Structured transflectors for enhanced ambient and backlight operation of transmissive liquid crystal displays

• US 20040223099A1
• Filed: 05/05/2003
• Published: 11/11/2004
• Est. Priority Date: 05/05/2003
• Status: Active Grant

• Current Assignee: 3M Innovative Properties Company (3M Company)
• Original Assignee: 3M Innovative Properties Company (3M Company)
• Inventors: Ouderkirk, Andrew J., Epstein, Kenneth A., McClure, Donald J., Marushin, Patrick H., Kotchick, Keith M.
• Granted Patent: US 7,088,405 B2
• Time in Patent Office: Days
• US Class Current: 349/114
• CPC Class Codes: G02B 27/142 Coating structures, e.g. thin films multilayers
• CPC Class Codes: G02B 27/147 using averaging effects by spatially variable reflectivity on a microscopic level, e.g. polka dots, chequered or discontinuous patterns, or rapidly moving surfaces G02B27/1086 takes precedence
• CPC Class Codes: G02F 1/133555 Transflectors

Abstract

Color transmissive displays have historically used only backlight for forming the color image, and have not used ambient light. Usually, such a display is not used in bright sunlight, since the color image becomes washed out. Transflective color displays form an image by reflecting ambient light or by transmitting backlight, and can be used in bright sunlight. The transflector in such displays reflects the ambient light while also transmitting the backlight. The requirements on the transflector, however, are different from those used in monochromatic displays. According to the invention, a color transflective display device uses comprises a transmissive display unit having a viewing side and a back side and defining picture elements. A structured transflector is disposed to the back side of the color display unit. The structured transflector includes a structured surface and a layered dielectric reflector disposed over the structured surface.

Claims

1. A transflective display device, comprising:

a color transmissive display unit having a viewing side and a back side and defining picture elements; and

a structured transflector disposed to the backside of the color display unit, the structured transflector including a structured dielectric reflector to reflect ambient light that has passed through the color display unit at a reflection angle different from an incident angle, the reflection and incident angles being measured relative to a display normal.

2. A device as recited in claim 1, wherein the dielectric reflector has a transmission in the range of 70%-90%.

3. A device as recited in claim 1, wherein the transmissive display unit is a liquid crystal display unit.

4. A device as recited in claim 1, further comprising a backlight unit to generate backlight, the structured transflector disposed between the color display unit and the backlight unit, the backlight passing through the structured transflector to the color display unit.

5. A device as recited in claim 1, wherein the structured reflector defines a plurality of sets of reflective facets, the reflective facets being nonperpendicular to an optical axis of the display device, the different sets of reflective facets being associated with respective different picture elements, the sets of reflective facets comprising at least two reflective facets.

6. A device as recited in claim 5, wherein the reflective facets of the plurality of sets of reflective facets are substantially rectilinear, first reflective facets of the sets of reflective facets being disposed at a first angle relative to the optical axis and second reflective facets of the sets of reflective facets being disposed at a second angle relative to the optical axis, a magnitude of the first angle being different from a magnitude of the second angle.

7. A device as recited in claim 6, wherein different reflective facets within at least one of the sets of reflective facets have different lengths.

8. A device as recited in claim 6, wherein base angles of different reflective facets within at least one of the sets are selected so as to provide a desired average reflection angle for the set of reflective facets.

9. A device as recited in claim 6, wherein different reflective facets within at least one of the sets of reflective facets have base angles in the range 2°

-20°

.

10. A device as recited in claim 9, wherein the base angles are in the range from 6°

-10°

.

11. A device as recited in claim 5, wherein at least one of the reflective facets is a non-linear facet.

12. A device as recited in claim 11, wherein the at least one of the reflective facets is curved.

13. A device as recited in claim 11, wherein the at least one of the reflective facets has at least two linear segments.

14. A device as recited in claim 1, wherein the structured dielectric reflector is disposed over a holographic surface.

15. A device as recited in claim 1, wherein the structured transflector further comprises a planarization layer disposed over the dielectric reflector and facing the transmissive display unit.

16. A device as recited in claim 15, wherein the planarization layer includes diffusing particles.

17. A device as recited in claim 15, wherein the planarization layer is an adhesive layer adhering the structured transflector to the transmissive display unit.

18. A device as recited in claim 17, further comprising light diffusing particles provided within the adhesive layer.

19. A device as recited in claim 1, further comprising a diffuser disposed between the structured transflector and the transmissive display unit.

20. A device as recited in claim 1, wherein the structured transflector generally lies in an x-y plane, and the structured reflector comprises tilted surfaces tilted relative to the x-y plane so that light normally incident to the x-y plane in a direction parallel to a z-axis, is reflected by the tilted surfaces in a direction having a component lying in a y-z plane.

21. A device as recited in claim 20, wherein at least one of the tilted surfaces is shaped so as to laterally reflect a portion of the incident light to have a directional component in the x-direction.

22. A device as recited in claim 21, wherein the at least one of the tilted surfaces is curved so as to laterally reflect a portion of the incident light to have the directional component in the x-direction.

23. A device as recited in claim 21, wherein the at least one of the tilted surfaces has a randomly varying surface so as to laterally reflect a portion of the incident light to have the directional component in the x-direction.

24. A device as recited in claim 1, wherein the structured reflector includes sets of tilted surfaces, a set of tilted surfaces corresponding to a respective picture element of the transmissive display unit.

25. A device as recited in claim 24, wherein different tilted surfaces within a set of tilted surfaces have different pitches.

26. A device as recited in claim 1, wherein the structured dielectric reflector includes a substrate comprising a material having a relatively low refractive index, and a single layer of material having a relatively high refractive index disposed over the substrate, and further comprising a planarization layer over the dielectric reflecting layer, the planarization layer comprising a material of a relatively low refractive index.

27. A device as recited in claim 26, wherein the substrate has a refractive index in the range from approximately 1.3-approximately 1.8, the dielectric reflector includes at least one layer having a refractive index in the range from approximately 1.8-2.3, and the refractive index of the layer on the other side of the dielectric reflector from the substrate is in the range from 1 to approximately 1.8.

28. A device as recited in claim 26, wherein the refractive index of the planarization layer is substantially the same as the refractive index of the substrate.

29. A device as recited in claim 1, wherein the structured dielectric reflector includes a plurality of dielectric layers having alternating low and high refractive index.

30. A device as recited in claim 1, wherein the structured dielectric reflector includes a plurality of dielectric layers whose optical thicknesses are not odd integer multiples of one quarter of a selected wavelength.

31. A device as recited in claim 1, further comprising at least one light management film disposed between the light source and the structured transflector.

32. A device as recited in claim 31, wherein the at least one light management film includes a first prismatically ribbed, brightness enhancing film having ribs oriented in a first direction and a second prismatically ribbed, brightness enhancing film having ribs oriented in a second direction perpendicular to the first direction.

33. A device as recited in claim 1, further comprising a control unit coupled to the display unit to control an image displayed on the display unit.