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 user 2006-06-30 at 11:57:00 am Views: 66
  • #15910

    Cool light leads to greener chips

    A technique that could lead to cheap, environmentally friendly microchips has been developed by UK researchers.

    The team from University College London used low-temperature,
    ultraviolet lamps to make silicon dioxide, a vital component of almost
    all modern chips.

    Chip manufacturers currently use energy-intensive furnaces, heated to more than 1,000C, to make the material.

    The new technique operates at room temperature and so requires less power and fewer resources.

    “This finding means that the industry’s energy, and subsequent cost
    savings, could reduce the prices of electronic devices for consumers
    and, of course, create a positive environmental impact,” said Professor
    Ian Boyd of UCL, a member of the team behind the discovery.

    Complex designs

    Microchips are composed of complex electrical circuits made of a variety of silicon components, such as transistors.

    A transistor is a basic electronic switch. Every chip needs large
    numbers of them, sometimes hundreds of millions to function. The more
    there are, the more calculations they can do.

    It opens the door to a whole array of technologies and possibilities

    Professor Ian Boyd

    These transistors are made of a combination of a conducting material,
    to channel the electrical charge through the device, and an insulator
    that inhibits the flow of electricity.

    A common insulator is the oxidised form of silicon, silicon dioxide.

    The compound can also be used to channel electrical charge in memory devices.

    It is also often used as a “mask” that allows manufacturers to
    precisely pattern the chips with other elements to change the
    electrical properties of specific areas.

    For example, phosphorous atoms are commonly added to parts of the silicon to increase conductivity.

    This process, known as “doping”, allows chip-makers to change the
    electrical properties of specific areas of the chip to create precise
    pathways through which charge can flow.

    These form the intricate circuits needed in modern devices.

    Chip size

    Silicon dioxide forms very slowly at room temperature.

    In order to speed up the process, chip-makers heat the silicon wafers,
    from which chips are cut, to between 900C and 1,200C in the presence of

    This consumes a huge amount of energy.

    Also, as the wafer is heated, chip components that have already been incorporated can warp and distort its structure.

    This is a particular problem as researchers continue to chase Moore’s
    Law, which says the number of transistors on a chip will double every
    couple of years.

    As manufacturers try to squeeze smaller and smaller components on to chips, they are packed closer together.

    Heating the wafer with these densely packed chips can cause
    contamination of individual components as they become more fluid and
    “bleed” into one another.

    A low temperature manufacturing process would overcome
    these problems and allow chip-makers to continue to push the boundaries
    of chip size.

    Cool temperature

    The new technique uses a lamp that emits light from deep within the UV spectrum at a wavelength of 126 nanometres.

    The UV lamp is about 30cm long and looks like a common fluorescent
    tube. It is filled with argon gas that has a high voltage applied to

    These techniques cannot be used for electronics because the defect densities are far too high

    Dr Douglas Paul, University of Cambridge

    The emitted light causes oxygen molecules to break down into separate
    atoms. This dissociation creates one atom with a lot of energy and one
    with much less.

    The energetic atoms are the most useful for creating silicon dioxide.

    “They’re very aggressive, they’re very keen to oxidise the silicon,” explained Professor Boyd.

    “You don’t even need to heat the silicon,” he said. “It oxidises at room temperature.”

    Future products

    However, the silicon industry demands pure materials to manufacture microchips.

    According to Dr Douglas Paul, of the University of Cambridge
    semiconductor physics group, this may be the technique’s biggest
    stumbling block.

    “There have been many people who have shown similar
    results but all these techniques cannot be used for electronics because
    the defect densities are far too high,” he said.

    “By growing thermal oxides at high temperatures in present
    microelectronics manufacturing processes (from 700 to 1,000 degrees C)
    most of the defects are all annealed out and you end up with an
    extremely low defect density”.

    Professor Boyd admits that prolonged exposure to other UV
    wavelengths produces defects, but points out that his technique employs
    a wavelength of light that has never been used before.

    The next stage, he says, is to try the technique in
    clean-room facilities, similar to those used in chip-making plants, to
    prove the technology works on an industrial scale.

    The team says it is already talking to companies about using the technique.

    The researchers believe that eventually it could be used not just in
    chip manufacturing but also to create circuits on other materials
    including cloth, for smart clothing, paper for electronic books or in
    plastic electronics.

    “It opens the door to a whole array of technologies and possibilities,” said Professor Boyd.