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Introduction to Organic Introduction to Organic ElectronicsElectronics

Mohammad Agahian PanahiUniversity of Tehran, ECE faculty

VLSI Course PresentationInstructor: Dr. S. M. Fakhraie

Main References:

• J. M. Shaw, P. F. Sieldler “Organic electronics: Introduction” J. M. Shaw, P. F. Sieldler “Organic electronics: Introduction” IBM J. Res. & Dev. Vol. 45 No. 1 January 2001IBM J. Res. & Dev. Vol. 45 No. 1 January 2001• W. E. Howard, O. F. Prache “Microdisplays based upon W. E. Howard, O. F. Prache “Microdisplays based upon organic light emitting diodes” IBM J. Res. & Dev. Vol. 45 No. organic light emitting diodes” IBM J. Res. & Dev. Vol. 45 No. 1 January 20011 January 2001

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OutlineOutline

Organic vs. Inorganic TransistorsOrganic vs. Inorganic TransistorsOrganic LEDs (OLED)Organic LEDs (OLED)OLED ApplicationsOLED Applications

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Organic vs. InorganicOrganic vs. Inorganic Inorganic Transistors: silicon and gallium

arsenide semiconductors, metals such as aluminum and copper

Organic Transistors: Organic transistors are transistors that use organic molecules rather than silicon for their active material. This active material can be composed of a wide variety of molecules. Organic molecules are Polymers, Oligomers, etc.

Improvement in semiconducting, conducting, light emitting and physical properties (to be discussed)

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Polymers and Wiring ImprovementsPolymers and Wiring Improvements

Negative effect of interconnect of 7 layers of metal because of Resistance and Capacitance: propagation delay and cross talk.

R reduction: Copper instead of AluminumC reduction: Polymeric material SiLK

instead of oxide insulators.

Result: 37% improvement in wiring performance, so on-chip wiring is not a performance limiter for next decade.

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Charge (hole & electron) TransportCharge (hole & electron) Transport

Schematic of organic semiconducting p-type transistor with top contacts [1]

• Usually comprised of many individual molecules Usually comprised of many individual molecules held together by Van der Waals forces held together by Van der Waals forces

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Huge variety of choices for organic molecules for use in semiconductors

The ability of these materials to transport charge due to P-orbital overlap of neighbouring molecules provides semiconducting and conducting properties

Charge transport significantly different material to material

The major factor limiting mobility, takes place from molecule to molecule

P-orbital overlap is key to improvments in mobility of carriers

Charge (hole & electron) TransportCharge (hole & electron) Transport

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Classes of organic molecules for use in semiconductors and

their mobility [1]

• Lower mobility than silicon crystal, because they are polycrystalline • These carrier mobilities are useful for application that do not require high switching speeds

• Pentacene polymer has achieved mobilities comparable to that of the amorphous silicon used to fabricate the thin film transistors (TFTs) which drive the liquid crystal pixels in LCD flat panel displays

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Development of MobilityDevelopment of Mobility

Performance of organic and hybrid semiconductors [1]

• Mobilities of organic semiconductors have improved by five orders of magnitude over the past 15 years.

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AdvantagesAdvantages

Manufactured in low temperaturesManufactured in low temperatures Low cost & great flexibility in their synthesisLow cost & great flexibility in their synthesis

Inkjet printingInkjet printing Vacuum evaporationVacuum evaporation Solution castingSolution casting ……

Good mechanical propertiesGood mechanical properties FlexibilityFlexibility ToughnessToughness

[2]

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DisadvantageDisadvantage

lower mobility and switching speeds lower mobility and switching speeds compared to silicon waferscompared to silicon wafers

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What is OLED ?What is OLED ?OLED stands for Organic Light Emitting DiodeOLED stands for Organic Light Emitting Diode

•Alq3 as electron and NPB as hole transport layer•Electrons injected from the cathode (Ca, Al, Ba, etc.)•Holes injected from anode (Indium thin oxide, PEDOT)•Transport and radiative recombination of electron & hole at emissive layer

Schematic of typical OLED [1]

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PropertiesProperties

•These devices promise to be much less costly to fabricate than traditional LEDs.

•OLEDs are available as distributed sources while the inorganic LEDs are point sources of light.

