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To: The Duke of URL© who wrote (177015)	2/12/2004 1:04:20 AM
From: richardred	Respond to of 186894

Yet another article, same subject: Intel Making Silicon Work for Optoelectronics By Jeff Chappell -- Electronic News, 2/11/2004 They say they still have some work to do, but Intel researchers said today they have fabricated a silicon photonic device with a modulation bandwidth exceeding 1GHz. R&D data published by Intel Corp. researchers today in the scientific journal Nature suggest that cheap silicon-based optical devices may eventually be possible. The work could conceivably pave the way for the use of high-speed optoelectronics in every-day consumer devices. Optical devices have always been the realm of exotic III-V materials -- indium, gallium and so forth -- as opposed to silicon, which is cheaper, more abundant and easier to work with. It has limited the use of optoelectronics to expensive, high-end applications, such as network infrastructure and Internet backbones. Silicon-based photonic devices haven't proven viable because silicon optical modulators are slow compared to those fabricated from compound III-V semiconducting materials or other optoelectronic materials. Up until this point, experimental silicon-based optoelectronic devices have only achieved modulation bandwidths of around 20MHz. But in a letter to Nature published on the journal's Website today and in its print edition slated for publication Thursday, Intel researchers based at the chipmaker's Santa Clara, Calif. headquarters and in Israel said they have achieved an all-silicon device that achieves high-speed optical phase modulation. . "As this technology is compatible with conventional complementary MOS (CMOS) processing, monolithic integration of the silicon modulator with advanced electronics on a single silicon substrate becomes possible," the researchers said. With further engineering improvements, speeds beyond 1GHz may be possible, the researchers suggested. The research could pave the way for the use of cheap optical devices in PCs and consumer electronics, giving them vast improvements in data transmission rates. Intel Presents the Nuts & Bolts of High Speed Silicon Phase Modulation Intel used a MOS capacitor phase shifter at the heart of its photonic silicon device, which differs from past approaches. The researchers built their device on a silicon-on-insulator wafer, using a p-type doped polysilicon rib with a gate oxide sandwiched between them. The researchers created the polysilicon rib by depositing amorphous silicon using low pressure chemical vapor deposition followed by a high temperature anneal to form the crystallized polysilicon. The annealing process is designed to minimize polysilicon grain boundaries, which can cause optical loss and limit the electric activation of dopants, the researchers said. "In order to minimize the optical absorption by metal contacts, we used a wide (approximately 10.5 micron) polysilicon layer on the top of the oxide layers on both sides of the polysilicon rib," the researchers stated. The researchers then placed aluminum contacts on top of the polysilicon, placing them to the side rather than on top of the rib waveguide, avoiding the typical approach in silicon optoelectronic devices. The metal contacts' optical absorption is then all but eliminated, they said. Furthermore, the oxide regions on either side of the rib maintain optical confinement and prevent the optical field from penetrating into the areas of the device where the metal contacts are located. "Our MOS phase modulators were fabricated in an existing Intel CMOS production facility, demonstrating compatibility with standard CMOS processing," the researchers noted. Compared with compound semiconductor devices, the silicon modulators still lose a considerable chunk of the optical signal, the researchers acknowledge, despite the exponential leap they have achieved over previous silicon optoelectronic devices. The 1GHz speed they achieved is still far behind the 2.5GHz and faster III-V-based devices used today. The modulator in Intel's silicon device still suffers a considerable signal loss because of the use of polysilicon, the researchers said. They suggested that this could be overcome in the future by using single crystal silicon deposited over the gate oxide with an epitaxial lateral overgrowth technique, and this is where their future research will be directed. Further improvements could be realized through engineering, such as device shrinkage, thinning the gated oxide layer and reducing the device voltage, the researchers said. These improvements would raise the device speed without contributing to optical signal loss.