SEL EXHIBIT NO. 2028
`INNOLUX CORP. v. PATENT OF SEMICONDUCTOR ENERGY
`LABORATORY CO., LTD.
`
`IPR2013-00028
`
`

`

`(12) United States Patent
`Lee et al.
`
`(10) Patent No.2
`(45) Date of Patent:
`
`US 6,219,124 B1
`*Apr. 17, 2001
`
`US006219124B1
`
`(54) LIQUID CRYSTAL DISPLAY DEVICE WITH
`REDUCED RESISTANCE TO COMMON
`VOLTAGES, AND RELATED METHODS
`
`5,825,439 * 10/1998 Noriyama ........................... .. 349/152
`
`* cited by examiner
`
`(75)
`
`Inventors: Jung-hee Lee; Kweon-sam Hong, both
`of Kyungki-do
`
`(73) Assignee: Samsung Electronics Co., Ltd. (KR)
`
`Primary Exczminer—William L. Sikes
`Assistant Exczminer—Dung Nguyen
`(74) Attorney, Agent, or Firm—Myers, Bigel Sibley &
`Sajovec
`
`(*) Notice:
`
`This patent issued on a continued pros-
`ecution application filed under 37 CFR
`1.53(d), and is subject to the twenty year
`patent
`term provisions of 35 U.S.C.
`154(a)(2).
`
`Subject to any disclaimer, the term of this
`patent is extended or adjusted under 35
`U.S.C. 154(b) by 0 days.
`
`(21) Appl. No.: 08/838,727
`
`(22) Filed:
`
`Apr. 10, 1997
`
`(30)
`
`Foreign Application Priority Data
`
`Apr. 10, 1996
`
`(KR)
`
`............................................... .. 96-10756
`
`Int. Cl.7 ................................................. .. G02F 1/1343
`(51)
`
`(52) U.S. Cl.
`................ ..
`349/147; 349/148
`(58) Field of Search ................................... .. 349/147, 144,
`349/148, 149, 51, 152
`
`(56)
`
`References Cited
`U.S. PATENT DOCUMENTS
`
`5,285,300 *
`5,323,252 *
`5,717,475 *
`
`2/1994 Suzuki et al.
`6/1994 Yoshida etal.
`2/1998 Kamio etal.
`
`........................ .. 359/54
`359/54
`...................... .. 349/147
`
`(57)
`
`ABSTRACT
`
`A liquid crystal display device that comprises a thin film
`transistor array panel including a voltage transfer circuit that
`includes a pad region for receiving a common voltage, a
`short region for transferring the common voltage, and a
`center region that connects the pad region to the short
`region. The center region includes a composite conductive
`layer comprising a first electrically conductive layer of a first
`resistance and a second electrically conductive layer of a
`second resistance, wherein the first resistance is less than the
`second resistance. The first electrically conductive layer of
`the composite conductive layer preferably comprises a mate-
`rial of relatively low resistance, such as aluminum or an
`aluminum alloy. In addition, the first electrically conductive
`layer may include an anodic oxide layer for inhibiting
`hillock formations. The liquid crystal display device further
`includes a color filter panel which includes a common
`electrode and a conductive member that electrically con-
`nects the common electrode to the short region of the thin
`film transistor array panel. In another embodiment, the first
`electrically conductive layer extends from the pad region to
`the short region and is exposed at either region. In yet
`another embodiment, the first electrically conductive layer
`extends from the center region to the short region Where it
`is exposed at the short region.
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`4 Claims, 2 Drawing Sheets
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`U.S. Patent
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`Apr. 17, 2001
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`Sheet 1 of 2
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`US 6,219,124 B1
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`(PRIOR ART)
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`U.S. Patent
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`Apr. 17, 2001
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`Sheet 2 of 2
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`US 6,219,124 B1
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`US 6,219,124 B1
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`1
`LIQUID CRYSTAL DISPLAY DEVICE WITH
`REDUCED RESISTANCE TO COMMON
`VOLTAGES, AND RELATED METHODS
`
`FIELD OF THE INVENTION
`
`The present invention generally relates to display devices,
`and more particularly, to liquid crystal display devices.
`BACKGROUND OF THE INVENTION
`
`A liquid crystal display (LCD) typically includes a thin
`film transistor array panel, a color filter panel, and a liquid
`crystal layer sandwiched between the thin film transistor
`array and the color filter panel.
