LG Display Co. v. AU Optronics Corp. (709 F. Supp. 2d 311, 2010)

OPINION

FARNAN, District Judge.

In the second phase of this patent infringement action, LG Display Co., Ltd. (“LGD”) alleges infringement of four patents (collectively, the “LGD Patents”) against AU Optronics Corporation (“AUO”) and Chi Mei Optoelectronics Corporation (“CMO”): U.S. Patent No. 5,019,-002 (claim 8); U.S. Patent No. 5,825,449 (claims 10 and 11); U.S. Patent No. 6,815,-321 (claims 7, 17 and 19) and U.S. Patent No. 7,218,374 (claim 9).

The claims and counterclaims for infringement and declaratory judgment in this case arise under the patent laws of the United States, Title 35, United States Code. Accordingly, the Court has subject matter jurisdiction over Jhis action pursuant to 28 U.S.C. §§ 1331, 1338(a), and 2201(a). Personal jurisdiction over the parties exists pursuant to 10 Del. C. § 3104, the Delaware long-arm statute. D.I. 1170 at 12. Likewise, venue in this district is appropriate under 28 U.S.C. §§ 1391(b), (c) and (d) and 1400. Neither jurisdiction nor venue is contested by the parties.

This Opinion constitutes the Court’s findings of fact and conclusions of law on the claims brought by the parties.

BACKGROUND

The background relevant to this action has been set forth fully by the Court in its previous Opinion concerning the issues raised in Phase I of the trial related to AUO’s asserted patents. Like AUO’s asserted patents, the patents asserted by LGD all relate to liquid crystal display (“LCD”) products or methods of producing and assembling such products. Id., Stipulated Fact No. 13. An LCD is a flat panel display device that is used to generate images in a variety of products, including such devices as computer monitors, television screens, notebook computers and mobile phones. Id., Stipulated Fact No. 14.

DISCUSSION

I. Claim Construction

A. The Legal Principles of Claim Construction

Claim construction is a question of law. Markman v. Westview Instruments, Inc., 52 F.3d 967, 977-78 (Fed.Cir.1995), aff'd, 517 U.S. 370, 388-90, 116 S.Ct. 1384, 134 L.Ed.2d 577 (1996). When construing the claims of a patent, a court considers the literal language of the claim, the patent specification and the prosecution history. Markman, 52 F.3d at 979. Of these sources, the specification is “always highly relevant to the claim construction analysis. Usually it is dispositive; it is the single best guide to the meaning of a disputed term.” Phillips v. AWH Corporation, 415 F.3d 1303, 1312-17 (Fed.Cir.2005) (citing Vitronics Corp. v. Conceptronic, Inc., 90 F.3d 1576, 1582 (Fed.Cir.1996)). However, “[e]ven when the specification describes only a single embodiment, the claims of the patent will not be read restrictively unless the patentee has demonstrated a clear intention to limit the claim scope using ‘words or expressions of manifest exclusion or restriction.’ ” Liebel-Flarsheim Co. v. Medrad, Inc., 358 F.3d 898, 906 (Fed.Cir.2004) (quoting Teleflex, Inc. v. Ficosa N. Am. Corp., 299 F.3d 1313, 1327 (Fed.Cir.2002)).

A court may consider extrinsic evidence, including expert and inventor testimony, dictionaries, and learned treatises, in order to assist it in understanding the underlying technology, the meaning of terms to one skilled in the art and how the invention works. Phillips, 415 F.3d at 1318-19; Markman, 52 F.3d at 979-80. However, extrinsic evidence is considered less reliable and less useful in claim construction than the patent and its prosecution history. Phillips, 415 F.3d at 1318-19 (discussing “flaws” inherent in extrinsic evidence and noting that extrinsic evidence “is unlikely to result in a reliable interpretation of a patent claim scope unless considered in the context of intrinsic evidence”).

In addition to these fundamental claim construction principles, a court should also interpret the language in a claim by applying the ordinary and accustomed meaning of the words in the claim. Envirotech Corp. v. Al George, Inc., 730 F.2d 753, 759 (Fed.Cir.1984). If the patent inventor clearly supplies a different meaning, however, then the claim should be interpreted according to the meaning supplied by the inventor. Markman, 52 F.3d at 980 (noting that patentee is free to be his own lexicographer, but emphasizing that any special definitions given to words must be clearly set forth in patent). If possible, claims should be construed to uphold validity. In re Yamamoto, 740 F.2d 1569,1571 (Fed.Cir.1984).

