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`(54) TRANSFLECTIVE LIQUID CRYSTAL
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`DISPLAY DEVICE
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`(75)
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`Inventors:
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`;
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`Takahiro Ochiai, Chiba(JP);
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`Takayuki Nakao, Atsugi (JP);
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`Daisuke Sonoda, Chiba (JP);
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`Hidekazu Miyake, Mobara (JP);
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`Toshio Miyazawa, Chiba (JP);
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`Masahiro Maki, Mobara(JP):
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`Tohru Sasaki, Mobara (JP)
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`(51)
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`as) United States
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`a2) Patent Application Publication 10) Pub. No.: US 2008/0007679 A1
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` Ochiaiet al. (43) Pub. Date: Jan. 10, 2008
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`US 20080007679A1
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`Publication Classification
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`Int. Cl.
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`(2006.01)
`G02F 1/1335
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`(52) U.S. Ch. cccessssssssssssssssssssesetssssssseeeesutnsnene 349/114
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`ABSTRACT
`(57)
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`The manufacturing yield of transflective liquid crystal dis-
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`play devices is to be enhanced. In a transflective liquid
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`crystal display device including a liquid crystal display
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`panel having a pair of substrates and a liquid crystal layer
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`held betweenthe pair of substrates, the liquid crystal display
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`panelhasa plurality of subpixels each having a transmissive
`Correspondence Address:
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`part and a reflective part, wherein one of the pair of
`Stanley P. Fisher
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`substrates has: an active element; a first
`insulating film
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`disposed in a higher layer than the electrode of the active
`Suite 1400, 3110 Fairview Park Drive
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`Falls Church, VA 22042-4503 element and havingafirst contact hole; a counter electrode
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`disposed in a higher layer than the first insulating film; a
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`reflective electrode disposedin the reflective part in a higher
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`layer than the counter electrode; a second insulating film
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`disposed in a higher layer than the counter electrode and the
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`reflective electrode and having a second contacthole; a pixel
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`electrode disposed in a higher layer than the second insu-
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`lating film; and an electroconductor formed in the first
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`contact hole and electrically connected to the electrode of
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`the active element, and the pixel electrode is electrically
`connected to the electroconductor via the second contact
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`hole.
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`(73) Assignee:
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`Hitachi Displays, Ltd.
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`(21) Appl. No.:
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`Filed:
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`(22)
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`11/812,770
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`Jun. 21, 2007
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`(30)
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`Foreign Application Priority Data
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`IP) woe eeceeecneeeteesees 2006- 188258
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`Jul. 7, 2006
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`US 2008/0007679 A1
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`FIG.1B
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`Jan. 10,2008 Sheet 5 of 22
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`US 2008/0007679 Al
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`AN inal 0
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`FIG.6C
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`FIG.6E
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`CH2a
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`Jan. 10,2008 Sheet 9 of 22
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`US 2008/0007679 Al
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`Jan. 10,2008 Sheet 10 of 22
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`US 2008/0007679 A1
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`FIG.8
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`Jan. 10,2008 Sheet 11 of 22
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`FIG.9
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`Jan. 10,2008 Sheet 12 of 22
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`FIG.10
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`FIG.11
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`V-CT-H
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`Jan. 10,2008 Sheet 15 of 22
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`Jan. 10,2008 Sheet 19 of 22
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`CH1
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`Jan. 10,2008 Sheet 20 of 22
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`Jan. 10,2008 Sheet 21 of 22
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`FIG.21
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`FIG
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`FIG
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`Jan. 10, 2008
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`TRANSFLECTIVE LIQUID CRYSTAL
`DISPLAY DEVICE
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`CLAIM OF PRIORITY
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`[0001] The present application claimspriority from Japa-
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`nese Application JP 2006-188258 filed on Jul. 7, 2006, the
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`content of which is hereby incorporated by reference into
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`this application.
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`BACKGROUND OF THE INVENTION
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`1. Field of the Invention
`[0002]
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`[0003] The present invention relates to transflective liquid
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`crystal display devices, and moreparticularly to a transflec-
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`tive liquid crystal display device of an in-plane switching
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`type or a vertical alignmenttype.
