
`
`M. NISHIKAWA*
`
`Yoklcaichi Research Laboratories, JSR C0,, Yokkaichi, Mie 510-8552, Japan
`
`J. L. WEST
`
`Liquid Crystal Institute, Kent State University, Kent, Ohio 44242, USA
`
`and YU. REZNIKOV
`
`Institute of Physics of National Academy of Science, Prospect Nauki 46,
`Kyiv 252022, Ukraine
`
`(Received 5 October 1998; accepted 4 November 1998)
`
`(LC) alignment produced by polarized UV exposure was
`liquid crystal
`Unidirectional
`examined using polyimides (Pls) synthesized using different diamincs. The dichroic ratio of
`the resulting LC cells suggests that the UV photosensitivity is primarily controlled by the
`chemical structures of the Pls used. The UV absorption and fluorescence spectra of the Pl
`films, and molecular conformations of the diamines, indicate that the photosensitivity is
`controlled by the UV absorption efficiencies and molecular conformations of the Pls.
`
`1.
`
`Introduction
`
`Most electro-optic applications of liquid crystals (LCs)
`require a high level of LC molecular orientation. A good’
`example is the twisted nematic LC display which is
`fabricated using mechanically rubbed polyimide (PI)
`alignment films [1]. However, there are several problems
`with this method such as the creation of contaminating
`particles and the production of electrostatic charges,
`which lower
`the production yield of LC displays.
`Therefore, alternative non-rubbing techniques to align
`LCs are required.
`‘
`Langmuir—Blodgett films [2], stretched polymers [3],
`micro-grooves [4], stamped polymers [5], and polarized
`ultraviolet light (PUV) exposure of polymers [6], have
`been developed to produce unidirectional LC alignment.
`LC alignment produced using PUV exposure is the
`most promising non-rubbing technique, overcoming
`the problems mentioned above and greatly simplifying
`the production of multi-domain displays [7].
`Photo-induced isomerization of
`azo
`compounds
`doped in polymers [6, 8-10], ciswtrans isomerization
`[11] or cross—linl<ing [12~16] of poly(vinyl cinnamate)
`derivatives, and photodecomposition of Pls [17—23],
`have been shown to produce LC alignment on exposure
`to PUV, Much effort has been concentrated on the
`
`*Author for correspondence.
`
`development of photo—reactive PIs, which are more heat
`resistant than azo compounds and poly(vinyl cinnamate)
`derivatives. One of the key targets for photo—alignment
`materials is to increase their photosensitivity as well as
`the quality of LC alignment. However, the parameters
`of PI materials which aifect their photosensitivity have
`not yet been clarified. In this paper, we explore the elfect
`of PI chemical structures on their photosensitivity for
`LC alignment.
`
`2. Experimental
`2.1. Synthesis of PIs
`The PI materials used in this experiment are shown
`in figure 1. They were prepared by heat curing the
`precursor polyamic acids, which were synthesized by
`reaction between equi—molar quantities of cyclobutane
`tetracarboxylic dianhydride and the appropriate diamines.
`
`2.2. Preparation of LC cells
`LC cells were prepared for measurement of the
`dichroic ratios of LCs aligned by PUV-exposed PI films
`[22]. PI films were deposited by first spin-coating dilute
`solutions of the respective polyamic acids on ITO glass
`substrates which were then cured at 250°C for 1h to
`
`complete the imidization [24]. The thickness of the PI
`film was controlled at 50nm. The PI films were exposed
`to PUV incident normal
`to the surface. We used a
`
`Journal ofLiqu1’d Crystals ISSN 0267-8292 print/ISSN 1366-5855 online © 1999 Taylor & Francis Ltd
`http://www.tand£eo.uk/JNLS/lethtm
`http://www.taylorandfrancis.com/JNLS/let.htm
`
`Page 3 of 8
`
`Page 3 of 8
`
`

`
`
`
`Table LC alignment on PIs.
`
`LC alignment direction
`
`PI
`
`Rubbing
`
`
`
`Polarized UV
`
`Tmin,/min
`
`PI-1
`PI-2
`Pl—3
`PI-4
`PI—5
`PI—6
`PI—7
`PI-8
`PI-9
`PI—10
`
`Parallel
`Parallel
`Parallel
`Parallel
`Parallel
`Parallel
`Parallel
`Perpendicular
`Parallel
`Parallel
`
`Perpendicular
`' Perpendicular
`Perpendicular
`Perpendicular
`Perpendicular
`Perpendicular
`Perpendicular
`Parallel
`Perpendicular
`Perpendicular
`
`92.8
`2.7
`2.4
`2.4
`7.0
`92.4
`64.1
`23 .1
`22.4
`57.7
`
`3.2. Phatoseiisitivity 0fLC alignment
`Figure 2 shows the dichroic ratios of the LC cells as
`a function of the PUV exposure time. The dichroic ratios
`12
`
`_
`
`(PI)
`
`10'
`
`
`
`DichroicratioofLCcell
`
`
`
`0
`
`.l
`
`1
`l
`
`.