B. CMO’s Motion For Leave To File A Memorandum In Response To LG Display’s And AUO Optronics’ Posh-Trial Briefs Addressing Key Disputed Claim Constructions (D.I. USA)

Before addressing the claim construction disputes raised by the parties, the Court must first address the Motion For Leave To File A Memorandum In Response To LG Display’s And AUO Optronics’ Post Trial Briefs Addressing Key Disputed Claim Constructions filed by CMO. Although this action has been stayed to the extent it involves CMO, CMO contends that the claim construction disputes concerning the LGD patents impact its defense of the suit brought by LGD against CMO. Therefore, CMO requests an opportunity to be heard on the claim construction issues. AUO does not oppose CMO’s Motion, but LGD has filed an opposition.

LGD contends that CMO’s Motion is improper because it was filed two days before the close of post-trial briefing, and CMO failed to meet and confer with LGD before its filing. LGD also contends that CMO participated in the claim construction briefing, and therefore, additional briefing here, in the post-trial phase of LGD’s claims against AUO, is unnecessary. According to LGD, CMO’s briefing is unfair because it provides CMO with an opportunity to argue its infringement defenses prematurely. Because claim construction is a matter of law, LGD further contends that CMO incorrectly assumes that inconsistent results could occur between the AUO trial and the CMO trial. LGD also contends that CMO’s Motion unfairly interjects information outside the trial record, including information that was excluded by the Court in the context of pretrial rulings on motions in limine, and therefore, LGD maintains that CMO’s Motion is prejudicial to LGD.

At this juncture, the Court is not inclined to grant CMO leave to file a response to LGD and AUO’s post-trial briefs. CMO has voiced its position regarding the claim construction of LGD’s patents in the context of extensive claim construction briefing and the Markman hearing held in this case. To the extent CMO’s positions are already on the record, the Court will consider them in rendering its claim construction decisions here; however, the Court will not permit CMO to interject itself into the post-trial briefing of LGD and AUO where proceedings against CMO have been stayed. Accordingly, the Court will deny CMO’s Motion For Leave To File A Memorandum In Response To LG Display’s And AU Optronics’ Post Trial Briefs Addressing Key Disputed Claim Construction.

C. LGD’s Patents

The parties dispute a number of claim terms from the asserted patents. The Court has selected for construction those terms that appear most pertinent to the disputes and trial positions argued by the parties in the post-trial briefing.

1. U.S. Patent No. 5,019,002

LGD asserts claim 8 of the '002 patent. Claim 8 is a dependent claim that stems from claim 1. Accordingly, the relevant claims of the '002 patent are provided below, in full:

1. A method of manufacturing active matrix display backplanes and displays therefrom, comprising: providing a substrate;

forming a pattern of pixels on said substrate;

forming a plurality of row and column intersecting pixel activation lines, interconnecting substantially all of said row lines to one another and substantially all of said column lines to one another;

forming an outer electrostatic discharge guard ring on said substrate coupled to said interconnected row and column lines via a resistance to provide protection from electrostatic discharges between said row and column activation lines during manufacture of the displays; and removing said outer guard ring and row and column interconnections prior to completion of the display.

8. The method as defined in claim 1 including forming an inner electrostatic discharge guard ring on said substrate coupled to said row and column lines via shunt switching elements to provide protection from electrostatic discharges between said row and column activation lines during manufacture of the displays and thereafter.

The parties agree that one of ordinary skill in the art with respect to the '002 patent at the time of its filing is a person with a bachelor’s or advanced degree in engineering or a related field, and one or more years of experience associated with semiconductors or flat panel displays. Trial Tr. II 1521:3-12 (Schlam); D.I. 1425 at 78.

a. “interconnecting substantially all ...”

LGD contends that the phrase “interconnecting substantially all of said row lines to one another and substantially all of said column lines to one another” as required by the '002 patent means “electrically connecting with conductive material all or nearly all row lines to at least one other row line and electrically connecting with conductive material all or nearly all of the column lines to at least one other column line.” D.I. 376 at Exh. B-3. LGD contends that its construction is supported by the intrinsic record which shows either each row line interconnected to one other row line and each column line interconnected to one other column line, or serially connecting the row lines and column lines where each row or column line is interconnected on one end to one row or column line and is interconnected on the other end to another row or column line.