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`[0004]
`2. Description of the Related Art
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`[0005] Transflective liquid crystal display devices each
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`having a transmissive part and a reflective part
`in one
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`subpixel are used as display units for mobile devices.
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`Such transflective liquid crystal display devices use
`[0006]
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`a system in which electric fields are applied to liquid crystals
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`held betweena pair of substrates in a direction normalto the
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`planes of the paired substratesto drive the liquid crystals. In
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`this case, to match the characteristics of the transmissive part
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`and the reflective part, a level gap is provided between the
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`transmissive part and the reflective part, and further a phase
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`differential plate is arranged between a polarization plate
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`[0007] On the other hand, IPS type transflective liquid
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`crystal display devices are also known, in each of which
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`pixel electrodes (PIX) and counter electrodes (CT) are
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`formed over the same substrate, and gray scale levels are
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`controlled by applying electric fields to these liquid crystals
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`by rotating them within the substrate plane. For this reason,
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`these devices have a significant feature that the relative
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`shades of the display image are not reversed whenthe screen
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`is looked at askew. To take advantage of this feature, it is
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`proposed to structure a transflective liquid crystal display
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`device by using an IPS type liquid crystal display device.
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`[0008] However, structuring a transflective liquid crystal
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`display device by using an IPS type liquid crystal display
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`device involves a problem (1) that, when the transmissive
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`part is normally black, the reflective part becomes normally
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`white, namely the relative shades are reversed between the
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`transmissive part and the reflective part.
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`In view of this point, the present applicant has
`[0009]
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`already applied for a patent on a transflective liquid crystal
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`display device having a new pixel structure (see Japanese
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`Patent Application No. 2005-322049) intended to solve this
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`problem (1).
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`[0010] This transflective liquid crystal display device on
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`which a patent is pending has a pixel structure for each
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`subpixel in which an independent counter electrode for each
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`of the transmissive part and the reflective part is provided
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`against a common pixel electrode of the transmissive part
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`and the reflective part, and reversal of the relative shades
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`between them is prevented by applying different reference
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`voltages (a counter voltage and a common voltage) to the
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`transmissive part and the reflective part.
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`[0011]
`In the IPS type liquid crystal display device, the
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`pixel electrode (PIX)is disposed on the liquid crystal side of
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`one of the paired substrates. In this arrangement, a hole is
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`bored in the counter electrode (CT), in which a contact hole
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`Page 24 of 34
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`is formed, and a driving voltage is applied to the pixel
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`electrode (PIX) through this contact hole.
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`[0012] However,
`the transflective liquid crystal display
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`device disclosed in Japanese Patent Application No. 2005-
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`322049 involves a problem (2) that, in boring a hole in the
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`counter electrode (CT) to apply a driving voltage to the pixel
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`electrode (PIX) arranged on the liquid crystal side of one of
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`the substrates and forming a contact hole therein, non-
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`display parts increase and the transmissivity drops.
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`[0013] Therefore, to solve this problem (2), the present
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`applicant has already applied for a patent on a transflective
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`liquid crystal display device having a novel pixel structure
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`(see Japanese Patent Application No. 2006-109659).
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`[0014] This transflective liquid crystal display device on
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`which a patent is pending is intended to prevent the trans-
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`missivity from dropping by using the gap between opposing
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`counter electrodes (CT) as the opening in the counter
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`electrodes (CT) required for the formation of the contact
`hole.
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`SUMMARY OF THE INVENTION
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`[0015] The present inventors studied the transflective liq-
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`uid crystal display device described in Japanese Patent
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`Application No. 2006-109659, and found the following
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`problems.
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`FIG. 23 showsthe essential part of the sectional
`[0016]
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`structure of the connecting part which electrically connects
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`the electrode of an active elementto a pixel electrode in the
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`pixelpart of the liquid crystal panel in the transflective liquid
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`crystal display device of Japanese Patent Application No.
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`2006-109659, and FIG.24,the essential part of the sectional
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`structure of the connecting part which electrically connects
`the electrode of an active element to a counter electrode via
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`an ITO film in the peripheral circuit part of the liquid crystal
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`panelin the transflective liquid crystal display device whose
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`application to the structure of Japanese Patent Application
`No. 2006-109659 is under consideration.
