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`a2, United States Patent
`US 6,771,342 B1
`(10) Patent No.:
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`Aug. 3, 2004
`(45) Date of Patent:
`Hirakata et al.
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`US006771342B1
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`(54) LIQUID CRYSTAL DISPLAY DEVICE AND
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`DISPLAY DEVICE
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`............ 437/42
`5/1996 Yamazaki etal.
`5,521,107 A
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`F997 Sakamoto ....... eee 257/764
`5,650,664 A
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`12/1997 Sanoet al. veces 349/139
`5,694,188 A
`ae A : 1008 Yanagawa ‘ a seteesenenes S949
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`anagawa et al.
`............
`;760,
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`5,814,834 A *
`9/1998 Yamazaki et al. oc... 257/59
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`5,815,226 A *
`9/1998 Yamazaki et al.
`.......... 349/111
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`5,897,345 A
`4/1999 Uochi
`cesseeccssssseeesseonee 438/151
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`6,013,928 A
`1/2000 Yamazaki et al.
`.......... 257/347
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`6,133,620 A
`10/2000 Uochi
`o.eeeceeseesseeseseeeene 257/649
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`6,160,600 A
`12/2000 Yamazaki et al.
`.......... 349/138
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`
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`FOREIGN PATENT DOCUMENTS
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`
`
`4-163528
`6/1992
`*
`
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`07-036058
`2/1995
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`
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`Ip
`JP
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`* cited by examiner
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`Primary Examiner—Tarifur R. Chowdhury
`
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`(74) Attorney, Agent, or Firm—Fish & Richardson PC
`
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`ABSTRACT
`(57)
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`In a liquid crystal display device which performs image
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`display by controlling a liquid crystal layer by a lateral
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`electric field that is parallel with a substrate,
`the lateral
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`electric field is formed by a black matrix and a pixel
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`electrode. That is, a common electrode and a black matrix
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`are commonized which are separately provided convention-
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`ally. Further, a storage capacitor is formed in an area where
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`the black matrix and a pixel line coextend with a third
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`interlayer insulating film interposed in between. Since the
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`storage capacitor is formed by using all the area where a
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`thin-film transistor is covered with the black matrix, suffi-
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`cient capacitance can be secured even if the widths of
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`electrodes wiring lines are reduced in the future.
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`46 Claims, 11 Drawing Sheets
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`(75)
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`(*) Notice:
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`(22)
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`(30)
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`(51)
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`Inventors: Yoshiharu Hirakata, Kanagawa(JP);
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`Noe
`*
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`OaNeneKanagawa UW:
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`pe
`LORYO
`LIE);
`»
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`Takeshi Fukunaga, Kanagawa (JP)
`;
`;
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`(73) Assignee: Semiconductor Energy Laboratory
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`Co., Ltd., Kanagawa-ken (JP)
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`Subject to any disclaimer, the term ofthis
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`patent is extended or adjusted under 35
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`U.S.C. 154(b) by 0 days.
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`(21) Appl. No.: 08/811,152
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`Filed:
`Mar.4, 1997
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`Foreign Application Priority Data
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`(IP) w..ceeeceeseesssecsssensseeecnesensesensaes 8-078346
`Mar. 5, 1996
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`... 8-096318
`Mar. 26, 1996
`(JP)
`....
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`cecssccsssessessesssessesssesseesseseesseess 8-113166
`Apr. 9,1996
`(IP)
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`Int. Ch? vee G02F 1/1343; GO2F 1/136;
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`G02F 1/1333
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`(52) US. Che ceeccesccccssescessseeee 349/141; 349/43; 349/110;
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`349/138
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`(58) Field of Search oo... eee 349/42, 43, 110,
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`349/111, 138, 141; 257/59, 72
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`(56)
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`References Cited
`U.S. PATENT DOCUMENTS
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`3,774,989 A
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`5,055,899 A
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`5,339,181 A
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`11/1973 Takahashi............. 350/160 LC
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`10/1991 Wakai et al. oo... 357/23.7
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`8/1994 Kim et al. v..ceeeseeseeee 359/59
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`US 6,771,342 B1
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`Fig. 2A
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`Fig. 3A
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`Fig. 8A
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`1
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`LIQUID CRYSTAL DISPLAY DEVICE AND
`DISPLAY DEVICE
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`US 6,771,342 B1
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`2
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`No. Hei. 7-36058). However,it is expectedthat as the degree
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`of electrode miniaturization increases,
`the area where to
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`form a storage capacitor becomes smaller, making it impos-
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`sible to secure a necessary and sufficient capacitance. If it is
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`attempted to form a storage capacitor having a necessary
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`capacitance, the area occupied by the capacitance element
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`will necessarily become large, to lower the open area ratio
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`(aperture ratio).