`10
`
`100
`
`Polarized UV exposure lime/ min
`
`»—O- Pl-6
`
`
`
`DichroicratioofLCcell
`
`€\
`
`.l
`
`V
`
`I
`
`I0
`
`100
`
`Polarized UV exposure time/min
`
`and
`time
`Figure 2. Relationship between UV exposure
`dichroic ratios of LC cells using (a) Pl-1-5 and (b) PI-6-10.
`
`L
`
`0
`
`,‘m
`E
`
`0
`
`1
`
`W _
`R
`
`- R -
`
`PI—1
`
`p1—2
`
`91-3
`
`._@CHz
`
`H
`
`’—<\’—/’O"<\77//>—~ ~< /}~s—-<\
`
`/>—
`
`PM
`
`'
`
`_
`
`131-4
`'\
`2
`
`w<
`
`—\
`4% ow
`p1-7
`an 0
`3
`
`PI-6
`0
`/-~\
`we/>~i{>
`PI-8
`’ /my
`*3
`Q/NJ
`“'9
`PI—10
`» 1
`r
`\
`CF:
`CH:
`043%»
`M ::,.:u—=::<J— w
`Figure 1. Chemical structures of thc Pls used.
`
`450 W—Xe lamp (Oriel, model 6266) as a UV source, and
`a surface film polarizer (Oriel, model 27320). LC cells
`for dichroic ratio measurements were fabricated using
`two PUV-exposed substrates with parallel polarization
`axes. Dichroic LC, ZLI-2293 (Merck) with 0.5% M-618
`(Mitsuitoatsu, Am“ : 550nm) was filled into the cells in
`the isotropic state (120°C) and slowly cooled to room
`temperature to preclude flow alignment.
`
`2.3. A/Ieasurement methods
`The dichroic ratios of the LC cells and UV-visible
`
`absorption spectra of the Pl films were measured using
`one polarizer and a Perkin Elmer Lambda 19 UV—visible
`spectrometer,
`[22]. The fluorescence spectra of the
`PI films were measured using a spectra fluorimeter,
`(Instruments S. A. Fluorolog 270M). The fluorescence
`spectra were measured in a front-face arrangement and
`the bandpasses were lnm for both the excitation and
`emission monochromators. The molecular conformations
`of diamines used in the PIs were calculated by MOPAC
`Ver. 6 program with AMI parameters [25].
`
`3. Results and discussion
`
`3.1. LC aligmnem‘ on various PI films
`The LC alignment produced by either rubbed or
`normally exposed with PUV are summarized in the
`table. In most cases, the LC aligns parallel to the rubbing
`— direction and perpendicular to the UV polarization. This
`is consistent with results reported previously [17, 18].
`However, the LC aligns perpendicular to the rubbing '
`direction and parallel to the exposed UV polarization
`for Pl-8 which contains fluorene diamine.
`
`Page 4 of 8
`
`Page 4 of 8
`
`

`
`
`
`of the LC cells initially increase logarithmically with UV
`dosage, and then approach a constant value of about
`10.5, which is comparable to that of the LC cell with
`rubbed PI alignment films. Figure 3 shows the typical
`relationship between PUV exposure time and the
`dichroic ratios of the LC cells. In this figure, we define
`the dichroic ratio of the LC cell at lower UV dosage by
`the following equation:
`‘
`
`dichroic ratio = A + B log(T)
`
`(1)
`
`where A is a constant, B the slope of the dichroic ratio
`of the LC cell, and T the PUV exposure time. Using
`this equation, we can estimate the photosensitivity of
`the LC alignment for UV dosage at the minimum PUV
`exposure time (Tmm) as 10.5. The photosensitivities of
`LC alignment (Tmin) of PI materials are also summarized
`in the table.
`
`3.3. Analyses ofphotosensitivity of LC alignment
`We measured the UV absorption spectra of the PI
`films prepared on quartz substrates to investigate their
`photosensitivity. Figure 4 shows the UV absorption
`spectra of 50 nm PI films.