`In this design, the thin film transistor array panel will
`generally include thin film transistors, pixel electrodes, gate
`lines and data lines. The color filter panel, on the other hand,
`will generally include color filters and a common electrode.
`In operation, a gate electrode of a thin film transistor in the
`transistor array panel is supplied with a gate driving signal
`from a gate driver via a gate line which activates the thin film
`transistor. Therefore, a data signal applied to a source
`electrode of the thin film transistor from a data driver via a
`
`data line is supplied to the pixel electrode in order to switch
`the LCD pixel of the liquid crystal layer. In addition, the
`common electrode of the color filter panel is supplied with
`a common voltage through dummy pads of an out lead
`bonding (OLB) region and conductive members made of
`silver paste which are formed in the outer regions of the thin
`film transistor array panel. It is desirable that the paths
`through which the gate driving signals and common voltages
`pass have low resistivity in order to improve low voltage
`operation and reduced cross-talk. However, the paths of the
`common voltages encounter numerous resistances such as
`the contact resistance of the dummy pads, the resistance of
`the dummy pads themselves,
`the contact resistance of a
`common voltage driving circuit, the contact resistance of the
`conductive members connecting the dummy pads and the
`common electrode, and the resistance of the common elec-
`trode which is typically made of indium-tin-oxide (ITO).
`Several of these resistances are discussed in more detail
`below with reference to FIG. 1 which shows a cross-
`
`sectional view of a voltage transfer circuit from an OLB pad
`region to a short region that is connected to a common
`electrode.
`
`In FIG. 1, a thin film transistor array panel includes a
`lower substrate 1 on which a gate insulating layer 3 is
`formed. A metal layer 5 which is connected to a data line is
`formed on the insulating layer 3. The metal
`layer 5 is
`typically made of chromium (Cr). Apassivation layer 7 with
`two holes is formed on the metal layer 5, and an ITO layer
`9 is formed thereover and connected to the metal layer 5
`through the two holes. The thin film transistor array panel
`includes a dummy pad region B for receiving the external or
`common voltage and a short region A where a conductive
`member 11 electrically connects the thin film transistor array
`panel to the color filter panel. The color filter panel includes
`an upper substrate 19 covering a black matrix 13. Adjacent
`to the black matrix 13 is an overcoat layer 15. In addition,
`a common electrode 17 which is typically made of ITO is
`formed over the common electrode 17. Accordingly,
`the
`conductive member 11 contacts the ITO layer 9 of the thin
`film transistor array panel at the short region A and the
`common electrode 17 of the color filter panel, as shown.
`When a common voltage supply from the common volt-
`age driving circuit is applied to the dummy pad region B, the
`resulting voltage at the common electrode 17 is less than the
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`applied common voltage because of the resistance in the pad
`region B having the structure of insulator/Cr/ITO layers, the
`resistance in the short region A having the structure of
`insulator/Cr/ITO layers, the resistance in a central region
`between the pad region B and the short region A having the
`structure of insulator/Cr/passivation/ITO layers, and the
`resistance in the conductive member 11. In particular, it is
`noted that the resistivity in the pad region B is relatively
`large due to its structure of the Cr/ITO layers. Further, the
`resistance from the center region to the short region A is
`relatively large due to the large resistivity of the chromium
`comprising the metal layer 5. As a result of the resistance to
`the common voltage, an increase in cross-talk may occur in
`the liquid crystal display. Thus, it would be desirable to be
`able to reduce the resistivity to the common voltage applied
`in order to reduce the presence of cross-talk in the LCD.
`SUMMARY OF THE INVENTION
`
`It is therefore an object of the present invention to provide
`a liquid crystal display (LCD) with decreased resistance to
`a common voltage applied to a common electrode of a color
`filter panel, and methods of forming same.
`Another object of the present invention is to provide an
`LCD having reduced cross-talk, and methods of forming
`same.
`
`Another object of the present invention is to provide an
`LCD having improved electrode and display characteristics,
`and methods of forming same.