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`Conventionally,
`the light quantity of a backlight
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`increased to compensate for a low open area ratio (low
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`aperture ratio), to thereby secure necessary brightness of a
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`screen, However, because of increased power consumption,
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`this is a large obstacle to incorporation of a liquid crystal
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`display device into devices that are required to be portable.
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`As described above, a technique is now desired which can
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`secure a necessary storage capacitance without sacrificing
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`the open area ratio (aperture ratio). To improve the open area
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`ratio (aperture ratio) with the IPS mode,it is desired that the
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`electrode width be reduced to less than 1-2 wm. Although
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`submicron or even finer patterning techniques have already
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`been established, they are now encountering difficulties in
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`mass production,
`resulting in delay of technological
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`progress.
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`BACKGROUND OF THE INVENTION
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`1. Field of the Invention
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`The present invention relates to a liquid crystal display
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`device in which control is made by semiconductor devices
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`that are formed by using a crystalline silicon film. The
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`invention can be applied to MIM, passive matrix, active
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`matrix, and other liquid crystal display devices.
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`2. Description of the Related Art
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`In recent years, techniques of forming thin-film transistors
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`(TFTs) on an inexpensive glass substrate have been devel-
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`oped at high speed. This is because of an increased demand
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`for higher-resolution liquid crystal display devices as dis-
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`play media of multimedia.
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`For example, in an active matrix display device, thin-film
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`transistors are provided for millions of respective pixels
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`arranged in matrix form and chargeto enter or exit from each
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`pixel electrode is controlled by the switching function of the
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`thin-film transistor. Image display is performed by control-
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`ling the amountof light that passes through a liquid crystal
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`SUMMARYOF THE INVENTION
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`panel by changing the electro-optical characteristic of a
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`liquid crystal in accordance with an image signal supplied
`An object of the present inventionis, therefore, to propose
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`from a data line. Since a voltage applied to the liquid crystal
`a technique for forming storage capacitors which well
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`is desired to be constant until the next writing, the image
`matches fine processing technologies, as well as to provide
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`signal potential is held by a storage capacitor for a given
`a technique for forming a pixel area having a large open area
`time.
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`ratio (large aperture ratio).
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`As a driving method of the above type of liquid crystal
`According to one aspect of the invention, there is pro-
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`display device, the IPS mode now attracts much attention in
`vided a liquid crystal display device comprising a first
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`which a parallel electrode structure is employed and the
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`substrate comprising a pixel electrode and a commonelec-
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`device is driven by controlling an electric field that
`is
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`trode both being made of a conductive material, the common
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`parallel with a substrate.
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`electrode being a black matrix; a second substrate opposed
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`A liquid crystal display device driven by the IPS mode is
`to the first substrate; and a liquid crystal held between the
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`featured by a large viewing angle, high contrast, etc. and has
`first and second substrates, and driven by anelectric field
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`thin-film transistors, gate lines, data lines (source lines),
`formed between the pixel electrode and the common
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`pixel electrodes, a common line, and a commonelectrode
`electrode, the electric field having a componentparallel with
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`the substrates.
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`extending therefrom in a pixel area on the same substrate.
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`In particular, in the IPS mode in whichalateral electric
`According to another aspect of the invention, there is
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`field is controlled, each pixel electrode is interposed
`provided a liquid crystal display device comprisingafirst
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`between commonelectrodes that are arranged parallel with
`substrate comprising a second interlayer insulating film
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`the pixel electrode so that an electric field applied to the
`made of an organic resin material or an inorganic material;
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`pixel electrode does not influence other pixels etc. Since a
`a pixel line and a pixel electrode extending from the pixel
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`certain area should be secured for those electrodes, the open
`line which are formed on the second interlayer insulating
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`area ratio (aperture ratio), i.e., the ratio of an area which
`film; and a third interlayer insulating film and a common
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`transmits light for display, of the pixel area is lowered.
`electrode, the common electrode being a black matrix; a
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`Further, to secure a sufficient charge holding time,a liquid
`second substrate opposed to the first substrate; a liquid
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`crystal display requires a structure in which a storage
`crystal layer held between the first and second substrates,
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`capacitor is added to a pixel electrode. This is not limited to
`and driven by an electric field formed between the pixel
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`liquid crystal displays driven by the IPS mode, but appli-
`electrode and the commonelectrode, the electric field having
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`cable to conventional liquid crystal display devices.
