Transflective display having improved contrast

• US 20070115410A1
• Filed: 09/03/2004
• Published: 05/24/2007
• Est. Priority Date: 09/19/2003
• Status: Active Grant

• Current Assignee: Innolux Hong Kong Holding Ltd (InnoLux Corporation)
• Original Assignee: Koninklijke Philips Electronics N.V. (Koninklijke Philips N.V.)
• Inventors: Beeren, Rudolf, Gotink-Meinders, Nicole Alide
• Granted Patent: US 7,760,296 B2
• Time in Patent Office: Days
• US Class Current: 349/114
• CPC Class Codes: G02F 1/133536 Reflective polarizers G02F1/13362 takes precedence
• CPC Class Codes: G02F 1/133555 Transflectors
• CPC Class Codes: G02F 2201/08 light absorbing layer

Abstract

The present invention provides for improved contrast in the transmissive mode of a transflective liquid crystal display having a rear stack polarizing means (302) which is transmissive for light having a desired polarization and reflective for light having an opposite, undesired polarization. The contrast is improved due to enhancements of the black state provided by the inclusion of a reflection preventing means (306). The reflection preventing means is arranged between the transflector (301) and the rear stack polarizer (302), and serves to stop light transmitted through the rear stack polarizer (302) towards the transflector (301) from being reflected by the transflector (301) back to the rear polarizer (302). Thereby undesired reflections having wrong polarization are stopped from being transmitted through the transflector (301) and thus from affecting the transmissive mode black state of the display.

Claims

1. A transflective liquid crystal display device (400) comprising:

a liquid crystal layer (412), a transflector (413), rear polarizing means (404), and a backlight (405), sandwiched in said order;

said backlight (405) being operative to emit light towards said transflector (413);

said transflector (413) being transmissive for a first part of said light and non-transmissive for a second part of said light; and

said rear polarizing means (404) being operative to transmit light having a first polarization and to reflect light having a second polarization, opposite to said first polarization;

said display device further comprising reflection preventing means (414) arranged between said transflector (413) and said reflection preventing means (414);

said reflection preventing means (414) being operative to prevent said second part of light from propagating back towards said rear polarizing means (405).

2. A transflective liquid crystal display according to claim 1, wherein said rear polarizing means (404) is a twisted nematic polymer layer.

3. A transflective liquid crystal display according to claim 1, wherein said transflector (413) is a hole-in-mirror type of transflector and thus comprises an area that is transmissive for light and an area that is non-transmissive for light.

4. A transflective liquid crystal display according to claim 1, wherein said reflection preventing means (414) comprises a black, light absorbing layer (414).

5. A transflective liquid crystal display according to claim 4, wherein said black, light absorbing layer (414) comprises chromium oxide.

6. A transflective liquid crystal display according to claim 3, wherein said transflector (413) and said black, light absorbing layer (414) has a corresponding pattern of areas transmissive and non-transmissive for light.

7. A transflective liquid crystal display according to claim 1, wherein said reflection preventing means (414) comprises a stack of antireflection layers.

8. A transflective liquid crystal display according to claim 1, wherein said liquid crystal (412) is of the twisted nematic type, a super twisted nematic type or a non-twisted nematic type.