`These and other objects are provided in accordance with
`the present invention by LCD devices having voltage trans-
`fer circuits with preferred composite conductive layers. The
`composite conductive layer comprises a first electrically
`conductive layer of a first resistance and a second electri-
`cally conductive layer of a second resistance, wherein the
`first resistance is less than the second resistance. Thus, the
`overall resistance of the composite conductive layer is
`reduced by the lower resistance of the first layer. Therefore,
`material having a relatively high resistance but a favorable
`operational characteristic such as a favorable contact for-
`mation with indium-tin-oxide (ITO), can be utilized in the
`second conductive layer without significantly increasing the
`resistance of the composite conductive layer.
`In a first embodiment of the present invention, a liquid
`crystal display device comprises a thin film transistor array
`panel, a color filter panel including a common electrode, and
`a conductive member that electrically connects the common
`electrode to the thin film transistor array panel. The thin film
`transistor array panel comprises a voltage transfer circuit
`that includes a pad region for receiving a common voltage,
`a short region for transferring the common voltage, and a
`center region that connects the pad region to the short
`region. The center region includes a composite conductive
`layer comprising a first electrically conductive layer of a first
`resistance and a second electrically conductive layer of a
`second resistance, wherein the first resistance is less than the
`second resistance.
`
`The first conductive layer preferably comprises aluminum
`or an alloy thereof. As for the second conductive layer, it
`preferably comprises chromium (Cr), molybdenum (Mo),
`titanium (Ti), or tantalum (Ta). In addition, a liquid crystal
`display device may include an anodic oxide layer formed on
`the first conductive layer in order to reduce hillock forma-
`tion.
`
`In the first embodiment, the second conductive layer of
`the composite conductive layer extends from the pad region
`to the short region of the voltage transfer circuit. Further, an
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`US 6,219,124 B1
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`3
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`indium-tin-oxide (ITO) layer formed over the composite
`conductive layer contacts the second conductive layer at the
`pad region and the short region.
`In a second embodiment,
`the first conductive layer
`extends from the pad region to the short region and is
`exposed in either region. Therefore, the conductive member
`contacts the first conductive layer at the short region in order
`to form the electrical connection to the common electrode of
`
`the color filter panel. At the pad region, the common voltage
`is applied directly to the first conductive layer. As with the
`first embodiment, an anodic oxide layer may be formed on
`the first conductive layer for inhibiting hillock formation.
`In a third embodiment, the first conductive layer extends
`from the center region to the short region and the second
`conductive layer extends from the pad region to the center
`region. Further, an ITO layer is formed over the composite
`conductive layer in the pad region and the center region, and
`contacts the second conductive layer at
`the pad region.
`Again, an anodic oxide layer may be formed on the first
`conductive layer for inhibiting hillock formations.
`Methods for fabricating liquid crystal display devices in
`accordance with the present invention comprise the follow-
`ing steps. A first step includes forming a thin film transistor
`array panel including a voltage transfer circuit that includes
`a pad region for receiving a common voltage, a short region
`for transferring the common voltage, and a center region that
`connects the pad region to the short region, wherein the
`center region includes a composite conductive layer com-
`prising a first electrically conductive layer of a first resis-
`tance and second electrically conductive layer of a second
`resistance and wherein the first resistance is less than the
`
`second resistance. A second step includes forming a color
`filter panel
`including a common electrode. A third step
`includes forming a conductive member that electrically
`connects the common electrode to the short region of the
`thin film transistor array panel. In the above method, it is
`preferred that the first conductive layer of the composite
`conductive layer comprises aluminum or an alloy thereof.
`Further, the second conductive layer preferably comprises
`either Cr, Mo, Ti or Ta. In addition, another step may include
`forming an anodic oxide layer on the first conductive layer
`in order to inhibit hillock formations.
`
`Other features and advantages of the present invention
`will become apparent
`to one with skill
`in the art upon
`examination of the following drawings and detailed descrip-
`tion.
`It is intended that all such additional features and
`
`advantages be included herein in the scope of the present
`invention, as defined by the appended claims.
`BRIEF DESCRIPTION OF THE DRAWINGS
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`FIG. 1 is a cross-sectional view of a voltage transfer
`circuit of a liquid crystal display (LCD) in accordance with
`the prior art.
`FIG. 2 is a cross-sectional view of a voltage transfer
`circuit of an LCD in accordance with a first embodiment of
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`the present invention.
`FIG. 3 is a cross-sectional view of a voltage transfer
`circuit of an LCD in accordance with a second embodiment
`
`of the present invention.
