Tommie W. Kelley

High Performance Organic Thin Film Transistors

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 cm 2 /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.

Point contact current–voltage measurements on individual organic semiconductor grains by conducting probe atomic force microscopy

Conducting probe atomic force microscopy (CP-AFM) was used to make point contact current–voltage (I–V) measurements on individual microscopic grains of the organic semiconductor sexithiophene (6T). The 6T grains ranged from 1 to 6 molecules (2–14 nm) in thickness, 1–2 μm in length and width, and were deposited by thermal evaporation onto SiO2 substrates previously patterned with 200 nm wide Au wires. Au-coated AFM probes were used to image the substrates in air to identify individual 6T grains which grew in contact with a wire. The same probes were used to record the I–V characteristics of single grains. Analysis of the differential resistance as a function of probe wire separation yielded typical grain resistivities of 100 Ω cm and contact resistances of ∼100 MΩ. Over the 0–3 V range probed, the shape of the I–V curves can be attributed to a combination of the nonlinear I–V characteristics of the Au-6T junctions and the ohmic response of the grain. In general, we have shown that CP-AFM is a reliable meth...

Polymeric aperture masks for high performance organic integrated circuits

The use of polymeric aperture masks to fabricate high performance pentacene-based integrated circuits is presented. The aperture masks are fabricated using a laser ablation process with capabilities of generating 10 μm features. A mask set consisting of 4–6 aligned layers has been fabricated and has been used to demonstrate functional rf-powered integrated circuits with 20 μm gate lengths. Devices consisted of shadow-mask patterned layers of gold, alumina, and pentacene. TFT mobilities greater than 2 cm2/V s were measured and propagation delays from 7-stage ring oscillators of less than 5 μs were observed. This all-additive, dry patterning method has been extended to the production of samples as large as 6 in.×6 in. Larger aperture masks are under investigation and continuing efforts are focused on automation of the alignment process.

39.2: Invited Paper: Large area, High Performance OTFT Arrays

Recent efforts at 3M have extended the use of polymeric aperture masks and surface modification methods to produce large area (approximately 6″×6″) arrays of high mobility pentacene TFTs on a variety of substrates. Results of high performance organic TFTs in active matrix display backplanes will be presented.

Industrial Uses of Computational Models in the Development of Novel Nanosystems

Nanosystems represent new opportunities, new research and development efforts and new possibilities for advanced materials. Many industrial scientists are focusing on nanotechnology and many chemical industries are indeed funding ambitious but valuable efforts. These efforts are based on the belief and realization that nanosystems are basic and important blocks for building new businesses. Industrial computational experts find themselves at the right intersect: an intersect where their technology is uniquely capable to access understanding, to stimulate thoughts and possibilities, to run “what-if” scenarios, and to “truly” discover new nanosystems capable of providing the advanced material capability that future businesses foresee. This paper will focus on describing computational methodologies that we are currently using. The paper will also extend to cover the application of these methods to aromatics, in particular, pentacenes and benzene derivatives.