In-plane switching liquid crystal display apparatus with reduced capacitance between pixel electrodes and common electrodes

• US 6,507,383 B1
• Filed: 06/29/2000
• Issued: 01/14/2003
• Est. Priority Date: 03/21/2000
• Status: Expired due to Term

• Current Assignee: Panasonic Liquid Crystal Display Company Limited (Panasonic Holdings Corporation)
• Original Assignee: Hitachi, Ltd.
• Inventors: Nishimura, Etsuko, Ono, Kikuo, Abe, Makoto, Wakagi, Masatoshi, Nakayoshi, Yoshiaki
• Primary Examiner(s): Ton, Toan
• Assistant Examiner(s): Rude, Timothy L
• Application Number:
  US09/582,655
• Time in Patent Office: 929 Days
• Field of Search: 349/141
• US Class Current: 349/141
• CPC Class Codes: G02F 1/133345 Insulating layers G02F1/1335, G02F1/1337, G02F1/135, G02F1/136 take precedence
• CPC Class Codes: G02F 1/134363 for applying an electric field parallel to the substrate, i.e. in-plane switching [IPS]

Abstract

A liquid crystal display unit in which a voltage is applied to a pixel electrode and a common signal electrode constituted by two upper and lower transparent conductive layers having insulation layers disposed therebetween so that a liquid crystal is driven to control display can improve any one or both of reduction of a writing time of the liquid crystal (reduction of a capacitance between the pixel electrode and the common signal electrode) and reduction of a driving voltage of the liquid crystal. An inter-layer insulation layer between the transparent electrodes formed of different layers is constituted by at least one or a laminated structure of a part of a gate insulation layer, a part of a surface protection layer of a thin film transistor and an applied-type insulation layer and insulation layers in an area which is positioned above the lower transparent electrode.

Claims

1. A liquid crystal display unit including a pair of substrates, a liquid crystal layer disposed between said pair of substrates, a plurality of scanning signal lines, a plurality of image signal lines intersecting said plurality of scanning signal lines in matrix manner and a plurality of thin film transistors each formed in the vicinity of each intersection between said scanning signal lines and said image signal lines disposed on one of said substrates, a plurality of pixels at least one of which is formed in each area enclosed by said plurality of scanning signal lines and image signal lines and each of which includes a common signal electrode connected across a plurality of pixels and a pixel electrode connected to said thin film transistor corresponding thereto, said common signal electrode and said pixel electrode partially overlapping each other through an inter-layer insulation layer, at least part of each of said pixel electrode and said common signal electrode being constituted by a transparent conductive layer, one of said pixel electrode and said common signal electrode disposed on the side of said liquid crystal layer through an insulation layer being formed into slits or teeth of a comb,

wherein at least one of insulation layers included in said inter-layer insulation layer is selectively formed in an area which is positioned above one of said pixel electrode and said common electrode which is disposed nearer to said one of substrates with said insulation layer therebetween and where said pixel electrode or said common electrode disposed above does not exist;

and

wherein a liquid crystal having Δ

∈

of a negative value is used as said liquid crystal layer and when $\frac{1}{\underset{k=l}{\overset{n}{\sum <br><br>}}<br><br>\frac{d_k}{{\mathrm{\varepsilon <br><br>}}_k}}$

 

is S_A where the number of insulation layers included in said inter-layer insulation layer is n and a dielectric constant of a k-th insulation layer is ∈

_k, a thickness thereof being d_k, and $\frac{1}{\left(\underset{i=l}{\overset{m}{\sum <br><br>}}<br><br>\frac{d_1}{{\mathrm{\varepsilon <br><br>}}_1}\right)+\frac{\underset{k=l}{\overset{n}{\sum <br><br>}}<br><br>d_k-\underset{i=l}{\overset{m}{\sum <br><br>}}<br><br>d_1}{{\mathrm{\varepsilon <br><br>}}_{\mathrm{LC}}}}$

(where m≧

1) is S_B where the number of insulation layers disposed between a first orientation layer disposed above a first substrate and a first electrode of said pixel electrode and said common electrode, nearer to said first substrate through insulation layers in an area which is positioned above said first electrode and where a second electrode does not exist is m and a dielectric constant of an insulation layer constituting a first layer is ∈

₁, a thickness thereof being d₁, a dielectric constant of a liquid crystal in a vertical direction to a director of the liquid crystal being ∈

_LC, S_A<

S_B is satisfied.

