Thin film transistor and display device including same

• US 5,365,079 A
• Filed: 02/05/1993
• Issued: 11/15/1994
• Est. Priority Date: 04/30/1982
• Status: Expired due to Term

• Current Assignee: Seiko Epson Corporation (Seiko Group)
• Original Assignee: Seiko Epson Corporation (Seiko Group)
• Inventors: Oshima, Hiroyuki, Mano, Toshihiko, Kodaira, Toshimoto
• Primary Examiner(s): JACKSON JR, JEROME
• Application Number:
  US08/014,053
• Time in Patent Office: 648 Days
• Field of Search: 357/23.7, 357/4, 357/59, 257/72, 257/71, 257/59, 359/59
• US Class Current: 257/59
• CPC Class Codes: G02F 1/133512 Light shielding layers, e.g. black matrix G02F1/136209 takes precedence
• CPC Class Codes: G02F 1/13454 Drivers integrated on the active matrix substrate G02F1/136277 takes precedence
• CPC Class Codes: G02F 1/136209 Light shielding layers, e.g. black matrix, incorporated in the active matrix substrate, e.g. structurally associated with the switching element
• CPC Class Codes: G02F 1/136213 Storage capacitors associated with the pixel electrode
• CPC Class Codes: G02F 1/136227 Through-hole connection of the pixel electrode to the active element through an insulation layer
• CPC Class Codes: G02F 1/1368 in which the switching element is a three-electrode device G02F1/136277 takes precedence
• CPC Class Codes: G02F 2202/104 poly-Si
• CPC Class Codes: H01L 23/53209 based on metals, e.g. alloys, metal silicides H01L23/53285 takes precedence
• CPC Class Codes: H01L 23/5386 Geometry or layout of the interconnection structure
• CPC Class Codes: H01L 27/1248 with a particular composition or shape of the interlayer dielectric specially adapted to the circuit arrangement
• CPC Class Codes: H01L 27/1255 integrated with passive devices, e.g. auxiliary capacitors
• CPC Class Codes: H01L 29/41725 Source or drain electrodes for field effect devices with monocrystalline semiconductor on source/drain region H01L29/0843
• CPC Class Codes: H01L 29/458 for thin film silicon, e.g. source or drain electrode
• CPC Class Codes: H01L 29/78633 with a light shield
• CPC Class Codes: H01L 2924/00 Indexing scheme for arrangements or methods for connecting or disconnecting semiconductor or solid-state bodies as covered by H01L24/00
• CPC Class Codes: H01L 2924/0002 Not covered by any one of groups H01L24/00, H01L24/00 and H01L2224/00

Abstract

Improved thin film transistors resistant to photo-induced current and having improved electrical contact between electrodes and the source or drain regions are provided. The thin film transistors formed in accordance with the invention are particularly well suited for use in an active matrix substrate for a liquid crystal display panel. The liquid crystal display panels include an additional insulating layer formed between crossing orthogonal source lines and gate lines to provide a higher breakdown voltage between the source lines and gate lines than at the gate insulating layer of the thin film transistors.

Claims

1. A liquid crystal display device, comprising:

a pair of opposed and spaced apart insulating substrates;

a liquid crystal material in the space between the substrates;

a plurality of substantially parallel source lines and a plurality of substantially parallel gate lines orthogonal to the source lines disposed on one substrate and a cross-over insulator formed of two insulating layers between the intersecting source and gate lines, the intersecting source and gate lines and two layer cross-over insulator therebetween forming a cross-over capacitor having a cross-over capacitance;

a plurality of picture elements in a matrix array at the intersections of the source and gate lines;

each picture element including a transparent liquid crystal driving electrode and a switching element coupled to the associated intersecting source and gate lines and a gate insulating layer under the gate line at the switching element; and

a display capacitor electrode formed on the substrate and covered by the liquid crystal driving electrode and a capacitive insulating layer between the display capacitor electrode and the liquid crystal driving electrode for forming a display capacitor having a display capacitance;

wherein the cross-over capacitance per unit area of the two layer cross-over capacitor is less than the display capacitance per unit area of said display capacitor.

2. The liquid crystal display device of claim 1, wherein the total thickness of the insulating layers of the cross-over capacitor is at least 5000 Å

.

3. The liquid crystal display device of claim 1, wherein the thickness of the insulating layer of the display capacitor is less than 5000 Å

.

4. The liquid crystal display device of claim 1, wherein the total thickness of the insulating layers of the cross-over capacitor is at least 5000 Å

and the thickness of the insulating layer of the display capacitor is less than about 5000 Å

.

5. The liquid crystal display device of claim 1, wherein the thickness off the insulating layer of the display capacitor is about 1000 Å

or less.

6. A liquid crystal display device of claim 1, wherein the switching element is a thin film transistor.

7. A liquid crystal display device as described in claim 1, wherein the thickness of said cross-over insulator at the intersection of the source and gate lines is greater than the thickness of the insulator in any other region of the picture element.

8. The liquid crystal display device of claim 1, wherein at least a portion of said driving electrode is disposed over at least a portion of one of said gate lines and switching elements.

