Liquid crystal display device

1. A liquid crystal display device comprising:

first and second substrates, at least one of which is transparent;

a liquid crystal layer which is disposed between the first and second substrates;

an electrode group which is formed on at least one of the first and second substrates and applies an electric field to the liquid crystal layer;

a plurality of active elements which is connected to the electrode group;

an alignment film which is disposed on at least one of the first and second substrates and has one surface contacting the liquid crystal layer; and

an underlying layer which is disposed on at least one of the first and second substrates and contacts the other surface of the alignment film,

wherein the alignment film includes a plurality of types of organic compounds having refractive indexes and polarities respectively different from one another, each of the plurality of types of organic compounds being separated in the film thickness direction according to the polarities;

wherein the refractive index of the alignment film monotonically increases from a boundary surface between the alignment film and the liquid crystal layer to a boundary surface between the alignment film and the underlying layer, and

wherein the minimum refractive index nLC of the liquid crystal layer, the refractive index nF2 of the alignment film at the boundary surface between the liquid crystal layer and the alignment film, the refractive index nF1 of the alignment film at the boundary surface between the alignment film and the underlying layer, and the refractive index nS2 of the underlying layer have a relationship of an equation (I) in which nLC≦nF2<nF1≦nS2.

2. The liquid crystal display device according to claim 1 ,

wherein the underlying layer is a transparent layer through which visible light is transmitted,

wherein the electrode group includes a common electrode and a pixel electrode, and

wherein a surface opposite to a surface contacting the alignment film in the underlying layer contacts any one of the common electrode and the pixel electrode.

3. The liquid crystal display device according to claim 2 , wherein the refractive index nS2 of the underlying layer and the refractive index nPE of the one electrode at the boundary surface between the underlying layer and the one electrode have a relationship of an equation (II) in which |nS2−nPE|≦0.1.

4. The liquid crystal display device according to claim 2 ,

wherein a part of the surface opposite to the surface contacting the alignment film in the underlying layer contacts the one electrode and the other part thereof contacts an interlayer isolation film, and

wherein the refractive index nS2 of the underlying layer and the refractive index nL1 of the interlayer isolation film have a relationship of an equation (III) in which |nS2−nLI|≦0.1.

5. The liquid crystal display device according to claim 2 , wherein the refractive index of the surface of the one electrode is lower than the internal refractive index.

6. The liquid crystal display device according to claim 1 ,

wherein the electrode group includes a common electrode and a pixel electrode,

wherein the underlying layer includes an interlayer isolation film contacting a surface opposite to a surface contacting the liquid crystal layer in the alignment film and any one of the common electrode and the pixel electrode provided in a part of a surface on the side of the alignment film in the interlayer isolation film and protruding toward the alignment film,

wherein the alignment film is formed on the underlying layer, and

wherein the film thickness of the alignment film is larger than that of the one electrode.

7. The liquid crystal display device according to claim 1 , wherein the alignment film has an in-plane optical anisotropy.

8. The liquid crystal display device according to claim 7 , wherein the direction of the in-plane optical anisotropic axis of the alignment film is equal to the alignment regulation direction of the liquid crystal layer.

9. The liquid crystal display device according to claim 1 , wherein in the plurality of types of organic compounds forming the alignment film, the refractive index in the visible range of the organic compound having the highest refractive index is 1.7 or more.

10. The liquid crystal display device according to claim 1 , wherein the alignment film is formed of polyimide using polyamic acid ester as a precursor.

11. The liquid crystal display device according to claim 1 , wherein the alignment film obtains liquid crystal alignment capability by photo-alignment treatment.

12. The liquid crystal display device according to claim 1 , wherein the alignment film obtains liquid crystal alignment capability by a rubbing treatment.

13. The liquid crystal display device according to claim 1 , wherein an area obtaining liquid crystal alignment capability of the alignment film is within a range of 20 nm from a surface of the alignment film.

14. The liquid crystal display device according to claim 1 , wherein compounds forming the alignment film are cross-linked to each other after the alignment film obtains liquid crystal alignment capability.

15. The liquid crystal display device according to claim 1 , wherein the coating ratio with respect to a display area of the alignment film is 50% or more.