1. A Multi-Performance Film for Highly Efficient LCD Backlights
多重性能薄膜應用於高效率的背光模組
Speaker: Jen-Chieh Hsieh (謝仁杰)
Advisor: Prof. Han-Ping D. Shieh (謝漢萍教授)
Prof. Yi-Pai Huang (黃乙白 助理教授)
Dept. of Photonics & Inst. of Electro-Optical Eng.1, Display Institute2,
National Chiao Tung University, Hsinchu, Taiwan
(國立交通大學)
March 6th, 2008 1

2. Outline Introduction Direct-lit backlight unit
Motivation and Objective
Multi-Performance Film (MPF)
Principle
Fabrication method
Simulation and Experimental results
Discussions
Conclusions and Future works
1st I will introduce the background of the direct-lit backlight unit and its issue.
After that are motivation and objective.
And then I will introduce purposed idea “MPF”, and fabrication method.
After that, I will show you sim and exp results.
Finally, dis, con and fut work will be given.

3. Introduction Liquid crystal (LC)-TV tend to develop bigger size!
Require higher brightness
Brightness outputted from display: > 500 cd/m2
Direct-lit backlight unit for LC-TV
Provide highly bright and uniform light source
Output brightness: > cd/m2
(transmittance of LC-panel is ~5%)
Uniformity: > 85%
As we know, LC-TV are more popular in recent, and it will replace all traditional CRT TV in the future.
Now, LC-TV tend to develop bigger size, however, big size display does not like small size display, it require higher brightness.
In general, the brightness outputted from display has to higher than 500 nits.
Therefore, for this purpose, direct-lit backlight unit is usually utilized in LC-TV.
Because, it can provide highly bright and uniform light source.
And the general specification of direct-lit B/L, for example, brightness has to higher than ..., and uniformity has to higher ....

4. Introduction Conventional direct-lit backlight unit Quality of B/L?
Top diffuser
(adjust light distribution for output)
Brightness enhancing film (BEF)
(enhance normal brightness)
Bottom diffuser
(adjust suitable light distribution for input of BEF)
Finally, we can get a flat light source. But, how about the quality of a B/L unit?
In general, the most important issue is Lamp-Mura defect.
Diffusive plate
Lamp
(CCFLs)
(output uniform light distribution)
Reflector

5. How to eliminate Lamp-Mura efficiently?
Motivation
Issue: Lamp-Mura defects
A kind of period pattern caused by lamps with
strong brightness
Optical films without enough scattering ability
General solutions: (M. Schiavoni, et al., SID’07 Digest)
Stack more diffusers
Increase more lamps
Increase distance from lamp to film
 high cost, low brightness
 high cost
 Large volume
Objective of this research:
Study and develop Multi-performance film (MPF)
to replace conventional BEF to eliminate Lamp-mura defects without increasing cost and kept optical performance
How to eliminate Lamp-Mura efficiently?
What is Lamp-Mura?
In the right picture, we can see this a output image from B/L unit, the bright and dark period pattern is Lamp-Mura.
It is caused by strongly bright lamps. On the other hand, we can say, because optical films have not enough scattering ability to eliminate Lamp-Mura.

6. Enhance normal brightness
Principle of MPF
Multi-performance film (MPF)
Concave lens structure on the surface
α = 90°
n1=1.6000
n2=1.5663
R is variable R n2 α
Enhance normal brightness n1
Scattered
Passed
Blocked
Straight
Features of MPFs:
Integrated functions of BEF and diffuser
High light-coupling efficiency
Convention BEF
MPF

7. Fabrication method Screen printing process by Emphasis Materials Co.
Advantages of screen printing process:
Low cost in fabrication
Flexible design in different curved-prism structures

8. Fabrication results Captured results by OM
Surface profiles by Alpha-step
0% (BEF) % %
Summaries of MPFs:
Integrated functions of brightness enhancement and scattering
Simple, low cost and flexible design in fabrication process

9. Demonstration target 3 cases to do comparison
32” direct-lit backlight unit
12 straight lamps
Input power (one lamp): ~6W
Output brightness: ~20000 nit
3 cases to do comparison
Vertical
Horizontal
MPF Case
Reference Case
HEDP: highly efficient diffusive plate
Applied on present product
Have no Lamp-Mura
MPF-Plate Case

10. Definition of contrast
Contrast (or Modulation)
Measure 9 points between one pitch by Conoscope
Lmax
Luminance
Position at vertical direction
Lmin
For example:
Contrast = 0  No Lamp-mura
Contrast = 1  Worst θ
0 °
one pitch
lamp
point 9
point 0
films

11. 10% MPF is best with no Lamp-mura
Experimental results
Compare brightness and contrast at normal direction between Ref. Case and MPF Case in different filling ratios of MPFs
10% MPF is best with no Lamp-mura

12. Experimental results Comparison of CCD captured results
20 cm
Measured area
Reference
MPF (0%)
MPF(10%)
MPF-Plate
MPF can be efficient to eliminated Lamp-Mura defects with 10% filling ratio

13. Experimental results
Comparison of normal brightness and FWHM luminance viewing angle
*FWHM: full width at half maximum
MPF can enhance luminance viewing angle at vertical and horizontal direction
Non-reduced brightness
10% brightness decreased
More than 45% FWHM enhancement (80°116°)
~13% FWHM enhancement (80°90°)

14. Experimental results Comparison of output lighting efficiency
MPF can enhance output lighting efficiency higher than 8% in MPF case and MPF-Plate case
~8% enhancement
~19% enhancement

15. Discussion (1) Summary of comparison MPF case MPF-Plate case
High luminance viewing angle
High output lighting efficiency
Low cost (without HEDP)
MPF-Plate case
Low brightness at normal
Higher luminance viewing angle
Higher output lighting efficiency
 suitable to apply to present B/L product
Reference Case
 suitable for large viewing angle request
 increase brightness of light source
MPF Case

16. Discussion (2) Tendence of B/L unit: Slim! Patterned-MPFs
When B/L unit become slim, the Lamp-Mura defect will be more serious!
MPFs have limitation to eliminate Lamp-Mura in decreasing thickness of B/L unit
Patterned-MPFs
Optimized filling ratio at corresponding position by screen printing process
Smaller amount of lamp and thinner thickness
Customization

17. Conclusions
MPF has been designed and realized to eliminated Lamp-Mura defects efficiently
Reference
MPF (0%)
MPF(10%)
MPF-Plate(10%)

18. Conclusions
MPF can apply to different B/L structures to improve optical performances
MPF case
Free Lamp-Mura
Non-reduced brightness
~13% enhancement in FWHM
~8% enhancement in output lighting efficiency
MPF case
Free Lamp-Mura
10% brightness decreased
~45% enhancement in FWHM
~19% enhancement in output lighting efficiency
MPF Case
MPF-Plate Case

19. Conclusions
MPF can use pattern technology to develop Patterned-MPFs that have some features:
Slimmer B/L and smaller amount of lamp in use are possible
Customization is possible

20. Future works Short-term Long-term
Finish simulation of MPF and Patterned-MPF
Find threshold contrast of free Lamp-Mura by experiment
Long-term
Realize patterned-MPFs
Design 2-D MPF/Patterned-MPF for LED B/L unit

21. Thank You for Your Kind Attention! 21

23. Measurement instrument
Conoscope
Measure angular luminance distribution
BTDF measuring device
Measure BTDFs of films by cooperating with Conoscope
CCD
Capture spatial luminance distribution

24. Experimental results
Compare brightness and contrast between Ref. Case and MPF Case in different filling ratios of MPFs
Viewing angle: 0 °
Viewing angle: 60 °