Liquid crystal display device

• US 20030227590A1
• Filed: 06/06/2003
• Published: 12/11/2003
• Est. Priority Date: 06/06/2002
• Status: Active Grant

• Current Assignee: Panasonic Intellectual Property Corporation of America (Panasonic Holdings Corporation)
• Original Assignee: Hitachi Displays Limited (Japan Display Incorporated)
• Inventors: Ono, Kikuo, Oke, Ryutaro, Ochiai, Takahiro
• Granted Patent: US 6,816,221 B2
• Time in Patent Office: Days
• US Class Current: 349/141
• CPC Class Codes: G02F 1/134363 for applying an electric field parallel to the substrate, i.e. in-plane switching [IPS]
• CPC Class Codes: G02F 1/136286 Wiring, e.g. gate line, drain line

Abstract

An active matrix type liquid crystal display device according to the invention includes in each pixel a semiconductor layer of a thin film transistor, a first insulating film formed on the semiconductor layer, a gate line formed on the first insulating film, a second insulating film formed on the gate line, and a drain line formed on the second insulating film. The bottom side of the gate line is opposed to the semiconductor layer with the first insulating film interposed therebetween, and the top side of the gate line is covered with a metal electrode formed on the second insulating film by the same process as the drain line, whereby leak electric fields from the gate line are shielded. Particularly in an IPS type liquid crystal display device using low temperature poly silicon TFTs is constructed in the above-described manner, a wide viewing angle and a bright display image are obtained.

Claims

1. An active matrix type liquid crystal display device of a lateral electric field type, comprising:

a first substrate and a second substrate disposed in opposition to each other with a liquid crystal layer interposed therebetween;

a plurality of gate lines formed on the first substrate;

a plurality of drain lines formed to intersect the plurality of gate lines in matrix form;

thin film transistors respectively formed with respect to intersections of the gate lines and the drain lines; and

pixels each provided in an area surrounded by a pair of gate lines adjacent to one another and a pair of drain lines adjacent to one another, the first substrate including in each of the pixels;

a semiconductor layer formed on the first substrate;

a first insulating film formed on the semiconductor layer;

a gate line formed on the first insulating film;

a second insulating film formed on the gate line;

a drain line formed on the second insulating film;

a third insulating film formed on the drain line; and

a common electrode or a common electrode line formed on the third insulating film,

the semiconductor layer being connected to a corresponding one of the thin film transistors near which one of the pair of the gate lines adjacent to one another is formed, and having an area which is formed under another of the pair of the gate lines adjacent to one another with the first insulating film interposed therebetween.

2. An active matrix type liquid crystal display device according to claim 1, wherein the semiconductor layer is formed under the another of the pair of the gate lines adjacent to one another with the first insulating film interposed therebetween, and an electrode is formed over the another of the pair with at least the second insulating film interposed therebetween.

3. An active matrix type liquid crystal display device according to claim 2, wherein the electrode is a metal electrode formed with the second insulating film interposed between the electrode and the another gate line.

4. An active matrix type liquid crystal display device according to claim 2, wherein a shield electrode for leak electric fields from the another gate line is formed by the semiconductor layer formed under the another of the pair of the gate lines adjacent to one another with the first insulating film interposed therebetween and the electrode formed over the another gate line with at least the second insulating film interposed therebetween.

5. An active matrix type liquid crystal display device according to claim 2, wherein at least a side portion of the another of the pair of the gate lines adjacent to one another is, in plan view, covered with the common electrode and the electrode formed with at least the second insulating film interposed between the electrode and the another of the pair.

6. An active matrix type liquid crystal display device according to claim 1, wherein the third insulating film is an organic film.

7. An active matrix type liquid crystal display device according to claim 1, wherein the common electrode formed on the third insulating film is a transparent electrode.

8. An active matrix type liquid crystal display device according to claim 4, wherein the insulating film interposed between the semiconductor layer and the electrode which constitute the shield electrode is formed by stacking a gate insulating film of the thin film transistor and an interlayer insulating film which separates the gate line and the drain line.

13. An active matrix type liquid crystal display device according to claim 1, wherein the semiconductor layer connected to the thin film transistor is made of a poly-crystalline silicon film.

9. An active matrix type liquid crystal display device of a lateral electric field type, comprising:

a first substrate and a second substrate disposed in opposition to each other with a liquid crystal layer interposed therebetween;

a plurality of gate lines formed on the first substrate;

a plurality of charge-holding capacitance lines;

a plurality of drain lines formed to intersect the plurality of gate lines in matrix form;

thin film transistors respectively formed with respect to intersections of the gate lines and the drain lines; and

pixels each provided in an area surrounded by a pair of gate lines adjacent to one another and a pair of drain lines adjacent to one another,

the first substrate including in each of the pixels;

a semiconductor layer formed on the first substrate;

a first insulating film formed on the semiconductor layer;

a gate line formed on the first insulating film;

a second insulating film formed on the gate line;

a drain line formed on the second insulating film;

a third insulating film formed on the drain line; and

a common electrode formed on the third insulating film,

the charge-holding capacitance lines each of which extends in an extending direction of a corresponding one of the drain lines being provided under the corresponding drain line,

the common electrode which extends in an extending direction of each of the drain lines being provided over each of the drain lines.

10. An active matrix type liquid crystal display device according to claim 9, wherein, in each of the pixels, the semiconductor layer extends under the drain line and has an area which extends into a portion under a corresponding one of the charge-holding capacitance lines extending in the extending directions of the respective drain lines and forms a charge-holding capacitance.

11. An active matrix type liquid crystal display device according to claim 10, wherein the semiconductor layer is connected to a corresponding one of the thin film transistors near which one of the pair of the gate lines adjacent to one another is formed, and has an area which is formed under another of the pair of the gate lines adjacent to one another with the first insulating film interposed therebetween,

the semiconductor layer forming a shield electrode for leak electric fields with respect to one of the pair of the gate lines adjacent to one another, and forming a charge-holding capacitance with respect to the corresponding one of the charge-holding capacitance lines extending under the respective drain lines.

12. An active matrix type liquid crystal display device according to claim 9, wherein the charge-holding lines and the common lines are connected to one another outside a display area and are given the same potential.

14. An active matrix type liquid crystal display device according to claim 9, wherein the semiconductor layer connected to the thin film transistor is made of a poly-crystalline silicon film.