Introduction to display technologies Jean-Michel Lechevallier

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

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

Summary > 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.

1. Introduction to LCD.  History : 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.

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

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

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

1. Introduction to LCD.  Optical modes. ReflectiveReflectiveTransmissiveTransmissiveTransflectiveTransflective Backlight ON Backlight OFF Frontlight ON Frontlight OFF = LCD panel = backlight or frontlight

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

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

 LED and chromatic characteristics.  LED and their chromatic characteristics. 1. Introduction to LCD.

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

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

3. LCD module architecture.  Complete architecture of a module. TAB COG Driver

4. Color LCD 4.1. Passive matrix >Color cell Transmissive display

4. Color LCD 4.1. Passive matrix >Color cell Reflective display

4. Color LCD 4.1. Passive matrix >Color cell Transflective display solution 1 : with a transflective sheet The display reflectivity is adjusted by changing the reflectivity (transmissivity) of the transflector.

4. Color LCD 4.1. Passive matrix >Color cell Transflective display solution 2 : reflective surface on color filters Reflective area Transmissive area

4. Color LCD 4.1. Passive matrix >Optical modes comparison

4. Color LCD 4.1. Passive matrix >Grey scale generator 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 PWM = Pulse Width Modulation Advantage: No jittering Disadvantage: higher power consumption ON OFF ON OFF ON OFF T frame tHtH tHtH Duty cycle=t H /T frame ExampleGL=3/7ExampleGL=3/7 Frames

4. Color LCD 4.2. Active matrix >Introduction to TFT

4. Color LCD 4.2. Active matrix >Introduction to TFT  TFT cell structure

4. Color LCD 4.2. Active matrix >Advantages of TFT compared to CSTN  contrast  color saturation  response time  viewing angles >Disadvantages of TFT compared to CSTN  power consumption  cost

4. Color LCD 4.2. Active matrix >TFT LTPS (Low temperature Poly Silicon) 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.

4. Color LCD 4.2. Active matrix >Advantages and disadvantages of LTPS Advantages: higher electron mobility higher aperture ratio => enable to increase the resolution Disadvantages : production yield cost

4. Color LCD 4.2. Active matrix >System On Module Display area Sensor Memories Interface Controller Driver,DAC Embedded functions : - driver / controller - memories - peripheral audio functions - scanner - finger print recognition - etc.

5. Other technologies Field sequential >Introduction

5. Other technologies 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 >Advantages / Disadvantages

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

5. Other technologies OLED. Advantages / Disadvantages 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

5. Other technologies Others. >

6. Display technical characteristics 6.1. 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)

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

7. Comparison >

7. Comparison Color gamut >

FIN >