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Organic ElectronicsOrganic Electronics
Yousof Mortazavi
VLSI Course Presentation
December 2004
2
ReferencesReferences
• L. Ficke,M. Cahay, “The bright future of organic LEDs”, IEEE Potentials, Jan. 2004.
• J. N. Bardsley, “International OLED technology roadmap”, IEEE J. Selected Topics in Quantum Electronics, Vol. 10, No. 1, Feb. 2004.
• T. Y. Winarski, “Patenting bright ideas; the current state of patented technology in the field of organic light emitting diodes”, IEEE Circuits and Devices Magazine, Apr. 2004.
• T. Shimoda, T. Kawase, “All-polymer thin film transistor fabricated by high-resolution ink-jet printing”, In Proceedings IEEE International Solid-State Circuits Conference, 2004.
• S. Forrest, P. Burrows, M. Thompson, “The dawn of organic electronics”, IEEE Spectrum, Aug. 2000.
• G. Schmid, et al., “Organic electronics: perspectives towards applications”, ISSCC 2004.
• K. Nomoto, et al., “A bottom-contact organic-thin-film-transistor for flexible display application”, ISSCC 2004.
• M. G. Kane, “Organic electronics: what is it good for?”, ISSCC 2004.• D. Gundlach, et al., “High-mobility, low voltage organic thin film transistors”,
IEDM 1999.
3
OutlineOutline
• Motivations
• OLED Fundamentals
• OTFTs
• Advantages of Organic Electronics
• Applications
• OLEDs for Color Displays
• Challenges
4
MotivationsMotivations• Microelectronics vs. “Macroelectronics”:
– Microelectronics: try to make smaller transistors to reduce cost and boost performance
– Macroelectronics: reduce costs in order build ever larger devices, with acceptable performance
• Thin Film Transistors:– Active layer is silicon (a-Si) deposited on
glass .– For high mobilities, a-Si can be crystallized
(p-Si) by laser-pulses at high temperatures.– Can’t easily use flexible substrates, such as
plastics
• Organic Thin Film Transistors– Organic semiconductors were discovered in
1987.– Organic compounds are a natural match for
plastic substrates.– Use of polymers allows large-areas to be
coated and patterned without conventional photolithography (e.g. spin-coaters and ink-jet printers).
– Organic TFTs may be made large or small (30 nm @ Cornell U.)
Cost/area Cost/function
Bulk Si ICs $10K/ft2100 µcents/
transistor
a-Si TFTs on glass $150/ft2
1 mcents/
transistor
Printed Organic TFTs $30/ft2
200 µcents/
transistor
[Kane (ISSC’04)]
5
OLED FundamentalsOLED Fundamentals
• In 1987, Tang, et al. published “Organic electroluminescent diodes”.
• Currently more than 500 U.S. Patents have been issued on organic electronics.
• Challenges:– Choice of anode for ohmic
contact (for low voltage devices)
– Diffusion of In, O into HTL HIL interface between ITO and HTL
– Protection from oxygen and water encapsulation
ITO-Covered Substrate
HTL
ETL
Metal
Cathode
Transparent Anode
6
OTFT (OFET)OTFT (OFET)
• Typical OTFT:– Bottom gate, inverted staggered
structure– Pentacene (C22H14) active– Gate dielectric
• SiO2
• PMMA• PVP
• OTFTs operation:– accumulation – depletion
• Mobilities as high as 1 cm2/Vs has been obtained with Ion/Ioff ratio of 108.
• Very low fabrication temperature (<60°C) allows use of cheap plastics.
• Conventional MOSFET equations are used to model OTFTs however, mobility is voltage dependent.
Pentacene:Formula: C22H14
Metling Point: 300°COptical Bandgap: 2.8 eV
SAM dielectric to reducegate thickness to 2.5 nm[Schmid et al.]
W/L = 240 µm/44 µmTgate= 1700 Å.
7
Advantages of Organic ElectronicsAdvantages of Organic Electronics
• Thin, lightweight, flexible displays
• Low voltage, low power, emissive source
• High brightness • Broad color gamut• Wide viewing angle (~180º)• Good contrast• High resolution (<5 µm pixel
size) • Fast switching (1-10 µs)• Low bill of materials and
fabrication cost [Bardsley, 2004] Dupont Thermal Multilayer
Transistor Process
8
ApplicationsApplications
• Flexible Displays– PM-OLED– AM-OLED– Wearable Displays
• Sensor Arrays– Artificial Skin– Gas Sensors
• RF ID Tags– Inductors– Capacitors
• X-ray imaging panels
• Solid-State Lighting
9
OLEDs for Color DisplaysOLEDs for Color Displays
[Forrest, et al.]
10
ChallengesChallenges
• Choice of electrodes• Encapsulation• Reliability and yield• Lifetime• Brightness control
with feedback• Particle migration
control with AC driver
A. Giraldo, et al.
Thank YouThank You
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