`In previous papers we proposed that selective decom-
`position of PI by PUV exposure aligns the LC along the
`optic axis of remaining PI chains [22, 26]. Here we define
`the absorption efliciency of PI film by the following
`equation:
`
`400 nm
`
`absorption efficiency = J
`
`200 nm
`
`f(x)g(x)h(x)i(.\')dx
`
`where f(x) describes the irradiance of the UV source,
`g(x) describes the transmittance of film polarizer,
`l1(x)
`describes the polarization efiiciency of film polarizer,
`
`(2)
`
`200 220 240 260 280 300 320 340 360 380 400
`
`Wavelength/ nm
`
`filmat50nm
`
`AbsorbanceofPI
`AbsorbanceofPIfilmat50nm 0.2
`
`1.0
`
`J
`.
`.
`()_0
`200 220 240 260 280 300 320 340 360 380 4UU
`
`Wavelength / nm
`
`spectra
`Figure 4. UV absorption
`(b) PI-6-10.
`
`of
`
`((1) PI-l~5 and
`
`10.5
`
`ratioofLCcell
`Dichroic
`
`.1
`
`1
`
`10
`
`100
`
`and i(.\’) describes the function of UV absorption of PI
`film. If the selective decomposition of the PI is related
`to the UV absorption of the PI film, the absorption
`efiiciency of the PI film is correlated with the sensitivity
`of the LC alignment to UV dosage. Figures 5, 6, and 7
`show the irradiance of the Xe lamp, the transmittance
`of the film polarizer, and the polarization etficiency of the
`film polarizer as functions of wavelength. The irradiation
`of the Xe lamp is taken directly from the manufacturer’s
`catalogue. The transmittance and polarization efficiency
`of the film polarizer were measured using the UV—visible
`spectrometer. The polarization efliciency is defined by
`the following equation:
`
`Polarized UV exposure time /min
`
`polarization efficiency
`
`Figure 3. Definition of Tm," of photo-alignment.
`
`: (Tpara _ Tper)//(Tpara + jper) X 100(cy°]
`
`Page 5 of 8
`
`Page 5 of 8
`
`

`
`578
`
`M. Nishikawa er al.
`
`100
`
`'o".,*‘
`.
`‘r,
`
`"”
`
`'—'
`
`'0'
`PI-7
`
`"‘
`
`'
`
`:
`
`'2 PI-10
`
`r. O
`‘a
`3,
`
`“-9
`
`O
`H-8
`
`3
`2
`'~,_OP1.5
`
`6'H""IllItlllyéfilllllltlllllglng
`PI-2
`
`'"
`
`E ‘
`
`E
`E 20
`.30
`Ts
`9 10
`C
`E
`*5
`.5
`E
`
`s
`
`2
`
`v
`
`1
`
`r
`
`r-
`
`v
`
`r -r r
`
`r—'-
`v
`u —r—-—r
`p
`Jf__/J—\—\,—I‘/
`
`«/
`
`/
`_
`
`.
`
`_
`
`-
`
`~
`
`-
`~
`
`60|-——v
`(3)
`50!,
`
`—,
`.5
`E 40,
`
`3E\E
`
`30»
`
`'~/1
`c’
`‘E:
`u 20-
`
`0 E
`
`‘C
`~
`E 10-
`
`0...).
`200
`
`L
`I
`X
`L
`I
`I
`‘J
`_I_
`4.
`I
`‘
`220 240 260 280 300 320 340 360 380 400
`
`Wavelength/ um
`
`1
`
`I
`._ I
`1
`_IjL La}...
`100
`so
`so
`20
`40
`Absorption effieiencv of PI film
`
`__I
`
`|
`
`120
`
`Figure 6. Relationship between absorption efficiencies of PI
`films and 'I;,,i,, of photo-alignment.
`
`PI-6
`’
`:°— PI-7
`Other Pls
`
`400
`
`450
`
`500
`
`550
`
`600
`
`
`
`
`
`Fluorescenceintensity
`
`300
`
`350
`
`Wavelength /nm
`
`Figure 7. Fluorescence spectra of PI films.
`
`Where 71mm and 7;“ are the maximum and minimum
`transmittance axes of the film polarizer, respectively.
`Figure 6 shows the relationship between Tmm and the
`absorption efficiencies of the Pl films. The Tmin tends to
`decrease with an increase in the absorption efliciency of
`the Pl film, as shown by the dashed line. Previous papers
`reported that the decomposition of PI containing the
`cyclobutane moiety was affected by the absorption of
`the PI material [27, 28]; our results agree. However,
`PI-6, 7, and 8 deviate from the dashed line shown
`in figure 8.
