Liquid display device

• US 20010048498A1
• Filed: 02/09/2001
• Published: 12/06/2001
• Est. Priority Date: 03/30/2000
• Status: Active Grant

• Current Assignee: Panasonic Liquid Crystal Display Company Limited (Panasonic Holdings Corporation)
• Original Assignee: Hitachi Displays Limited (Japan Display Incorporated)
• Inventors: Tomioka, Yasushi, Kondo, Katsumi, Oaku, Hitoshi, Okishiro, Kenji, Umeda, Yoshiyuki
• Granted Patent: US 6,704,082 B2
• Time in Patent Office: Days
• US Class Current: 349/123
• CPC Class Codes: G02F 1/133397 for suppressing after-image or image-sticking
• CPC Class Codes: G02F 1/133723 Polyimide, polyamide-imide
• CPC Class Codes: G02F 1/134363 for applying an electric field parallel to the substrate, i.e. in-plane switching [IPS]

Abstract

In a liquid crystal display device of IPS mode, occurrence of a sticking-image and after-image phenomenon is prevented.

A liquid crystal display device comprising a pair of substrates, at least one of the substrates being transparent; a liquid crystal layer interposed between the pair of substrates; and pixel electrodes and common electrodes and active elements arranged on at least one substrate between the pair of substrates, wherein a pair of alignment layers are made of an organic polymer of polyamic acid group or polymamide ester group having a relative imidization ratio above 60%; or at least one layer of an insulation film is interposed between the alignment layer in a side of the substrate having the group of electrodes formed thereon, and the pixel electrode and the common electrode disposed under the alignment layer to prevent occurrence of the sticking image and the after image by flattening the electrode portions to moderate electric field concentration.

Claims

1. A liquid crystal display device comprising a pair of substrates, at least one of said substrates being transparent;

a liquid crystal layer interposed between said pair of substrates; and

pixel electrodes and common electrodes and active elements arranged on at least one substrate between said pair of substrates, liquid crystal of said liquid crystal layer being controlled to perform display by applying a voltage between said pixel electrode and said common electrode, wherein

an alignment layer is disposed on a surface in contact with said liquid crystal layer of each of said pair of substrates, and

said alignment layer is made of an organic polymer selected from the group consisting of polyamic acid group polymers and polymamide ester group polymers having a relative imidization ratio above 60%.

2. A liquid crystal display device according to

claim 1

, wherein said alignment layer is made of an organic polymer selected from the group consisting of polyamic acid group polymers and polymamide ester group polymers having a relative imidization ratio above 70%.

3. A liquid crystal display device according to any one of claims 1 and 2, wherein said active element is a thin film transistor.

4. A liquid crystal display device according to any one of

claims 1

to

3

, wherein at least one of said pixel electrode and said common electrode is formed of a transparent electric conductive film.

5. A liquid crystal display device according to

claim 4

, wherein said transparent electric conductive film is an ion doped titanium oxide film or an ion doped zinc oxide (ZnO) film.

6. A liquid crystal display device according to any one of

claims 1

to

5

, wherein alignment control directions of the liquid crystal in the two interfaces between said liquid crystal layer and said pair of substrates are nearly equal to each other.

7. A liquid crystal display device according to any one of

claims 1

to

6

, wherein said amic acid group organic polymer contains at least one kind of group selected from the group consisting of methyl ester group, ethyl ester group and propyl ester group.

8. A liquid crystal display device according to any one of

claims 1

to

7

, wherein at least one of said pair of alignment layers is a layer made of a photo-reactive material.

9. A liquid crystal display device according to

claim 8

, wherein said alignment layer is formed by irradiating nearly linearly polarized light onto said layer made of the photo-reactive material.

10. A liquid crystal display device according to any one of

claims 1

to

9

, wherein a pretilt angle of said liquid crystal layer is smaller than 5 degrees.

11. A liquid crystal display device comprising a pair of substrates, at least one of said substrates being transparent;

a liquid crystal layer interposed between said pair of substrates; and

pixel electrodes and common electrodes and active elements arranged on at least one substrate between said pair of substrates, liquid crystal of said liquid crystal layer being controlled to perform display by applying a voltage between said pixel electrode and said common electrode, wherein

an alignment layer is formed on a surface in contact with said liquid crystal layer of each of said pair of substrates, and

at least one layer of an insulation film is disposed between said alignment layer in a side of the substrate having said electrodes formed thereon and an electrode which is closer to said alignment layer between said pixel electrode and said common electrode.

13. A liquid crystal display device according to any one of claims 11 and 12, wherein a thickness T of said insulation film interposed between said alignment layer in a side of the substrate having said electrodes formed thereon and an electrode which is closer to said alignment layer between said pixel electrode and said common electrode is larger than a value of one fourth of an interval L between said pixel electrode and said common electrode.

14. A liquid crystal display device according to any one of claims 11 and 12, wherein a thickness T of said insulation film interposed between said alignment layer in a side of the substrate having said electrodes formed thereon and an electrode which is closer to said alignment layer between said pixel electrode and said common electrode is larger than a value of one half of an interval L between said pixel electrode and said common electrode.

15. A liquid crystal display device according to

claim 11

, wherein a magnitude of dielectric constant ∈

_PAS of said insulation film is smaller than an average dielectric constant ∈

_LC of said liquid crystal layer.

