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An Overview of OLED Display Technology

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An Overview of OLED Display Technology Powered By Docstoc
					       An Overview of OLED Display Technology

                                                Homer Antoniadis
                                           OSRAM Opto Semiconductors Inc.
                                                  San Jose, CA




Homer Antoniadis | OLED Product Development|
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      Outline


         ! OLED device structure and operation
         ! OLED materials (polymers and small molecules)
         ! Evolution of OLED performance
         ! OLED process and fabrication technologies
         ! White emitting OLEDs
         ! Color capabilities
         ! Products and demonstrators



Homer Antoniadis | OLED Product Development|
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            OLED display and pixel structure

                                      Display                                            Pixel

                                                        Cover glass


         Cathode
                                                                               Cathode (Ba,Ca/Al 2000 Å)
                                                      Emissive polymer layer
                                                                                Emissive polymer layer
                                                                                       ~ 800 Å

      Conducting                                                               Conducting polymer layer
    polymer layer                                                                     ~ 1200 Å


                                                      Epoxy                    Anode (ITO 1500 Å)


    Anode
                                                                               Single pixel structure


                                    Glass substrate



   Human hair is 200X the thickness of the OLED layers

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     OLED Device Operation Principles

                                                           OLEDs rely on organic materials (polymers or small
                                                           molecules) that give off light when tweaked with an
                                                           electrical current
    _ _ _ _ _ _ _
   Cathode                                                 ! Electrons injected from cathode
   Emissive polymer
       _+           _ __                                   ! Holes injected from anode
                    +
                                               V           ! Transport and radiative recombination of electron hole
     +              +       +                                pairs at the emissive polymer
   Conducting polymer

   + + + + + + ++ +
   Anode

                                                                 OLED device operation (energy diagram)
                                                                                         Conducting                              Cathode-
                                                                                                           Emissive polymer
                                                              Transparent                 polymer                                layer (s)
              light                                            substrate
                                                                            Anode
                                                                             (ITO)
                                                                                              LUMO             e
                                                                                                                -            -
                                                                                                                             e

                                                                                                                    LUMO


                                                   Light                                      HOMO
                                                                                         h+           h+
                                                                                                                    HOMO
                                                                                                              h+
                                                                            ca. 100 nm    10 - >100 nm             <100 nm       >100 nm


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                                              Optoelectronic Device Characteristics
                                 Luminance-Current-Voltage                                                                 Efficiency-Luminance-Voltage
                                 10
                                      0
                                                                                                          12                                                        12
                                      -1
                                 10                                                                                                                                 10
       Current Density (A/cm )




                                                                                                          10
     2




                                                                                      Efficiency (cd/A)
                                      -2
                                 10




                                                                                                                                                Efficiency (cd/A)
                                                                                                                                                                    8
                                 10
                                      -3
                                                                                                           8
                                      -4                                                                                                                            6
                                 10
                                                                                                           6
                                 10
                                      -5
                                                                                                                                                                    4

                                 10
                                      -6                                                                   4
                                                                                                                                                                    2
                                      -7
                                 10
                                                                                                           2                                                        0
                                       -8     -6   -4    -2   0     2     4   6   8                         10       100     1000       10000                            0   2      4          6   8
                                                                                                                                    2
                                                        Voltage (Volts)                                            Luminance (cd/m )                                             Voltage (V)
                                      5
                                 10

                                      4
                                                                                                                 LUMINANCE is the luminous intensity per unit
                                 10
                                                                                                                 area projected in a given direction
 Luminance (cd/m )
2




                                      3
                                 10
                                                                                                                 The SI unit is the candela per square meter
                                 10
                                      2
                                                                                                                 (cd/m2), which is still sometimes called a nit
                                      1
                                 10
                                                                                                                 The footlambert (fL) is also in common use:
                                 10
                                      0
                                                                                                                 1 fL = 3.426 cd/m2
                                  -1
                                 10                                                                              http://www.resuba.com/wa3dsp/light/lumin.html
                                          0        2          4           6       8
                                                        Voltage (Volts)