2. A liquid crystal display unit according to claim 1, wherein when $\frac{1}{\sum _{}^{}}$

k=1n

dkɛ

k

is S_A where any insulation layer does not exist between said first orientation layer disposed above said first substrate and said first electrode in the area which is positioned above said first electrode of said pixel electrode and said common electrode nearer to said first substrate through the insulation layers and where said second electrode does not exist and the number of insulation layers included said inter-layer insulation layer is n, a dielectric constant of said k-th insulation layer being ∈

_k, a thickness thereof being d_k and $\frac{{\mathrm{\varepsilon <br><br>}}_{\mathrm{LC}}}{\underset{k=1}{\overset{n}{\sum <br><br>}}<br><br>d_k}$

is S_B where a dielectric constant of the liquid crystal in the vertical direction to the director of the liquid crystal ∈

_LC, S_A<

S_B is satisfied.

4. A liquid crystal display unit according to claim 1, wherein when $\frac{1}{\sum _{}^{}}$

k=1n

dkɛ

k

is S_A where any insulation layer does not exist between said first orientation layer disposed above said first substrate and said first electrode in the area which is positioned above said first electrode of said pixel electrode and said common electrode nearer to said first substrate through the insulation layers and where said second electrode does not exist and the number of insulation layers included said inter-layer insulation layer is n, a dielectric constant of said k-th insulation layer being ∈

_k, a thickness thereof being d_k and $\frac{{\mathrm{\varepsilon <br><br>}}_{\mathrm{LC}}}{\underset{k=1}{\overset{n}{\sum <br><br>}}<br><br>d_k}$

is S_B where a dielectric constant of the liquid crystal in the parallel direction to the director of the liquid crystal being ∈

_LC, S_A<

S_B is satisfied.

5. A liquid crystal display unit according to any of claims 1 to 4, wherein at least one of the number of layers, a thickness of material forming the layers and a dielectric constant of the material forming the layers is different among said inter-layer insulation layer and insulation layers disposed between said first orientation layer formed above said first substrate and said first electrode in the area which is positioned above said first electrode and where said second electrode does not exist.

6. A liquid crystal display unit according to any of claims 1-4, wherein said inter-layer insulation layer is constituted by a single layer and said single layer is selectively formed in conformity with a shape of said second electrode in a part of an area where said second electrode is disposed rather than the area which is positioned above said first electrode and where said second electrode does not exist.

7. A liquid crystal display unit according to claim 6, wherein said inter-layer insulation layer is a part of a first insulation layer having function of a gate insulation layer of said thin film transistor or a part of a second insulation layer having function of a surface protection layer of said thin film transistor.

8. A liquid crystal display unit according to claim 6, wherein said inter-layer insulation layer is a third insulation layer other than a first insulation layer having function of a gate insulation layer of said thin film transistor or a second insulation layer having function of a surface protection layer of said thin film transistor.

9. A liquid crystal display layer according to any of claims 1-4, wherein said inter-layer insulation layer is constituted by two layers and at least one layer thereof is selectively formed in conformity with a shape of said second electrode in a part of an area where said second electrode is disposed rather than the area which is positioned above said first electrode and where said second electrode does not exist.

10. A liquid crystal display layer according to claim 9, wherein said inter-layer insulation layer is constituted by two layers including a part of a first insulation layer having function of a gate insulation layer of said thin film transistor and a part of a second insulation layer having function of a surface protection layer of said thin film transistor.

