Transflective liquid crystal display

• US 8,089,590 B2
• Filed: 08/06/2007
• Issued: 01/03/2012
• Est. Priority Date: 08/06/2007
• Status: Active Grant

• Current Assignee: InnoLux Corporation, University of Central Florida Research Foundation Inc. (State University System of Florida)
• Original Assignee: Chi Mei Innolux Corporation (InnoLux Corporation), University of Central Florida Research Foundation Inc. (State University System of Florida)
• Inventors: Lu, Ruibo, Wu, Shin-Tson, Wei, Chung-Kuang, Li, Wang-Yang
• Primary Examiner(s): Healy, Brian M.
• Assistant Examiner(s): Radkowski, Peter
• Application Number:
  US11/834,376
• Publication Number:
  US 20090040432A1
• Time in Patent Office: 1,611 Days
• Field of Search: 349/56, 349/84, 349/139, 349/143, 349/144
• US Class Current: 349/114
• CPC Class Codes: G02F 1/133555 Transflectors
• CPC Class Codes: G02F 1/133707 Structures for producing distorted electric fields, e.g. bumps, protrusions, recesses, slits in pixel electrodes
• CPC Class Codes: G02F 1/134318 having a patterned common electrode
• CPC Class Codes: G02F 1/1393 the birefringence of the liquid crystal being electrically controlled, e.g. ECB-, DAP-, HAN-, PI-LC cells G02F1/1396, G02F1/141 take precedence
• CPC Class Codes: G02F 2202/40 Materials having a particular birefringence, retardation

Abstract

A transflective display includes pixels each including a reflective (R) sub-pixel, a transmissive (T) sub-pixel, and electrodes having features to cause multiple domains to form in a liquid crystal layer of the R sub-pixel and the T sub-pixel. The electrodes in the R sub-pixels have features that are different from features of the electrodes in the T sub-pixel to cause the liquid crystal layer in the R sub-pixel to have an optical phase retardation that is between 20% to 80% of an optical phase retardation of the liquid crystal layer in the T sub-pixel. The R sub-pixel and the T sub-pixel have substantially the same cell gap and are driven by the same pixel voltage.

Claims

1. An apparatus comprising:

display pixels each comprising a reflective (R) sub-pixel, a transmissive (T) sub-pixel, and electrodes having features to cause multiple domains to form in a liquid crystal layer of the R sub-pixel and the T sub-pixel, the electrodes in the R sub-pixels having features that are different from features of the electrodes in the T sub-pixel to cause the liquid crystal layer in the R sub-pixel to have an optical phase retardation that is between 20% to 80% of an optical phase retardation of the liquid crystal layer in the T sub-pixel, the R sub-pixel and the T sub-pixel have a same cell gap and being driven by a same pixel voltage.

2. The apparatus of claim 1 wherein the features comprise at least one of openings and protrusions.

3. The apparatus of claim 1 wherein the features comprise elongated slits.

4. The apparatus of claim 1 wherein the features comprise one or more openings that are formed on a common electrode of the R sub-pixel and one or more openings that are formed on a common electrode of the T sub-pixel.

5. The apparatus of claim 1 wherein the features comprise one or more openings formed on a reflective electrode of the R sub-pixel and one or more openings formed on a pixel electrode of the T sub-pixel.

6. The apparatus of claim 1 wherein the features comprise one or more openings in at least one electrode of the R sub-pixel and one or more openings in at least one electrode of the T sub-pixel, the openings in the R sub-pixel having an area that is of a first percentage of an area of the R sub-pixel, the openings in the T sub-pixel have an area that is of a second percentage of an area of the T sub-pixel, and the first percentage is greater than the second percentage.

7. The apparatus of claim 1 wherein the features comprise protrusions having triangular-shaped cross sections.

8. The apparatus of claim 1 wherein the features comprise one or more protrusions in at least one electrode of the R sub-pixel and one or more protrusions in at least one electrode of the T sub-pixel, the one or more protrusions in the R sub-pixel having a base area that is of a first percentage of an area of the R sub-pixel, the one or more protrusions in the T sub-pixel have a base area that is of a second percentage of an area of the T sub-pixel, and the first percentage is greater than the second percentage.

9. The apparatus of claim 1 wherein the liquid crystal layer in the R sub-pixel has an optical phase retardation that is between 40% to 60% of the optical phase retardation of the liquid crystal layer in the T sub-pixel.

10. The apparatus of claim 9 wherein ambient light passes the liquid crystal layer of the R sub-pixel twice, and backlight passes the liquid crystal layer in the T sub-pixel once, such that the phase retardation imparted to the ambient light is 80% to 120% of the phase retardation imparted to the backlight.

11. The apparatus of claim 1 wherein ambient light passes the liquid crystal layer of the R sub-pixel twice, and backlight passes the liquid crystal layer in the T sub-pixel once, such that the phase retardation imparted to the ambient light is 40% to 160% of the phase retardation imparted to the backlight.

12. A transflective display comprising:

pixels each comprising

a reflective (R) sub-pixel having a liquid crystal layer between a common electrode and an at least partially reflective electrode, at least one of the common electrode and the at least partially reflective electrode having first features to cause multiple domains to be formed in the liquid crystal layer of the R sub-pixel when a voltage is applied to the common electrode and the at least partially reflective electrode; and

a transmissive (T) sub-pixel having a liquid crystal layer between a common electrode and a transparent electrode, at least one of the common electrode and the transparent electrode having second features to cause multiple domains to be formed in the liquid crystal layer of the T sub-pixel when the voltage is applied to the common electrode and the transparent electrode;

wherein the first and second features affect electric field distributions in the R and T sub-pixels to cause the liquid crystal layer in the R sub-pixel to have an optical phase retardation that is between 20% to 80% of an optical phase retardation of the liquid crystal layer in the T sub-pixel.

