LED Modern Applications and Future Advancements

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LED Modern Applications and Future Advancements

• Timothy Delf
• Jason Brownlee
• February 18, 2005
• ECE 3611
• Dr. Stanley G. Burns

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Focus of Report

• LED Background
• Structure and Concepts Regarding LEDs
• Future Advancements New Technology
• OLED
• White LEDs
• Problems Facing LED Advancements

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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 dont emit ultraviolet light, which degrades
  electrical components, and they emit minimal
  infrared light, the main component of heat

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Background (Cont.)

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

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Colors Available

• Red
• Amber
• Yellow
• Green
• Blue
• White

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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

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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.

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All diodes can produce light

• Most just dont produce visible light
• Wavelength of the photon must be between 400 nm
  and 750 nm

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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

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(a) Diode absorbs photons(b) LED reflects
photons(c) Bulb holds photons at top
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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)

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Future Advancements OLED-Advantages Over Liquid
Crystal Display (LCD)

• Dont require a backlight
• Faster response time
• Smaller and thinner
• Less power consumption
• Cheaper to make

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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

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Future Advancements OLED

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Future AdvancementsWhite LED

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

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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

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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

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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

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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.

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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

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Questions?