Ferroelectric liquid crystal display device comprising gate-overlapped lightly doped drain structure

• US 9,214,532 B2
• Filed: 08/20/2007
• Issued: 12/15/2015
• Est. Priority Date: 11/09/1998
• Status: Expired due to Fees

• Current Assignee: Semiconductor Energy Laboratory Co., Ltd.
• Original Assignee: Semiconductor Energy Laboratory Co., Ltd.
• Inventors: Yamazaki, Shunpei, Adachi, Hiroki
• Primary Examiner(s): Nadav, Ori
• Application Number:
  US11/841,307
• Publication Number:
  US 20080048189A1
• Time in Patent Office: 3,039 Days
• Field of Search: 257/69, 257/72, 257/344, 257/347, 257/351, 257/412, 438/305
• US Class Current: 1/1
• CPC Class Codes: H01L 2029/7863 with an LDD consisting of more than one lightly doped zone or having a non-homogeneous dopant distribution, e.g. graded LDD
• CPC Class Codes: H01L 27/124 with a particular composition, shape or layout of the wiring layers specially adapted to the circuit arrangement, e.g. scanning lines in LCD pixel circuits wiring structures per se H01L23/52
• CPC Class Codes: H01L 29/42384 for thin film field effect transistors, e.g. characterised by the thickness or the shape of the insulator or the dimensions, the shape or the lay-out of the conductor
• CPC Class Codes: H01L 29/4908 for thin film semiconductor, e.g. gate of TFT
• CPC Class Codes: H01L 29/6675 Amorphous silicon or polysilicon transistors
• CPC Class Codes: H01L 29/66757 Lateral single gate single channel transistors with non-inverted structure, i.e. the channel layer is formed before the gate
• CPC Class Codes: H01L 29/78621 with LDD structure or an extension or an offset region or characterised by the doping profile
• CPC Class Codes: H01L 29/78627 with a significant overlap between the lightly doped drain and the gate electrode, e.g. GOLDD

Abstract

The present invention relates to a semiconductor device including a circuit composed of thin film transistors having a novel GOLD (Gate-Overlapped LDD (Lightly Doped Drain)) structure. The thin film transistor comprises a first gate electrode and a second electrode being in contact with the first gate electrode and a gate insulating film. Further, the LDD is formed by using the first gate electrode as a mask, and source and drain regions are formed by using the second gate electrode as the mask. Then, the LDD overlapping with the second gate electrode is formed. This structure provides the thin film transistor with high reliability.

Claims

1. A display device comprising:

a pixel circuit over a substrate, comprising;

a gate wiring over the substrate;

a source wiring crossing the gate wiring;

a first pixel and a second pixel adjacent to each other with the gate wiring interposed therebetween, the first pixel comprising;

a pixel TFT comprising;

a first portion of a semiconductor layer comprising a channel formation region, a pair of LDD regions, a source region and a drain region;

a gate insulating film provided over the semiconductor layer; and

a gate electrode provided over the gate insulating film, each of the pair of LDD regions comprising a first top portion overlapping with the gate electrode and a second top portion not overlapping with the gate electrode, a capacitor comprising a capacitor electrode, a second portion of the semiconductor layer overlapped with the capacitor electrode, and a portion of the gate insulating film overlapped with the capacitor electrode;

wherein the gate electrode is a portion of the gate wiring,

wherein the first portion of the semiconductor layer is overlapped with the source wiring,

an insulating film comprising silicon nitride over the pixel TFT,

wherein the gate electrode comprises a first conductive layer, a second conductive layer provided over the first conductive layer, and a third conductive layer provided over the second conductive layer, the third conductive layer being in direct contact with a side surface of the second conductive layer, a side surface of the first conductive layer, and the gate insulating film;

wherein the first conductive layer and the third conductive layer each comprise a material selected from the group consisting of titanium, tantalum, tungsten and molybdenum, and

wherein the second conductive layer comprises a material selected from the group consisting of aluminum and copper.

2. A display device according to claim 1, wherein the semiconductor layer comprises a microcrystal semiconductor.

3. A display device according to claim 1, wherein the semiconductor layer comprises a crystalline semiconductor.

4. An electronic equipment comprising the display device according to claim 1,

wherein the electronic equipment belongs to the group consisting of personal computer, a digital camera, a video camera, a portable information terminal such as a mobile computer, a cellular phone, or an electronic book and a navigation system for vehicles.

5. A display device according to claim 1,

wherein the first conductive layer overlaps with the channel formation region and the third conductive layer covers a top portion and side portions of the first conductive layer.

6. A display device according to claim 1,

wherein the display device is a liquid crystal display device.

7. A display device according to claim 1,

wherein the display device is an electroluminescence display device.

