Organic ElectronicsOrganic Electronics

Yousof Mortazavi

VLSI Course Presentation

December 2004

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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.

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OutlineOutline

• Motivations

• OLED Fundamentals

• OTFTs

• Advantages of Organic Electronics

• Applications

• OLEDs for Color Displays

• Challenges

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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)]

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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

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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.

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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

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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

 

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OLEDs for Color DisplaysOLEDs for Color Displays

[Forrest, et al.]

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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