Bottom-Gate Geometry Increases Materials Options in All-Polymer Integrated Circuits
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in Munich, the Fraunhofer Institute for Solar Energy Systems in Freiburg, and The Max Planck Institute for Polymer Research in Mainz say that this advance significantly reduces the lasing threshold and improves the efficiency of organic laser devices. These results were announced in the September 11 issue of Applied Physics Letters. A mechanically flexible poly(ethylene terephthalate) (PET) substrate with an acrylic coating was embossed with a 2D periodic height modulation nanopattern using ultraviolet (UV) radiation. The active laser material, a ladder-type poly(p-phenylene) (LPPP), was then deposited in a 300-nm thick layer on this substrate by spincoating. A Ti:sapphire laser producing pulses of approximately 150 fs duration at a wavelength of 400 nm was used for excitation. When focused to a spot approximately 150 µm in diameter on the LPPP surface, nearly diffraction limited monomode laser emission was observed perpendicular to the surface above a pump pulse energy of 1.2 nJ. The 2D photonic bandgap structure significantly limits lasing from other lateral modes. The peak intensity of the emission occurred at 491 nm. Comparison of the 2D laser with a one-dimensional (1D) periodic height modulated laser of the same maximum amplitude showed a dramatic increase in the emission intensity in the 2D case, as well as a 30% reduction in the laser threshold energy. Also, the divergence of emission was drastically reduced in the 2D laser, resulting in highly directed nonpolarized emission. The researchers explain the observed effects in terms of the Laue formulation
for the feedback mechanism in a 2D photonic band structure, involving elastic Bragg scattering to couple wavevectors having the same energy. TIM PALUCKA
Bottom-Gate Geometry Increases Materials Options in All-Polymer Integrated Circuits Investigators at the Philips Research Laboratories in The Netherlands have shown that bottom-gate structures for organic field-effect transistors open the door to a wide variety of polymeric materials, including the high mobility semiconducting materials pentacene and regioregular poly(3-hexylthiophene), or P3HT. Reporting in the September 4 issue of Applied Physics Letters, G.H. Gelinck,
T.C.T. Geuns, and D.M. de Leeuw also demonstrated that low-ohmic vertical interconnects (vias) between the top and bottom layer can be etched photochemically, making eventual scaling up of the technology feasible. Top-gate structures sandwich the semiconductor between the first electrode and the gate dielectric, imposing materials compatibility restraints on the organic semiconductor employed. Previous work using a top-gate electrode with polythienylenevinylene (PTV) as the semiconductor resulted in transistors with low field-effect mobilities (approximately 1 × 10-3 cm2/Vs). Since the semiconductor is not sandwiched in the bottom-gate structure, materials compatibility is a lesser concern; high mobility organic
SBIR Update Diversified Technologies, Inc. (Bedford, Massachusetts) has been awarded $3,000,000 under a total of six Phase I and
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