•One of the great benefits of an OLED display over the traditional LCD displays is that OLEDs do not require a backlight to function. This means that they draw far less power

]2[

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Potentials of OLEDsPotentials of OLEDs

Suitable for thin, lightweight, printable Suitable for thin, lightweight, printable displaysdisplays

Good contrastGood contrastHigh resolution (< 5 micron pixel size)High resolution (< 5 micron pixel size)Fast switching (1-10 micro seconds)Fast switching (1-10 micro seconds)Wide viewing angleWide viewing angleLow cost of materials and fabricationLow cost of materials and fabrication

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OLED TypesOLED Types Small-molecule OLEDSmall-molecule OLED

Developed by Eastman-KodakDeveloped by Eastman-Kodak Made by vacuum evaporating small molecules to Made by vacuum evaporating small molecules to

substrate similar to that used in semiconductor substrate similar to that used in semiconductor manufacturingmanufacturing

Expensive processExpensive process

Polymer OLEDPolymer OLED Developed by Cambridge Display TechnologyDeveloped by Cambridge Display Technology Know as PLED (Polymer LED)Know as PLED (Polymer LED) Cheap & Easier production technique: Made by Cheap & Easier production technique: Made by

depositing the polymer on substrate through an inkjet depositing the polymer on substrate through an inkjet printing process printing process

Fabrication of large screen sizesFabrication of large screen sizes

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Inkjet printingInkjet printing

Advantage: high resolution, material saving, low cost

[3]

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AdvantagesAdvantages Lower cost than LCDs and Plasma displays, can be printed onto a substrate Lower cost than LCDs and Plasma displays, can be printed onto a substrate

using traditional inkjet technologyusing traditional inkjet technology

more scalable manufacturing process enables the possibility of much larger more scalable manufacturing process enables the possibility of much larger displays and highr resolutiondisplays and highr resolution

Unlike LCDs which employ a back-light and are incapable of showing true Unlike LCDs which employ a back-light and are incapable of showing true black, an off OLED element produces no light allowing for infinite contrast black, an off OLED element produces no light allowing for infinite contrast ratios.ratios.

The range of colors, brightness, and viewing angle possible with OLEDs are The range of colors, brightness, and viewing angle possible with OLEDs are greater than that of LCDs or plasma displays.greater than that of LCDs or plasma displays.

Without the need of a backlight, OLEDs use less than half the power of LCD Without the need of a backlight, OLEDs use less than half the power of LCD displays and are well-suited to mobile applications such as cell phones and displays and are well-suited to mobile applications such as cell phones and digital cameras.digital cameras.

OLEDs can be printed onto flexible substratesOLEDs can be printed onto flexible substrates

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DisadvantageDisadvantage

Relationshio between brightness and lifetime is Relationshio between brightness and lifetime is linear, high brightness level require the display linear, high brightness level require the display driving voltage levels to be increased which driving voltage levels to be increased which trades off expected life timetrades off expected life time

intrusion of moisture into displays damages and intrusion of moisture into displays damages and destroys the organics materialsdestroys the organics materials• improved sealing processes are important for

practical manufacturing

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OLED ApplicationsOLED Applications

Current ApplicationsCurrent ApplicationsDigital camera (Kodak)Digital camera (Kodak)Mobile phone screen (Motorola, NEC, Mobile phone screen (Motorola, NEC,

Samsung)Samsung)Car stereo (Pioneer, Kenwood)Car stereo (Pioneer, Kenwood)40 inch OLED display (Samsung) [3]40 inch OLED display (Samsung) [3]

Future ApplicationsFuture ApplicationsFlexible displaysFlexible displaysMicrodisplaysMicrodisplays

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Flexible DisplaysFlexible Displays

Flexible substrate requirementsFlexible substrate requirements TransparencyTransparency RobustnessRobustness Low costLow cost StabilityStability

Low coefficient of thermal deformationLow coefficient of thermal deformation Low moisture absorptionLow moisture absorption Resistant to chemical and solventsResistant to chemical and solvents

Processing temperature limited by:Processing temperature limited by: Deformation temperature of substrateDeformation temperature of substrate

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Flexible DisplayFlexible Display

Monochrome (green) flexible OLED display [2](click to play)

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MicrodisplaysMicrodisplays

High resolution at small areaHigh resolution at small area

Headsets for viewing movies and Headsets for viewing movies and cell phones with cell phones with full screenfull screen internet accessinternet access

Wearable headset monitors [4]Schematic view of the optics of a microdisplay

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Packaged OLED-on-silicon chipOLED-on-silicon SXGA microdisplay specification

Cross section of the OLED-on-silicon SXGA microdisplay [4]

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ReferencesReferences 1. J. M. Shaw, P. F. Sieldler “Organic electronics: 1. J. M. Shaw, P. F. Sieldler “Organic electronics:

Introduction” IBM J. Res. & Dev. Vol. 45 No. 1 January Introduction” IBM J. Res. & Dev. Vol. 45 No. 1 January 20012001

2. web resource: 2. web resource: www.oled-display.net

3. Clarck W. Crawford, “Organic Light Emitting Diodes 3. Clarck W. Crawford, “Organic Light Emitting Diodes Have Bright Future in Flat Panel Displays”, Technology Have Bright Future in Flat Panel Displays”, Technology commercialization Alliance, 2003commercialization Alliance, 2003

4. W. E. Howard, O. F. Prache “Microdisplays based 4. W. E. Howard, O. F. Prache “Microdisplays based upon organic light emitting diodes” IBM J. Res. & Dev. upon organic light emitting diodes” IBM J. Res. & Dev. Vol. 45 No. 1 January 2001Vol. 45 No. 1 January 2001