`To analyse other mechanisms of relaxation from the
`photo-excited state [29] we measured the fluorescence
`spectra of 30 pm thick PI films coated on quartz to
`prevent emission from the substrate. The PI films were
`excited at their absorption maximum, and the emissions
`from the Pl
`films were monitored as a function of
`
`Transmittanceofpolarizer/%
`
`0
`100
`
`I
`220
`
`I
`240
`
`|
`260
`
`I
`280
`
`J
`300
`
`I
`320
`
`I
`340
`
`I
`360
`
`x
`
`I A__l
`380
`400
`
`Wavelength /nm
`
`100
`
`-1
`
`v
`
`v
`
`r
`
`-—v—v%— v-v—-v
`
`I
`
`~—r
`
`v
`
`(C)
`
`c\‘’
`
`-
`//X
`—
`
`—
`
`_
`
`-
`
`T; 80-
`.5
`5
`3<«—« 60»
`\UC
`.2U
`Q)
`E.‘
`.9.
`
`O>
`
`_
`
`20*
`
`EO
`Q-
`
`I atja I 4.;
`I
`.|_..L_— '
`I
`I
`|__.l L?!
`0
`200 220 240 260 280
`300 320 340 360 380 400
`
`Wavelength /nm
`
`Figure 5. Relationship between wavelength and (a) irradiance ’
`of Xe lamp,
`(b)
`transmittance of film polarizer, and
`(c) polarization etficiency of film polarizer.
`
`Page 6 of 8
`
`Page 6 of 8
`
`

`
`
`
`
`
`
`PI— 1
`
`Clix}?
`O5 6)
`Top view “E: 7 V‘
`J
`.
`3
`
`“V
`C .
`
`. i
`
`‘.‘&<:
`
`Side view I
`
`I
`
`Figure 8. Molecular conformation
`of diamines in PIS.
`
`wavelength.T Figure 7 gives the fluorescence spectra
`of the PI films. PI—6 and PI-7 show relatively strong
`fluorescence compared with the other PI films competing
`with photoreaction. This could be one reason why PI-6
`and PI—7 have relatively lower photosensitivity.
`We calculated the molecular conformations of the
`
`diamines used in the Pls. Figure 8 shows the typical
`molecular conformations for diamines used in PI-1, 2,
`8, and 9. In most cases, the optic axes in the diamines
`align along the main chain of the resulting PIs. On the
`other hand,
`the diamine in PI-8 has two optic axes
`produced by the diphenyl methane and fluorene units.
`This interplay between the two optic axes in Pl—8 results
`in lower photosensitivity for UV dosage. Furthermore,
`the fluorene unit in Pl-8, which has a large birefringence,
`is aligned perpendicular to the axis of the main chain.
`The LC aligns in the opposite sense to the other Pls, as
`shown in the table, because the fluorene units are,
`perpendicular to the main chain.
`
`4. Conclusion
`
`In summary, we have measured the photosensitivity
`01' the LC alignment on various PI films to polarized
`UV exposure. The photosensitivity of the LC alignment
`for UV dosage is significantly affected by the chemical
`structures of Pls. The absorption efficiency of the PI
`film (defined from the UV absorption of the film, the
`irradiance of the UV lamp,
`the transmittance of the
`film polarizer, and the polarization eflficiency of the film
`polarizer) correlates with the photosensitivity of LC
`alignment for UV dosage. In addition, the result of the
`fluorescence spectrum measurements, taken with molecular
`conformation of the Pls, suggest that charge—transfer in
`the PI upon UV exposure and the molecular conformation
`of PI also affect the photosensitivity of the LC alignment.
`
`We acknowledge Drs L. C. Chien and B. Taheri of
`Kent State University and Drs N. Bessho and Y. Matsuki
`of JSR Co.
`for their support
`in this research. The
`research was supported in part by NSF Science and
`Technology Center ALCOM, DMR 89-20147.
`
`+The experimental accuracy of the fluorescence was i 10%.
`
`References
`
`I992, Jpn.
`
`‘M., MIYAMoTo, T., KAWAMURA,
`[1] NISHIKAWA,
`TSUDA, Y., and BESSHO, N., 1992, Proc. Japan Display
`’92, 819.
`[2] SASAKI, T., FUJ11, H., and NISHIKAWA, M.,
`J. appl. Phys., 31, L632.
`[3] AOYAMA, H., YAMAZAK1, Y., N/IATSUURA, N., MADA, H.,
`and KOBAYASHI, S., 1981, Mol. Cryst.
`liq. Cryst, 72,
`127.
`[4] KAWATA, Y., TAKATOH, K., HASEGAWA, M.,
`SAKAMoTo, M., 1994, Liq. Cry.st., 16, 1027.
`[5] LEE, E. S., VETTER, P., MIYASHITA, T., UCHIDA, T.,
`KANO, M., ABE, M., and SUGAWARA, K., 1993, Jpn.
`J. appl. Phys, 32, LI436.
`[6] GIBBoNs, W. M., SHANNON, P. 1, SUN, S. T., and
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