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`[0017]
`In FIG. 23 and FIG.24, reference numerals 15, 16
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`and 17 denote inter-layer insulating films; reference sign CT
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`denotes a counter electrode; DD and DD1, electrodes func-
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`tioning as the drain electrodes of thin-film transistors (active
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`elements); PIX, a pixel electrode; RAL, a reflective elec-
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`trode; and CH2, CH3 and CH4, contact holes.
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`[0018] The transflective liquid crystal display device
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`described in Japanese Patent Application No. 2006-109659,
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`as shown in FIG. 23, has a structure in which the pixel
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`electrode (PIX)
`is brought
`into direct contact with the
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`electrode (DD)of a thin-film transistor via a contact hole
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`CH3. This structure is realized by forming the inter-layer
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`insulating film 17 inside the contact hole CH2 of the
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`inter-layer insulating film 16 as well, boring a hole in this
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`inter-layer insulating film 17 and utilizing its pattern to
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`machine the inter-layer insulating film 15 underneath and
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`thereby to bore the contact hole CH3.
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`[0019] However, when boring the contact hole CH3, the
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`difference in film quality between the inter-layer insulating
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`film 15 and the inter-layer insulating film 17 may invite
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`some trouble in machining them together, which would
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`result in faulty electrical connection of the pixel electrode
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`(PIX) to the electrode (DD)of the thin-film transistor.
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`[0020]
`In view of this problem,
`the present
`inventors
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`examined the possibility of machining the inter-layer insu-
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`lating film 15 before machining the inter-layer insulating
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`film 17. In this case, however, the electrode (DD) of the
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`Page 24 of 34
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`

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`US 2008/0007679 Al
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`Jan. 10, 2008
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`thin-film transistor was dissolved whenthe reflective elec-
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`(4) In the configuration described in either one of
`[0029]
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`(1) to (3) above, the electroconductor is formed at the same
`trode (RAL) was patterned, resulting again in faulty elec-
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`step as the counter electrode and electrically separated from
`trical connection of the pixel electrode (PIX)to the electrode
`the counter electrode.
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`(DD) of the thin-film transistor. This faulty connection
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`[0030]
`(5) In the configuration described in either one of
`invites a fall
`in the manufacturing yield of transflective
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`(1) to (4) above,the electrode of the active element contains
`liquid crystal display devices.
`in the surface thereof 1% or more of the material of the
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`[0021]
`In the peripheral circuit part, controlling the poten-
`reflective electrode.
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`tial to be supplied to the counter electrode (CT) with a
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`(6) In the configuration described in either one of
`[0031]
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`thin-film transistor requires electrical connection between
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`(1) to (5) above,the electrode ofthe active elementis formed
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`the electrode (DD1) of the thin-film transistor and the
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`of a materialthat is etched with the etchantor etching gas for
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`counter electrode (CT). Where the fabricating process
`the reflective electrode.
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`described with reference to FIG. 23 is to be used,
`it is
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`[0032]
`(7) In the configuration described in either one of
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`necessary to electrically connect the electrode (DD1) of the
`(1) to (6) above, the pixel electrode is arranged superposed
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`thin-film transistor and the counter electrode (CT) by using
`over the counter electrode, and the pixel electrode,
`the
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`the top layer ITO film 20 (machinedat the same step as the
`second insulating film and the counter electrode together
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`pixel electrode (PIX)) as shownin FIG. 24, and the increase
`constitute a holding capacitance.
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`in connection resistance due to the high chain resistance of
`(8) In the configuration described in either one of
`[0033]
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`the ITO poses a problem. An increased connection resistance
`(1) to (7) above, each of the plurality of subpixels has the
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`givesrise to fluctuationsin the driving voltage appliedto the
`pixel electrode shared between the transmissive part and the
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`counter electrode (CT), which presumably invites deterio-
`reflective part and the counter electrodes independentfor the
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`transmissive part and the reflective part; and the driving
`ration in display quality.
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`voltages applied to the counter electrodes differ between the
`[0022] An object of the present invention is to provide a
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`transmissive part and the reflective part.
`technique which enables the manufacturing yield of trans-
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`(9) In the configuration described in either one of
`[0034]
`flective liquid crystal display devices to be enhanced.
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`(1) to (7) above,the reflective part is provided with a phase
`[0023] Another object of the invention is to provide a
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`differential plate.
