1. Tutorial 6 Derek Wright Wednesday, March 2 nd, 2005

2. Sensors and Image Systems Liquid Crystal Displays Organic Light Emitting Diode Field Emission and Plasma Displays Electronic Paper

3. Display Types Light Generating –Each pixel generates photons based on image data Light Controlling –Each pixel controls whether or not light passes through based on image data

4. Passive Matrix Rows (or columns) can only be driven one at a time Rows are driven sequentially Columns determine which pixels are on and which are off (based on image data) Each row is only being driven for (1/rows) Each pixel mush be driven extra bright to fool the human eye into thinking it’s always on

5. Passive Matrix

6. Active Matrix Each pixel has it’s own circuit that loads and stores that pixel’s data This allows the pixel to remain on while data is loading in other rows Enables bigger higher-resolution displays Pixels do not have to be driven too hard as in passive matrix

7. Active Matrix V DD V Data V Address

8. Liquid Crystal Phases

9. Liquid Crystal Displays Liquid Crystal Displays (LCDs) exploit liquid crystal’s ability to bend light Polarized light enters the back of a liquid crystal pixel The light passes through nematic phase liquid crystal, which bends the light’s polarization plane The light passes through another polarizer (NW) When an E-field is applied, the liquid crystal doesn’t bend the light and it can’t pass through the polarizer (NW)

10. Twisted Nematic Effect

11. LCD Benchmarks Current highest resolution: –368 ppi –3840 x 2400 QUXGA @ 22.2” Biggest size: –Sharp @ 65” with 1920 x 1080 Cost: –$400 for 15”, $9,000 for 45”

12. Reflective LCDs No backlight Designed to reflect ambient light Bad in the dark Good under bright conditions, like outdoors Low power with no backlight

13. Reflective LCDs

14. Transreflective LCDs Combine features of both transmissive and reflective LCDs Reflective for high ambient lighting Transmissive for low ambient lighting Less power than a fully transmissive LCD Each pixel is divided into a reflective part and a transmissive part

15. Projection Displays An image is produced using either transmissive or reflective means Optical mirrors and lenses magnify the image to occupy a large area Liquid Crystal on Semiconductor (LCoS) current leader in projection televisions CMOS process means cheap and on-chip integration

16. LCoS

17. OLEDs Organic Light Emitting Diodes Organic molecules can be tailored to act as an LED They can emit photons Brighter than current TVs Fast switching Should eventually be cheap

18. OLED Deposition OLEDs can be deposited using many different means –Depends on the physical properties of the organic molecule Vapour-phase deposition Liquid-phase deposition –Enables really cheap manufacturing methods, like using an ink-jet printer to pattern the layers

19. OLED Structure

20. Single vs. Double Layer

21. Field Emission Occurs under high voltage Electrons are stripped off of an electron emitter Accelerated using externally applied E- field Sharp tips release more electrons Different than tunneling current

22. Coming to a sharp point deforms the E- field at the tip This makes it easier for electrons to tunnel across the potential barrier Material should have a low work function and be resistant to sputtering Field Emission Tips

23. Potential Barrier To strip electrons off the surface they need to overcome the potential barrier It can be lowered with an externally applied E-field Tip shape affects local E-field metal W0W0 WFWF eE 1 eE 2 Energy Distance from cathode surfacez=0 vacuum 

24. Phosphor Screens Made of inorganic powders with particle grain size 3 to 8  m Electron impact causes photon emission, just like in CRT Layer can’t be too thick or emitted photons will get re-adsorbed Layer can’t be too thin or too many electrons will pass through without impact Optimal thickness = ~2x grain size

25. Plasma Displays Each pixel in a plasma display is like a tiny fluorescent light bulb A plasma is “fired” Xenon gas emits UV photons A phosphor coating converts the UV into visible light

26. Electronic Paper Ultimate goal of display technologies: –Emulate printed paper Ultra-low power Perfectly bistable (keeps image with no power) Flexible, foldable High contrast ratio Appear paper white Lightweight User-friendly

27. Electrophoretic Displays A solution of black dye and suspended white particles The white particles move in an applied E- field There’s a transparent electrode (ITO) and a back electrode Voltage is used to move the white particles to the surface for a white pixel, or to the bottom for a dark pixel

28. Electrophoretic Displays

29. Improvements can be made “microencapsulating” dye and pigment Prevents lateral motion between pixels Pigments tend to want to stick together under high field –Microcapsules prevent agglomeration of sizes bigger than the capsule –Improves display lifetime

30. Electrophoretic Displays

31. Rotating Ball Displays Tiny balls (~100  m) are made with one half white and one half black There is a macroscopic charge on the balls, so that black is positive and white is negative (or vice versa) The balls are suspended in oil and sandwiched between transparent and flexible substrates An external E-field “printer” is used to write the pattern to the display

32. Rotating Ball displays

33. Thank You! This presentation will be available on the web.