LED Modern Applications and Future Advancements by 1Eztw8ZD

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									  LED Modern Applications and
     Future Advancements

• Timothy Delf
• Jason Brownlee
• February 18, 2005

• ECE 3611
• Dr. Stanley G. Burns
           Focus of Report
• LED Background
• Structure and Concepts Regarding LEDs
• Future Advancements & New Technology
    • OLED
    • White LEDs
• Problems Facing LED Advancements
                   Background
• Available in multiple wavelengths & colors
• Long life at 100,000 hours LED's are the light source with
  the longest life currently available in the world.
• LED's operate as 12 and 24-volt DC systems
• High luminescence efficiency
• Based on the general properties of a simple twin-element
  semiconductor diode
• LEDs don’t emit ultraviolet light, which degrades
  electrical components, and they emit minimal infrared
  light, the main component of heat
           Background (Cont.)

•   Extremely quick refresh rate
•   Exceptionally wide color palette
•   Potential for mind-boggling efficiency
•   Numerous Applications (cell phones, signs,
    stereos, etc.)
             Colors Available

•   Red
•   Amber
•   Yellow
•   Green
•   Blue
•   White
             Structure and Concepts
                Regarding LEDs
•   Heart of a light emitting diode is a
    semiconductor chip.
•   The diode semiconductor contains
    several very thin layers of material
    that are sequentially deposited onto
    a supporting substrate.
•   Diode chip is mounted in a reflector
    cup connected to a lead frame, and
    is bonded to the anode and cathode
    terminals of the frame through
    miniature bonding wires.
•   Entire assembly is then encased in
    a solid epoxy dome lens
            Structure and Concepts
               Regarding LEDs
•   A diode comprises a N-type
    material bonded to P-type
    material, with electrodes on
    each end.
•   Connecting the N-type side of
    the diode to the negative end of
    a circuit and the P-type side to
    the positive end eliminates
    depletion zone.
•   Free electrons moving across a
    diode can fall into empty holes
    from the P-type layer.
•   Creates Photons - basic units of
    light.
   All diodes can produce “light”

• Most just don’t
  produce visible light
• Wavelength of the
  photon must be
  between 400 nm and
  750 nm
   Even if a diode does produce
visible light it must also meet these
    requirements to be effective

 • Must not absorb the photons emitted

 • Instead release photons outward

 • Plastic bulb to concentrate light
(a) Diode absorbs photons
(b) LED reflects photons
(c) Bulb holds photons at top
       Future Advancements: OLED

• Organic light-emitting diode--
  display device that sandwiches
  carbon-based films between
  two charged electrodes
• When voltage is applied to the
  OLED cell, the injected positive
  and negative charges recombine
  in the emissive layer and create
  electro luminescent light
• Beginning to replace LCD
  technology in handheld devices
  (PDA, Cell phone, etc)
Future Advancements: OLED-
Advantages Over Liquid Crystal
       Display (LCD)

 •   Don’t require a backlight
 •   Faster response time
 •   Smaller and thinner
 •   Less power consumption
 •   Cheaper to make
      Future Advancements: OLED
• Doping or enhancing organic
  material helps control the
  brightness and color of light
• Active matrix OLED displays
  stack cathode, organic, and
  anode layers on top of another
  layer – or substrate – that
  contains circuitry
• Passive matrix OLED displays
  stack layers in a linear pattern,
  much like a grid, with
  “columns” of organic and
  cathode materials superimposed
  on “rows” of anode material
    Future Advancements: OLED
•
       Future Advancements:
            White LED

• Caused by adding phosphor to material used
  to create blue LEDs
• InGaN + Phosphor
• Useful for automobile headlights, etc
• Eventually used for general illumination
    General Illumination: LED

• Not possible yet
• Needs greater efficiency
• Perfection of light that is perceived as true
  white to human eye
• Eventually could take over the incandescent
  and fluorescent light bulb
        Problems Facing LED
           Advancements

• White LED lights include a lack of high
  efficiency at all colors, especially in the
  yellow/green where luminosity is the
  highest
• Lack of efficient color mixing
• LEDs dissipate heat by conduction rather
  than radiation
         Efficiency Problems

• Some electron-hole combinations create
  heat-producing vibrations instead of
  photons
• Some internal resistance also produces heat
• Research on using different materials will
  hopefully solve this
        Problems with OLEDs
• Color OLEDs still aren't as long-lived as they need
  to be; reds and blues tend to die after a few
  thousand hours, leaving plenty of green and not
  much else.
• While OLEDs deliver positive qualities like high
  contrast ratio, wide viewing angle, and lots of
  brightness, the down side is that the paper thin-
  film material reacts immediately when it comes in
  contact with water, creating black spots on the
  surface.
               Conclusion

•   LEDs have a promising future
•   OLED display could take over LCD
•   True white LED becoming possible
•   Eventually replacing incandescent &
    fluorescent light bulbs for general
    illumination
Questions?

								
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