Three state transflective liquid crystal display

• US 6,707,519 B1
• Filed: 10/04/1999
• Issued: 03/16/2004
• Est. Priority Date: 02/04/1998
• Status: Expired due to Term

• Current Assignee: 138 East LCD Advancements Limited (Vector Capital Corporation)
• Original Assignee: Seiko Epson Corporation (Seiko Group)
• Inventors: Maeda, Tsuyoshi, Okumura, Osamu, Seki, Takumi, Okamoto, Eiji
• Primary Examiner(s): NGO, HUYEN LE
• Application Number:
  US09/402,555
• Time in Patent Office: 1,625 Days
• Field of Search: 349/114, 349/62, 349/98, 349/115, 349/117, 349/119, 349/112
• US Class Current: 349/114
• CPC Class Codes: G02F 1/133555 Transflectors
• CPC Class Codes: G02F 1/133626 providing two modes of illumination, e.g. day-night
• CPC Class Codes: G02F 1/13363 Birefringent elements, e.g. for optical compensation
• CPC Class Codes: G02F 1/133638 Waveplates, i.e. plates with a retardation value of lambda/n
• CPC Class Codes: G02F 1/134336 Matrix
• CPC Class Codes: G02F 2202/40 Materials having a particular birefringence, retardation
• CPC Class Codes: G02F 2413/04 Number of plates greater than or equal to 4
• CPC Class Codes: G02F 2413/08 with a particular optical axis orientation

Abstract

A liquid crystal device of the present invention performs transmissive display using light from an illumination devices 111 and 112 in a dark environment, and reflective display using light reflected by a transflective layer 123 provided on the inner side of a liquid crystal cell in a bright environment. A retardation plate is provided adjacent to a polarizer 109 and an illumination device so that the rotational direction of polarization of the light emitted from the illumination device is the same as that of the polarization of the light reflected by the transflective layer in a dark display state.

Claims

1. A liquid crystal device having a reflective display function by reflecting light incident on a liquid crystal layer from one side thereof by a transflective layer, and a transmissive display function by transmitting light incident from another side of the liquid crystal layer opposite to the one side;

wherein said liquid crystal device has a bright display state as a first display state and a dark display state as a second display state, which can be respectively selected by changing a voltage applied to the liquid crystal layer; and

in the second display state, the light incident on the liquid crystal layer from the one side passes through the liquid crystal layer and is reflected by the transflective layer to be changed to circularly polarized light or elliptically polarized light with a predetermined rotational direction;

the liquid crystal device comprising;

a first polarizer arranged on the one side;

an optical element provided on the other side, for changing light incident on the transflective layer from the other side to polarized light with the predetermined rotational direction;

wherein the rotational direction of the circularly polarized light or the elliptically polarized light resulting from the light incident through the optical element on the transflective layer from the other side is the same as that of the circularly polarized light or the elliptically polarized light resulting from the light reflected by the transflective layer in the second display state.

2. A liquid crystal device according to claim 1, wherein the second display state of the liquid crystal layer provides an ellipticity of reflected light incident on the liquid crystal layer from the one side by the transflective layer, the ellipticity being the same as that of transmitted light incident on the liquid crystal layer from the other side through the transflective layer.

3. A liquid crystal device according to claim 1, wherein a medium brightness display state as a third display state that is between the first and second states can be selected by changing the voltage applied to the liquid crystal layer.

4. A liquid crystal device according to claim 1, wherein in the second display state, the light incident on the liquid crystal layer from the one side is reflected by the transflective layer to be changed to circularly polarized light with the predetermined rotational direction;

and

in the first display state, the light incident on the liquid crystal layer from the one side is reflected by the transflective layer to be changed to linearly polarized light.

5. A liquid crystal device according to claim 1, wherein the optical element comprises a second polarizer provided on the other side, and a retardation plate provided between the second polarizer and the liquid crystal layer.

6. A liquid crystal device according to claim 5, wherein the transmission axis of the second polarizer, and the axis and retardation value of the retardation plate are set so that when the light incident on the liquid crystal layer from the other side is transmitted through the transflective layer, ellipticity is at least 0.85.

7. A liquid crystal device according to claim 5, wherein the retardation plate comprises a 1/4 wavelength plate.

8. A liquid crystal device according to claim 1, wherein the optical element comprises a reflective polarizer provided on the other side, and a retardation plate provided between the reflective polarizer and the liquid crystal layer.

9. A liquid crystal device according to claim 8, wherein the transmission axis of the reflective polarizer, and the axis and retardation value of the retardation plate are set so that when the light incident on the liquid crystal layer from the other side is transmitted through the transflective layer, ellipticity is 0.85 or more.

10. A liquid crystal device according to claim 8, wherein the retardation plate comprises a 1/4 wavelength plate.

11. A liquid crystal device according to claim 1, wherein the optical element comprises a liquid crystal polymer exhibiting a cholesteric phase.

