Semi-transmissive liquid crystal display device

• US 20030218664A1
• Filed: 05/21/2003
• Published: 11/27/2003
• Est. Priority Date: 05/24/2002
• Status: Active Grant

• Current Assignee: NLT Technologies, Ltd.
• Original Assignee: NEC Corporation
• Inventors: Watanabe, Makoto, Nishida, Shinichi, Sakamoto, Michiaki
• Granted Patent: US 6,914,656 B2
• Time in Patent Office: Days
• US Class Current: 347/114
• CPC Class Codes: G02F 1/133371 Cells with varying thickness of the liquid crystal layer
• CPC Class Codes: G02F 1/133555 Transflectors
• CPC Class Codes: G02F 1/133638 Waveplates, i.e. plates with a retardation value of lambda/n
• CPC Class Codes: G02F 1/134363 for applying an electric field parallel to the substrate, i.e. in-plane switching [IPS]

Abstract

In a semi-transmissive liquid crystal display device having a reflective region 5 and a transmissive region therein, a one-half wavelength plate 29 is disposed between a lower substrate 11 and a polarizer 21a provided on a side of the lower substrate. This makes liquid crystal molecules in at least the transmissive region 6 driven by a horizontal electric field and allows the device to operate in a normally-black mode in both the reflective region 5 and the transmissive region 6, realizing a semi-transmissive liquid crystal display device having wide viewing angle characteristics.

Claims

1. A semi-transmissive liquid crystal display device comprising:

a pair of substrates disposed facing each other through a liquid crystal layer and defined as a lower substrate and an opposing substrate;

a plurality of pixel areas provided in one of said pair of substrates, each of said plurality of pixel areas having a reflective region and a transmissive region therein and further having an electrode configuration allowing electrodes to drive liquid crystal molecules with a horizontal electric field generated between said electrodes in said transmissive region; and

a one-half wavelength plate provided on an area corresponding to said transmissive region.

2. The semi-transmissive liquid crystal display device according to claim 1, wherein said reflective region has an electrode configuration allowing electrodes to drive liquid crystal molecules with a vertical electric field generated between said electrodes in said reflective region.

3. The semi-transmissive liquid crystal display device according to claim 1, wherein said reflective region has an electrode configuration allowing electrodes to drive liquid crystal molecules with a horizontal electric field generated between said electrodes in said reflective region.

4. The semi-transmissive liquid crystal display device according to claim 1, wherein twist angles in said reflective region and said transmissive region are approximately the same.

5. The semi-transmissive liquid crystal display device according to claim 3, wherein said reflective region has a reflector formed therein and said reflector is formed in a level positioned nearer an alignment film on a side of said opposing substrate than an alignment film formed in said transmissive region and located on a side of said lower substrate.

6. The semi-transmissive liquid crystal display device according to claim 3, wherein said electrodes used to generate a horizontal electric field and drive liquid crystal molecules with the horizontal electric field in said reflective region are transparent electrodes and formed in said reflective region.

7. The semi-transmissive liquid crystal display device according to claim 1, wherein said reflective region has an electrode configuration allowing electrodes to drive liquid crystal molecules with a horizontal electric field generated between said electrodes in said reflective region and further has at least one of a common electrode used to supply a reference potential and a pixel electrode corresponding to a pixel to be displayed.

8. The semi-transmissive liquid crystal display device according to claim 1, wherein said reflective region has an electrode configuration allowing electrodes to drive liquid crystal molecules with a horizontal electric field generated between said electrodes in said reflective region and wherein said reflective region and said transmissive region have said electrode configuration allowing a common electrode and a pixel electrode to be formed in said reflective region and said transmissive region, respectively.

9. The semi-transmissive liquid crystal display device according to claim 7, wherein at least one of a common electrode and a pixel electrode, both formed in said reflective region, is a reflecting electrode.

10. The semi-transmissive liquid crystal display device according to claim 9, wherein said common electrode is a reflecting electrode and formed in a level positioned nearer a liquid crystal layer than a data line and wherein said data line is covered through an insulation film with said common electrode formed wider than said data line.

11. The semi-transmissive liquid crystal display device according to claim 9, wherein said common electrode is a reflecting electrode and formed in a level positioned nearer a liquid crystal layer than a scanning line and wherein said scanning line is covered through an insulation film with said common electrode formed wider than said scanning line.

12. The semi-transmissive liquid crystal display device according to claim 9, wherein said common electrode is a reflecting electrode and formed in a level positioned nearer a liquid crystal layer than a channel region of a thin film transistor and wherein said channel region is completely covered through an insulation film with said common electrode.

13. The semi-transmissive liquid crystal display device according to claim 7, wherein said common electrode is connected to a common electrode interconnect line made of an opaque metal through a contact hole in each pixel and wherein said pixel electrode is connected to an auxiliary pixel electrode made of an opaque metal through a contact hole in each pixel.

14. The semi-transmissive liquid crystal display device according to claim 7, wherein said common electrode and said pixel electrode are formed at the same level.

15. The semi-transmissive liquid crystal display device according to claim 13, wherein said common electrode interconnect line and said auxiliary pixel electrode are formed to overlap each other while sandwiching an insulation film therebetween.

16. The semi-transmissive liquid crystal display device according to claim 13, wherein at least a part of said auxiliary pixel electrode is formed below said pixel electrode formed at the same level as said common electrode and in a comb shape.

17. The semi-transmissive liquid crystal display device according to claim 4, wherein said twist angle is not greater than 15 degrees.

18. The semi-transmissive liquid crystal display device according to claim 4, wherein product of a birefringence of liquid crystal layer and a gap formed by a liquid crystal layer in said reflective region takes a value of 0.098 μ

m to 0.178 μ

m.

19. The semi-transmissive liquid crystal display device according to claim 4, wherein product of a birefringence of liquid crystal layer and a gap formed by a liquid crystal layer in said transmissive region takes a value of 0.195 μ

m to 0.355 μ

m.