ISEP 2012 conference - Presenting Colour EPD


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Jim Watts, Principal Engineer held a presentation on Plastic Logic's colour electrophoretic displays, which are manufactured in the company's volume factory.

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ISEP 2012 conference - Presenting Colour EPD

  1. 1. Presenting a 10.7” flexible colour electronic paper display fabricated using a qualified manufacturing process. James D. Watts (Jim Watts) - C.Eng, M.Phil, B.Eng (Hons) DIS, MIETPresented at the International Symposium on Electronic Paper, October 31st 2012.
  2. 2. Content Plastic Logic introduction • Plastic electronics technology • Development of flexible backplanes • Qualified production process Colour display technology • OTFT device architecture • Spatially separated colour filter array • Review the colour performance • Considerations associated with EP colour Summary ISEP2012 Proprietary to Plastic Logic 2
  3. 3. Introducing Plastic Logic ISEP2012 Proprietary to Plastic Logic 3
  4. 4. Plastic Electronics TechnologyUses plastic instead of traditional silicon semiconductors and glassEnables a revolutionary design and form-factor Shatterproof, Thin, Large and Light Display ISEP2012 Proprietary to Plastic Logic 4
  5. 5. Company History Display Development10+ transistors 100+ transistors 1.2 M transistors Colour EPD 2.8 M transistors Research, Process Development & Manufacturing 2000: Cambridge Technology 2008: Dresden Display Factory Cambridge University Center translating research First plastic electronics factory in Research in organic electronics into products the world ISEP2012 Proprietary to Plastic Logic 5
  6. 6. R&D and Production Set-Up Technology Transfer Cambridge R&D Prototype Line (14”) Cambridge R&D Prototype Line  Ideal for proving new concepts  Highly configurable process  New designs in < 1 month  1” Chips to A4 displays  R&D Engineers ISEP2012 Proprietary to Plastic Logic 6
  7. 7. R&D and Production Set-Up Technology Transfer Dresden Factory (Gen 3.5) Dresden Gen. 3.5 Factory  Backplane Manufacturing  Qualified volume process  Production equipment  Fully Automated Handling  Process, Equipment, Integration Engineers  Thousands of displays/week ISEP2012 Proprietary to Plastic Logic 7
  8. 8. The Manufacturing ChallengeIt is one thing to show a single display at a tradeshow…...quite another to develop a high yield manufacturing process ISEP2012 Proprietary to Plastic Logic 8
  9. 9. Plastic Logic’s Manufacturing Process Key differences in manufacturing organic and flexible electronics: − Utilize solution processing to fabricate OTFTs − Process is designed to use lower temperatures which permits the use of lower cost flexible substrates − Exploit direct-write fabrication techniques to improve overlay tolerances and feature registration Have developed unique process know-how and IP: − Handling plastic sheets through assembly processes − Large area deposition technologies of organic and inorganic materials − Cleaning and conditioning of the layers to improve device performance Passed through the “Industrialisation” phase − Reproducibility − Homogeneity ISEP2012 Proprietary to Plastic Logic 9
  10. 10. Processing challenges in the development phaseOptimising process conditions is a critical part of industrialisation processMonitoring data from coating process in the first year (2009)Thickness mean Monitoring data from same process one year later Thickness mean ISEP2012 Proprietary to Plastic Logic 10
  11. 11. Display Testing and Reliability Flexible displays require special handling practises Test development for transistor and display parameters − Definition of test specifications − Electrical and Optical tests for production − Test methods for OTFT and other characterisation structures Reliability optimization for quality and lifetime behaviour − Accelerated test under different environmental conditions for lifetime projections − Based on existing models for Si-based integrated circuits − Parameters adapted to organic materials in terms of temperature sensitivities and reaction to cycling ISEP2012 Proprietary to Plastic Logic 11
  12. 12. Reliability tests Name Test Purpose Thermo cycling TST Mechanical robustness & CTE mismatch High Temperature Storage HTS Storage of transport conditionsAdvance Humidity Storage AHS Stability against moisture ingress Low Temperature Storage LTS Storage of transport conditions Real World Usage RWU Display use in non-accelerated modeAdvance Humidity Operation AHO Accelerated operation at high humidityLow Temperature Operation LTO Accelerated operation at low temperature Ambient Operation AO Accelerated operation at ambient conditions Solar storage SOR Solar robustness Altitude test ALT Pressure sensitivity ISEP2012 Proprietary to Plastic Logic 12
  13. 13. Colour electrophoretic displays ISEP2012 Proprietary to Plastic Logic 13
  14. 14. Colour EP Display Architecture Colour Filter Array (CFA) Encapsulation sheet layer Plastic Substrate E Ink Imaging Film Electrophoretic Frontplane (FP) Plastic Logic Backplane Technology Low Distortion Plastic Plastic Substrate Logic Backplane Colour Filter patterned by multiple approaches (wet printing, sheet-to-sheet alignment). During CFA pattern formation, the backplane pixel electrodes are not visible (obscured by FP media layer). Backplane:  1280 x 960 pixels (monochrome) == 640 x 480 Colour  150PPI (monochrome) ==75PPI Colour  Active Area: 217.6mm x 163.2mm (unchanged) ISEP2012 Proprietary to Plastic Logic 14
  15. 15. Process for overlaying a colour filterBlack and White pixel array Coloured sub-pixel array Greyscale image showing overlay Display Colour pixel G R B W 170mSchematic Plan view Colour sub-pixelOTFT cross-sectional Frontplane mediaview of single sub-pixel Pixel Electrode and Via Pixel Gate Capacitor Interlayer Dielectric Gate Interconnect Semiconductor Gate Dielectric Data line Drain Flexible Substrate ISEP2012 Proprietary to Plastic Logic 15