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              Evolution of LED performance

                                               SM OLED



                                                    Polymer
                                                    OLED




      Courtesy of Agilent Technologies

Homer Antoniadis | OLED Product Development|
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     Electroluminescent Conjugated Polymers


         Conducting polymers
         ! Polyaniline (PANI:PSS)                                       NH

         ! Polyethylenedioxythiophene
           (PDOT:PSS)                                             PANI           PDOT           PSS

         Emissive polymers
                                                            R1
         ! Polyphenylenevinylene (R-PPV)

         ! Polyfluorene (PF)                                       R1
                                                                             n
                                                                                                      n
                                                                                        R1 R1
                                                                 R-PPV
         Processed by :                                                                  PF
         Spin casting, Printing, Roll-to-roll web coating

         IP owned by Cambridge Display Technology


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    Multiple emission colors achieved by Covion

       Different emission colors can be obtained with a variety of chemical structures




                                                                 300 nm   500 nm         700 nm

 PPP
                                                   n




 PPV
                                                            OR
                                                                 CN
 PT or
                                               S
CN-PPV                                                 RO




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Multiple emission colors achieved by Dow Chemical




                                                        n
                                               R1 R 1

                                                PF




Homer Antoniadis | OLED Product Development|
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     Polymer OLED display fabrication steps



                        Deposit and pattern anode (ITO)



                                               Pattern polymer layers
                                                (first conducting then emissive)
                                               Spin coating
                                               Ink Jet printing
                                               Screen printing
                                               Web coating

   Vacuum deposit and pattern cathode (Ba,Ca/Al)




Homer Antoniadis | OLED Product Development|
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             Ink Jet Printing to Pattern Polymers
             (Full Color Applications)



       Ink Jet Head




                   Red                 Green      Blue
                  emitter              emitter   emitter




                     Substrate



                 Ink Jet printing to define and pattern R, G, B emitting subpixels



Homer Antoniadis | OLED Product Development|
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     The Holy Grail: Flexible OLEDs




                                               Sheila Kennedy, Harvard Univ., 1999

Homer Antoniadis | OLED Product Development|
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Polymer and Small Molecule Device Structures



                                           Small molecule         Polymer

           Cathode - Li/Al                                                         Cathode – Ba, Ca/Al
                  ETL - Alq3
                                                                                   ETL - PPV, PF
        EML - doped Alq3

                 HTL - NPB                                                         HIL - PDOT, Pani
               HIL - CuPc
             Anode - ITO                                                           Anode - ITO
         Substrate - glass                                                         Substrate - glass




                                      Multi-layer structure    Bilayer structure
                                      made all in vacuum      made from solution



Homer Antoniadis | OLED Product Development|
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            Electroluminescent Small Molecules


   Hole transport small molecules
          ! Metal-phthalocyanines              N                     N
          ! Arylamines, starburst amines
                                                       NPD

   Emissive small molecules
          ! Metal chelates, distyrylbenzenes                 N
                                                       O
          ! Fluorescent dyes                       N       Al O
                                                       O
                                                                 N

          Processed and deposited by :
          thermal evaporation in vacuum                Alq3

          IP owned by Eastman Kodak


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         Full color patterning with small molecules

                                           substrate
                                                       R emission layer      Cathode separator   Shadow mask


                                                       ITO




                                                              G emission layer               Shadow mask


                                                       ITO
                NPD                            Alq3


                                                                          B emission layer   Shadow mask


                                                       ITO



        Small molecules are thermally
                                                               R, G, B pattering is defined by
          evaporated in vacuum                                   shadow masking in vacuum



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White emitting small molecule OLEDs




                                               Initial Luminance 1000nits




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     Phosphorescent small molecule OLED
     (both singlets and triplets are harvested)




                                               ηext=19% and ηint =87%
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      Full-color/Multi-color Approaches

   RGB- polymer emitters                                  Color filters                 Color Changing Media
                                                          White emitter                        (CCMs)