16. A liquid crystal display device according to any one of

claims 11

to

15

, which is constructed so that an interval L between said pixel electrode and said common electrode within a display region where change of an optical characteristic due to liquid crystal movement contributes to display and a thickness D of said liquid crystal layer within said display region may satisfy the relation L<

2D.

17. A liquid crystal display device according to any one of

claims 11

to

16

, wherein level difference on a surface of said alignment layer in contact with the liquid crystal at uppermost portions of said pixel electrode and said common electrode is flattened by at least one of said insulation film and said alignment layer.

18. A liquid crystal display device according to

claim 17

, wherein the level difference on a surface of said alignment layer in contact with the liquid crystal in the side of the substrate on which said pixel electrodes and said common electrodes are formed is smaller than 50 nm.

19. A liquid crystal display device according to any one of

claims 11

to

18

, wherein said insulation film is formed in a range covering over all the display region where change of an optical characteristic due to liquid crystal movement contributes to display.

20. A liquid crystal display device according to any one of

claims 11

to

19

, wherein at least one layer of said insulation films is an inorganic insulation film.

21. A liquid crystal display device according to any one of

claims 11

to

19

, wherein at least one layer of said insulation films is an organic insulation film.

22. A liquid crystal display device according to any one of

claims 11

to

19

, wherein said insulation film is composed of two layers of an organic insulation film and an inorganic insulation film.

23. A liquid crystal display device according to any one of claims 20 and 22, wherein at least one layer of said insulation films is an inorganic insulation film made of at least one kind of material selected from the group consisting of silicon nitride, silicon oxide and polysiloxane group materials.

24. A liquid crystal display device according to any one of claims 21 and 22, wherein said organic insulation film is made of at least one kind of organic polymer selected from the group consisting of polyimide group polymers, acrylic group polymers and epoxy-acrylate group polymers.

25. A liquid crystal display device according to any one of claims 11 and 24, wherein said said active element is a thin film transistor.

26. A liquid crystal display device according to any one of

claims 11

to

25

, wherein at least one of said pixel electrode and said common electrode is formed of a transparent electric conductive film.

27. A liquid crystal display device according to

claim 26

, wherein said transparent electric conductive film is an ion doped titanium oxide film or an ion doped zinc oxide (ZnO) film.

28. A liquid crystal display device according to any one of

claims 11

to

27

, wherein alignment control directions of the liquid crystal in the two interfaces between said liquid crystal layer and said pair of substrates are nearly equal to each other.

29. A liquid crystal display device according to any one of

claims 11

to

28

, wherein said pair of alignment layers individually formed on the surfaces in contact with said liquid crystal layer of said pair of substrates are made of an organic polymer selected from the group consisting of polyamic acid group polymers and polymamide ester group polymers having a relative imidization ratio above 60%.

30. A liquid crystal display device according to any one of

claims 11

to

28

, said alignment layer is made of an organic polymer selected from the group consisting of polyamic acid group polymers and polymamide ester group polymers having a relative imidization ratio above 70%.

31. A liquid crystal display device according to any one of claims 29 and 30, wherein said amic acid group organic polymer contains at least one kind of group selected from the group consisting of methyl ester group, ethyl ester group and propyl ester group.

32. A liquid crystal display device according to any one of

claims 11

to

28

, wherein a surface elastic modulus of said pair of alignment layers formed on the surfaces in contact with said liquid crystal layer of said pair of substrates is larger than 1 GPa.

33. A liquid crystal display device according to any one of

claims 11

to

28

, wherein a glass transition temperature Tg of interfaces between said pair of alignment layers formed on the surfaces in contact with said liquid crystal layer of said pair of substrates and said liquid crystal layer is higher than a nematic-isotropic phase transition temperature T(N—

I) of a liquid crystal composition forming said liquid crystal layer.

34. A liquid crystal display device according to any one of

claims 11

to

28

, wherein a glass transition temperature Tg of interfaces between said pair of alignment layers formed on the surfaces in contact with said liquid crystal layer of said pair of substrates and said liquid crystal layer is higher than 220°

C.

35. A liquid crystal display device according to any one of

claims 11

to

28

, wherein said alignment layer is made of an organic polymer of dehydration ring closure of polyamic acid composed of diamine compounds expressed by a chemical formula N2N—

R—

NH2 and tetracarboxilic acid anhydride expressed by a chemical formula and total number of bonding groups making a molecular axis of polymer rotatable such as —

O—

, —

S—

, —

CH₂—

, —

C(CH₃)₂—

,—

C(CF₃)₂—

, —

SO₂—

, bonding group in the meta position, and bonding group in the ortho position contained in the R position and the X position in the repetitive structure of the organic polymer is equal to and less three.

36. A liquid crystal display device according to any one of

claims 11

to

35

, wherein at least one of said pair of alignment layer is a photo-reactive material layer.

37. A liquid crystal display device according to

claim 36

, wherein said alignment layer is formed by irradiating nearly linearly polarized light onto said layer made of the photo-reactive material.

38. A liquid crystal display device according to any one of

claims 11

to

37

, wherein a pretilt angle of said liquid crystal layer is smaller than 5 degrees.

12. A liquid crystal display device comprising a pair of substrates, at least one of said substrates being transparent;

a liquid crystal layer interposed between said pair of substrates; and

pixel electrodes and common electrodes and active elements arranged on at least one substrate between said pair of substrates, liquid crystal of said liquid crystal layer being controlled to perform display by applying a voltage between said pixel electrode and said common electrode, wherein

at least two layers of insulation films are disposed between said pixel electrode and said common electrode.