In response, AUO contends that this phrase should be construed as “joining almost all of the row lines together and joining almost all of the column lines together.” Id. AUO contends that this construction is consistent with the plain meaning of the phrase, the teachings of the patent, and the claim construction the Court rendered in previous litigation concerning this patent. AUO also contends that LGD’s claim construction reads out the word “substantially” from the claim and attempts to broaden the claim to include semiconductor material as conductive material.

CMO contends that this phrase should be construed as “electrically connecting with conductors nearly all, but not all, of said row lines to one another and nearly all, but not all, of said column lines to one another.” Id. CMO contends that this construction is consistent with the Court’s previous construction, and LGD should not be permitted to reargue a claim construction it already argued in previous litigation.

As AUO and CMO note, the Court construed at least part of this phrase in previous litigation involving the '002 patent. In LG Philips LCD Co., Ltd. v. Tatung Co., the Court construed the term “interconnecting” to mean “electrically connecting with conductors.” 434 F.Supp.2d 292, 296 (D.Del.2006). The Court is not persuaded that its previous reasoning with respect to this construction is erroneous, and the Court finds no support in the specification for AUO’s proposed construction of “joining” as a means of clarifying any ambiguity that may exist from the term “interconnecting.” The Court also considered LGD’s argument in the previous litigation that the Court’s construction improperly limits the claim term to conductors; however, the Court noted that “the consistent use of a claim term by the inventor in the specification may serve to limit the scope of a claim.” Id.

In addition, the Court is persuaded that LGD’s construction reads out the term “substantially all” from the claim language by permitting “all.” Accordingly, the Court concludes that “interconnecting substantially all of said row lines to one another and substantially all of said column lines to one another” means “electrically connecting with conductors nearly all, but not all, of said row lines to one another and nearly all, but not all, of said column lines to one another.”

b. “resistance”

LGD contends that the term resistance should be defined as “a circuit component designed to provide opposition to electric current flowing through itself and to minimize current surge in the TFT array from electrostatic discharge.” D.I. 376 at Exh. B-8. LGD contends that its construction is appropriate, because the specification indicates that resistance minimizes discharge current surge. LGD also contends that its construction is similar to the construction adopted by the Court in the Tatung case, except that it offers further clarification by (1) replacing the term “resistance” in the construction with its plainly understood dictionary meaning, i.e. “the opposition offered by a body or substance to the passage through it of a steady electric current;” and (2) “clarifying] that the current surge must be minimized in the TFT array, to be consistent with the claims and specification.” D.I. 384 at 10.

CMO contends that the term “resistance” should be defined consistently with the definition rendered by the Court in the Tatung case. Specifically, CMO contends that “resistance” means “a circuit component that has a specified resistance to the flow of electric current and is used to minimize the current surge from an electrostatic discharge.” D.I. 376 at Exh. B-8.

In response, AUO contends that the proper construction of resistance is “a circuit component that has a specified ratio between voltage and the flow of electric current, and is used to minimize the current surge from electrostatic discharge.” Id. AUO also contends that its construction is consistent with the Court’s previous construction, except that the term “resistance” is replaced with the plain technical meaning of the term resistance from the IEEE Standard Dictionary of Electrical and Electronic Terms. AUO contends that LGD’s construction eliminates the “specified” value of resistance that the Court incorporated into its prior construction.

In reply, LGD contends that AUO’s construction seeks to limit the term “resistance” to a “resistor.” LGD contends that this construction is not supported by the specification, and one skilled in the art would not understand the term “resistance” to be limited to a resistor. D.I. 430 at 4.

In the Tatung action, the Court specifically rejected a construction which would “limit ‘resistance’ to one specific electric component, a resistor.” 434 F.Supp.2d at 298. In so doing, the Court noted that the term “resistance” is used in the claims in a manner somewhat different from its ordinary meaning to one of skill in the art. Id. at 299. Specifically, the Court stated that “[i]n the claims, the term ‘resistance’ is used consistently to denote only a circuit component used to couple the outer ESD guard ring to the interconnected row and column lines and the pickup pad.” Id. (citations omitted). With this understanding, the Court will not depart from its previous construction or rationale, and will define “resistance” as “a circuit component that has a specified resistance to the flow of electric current and is used to minimize the current surge from an electrostatic discharge.”

c. “removing said outer guard ring and row and column interconnections”

LGD contends that the phrase “removing said outer guard ring and row and column interconnections” should be construed consistently with the definition provided by the Court in the Tatung litigation. Specifically, LGD contends that the “outer electrostatic discharge guard ring” should be defined as “a closed or open ring, or open L or C-shaped line, outside the active matrix display to provide protection from electrostatic discharge” and “removing said outer guard ring and row and column intersections” should be defined as “physically disconnecting said guard ring and row and column interconnections.” D.I. 376 at Exh. B-7 & B-10. CMO agrees with these constructions. Id.