13. The display of claim 12 wherein each of the first features and the second features comprise at least one of openings and protrusions.

14. The display of claim 12 wherein the first and second features comprise openings, the openings in the R sub-pixel have an area that is of a first percentage of an area of the R sub-pixel, the openings in the T sub-pixel have an area that is of a second percentage of an area of the T sub-pixel, and the first percentage is greater than the second percentage.

15. The display of claim 12 wherein the first and second features comprise openings, and at least one opening comprises an elongated slit.

16. The display of claim 12 wherein each of the common electrode and the at least partially reflective electrode of the R sub-pixel has an opening.

17. The display of claim 12 wherein each of the common electrode and the transparent electrode of the T sub-pixel has an opening.

18. The display of claim 12 wherein the at least partially reflective electrode of the R sub-pixel is electrically connected to the transparent electrode of the T sub-pixel.

19. The display of claim 12 wherein the at least partially reflective electrode comprises a transflective electrode having a reflectance greater than 30% and a transmittance greater than 30%.

20. The display of claim 19 wherein the transflective electrode comprises a metal grating having periodically spaced apart metal ribs.

21. The display of claim 12, further comprising a circular polarizer.

22. The display of claim 12, further comprising:

a first circular polarizer between the liquid crystal layer and a backlight module;

a second circular polarizer, the liquid crystal layer being between the first and second circular polarizers;

a first a-plate compensation film between the first circular polarizer and the liquid crystal layer;

a second a-plate compensation film between the second circular polarizer and the liquid crystal layer; and

a c-plate compensation film between the second a-plate and the liquid crystal layer.

23. The display of claim 12 wherein the liquid crystal layer of the R sub-pixel has a cell gap that is the same as a cell gap of the liquid crystal layer of the T sub-pixel.

24. An apparatus comprising

display pixels each comprising

reflecting and transmitting sub-pixels having substantially the same cell gap and having respective different driving electrode features that impart matching voltage-transmission and voltage-reflectance characteristics to the sub-pixels to permit a single gray-scale gamma curve to be used to drive the pixel in both a transmissive mode and a reflective mode, the different driving electrode features comprising at least one of different opening ratios and different protrusion ratios.

25. An apparatus comprising:

display pixels each comprising

a reflective (R) sub-pixel and a transmissive (T) sub-pixel and electrodes having features to cause multiple domains to form in a liquid crystal layer of each of the R and T sub-pixels, the features of electrodes of the R sub-pixel being different from the features of electrodes of the T sub-pixel to cause longitudinal electric fields and fringe electric fields to form in the R and T sub-pixels such that the R sub-pixel has a higher percentage of regions with fringe electric fields than that of the T sub-pixel.

26. The apparatus of claim 25 wherein the features comprises at least one of openings and protrusions.

27. A method of operating a display comprising:

driving a reflective (R) sub-pixel and a transmissive (T) sub-pixel of a pixel of a liquid crystal display using a common pixel voltage, the R sub-pixel and the T sub-pixel each having a liquid crystal layer, the R and T sub-pixels having a same cell gap;

generating a first electric field in the R sub-pixel to cause multiple domains to be formed in the liquid crystal layer of the R sub-pixel; and

generating a second electric field in the T sub-pixel to cause multiple domains to be formed in the liquid crystal layer of the T sub-pixel, the first electric field having a distribution that is different from that of the second electric field to cause the liquid crystal layer in the R sub-pixel to have an optical phase retardation that is between 20% to 80% of an optical phase retardation of the liquid crystal layer in the T sub-pixel.

28. A method comprising:

generating a first electric field in a liquid crystal layer of a reflective (R) sub-pixel of a pixel of a display, the first electric field having a longitudinal field portion and a fringe field portion;

forming multiple domains in the liquid crystal layer of the R sub-pixel based on the longitudinal and fringe field portions of the first electric field to cause the liquid crystal layer of the R sub-pixel to have a first optical phase retardation;

generating a second electric field in a liquid crystal layer of a transmissive (T) sub-pixel of the pixel, the second electric field having a longitudinal field portion and a fringe field portion; and

forming multiple domains in the liquid crystal layer of the T sub-pixel based on the longitudinal and fringe field portions of the second electric field to cause the liquid crystal layer of the T sub-pixel to have a second optical phase retardation such that the first optical phase retardation is between 20% to 80% of the second optical phase retardation.

29. The method of claim 28, further comprising imparting a phase retardation of λ

/2 to ambient light modulated by the R sub-pixel when the ambient light passes the liquid crystal layer of the R sub-pixel twice.

30. The method of claim 28, further comprising imparting a phase retardation of λ

/2 to backlight modulated by the T sub-pixel when the backlight passes the liquid crystal layer of the T sub-pixel once.

31. The method of claim 28, further comprising passing back light through a first circular polarizer, a first a-plate compensation film, the liquid crystal layer of the T sub-pixel, a c-plate compensation film, a second a-plate compensation film, and a second circular polarizer in sequence.