AVS 53rd International Symposium
    Electronic Materials and Processing Thursday Sessions
       Session EM1-ThA

Invited Paper EM1-ThA7
Contact-Related Effects in Organic Thin Film Transistors

Thursday, November 16, 2006, 4:00 pm, Room 2001

Session: Contacts to Organic and Molecular Devices
Presenter: D.J. Gundlach, National Institute of Standards and Technology
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Organic thin film transistors (OTFTs) have received considerable attention in recent years and it is anticipated that OTFTs will find wide use in low-cost large-area electronic applications. OTFT performance can be limited by (1) the charge injection at the contacts or (2) the transport of charge in the field accumulated channel. In this presentation we will discuss parasitic contact related effects in OTFTs for different designs and compare experimentally observed contact-related effects with results from numerical simulations for devices employing inverted coplanar and inverted staggered designs. Organic single crystals with considerably fewer structural defects, such as grain boundaries, and having a low deep state density of electrically active traps provide ideal systems for studying charge injection and transport. The current-voltage characteristics of thin lamellar organic single crystals with gold contacts formed to opposite sides reveal that contact formation is complex and variable, even when high quality crystals and well-controlled contact formation methods are used. The current-voltage characteristics under low-level injection conditions provide a first indication of the contact quality. However, considerably more insight to the contact quality and injection process are gained from an analysis of the dependence of the activation energy on the applied voltage (extracted from the temperature dependence of the current-voltage characteristics), where a monotonic decrease in activation energy is expected when ohmic contacts are formed to crystals. Importantly, we discuss challenges in using OTFTs and organic single crystal field-effect transistors to study charge transport in organic semiconductors and possible contact-related limitations to the device reliability.