11. A liquid crystal display unit according to claim 9, wherein one layer of said inter-layer insulation layers is a part of a first insulation layer having function of a gate insulation layer of said thin film transistor or a part of a second insulation layer having function of a surface protection layer of said thin film transistor and the other is a third insulation layer other than said first and second insulation layers, which is selectively formed in conformity with the shape of said second electrode in the part of the area where said second electrode is disposed rather than the area which is positioned above said first electrode and where said second electrode does not exist.

12. A liquid crystal display unit according to claim 9, wherein one layer of said inter-layer insulation layers is any of a part of a first insulation layer having function of a gate insulation layer of said thin film transistor or a part of a second insulation layer having function of a surface protection layer of said thin film transistor and the other is a fourth insulation layer other than said first and second insulation layers, which is formed in a part of an area except an area for forming a through-hole for connecting said second electrode to other electrode wiring and an area for exposing a terminal.

13. A liquid crystal display unit according to claim 9, wherein said inter-layer insulation layer is constituted by a laminated layer including a third insulation layer other than a first insulation layer having function of a gate insulation layer of said thin film transistor or a second insulation layer having function of a surface protection layer of said thin film transistor, which is selectively formed in conformity with the shape of said second electrode in the part of the area where said second electrode is disposed rather than the area which is positioned above said first electrode and where said second electrode does not exist, and a fourth insulation layer formed in a part of an area except an area for forming a through-hole for connecting said second electrode to other electrode wiring and an area for exposing a terminal.

14. A liquid crystal display unit according to any of claims 1-4, wherein said inter-layer insulation layer is constituted by three or more layers and at least one layer thereof is selectively formed in conformity with a shape of said second electrode in a part of an area where said second electrode is disposed rather than the area which is positioned above said first electrode and where said second electrode does not exist.

15. A liquid crystal display unit according to claim 14, wherein said inter-layer insulation layer includes a part of a first insulation layer having function of a gate insulation layer of said thin film transistor, a part of a second insulation layer having function of a surface protection layer of said thin film transistor, and all of a third insulation layer except said first and second insulation layers, which is selectively formed in conformity with the shape of said second electrode in a part of an area which is positioned above said first electrode and where said second electrode is disposed.

16. A liquid crystal display unit according to claim 14, wherein said inter-layer insulation layer includes a part of a first insulation layer having function of a gate insulation layer of said thin film transistor, a part of a second insulation layer having function of a surface protection layer of said thin film transistor, and all of a fourth electrode except said first and second electrodes, which is formed in a part of an area except an area for forming a through-hole for connecting said second electrode to other electrode wiring and an area for exposing a terminal.

17. A liquid crystal display unit according to claim 14, wherein said inter-layer insulation layer includes at least any one of a part of a first insulation layer having function of a gate insulation layer of said thin film transistor and a part of a second insulation layer having function of a surface protection layer of the thin film transistor, a third insulation layer except said first and second insulation layers, which is selectively formed in conformity with a shape of said second electrode in a part of an area which is positioned above said first electrode and where said second electrode is disposed, and a fourth insulation layer formed in a part of an area except an area for forming a through-hole for connecting said second electrode to other electrode wiring and an area for forming a terminal.

18. A liquid crystal display unit according to any of claims 1-4, wherein when a width of a pattern of said insulation layer selective formed in conformity with said second shape in a part of the area where said second electrode is disposed rather than the area which is positioned above said first electrode and where said second electrode does not exist is W_ISO (μ

m) and a width of said second electrode and a space between said second electrodes formed into slits or teeth of a comb are W_EL (μ

m) and W_SP (μ

m), respectively,

19. A liquid crystal display unit according to claim 17, wherein said third and fourth insulation layers are constituted by applied-type insulation layers.

20. A liquid crystal display unit according to claim 19, wherein said applied-type insulation layer is formed by means of printing, spin coat or the like and more particularly said applied-type insulation layer is an insulation layer made of organic resin or Si.

