High Performance Organic Thin Film Transistors
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High Performance Organic Thin Film Transistors Tommie W. Kelley†,*, Dawn V. Muyres†, Paul, F. Baude†, Terry P. Smith†, and Todd D. Jones§ 3M Company, Electronics and Inorganics† and Organic Materials§ Technology Centers, St. Paul, Minnesota *
Corresponding author, 3M Center, 201-1N-35,St. Paul, MN 55144-1000
ABSTRACT We report here methods of surface modification and device construction which consistently result in lab-scale pentacene-based TFTs with mobilities at or above 5 cm2/Vs. Surface modifications include polymeric ultrathin films presenting a passivated interface on which the semiconductor can grow. High performance TFTs have been fabricated on a variety of dielectric materials, both organic and inorganic, and are currently being implemented in manufacturable constructions. Our surface modifications have also proven useful for substituted pentacene materials and for a variety of other organic semiconductors. In addition, we report an all organic active layer, rf-powered integrated circuit. Further experiments and statistical analyses are underway to explain the elevated mobility in our samples, and efforts have been made to confirm these results through collaboration. INTRODUCTION Control of device interfaces has been a research focus for several groups in the area of organic electronics. Efforts have included treatment of metal electrodes to modify injection barriers [1-2], treatment of dielectric interfaces to improve molecular ordering [3-6], and passivation of interlayers in organic light-emitting diodes (OLEDs) to avoid electromigration or to improve device voltage characteristics [7-8]. Recently, we have developed ultrathin homopolymer coatings as dielectric layer modifiers for improved performance in pentacene thin film transistors, TFTs. This is an extension of previous efforts to modify device interfaces where we utilized phosphonic acid-based selfassembled monolayers (SAMs) to improve the performance of pentacene TFTs with alumina dielectrics [9-10]. Many researchers have shown excellent results in individual organic transistors, but none have reported statistical process control. We have achieved this through the application of Six Sigma: a systematic, process-improvement methodology for identifying and controlling unknown sources of variability. The approach is to reduce a complex problem to a manageable statistical problem, apply statistical techniques to identify the critical variables, and establish a control plan for those variables. Utilizing homopolymer surface-modifying coatings and the process knowledge obtained from our Six Sigma project, we have improved device mobilities reliably and reproducibly from a baseline of 1 cm2/Vs obtained on alumina to an average of 5 cm2/Vs on surface-treated alumina. Furthermore, this improvement has been both sustainable for individual devices and applicable to fully patterned, integrated circuits fabricated in a similar manner.
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EXPERIMENTAL PROCEDURE Sample preparation. Doped silicon wafers were obtained from Silicon Valley Microelect
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