`a componentparallel with the substrates; and a storage
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`However, the provision of electrodes for forming storage
`capacitor formed byat least parts of the pixel line and the
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`capacitors (capacitance electrodes) could be a factor of
`black matrix which parts coextend on the second interlayer
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`lowering the open area ratio (aperture ratio). In view ofthis,
`insulating film with the third interlayer insulating film
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`a technique has been proposed in which capacitance elec-
`interposed in between.
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`trodes formed in the samelaser as gate lines also serve as a
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`provided a liquid crystal display device comprisingafirst
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`substrate comprising a second interlayer insulating film
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`cannot fully serve as the black matrix because of a problem
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`relating to parasitic capacitance.
`a pixel line and a pixel electrode extending from the pixel
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`Another technique has been proposed in which a storage
`line which are formed on the second interlayer insulating
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`capacitor as mentioned aboveis formed by utilizing an area
`film; and a third interlayer insulating film, a common
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`where a pixel electrode and a common electrode overlap
`electrode, and a capacitance-forming electrode, the common
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`with each other (Japanese Unexamined Patent Publication
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`US 6,771,342 B1
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`trode being a black matrix; and capacitor-forming electrodes
`between the first and second substrates, and driven by an
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`formed in a layer different than the pixel lines and the pixel
`electric field formed between the pixel electrode and the
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`electrodes; an opposed substrate that is opposedto the active
`common electrode, the electric field having a component
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`matrix substrate; a liquid crystal layer held between the
`parallel with the substrates; and a storage capacitor formed
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`active matrix substrate and the opposed substrate, and driven
`by at least parts of the pixel line and the capacitor-forming
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`by an electric field formed between each of the pixel
`electrode which parts coextend on the second interlayer
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`electrodes and the common electrode,
`the electric field
`insulating film with the third interlayer insulating film
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`having a componentparallel with the substrates; and storage
`interposed in between.
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`capacitors each formed byatleast parts of the pixel line and
`The invention can be applied to any of the MIM,passive
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`the capacitor-forming electrode which parts coextend on the
`matrix, active matrix, and like liquid crystal display devices.
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`second interlayer insulating film with the third interlayer
`Further, a dispersion-type liquid crystal display device can
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`insulating film interposed in between.
`be constructed by utilizing the invention. In this case, a
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`In the above configurations, the thin-film transistor which
`second substrate is not necessary.
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`The invention has been made in view of the reduction in
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`controls a voltage applied to the pixel electrode can use, as
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`the active layer, an amorphoussilicon film or a crystalline
`the widths of electrodes and wiring lines which will proceed
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`silicon film (polysilicon film).
`in the future. The techniquesof the inventionare particularly
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`Where a pixel area is required to have high response
`effective in manufacturing a liquid crystal display device
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`speed, where a driver circuit is to be constructed which
`that requires microprocessing.
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`requires high-speed operation, or in similar cases,
`it
`is
`According to a further aspect of the invention, there is
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`desirable to employ a thin-film transistor which uses a
`provideda liquid crystal display device comprising an active
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`crystalline silicon film as the active layer.
`matrix substrate comprising gate lines and data lines
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`A thin-film transistor using a crystallinesilicon film as the
`arranged in matrix form on the same active matrix substrate;
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`active layer is superior in electrical characteristics to that
`thin-film transistors formed at respective intersections of the
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`using an amorphoussilicon film. For example, the field-
`gate lines and the data lines; pixel lines connected to the
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`effect mobility is not less than 20 cm?/Vs in the case of an
`respective thin-film transistors and pixel electrodes extend-
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`n-channel thin-film transistor and notless than 10 cm7/V.s in
`ing from the respective pixel lines; and a commonelectrode
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`the case of a p-channel thin-film transistor.
`at least partially opposed to each of the pixel electrodes, the
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`common electrode being a black matrix; an opposed sub-
`According to still another aspect of the invention,there is
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`strate that is opposed to the active matrix substrate; and a
`provided a manufacturing method of a liquid crystal display
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`liquid crystal layer held between the active matrix substrate
`device comprising an active matrix substrate comprising
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`and the opposed substrate, and driven by an electric field
`gate lines and data lines arranged in matrix form on the same
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`formed between each of the pixel electrodes and the com-
`active matrix substrate;
`thin-film transistors formed at
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`monelectrode, the electric field having a componentparallel
`respective intersections of the gate lines and the data lines,
`with the substrates.
