Display device

• US 7,687,988 B2
• Filed: 10/27/2006
• Issued: 03/30/2010
• Est. Priority Date: 11/04/2005
• Status: Active Grant

• Current Assignee: Semiconductor Energy Laboratory Co., Ltd.
• Original Assignee: Semiconductor Energy Laboratory Co., Ltd.
• Inventors: Egi, Yuji, Nishi, Takeshi, Ishitani, Tetsuji, Moriya, Koji
• Primary Examiner(s): Patel; Vip
• Application Number:
  US11/553,747
• Publication Number:
  US 20070121033A1
• Time in Patent Office: 1,250 Days
• Field of Search: 313/479, 313/111, 313/112, 313/498, 313/506, 313/509, 313/512
• US Class Current: 313/506
• CPC Class Codes: G02B 5/3033 in the form of a thin sheet or foil, e.g. Polaroid
• CPC Class Codes: G02B 6/0051 Diffusing sheet or layer
• CPC Class Codes: G02B 6/0055 Reflecting element, sheet or layer
• CPC Class Codes: G02B 6/0056 for producing polarisation effects, e.g. by a surface with polarizing properties or by an additional polarizing elements
• CPC Class Codes: G02F 1/133528 Polarisers
• CPC Class Codes: G02F 1/1393 the birefringence of the liquid crystal being electrically controlled, e.g. ECB-, DAP-, HAN-, PI-LC cells G02F1/1396, G02F1/141 take precedence

Abstract

The invention provides a display device of which a contrast ratio is enhanced. By providing stacked polarizing plates so as to be in a cross nicol state, a contrast ratio of a display device can be enhanced. The stacked polarizing plates are stacked outside a light-transmissive insulating substrate in a parallel nicol state. When the number of polarizing plates is four or five in total, a contrast ratio becomes the highest.

Claims

1. A display device comprising:

a first light-transmissive substrate and a second light-transmissive substrate opposed to each other;

a display element disposed between the first and second light-transmissive substrates;

first stacked polarizing plates adjacent to the first light-transmissive substrate wherein the first light-transmissive substrate is located between the display element and the first stacked polarizing plates;

second stacked polarizing plates adjacent to the second light-transmissive substrate wherein the second light-transmissive substrate is located between the display element and the second stacked polarizing plates,

wherein absorption axes of the first stacked polarizing plates are arranged in a parallel nicol state,

wherein absorption axes of the second stacked polarizing plates are arranged in a parallel nicol state, and

wherein the absorption axes of the first stacked polarizing plates are arranged relative to the absorption axes of the second stacked polarizing plates in a cross nicol state.

2. The display device according to claim 1, wherein at least a first polarizing plate and a second polarizing plate in the first stacked polarizing plates are provided in contact with each other.

3. The display device according to claim 1, wherein the display element is a liquid crystal element.

4. The display device according to claim 1, further comprising a color filter provided between the first light-transmissive substrate and the second light-transmissive substrate.

5. The display device according to claim 1, further comprising a black matrix provided between the first light-transmissive substrate and the second light-transmissive substrate.

6. The display device according to claim 1, further comprising a thin film transistor formed over the first light-transmissive substrate.

7. The display device according to claim 6, wherein the thin film transistor comprises a crystalline semiconductor film as an active layer.

8. The display device according to claim 6, wherein the thin film transistor comprises an amorphous semiconductor film.

9. A display device comprising:

a first light-transmissive substrate and a second light-transmissive substrate opposed to each other;

a display element disposed between the first and second light-transmissive substrates;

m first polarizing plates stacked adjacent to the first light-transmissive substrate wherein the first light-transmissive substrate is located between the display element and the first polarizing plates; and

n second polarizing plates stacked adjacent to the second light-transmissive substrate wherein the second light-transmissive substrate is located between the display element and the second polarizing plates,

wherein absorption axes of the first polarizing plates are arranged in a parallel nicol state,

wherein absorption axes of the second polarizing plates are arranged in a parallel nicol state,

wherein the absorption axes of the first polarizing plates are arranged relative to the absorption axes of the second polarizing plates in a cross nicol state such that the display device has a third transmittance,

wherein a ratio between a first transmittance and a second transmittance is smaller than a ratio between the third transmittance and a fourth transmittance,