9. The liquid crystal display device of claim 1, wherein at least one of said substrates is glass.

10. The liquid crystal display device of claim 1, wherein each switching element includes a transistor having a thin film semiconductor layer on one of said substrates, said transistor including a channel region, a source and a drain region spaced apart by said channel region in said semiconductor layer, said gate insulating layer on the surface of said semiconductor layer, a second semiconductor layer selectively patterned to form the gate lines and a gate electrode of the transistor, a first thin insulating layer formed across said one substrate, a second thicker insulating layer formed across the surface and selectively removed except in the region where the gate lines intersect the source lines, the driving electrodes disposed in the first insulating layer and the source lines disposed over the first and second insulating layers at the intersection with the gate lines.

11. The liquid crystal display device of claim 10, wherein the first insulating layer at the intersection comprises a material selected from the group consisting of silicon oxide, silicon nitride and aluminum oxide.

12. The liquid crystal display device of claim 10, wherein the first insulating layer is about 1000 angstroms thick.

13. The liquid crystal display device of claim 10, wherein said second insulating layer is also disposed over said first insulating layer on each transistor.

14. The liquid crystal display device of claim 13, wherein the first insulating layer comprises a material selected from the group consisting of silicon oxide, silicon nitride and aluminum oxide and the second insulating layer comprises another of said group.

15. The liquid crystal display device of claim 14, wherein said first insulating layer is about 1000 angstroms thick and said second insulating layers about 5000 angstroms thick.

16. The liquid crystal display device of claim 10, wherein said semiconductor thin film is selected from the group consisting of polycrystalline silicon, amorphous silicon and cadmium selenide.

17. The liquid crystal display device of claim 16, wherein said thin film comprises polycrystalline silicon.

18. The liquid crystal display device of claim 10, wherein said insulating substrate is selected from one of glass and quartz.

19. The liquid crystal display device of claim 10, wherein the driving electrode is a transparent electrode in contact with the drain region of the transistor.

20. The liquid crystal display device of claim 19, wherein said transparent electrode is selected from the group consisting of indium oxide, tin oxide or indium tin oxide.

21. The liquid crystal display device of claim 19, wherein the contact portion between said display electrode and one of said source region and drain region is covered by a metallic layer.

22. The liquid crystal display device of claim 21, wherein said metallic layer is aluminum.

23. The liquid crystal display device of claim 10, wherein said first and second insulating layers are silicon dioxide.

24. The liquid crystal display device of claim 10, wherein said first thin insulating layer is silicon nitride disposed on the semiconductor layer and said second thicker insulating layer is silicon dioxide disposed on the silicon nitride layer.

25. The liquid crystal display device of claim 10, wherein said gate insulating layer is a thermal oxide layer.

26. A liquid crystal display device, comprising:

a pair of opposed and spaced apart insulating substrates;

a liquid crystal material in the space between the substrates;

a plurality of substantially parallel source lines and a plurality of substantially parallel gate lines orthogonal to the source lines disposed on one substrate and a cross-over insulator formed of two insulating layers between the intersecting lines, the intersecting lines and two layer insulator therebetween forming a cross-over capacitor having a cross-over capacitance;

a plurality of picture elements in a matrix array at the intersections of the source and gate lines;

each picture element including a transparent liquid crystal driving electrode and a switching element coupled to the associated intersecting source and gate lines and a gate insulating layer under the gate line at the switching element; and

a display capacitor electrode formed on the substrate and covered by the liquid crystal driving electrode and a capacitive insulating layer between the display capacitor electrode and the liquid crystal driving electrodes for forming a display capacitor having a display capacitance;

wherein the thickness of the cross-over insulating layer of the cross-over capacitor is greater than the capacitive insulating layer of the display capacitor so that the breakdown voltage of the cross-over insulator of the cross-over capacitor is greater than the breakdown voltage of the gate insulating layer and wherein the cross-over capacitance per unit area of the cross-over capacitor is less than the display capacitance per unit area of said display capacitor.

27. The liquid crystal display device of claim 26, wherein the thickness of the cross-over insulating layers of the cross-over capacitor is at least 5000 angstroms.

28. The liquid crystal display device of claim 26, wherein the thickness of the capacitor insulating layer of the display capacitor is less than 5000 angstroms.

29. The liquid crystal display device of claim 26, wherein the thickness of the cross-over insulating layers of the cross-over capacitor is at least 5000 angstroms and the thickness of the capacitive insulating layer of the display capacitor is less than about 5000 angstroms.

30. The liquid crystal display device of claim 26, wherein the thickness of the capacitive insulating layer of the display capacitor is about 1000 angstroms.

31. The liquid crystal display device of claim 26, wherein the switching element is a thin film transistor.

32. The liquid crystal display device of claim 26, wherein the capacitive insulating layer extends into and forms part of the cross-over insulator.

33. The liquid crystal display device of claim 26, wherein the capacitance of the display capacitor is greater than the capacitance of the liquid crystal material.

34. The liquid crystal display device of claim 27, wherein the thickness of the capacitive insulating layer of the display capacitor is about 1000 angstroms.

35. The liquid crystal display device of claim 29, wherein the switching element is a thin film transistor.

36. The liquid crystal display device of claim 34, wherein the switching element is a thin film transistor.

37. The liquid crystal display device of claim 29, wherein the capacitance of the display capacitor is greater than the capacitance of the liquid crystal material.

38. The liquid crystal display device of claim 31, wherein the capacitance of the display capacitor is greater than the capacitance of the liquid crystal material.