  16. 16. Process for resetting distortion Pixel Plastic Logic have Electrode presented a process for coping with the issue of Interlayer overlay distortion for multi- Via Dielectric layered stacks made of plastics The new process resets distortion at the top pixel electrode layer with no loss in pixel performance. This means pre-patterned layers can be placed on top (eg Colour Filter) Glass Backplane: All stack Plastic Backplane: Top Pixels layers on a regular grid maintained on a regular grid ISEP2012 Proprietary to Plastic Logic 16
  17. 17. Displaying colour – demand on single pixel driving Displaying Red Displaying Green Displaying Blue Displaying Cyan Displaying Yellow Displaying Magenta ISEP2012 Proprietary to Plastic Logic 17
  18. 18. Colour plots - consistency 15 10 5 BATCH1 b* 0 BATCH2 BATCH3 -5 -10 -15 -15 -10 -5 0 5 10 15 a*Data for 30 samples taken from three production batches ISEP2012 Proprietary to Plastic Logic 18
  19. 19. Topic 1 - Image renderingTopic introduction:To display an image in colour on an electrophoretic display with a colour filter layer,the image first needs to be processed to map to the layout of the colour filter.Typically various parameters (i.e., saturation and brightness) are also adjustedduring this process to maximize the final colour viewing experience. Before After Examples of files before and after colour conversion. IMC application software. ISEP2012 Proprietary to Plastic Logic 19
  20. 20. Topic 2 – Colour linearity• GRBW configuration offers independent control of the white sub-pixel• What should we do with this?Example 1: White sub-pixel follows minimum luminance ofthe red, green and blue sub-pixels i.e., W=min{R,G,B}Example 2: White sub-pixel follows minimum luminanceweighting of the red, green and blue sub-pixels using{0.299Red, 0.587Green, 0.114Blue} i.e., W=lum{R,G,B} ISEP2012 Proprietary to Plastic Logic 20
  21. 21. Topic 2 – Colour Linearity (Diluted colour)(Pure colour) Pure colour Diluted colour At 15th stateAt 8th state GR GR GR GR BW .. red .. BW BW red .. BW …. driving red example when W=min{R,G,B}GRBW 1 .. .. 7 8 9 .. .. 15 GR BWGRBW GR BWGRBW GR BWGRBW GR BWThe problem:− The diagram above shows 15 transitions from dark to light for various colours. The first 7 transitions are to brighten the pure colour from black, the final 7 transitions are to brighten the overall colour-pixel (by raising the brightness of the remaining colour sub-pixels).− The four box diagrams placed above the chart are given as an example for the colour red. In reality, the diagram above is more complicated as there are actually two sets of 0-15 transitions (because we can drive 16 grey levels for each) ISEP2012 Proprietary to Plastic Logic 21
  22. 22. Topic 2: W=min{R,G,B} W=min{R,G,B} ISEP2012 Proprietary to Plastic Logic 22
  23. 23. Topic 2: W=lum{R,G,B} W=lum{0.299R , 0.587G, 0.114B} ISEP2012 Proprietary to Plastic Logic 23
  24. 24. Topic 3 – Drive waveform controlling bloomingPhotograph revealing display effect of pixel blooming. ISEP2012 Proprietary to Plastic Logic 24
  25. 25. Topic 3: Drive waveform controlling updates• The waveform design for colour displays has a more significant impact on the waveform update appearance compared to monochrome displays.• With colour there is now a risk that unwanted colours are displayed during page turns, which can be distracting and detrimental to the visual experience• Minimising this effect whilst maintaining fast updates are vital considerations when developing drive waveform schemes. ISEP2012 Proprietary to Plastic Logic 25
  26. 26. Topic 3: Drive waveform controlling updates• Consider updating a colour pixel from white to red: • A standard method for driving monochrome EPD, which ensures all updating pixels finish at the same time, would result in the sub-pixel arrangement shown below during an update • In this example, during this transition it could be possible to introduce an interim state which forces the colour pixel to momentarily display cyan. Colour sub pixel appearance during the display update. ISEP2012 Proprietary to Plastic Logic 26
  27. 27. Summary ISEP2012 Proprietary to Plastic Logic 27
  28. 28. Qualified Flexible Displays: Now Available Display size 10.7” Backplane Grey Levels 16 Sub-pixel density 150ppi Contrast Ratio 12:1 Colour gamut 2% NTSC Highly flexible Paper-like finish Excellent readability Bi-stable EP media supports long battery life Colour ideal for office applications like charts and graphs 1280 x 960 Flexible Colour Display ISEP2012 Proprietary to Plastic Logic 28
  29. 29. Plastic Logic’s Displays• Plastic Logic have presented a 10.7” flexible colour electronic paper display fabricated using its qualified manufacturing process• The colour display is lightweight, robust and highly flexible• Plastic Logic is constantly searching for partners wishing to create new markets and opportunities for our display technology.• Please visit our YouTube channel to view our latest technology demonstrations: − ISEP2012 Proprietary to Plastic Logic 29
  30. 30. THANK YOU Plastic Logic Ltd 34, Cambridge Science Park Cambridge, CB4 0FX UK Tel.: +44 (0) 1223 706034 Email: www.plasticlogic.comThis presentation is for the general purpose of supplying information. PLL shall be in no manner liable for loss arising from any partys reliance onthe contents of this presentation. Any party requiring specific advice or guidance should contact PLL separately on that specific matter.You may need to own or be licensed to use complimentary technologies in order to use our flexible display technology in this application. It is yourresponsibility to ensure that you secure such rights, if necessary. ISEP2012 Proprietary to Plastic Logic 30