Advantages:                                    Advantages:                            Advantages:
- power efficient                              - well-established technology (LCD)    homogeneous aging of emitter (?)
- lower production cost                        - no patterning of emitter necessary   more efficient than filters
- mature ITO technology                        - homogeneous aging of emitter (?)     no patterning of emitter necessary

                                               Disadvantages:                         Disadvantages:
Disadvantages:
                                               - power inefficient                    ITO Sputtering on CCMs
- emitters have to be optimized
                                                                                      stable blue emitter necessary
  separately (common cathode?)                 - ITO sputtering on filters
                                                                                      aging of CCMs
- differential aging of emitters               - efficient white emitter necessary
- patterning of emitters necessary



Homer Antoniadis | OLED Product Development|
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Obtaining a Full Color OLED Display

                                                                                                      1.0




                                                                          EL Intensity (normalized)
                                                                                                      0.8
                                                                                                      0.6

                                                                                                      0.4

                                                                                                      0.2
                                                                                                      0.0
                                       Green polymer                                                     400 450 500 550 600 650 700 750
                                                                                                                 Wavelength (nm)
           AM TFT screen
                                                 Red polymer       Ink Jet printing of R,G,B emissive polymers
                                                                            defines the R,G,B subpixels
                                                                                                  (xR, yR)      (xG, yG)      (xB, yB)
   Blue polymer


                                                               R      G                                B




Homer Antoniadis | OLED Product Development|
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     Device Color, Efficiency and Lifetime


                                                        Polymers                    Small Molecules

                                               Efficiency   Half-Life* (hrs)   Efficiency   Half-Life* (hrs)
                     Color
                                                 (cd/A)     @150 nits, RT        (cd/A)     @150 nits, RT

                      Red                         1-2          >20,000            4-5          >40,000

                    Green                        8-10           15,000            8-9          >40,000

                     Blue                          4            3,000              3            10,000

                    Yellow                       8-10          >30,000             8           >30,000

                    White                         2-4           5,000             6-8           20,000

          *Extrapolated Lifetime under constant current conditions


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     Small Molecule Passive Matrix Display Products




                                                                                      96x64 Full Color
                                                                                        PM Display

                                               Motorola (by Appeal)

                                                                      Samsung Electronics
                                                                      Kodak Licensed SNMD to
                                                                      Manufacture PM OLED Displays




                                               Lucky Goldstar (LG)




Homer Antoniadis | OLED Product Development|
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     Small Molecule Active Matrix Display Products




                       Eastman Kodak: Digital camera   Sanyo: Cell Phone with Digital camera




Homer Antoniadis | OLED Product Development|
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Top Emitting Active Matrix OLED Display

  Top Emission Adaptive Current Drive technology, allows OLEDs to
  be larger and higher in brightness and resolution.
  A 13-inch full-color AMOLED using poly-Si TFT was made where
  the light emits through the transparent cathode and thus, the filling
  factor does not depend on the TFT structure.

  The schematic vertical structure of the device is
  substrate/TFT/metal anode/organic layers/transparent
  cathode/passivation layer/transparent sealing.

  Display format: 800 x 600 (SVGA); pixel pitch 0.33x0.33mm2




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     Polymer Passive Matrix Display Products




                                               Philips: Electrical Shaver
                                                                            Delta Electronics: Display for MP3 player




Homer Antoniadis | OLED Product Development|
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     OSRAM Opto Semiconductors evaluation kit




 San Jose, CA – May 15, 2003 -- Osram Opto Semiconductors, a global leader of solid-state lighting devices,
 today announced its Pictiva™ Evaluation Kit. Announced earlier this week, the Pictiva brand is Osram’s suite
 of organic light emitting diode (OLED) technologies. Pictiva displays offer a high level of brightness and
 contrast, video capabilities, wide viewing angles and a thin-profile, enabling developers and engineers to have
 greater design flexibility when developing the next-generation state-of-the-art electronics products.


Homer Antoniadis | OLED Product Development|
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