`FIG. 4 is a cross-sectional view of a voltage transfer
`circuit of an LCD in accordance with a third embodiment of
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`the present invention.
`DETAILED DESCRIPTION OF THE
`PREFERRED EMBODIMENTS
`
`The present invention will now be described more fully
`hereinafter with reference to the accompanying drawings, in
`
`4
`which preferred embodiments of the invention are shown.
`This invention may, however, be embodied in different
`forms and should not be construed as limited to the embodi-
`ments set forth herein. Rather, these embodiments are pro-
`vided so that this disclosure will be thorough and complete,
`and will fully convey the scope of the invention to those
`skilled in the art. The elements of the drawings are not
`necessarily to scale, emphasis instead being placed upon
`clearly illustrating the principles of the present invention.
`Furthermore, like numbers refer to like elements throughout.
`With reference to FIG. 2, a voltage transfer circuit of a
`liquid crystal display (LCD) device in accordance with a
`first embodiment of the present invention is illustrated. The
`voltage transfer circuit is formed on a lower substrate 100
`and includes a short region A, a pad region B, and a center
`region C. The lower substrate 100 includes an active region
`(not shown) having thin film transistors and pixel electrodes,
`as is well known in the art. An example of a configuration
`of an active region of an LCD device can be found, for
`example, in U.S. Pat. No. 5,940,055 entitled “Liquid Crystal
`Displays With Row-Selective Transmittance Compensation
`And Of Operation Thereof”, filed on Mar. 13, 1997 and
`having application Ser. No. 08/816,866 (Attorney Docket
`No. 5649-238),
`the disclosure of which is incorporated
`herein by reference as if set forth in full. An aluminum
`layer 102 is formed on the lower substrate 100 in a center
`region C. A gate insulating layer 103 is formed on the lower
`substrate 100 outside the pad region B and short region A.
`An aluminum oxide layer 104 (e.g., A1203) may be formed
`by anodic oxidation on the surface of the aluminum layer
`102 in order to inhibit hillock formation. A chromium layer
`105 is then formed over the aluminum layer 102 and the
`substrate 100 so as to cover the aluminum layer 102 and to
`contact the substrate 100 in the pad region B and the short
`region A, as shown. Apassivation layer 107 is formed on the
`chromium layer 105 and is patterned to form two openings,
`one at the pad region B and one at the short region A. An
`indium-tin-oxide (ITO) 109 is then formed over the passi-
`vation layer 107 and the openings therein so as to contact
`and cover the chromium layer 105 in the pad region B and
`the short region A. A conductive member 111 is formed in
`the short region A to establish an electrical contact with a
`color filter panel. The color filter panel comprises an upper
`substrate 200, a black matrix 113, an overcoat layer 115, and
`a common electrode 117.
`
`Thus, the chromium layer 105 and the aluminum layer
`102 form a composite conductive layer for transferring the
`voltage received at the pad region B to the short region A
`where it is then transferred to the common electrode 117 via
`the conductive member 111. However, chromium has a
`relatively high resistance which can lead to an increased
`time constant (RC) delay associated with a data line and can
`reduce the maximum viewing angle of the display.
`Therefore,
`in order to decrease resistance in the voltage
`transfer circuit, the aluminum layer 102 of relatively lower
`resistance is provided in the center region C. The aluminum
`layer 102 is preferably separated from the ITO layer 109 by
`the chromium layer 105 above because it has been deter-
`mined by the inventors herein that the use of a chromium
`layer to separate an ITO layer from an aluminum layer
`reduces the likelihood that parasitic aluminum oxide (A1203
`clusters will form in the ITO layer in response to aluminum-
`metal migration.
`These oxide clusters typically act as electrical insulators
`and increase contact resistance. As will be understood by
`those skilled in the art, these insulating clusters are typically
`formed when current passes through an aluminum/ITO
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`contact and causes aluminum atoms to migrate into the ITO.
`This parasitic phenomenon is typically referred to as “metal
`migration”. Accordingly, the chromium layer 105 extends
`from pad region B to the short region “A” and contacts the
`ITO layer 109 in both regions so that direct electrical contact
`between Al and ITO does not occur.