12. A liquid crystal device according to claim 1, further comprising an illumination device arranged on a first side of the optical element opposite to a second side of the optical element, the second side of the optical element being adjacent the liquid crystal layer.

13. A liquid crystal device comprising:

a liquid crystal cell having a liquid crystal layer between a first substrate and a second substrate opposed thereto;

a transflective layer arranged on a first side of the second substrate that is between the liquid crystal layer and the second substrate, for reflecting and transmitting incident light with predetermined reflectance and transmittance;

an illumination device arranged on a second side of the second substrate opposite the first side of the second substrate;

one of a polarizer or reflective polarizer arranged between the liquid crystal cell and the illumination device; and

a retardation plate arranged between the polarizer or reflective polarizer, and the liquid crystal cell, for changing linearly polarized light produced by passing the light, emitted from the illumination device, through the polarizer or reflective polarizer to circularly polarized light or elliptically polarized light;

wherein light emitted from the illumination device passes through the retardation plate, the retardation plate providing a circularly polarized light or elliptically polarized light that has the same rotational direction as that of polarized light produced when light incident from a direction of the first substrate in a dark display state is reflected by the transflective layer.

14. A liquid crystal device according to claim 13, wherein the transmission axis of the polarizer or reflective polarizer, and the axis and retardation value of the retardation plate are set so that when the light emitted from the illumination device is transmitted through the retardation plate, ellipticity is at least 0.85.

15. A liquid crystal device according to claim 14, wherein the retardation plate comprises at least a 1/4 wavelength plate.

16. A liquid crystal device comprising:

a liquid crystal cell having a liquid crystal layer between a first substrate and a second substrate opposed thereto;

a transflective layer arranged on a side of the second substrate facing the liquid crystal layer, for reflecting and transmitting incident light with predetermined reflectance and transmittance;

an illumination device arranged on another side of the second substrate different from the side facing the liquid crystal layer; and

a selective reflecting layer arranged between the liquid crystal cell and the illumination device, for selectively reflecting and transmitting circularly polarized light or elliptically polarized light according to its rotational direction;

wherein light emitted from the illumination device is transmitted through the selective reflecting layer of the liquid crystal cell, the selective reflecting layer providing a circularly polarized light or elliptically polarized light that has the same rotational direction as that of circularly polarized light or elliptically polarized light produced when light incident from the first substrate in the dark display state is reflected by the transflective layer.

17. A liquid crystal device according to claim 16, wherein selective reflection of a cholesteric liquid crystal is utilized for the selective reflecting layer.

18. An electronic apparatus comprising a liquid crystal device as a display unit, wherein a liquid crystal device according to claim 16 is provided.

19. A transflective liquid crystal device comprising:

a liquid crystal layer disposed between first and second substrates;

a polarizer formed on the first substrate for absorbing a predetermined linearly polarized light;

an optical element formed on the second substrate for changing incident light to linearly polarized light with a predetermined rotational direction;

a transflective layer disposed between the liquid crystal layer and the second substrate for reflecting and transmitting incident light with predetermined reflectance and transmittance values to perform reflective and transmissive functions;

wherein the transflective layer reflects the light incident from the first substrate for the reflective function, and transmits the light incident on the second substrate for the transmissive function;

wherein the device selects the display state between bright and dark display states depending on an applied voltage; and

wherein the rotational direction of circularly polarized light or elliptically polarized light resulting from the light incident through the optical element, which is on the transflective layer, from the first substrate is the same as that of the circularly polarized light or the elliptically polarized light resulting from the light reflected by the transflective layer in the second display state.

20. The device of claim 19 further comprising an illumination device formed on a side of the second substrate opposite to the liquid crystal layer for emitting light incident from the second substrate on the transflective layer, thereby permitting transmissive display function in the dark display state.

21. The device of claim 19 wherein the transflective layer reflects the linearly polarized light incident on the liquid crystal layer from the first substrate to linearly polarized light in the bright display state thereby emitting an image light.

22. The device of claim 19 wherein the transflective layer reflects the light incident on the liquid crystal layer from the first substrate to elliptically polarized light with the predetermined rotational direction in the dark display state.

23. The device of claim 22 wherein the transflective layer transmits the linearly polarized light from the optical element, which is originally incident on the liquid crystal layer from the second substrate in the dark display state.

24. The device of claim 22 wherein the reflected light and transmitted light by the transflective layer have the same rotational direction, thereby preventing a contrast of the transmissive function from being decreased in the dark display state.

25. The device of claim 19 wherein the optical element comprises a second polarizer and a retardation plate.

26. The device of claim 19 wherein the optical element comprises a selective reflecting layer which uses selective reflection of a cholesteric liquid crystal.