Active matrix liquid crystal display substrate with island structure covering break in signal bus line and method of producing same

• US 5,867,233 A
• Filed: 03/26/1997
• Issued: 02/02/1999
• Est. Priority Date: 03/28/1996
• Status: Expired due to Term

• Current Assignee: Vista Peak Ventures LLC (Dominion Harbor Enterprises, LLC)
• Original Assignee: NEC Corporation
• Inventors: Tanaka, Hiroaki
• Primary Examiner(s): Gross, Anita Pellman
• Assistant Examiner(s): CHOWDHURY, TARIFUR RASHID
• Application Number:
  US08/828,743
• Time in Patent Office: 678 Days
• Field of Search: 349/42, 349/43, 349/47, 349/143, 438/158, 438/161
• US Class Current: 349/43
• CPC Class Codes: G02F 1/1368 in which the switching element is a three-electrode device G02F1/136277 takes precedence

Abstract

In an active matrix substrate of a liquid crystal display using a TFT as a switching device for each pixel, a gate bus line and a drain bus line extending perpendicular to each other are formed simultaneously by patterning a metal film, and one of the two bus lines is broken to provide a gap across which the other extends. The gap is covered by an island structure of a gate dielectric film and a semiconductor layer formed to provide the TFT, and a supplementary bus line makes direct contact with the broken bus line on both sides of the gap to provide a bridge over the gap. The supplementary bus line is formed together with a pixel electrode by patterning a transparent conductor film. By this arrangement of bus lines, the total number of photolithography steps in the production process is decreased so that the production cost can be reduced.

Claims

1. An active matrix substrate of an active matrix liquid crystal display using a thin-film transistor (TFT) as a switching device for each pixel, the active matrix substrate comprising:

an insulating substrate;

a gate bus line and a drain bus line which are formed simultaneously by patterning a metal film on said substrate and extend perpendicular to each other, one of the gate bus line and the drain bus line being broken to provide a gap across which the other extends;

an island structure of a laminate of a gate dielectric film and a semiconductor layer formed on said substrate at least over a TFT area and a bus line intersection area which contains said gap;

a gate electrode on said dielectric film in said TFT area;

a source electrode and a drain electrode each in contact with said semiconductor layer in said TFT area;

a transparent pixel electrode connected to said source electrode; and

a supplementary bus line which is in direct contact with said one of the gate bus line and the drain bus line on both sides of said gap to provide a bridge over said gap and is separated from the other bus line by said island structure in said intersection area.

2. An active matrix substrate according to claim 1, wherein said supplementary bus line and said pixel electrode are formed simultaneously by patterning a transparent conductor film.

3. An active matrix substrate of an active matrix liquid crystal dispaly using a thin-film transistor (TFT) as a switching device for each pixel, the active matrix substrate comprising:

an insulating substrate;

a gate electrode formed on a surface of said substrate;

a gate bus line and a drain bus line which are formed on said surface of said substrate and extend perpendicular to each other, one of the gate bus line and the drain bus line is broken to provide a gap across which the other extends without intersecting said one;

an island structure of a gate dielectric film and a semiconductor layer formed on said surface of said substrate at least over a TFT area containing said gate electrode and a bus line intersection area containing said gap;

a source electrode and a drain electrode formed on said island structure;

a transparent pixel electrode which is formed on said surface of said substrate and is contiguous to said source electrode; and

a supplementary bus line which extends over said island structure in said intersection area and makes direct contact with said one of the gate bus line and the drain bus line on both sides of said gap to provide a bridge over said gap.

4. An active matrix substrate according to claim 3, wherein said gate electrode, said gate bus line and said drain bus line are formed simultaneously by patterning a metal film, said source electrode, said drain electrode, said pixel electrode and said supplementary bus line being formed simultaneously by patterning a transparent conductor film.

5. An active matrix substrate according to claim 3, wherein said one of the gate bus line and the drain bus line is the drain bus line.

6. An active matrix substrate of an active matrix liquid crystal dispaly using a thin-film transistor (TFT) as a switching device for each pixel, the active matrix substrate comprising:

an insulating substrate;

a source electrode and a drain electrode formed on a surface of the substrate;

a transparent pixel electrode which is formed on said surface of the substrate and is contiguous to said source electrode;

a supplementary bus line which is formed on said surface of the substrate;

an island structure of a gate dielectric film and a semiconductor layer formed on said surface of the substrate at least over a TFT area including the source and drain electrodes and a bus line intersection area through which said supplementary bus line extends;

a gate electrode formed on said island structure; and

a gate bus line and a drain bus line which extend perpendicular to each other, wherein one of the gate bus line and the drain bus line extends on said island structure in said intersection area and the other is in direct contact with said supplementary bus line and is broken in said intersection area to provide a gap across which said island structure and the bus line thereon extend.

7. An active matrix substrate according to claim 6, wherein said source electrode, said drain electrode, said pixel electrode and said supplementary bus line are formed simultaneously by patterning a transparent conductor film, said gate electrode, said gate bus line and said drain bus line being formed simultaneously by patterning a metal film.

8. An active matrix substrate according to claim 6, wherein said one of the gate bus line and the drain bus line is the drain bus line.

9. A method of producing an active matrix substrate of an active matrix liquid crystal display using a thin-film transistor (TFT) as a switching device for each pixel, the method comprising the steps of:

(a) depositing a metal film on an insulating substrate;

(b) patterning said metal film to form a gate electrode, a gate bus line and a drain bus line which extends perpendicular to said gate bus line, one of said gate bus line and said drain bus line being broken to provide a gap across which the other extends without intersecting said one;

(c) forming an island structure of a gate dielectric film and a semiconductor layer on said substrate at least over a TFT area containing said gate electrode and a bus line area containing said gap and said other of the gate bus line and the drain bus line;

(d) depositing a transparent conductor film on said substrate inclusive of said island structure and the broken bus line; and

(e) patterning said transparent conductor film to form a source electrode and a drain electrode on said island structure in said TFT area, a pixel electrode contiguous to said source electrode and a supplementary bus line which extends over said island structure above said gap and makes direct contact with said one of the gate bus line and the drain bus line on both sides of said gap to provide a bridge over said gap.

10. A method according to claim 9, wherein said one of the gate bus line and the drain bus line is the drain bus line, said supplementary bus line being contiguous to said drain electrode.

11. A method of producing an active matrix substrate of an active matrix liquid crystal display using a thin-film transistor (TFT) as a switching device for each pixel, the method comprising the steps of:

(a) depositing a transparent conductor film on an insulating substrate;

(b) patterning said transparent conductor film to form a source electrode, a drain electrode, a pixel electrode contiguous to said source electrode and a supplementary bus line;

(c) forming an island structure of a semiconductor layer and a gate dielectric film on said substrate at least over a TFT area containing the source and drain electrodes and a bus line intersection area through which said supplementary bus line extends, the island structure being formed such that a portion of the drain electrode and said supplementary bus line on both sides of said elongate area are exposed;

(d) depositing a metal film on said substrate inclusive of said island structure and said supplementary bus line; and

(e) patterning said metal film to form a gate electrode on said island structure in said TFT area together with a gate bus line and a drain bus line, wherein one of the gate bus line and the drain bus line extends on said island structure in said intersection area and the other is in direct contact with said supplementary bus line and is broken in said intersection area to provide a gap across which said island structure and the bus line thereon extend.

12. A method according to claim 11, wherein said one of the gate bus line and the drain bus line is the gate bus line.