`
`With reference to FIG. 3, a voltage transfer circuit of an
`LCD in accordance with a second embodiment of the
`
`present invention is illustrated. As shown, an aluminum
`layer 102, a portion of which is covered by an aluminum
`oxide layer 104, extends from a pad region B to a short
`region A. A chromium layer 105 is formed over the alumi-
`num layer 102 and is patterned to expose the aluminum layer
`102 in the pad region B and the short region A. Apassivation
`layer 107 is then formed over the chromium layer 105 and
`is also patterned so as to expose the aluminum layer 102 in
`the pad region B and the short region A, as shown. In this
`embodiment, a connector member 111 contacts the alumi-
`num layer 105 at the short region A and electrically connects
`the aluminum layer 105 to a common electrode 117 on an
`upper substrate 200. The composite conductive layer, as in
`the first embodiment, comprises the aluminum layer 102 and
`the chromium layer 105. Note, an ITO layer is not neces-
`sarily formed on the thin film transistor array panel in this
`embodiment.
`
`With reference to FIG. 4, a voltage transfer circuit of an
`LCD in accordance with a third embodiment of the present
`invention is illustrated. This embodiment is essentially a
`hybrid of the first and second embodiments wherein the pad
`region B and center region C are substantially identical to
`that of the first embodiment and the short region A is
`substantially identical to that of the second embodiment.
`Specifically, an aluminum layer 102 extends from a center
`region C to a short region A. A chromium layer 105, on the
`other hand, extends from a pad region B to the center region
`C. An ITO layer 109 extends from the pad region B to the
`center region C and contacts the chromium layer 105 at the
`pad region B. As with the first and second embodiments, the
`composite conductive layer comprises the aluminum layer
`102 and the chromium layer 105.
`It should be noted that
`for each of the above
`embodiments, the layer 105 may be formed from refracta-
`tory metals other than chromium, such as molybdenum
`(Mo), titanium (Ti) or tantalum (Ta). Also, layer 102 may be
`formed out of an aluminum alloy such as aluminum—
`neodymium alloy (Al—Nd).
`Amethod for fabricating a liquid crystal display device in
`accordance with the present invention comprises the follow-
`ing steps. A first step includes forming a thin film transistor
`array panel
`including a voltage transfer segment
`that
`includes a pad region for receiving a common voltage, a
`short region for transferring the common voltage, and a
`
`6
`center region that connects the pad region to the short
`region. The center region includes a composite conductive
`layer comprising a first electrically conductive layer of a first
`resistance and a second electrically conductive layer of a
`second resistance, wherein the first resistance is less than the
`second resistance. A second step includes forming a color
`filter panel that includes a common electrode. A third step
`includes forming a conductive member that electrically
`connects a common electrode to the short region of the thin
`film transistor array panel. In addition, another step may
`include the formation of an anodic oxidation layer on the
`first conductive layer.
`
`In the drawings and specification, there have been dis-
`closed typical preferred embodiments of the invention and,
`although specific terms are employed, they are used in a
`generic and descriptive sense only and not for purposes of
`limitation, the scope of the invention being set forth in the
`following claims.
`What is claimed is:
`1. A liquid crystal display device, comprising:
`
`including a voltage
`a thin film transistor array panel
`transfer circuit that includes a pad region for receiving
`a common voltage, a short region for transferring said
`common voltage, a center region that connects said pad
`region and said short region, wherein said thin film
`transistor array panel
`includes a wire of a double-
`layered structure including an upper layer and a lower
`layer having lower resistance than that of the upper and
`directly formed on a substrate, a passivation layer
`having first and second contact holes respectively
`exposing said wire on said pad region and said short
`region, and a transparent conductive layer which is
`formed from said pad region to said short region and
`connected to said wire through said first and second
`contact holes, respectively;
`a color filter panel including a common electrode; and
`a conductive member that electrically connects said com-
`mon electrode of the color filter panel to said transpar-
`ent conductive layer or the wire of said short region of
`said thin film transistor array panel.
`2. The liquid crystal display of claim 1, wherein the upper
`layer comprises a material chosen from the group consisting
`of chromium, molybdenum, titanium and tantalum, and the
`lower layer comprises aluminum or aluminum alloy.
`3. The liquid crystal display of claim 1, wherein said
`transparent conductive layer is made of indium tin oxide.
`4. The liquid crystal display of claim 1, further comprising
`a gate insulating layer, which is formed on said substrate and
`is removed from said pad region to said short region.
`
`