Research in organic electronics has included advances in materials, devices, and processes. Device architectures, increasingly complex circuitry, reliable fabrication methods, and new semiconductors are enabling the incorporation of organic electronic components in products including OLED displays and flexible electronic paper.

Pentacene-based thin-film integrated circuits patterned only with polymeric shadow masks and powered by near-field coupling at radio frequencies of 125 kHz and above 6 MHz have been demonstrated. Sufficient amplitude modulation of the rf field was obtained to externally detect a clock signal generated by the integrated circuit. The circuits operate without the use of a diode rectification stage. This demonstration provides the basis for more sophisticated low-cost rf transponder circuitry using organic semiconductors.

We show novel and selective means to modify the dielectric surfaces in organic TFTs. Modification schemes include alkylphosphonic acid monolayers that have a strong affinity for alumina surfaces. Monolayers form robust, extremely uniform thin films and are deposited through simple spin-coating with a dilute solution of the monolayer precursor in solvent. Adding monolayers to organic TFTs has resulted in polycrystalline devices with mobilities nearly equal to single-crystal values while maintaining acceptable values of other device parameters (for example, the threshold voltage, on/off ratio, and subthreshold slope) required for fully functional integrated circuits.

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.

We report the structural and electrical characterization of two new p-channel organic semiconductors, 5,5'-bis(2-tetracenyl)-2,2'-bithiophene (1) and 5,5'-bis(2-anthracenyl)-2,2'-bithiophene (2). Both compounds exhibited a high degree of thermal stability with decomposition temperatures of 530 degrees C and 425 degrees C for 1 and 2, respectively. The thin-film structures of 1 and 2 were examined using wide-angle X-ray diffraction (XRD), grazing incidence X-ray diffraction (GIXD), and atomic force microscopy (AFM). Films of 1 and 2 pack in similar triclinic unit cells with the long axes of the molecules nearly perpendicular to the substrate. Thin-film transistors (TFTs) based on 1 and 2 exhibit contact-corrected linear regime hole mobility as high as 0.5 cm2/Vs and 0.1 cm2/Vs, respectively. The specific contact resistance at high gate voltages for gold top contacts was 2 x 10(4) Ohms cm and 3 x 10(4) Ohms cm for 35 nm thick films of 1 and 2, respectively. Long-term air stability tests revealed less degradation of the electrical properties of 1 and 2 in comparison to pentacene. Variable temperature measurements revealed activation energies as low as 22 and 27 meV for 1 and 2, respectively. The temperature and gate voltage dependence of the mobility are discussed in terms of a double exponential distribution of trap states and a model accounting for the layered structure of the organic films. The enhanced air and thermal stability over pentacene, combined with good electrical performance characteristics, make 2 a promising candidate for future organic TFT applications.