8. A display device comprising:

a substrate;

a transistor over the substrate, the transistor comprising a semiconductor layer formed on an insulating surface, the semiconductor layer comprising a channel formation region;

an electrode of a capacitor over the substrate, the electrode comprising an n-type semiconductor layer formed on the insulating surface;

a first insulating film over the transistor and the electrode of the capacitor;

a first electrode over the first insulating film and electrically connected to the transistor;

a light emitting layer over the first electrode, the light emitting layer comprising an organic compound;

a second electrode over the first electrode so that the light emitting layer is disposed between the first electrode and the second electrode;

a covering material over the second electrode, wherein a main surface of the covering material faces the second electrode;

a first sealing material interposed between the substrate and the covering material, wherein the first sealing material is disposed along peripheries of the substrate and the covering material; and

a second sealing material outside of and along the first sealing material, wherein the second sealing material is continuous and is in contact with a side surface and a first part of a rear surface of the covering material and is not in contact with a second part of the rear surface,

wherein the rear surface is a surface opposite to the main surface, and

wherein the side surface is a surface between the main surface and the rear surface.

9. A display device according to claim 8,

wherein the semiconductor layer comprises a microcrystal semiconductor.

10. A display device according to claim 8,

wherein the semiconductor layer comprises a crystalline semiconductor.

11. A display device according to claim 8,

wherein the transistor comprises a gate insulating film over the channel formation region and a gate electrode over the gate insulating film,

wherein the gate electrode comprises a first conductive layer, a second conductive layer provided over the first conductive layer, and a third conductive layer provided over the second conductive layer, the third conductive layer being in direct contact with a side surface of the second conductive layer, a side surface of the first conductive layer, and the gate insulating film;

wherein the first conductive layer and the third conductive layer each comprise a material selected from the group consisting of titanium, tantalum, tungsten and molybdenum, and

wherein the second conductive layer comprises a material selected from the group consisting of aluminum and copper.

12. A display device according to claim 11,

wherein the first conductive layer overlaps with the channel formation region and the third conductive layer covers a top portion and side portions of the first conductive layer.

13. A display device according to claim 8,

wherein the display device further comprises a second insulating film comprising silicon nitride over the transistor and the electrode of the capacitor.

14. A display device according to claim 8,

wherein the display device further comprises a transparent conductive film over the n-type semiconductor layer.

15. An electronic equipment comprising the display device according to claim 8, wherein the electronic equipment belongs to the group consisting of personal computer, a digital camera, a video camera, a portable information terminal such as a mobile computer, a cellular phone, or an electronic book and a navigation system for vehicles.

16. A display device according to claim 8, wherein the second sealing material is in contact with a part of the main surface of the covering material.

17. A display device comprising:

a substrate having an insulating surface;

a transistor comprising a crystalline silicon layer over the insulating surface, a gate insulating film over the crystalline silicon layer, and a gate electrode over the gate insulating film;

a capacitor over the insulating surface, the capacitor including a first capacitor electrode comprising an n-type semiconductor layer, a first insulating film formed of the same layer as the gate insulating film over the first capacitor electrode, and a second capacitor electrode comprising the same layer as the gate electrode over the first insulating film;

a second insulating film over the transistor and the capacitor;

a first electrode over the second insulating film and electrically connected to the transistor;

a light emitting layer over the first electrode, the light emitting layer comprising an organic compound;

a second electrode over the first electrode so that the light emitting layer is disposed between the first electrode and the second electrode;

a covering material over the second electrode, wherein a main surface of the covering material faces the second electrode;

a first sealing material interposed between the substrate and the covering material, wherein the first sealing material is disposed along peripheries of the substrate and the covering material; and

a second sealing material outside of and along the first sealing material, wherein the second sealing material is continuous and is in contact with a side surface and a first part of a rear surface of the covering material and is not in contact with a second part of the rear surface,

wherein the rear surface is a surface opposite to the main surface, and

wherein the side surface is a surface between the main surface and the rear surface.

18. A display device according to claim 17,

wherein the gate electrode comprises a first conductive layer, a second conductive layer provided over the first conductive layer, and a third conductive layer provided over the second conductive layer, the third conductive layer being in direct contact with a side surface of the second conductive layer, a side surface of the first conductive layer, and the gate insulating film;

wherein the first conductive layer and the third conductive layer each comprise a material selected from the group consisting of titanium, tantalum, tungsten and molybdenum, and

wherein the second conductive layer comprises a material selected from the group consisting of aluminum and copper.

19. A display device according to claim 18,

wherein the first conductive layer overlaps with a channel formation region of the transistor and the third conductive layer covers a top portion and side portions of the first conductive layer.

20. A display device according to claim 17,

wherein the display device further comprises a third insulating film comprising silicon nitride over the transistor and the capacitor.

21. An electronic equipment comprising the display device according to claim 17,

wherein the electronic equipment belongs to the group consisting of personal computer, a digital camera, a video camera, a portable information terminal such as a mobile computer, a cellular phone, or an electronic book and a navigation system for vehicles.

22. A display device according to claim 17, wherein the second sealing material is in contact with a part of the main surface of the covering material.