21. A liquid crystal display unit according to claim 19, wherein said applied-type insulation layer used as said third insulation layer is of photo-image type.

22. A liquid crystal display unit according to claim 19, wherein said third insulation layer is processed in self-alignment with said second electrode collectively, so that said first area is formed in said second area selectively.

23. A liquid crystal display unit according to claim 19, wherein a thickness of said third insulation layer is 0.2 μ

m to 4.0 μ

m.

24. A liquid crystal display unit according to claim 19, wherein a dielectric constant of said third insulation layer is 1.5 to 6.5.

25. A liquid crystal display unit according to claim 19, wherein a thickness of said applied-type insulation layer used as said fourth insulation layer is 0.1 μ

m to 2 μ

m.

26. A liquid crystal display unit according to claim 17, wherein when a fifth insulation layer having a dielectric constant equal to or larger than 7.0 is selectively formed in a first area which is positioned above said first electrode and where said second electrode does not exist and a thickness of a fifth insulation layer is D_A, a total thickness of insulation layers disposed between a first orientation layer disposed above said first substrate and said first electrode in an area which is positioned above said first electrode and where said second electrode does not exist being D_B, a thickness of said inter-layer insulation layer being D_C, a thickness of said second electrode being D_D, D_A+D_B≦

D_C+D_D is satisfied.

3. A liquid crystal display unit including a pair of substrates, a liquid crystal layer disposed between said pair of substrates, a plurality of scanning signal lines, a plurality of image signal lines intersecting said plurality of scanning signal lines in matrix manner and a plurality of thin film transistors each formed in the vicinity of each intersection between said scanning signal lines and said image signal lines disposed on one of said substrates, a plurality of pixels at least one of which is formed in each area enclosed by said plurality of scanning signal lines and image signal lines and each of which includes a common signal electrode connected across a plurality of pixels and a pixel electrode connected to said thin film transistor corresponding thereto, said common signal electrode and said pixel electrode partially overlapping each other through an inter-layer insulation layer, at least part of each of said pixel electrode and said common signal electrode being constituted by a transparent conductive layer, one of said pixel electrode and said common signal electrode disposed on the side of said liquid crystal layer through an insulation layer being formed into slits or teeth of a comb,

wherein at least one of insulation layers included in said inter-layer insulation layer is selectively formed in an area which is positioned above one of said pixel electrode and said common electrode which is disposed nearer to said one of substrates with said insulation layer therebetween and where said pixel electrode or said common electrode disposed above does not exist;

and

wherein a liquid crystal having Δ

∈

of a positive value is used as said liquid crystal layer and when $\frac{1}{\underset{k=l}{\overset{n}{\sum <br><br>}}<br><br>\frac{d_k}{{\mathrm{\varepsilon <br><br>}}_k}}$

 

is S_A where the number of insulation layers included in said inter-layer insulation layer is n and a dielectric constant of a k-th insulation layer is ∈

_k, a thickness thereof being d_k, and $\frac{1}{\left(\underset{i=l}{\overset{m}{\sum <br><br>}}<br><br>\frac{d_1}{{\mathrm{\varepsilon <br><br>}}_1}\right)+\frac{\underset{k=l}{\overset{n}{\sum <br><br>}}<br><br>d_k-\underset{i=l}{\overset{m}{\sum <br><br>}}<br><br>d_1}{{\mathrm{\varepsilon <br><br>}}_{\mathrm{LC}}}}$

 

(where m≧

1) is S_B where the number of insulation layers disposed between a first orientation layer disposed above a first substrate and a first electrode of said pixel electrode and said common electrode, nearer to said first substrate through insulation layers in an area which is positioned above said first electrode and where a second electrode does not exist is m and a dielectric constant of an insulation layer constituting a first layer is ∈

₁, a thickness thereof being d₁, a dielectric constant of a liquid crystal in the parallel direction to a director of the liquid crystal being ∈

_LC, S_A<

S_B is satisfied.