AUO contends that this entire limitation is indefinite and that the patent fails to clearly teach the removing step. AUO contends that LGD’s construction rests on an erroneous agreement between LGD and the previous defendant in the prior litigation. Alternatively, AUO contends that this phrase “removing said outer guard ring and row and column interconnections” should be construed as “physically disconnecting said guard rings and lines connecting/joining the row and column, intersecting pixel activation lines from the substrate.” Id. at B-10. AUO also contends that the “outer electrostatic discharge guard ring” should be construed as “a surrounding structure outside the active matrix display to provide protection from electrostatic discharges.” Id. at Exh B-7.

The Court has reviewed the parties’ arguments in light of the specification of the '002 patent and is not persuaded that it should depart from its previous claim construction for this term or the supporting rationale provided by the Court for that construction. 434 F.Supp.2d at 296-298. Accordingly, the Court concludes that the “outer electrostatic discharge guard ring” means “a closed or open ring, or open L or C-shaped line, outside the active matrix display to provide protection from electrostatic discharge” and “removing said outer guard ring and row and column intersections” means “physically disconnecting said guard ring and row and column interconnections.”

2. U.S. Patent No. 5,825,449 (the “'449 patent”)

LGD asserts claims 10 and 11 of the '449 patent against AUO. Claim 10 and claim 11 are independent claims. In full, claims 10 and 11 provide:

10. A liquid crystal display device comprising:

a substrate;

a first conductive layer on said substrate including:

a gate electrode,

a gate pad, and

a source pad;

a gate insulating film on said surface of said substrate, a portion of said gate insulating film overlying said gate electrode;

a semiconductor layer on said portion of said gate insulating film; an impurity-doped semiconductor layer on said semiconductor layer; a source electrode and a drain electrode on said semiconductor layer; a passivation layer overlying said source pad, said drain electrode, said gate pad, and said source electrode; a first contact hole provided through said passivation layer and said gate insulating film exposing said source pad;

a second contact hole provided through said passivation layer exposing said drain electrode; a third contact hole provided through said passivation layer and said gate insulating film exposing said gate pad; a fourth contact hole provided through said passivation layer exposing said source electrode; a pixel electrode electrically connected with said drain electrode via said second contact hole; and

a transparent conductive layer electrically connecting said source pad with said source electrode via said first contact hole and said fourth contact hole.

11. A method of manufacturing a liquid crystal display device, comprising the steps of:

forming a first conductive layer on a substrate;

patterning said first conductive layer to form a gate electrode, a gate pad and a source pad;

forming an insulating film on said substrate including said patterned conductive layer;

forming a semiconductor layer on said insulating film; forming an impurity-doped semiconductor layer on said semiconductor layer; patterning said impurity-doped semiconductor layer and said semiconductor layer to form an active layer; forming a second conductive layer overlying said substrate including said active layer;

patterning said second conductive layer to form source electrode and a drain electrode on said active layer; forming a passivation film overlying said substrate including said source pad, a portion of said drain electrode, said gate pad portion, and a portion of said source electrode; selectively etching said passivation film and said insulating film to form a first contact hole exposing said source pad, a second contact hole exposing said portion of said drain electrode, a third contact hole exposing said gate pad portion, and a fourth contact hole exposing said portion of said source electrode;

patterning a pixel electrode electrically connected to said drain electrode via said second contact hole;

patterning a first transparent conductive layer electrically connected to said gate pad through said third contact hole; and

patterning second transparent conductive layer electrically connecting said source pad to said source electrode via said first and fourth contact holes.

The parties agree that one of ordinary skill in the art with respect to the '449 patent would be a person with at least a bachelor’s degree in engineering or related science, and one or two years of experience in the semiconductor or flat panel industry. Trial Tr. 1523:4-13 (Schlam); D.I. 1425 at ¶ 1429.

a. “layer” and “conductive layer”

LGD contends that one of ordinary skill in the art would construe the term “layer” to mean “thickness of material,” and the term “conductive layer” to mean “thickness of electrically conductive material.” D.I. 376 at Exh. C-2. Although the specification of the '449 patent refers to the conductive layer that forms the gate pads, gate electrode and source pad as being of the same material, LGD contends that this limitation should not be imported into the claims. According to LGD more than one material may constitute the conductive layer, and these materials are inseparable. Therefore, LGD maintains that the claims should not be limited to a single material.

