*NEWS*EPSON’S LATEST TECHNOLOGY

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*NEWS*EPSON’S LATEST TECHNOLOGY

 user 2006-05-29 at 11:28:00 am Views: 70
  • #15578

    Liquid silicon promises ‘green’ devices
    In
    pursuit of printable silicon devices, Seiko Epson Corp. has developed a
    liquid-silicon material and formed a silicon film and a transistor
    through a spin-coating process. The material, jointly developed with
    JSR Corp., is cyclopentasilane (CPS), a silane compound of hydrogen and
    silicon.”If we can improve the process, we would be able to deliver
    brand-new electronic devices that are environmentally friendly,” said
    Tatsuya Shimoda, deputy managing director of corporate R&D at Seiko
    Epson.Epson believes liquid materials could lower the cost of
    semiconductor fabrication, in part because they would eliminate large
    vacuum equipment from the production line. The introduction of inkjet
    printing technology would further lower the cost. Leveraging its
    printer technology, Epson had already applied a microliquid process to
    fabricate devices such as color filters and organic-LED displays.In the
    work with JSR, polysilane is polymerized from highly purified CPS by
    exposing ultraviolet light from the outside and avoiding contamination.
    Since polysilane is insoluble, the JSR and Seiko Epson researchers
    developed a version of the material that contains only Si and H. They
    found that this form of polysilane dissolves into CPS, some of which
    are left unpolymerized. The highly pure polysilane liquid becomes a
    polysilicon film by spin coating or inkjet printing in a nitrogenous
    atmosphere, followed by baking at over 500°C and excimer-laser
    annealing.For their experimental fabrication of transistors, the
    engineers used spin coating or inkjet printing in place of a
    conventional chemical-vapor-deposition (CVD) process to form the
    polysilicon layer. They used a conventional process to form the gate,
    source and drain. “We’ve cleared the most difficult process in
    fabricating a transistor with our liquid-silicon material,” said
    Masahiro Furusawa, manager of the Flex Group at Epson’s Technology
    Platform Research Center.A transistor made from a spin-coated film,
    with patterning done by conventional photolithography, had a mobility
    of 108cm2/Vs-almost the same as a polysilicon TFT made by the CVD
    method. This shows that the material has high potential, said
    Furusawa.The transistor made by inkjet patterning, meanwhile, had a
    mobility of 6.8cm2/Vs. “The mobility is not high yet, but this is
    mainly because we have not optimized the process, material and
    substrate. We believe that the printed silicon TFTs show sufficient
    potential,” said Furusawa.For the prototype transistors, the team used
    a glass substrate. But the polysilane is repellent against glass,
    causing the film to become as thick as 300nm. “Some breakthrough is
    necessary for the substrate, especially when used with inkjet
    printing,” Furusawa said. “Conventional polysilicon film is about 100nm
    thick. If the film becomes thin, laser annealing can make a better
    crystal.”Epson is also attempting to make the ink droplet smaller for
    minuter patterning. In inkjet printers in volume production, a droplet
    of 2pL enables 15µm patterning. The company is now studying nanolevel
    droplets to enable a 0.5µm pattern.”It was a dream to make a display
    with inkjet printing 10 years ago, but we’ve realized it,” Shimoda
    said. “So it is not a dream now to make a Pentium with the microliquid
    process.”