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`and each having,as an active layer, a crystalline silicon film;
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`a second interlayer insulating film formed above the thin-
`According to another aspect of the invention, there is
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`film transistors; pixel
`lines connected to the respective
`provideda liquid crystal display device comprising an active
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`thin-film transistors and pixel electrodes extending from the
`matrix substrate comprising gate lines and data lines
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`respective pixel
`lines; and a common electrode at
`least
`arranged in matrix form on the same active matrix substrate;
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`partially opposed to each of the pixel electrodes; an opposed
`thin-film transistors formed at respective intersections of the
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`substrate that is opposed to the active matrix substrate; and
`gate lines and the data lines; a second interlayer insulating
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`a liquid crystal layer held between the active matrix sub-
`film and a third interlayer insulating film formed above the
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`strate and the opposed substrate, and driven by anelectric
`thin-film transistors; pixel lines connected to the respective
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`field formed between each of the pixel electrodes and the
`thin-film transistors and pixel electrodes extending from the
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`45
`common electrode, the electric field having a component
`respective pixel
`lines; and a common electrode at
`least
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`parallel with the active matrix substrate, said manufacturing
`partially opposed to each of the pixel electrodes, the com-
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`method comprising the steps of forming a second interlayer
`mon electrode being a black matrix; an opposed substrate
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`insulating film made of an organic resin material and/or an
`that is opposed to the active matrix substrate; a liquid crystal
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`layer held between the active matrix substrate and the inorganic material so as to cover data lines andafirst
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`50
`opposed substrate, and driven by an electric field formed
`interlayer insulating film that covers gate lines; forming a
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`between each of the pixel electrodes and the common
`black matrix on the second interlayer insulating film; form-
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`electrode, the electric field having a componentparallel with
`ing a third interlayer insulating film so as to cover the black
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`the substrates; and storage capacitors each formedbyatleast
`matrix; forming contact holes through the second and third
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`parts of the pixel line and the black matrix which parts
`interlayer insulating films; and forming, on the third inter-
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`coextend on the second interlayer insulating film with the
`layer insulating film, pixel lines and pixel electrodes extend-
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`third interlayer insulating film interposed in between.
`ing from the respective pixel lines, wherein each of storage
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`capacitors is formedbyat least parts of the pixel line and the
`According to another aspect of the invention, there is
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`black matrix which parts coextend on the second interlayer
`provideda liquid crystal display device comprising an active
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`insulating film with the third interlayer insulating film
`matrix substrate comprising gate lines and data lines
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`interposed in between.
`arranged in matrix form on the same active matrix substrate;
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`thin-film transistors formed at respective intersections of the
`According to another aspect of the invention, there is
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`gate lines and the data lines; a second interlayer insulating
`provided a manufacturing method of a liquid crystal display
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`film and a third interlayer insulating film formed above the
`device comprising an active matrix substrate comprising
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`thin-film transistors; pixel lines connected to the respective
`gate lines and data lines arranged in matrix form on the same
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`active matrix substrate;
`thin-film transistors formed at
`thin-film transistors and pixel electrodes extending from the
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`respective pixel lines; a commonelectrodeat least partially
`respective intersections of the gate lines and the data lines,
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`opposed to each of the pixel electrodes, the common elec-
`and each having,as an active layer, a crystalline silicon film;
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`Page 14 of 25
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`Page 14 of 25
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`

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`US 6,771,342 B1
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`line 105 and a pixel electrode 106
`Further, a pixel
`a second interlayer insulating film formed above the thin-
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`extending therefrom are formed !above the black matrix 104
`film transistors; pixel
`lines connected to the respective
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`through a third interlayer insulating film. FIG. 1B shows a
`thin-film transistors and pixel electrodes extending from the
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`state that the pixel line 105 and the pixel electrode 106 are
`respective pixel
`lines; and a common electrode at
`least
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`laid on the structure of FIG. 1A.
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`partially opposed to each of the pixel electrodes; an opposed
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`substrate that is opposed to the active matrix substrate; and
`Although the pixel line 105 and the pixel electrode 106
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`a liquid crystal layer held between the active, matrix sub-
`constitute an integral part in FIG. 1B, the present inventors
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`strate and the opposed substrate, and driven by an electric
`clearly distinguish between those members based on their
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`field formed between each of the pixel electrodes and the
`functions. That is, the pixel electrode 106 is defined as the
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`common electrode, the electric field having a component
`portion extending from the pixel line 105 to the pixel region
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`parallel with the active matrix substrate, said manufacturing
`(i.e., the opening of the black matrix 104).