AUO and CMO do not appear to dispute the construction of the term “layer,” but instead focus on the term “conductive layer.” AUO contends that “conductive layer” should be construed in accordance with its plain meaning. Id. CMO contends that a “conductive layer” means “[a] thickness of electrically conductive material that may include one or more patterned features, all of a single material.” Id.

The Court has reviewed the parties’ positions in light of the claim language and the specification of the '449 patent, and concludes that a single material limitation is not required. '449 patent, col. 3, 11. 44-49, col. 4, 11. 46-61. In discussing Fig. 2a, the patent explains that the “conductive layer is formed on a transparent glass substrate 1 and patterned to form a gate electrode 2, a storage capacitor electrode 2D, and a gate pad 2C, all of the same material.” Id. at col. 3, 11. 44-46. However, the Court is not persuaded that the limitation of one embodiment should be imported into the claims. Accordingly, the Court concludes that a “layer” means “thickness of material,” and a “conductive layer” means “thickness of electrically conductive material.”

b. “gate electrode” and “source electrode”

LGD contends that the term “gate electrode” means “a patterned, electrically conductive material that controls current flow through the channel between the source electrode and drain electrode.” D.I. 376 at Exh. C-ll. LGD further contends that the term “source electrode” means “a patterned, electrically conductive material formed over the source region. Current flows through the channel between the source electrode and the drain electrode under the control of the gate electrode.” Id. at C-18.

CMO’s construction of gate electrode is the same as LGD’s proposed construction. Id. at C-ll. CMO’s construction of source electrode is slightly different because CMO advocates construing “a source electrode and a drain electrode” together. Thus, CMO’s definition of “source electrode” adds elements relevant to the drain electrode. Specifically, CMO contends that a “source electrode” is a “patterned electrically conductive material formed over the source region and drain region, respectively of a transistor. Current flows through the channel between the source electrode and the drain electrode and the drain electrode of the transistor under control of the gate electrode of the transistor.” Id. at C-18.

AUO’s construction of the term “gate electrode” is also similar to LGD’s construction, but varies in where the patterned electrically conductive material is formed. Specifically, AUO contends that a “gate electrode” is “a patterned electrically conductive material formed in the gate region. Current flows through the channel between the source electrode and the drain electrode under control of the gate electrode.” Id. at C-ll. With respect to the term “source electrode,” AUO agrees with LGD’s construction. Id. at C-18.

Reviewing the specification and the claim language, the Court concludes that LGD’s proposed constructions are most consistent with the claim language and the specification. '449 patent, col. 1,11. 22-38, 56-60; col. 2, 11. 37-44, 56-61; col. 3, 11. 44-49; col. 4, 11. 47-53; col. 4, 1. 65-col. 5, 1. 1, col. 5, 11. 29-38, Figs. 1-3. CMO’s construction of “gate electrode” adds the term “drain electrode,” and the Court is not persuaded that these terms must be construed together as CMO contends. Accordingly, the Court concludes that “gate electrode” means “a patterned, electrically conductive material that controls current flow through the channel between the source electrode and drain electrode,” and “source electrode” means “a patterned, electrically conductive material formed over the source region. Current flows through the channel between the source electrode and the drain electrode under the control of the gate electrode.”

c.“source pad”

LGD contends that the term “source pad” means “a portion of patterned, electrically conductive material that is provided near the periphery of the thin film transistor array to receive a data signal.” D.I. 376 at Exh. C-13. LGD contends that the '449 patent discloses that the source pad receives signals for the driving circuit, but the source pad may extend past the point of contact with the data driving circuit. D.I. 1396 at ¶ 1445-1446.

The constructions of AUO and CMO are similar, except that AUO does not provide for “a portion,” and both AUO and CMO require “the thin film transistor array to receive a data signal from a data driving circuit.” D.I. 376 at Exh. C-19. In this regard, CMO and AUO point out that the specification of the '449 patent makes it clear that the gate and source pads receive data from “gate drive and data driver respectively.” '449 patent col. 1, 11. 27-30. AUO also contends that there is no intrinsic support to limit the gate/source pad to only “a portion.”

