Nanoscale Organic Electronic Devices Formed by Lamination With Stamps
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Nanoscale Organic Electronic Devices Formed by Lamination With Stamps Jana Zaumseil, Takao Someya, Zhenan Bao, Yueh-Lin Loo, Kirk Baldwin, Raymond Cirelli and John A. Rogers Bell Laboratories, Lucent Technologies, Murray Hill, NJ 07974, U.S.A. ABSTRACT Lamination of metal-coated elastomeric stamps against thin films of electroactive organics provides non-invasive, high resolution electrical contacts for investigations of charge transport in these materials. This approach uses the features of relief on the stamps to define, with nanometer resolution, the geometry and separation of electrodes that are formed by uniform evaporation of a thin metal film onto the stamp. Soft, room temperature contact of an element of this type with an organic semiconductor film on a gate dielectric and a gate yields a high performance top contact transistor with source/drain electrodes supported by the stamp. We review here our use of this approach to study the electrical properties of the organic semiconductor pentacene in thin film transistors structures. We also introduce a method for using the same techniques and structures to probe transport through organic monolayers. INTRODUCTION Recent interest in the science and the emerging applications of electroactive organic and bio-organic materials[1] motivates research into non-invasive methods for forming high resolution electrical contacts to these chemically and mechanically fragile ‘soft’, molecular materials. One approach uses room temperature lamination of electrical contacts that consist of thin metal films deposited onto elastomeric supports [2,3]. This technique provides a route to efficient, non-invasive electrical contacts for a wide range of organic semiconductors and light emitters. These contacts can be used both for basic studies of charge transport in these ‘soft’ materials and for building high performance devices out of them. This paper summarizes some of our recent work in this area [3] that demonstrates this approach for forming contacts to the semiconductor pentacene in transistor structures with channel lengths that range of 250 mm to 150 nm. It also describes how similar structures can be used to measure charge transport in insulating long chain organic monolayers. EXPERIMENT Figure 1 illustrates the steps for building stamp-based laminated transistors. Casting and curing a prepolymer to the elastomer polydimethylsiloxane against ‘masters’ that consist of patterned photoresist on silicon substrates forms the stamps. Exposing these stamps briefly (1-2 s) to an oxygen plasma produces surface hydroxyl groups. Electron beam deposition of Ti (1 nm; 0.3 nm /s) followed by Au (15 nm; 1 nm/s) with a flux of metal perpendicular to the surface of the stamp leads to deposition predominantly on the raised and recessed regions and not on the sidewalls. In this way, blanket uniform deposition yields
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patterned and electrically isolated thin metal electrodes with the geometry and resolution of the relief structure. Films formed according to these procedures have g
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