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`method comprising the steps of forming a second interlayer
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`Thatis, the pixel line 105 and the pixel electrode 106 are
`insulating film made of an organic resin material and/or an
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`considered entirely different from each other because the
`inorganic material so as to cover the data lines andafirst
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`15
`pixel line 105 is provided to form a storage capacitor with
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`interlayer insulating film that covers the gate lines; forming
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`the black matrix 104 whereas the pixel electrode 106 is
`contact holes through the second interlayer insulating film;
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`providedto formalateral electric field betweenitself and the
`forming, on the secondinterlayer insulating film, pixel lines
`black matrix 104.
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`and pixel electrodes extending from the respective pixel
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`In the abovestructure, a storage capacitor is formed by the
`lines; forminga third interlayer insulating film so as to cover
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`black matrix 104 and the pixel line 105 with the third
`the pixel lines and the pixel electrodes; and forming a black
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`interlayer insulating film interposed in betweenin the region
`matrix on the third interlayer insulating film, wherein each
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`where the black matrix 104 and the pixel line 105 overlap
`of storage capacitors is formed byat least parts of the pixel
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`with each other. The third interlayer insulating film needs to
`line and the black matrix which parts coextend on the second
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`be constituted of an insulating film having a larger relative
`interlayer insulating fill with the third interlayer insulating
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`dielectric constant than the secondinterlayer insulating film.
`film interposed in between.
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`Although as shown in FIG. 1B a storage capacitor is
`One of the main points of the technical means of the
`formed in the same manner as in the above case in small
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`invention resides in the commonization of a black matrix
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`regions where the pixel electrode 106 exists over the black
`and commonelectrodes.It is intended to realize a configu-
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`ration in whichalateral electric field is formed between the
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`matrix 104,it can substantially be disregarded in the case of
`30
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`improving the open area ratio (aperture ratio) by reducing
`black matrix (having substantially the same function as the
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`the electrode width, which is one of the main points of, the
`commonelectrodes) and a pixel electrode that extends from
`invention.
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`a pixelline.
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`Lateral electric fields (indicated by arrows in FIG. 1B) for
`Further, in a liquid crystal display device having such a
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`driving the liquid crystal are formed between the pixel
`parallel electrode structure, a storage capacitor is formed by
`electrode 106 and the black matrix 104.
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`the black matrix and a pixel line that is connected to a
`thin-film transistor.
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`The idea of commonizing the black matrix and the
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`commonelectrodes, which are considered separate members
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`conventionally, is entirely new, and the formation of the
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`storage capacitor by the black matrix and the pixel line is
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`entirely different from the technique disclosed in the above-
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`mentioned publication No. Hei. 7-36058.
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`45
`Another important feature of the invention is that a
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`manufacturing process can be simplified greatly by com-
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`monizing the black matrix and the commonelectrodes.
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`FIGS. 1A and 1B are top views of a pixel region,
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`accordingto the invention,of a liquid crystal display device.
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`In FIG. 1A, reference numerals 101 and 102 denote a gate
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`line for transmitting a gate signal and a data line for
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`transmitting an image signal, respectively. (In FIG. 1A,the
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`gate lines 101 and the data lines 102 are shown by broken
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`lines because they exist under a black matrix.)
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`The gate lines 101 and the data lines 102 are arranged in
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`matrix form on the same substrate, and thin-film transistors
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`are disposed for each intersection of those lines. Reference
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`numeral 103 denotes a semiconductor layer that constitutes
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`the active layer of the thin-film transistor. A black matrix 104
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`(hatched in FIGS. 1A and 1B) are formed above the gate
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`lines 101, the data lines 102, and the semiconductor layer
`103 so as to cover those members.
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`The data lines 102 and the black matrix 104 are insulated
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`from each other by a second interlayer insulating film of
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`0.1-5.0 wm in thickness. The second interlayer insulating
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`film is made of an organic or inorganic material.
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`BRIEF DESCRIPTION OF THE DRAWINGS
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`FIGS. 1A and 1B are top views showing the structure of
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`a pixel region of a liquid crystal display device according to
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`a first embodimentof the invention;
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`FIGS. 2A-2D, 3A-3B, and FIG. 4 are sectional views
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`showing a manufacturing process of the pixel region of a
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`liquid crystal display device according to the first embodi-
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`FIGS. 5A and 5B are sectional views showing the struc-
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`ture of a pixel region of a liquid crystal display device
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`according to a fourth embodiment of the invention;
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`FIG. 6 is a top view showing a pixel region of a liquid
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`crystal display device according to a fifth embodimentof the
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`invention;
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`FIG. 7 is a top view showing a pixel region of a liquid
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`crystal display device according to a sixth embodiment of
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`the invention;
`FIGS. 8A and 8B show the structure of an island-like
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`semiconductor layer and modes of its operation;
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`FIGS. 9A-9D show energy bandstates of the island-like
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`semiconductor layer;
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