The '449 patent was previously the subject of litigation in the Central District of California between LG Phillips LCD Co., LTD. and Tatung Co. of America, Tatung Company and Chunghwa Picture Tubes, Ltd. (the “California litigation”). In the California litigation, the court construed source pad consistently with the construction proffered by CMO. LG Philips LCD Co., Ltd. v. Tatung Co. of America, Civ. Act No. 02-6775-CBM (JTLx), at 17, 2005 WL 6219893 (C.D.Cal. May 5, 2005). While the Court is not bound by this construction, the Court concludes that it is consistent with the specification which makes it clear that the data is received from the gate drive and data driver respectively. '449 patent, col. 1, 11. 27-30, 52-55; col. 1,1. 67-col. 2,1. 4. Accordingly, the Court concludes that the term “source pad” means “a portion of patterned, electrically conductive material that is provided near the periphery of the thin film transistor array to receive a data signal from a data driving circuit.”

d.“on” and “formed on”

LGD contends that the terms “on” and “formed on” mean “above and in contact with.” D.I. 376 at C-3. The Court does not understand the parties to genuinely dispute this construction. D.I. 1425 at 236 (“Both LGD and AUO agree that the term ‘formed on’ as recited in the '449 patent requires at least “above and in contact with.”).” Accordingly, the Court construes the terms “on” and “formed on” to mean “above and in contact with.”

e.a source electrode and a drain electrode on a said semiconductor layer

LGD contends that “a source electrode and a drain electrode on said semiconductor layer” means “a source electrode and a drain electrode above and in contact with the semiconductor layer.” D.I. 376 at Exh. C-17.

AUO contends that there is ambiguity as to what layer is referred to as “said semiconductor layer” in the claim language. AUO contends that one of ordinary skill in the art would understand that the electrodes would need to be above and in contact with an impurity-doped semiconductor layer in order for the TFT to function. AUO contends that LGD’s position ignores what is commonly understood as “above and in contact with,” and ignores the construction of “source electrode,” which requires that the conductive material be formed over the source region. D.I. 1429 at 13. Thus, AUO’s proposed construction for the phrase “a source electrode and a drain electrode on said semiconductor layer” is “the source electrode and the drain electrode above, supported by, and in contact with the semiconductor layer.” D.I. 376 at Exh. C-17. CMO’s construction of this phrase is identical to LGD’s proposed construction. Id.

The Court adopts the claim construction proposed by LGD and CMO. This construction is consistent with the Court’s definition of the term “on,” and with the plain claim language and the requirements of the specification. '449 patent, col. 1, 11. 40-51; col. 1, 1. 61-col. 2, 1. 4; col. 2, 11. 37-col. 3, 1. 15; col. 3, 1. 50-col. 4, 1. 5, col. 4, 1. 65-col. 5, 1. 15, Figs. 1-3. Accordingly, the phrase “a source electrode and a drain electrode on said semiconductor layer” means “a source electrode and a drain electrode above and in contact with the semiconductor layer.”

3. U.S. Patent No. 6,815,321 (the “'321 patent”)

LGD asserts claims 7, 17 and 19 of the '321 patent. Claim 7 is an independent claim. Claims 17 and 19 are dependent claims that stem from independent claim 16. In full, the asserted claims provide:

7. A method of forming a thin film transistor comprising:

forming a first metal layer on a substrate,

forming a second metal layer on the first metal layer; simultaneously patterning the first and second metal layers to form a double-layered metal gate, so that a total width of the first metal layer is greater than a total width of the second metal layer by about 1 to 4 p.m.

16. A method of waking a thin-film transistor, comprising the steps of:

depositing a first metal layer on a substrate, the first metal layer including aluminum; depositing a second metal layer on the first metal layer without forming a photoresist on the first metal layer beforehand;

forming a single photoresist having predetermined width on the second metal layer;

patterning the first and second metal layers simultaneously in a single etching step using the single photoresist as a mask, the first metal layer being etched to have a width greater than a width of the second metal layer by about 1 to 4 m; and removing the photoresist.

17. The method of making a thin film transistor as claimed in claim 16, further comprising the steps of:

forming a first insulating layer on the substrate including the gate;

forming a semiconductor layer and an ohmic contact layer on a portion of the first insulating layer at a location corresponding to the gate;

forming a source electrode and a drain electrode extending onto the first insulating layer on two sides of the ohmic contact layer, and removing a portion of the ohmic contact layer exposed between the source and the drain electrodes; and

forming a second insulating layer covering the semiconductor layer, the source electrode, the drain electrode and the first insulating layer.

19. The method of making a thin film transistor as claimed in claim 16, wherein the first metal layer has thickness of about 500