`technique which enables the display quality of transflective
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`(10) A transflective liquid crystal display device
`[0035]
`liquid crystal display devices to be improved.
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`includes a liquid crystal display panel having a pair of
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`[0024] These and other objects and novel features of the
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`substrates and a liquid crystal layer held between the pair of
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`invention will become more apparent from the description in
`substrates, the liquid crystal display panel having a plurality
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`this specification when taken into conjunction with the
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`of subpixels each having a transmissive part andareflective
`accompanying drawings.
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`part, wherein one of the pair of substrates has: an active
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`[0025] Abrief summary oftypical aspects of the invention
`element;a first insulating film disposed in a higher layer than
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`disclosed in the present application is given below.
`the electrode of the active element and havinga first contact
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`(1) A transflective liquid crystal display device
`[0026]
`hole; a common electrode in a higher layer than the first
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`includes a liquid crystal display panel having a pair of
`insulating film; a reflective electrode disposed in the reflec-
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`substrates and a liquid crystal layer held between the pair of
`tive part in a higher layer than the commonelectrode; a
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`substrates, the liquid crystal display panel having a plurality
`second insulating film disposed in a higher layer than the
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`of subpixels each having a transmissive part andareflective
`commonelectrode andthe reflective electrode and having a
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`part, wherein one of the pair of substrates has: an active
`second contact hole; a pixel electrode disposed in a higher
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`element; a first insulating film disposedin a higher layer than
`layer than the secondinsulating film; and an electroconduc-
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`the electrode of the active element and havinga first contact
`tor formedin the first contact hole andelectrically connected
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`hole; a counter electrode disposed in a higher layer than the
`to the electrode of the active element, the pixel electrode
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`first insulating film; a reflective electrode disposed in the
`being electrically connected to the electroconductor via the
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`second contact hole.
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`reflective part in a higher layer than the counter electrode; a
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`second insulating film disposed in a higher layer than the
`(11) In the configuration described in (10) above,
`[0036]
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`counter electrode andthe reflective electrode and having a
`the electroconductor is disposed inside and outside the first
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`contact hole all over.
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`second contact hole; a pixel electrode disposed in a higher
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`layer than the secondinsulating film; and an electroconduc-
`(12) In the configuration described in (10) or (11)
`[0037]
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`tor formedin the first contact hole andelectrically connected
`above, the one substrate has a third insulating film disposed
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`to the electrode of the active element, and the pixel electrode
`in a higher layer than the electrode of the active element and
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`is electrically connected to the electroconductor via the
`in a lower layer than the first
`insulating film;
`the third
`second contact hole.
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`insulating film has a third contact hole; and the electrocon-
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`[0027]
`(2) In the configuration described in (1) above, the
`ductoris electrically connected to the electrode of the active
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`elementvia the first and third contact holes.
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`electroconductor is disposed inside and outside the first
`contact hole all over.
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`(13) In the configuration described in either one of
`[0038]
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`(10) to (12) above, the electroconductor is formed at the
`[0028]
`(3) In the configuration described in (1) or (2)
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`same step as the commonelectrode and electrically sepa-
`above, the one substrate has a third insulating film disposed
`rated from the commonelectrode.
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`in a higher layer than the electrode of the active element and
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`in a lower layer than the first
`insulating film;
`the third
`[0039]
`(14) In the configuration described in either one of
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`insulating film has a third contact hole; and the electrocon-
`(10) to (13) above,
`the electrode of the active element
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`containsin the surface thereof 1% or more of the material of
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`
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`ductoris electrically connected to the electrode of the active
`elementvia the first and third contact holes.
`the reflective electrode.
