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Introduction to display technologies

Introduction to display technologies. Jean-Michel Lechevallier. Summary. 1. Introduction to LCD. History. How it works. Optical modes. CCFL, EL, Led. Lightguides. Optical films. LED and their chromatic characteristics. 2. Bistable LCD. 3. LCD module architecture.

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Introduction to display technologies

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  1. Introduction to display technologies Jean-Michel Lechevallier

  2. Summary • 1. Introduction to LCD. • History. • How it works. • Optical modes. • CCFL, EL, Led. • Lightguides. • Optical films. • LED and their chromatic characteristics. • 2. Bistable LCD.

  3. 3. LCD module architecture. LCD - driver connection. Complete architecture of a module. 4. Color LCD. 4.1. Passive matrix. Color cell (Transmissive, Reflective, Transflective). Optical modes comparison Grey scale generation (FRC, PWM). 4.2. Active matrix. Introduction to TFT. LTPS System on module. Summary

  4. 5. Other technologies. 5.1. Field sequential 5.2. OLED 5.3. Others. 6. Display technical characteristics. 6.1. Main characteristics. 6.2. Measurement methods. 7. Comparison. CSTN, TFT, OLED. Summary

  5. History. 1. Introduction to LCD. 1888 : discovery of liquid crystal phase by an Austrian botanist, Dr Rheinitzer 1968 : first liquid crystal display built by RCA years 1970 : developement of first LCD for mass production in Japan.

  6. How it works (1/3). 1. Introduction to LCD.

  7. 1. Introduction to LCD. How it works (2/3). TN, STN, DSTN, FSTN technologies.

  8. 1. Introduction to LCD. How it works (3/3). Alignment layers.

  9. Optical modes. Backlight ON Backlight ON Backlight OFF Frontlight OFF Frontlight ON Transmissive Reflective Transflective = LCD panel = backlight or frontlight 1. Introduction to LCD.

  10. sources : CCFL, EL, Led. Lightguides : FrontlightBacklight 1. Introduction to LCD.

  11. Optical films main supplier : 3M 1. Introduction to LCD. 2 technologies: - microreplication : adjustment of the light reflection angles => ex. : BEF, xBEF - multi layer : light filtering => ex. : DBEF

  12. LED and chromatic characteristics. 1. Introduction to LCD. • LED and their chromatic characteristics.

  13. Bistable LCD - BiNem technology from Nemoptic 2. Bistable LCD.

  14. 3. LCD module architecture. • LCD - driver connection. • COB : Chip On Board, • TAB : Tape Automated Bonding (TCP : Tab Carrier Package), • COF : Chip On Foil - Flex, • COG : Chip On Glass.

  15. 3. LCD module architecture. • Complete architecture of a module. TAB COG Driver Driver

  16. Color cell 4. Color LCD4.1. Passive matrix Transmissive display

  17. Color cell 4. Color LCD4.1. Passive matrix Reflective display

  18. Color cell 4. Color LCD4.1. Passive matrix Transflective display solution 1 : with a transflective sheet The display reflectivity is adjusted by changing the reflectivity (transmissivity) of the transflector.

  19. Color cell 4. Color LCD4.1. Passive matrix Transflective display solution 2 : reflective surface on color filters Reflective area Transmissive area

  20. Optical modes comparison 4. Color LCD4.1. Passive matrix

  21. Grey scale generator 4. Color LCD4.1. Passive matrix PWM = Pulse Width Modulation Advantage: No jittering Disadvantage: higher power consumption FRC = Frame Rate Control alternatively light on and off pixels during several frames => the average light creates the grey level. Advantages: lower power consumption better contrast less flickering Disadvantage : jittering tH Example GL=3/7 ON OFF ON OFF ON OFF OFF Tframe Frames 1 2 3 4 5 6 7 Duty cycle=tH/Tframe

  22. Introduction to TFT 4. Color LCD4.2. Active matrix

  23. Introduction to TFT TFT cell structure 4. Color LCD4.2. Active matrix

  24. Advantages of TFT compared to CSTN contrast color saturation response time viewing angles 4. Color LCD4.2. Active matrix • Disadvantages of TFT compared to CSTN • power consumption • cost

  25. TFT LTPS (Low temperature Poly Silicon) 4. Color LCD4.2. Active matrix LTPS : electron mobility increased compared to amorphous TFT technology : electron mobility p-SI TFT = 200cm²/V.S a-Si TFT = 0.5cm²/V.S => enable to reduce transistor size and embed more electronic functions on the glass substrate.

  26. Advantages and disadvantages of LTPS 4. Color LCD4.2. Active matrix Advantages: higher electron mobility higher aperture ratio => enable to increase the resolution Disadvantages : production yield cost

  27. System On Module Memories Interface Driver,DAC Controller Sensor Display area 4. Color LCD4.2. Active matrix Embedded functions : - driver / controller - memories - peripheral audio functions - scanner - finger print recognition - etc.

  28. Introduction 5. Other technologies.5.1. Field sequential

  29. Advantages / Disadvantages 5. Other technologies.5.1. Field sequential Advantages: up to 85% of NTSC color gamut High resolution (1dot/pixel) Disadvantages: the display is black and white in reflective mode dedicated controller specific LC cells (very fast response time) a sorting of tricolor LED is necessary to reduce color variations Necessary to adjust the color balance

  30. Introduction Light Current Cathode (AL:Li) Emission Layers Hole Injection Layer － － － － － － － － － － + + + + + + + + + + + Electron － Anode (ITO) Hole + Light Glass Substrate 5. Other technologies.5.2. OLED.

  31. Advantages / Disadvantages 5. Other technologies.5.2. OLED. Advantages contrast viewing angles very thin module (no backlight) response time (1µs) color saturation Disadvantages lifetime (especially for blue) Brightness is a bit low power consumption emissive technology

  32. 5. Other technologies.5.3. Others.

  33. 6. Display technical characteristics6.1. Characteristics Contrast (transmissive and reflective) Transmittance (%) Reflectance (%) Response time (ms) Viewing angles (transmissive and reflective) (degrees) Chromatic co-ordinates (transmissive and reflective) (defined in CIE 1931 diagram) Color gamut (surface or % of NTSC triangle) Open ratio (%) Aperture ratio (%) Brightness (cd/m²) Backlight uniformity (%) Power consumption (mW)

  34. 2 methods for measurements in reflective mode (contrast, reflectivity, …) 6. Display technical characteristics 6.2. Measurement methods Specular diffuse Use a point light source. Use a sphere to diffuse the light in every direction => this method is the most representative of normal lighting condition.

  35. 7. Comparison

  36. 7. ComparisonColor gamut

  37. FIN Applause ...

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