wherein the first transmittance is associated with an arrangement having m first polarizing plates and n second polarizing plates arranged such that the absorption axes of the first polarizing plates are arranged relative to the absorption axes of the second polarizing plates in a parallel nicol state,

wherein the second transmittance is associated with an arrangement having m-1 first polarizing plates and n second polarizing plates arranged such that the absorption axes of the first polarizing plates are arranged relative to the absorption axes of the second polarizing plates in a parallel nicol state,

wherein the fourth transmittance is associated with an arrangement having m-1 first polarizing plates and n second polarizing plates arranged such that the absorption axes of the first polarizing plates are arranged relative to the absorption axes of the second polarizing plates in a cross nicol state, and

wherein n and m are integers having values of two or more.

10. The display device according to claim 9, wherein at least a first polarizing plate and a second polarizing plate in the first polarizing plates are provided in contact with each other.

11. The display device according to claim 9, wherein the display element is a liquid crystal element.

12. The display device according to claim 9, further comprising a color filter provided between the first light-transmissive substrate and the second light-transmissive substrate.

13. The display device according to claim 9, further comprising a black matrix provided between the first light-transmissive substrate and the second light-transmissive substrate.

14. The display device according to claim 9, further comprising a thin film transistor formed over the first light-transmissive substrate.

15. The display device according to claim 14, wherein the thin film transistor comprises a crystalline semiconductor film as an active layer.

16. The display device according to claim 14, wherein the thin film transistor comprises an amorphous semiconductor film.

17. A display device comprising:

a first light-transmissive substrate and a second light-transmissive substrate opposed to each other;

a display element disposed between the first and second light-transmissive substrates;

first stacked polarizing plates adjacent to the first light-transmissive substrate wherein the first light-transmissive substrate is located between the display element and the first stacked polarizing plates;

second stacked polarizing plates adjacent to the second light-transmissive substrate wherein the second light-transmissive substrate is located between the display element and the second stacked polarizing plates,

wherein absorption axes of the first stacked polarizing plates are arranged in a parallel nicol state,

wherein absorption axes of the second stacked polarizing plates are arranged in a parallel nicol state,

wherein the absorption axes of the first stacked polarizing plates are arranged relative to the absorption axes of the second stacked polarizing plates in a cross nicol state,

wherein a ratio of a first transmittance to a second transmittance is higher than a ratio of a third transmittance to a fourth transmittance,

wherein the first transmittance is associated with an arrangement having the first stacked polarizing plates and the second stacked polarizing plates arranged such that the absorption axes of the first stacked polarizing plates are arranged relative to the absorption axes of the second stacked polarizing plates in a parallel nicol state,

wherein the second transmittance is associated with an arrangement having the first stacked polarizing plates and the second stacked polarizing plates arranged such that the absorption axes of the first stacked polarizing plates are arranged relative to the absorption axes of the second stacked polarizing plates in a cross nicol state,

wherein the third transmittance is associated with an arrangement having a first single-layer polarizing plate and a second single-layer polarizing plate arranged such that absorption axes of the first single-layer polarizing plate are arranged relative to absorption axes of the second single-layer polarizing plate in a parallel nicol state, and

wherein the fourth transmittance is associated with an arrangement having the first single-layer polarizing plate and the second single-layer polarizing plate arranged such that the absorption axes of the first single-polarizing plate are arranged relative to the absorption axes of the second single-layer polarizing plate in a cross nicol state.

18. The display device according to claim 17, wherein at least a first polarizing plate and a second polarizing plate in the first stacked polarizing plates are provided in contact with each other.

19. The display device according to claim 17, wherein the display element is a liquid crystal element.

20. The display device according to claim 17, further comprising a color filter provided between the first light-transmissive substrate and the second light-transmissive substrate.

21. The display device according to claim 17, further comprising a black matrix provided between the first light-transmissive substrate and the second light-transmissive substrate.

22. The display device according to claim 17, further comprising a thin film transistor formed over the first light-transmissive substrate.

23. The display device according to claim 22, wherein the thin film transistor comprises a crystalline semiconductor film as an active layer.

24. The display device according to claim 22, wherein the thin film transistor comprises an amorphous semiconductor film.