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`Page 25 of 34
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`Page 25 of 34
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`

`

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`US 2008/0007679 Al
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`Jan. 10, 2008
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`BRIEF DESCRIPTION OF THE DRAWINGS
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`[0047] These and other features, objects and advantages of
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`the present invention will become more apparent from the
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`following description when taken in conjunction with the
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`accompanying drawings wherein:
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`FIG. 1A showsa plan ofthe electrode structure of
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`the subpixel in a transflective liquid crystal display device,
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`whichis a first embodimentof the present invention;
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`[0049]
`FIG. 1B shows only the pixel electrode, counter
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`electrode andreflective electrode taken out of FIG. 1A;
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`FIG. 2 shows the essential part of a sectional
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`structure along line A-A' in FIG. 1A;
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`FIG. 3 shows the essential part of a sectional
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`structure along line B-B' in FIG. 1A;
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`FIG. 4 shows the essential part of a sectional
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`structure along line C-C' in FIG. 1A;
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`FIG. 5 shows the essential parts of the sectional
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`structures of the transmissive part and the reflective part in
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`the transflective liquid crystal display device of the first
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`embodiment;
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`FIG. 6A showsan essential part of the manufac-
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`turing process of the transflective liquid crystal display
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`device whichis the first embodiment of the invention;
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`FIG. 6B showsthe essential part following FIG. 6A
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`of the manufacturing process of the transflective liquid
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`crystal display device;
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`FIG. 6C showsthe essential part following FIG. 6B
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`(15) In the configuration described in either one of
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`of the manufacturing process of the transflective liquid
`(10) to (14) above, the electrode of the active elementis
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`formed of a material that is etched with the etchant or
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`crystal display device;
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`FIG. 6D showstheessential part following FIG. 6C
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`etching gas for the reflective electrode.
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`of the manufacturing process of the transflective liquid
`(16) In the configuration described in either one of
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`crystal display device;
`(10) to (15) above, the pixel electrode is arranged super-
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`FIG. 6E showstheessential part following FIG. 6D
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`posed over the commonelectrode, and the pixel electrode,
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`of the manufacturing process of the transflective liquid
`the second insulating film and the common electrode
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`crystal display device;
`together constitute a holding capacitance.
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`FIG. 6F showsthe essential part following FIG. 6E
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`(17) In the configuration described in either one of
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`of the manufacturing process of the transflective liquid
`(10) to (16) above, the other of the pair of substrates has a
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`counter electrode.
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`crystal display device;
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`FIG. 7 showsan equivalentcircuit to the pixel part
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`(18) A transflective liquid crystal display device
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`of liquid crystal display panel of the transflective liquid
`includes a liquid crystal display panel having a pair of
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`crystal display device which is the first embodiment of the
`substrates and a liquid crystal layer held between the pair of
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`invention;
`substrates, the liquid crystal display panel having a plurality
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`of subpixels each having a transmissive part andareflective [0061] FIG. 8 illustrates the voltage waveforms of the
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`part, wherein one of the pair of substrates has: an active
`subpixel ((PXL) (n, k)) as shown in FIG. 7;
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`element which supplies a driving potential to a counter
`FIG. 9 showsan equivalent circuit to the peripheral
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`electrode; a first insulating film disposed in a higher layer
`circuit part of the liquid crystal display panel in the trans-
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`than the electrode of the active element and havingafirst flective liquid crystal display device of thefirst embodiment;
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`contact hole; and the counter electrode disposed in a higher
`FIG. 10 shows the essential part of the sectional
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`layer than the first insulating film,
`the counter electrode
`structure of the connecting part surrounded by broken lines
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`in FIG.9;
`being electrically connected to the electrode of the active
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`elementvia the first contact hole.
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`[0064]
`FIG. 11 shows a plan ofthe electrode structure of
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`(19) In the configuration described in (18) above,
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`the subpixel in thetransflective liquid crystal display device,
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`which is the first embodiment of the invention;
`the subpixel hasa reflective electrode in the reflective part;
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`and a metal film formed at the samestep as the reflective
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`FIG. 12 showsthe reference voltages to be applied
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`electrode is electrically connected to the counter electrode
`to the counter electrode of the transmissive part and the
`inside and outside the first contact hole all over.
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`counter electrode of the reflective part in the transflective
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`[0045] Effects provided according to typical aspects of the
`liquid crystal display device of the first embodiment of the
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`invention;
`invention disclosed in the present application are stated
`below.
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`FIG. 13 showsa plan of the electrode structure of
`[0066]
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`[0046] According to the invention, it is made possible to
`the subpixelof the transflective liquid crystal display device;
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`achieve improvement of the display quality of transflective
`which is a second embodiment of the invention;
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`liquid crystal display devices while enhancing the manufac-
`[0067]
`FIG. 14 shows the essential part of a sectional
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`turing yield of transflective