1 Introduction to Organic Electronics Mohammad Agahian Panahi University of Tehran, ECE faculty VLSI Course Presentation Instructor: Dr. S. M. Fakhraie Main References: J. M. Shaw, P. F. Sieldler “Organic electronics: Introduction” IBM J. Res. & Dev. Vol. 45 No. 1 January 2001 J. M. Shaw, P. F. Sieldler “Organic electronics: Introduction” IBM J. Res. & Dev. Vol. 45 No. 1 January 2001 W. E. Howard, O. F. Prache “Microdisplays based upon organic light emitting diodes” IBM J. Res. & Dev. Vol. 45 No. 1 January 2001 W. E. Howard, O. F. Prache “Microdisplays based upon organic light emitting diodes” IBM J. Res. & Dev. Vol. 45 No. 1 January 2001

2 Outline Organic vs. Inorganic Transistors Organic vs. Inorganic Transistors Organic LEDs (OLED) Organic LEDs (OLED) OLED Applications OLED Applications

3 Organic 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)

4 Polymers 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 Aluminum C 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.

5 Charge (hole & electron) Transport Schematic of organic semiconducting p-type transistor with top contacts [1] Usually comprised of many individual molecules held together by Van der Waals forces Usually comprised of many individual molecules held together by Van der Waals forces

6 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) Transport

7 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

8 Development 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.

9 Advantages Manufactured in low temperatures Manufactured in low temperatures Low cost & great flexibility in their synthesis Low cost & great flexibility in their synthesis Inkjet printing Inkjet printing Vacuum evaporation Vacuum evaporation Solution casting Solution casting … Good mechanical properties Good mechanical properties Flexibility Flexibility Toughness Toughness [2]

10 Disadvantage lower mobility and switching speeds compared to silicon wafers lower mobility and switching speeds compared to silicon wafers

11 What is OLED ? OLED stands for Organic Light Emitting Diode OLED stands for Organic Light Emitting Diode Alq 3 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]

12 Properties 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]

13 Potentials of OLEDs Suitable for thin, lightweight, printable displays Suitable for thin, lightweight, printable displays Good contrast Good contrast High 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 angle Wide viewing angle Low cost of materials and fabrication Low cost of materials and fabrication

14 OLED Types Small-molecule OLED Small-molecule OLED Developed by Eastman-Kodak Developed by Eastman-Kodak Made by vacuum evaporating small molecules to substrate similar to that used in semiconductor manufacturing Made by vacuum evaporating small molecules to substrate similar to that used in semiconductor manufacturing Expensive process Expensive process Polymer OLED Polymer OLED Developed by Cambridge Display Technology Developed by Cambridge Display Technology Know as PLED (Polymer LED) Know as PLED (Polymer LED) Cheap & Easier production technique: Made by depositing the polymer on substrate through an inkjet printing process Cheap & Easier production technique: Made by depositing the polymer on substrate through an inkjet printing process Fabrication of large screen sizes Fabrication of large screen sizes

15 Inkjet printing Advantage: high resolution, material saving, low cost [3]

16 Advantages Lower cost than LCDs and Plasma displays, can be printed onto a substrate using traditional inkjet technology Lower cost than LCDs and Plasma displays, can be printed onto a substrate using traditional inkjet technology more scalable manufacturing process enables the possibility of much larger displays and highr resolution more scalable manufacturing process enables the possibility of much larger displays and highr resolution 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 ratios. 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 ratios. The range of colors, brightness, and viewing angle possible with OLEDs are greater than that of LCDs or plasma displays. The range of colors, brightness, and viewing angle possible with OLEDs are greater than that of LCDs or plasma displays. 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 digital cameras. 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 digital cameras. OLEDs can be printed onto flexible substrates OLEDs can be printed onto flexible substrates

17 Disadvantage Relationshio between brightness and lifetime is linear, high brightness level require the display driving voltage levels to be increased which trades off expected life time Relationshio between brightness and lifetime is linear, high brightness level require the display driving voltage levels to be increased which trades off expected life time intrusion of moisture into displays damages and destroys the organics materials intrusion of moisture into displays damages and destroys the organics materials improved sealing processes are important for practical manufacturing

18 OLED Applications Current Applications Current Applications Digital camera (Kodak) Digital camera (Kodak) Mobile phone screen (Motorola, NEC, Samsung) Mobile phone screen (Motorola, NEC, Samsung) Car stereo (Pioneer, Kenwood) Car stereo (Pioneer, Kenwood) 40 inch OLED display (Samsung) [3] 40 inch OLED display (Samsung) [3] Future Applications Future Applications Flexible displays Flexible displays Microdisplays Microdisplays

19 Flexible Displays Flexible substrate requirements Flexible substrate requirements Transparency Transparency Robustness Robustness Low cost Low cost Stability Stability Low coefficient of thermal deformation Low coefficient of thermal deformation Low moisture absorption Low moisture absorption Resistant to chemical and solvents Resistant to chemical and solvents Processing temperature limited by: Processing temperature limited by: Deformation temperature of substrate Deformation temperature of substrate

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

21 Microdisplays High resolution at small area High resolution at small area Headsets for viewing movies and cell phones with full screen internet access Headsets for viewing movies and cell phones with full screen internet access Wearable headset monitors [4] Schematic view of the optics of a microdisplay

22 Packaged OLED-on-silicon chipOLED-on-silicon SXGA microdisplay specification Cross section of the OLED-on-silicon SXGA microdisplay [4]

23 References 1. J. M. Shaw, P. F. Sieldler “Organic electronics: Introduction” IBM J. Res. & Dev. Vol. 45 No. 1 January J. M. Shaw, P. F. Sieldler “Organic electronics: Introduction” IBM J. Res. & Dev. Vol. 45 No. 1 January web resource: 2. web resource: 3. Clarck W. Crawford, “Organic Light Emitting Diodes Have Bright Future in Flat Panel Displays”, Technology commercialization Alliance, Clarck W. Crawford, “Organic Light Emitting Diodes Have Bright Future in Flat Panel Displays”, Technology commercialization Alliance, W. E. Howard, O. F. Prache “Microdisplays based upon organic light emitting diodes” IBM J. Res. & Dev. Vol. 45 No. 1 January W. E. Howard, O. F. Prache “Microdisplays based upon organic light emitting diodes” IBM J. Res. & Dev. Vol. 45 No. 1 January 2001